Meeting Abstracts

Special Event–Tickets Still Available! Evening on the Paseo del Rio (River Walk)

Wednesday, September 22, 6:30–9:00pm $130/person

Join us for an evening on the beautiful San Antonio River. We will begin at dusk with a cruise on the river in open-air barges. Enjoy cocktails and other beverages for a relaxing hour as the lights along the River Walk begin to sparkle.

The barges will drop us off right at the Briscoe Western Art Museum where we will then enjoy nouvelle Mexican cuisine in The River View Room, situated on the first floor of the museum’s Jack Guenther Pavilion. The pavilion brings together exquisite modern architecture—luscious white oak paneling and rich earth tones—an idyllic location, and floorto-ceiling windows offering stunning vistas and unparalleled views of the River Walk. Its attached patio with waterfall cascading into the river creates an outdoor setting that is sure to delight. There is no official dress code, but we recommend dressy casual to semi-formal attire in keeping with the venue’s setting. As always, layers are recommended— though the river cruise will be warm, the venue is, of course, air conditioned.

Abstracts

Refining the Estimate of Slip Rate and Earthquake Potential of the Owl Lake Fault (Eastern California) Using Data and Dating of Faulted Landforms

Altuntas, Gozde, University of Missouri Columbia, gozdesengez@gmail.com; Sean Polun, polunsg@missouri.edu; Francisco Gomez, fgomez@missouri.edu (Poster) The Owl Lake Fault is an active, ~25-km-long, left-lateral strike-slip fault that splays NE from the Garlock Fault in eastern California and transfers regional strain to the fault systems in Death Valley. As an active fault, the Owl Lake Fault is a poorly understood link between the extension of Death Valley and other active faults within Mojave Desert. A significant limitation on the understanding of the Owl Lake Fault’s role in this regional tectonic framework is the wide range of estimates on its slip rate, which range from 0.5 to 7.8 mm/yr. Constraining the slip rate will provide key information on this tectonic linkage. Improved understanding of the Owl Lake Fault as a seismogenic structure has direct implication for the assessment of the earthquake hazard in Eastern California. The study provides new insight on the slip rate and seismogenic behavior of the Owl Lake Fault through the analysis of high-resolution topographic data (lidar and low-altitude photogrammetry) and new age constraints. Airborne lidar data (approximately 10 points/m2) enable detailed mapping of the Owl Lake Fault and measurement of multiple large offsets. Additionally, the Owl Lake Fault kinematics change from predominantly strike-slip in the SW to a combination of strike-slip and normal faulting in the NE, associated with strike changes in fault geometry. Subsequent to lidar mapping, field work facilitated the ground-truth verification of initial mapping as well as more precise measurements of small fault offsets using kinematic GPS and low-altitude photogrammetry. Additionally, sample material has been collected for dating faulted landforms using terrestrial cosmogenic nuclide concentrations. The detailed, local “microtopography” permits assessing the smallest offsets (75 –100 cm) which are interpreted as reflecting the last coseismic offset.

Characterization of Weathered Granite (Grus) for Retaining Wall Design, Mineral King Road, Sequoia National Park

Arthurs, James, FHWA - Central Federal Lands, james.arthurs@dot.gov (TS #10) The Mineral King Road in Sequoia National Park provides the only vehicular access to the southern portion of the park. The road was originally constructed in 1873 to access silver claims and was gradually improved during the 20th century, with is present route being finalized in a 1915 reconstruction. The road is narrow, with steep grades and tight curves, and crosses terrain underlain by granite and grus. Grus, or decomposed granite, is a common weathered bedrock in the Sierra Nevada Mountains. The grus material behaves like a highly angular, consolidated sand, especially where it is confined. Where grus is unconfined, such as in a roadcut, grains of material can be removed by hand and the grus is easily eroded. At several locations along the route, roadside drainage culverts caused severe erosion of the grus and undermining of the roadway. As part of a project to rehabilitate the roadway, retaining walls are proposed to stabilize and protect the undermined areas. Appropriate characterization of the grus for wall design was critical, and included in situ and laboratory testing, and stability evaluation of the existing slopes on the project. Following this careful characterization, retaining wall analysis and design was performed using typical methods.

Evaluating the Engineering Properties of Coarse Aggregates

Asare-Adjei, Henry, CSIR-BRRI, Ghana, henryasareadjei@gmail.com; Juanita Selina Nkuah, jsnkuah@gmail.com (Poster) Ghana is developing rapidly in infrastructure such as roads, buildings, and other construction works. The developments of these infrastructures generate a high demand for construction materials such as quarry products of which aggregates are a major component. The quality of aggregates used in the construction of any civil engineering structure affects its general structural performance and integrity. Hence, the objective of the study was to evaluate the engineering properties of aggregates produced by KAS Product Limited, a major producer of aggregates in the country, to ascertain their suitability for use in construction works. Aggregates of size range 16mm to 10mm were collected from the quarry and subjected to various physical and strength tests such as: Water Absorption, Specific Gravity, Flakiness Index, Elongation Index, Aggregate Impact Value, Aggregate Crushing, Ten Percent Fines, and Los Angeles Abrasion Value Tests. The mean values obtained for the Specific Gravity, Water Absorption, Elongation Index, and Flakiness Index tests were 2.8%, 0.67%, 30.24%, 9.62% respectively showing that the aggregates were generally strong and workable. Mean values of 9.33%, 29.58%, and 20.36% were obtained for Aggregates Impact Value, Los Angeles Abrasive and Aggregate Crushing Value tests respectively, indicating the aggregates could resist gradual, impact loading as well as wearing. The results of the tests indicate that aggregates produced by KAS Products Limited, are suitable for use in concrete and road works according to the British standard (BS), Ghana Highway Authority (GHA), and American Society for Testing and Materials (ASTM) standard specifications for such purposes.

Filter Compatibility and Internal Stability Evaluations at Three Dam Sites

Ash, Sampson, Schnabel Engineering, sash@schnabel-eng.com; Zachary Ostrum, zostrum@schnabel-eng.com; Gary Rogers, grogers@schnabel-eng.com; Jonathan Harris, jharris@schnabel-eng.com (TS #4) Filter compatibility and internal stability were evaluated in three embankment dams constructed of rock and earthfill. Internal erosion is one the most common causes of failure for embankment dams and accounts for about half of total failures where mode of failure is known. Filter compatibility and internal stability is assessed quantitatively using geotechnical index testing, and qualitatively using construction history and geologic site conditions. The evaluations were used to inform risk analyses at the three dams. Filter compatibility evaluations are used to characterize the ability of embankment zones to filter material from adjacent or upstream zones. Several standardsbased filter evaluation methods are available. For the purposes of evaluating the three embankment dams, the Foster and Fell method (2001) was selected due to its applicability to existing dams, and suitability for use in risk assessments. Internal Stability evaluations are used to assess whether the in-situ material exhibits sufficiently wide ranges of particles sizes such that finer soil particles could migrate through the voids of coarser particles. Two different methods were used to identify two different types of internally unstable soils, the Wan and Fell method (2008) identifies potentially unstable broadly graded soils, and the USBR/Sherard (1979) identifies potentially unstable gap-graded soils. Spreadsheets were developed to quantitatively evaluate conditions using each of the methods described

above. Qualitative factors were considered during the evaluations of the three dams including construction history, construction methods, construction materials, and geologic foundation materials. Factors such as use of crushed rock versus rounded quartz sand for filters, or removal of cobble and boulders from samples prior to laboratory testing were important considerations for how the evaluations were performed and interpreted.

Geospatial Assessment of Barrier Island Erosion Along the Northern Gulf Coast

Babineaux, Claire, Northern Gulf Institute, Mississippi State University, ceb445@msstate.edu; Randall McMillen, randall@gri.msstate.edu; John Cartwright, johnc@gri.msstate.edu (TS #1A) Geospatial technologies are often utilized for the assessment of areas that are prone to various types of natural hazards. Coastal hazards, such as erosion and flooding, are common issues for the coastline of the United States. Rising sea levels and the increasing frequency and intensity of tropical storm systems are amplifying these issues. Government agencies (federal, state, and local) utilize many management techniques for coastal and barrier island environments. Research funded by the National Oceanic and Atmospheric Administration at Mississippi State University is mapping the shorelines of Mississippi’s barrier islands with high resolution DEMs. The DEMs were derived from lidar data sets from 2011, 2012, 2015, and 2019 with a maximum point spacing of one meter. The shoreline was mapped based on the zero-elevation value of each raster dataset and extracted to vector feature classes for further analysis. The delineated shorelines were then entered into the Digital Shoreline Analysis System v5.0 software developed by the U.S. Geological Survey to perform shoreline change analysis and calculate rate-of-change statistics.

Unstable Slope Management Program – Implementation along the Blue Ridge Parkway, North Carolina, Part 2

Banks, Brian, Schnabel Engineering, bbanks@schnabel-eng.com; Jason Holland, jholland@schnabel-eng.com; Majed Abdelhadi, majed.abdelhadi@dot.gov; Jennifer Bauer, jennifer@appalachianlandslide.com; Andrew Bain, Andrew.bain@wsp.com (TS #10) The Unstable Slope Management Program (USMP), developed by FHWA in 2019, is in its early stages of implementation. The program provides a framework to rank the hazards and risks associated with unstable slopes along roads and trails as part of a proactive geotechnical risk management strategy. As more fully described in Part 1 of this presentation, a consultant team implemented the USMP to inventory unstable slopes along 71 miles of the Blue Ridge Parkway in western North Carolina. This project was a first of its kind conducted by the Eastern Federal Lands Highway Division (EFLHD) on behalf of the National Park Service (NPS). In our presentation we will discuss the experience gained on this large-scale implementation of the USMP by a consultant team that resulted in a number of lessons learned and suggested best practices including schedule and resource expectations, safety protocols, experienced personnel, GIS and lidar usage, maintenance history, field equipment, and quality control. For example, the consultant team relied on the expertise of geologists and engineers with experience in recognizing and evaluating slope instability issues. We believe this ultimately led to a comprehensive unstable slope inventory as well as accurate relative ratings among the field teams. These personnel were able to use their experience to apply the project-specific slope selection criteria, which was in large part based on field evidence of slope instability. As a next step, EFLHD will proactively pursue risk mitigation strategies for the locations with the highest ratings. They will develop design concepts and comparative cost estimates to allow them to prioritize slopes to receive mitigation based on cost-benefit analysis. In this way, the USMP is the first step for EFLHD and NPS to take a proactive approach in managing its slope assets, reducing the maintenance burden, and ultimately increasing safety for park visitors.

Waking the Sleeping Giant: Historic Reactivation of Inactive, Dormant Landslides

Bauer, Jennifer, Appalachian Landslide Consultants, PLLC, jennifer@appalachianlandslide.com; Stephen Fuemmeler, stephen@appalachianlandslide.com; Philip Prince, philip@appalachianlandslide.com; Kenneth Gillon, ken@appalachianlandslide.com; Aras Mann, aras@appalachianlandslide.com; Rebecca Latham, latham@appalachianlandslide.com (TS #10) Prior to the availability of QL1 lidar topographic data, landslide geologists in Western North Carolina suspected the presence of large, inactive-dormant, debris and weathered rockslides, but did not have the detailed topographic mapping to confirm the boundaries with confidence. With the availability of updated lidar topography (processed to 0.5m DEM) in 2018, these large features become much easier to identify and delineate. Using geomorphic characteristics, ALC and the NC Geological survey are now classifying these inactive slides based on the Keaton and DeGraff (1996) activity state and relative age classifications: “Dormant - historic,” “Dormant - young,” “Dormant - mature,” and “Dormant - old” if confidence of the researcher allows. Development in the mountains of Western North Carolina is increasingly moving to higher topography and steeper slopes. Due diligence property evaluations by geologists have identified large, inactivedormant deep-seated landslides on these properties of interest. Some in the building community have questioned if these large, older slides can reactivate. Before the high resolution lidar, making this case with confidence was more difficult. With the more detailed topographic data, it is apparent that many slides that geologists have monitored for years are reactivations of larger, older features. This talk will discuss multiple examples of reactivation due to construction activities including underground linear infrastructure and provide the evidence that understanding and extra care must be taken when modifying these sleeping giants.

Unstable Slope Management Program – Implementation along the Blue Ridge Parkway, North Carolina, Part 1

Bauer, Jennifer, Appalachian Landslide Consultants, PLLC, jennifer@appalachianlandslide.com; Stephen Fuemmeler, stephen@appalachianlandslide.com; Brian Banks, bbanks@schnabeleng.com (TS #10) The Blue Ridge Parkway, connecting Great Smoky Mountains National Park in the south to Skyline Drive near Shenandoah National Park in the north, was primarily constructed between 1935 and 1966. Over the years, there have been many rockfalls and landslides on the cuts and fills of the roadway. In 2009, the North Carolina Geological Survey completed evaluation of many of the rock slopes, including a relative ranking of the potential for future movement. In 2021, the Eastern Federal Lands Highway Division contracted WSP, Schnabel Engineering, Inc., and Appalachian Landslide Consultants, PLLC to use the Unstable Slope Management Program (USMP), developed by the Federal Highways Administration in 2019, to inventory and assess slopes in three sections along the Blue Ridge Parkway in North Carolina. The USMP system determines relative numerical rankings based on rockfall or landslide characteristics, maintenance history, slope geometry, and potential impacts outside of the right-of-way, among other factors. The

USMP helps owners prioritize slopes for future mitigation, as well as helps limit liability, and adds to the geotechnical asset management program inventory. The team used laptop computers equipped with GIS software to view high resolution lidar hillshade data, precipitation data, slope and elevation data, and roadway information to increase accuracy and productivity. They entered slope location information in the GIS as well as into the USMP mobile application, which became important during the QC process. Past landslide inventory data and geologic mapping from the NCGS were also referenced in the GIS. Maintenance history is one of the most important factors in the rating, and team members captured history data in the GIS while riding with maintenance personnel discussing each slope. In three weeks, three field teams collected data on ~314 slopes; 190 cut slopes and 124 fill slopes. Eighty-three of these have a rating of Poor (>400 score).

Just Because It’s Legal Doesn’t Mean It’s Safe: The Case of 1,4-Dioxane

Bennett, Kyla, Public Employees for Environmental Responsibility (PEER), kbennett@peer.org (TS #8) The chemical 1,4-dioxane is a likely human carcinogen, and has contaminated the drinking water of roughly 88 million Americans in 45 states. The toxicity of 1,4-dioxane has been acknowledged for decades, yet it is still largely unregulated. Specifically, the US Environmental Protection Agency (EPA) does not have a regulatory limit for 1,4-dioxane in drinking water, and a patchwork of state regulations do not protect human health. This presentation will explore the longterm failure of EPA to act on 1,4-dioxane, and the devastating effects this has on New York and California water supplies. We will also examine how the industry is fighting any regulation of 1,4-dioxane in drinking water, and how industry influence is preventing regulators from protecting the public from this, and other, carcinogens.

Infrastructure Damage from Land Subsidence in California

Borchers, James, Consulting Hydrologist, Hydrogeologist, jimborchers@sbcglobal.net (TS #6) In California, land subsidence results from collapse of underground cavities, tectonics, natural sediment consolidation, oxidation of organic deposits, hydrocompaction of moisture deficient sediments, development of geothermal energy, and extraction of hydrocarbons, but primarily occurs as a result of groundwater extraction. Because several of these processes can be active at the same time, distinguishing the contributions of each to total subsidence at a particular locale sometimes is not possible without substantial investigation. Land subsidence from groundwater extraction has created what has been called the largest human alteration of the Earth’s surface— subsidence in excess of 1 foot and as great as 29 feet occurred over more than half of the San Joaquin Valley (5,200 square miles) between 1926 and 1970. Damage to canals, wells, roads, bridges, and pipelines approached $2 billion (2013 dollars) there. Groundwater mining between 1910 and 1969 caused subsidence as great as 14 feet and put 17 square miles of the northern Santa Clara Valley below the level of high tides in the adjacent San Francisco Bay. Costs to remediate the effects of land subsidence there exceeded $756 million (2013 dollars). Land subsidence during droughts, or in areas underserved by surface water, destroyed wells in the Sacramento, San Joaquin, and Santa Clara Valleys, and in coastal and arid southern California basins. Reconnaissance surveys by radar satellites during 2007–2020 indicate that high rates of groundwater extraction in the San Joaquin Valley have reinitiated land subsidence at historically high rates of about 1 foot per year in two large areas– a 7,000 km2 (2,700 mi2) swath between Tulare and Kettleman City, and a 3,200 km2 (1,200 mi2) area south of Merced and west of Madera. Remediation of severe impacts to the flow capacity of rivers, canals (including the California Aqueduct) and flood-bypass channels will exceed a $1 billion.

Levees of the Eden Landing Wildlife Preserve, Regional Benefits of Levee Characterization

Burger, David, Cal Engineering & Geology, dburger@caleng.com; Chris Nardi, cnardi@caleng.com (TS #7) Levees constructed within a tidal marsh between 1899 and 1954 were used as salt evaporators until 2003 when the Eden Landing site was established under California Fish and Wildlife as a protected wildlife refuge and included as part of the South Bay Salt Pond Restoration project (SBSPRP). Extensive geologic investigations were undertaken to support either levee certification or conversion of the site to the SBSPRP. Because the levees are situated on upwards of 30 feet of young bay mud deposits and centered within protected habitat, evaluation of the levees has presented geologic, geotechnical, environmental, and construction challenges. Improvements to the levees, site access, and exploration efforts required extensive collaboration between Federal, State, County, and local jurisdictions. More than 100 subsurface exploration locations, several geologic reconnaissances, and numerous engineering analyses were completed for the 25+ miles of levees. Variations in the historical areal loading of the young bay mud deposits have created substantially different geologic conditions within small areas. The variable loading conditions required extensive reliance on historical maps (circa 1900) of pre-development marsh conditions for planning of exploration and testing. Selected levees have been evaluated and certified under FEMA 44 CFR 65.10, while others have been breached as part of the SBSPRP and flood control efforts. Since 2008, improvements to the levees consisted of levee armoring, deep soil mixing and sheet pile cutoff walls, and selected breach locations. Additional conceptual projects have included levee raise and reconstruction, new levees and landmass designs, trail, and pedestrian bridges, new and upgraded tide gate structures, and new breaches. Both the certified flood control levees and restoration improvements have proved to be important components for effective long-term mitigation against sea level rise, incorporation into the San Francisco Bay Area trails system, and protected habitat for endangered species.

A 25-year History of Induced Sinkhole Development Due to Quarry Dewatering in Bucks County, Pennsylvania

Byle, Michael, Tetra Tech, Inc, Michael.Byle@tetratech.com; Ira Sasowsky ISasowsky@sasowsky.com, ids@uakron.edu; Anthony Rana, AJRanahydro@gmail.com (TS #6) Throughout the world, sinkholes are a characteristic and common landform of regions underlain by carbonate bedrock. If the landscape is in equilibrium with current conditions, the creation of new sinkholes, or the growth of existing ones, is generally a slow process. However, if conditions are changed by human activities, formerly stable land surfaces may be stressed and rapidly lowered, a process of induced sinkhole development. Depending on conditions, this may be relatively benign, or it may develop into threat to property and human safety. The specific causes of induced sinkhole development are quite varied, though frequently they are associated with surface-water drainage changes and/or large groundwater withdrawals. This presentation will report on the development of induced sinkholes over a 25-year period in a small tributary drainage basin in eastern Pennsylvania (Primrose Creek drainage basin). The site is unique in that a) it has clear topographic demarcated basin boundaries and geologic control; b) the stressor, the expansion and dewatering of a carbonate bedrock

quarry, is extreme and has been plainly identified; c) the groundwater withdrawals and water-level elevations have been heavily monitored; and d) the historical record of land conditions goes back a century or more. The data for the basin are presented and evaluated. The water level data for wells monitored for the longest period are compared to quarry mining and dewatering and the occurrence of sinkholes. The long-term monitoring indicates an episodic reduction in water levels together with lateral and vertical expansion of the quarry, and episodic occurrence of collapse sinkholes. Episodic nature is compared with mining activity including mining through geologic features and areas of varying karst permeability and dewatering to demonstrate correlation.

The 2021 National Landslide Hazards Act and Implications for Federal Land Management Agencies

Carpenter, Lynne, USDA Forest Service, Minerals & Geology Management, Geologic Hazards Program, lynne.chastain-carpenter@usda.gov (TS #5) The National Landslide Preparedness Act (NLPA) was signed into Law January 5, 2021. The primary purpose of the Act is to increase landslide preparedness by establishing a national-level landslide preparedness program. The NLPA directs the formation of an Interagency Coordinating Committee on Landslide Hazards (ICC), The ICC is directed to develop, by January 2022, a national strategy for landslide identification, management, and response as a major component of the National Landslide Hazards Reduction Program established by the Act. The National Landslide Hazards Reduction Program is intended to identify and inventory landslides through a publicly accessible database, mitigate landslide hazards, protect communities at risk of landslides, reduce landslide event losses, and improve landslide event communications and emergency preparedness. Management of landslide-prone areas on National Forest Service (NFS) lands under the NLPA is important for the following reasons: the USDA Forest Service manages the second largest federal land base; NFS lands generally have a high percentage of steep, unstable slopes and landslide-prone terrain; due to climate change, NFS lands can quickly change to more landslide-prone terrain (such as post-wildfire landscapes); the agency’s multiple use mission includes management of potentially landslideexacerbating activities such as mining and logging; management includes oversight of campgrounds, roads, pipelines, dams, telecommunication structures, and other infrastructure that may be impacted by landslides; and many non-federal lands with at-risk values exist adjacent to and downslope of NFS lands with landslide hazards. The NLPA establishes a framework for federal land management agencies to reduce losses and decrease hazards from landslides, requiring proactive identification and management of landslide risk areas by the USDA Forest Service.

Continuous Monitoring of an Earth Fissure in Chino, California – A Management Tool

Carpenter, Michael, U.S. Geological Survey, retired, mccarp@dakotacom.net; Richard Wilson, wilsonhydro@yahoo.com; Eric Lindberg, Eric.Lindberg@Waterboards.ca.gov (TS #6) Continuous measurements of deformation were made in Chino, California across an earth fissure and nearby unfissured soil during 2011–13 in two buried, horizontal, 150 mm pipes, 51 m long, which were connected by sealed boxes enclosing vertical posts at 6 m intervals. Horizontal displacements and normal strain were measured in one line using nine end-to-end quartz tubes that were attached to posts and spanned fissured or unfissured soil. The free ends of the tubes were supported by slings and moved relative to the attachment post of the next quartz tube. Linear variable differential transformer (LVDT) sensors measured the relative movements. Five biaxial tilt sensors were also attached to selected posts in that line. Relative vertical movement was measured at nine locations along the line in the second pipe using low-level differential pressure sensors. The second pipe was half full of water giving a free water surface along its length. Data were recorded on a Campbell CR10 using multiplexers. The quartz-tube horizontal extensometers exhibited more than 3 mm of predominantly elastic opening and closing in response to about 32 m of seasonal drawdown and recovery, respectively, in an observation well 0.8 km to the south. The nearest production well was 1.6 km to the west. The horizontal strain was 5.9 x 10-5 or 30 percent of the lowest estimate of strain-at-failure for alluvium. Maximum relative vertical movement was 4.8 mm. Maximum tilt in the fissure zone was 0.09 arc degrees while tilt at a separate sensor 100 m to the east was 0.86 arc degrees, indicating a wider zone of deformation than is spanned by the instrumentation. High correlation of horizontal displacements during drawdown, and especially recovery, with change in effective stress supports differential compaction as the mechanism for earthfissure movement. Continuous measurements of horizontal strain cou pled with water-level fluctuations and vertical borehole extensometry provide a real-time adaptive management tool for restricting pumping if strain approaches the lower limit of strain-at-failure or a stress-strain curve deviates from the previous mostly elastic regimen.

Integrating High-Resolution UAV-Sourced Data in a Machine Learning Framework for River Monitoring

Chen, Thomas, Academy for Mathematics, Science, and Engineering, thomaschen7@acm.org (TS #3) As climate change accelerates and human-caused pollution continues, the largest rivers in the world are at threat from a number of changes that can influence landscapes and ecology. As a result, it is crucial that computational mechanisms are developed to assess these changes, especially with the rise of big data and their applicability in a machine learning and artificial intelligence context. Unmanned aerial vehicles (UAVs), such as drones, are key assets in gathering visual imagery data that can be harnessed on a large scale in machine learning applications to assess rivers. When drones gather large quantities of such data, especially in a multitemporal context, deep learning algorithms such as convolutional neural networks (CNNs) can be trained to detect change over time and analyze pollution levels and micro- and macro-level ecological changes. However, when seeking to conduct research of this kind on river, it is often difficult to source a dataset of sufficient quantity from this method. Therefore, it is almost always necessary to utilize transfer learning, whereby a CNN is trained on data from a larger scope of river drone imagery and then reused as a starting point for a more specific task. In this work, we develop a framework for automated change detection of the Yangtze River. The output of the CNN that we train on multitemporal drone imagery, which is of the SqueezeNet architecture, is a digit from 0 to 6 indicating the degree of visual change. We do not explicitly define what this digit represents at first because it is a conglomeration of a number of factors that affect the visual appearance of the river, such as pollution, sediment, and seasonal change. We use a Markov logic network for transfer learning. The goal is to provide a baseline framework for automated large river monitoring.

Seismic and Volcanic Hazard Studies for SSHAC and PVHA Evaluations at Existing Nuclear Power Stations in Taiwan

Clahan, Kevin, Lettis Consultants International, clahan@lettisci.com (TS #5) In 2012, in response to the 2011 Tohuku earthquake, the Taiwan Atomic Energy Council (AEC) requested the Taiwan Power Company (TPC) to reevaluate seismic hazards and review the seismic design of nuclear facilities in Taiwan. Consequently, the TPC launched the “Seismic Reevaluation of Nuclear Facilities” project which follows the guidelines of the Senior Seismic Hazard Advisory Committee (SSHAC) Level 3 process (Budnitz et al., 1997; NRC, 2012). Lettis Consultants International (LCI) participated on the Technical Integration team and the Participatory Peer Review team for the SSCHAC Level 3 project. In parallel with the SSHAC project, LCI conducted paleoseismic and volcanic hazard studies across all of Taiwan to better characterize features which could affect the safe operation of nuclear facilities. The island of Taiwan is a product of both subduction and collision of the Philippine Sea plate and the stable Eurasian tectonic plate. The Philippine Sea plate subducts northwestward beneath the Eurasian plate as part of the Ryukyu subduction system in northeast Taiwan but overrides the Eurasian plate in southern Taiwan in the Luzon arc as part of the Manila subduction system. This active tectonic region was evaluated as part of the SSHAC study for Seismic Source Characterization (SSC) and Ground Motion Characterization (GMC) to perform PSHA studies at all four nuclear power stations in Taiwan. In addition, recent seismic hazard studies have identified new active fault features in both northern and southern Taiwan. This presentation will outline the efforts of the recently completed SSHAC study as well as the results and findings of the paleoseismic and volcanic hazard studies that supported the SSHAC evaluation.

IAEG Congress Update: How AEG Ranks and why Membership is so Valuable

Cohen-Waeber, Julien, Exponent, jwaeber@exponent.com (Poster) The AEG boasts a long-standing tradition of world-renowned practitioners and academics in the fields of environmental and engineering geology. Yet, for many, the 2018 San Francisco annual meeting was their first introduction to the International Association for Engineering Geology and the Environment (IAEG). As the United States national group, AEG represents our profession and our culture on the everimportant international stage that is IAEG. For decades, US based consultancies have been taking an increasingly active role in international projects while its participation in the IAEG remains relatively limited. This not only represents a missed opportunity for US practitioners to showcase their knowledge and expertise, but more importantly to learn from the tremendously diverse technical and cultural resources that IAEG has to offer. Currently, less than 200 of AEG’s roughly 1500 members represent the US national group among IAEG’s over 4000 members. Still, US membership with IAEG has increased by an impressive 50% since 2019. This is a trend AEG should strive to continue. It highlights the engagement of AEG’s membership in the international forum and underlines its presence as leaders in the profession. This update presents the current state of IAEG’s activities including publications, conferences, symposiums, and awards with particular attention to where AEG stands with respect to the IAEG’s 62 member nations, and the benefits of AEG’s involvement.

Arizona Department of Water Resources Land Subsidence Monitoring Program Using Interferometric Synthetic Aperture Radar (InSAR)

Conway, Brian; Arizona Department of Water Resources, bdconway@azwater.gov (TS #6) The Arizona Department of Water Resources (ADWR) land subsidence monitoring program has been greatly enhanced by the use of Interferometric Synthetic Aperture Radar (InSAR). ADWR’s InSAR program started in 2002 with the awarding of a three-year NASA Earth Science grant, allowing ADWR the opportunity to develop the InSAR program. Since 2005, ADWR has been collecting and processing monthly SAR data from various satellites, producing Level-2 and 3 InSAR-derived products for the State of Arizona. Since 2005 the program has developed important partnerships with numerous State, County, and Local Agencies, Water Districts and Water Companies who provide annual contributions to help support the data collection costs. ADWR has identified more than twenty-eight active land subsidence features that cover an area of 4,175 square miles, determining the spatial extent, deformation rates, and time-series history of each land subsidence feature. The process of collecting, processing, and interpreting InSAR data has resulted in ADWR producing land subsidence maps for each land subsidence feature covering different time periods. There currently is a total of 614 land subsidence maps that are available for download on ADWR’s website, https://new.azwater.gov/hydrology/fieldservices/land-subsidence-arizona. With the recent launching of higher-resolution SAR satellites, such as the Sentine-1 A/B satellites, ADWR has seen an increase with data availability (spatially and temporally). Engineers, hydrologists, geologists, GIS professionals, and scientists involved in the fields of water resources, structural engineering, geological engineering, hydrological engineering, land planning, floodplain management, and surveying greatly benefit from the InSAR data to identify and evaluate areas of land subsidence, uplift, earth fissures, faults, and many other geologic features.

Lessons Learned from Implementation of the SSHAC Process over 25 Years of Hazard Studies

Coppersmith, Kevin, Coppersmith Consulting, Inc., kevin@coppersmithconsulting.com; Ryan Coppersmith, ryan@coppersmithconsulting.com (TS #5) Guidance for conducting probabilistic hazard analyses using the Senior Seismic Hazard Analysis Committee (SSHAC) methodology was issued 25 years ago and the SSHAC approach has now been implemented for all nuclear power plants in the US, many other nuclear and critical facilities in the US, and in several other countries. During that time, additional documents have been issued by the US Nuclear Regulatory Commission (e.g., NUREG-2213) and American Nuclear Society (e.g., ANS-2.29) that provide detailed guidance on the implementation of probabilistic seismic hazard analyses (PSHA) using the SSHAC approach. This presentation will discuss the lessons learned from conducting SSHAC Level 3 and 4 projects for seismic and volcanic hazards analyses for the Yucca Mountain repository, nuclear facilities in the United States (e.g., CEUS SSC, Hanford, Idaho National Laboratory), and other countries (e.g., Canada, South Africa, Spain, Japan). Examples will include site-specific studies, multi-site phased studies, and integrated multi-site studies. Lessons will be described relating to the development of project databases, collection of new data, interactions of experts in workshops and working meetings, use of specialty contractors, and approaches to facilitating objective evaluations in the face of controversial technical issues. The examples discussed will illustrate the evolution of approaches over time, the use of SSHAC for multiple natural hazards, and future potential applications.

The Use of Seismic Shear Wave Testing to Supplement Geotechnical Drilling – Analysis of Rock Depth and Integrity along a Proposed Light Rail Alignment

Cross, Eric, Pyramid Geophysical Services, eric@pyramidenvironmental.com (TS #14) The Triassic Basin soil and rock formations in the Durham, North Carolina, region provide challenges for geotechnical design and construction. These formations consist of highly heterogenous stratigraphy including sands, silts and clays overlying a weathered rock unit that can contain boulders, fractures, and an inconsistent competent bedrock surface. A proposed light rail system was under design to extend through downtown Durham, and a geotechnical investigation was performed to better understand the behavior of the rock formation and its integrity. Pyramid Geophysical Services was contracted to perform a Multi-Channel Analysis of Surface Waves (MASW) seismic survey across specific portions of the proposed rail alignment where geotechnical borings either could not be performed, or where significant variability in the depth of competent rock was observed. The goal of the seismic survey was to “connect the dots” between the geotechnical borings and provide a more comprehensive understanding of bedrock behavior along the alignment. Pyramid performed a total of 542 separate MASW shots resulting in twenty individual 2D cross sections of velocity that were used to analyze the overburden, weathered rock thickness and depth to competent rock across the site. The results of the seismic testing were combined with geotechnical boring data to generate plan-view contour maps of competent bedrock depths across the site. Correlations between the geophysical interpretations and boring data were exceptionally high, and the resultant data set provided engineers with a clear understanding of geologic conditions with which to finalize design plans. This presentation will provide an overview of the MASW testing, the cross-section results, correlations to geotechnical borings and the final plan-view bedrock contours that were used for geotechnical design.

Quantitative Analysis of Community Growth into Geohazard Areas in the Arequipa Region of Peru

Eberle, Brook, Colorado School of Mines, baeberle@mymail.mines.edu; Paul Santi, psanti@mines.edu; Pablo Meza, pmezaa@unsa.edu.pe (Presented by Paul Santi) (TS #9) The Arequipa Region in Southern Peru is vulnerable to a unique set of geologic hazards which are a function of geology, climate, tectonic setting and the conditions of population settlement and local industries. The presence and expansion of mining in the region has the potential to directly affect geologic hazards by ground disruption and indirectly affect hazards by population increase and settlement in dangerous areas. We develop a set of geologic hazard maps for 12 communities in the region, and then quantify changes to hazard exposure based on community expansion patterns over time periods ranging from five to 17 years. Mapped hazards include debris flow, rockfall, flood, landslide, and earthquake liquefaction. Community expansion is measured from analysis of aerial imagery where developed areas are outlined at the beginning and end of the analyzed time. For the twelve communities evaluated, the percent of the area of each community exposed to hazards remained near constant, even with growth. Small changes were noted for specific hazards: rockfall is the most common hazard to have in increase in exposure, flood and liquefaction are the most likely to have decrease in exposure, while landslides are the most likely to have no change. The percent of area exposed to high and medium levels of hazards in a community tends to decrease as development expands over time, while area exposed to low levels of hazards increase. When analyzed by community characteristics, certain characteristics are associated with higher probability of larger changes in percent area exposed to hazards: river communities as opposed to coastal or mountain communities, small communities (< 0.5 km^2 in area), and communities located within 1.5 km of mining areas. Communities with extreme growth rates (more than 25% area increase per year) did not show different hazard exposure than communities with slower growth rates.

The Coyote Warp – An Alternative Landslide Explanation

Elliott, Bill, Retired Consulting Engineering Geologist, redbeds77@gmail.com (Poster) The Coyote Warp is located on the east side of the Sierra Nevada, between Bishop and Big Pine, California. It is a prominent physiographic feature that protrudes conspicuously into Owens Valley. Previous work suggested that the still visible old Eocene(?) erosion surface had been somehow warped down to the north, northeast and east by some mysterious tectonic forces. A fresh look at geologic and physiographic features suggest that the history of this huge mass of rock and soil is better attributed to gravity tectonics than to seismic tectonic forces. The back scarp is defined by a locus of lakes and in-line drainages. Side scarps are well-defined by deep arcuate drainages. The toe is buried by alluvium in Owens Valley. Topography is immature. Benches abound. Grabens and horsts are accompanied by hummocky topography. Deep V-cut canyons have no obvious drainage catchment basins to explain their origin. Springs, immature drainage development and ponded drainages are ubiquitous. Its age is at least pre-Wisconsin, as glacial drift covers the main Coyote Fat bench and thick lateral moraines line the side scarp drainages. Major earthquakes along the eastern Sierra fault zone as well as ice-loading during the most recent glaciations could well have provided nudges as well as driving forces. Future investigations would benefit from lidar, gravity, seismic, and subsurface work. Back calculations would be useful in determining probable subsurface geometry, as well as strength parameters.

Keep America Moving – Innovations in Landslide Investigation and Mitigation Affecting America’s Transportation System

Embry, Scott, GeoStabilization International, scott.embry@gsi.us (TS #10) The U.S. Geological Survey estimated annual losses from damages caused by Landslides to be between $2 billion and $4 billion annually. Even worse, these damages cause very dangerous conditions to the traveling public. Although the consequences of landslides are easily discerned, infrastructure owners are tasked with the dilemma of justifying the large expense of mitigating landslides prior to catastrophic failure or reacting to the landslides post failure. This presentation outlines new innovative landslide mitigation methods and technologies that are both relatively lower in cost when compared to traditional repair methods and robust enough to achieve standard design life (e.g., 75 years). Relevant technologies include soil nailing, micropiles, and GeoSynthetically Confined Soil (GCS®) walls, among others. Several case studies will be presented for remediation projects that occurred prior to and after catastrophic failure of landslide events. Relative economics will be shared for each scenario to help equip the infrastructure owners with data that can be used to help justify the expense of remediation at the early signs of imminent failure or if continued monitoring is warranted. Additionally, the repairs for landslides present many logistical challenges. Some of these challenges will be presented with the solutions that were used to overcome them.

Thru-Dam Seismic Tomography: Leveraging Geophysical Techniques for Condition Assessment of a Thin-arch Concrete Dam

Ensele, Trever, Collier Geophysics, trever@colliergeophysics.com; Roy Bowling, roy@colliergeophysics.com; Phil Sirles, phil@colliergeophysics.com; Doug Yadon, Douglas.Yadon@aecom.com; Linsey Chalfant, lchalfant@fcgov.com (TS #4) Halligan Dam is a 112-year-old, 70-foot-tall, concrete thin-arch dam located 25 miles northwest of Fort Collins, Colorado. The Halligan Water Supply Project by the City of Fort Collins proposes to expand the dam height by 25 feet to expand the potential storage of Halligan Reservoir by 8,100 acre-feet. As part of the design process for the dam expansion, condition assessment of the existing dam was performed. In addition to traditional coring and sampling techniques, a method was developed that could provide insight into the internal condition of the dam that would bridge the gap between point sampling methods. Crosshole Seismic Tomography (CST) is a seismic geophysical method used to image the distribution of seismic compressionalwave velocity (Vp) of geologic material between two parallel or sub-parallel boreholes. This method was adapted to image the Vp distribution of Halligan Dam using the upstream and downstream faces of the dam itself as analogs to the boreholes in the CST method. Using rope-access techniques, sensor arrays (comprised of both hydrophones and geophones) were installed on the upstream face, and hammer-impact sourcing was performed along the downstream face. This “Through-Dam Seismic Tomography” (TDST) technique was performed at three regularly spaced intervals along the length of Halligan Dam. Tomographic sections through the dam structure were computed using the Vp travel times recorded for all active source-receiver pairs for each source location. Results successfully show Vp trends and variations within the imaged sections of the dam. These measurements, alongside traditional concrete coring, provide key information for dam assessment and expansion design.

Lessons Learned – Case Histories on How Not to Build a Tunnel

Escandon, Richard F., Kleinfelder, Inc., rescandon@kleinfelder.com (TS #2) This presentation focuses on two small tunnel projects in soft ground in southern California where near cohesionless alluvial soils were anticipated. The first case involved a 400-foot-long tunnel planned beneath an active creek with young alluvial soils and shallow groundwater. The owner and their design consultant were originally concerned about the potential impact of cobbles and boulders during their planned bore and jack tunneling. A geotechnical investigation indicated the likelihood of encountering cobbles and boulders was low. However, the owner and their consultant did not consider the potential impact of shallow groundwater on the planned bore and jack means and methods which could have led to a disastrous result during tunneling. The second case involved three canal tunnels including a 500-foot-long, 11-foot-diameter tunnel beneath a major freeway with only 10 to 12 feet of cover. Ground improvement using sodium silicate chemical grout to stabilize the ground was planned prior to tunneling under the freeway. However, the contractor awarded the project was inexperienced in this type of ground improvement but elected to self-perform the grouting. Because of the lack of experience, the contractor was required to demonstrate their grouting methods at one of the smaller tunnels planned beneath a railroad spur. The contractors grouting program failed miserably and they were not allowed to self-perform the grouting beneath the freeway unless it was under the direction of an experienced grout “expert.” Concerns regarding the expert hired by the contractor lead to another test section demonstration by the expert which also failed. At this point the contractor was not allowed to self-perform the grouting and was directed to hire a recognized experienced ground improvement company for the grouting program.

Long Island Citizens React to Nation’s Highest Level of Dioxane in Drinking Water Wells

Esposito, Adrienne, Citizens Campaign for the Environment, aesposito@citizenscampaign.org (TS #8) 1,4-dioxane is considered a “likely human carcinogen” which has been found in drinking water wells throughout the nation. Out of 4,400 wells tested by the EPA, Long Island was home to the highest levels in the country. Long Island is a sole source aquifer, which means we are 100% dependent on groundwater for drinking water. To better understand 1,4-dioxane contamination in LI water supply wells, Citizens Campaign for the Environment (CCE) compiled drinking water quality reports from the EPA and local water suppliers and created an interactive map of 1,4-dioxane contamination for each water district on Long Island. Thirty-nine water districts had 1,4-dioxane detections and some wells contained levels over 100 times higher than the EPA’s cancer risk guideline for the chemical (.35 ppb). Many of these high detections are likely legacy contamination from past industrial practices, however there were 1,4-dioxane detections in areas with no history of heavy industry or manufacturing. CCE theorized that small levels of 1,4 Dioxane were likely from household products, which can contain 1,4-dioxane as a bi-product of manufacturing but do not list the chemical on the label. Unfortunately, we still have approximately 400,000 septic systems on Long Island. What washes down the drain, ends up in the aquifer system. CCE conducted first-of-its-kind testing on 80 popular household products, including shampoo, body washes and soaps, laundry detergent, and even baby products, and found that 80% of these products contained detectable levels of 1,4-dioxane. From this data, we created a consumer guide to help residents avoid products with high levels of 1,4-dioxane, conducted an extensive community outreach program, and lobbied for a 1,4-dioxane ban in household products in New York State. We successfully passed this landmark bill and in 2019, NY became the first state to pass legislation mandating the removal of 1,4-dioxane in products. In 2020, NY approved the strongest drinking water standard for 1,4-dioxane in the nation at 1 ppb. We believe that the extensive work done to combat 1,4-dioxane contamination in NY can serve as a guide for other states and federal regulators seeking to address this emerging contaminant.

When an Investigation Takes a Left Turn (A Detective Story)

Evans, Stephen, PanGeo, Inc., sevans@pangeoinc.com (TS #1B) In July 2019, we were called out to review indications of settlement of a three-story apartment building in Seattle, which we were told was experiencing settlement issues. The building was situated on steep slope area on the west side of Queen Abbe hill, on a bench about 12 feet above the level of a parking area west of the building. Another parking area was located east of the building at the third story level. A two-level concrete retaining wall structure east of the building provided separation between the lowest building level and the lot level. We initially visited the site on July 30, 2019, to observe settlement below the floor slab in one ground floor unit, where utility damage was reported. As expected, there were void spaces under the slab. To outline and assess the extent of the settlement, we next carried out an extensive drilling program to assess the soil conditions affecting the building, including borings in the lot to the east, at the building level, and in the lot to the west. However, as we spent time on site, we realized that we were observing damage to the building that was not con-

sistent with settlement alone. When a boring below the retaining wall system on the east side of the building suggested the retaining wall had little or no footing, we began to suspect that the wall was yielding, and pressing on the building through bridge structures that gave access to the second and third floors. Further studies confirmed this was a significant source of distress to the building. Plans are now in progress to stabilize the wall and relieve the lateral pressure on the building, and to address the settlement issues.

Rendered Animal Co-Products as Electron Donors for Subsurface Remediation

Finneran, Kevin, Clemson University, ktf@clemson.edu; John Houston, jkhoust@clemson.edu (TS #15) Electron donor amendment technologies have evolved over time, utilizing varying lipid or carbohydrate-based compounds. Several popular electron donor amendments contain soybean based emulsified vegetable oil (EVO), or low molecular mass organic acid compounds including acetate and formate. This project seeks to develop a group of novel electron donor amendments based on animal co-products to outperform conventional products. These co-products are comprised of waste generated in the animal rendering process such as feathers or bone. The now patented technology will lead to considerably lower cost electron donor amendments compared to commonly used substrates. Serum bottles were assembled with 50 grams of sediment collected from a local site contaminated with trichloroethylene (TCE). The bottles were dosed with various animal co-products at different concentrations (3.2mg/L – 1g/L). Additionally, 20 ml of aquifer water and 20 Mols of TCE were added to each bottle. Bottles were then sealed, and headspace was replaced with nitrogen. Control bottles were assembled with no electron donor, lactate, and emulsified vegetable oil. Chlorinated solvents and dissolved gases were monitored, and measurements continued until stoichiometric ethene production (our operationally defined point of “success”). Animal co-products are readily utilized as electron donors for in-situ chlorinated solvent remediation. Many co-products rendered for this study display comparable dichlorination rates to lactate and emulsified oil controls. Several co-products including feather meal (FMed) and meat and bone meal (MBM) reduced TCE completely to ethene faster and more completely than emulsified vegetable oil. Time to stoichiometric ethene production was typically twenty to thirty days faster with FMed and MBM. Data suggest protein content, and nitrogen release, accelerated complete dichlorination. One significant aspect of these co-products is the substantially lower cost when compared to alternate electron donors. Traditional soybean-based electron donors cost between $0.25-3.00 per pound, while animal co-products based electron donors cost between $0.005-0.225 per pound. Considering many sites may require thousands of pounds of electron donor amendment, the savings potential is significant. Furthermore, by lowering the cost of the electron donor substrate, many more sites could potentially benefit from access to this technology.

USACE Implementation of the Landslide Preparedness Act and a Case for Managing Landslides and other Slope Stability Hazards with a Risk-Based Portfolio Approach

Fontaine, April, U.S. Army Corps of Engineers, April.l.fontaine@usace.army.mil; Bateman, Vanessa, vanessa.c.bateman@usace.army.mil (TS #10) Despite owning a lot of federal property, the US Army Corps of Engineers generally only address impacts to infrastructure by landslides, which are often minimal at our projects. However, when there are impacts to infrastructure from landslides on USACE responsible lands, it has become clear that USACE needs a better way to identify and prioritize mitigation efforts, instead of simply asking for emergency funding. This involves taking a more risk-based and asset management-based approach, but funding, to date for this effort has not been available. With the passage of the Landslide Preparedness Act in January 2021, there is an opportunity to develop a risk-based landslide database to articulate and justify financial need, considering not only the likelihood of the event happening, but more accurately depicting the consequences to the public. While there have been many different hazard rating systems, risk has only been included in a few. Developments in the Dam Safety community of a risk-based approach can be applied to landslides, to better assist with capturing subjective probabilities of adverse events occurring, assist in capturing consequences of those events happening, both life safety and financial, and understanding uncertainty in our analysis. Using the Landslide Preparedness Act as a catalyst, USACE is planning a programmatic evaluation of landslides in our purview and their impacts to prioritize and justify mitigation of our highest risk slope stability problems.

Choosing the Appropriate Method to Predict Volume for Non-fire -related Debris Flows

Foran, Jack, Colorado School of Mines, jforan@mymail.mines.edu; Paul Santi, psanti@mines.edu (Poster) Debris flows constitute a significant hazard in many parts of the developed world. There currently exist many different methods to predict debris flow volumes on the basis of a single design rainstorm, most of which rely on multiple regression models with predictor variables such as basin area, precipitation, and the gradient of the watershed, among others. However, there does not currently exist a comprehensive guide to existing methods and how and where they should be utilized. Furthermore, the accuracy of the methods is not consistently measured. The goal of this project is to evaluate the performance of these predictive methods in a variety of climatic zones and identify where each method makes the best predictions of debris flow volume, for non-fire related sites, and to quantify the error associated these predictions. Preliminary findings from 12 predictive equations to 478 debris flow events from 9 different geographic and climatic regions suggest that most methods do not accurately predict debris flow volumes outside of the regions for which they have been validated. By classifying regions by climate zones and comparing residuals for each method in that zone, we identify the most accurate and usable predictive method for each zone. We also identify the simplest and most accessible variables that contribute to debris flow volume, as some equations require parameters that are difficult to obtain. For regions without historical records of measured debris flow volumes, knowing how to choose the appropriate prediction method will allow practitioners to effectively and accurately estimate non-fire related debris flow volumes as a first step in hazard assessment and towards designing mitigation.

103 Years of Debris Flows, Dodson, Columbia River Gorge, Oregon

Freitag, George, GRI, gfreitag@gri.com; Mike Marshall, mmarshall@gri.com (TS #13) The community of Dodson, Oregon, has been subject to repeated debris flows over the past 103 years. Dodson is located in eastern Multnomah County about 35 miles east of Portland and is situated at the toe of a 2 sq mi alluvial fan formed between the south walls of the Columbia River Gorge and the Columbia River. The fan source cliff area is composed of a 3,000 ft thick sequence of Columbia River Basalt, Troutdale Formation, and LKT Plio-Pleistocene basalt. In 1918 a debris flow on the order of 2M cy in volume closed the Columbia River

Highway. In 1996, following a significant rain on snow event, seven debris flows occurred, including the Tumalt Creek debris flow that affected Interstate I-84, damaged a passing freight train, and flowed into the Columbia River creating a small sediment delta. Mid-fan observations on the Tumalt Creek debris flow in 1996 documented pulse heights on the order of 15 ft from debarked fir trees and 10-ft-high sets of stacked 10-ton basalt boulders. The 1996 Royce debris flow enveloped a residence. In 2001 a debris flow west of Royce affected the I-84 frontage road. In 2021, debris flows again occurred in the Tumalt and Royce drainages, affected I-84 and resulted in a fatality. Lidar mapping reveals entrenched eroded channels near the fan head, channel levees, and multiple coalescing anastomosed channels in the mid-fan and distal regions. In 2017 the Eagle Creek fire burned the entire source and depositional area. High annual precipitation (average 77 in rain + 17 in snow) will continue to drive future debris flows.

Field-based Paleoflood Analyses in a Travel-restricted World: Updates from the Guadalupe River, Comal County, Texas

Freymuth, Bryan, US Army Corps of Engineers, bryan.s.freymuth@usace.army.mil; Keith Kelson, keith.l.kelson@usace.army.mil; Bryan Robinson, bryan.j.robinson@usace.army.mil (TS #4) Paleoflood analyses (PFA) are utilized increasingly in dam safety risk assessments for reducing uncertainties and improving confidence in flood frequency analyses. The basics of PFA rely on field-based geologic data documenting peak flood stages from paleostage indicators (PSI) or non-exceedance bounds (NEB). Multiple field-based PFA across the country were initiated by USACE in late 2019 and early 2020, but COVID-related travel restrictions in spring 2020 eliminated field data collection. Sustained restrictions forced reliance on office-based analyses of high-resolution topography, existing fluvial chronosequences, soil surveys, and archaeological data to identify paleoflood deposits and estimate flood age ranges. Although not ideal, positive benefits of restricted field access include improved pre-field preparation and, subsequently, better field data collection efficiency. An ongoing PFA along the Guadalupe River in central Texas developed an initial paleoflood chronology via virtual mapping efforts utilizing high-resolution hillshade terrain models, inundation extents, and existing geologic maps. Field reconnaissance verified a series of three fluvial terrace remnants based on height above the Guadalupe River, soil development, and down-valley longitudinal profiles. The terrace remnants occur at elevations between the stages of the 1913 flood of record (FOR) and probable maximum flood (PMF) and are interpreted as PSI based on sedimentologic and geomorphic characteristics. Peak discharges associated with paleoflood features were estimated based on calibrated HEC-RAS hydraulic models of the FOR and PMF, using both 1D and 2D simulations. Based on these efforts, the Guadalupe River reach near New Braunfels appears to be viable for paleoflood analysis should field data collection be possible in the future. This effort highlights the benefit of combining remote and traditional field mapping and shows that valuable paleoflood information can be developed from relevant office-based data if, and only if, augmented by subsequent field information. This approach may be applicable to other PFA reaches having restricted field access.

20 Years of Lessons Learned – Looking Back on a Dam Rewarding Career

Friend, Edwin, U.S. Army Corps of Engineers, edwin.r.friend@usace.army.mil (TS #4) Geological and geotechnical engineering are rooted in observing processes and identifying trends in data. Terzaghi was a master at this concept and sadly many of his lessons have been forgotten or not learned. As a profession we need to share not only our successes, but also our failures, near misses, and stressful situations, because it is from these events where we truly learn. This presentation will depict several lessons learned from the presenter’s personal experience and lessons he has identified as key case histories that helped him throughout his career in dam geological engineering. Lessons learned will deal with differing subsurface site conditions, dewatering of problematic materials, trench stability with slurry supported excavations, stability of clay shales, the value of investigation and construction experience, and others.

Potential Failure Modes Analysis (PFMA) of the Beaver Falls Project in Ketchikan, Alaska

Gagnon, Hawkins, Schnabel Engineering, jgagnon@schnabel-eng.com; Tom Fitzgerald, tfitzgerald@schnabel-eng.com; Jennifer Holstrom, JenniferH@City.Ketchikan.Ak.Us (TS #7) The fourth potential failure modes analysis (PFMA) for the Beaver Falls Project (FERC ID 1922) was performed by Ketchikan Public Utilities (KPU), the Federal Energy Regulatory Commission (FERC), and Schnabel Engineering on August 8, 2019. The Beaver Falls Project is located within Tongass National Forest on the western side of Revillagigedo Island in southeastern Alaska. Project structures are built around two natural lakes and the project includes two storage dams (Upper Silvis and Lower Silvis), one diversion dam, two spillways, three power conduits and two powerhouses. Due to the Project’s seismic, geologic, and physiographic setting, geomorphologic and seismic failure modes are key components of the Project risk. This presentation will highlight risk-driving geology-related potential failure modes (PFMs) and will cover the importance of geology to understanding project risk. Many of the hypothesized PFMs for the Beaver Falls Project are related to the potential for slope instability and/or earthquake loading. For Upper Silvis, PFMs include the possibility of a seiche wave created by a landslide causing dam overtopping, failure of the rock slope above the Upper Silvis powerhouse, failure of the penstock due to rockfall or impact, and spillway failure due to rockfall/debris. For Lower Silvis, PFMs include failure of Upper Silvis, failure of the penstocks due to rockfall or earthquake, and a seiche wave created by a landslide that overtops the dam.

Emergency Response and Mitigation for a Sequential Rockslide on US-95 near Riggins, ID, July 2020

Gates, William Chester, McMillen Jacobs Associates, gates@mcmjac.com; James Struthers, struthers@mcmjac.com; Jamie Schick, schick@mcmjac.com; Ethan Guzek, guzek@mcmjac.com; Luke Ferguson, ferguson@mcmjac.com (TS #10) (Presented by James Struthers) US-95 is the sole north-south route in the Idaho panhandle. The route borders the Salmon River canyon and cuts large unstable rockslopes with adverse dipping structures that have been historically prone to rockslides. In December 2012, a large rockslide occurred about five miles south of Riggins, Idaho blocking the highway and leaving a large unstable rock mass. Eight years later, on July 3rd and 10th, 2020, two large, sequential rockslides occurred blocking the highway and leaving a large unstable block stranded 200 feet above the highway. Idaho

Transportation Department (ITD) retained McMillen Jacobs to provide emergency response and geotechnical consultation including geologic characterization of the slope using rope access techniques, recommendations for rock scaling, installation of telemetered monitoring equipment, and development of mitigation strategies for the slope. Remote monitoring methods were used to develop criteria for safe drilling and reopening of the highway. Immediately, plans and specifications for the project were developed and advertised 21 days after the failure. Concurrently, we worked with Wallace Technical Blasting to develop a cushion blasting design to remove the remnant unstable rock mass. The project was awarded to Scarcella Brothers on August 18th for $3.2 million. Within seven days of the award, 122 blastholes were drilled, loaded with 6000 pounds of explosives, and shot on August 28th to remove the remaining unstable block. Following the blast, we developed final mitigation plans including design and installation of rock anchor reinforcement, on-slope rockfall mesh, brow stabilization, design of rockfall mitigation, and design of catchment systems and assisted ITD with the oversight of construction of the design with a full-time presence. Mitigation was completed on November 14th and followed immediately by repaving and full opening of US-95. ITD and McMillen Jacobs were awarded the Association of General Contractors Top Gold Medal for Excellence in Construction Partnering.

Application of the Block Theory Rock Erodibility Method to Evaluate Scour Potential and Risk at the Don Pedro Dam Emergency Spillway

George, Michael, BGC Engineering USA, Inc., mgeorge@bgcengineering.ca; Cole Christiansen, cchristiansen@bgcengineering.ca; Casey Smith, casmith@bgcengineering.ca; Evan Lucas, emlucas@tid.org (TS #4) Scouring processes in rock are complex and present several challenges for practitioners to confidently assess scour potential. This is particularly relevant for dams and spillways where scour can pose a significant risk to infrastructure and individuals present in the flood inundation zone downstream. Scour of rock, particularly in unlined channels, is predominantly controlled by removal of discrete blocks of rock by hydraulic forces. Stability of these blocks is largely governed by the orientations of discontinuities within the rock mass, but until recently, no method was available to incorporate 3D orientations of these discontinuities into scour assessment. The Block Theory Rock Erodibility Method is a new, physics-based methodology developed for that purpose of evaluating erodibility of 3D rock blocks subject to hydraulic loading. This presentation provides an overview of the Block Theory Rock Erodibility Method as well as an example application for evaluation of scour potential of the Emergency Spillway at Don Pedro Dam (the 9th highest dam in the United States) located in the Sierra Nevada foothills near La Grange, CA. The results of the scour assessment were used to inform a semi-quantitative risk assessment (SQRA) that was performed to identify key risk drivers at the site.

Assessing Rock Face Instability with Ground-based Interferometric Radar for Rock Faces in Eastern Utah

Gomez, Francisco, University of Missouri, fgomez@missouri.edu; Brent Rosenblad, rosenbladb@missouri.edu; Charles Miles, charles.miles@idsgeoradar.com (TS #5) Ground-based interferometric radar (GBIR) is an imaging-based technology with potential for early detection of unstable rock faces and earth slopes, owing to its capability to measure small (sub-millimeter) displacements by differencing phase between two radar images. Portable GBIR systems, in particular, provide a cost-effective means for infrequent scanning of rock faces to identify and characterize small movements that may pose a more significant risk. This study presents new results on the detectability threshold of GBIR, as well as an application to detecting potentially unstable rock faces. Quantifying the minimum detectable displacement was assessed using controlled experiments with a rock-like target that was moved with precisely controlled displacements at distances ranging from 40 to 150 meters. Results show the GBIR system was capable of reliably measuring displacements as low as about 0.2 mm with accuracy in the range of 0.1 to 0.2 mm. This detectable threshold is an order of magnitude improvement over techniques using EDM or LiDAR. An example of the utility of infrequent GBIR surveying is shown for a study site above a road near Moab, Utah. Repeat surveys were conducted twice per year (November and May) over a three-year duration. A large previously undocumented rock mass was identified after the second survey. Subsequent surveys demonstrated that the rock mass creeps downslope seasonally with up to 5 cm of displacement during the late winter or early spring. Additionally, several smaller, boulder-sized features were also identified. These results demonstrate how GBIR can efficiently identify small movements in rock faces that may pose a more significant risk.

Use of Low-Altitude Aerial Photogrammetry for Neotectonic and Geomorphic Investigations: Mapping, Morphometry, and Landform Modeling

Gomez, Francisco, University of Missouri, fgomez@missouri.edu; Sean Polun, polunsg@missouri.edu (Poster) Low-altitude aerial surveying is emerging as a tool that greatly improves the ease and efficiency of measuring landforms for quantitative geomorphic analyses. High-resolution, close-range photogrammetry produces dense, 3D point clouds that facilitate the construction of digital surface models, as well as a potential means of classifying ground targets using spatial structure. This study presents results from recent applications of sUAS-based photogrammetry, including high resolution surface morphometry of a lava flow, repeat-pass applications to mass movements, and fault scarp degradation modeling. In all cases, high-precision ground control points are key for accurate (and repeatable) orientation—relying on low-precision GPS coordinates (whether on the ground or geotags in the aerial photos) typically results in substantial rotations (tilt) of the reference frame. Using common ground control points between repeat surveys results in matching point clouds with RMS residuals better than 10 cm. In arid regions, the point cloud is used to assess lava flow surface roughness using multi-scale measurements of point cloud dimensionality. For the landslide study, the point cloud provides a basis for assessing possible displacements. In addition, the high resolution orthophotos facilitate mapping of fractures and their growth. For neotectonic applications, we compare fault scarp modeling results from UAV-derived point clouds versus field-based surveys (kinematic GPS and electronic distance measurements). High-resolution topography also permits improved mapping of subtle fault scarps using artificial sunshading. In summary, there is a wide-ranging toolbox of low-altitude aerial platforms becoming available for field geoscientists. In many instances, these tools will present convenience and reduced cost compared with the effort and expense to contract acquisitions of aerial imagery.

Regional Stress Estimation Method using Acoustic Televiewer Data

Goodfellow, Sebastian, KORE Geosystems, sgoodfellow@koregeosystems.com; Patrick Hooker, phooker@dgigeoscience.com; Chris Drielsma, cdrielsma@dgigeoscience.com; McLain Pray, jmpray@dgigeoscience.com (Presented by McLain Pray) (TS #14) Regional stress is traditionally a challenging and expensive measurement, and the available methods, such as overcoring, produce sparse data that are subject to high levels of uncertainty. DGI obtained principal stress orientations from Acoustic Televiewer (ATV) data, which was previously acquired for other geotechnical purposes (fracture analysis, fault modelling). Multiple holes drilled in different orientations were analyzed for borehole breakout patterns, and a global optimization algorithm was run to step through all possible stress states fitting the observed breakouts. The global minimum, defined as the stress state which minimizes the angular residual between observed breakout orientations and theoretical breakout orientations, was found and uncertainties calculated for sigma 1, 2, and 3. Extracting stress information out of ATV data resulted in a stress state calculation supported by hundreds of observations across the entire rock volume of interest.

UAS-Based Monitoring of Rockfall in Glenwood Canyon, Colorado: Preliminary Result

Graber, Andrew, Colorado School of Mines, apgraber@mymail.mines.edu; Paul Santi, psanti@mines.edu (TS #3) In any given year, the stretch of Interstate 70 passing through Glenwood Canyon, Colorado, experiences multiple rockfall events. In Fall 2020, the Grizzly Creek fire burned portions of the canyon and adjoining Grizzly Creek and Dead Horse Creek drainages, as well higher elevations of the White River uplift to the north and south of the canyon. Anecdotally, rockfall activity is expected to increase for a time after the fire, but the degree of this increase has not been well studied in the literature. In addition, the ongoing background risks of rockfall impacts to the highway necessitate monitoring and study of rockfall processes to better understand the hazards. This research seeks to use UAS-based rockfall monitoring and Structure from Motion photogrammetry to 1) quantify the increase in rockfall frequency resulting from the wildfire by monitoring a burned slope and an unburned slope with similar rockmass characteristics and 2) monitor two additional slopes close to the highway to evaluate rockfall frequency from two different lithologies that are common along the highway alignment. Data collection began in January 2021 and will continue at least through January 2022 with scans of each of the four slopes on a monthly basis. Rockfall frequency is computed using the M3C2 change detection algorithm applied to point clouds generated using Structure from Motion photogrammetry. We present preliminary results from change detection of rockfall in Glenwood Canyon and Grizzly Creek, as well as observations of burn damage and talus depositional behavior.

Remote Geoenvironmental Hazard Mapping in the Arequipa Region of Peru

Grady, Cassidy, Colorado School of Mines, clgrady@mymail.mines.edu; Paul Santi, psanti@mines.edu; Gabriel Walton, gwalton@mines.edu; Percy Colque, scolquer@unsa.edu.pe, Pablo Meza, pmezaa@unsa.edu.pe (TS #9) In the Arequipa region in Peru, numerous geoenvironmental hazards impact the daily life of small communities situated in the mountains, on the coastline, and in the hills in between. A lack of hazard susceptibility characterization in the region means that there is limited capability to predict and mitigate hazards, leaving small communities without the necessary tools to reduce their vulnerability to hazards. At present, there is a deficiency in the literature for efficient mapping of a wide range of hazards in various environments. The primary focus of this study is to remotely characterize geoenvironmental hazards at ten sites in the Arequipa region, including landslides, debris flows, flooding, erosion, liquefaction, rockfall, and seismic and volcanic hazards. An array of hazard mapping techniques is used to develop hazard inventories from aerial imagery and adaptations of existing hazard rating systems to produce preliminary hazard maps of the ten sites. Next, we calibrate the preliminary maps using field observations, local community knowledge, and other published hazard inventories. Then we create GIS-based models for automatic mapping of hazard identification and susceptibility and validate the models against our maps. These methodologies will decrease the dependency on timeconsuming field investigations to characterize geoenvironmental hazards in remote sites, providing preliminary maps that improve upon current approaches in the literature. While these maps are no substitute for field-confirmed maps, they are an important resource to help prioritize future mapping and investigation efforts. A diverse assortment of environments and hazards are included in this research. Thus, the resulting framework is expected to be relevant for further hazards analysis in Peru and other countries with similar hazards and geomorphic and climatic settings. Community members, local governments, and hazard and disaster-focused organizations will be able to implement these methodologies to prepare for hazardous events and develop mitigation strategies at a community level.

You Don’t Look Like a Geologist—Why are the Geosciences the Least Diverse of the STEM Fields?

Green, Deborah, GeologistWriter deb@geologistwriter.com (TS #12) As a young geologist I was often told, “You don’t look like a geologist.” I haven’t heard that in years, which speaks to the fact that more women are studying geology and going on to careers in the field. The face of a geologist isn’t necessarily male anymore. According to statistics from the American Geosciences Institute (AGI) at least forty percent of geology graduates are women. However, we are still an overwhelmingly white profession. The same report indicates less than twelve percent of geology graduates identify themselves as underrepresented minorities. For three years, beginning as the 2018–2019 Jahns Lecturer, I have been holding conversations with students and professionals on the lack of diversity in the field. There is no single reason, instead a number have come to light, including economic, cultural, and demographic issues. In 2020, due to the murder of George Floyd, millions more than ever before have opened their eyes to the issues of discrimination, individual and systemic, plaguing society. And so have many members of our profession, bringing additional momentum to understanding and mitigating the lack of inclusion in the geosciences.

Flood and Debris Flow History of the Montecito Watersheds, Santa Barbara County, California

Gurrola, Larry D., The Project for Resilient Communities (TPRC), lg@larrygurrola.com; J. David Rogers, rogersda@mst.edu (TS #5) Watersheds in the Santa Ynez Mountains of southern California discharge sediment-charged floods that debouche at canyon mouths to form coalesced debris fans on the coastal piedmont surface. Developed on the bajada, the community of Montecito was mauled on January 9, 2018, by post-fire debris flows (PFDF) resulting in 23 fatalities, over 500 homes destroyed or damaged, and closure of U.S. Hwy 101 for 13 days. Funded by TPRC, one of this study’s objective is to construct a historical inventory of flood events that records

physical evidence of the relative severity of damages, inundation paths, meteorological conditions, and type of events to understand the history of flood events for the last 200 years. Historic records establish nineteen debris flows and debris-laden flood events have occurred in the Montecito watersheds, in 1825, 1861–62, 1872, 1879, 1884, 1889, 1907, and 1911, three events in 1914, 1926, 1964, 1969, 1971, two events in 1995, 2018, and 2019. These events account for 66% of all events (29) recognized in southern Santa Barbara County. Nearly 80% of the Montecito events occurred during post-fire watershed conditions establishing that the catchments are sensitive to the environmental impacts of brush fires. Several PFDF events were triggered by rainfall intensities of 0.6 inches per 20-minute interval. Long duration, intense precipitation or multiple storm events with high antecedent moisture triggered not only debrischarged floods but also landslide dams. Reconstruction of early 20th century debris flows with latter 20th century events in Montecito reveal similar flow paths and avulsion sites. Avulsions repeatedly occur at points of constriction due to flow jams diverting the flow outside their low flow channels, and these out-of-bank flows spread coarse debris on the fan surfaces. This inventory establishes that debris- charged floods occur more frequently than previously realized and often impact the same flow path corridors.

Improving Rockslope Stability Investigations Using UAV-Based 3D Modeling

Guzek, Ethan, McMillen Jacobs Associates, guzek@mcmjac.com; Thomas Pallua, pallua@mcmjac.com (TS #3) Unstable rockslopes are surrounded by difficult-access terrain which presents challenges in obtaining large-scale measurements and gaining line-of-site to broad features located high above the ground surface. Imagery obtained using unmanned aerial vehicles (UAVs) provides “bigpicture” perspective, allowing critical features to be observed in context of the entire slope. Imagery sets also provide data to produce 3D point clouds and surfaces using photogrammetry techniques. These factors lead to increased project efficiency and refined stability analysis and design. Trained personnel can identify stability-controlling features across a given slope within hours of arriving onsite. Further, rope-access techniques and on-slope data collection can then be focused towards zones of apparent instability. In addition to mission planning, products of UAV-based photogrammetry and 3D modeling provide accurate data that can be directly incorporated into existing analyses and workflows. For instance, 2D cross-sections can be extracted and input into traditional limit-equilibrium stability models. Linear and surface area measurements can also be extracted directly from point clouds to provide block dimensions when determining the depth, strength, and number of anchors required to reinforce a particular slope. Beyond traditional practices, 3D data allows industry practitioners to reduce the number of assumptions and error during analysis of design elements. This includes QA/QC for items such as rock reinforcement embedment depths, blast pattern design regarding burden and release planes, and estimates of construction quantities. These methods have been used during several emergency responses to rockslides in the Western Unites States over the past year.

Evaluating Resilience of the Beach-Dune System at South Padre Island, TX

Hapke, Cheryl, Integral Consulting, chapke@integral-corp.com; Patrick Friend, pfriend@integral.com; Kristina Boburka, kboburka@myspi.org; Steven Watt, swatt@integral-corp.com; Chris Flanary, cflanary@integral-corp.com (TS #1A) South Padre Island, Texas, is a narrow low-relief barrier island along the south Texas coastline that is frequently affected by storms and sea level rise. The City of South Padre Island (SPI), on the southern end of the Island, is a top Gulf Coast tourist destination and provides a multitude of coastal recreational opportunities that contribute substantially to the region’s economic viability. A study is being undertaken at SPI to understand both long- and short-term evolution of beach-dune system. The purpose of the study is to determine a characteristic “resilient” beach morphology that the City of SPI can recommend as the best alternative for maintaining the important recreational and ecological functions of the system, but also provides a high level of protection from coastal hazards. The initial phase of the study evaluates the historical changes to the beach-dune morphology using a time series of twenty-five cross-shore profiles spanning twenty-six years. The historical changes are correlated to an equivalent time series of wave data to evaluate various processes that drive change to the system. The analysis includes examination of a variety of morphometrics, including beach morphology, volume, dune crest and toe elevations, beach width, and shoreline change. The beaches and dunes are re-nourished on a regular basis and the nourishments are accompanied by extensive dune vegetation planting. Presently the dune field is relatively wide (~ 150 feet) except in the northern reaches, where it narrows to nearly non-existent in some areas. Profile volumes show a distinct trend with beach volumes decreasing substantially in the north portion of the study area through all time periods. The initial results indicate that the northern section of the study area is substantially more vulnerable to flooding and erosion than the central and southern portions.

Controls on Debris Flow Avulsions: White Mountains of California and Nevada

Herbert, Lauren, Colorado School of Mines, lherbert@mymail.mines.edu; Paul Santi, psanti@mines.edu (TS #13) The process by which debris flows shift from an active channel and branch out into new channels or areas is termed avulsion. Debris flow avulsion poses serious risks for structures and populations residing on debris-flow fans, yet avulsion mechanisms are relatively unknown and unaccounted for in hazard assessments, as compared to better understood fluvial avulsions. However, avulsion is a critical mechanism controlling the distribution of debris flow deposits. This study analyzes six debris-flow fans in the White Mountains of California and Nevada to identify relationships between channel and avulsion characteristics, constrain the controlling factors on avulsion, and assess the probability that avulsion will occur at specified locations. This study aims to develop a method to predict avulsion based on the factors that control avulsion on debris-flow fans. The fans on the western flank of the White Mountains are an ideal study area for this work, as they have a long record of debris flow and avulsion events. A database of avulsion locations and their channel characteristics was compiled in the field. These were compared to the characteristics of other positions on the fan surface that show evidence of debris flows, but not avulsion. The database (n=58) of avulsion and non-avulsion characteristics was analyzed through stepwise, binary logistic regression. Results indicate that two-thirds of avulsion likelihood at a site can be attributed to its percentage of boulders, slope angle, channel width, and ratio between flow thickness and average slope. The accuracy of this model can be

improved with the consideration of a coarse channel plug, which increases the likelihood of avulsion. Application is demonstrated by runout simulations with forced avulsions from modeled channel plugs. These results improve our ability to predict and model debris flow avulsion so that it may be readily incorporated into geohazard assessments in the future.

Characterizing Potential for Seepage and Internal Erosion on Karst Foundation using a Holistic Data-Based Approach

Huebner, Matthew, Tennessee Valley Authority, mthuebner@tva.gov; Joshua Shinpaugh, jeshinpaugh0@tva.gov; Husein Hasan, hahasan@tva.gov; Jeffrey Munsey, jwmunsey@tva.gov (TS #9) Tennessee Valley Authority (TVA) Dam Safety recently completed a detailed investigation of several potential failure modes related to seepage and migration of embankment material, particularly into foundation karst features, at a dam located in the Valley and Ridge province of eastern Tennessee. The evaluation focused on identifying potential seepage patterns, specific vulnerabilities to soil erosion, defensive features, and the possibility that internal erosion could be presently occurring at the dam. This study consisted of a holistic approach that integrated numerous data sets in a spatial, temporal, three-dimensional context. Available data, including foundation mapping, design information, construction records, borehole data and grouting records, dam safety performance instrumentation data, inspection records, and remote sensing data (including InSAR) were compiled, spatially referenced, and synthesized as part of this investigation. Additionally, new land- and marine-based geophysical data were acquired to characterize subsurface conditions at the dam, with the primary focus on identifying potential karst cavities or seepage pathways. While the evaluation did not indicate internal erosion has initiated or is currently progressing, areas that could possibly represent potential seepage paths or advanced karst dissolution were identified, which informs our efforts for future investigations and highlights focus areas for routine dam safety inspections and monitoring. Overall, the results of this study highlight the benefits of directed geophysical studies designed to address specific project objectives to gain a better understanding of the geologic conditions at a site, and also demonstrate the importance of evaluating all pertinent data in a spatial context to better understand and inform risk estimates for geologically based failure modes.

Simulating Groundwater Pumpage Induced Land Subsidence using MODFLOW 6

Hughes, Joseph D., U.S. Geological Survey, jdhughes@usgs.gov; Jacob E. Knight; John H. Ellis; Jason K. Ramage (TS #6) Compressible fine-grained sediments are susceptible to inelastic compaction in response to groundwater pumpage in many aquifer systems in the world. Inelastic compaction of fine-grained sediments results in land subsidence, which can damage infrastructure and increase the frequency and intensity of flooding. The adverse effects of inelastic compaction resulting from groundwater pumpage have been observed in many unconsolidated, heterogeneous aquifer systems including the Central Valley, California, USA; the Houston-Galveston region, Texas, USA; the Ganges-Brahmaputra Delta, Bangladesh; the Jakarta basin, Indonesia; the lower Mekong Delta, Cambodia and Vietnam; and the Virginia Coastal Plain, USA. A skeletal storage, compaction, and subsidence (CSUB) package has been developed for MODFLOW 6 that can simulate elastic compaction of coarse-grained sediments and elastic and inelastic compaction of fine-grained sediments resulting from changes in pressure heads and geostatic stresses in an aquifer system. The CSUB package incorporates the functionality of the subsidence packages available in previous versions of MODFLOW. Unlike previous subsidence packages, the CSUB package can simulate compaction of fine-grained sediments that respond quickly and slowly to effective-stress changes. The CSUB package is being applied in the GULF-2023 model, which is a replacement for the Houston Area Groundwater model (HAGM). In the HAGM, compacting fine-grained sediments were assumed to respond quickly to water-level changes. Fine-grained sediments in the GULF-2023 model are represented as slowly compacting sediments. Sediment properties are being calibrated using a combination of benchmarks, subsidence contour maps, extensometer data from 12 sites, and vertical displacement data from 173 Global Positioning System (GPS) sites. GPS data, located throughout the model domain unlike the extensometer data which are limited to Galveston and Harris counties, have improved confidence in the GULF-2023 model’s ability to predict land subsidence. Preliminary projections indicate additional subsidence could occur with current groundwater pumping rates with little or no additional water-level declines.

Dam Grout Curtain Installation Made Easy with 3D Visual Modeling

Irsch, Brian, Schnabel Engineering, birsch@schnabel-eng.com (TS #7) A double-row grout curtain was constructed to reduce the permeability of the highly weathered, interbedded sandstone and shale foundation at the original spillway location during construction of a new relocated spillway. A 3D visual model was developed concurrently as field data was gathered during the drilling, water pressure testing and grouting. Data from the spreadsheet field records was parsed with internal software and converted into a 3D model in SketchUp, which could be viewed in the field on a laptop. Individual layers such as the geology, permeability from water pressure test results, and injected grout volumes were displayed together and could be individually controlled, to present the most relevant features and relationships for analysis. The 3D visual model easily revealed the location of high permeability areas allowing hydrogeologic analysis of the trends and/or anomalies to be quickly assessed and decisions made with respect to target pressures and grout mix selection. Performance of the grout mixes could also quickly be assessed by comparing grout volume injected to permeability, and subsequent permeability testing of the upstream curtain, as the grouting program progressed. This real-time visual assessment allows for more efficient and higher quality technical decisions, than looking at a 2D profile with numbers. Use of 3D models becomes even more useful on geologically complex sites, those with extensive data sets, or those with complicated grout line geometries.

Extinction is Forever! A Further Reason for Strict Control of Industrial Fly Ash and Power Plant Discharge Products

Isphording, Wayne, Tierra Consulting Associates, isphordingw@bellsouth.net (TS #15) The generation of electrical power by burning of coal has been shown to be clearly inefficient, when compared with the use of either gas or fuel oil. Further, waste products associated with coal burning plants (e.g., fly ash) are responsible for numerous deleterious environmental effects that are potentially harmful to the health of both human and animal life. A clear example of the impact of such wastes has been documented by “watchdog” environmental groups for the Barry Steam Plant located twenty-five miles north of Mobile, Alabama. Leaching of the exposed 600-acre fly ash waste site has generated levels of arsenic, lead, mercury, and other metals in the groundwater and surface water runoff that, on occasion, far exceed maximum values imposed by the EPA and the State of Alabama. The impact on the immediately adjacent Mobile Delta River System, often termed

“America’s Amazon” because of its rich biodiversity, has been further exacerbated by discharge of power plant cooling waters whose low dissolved oxygen content and elevated temperatures frequently exceed maximum allowable levels. Collectively these create a “dead zone” several miles in length up and down the river from where discharge waters from the plant enter the Mobile River. This zone is clearly visible on LANDSAT satellite imagery and has been implicated in the marked demise of anadromous fish species, such as the Gulf Sturgeon and Stripped Bass. Future plans by the power company to simply “de-water” and cover the waste pile and construct a redundant dike system around the waste site, have been shown to be ineffective at similar sites elsewhere in the State. Environmental groups are urging total removal and relocation of the fly ash to dry lined landfills, such as are now mandated elsewhere in a number of states, as a means of safeguarding the watershed.

Communicating Geologic and Seismic Hazards with Geotechnical and Structural Engineers

Johnson, Courtney, Slate Geotechnical Consultants, Inc., cjohnson@slategeotech.com (TS #9) In our built environment, there exist countless opportunities for geologists to assess geologic and seismic hazards and therefore just as many chances to communicate findings to engineers, clients, owners, and regulators. Many geologists spend a great deal of time communicating with and educating their non-geologist colleagues, project team members, and clients on geologic concepts and the hazards they have identified. Identification of such hazards, creating maps, and writing a report are just the first steps. Effective communication of how, how much, and how often those hazards may impact a structure or site starts with learning the language of not only the geotechnical engineers we often work closely with but also clients such as structural or civil engineers. Taking this step is imperative for successful project completion when hazards are involved because geologists are often relied upon to build context for project foundations (literally). In addition, the identification and assessment of geologic and seismic hazards becomes even more crucial as resilience and risk-informed decision making become larger factors in the consideration of mitigation measures. Examples will be provided where technical language differences resulted in confusion on scope and budget. These lessons learned show how early two-way discussions and learning to ask the right questions can help rectify issues early in the project. Pulling from experience working on all types of structures at various scales of scope, schedule, and budget, other examples of both successes and failures in hazard communication will be provided.

TBM Hard Rock Mining through Difficult Ground and High Groundwater Pressure in the Mid-Hudson Valley of New York The NYCDEP Bypass Tunnel – A Triumph in Tunneling

Jordan, Eric W., Parsons Corporation, eric.jordan@parsons.com (TS #2) New York City is presently constructing a new hard-rock, high-pressure water tunnel to bypass documented leaks in the City’s primary water supply tunnel, the Delaware Aqueduct. The Delaware Aqueduct conveys approximately 50 percent of New York City’s drinking water on a typical day. The existing leaks in the aqueduct coincide with water bearing, fault zones. A new, state-of-the-art Robbins single shield, segmental tunnel boring machine was designed to mine through variable ground conditions with hydrostatic pressure approaching 20 bar. The project required innovative approaches by the owner, contractor, and construction manager to mine almost 2.5 miles with variable conditions under the Hudson River. Project purpose, strategies, design, technical challenges, and solutions are described in the paper.

Using Elevated Concentrations of Chromium and Nickel as an Indicator for the Presence of Chrysotile Asbestos in Serpentinite Rock Units

Kalika, Sarah, DiabloGeo Environmental, skalika@diablogeo.com (TS #15) Serpentine, a magnesium silicate mineral formed when peridotite is altered by extremely hot water during tectonic plate subduction and partial crustal melting from heat from the upper mantle, is composed of the platy minerals lizardite and antigorite crisscrossed by veins of chrysotile. In California, serpentinite is typically found within the Coast Range, Klamath Mountains and Sierra Nevada foothills. When analyzed for metals presence, serpentinite rocks typically contain elevated chromium (Cr), nickel (Ni), and chrysotile. When project sites are evaluated for the presence of potentially hazardous substances or waste soil is analyzed for landfill disposal pre-approval, metals are part of the list of required analytes, but often evaluation for the presence of asbestos is not included. Following years of anecdotal observation, this research intended to evaluate whether the presence of elevated chromium and nickel concentrations could be a reliable indicator for the presence of chrysotile asbestos. If such a correlation could be made, at what concentrations would the presence of Cr and Ni be a predictor for chrysotile? This study used data from soil samples collected within California’s Coast Ranges and reported within site investigation reports published for public use on the California Department of Toxic Substances Control Envirostor database and California’s State Water Resources Control Board Geotracker database. Data was evaluated using statistical tools to establish a threshold concentration for Cr and Ni, above which, serpentinite is likely to be the source and warrants additional analysis for the presence of chrysotile asbestos.

Let’s Get Real – Stories from Women in the Geoscience Workplace and Listening to Learn

Kalika, Sarah, DiabloGeo Environmental, sarah@georx.net (TS #12) Women, people of color, LGBTQ, and others often experience an alternate workplace or life experience that messes with our psyches. Many of us have experienced the feeling that despite your education and knowledge—you don’t belong or you’re playing a part that isn’t actually deserved. Was I admitted to college because they were trying to include more women into my STEM program? Will I keep my job if I show my “true” self? Women, POC, and LGBTQ professionals often adapt by creating a workplace persona that differs from their real self. Examples include a set of “professional” clothing, conservative haircuts, even speaking differently. Workplace micro-aggressions and inappropriate behavior continue to exist and often there is not a clear path established by a company or university to lodge a complaint and prevent this behavior from happening in the future. This presentation will summarize a few real-life stories from professional workplaces in an effort to share knowledge of things that still happen that weigh all of us down. Companies lose talented employees when they protect inequality and toxicity. Universities lose talented students. What do we do about this? The first step should be to open our ears to the stories of others. When we listen to learn, we gather information that helps us eliminate our blind spots, feel empathy toward others, and make conscious choices. Understanding that not everyone comes from the same backgrounds and being willing to learn, include, and support— not marginalize, dismiss, and cancel—can create change that benefits all of us.

GIS-Based Analysis of Deforestation near Seongheung Mine in North Korea

Kim, Yebin, Seoul National University, yebin96@snu.ac.kr; Hyeong-Dong Park, hpark@snu.ac.kr (Poster) Although North Korea has abundant minerals, the number of mines out of operation is increasing. One of the reasons is that the infrastructure is outdated, making natural disaster response and restoration difficult. Mining activities cause deforestation, but reforestation is mitigation method for natural disasters. In this study, to understand the status of deforestation and analyze landslide susceptibility near Seongheung Mine, Pyeonganam-do in North Korea, remote sensing, and GIS analysis for data-scarce area were conducted using Landsat 8 OLI (Operational Land Imager), ASTER DEM. Slope, aspect, elevation, curvature, TWI (Topographical Wetness Index), distance from road and water were used to estimate landslide susceptibility. As a result, it was confirmed that deforestation is in progress, thus, the appropriate mine reclamation must be carried out for sustainable mine development. Acknowledgement: This work was supported by a grant from the Human Resources Development program of the Korea Institute of Energy Technology Evaluation and Planning (KETEP), funded by the Ministry of Trade, Industry, and Energy of the Korean Government.

Groundwater Use Changes in the Arizona and California Basin and Range: A Sustainability Examination

Knight, Michael, Gannett Fleming, Inc., mknight@gfnet.com; Byron Dixon, bdixon@gfnet.com; Thomas Waddington, twaddington@gfnet.com (TS #1B) Land use changes that alter consumptive water use patterns have the potential to increase groundwater availability within subsidiary basins of the Basin and Range Province. Evolving changes are significant because water is so valuable and contentious near regional population centers. Water consumption in Arizona’s Gila Bend Basin and California’s Harper Lake Basin has undergone measurable reduction in the last decade because agricultural land uses have been replaced by the renewable energy industry. Reduced demand for groundwater has accompanied Concentrated Solar Plant (CSP) development that replaced crop irrigation systems with groundwater systems for mechanical cooling. Ideally, groundwater for CSP cooling would have a lower ionic load than is available, but superb regional solar characteristics, outweigh ambient water quality concerns. The Province’s groundwater is found within alluvium comprising a system of interconnected and isolated sub-basin aquifers. Sub-basin groundwater has been tapped regionally but not without concerns for inherent recharge limitations; water table declines; land subsidence; and soil salinity. Many such impacts are not recoverable, so even minor changes have magnified importance. In the Harper Lake Basin, a fee structure imposed by the Water Master aims to reduce consumption and support aquifer replenishment. In Arizona’s Butler Valley, studies on State Trust Land examined replenishment options for restoring groundwater that has supported agricultural concerns. Stemming impacts from irrigation is challenging because Butler Valley lacks replenishing natural inflows. If implemented, the water bank will be available for other uses. Reversing impacts in the Province’s alluvial aquifers is clearly possible but many opposing factors exist including arid conditions, low natural recharge rates and increasing population demands. Subtle land use changes can have favorable long-term groundwater sustainability outcomes, but these may be difficult to discern, and they compete with increasing regional demands.

BCRUA Phase 2 Tunnel, Delivering Water through the Glen Rose Formation

Koziol, Matt, Schnabel Engineering, mkoziol@schnabel-eng.com; Kemp Lewis, klewis@schnabel-eng.com (TS #2) Brushy Creek Regional Utility Authority (BCRUA) is a partnership established to deliver raw water from Lake Travis, which is owned and regulated by the Lower Colorado River Authority, to meet the rising demands of the rapidly growing cities of Round Rock, Leander, and Cedar Park, Texas. Phase 2 of the project includes the design and construction of two new lake taps in Lake Travis, a two-mile intake tunnel, a pump station with an underground cavern, a 300-ft-deep wet well and access shaft, six pump well shafts, a half-mile transmission pipeline tunnel, and a secant pile and blind bore shaft. The project site is located within the Edwards Plateau, which is a physiographic region bounded by the Llano Uplift to the West, the Balcones Escarpment to the South and East, and the Blacklands Prairie to the East. A majority of the underground project features will be constructed in the Glen Rose Formation, which is comprised of Lower Cretaceous aged rocks alternating from thin- to medium-bedded soft and hard limestone, dolostone, and siltstone/marl. Softer limestones are mostly biomicrite (fossil fragments in a fine-grained calcium carbonate matrix), marly limestone (clayey limestone or clayey biomicrite), or marl (lithified material of calcareous clay origin or calcareous clay-like material). The presentation will describe these key project features and the geologic exploration including the methods utilized, locations, and in-situ and laboratory testing conducted. A summary of the results of the investigation will be presented along with a summary of previous tunneling experience in this formation. Design considerations with regard to the anticipated behavior of the geology for construction of the tunnels and shafts and requirements for construction means and methods and rock support will be discussed.

Landslide Susceptibility Prediction in Arid-Mountainous Terrain Using Machine and Deep Learning Models

Kumar, Chandan, Colorado School of Mines, chandankumar@mines.edu; Paul Santi, psanti@mines.edu; Gabriel Walton, gwalton@mines.edu; Cassidy Grady, clgrady@mymail.mines.edu; Carlos Luza, cluzah@unsa.edu.pe (TS #13) Landslides are common natural hazards that threaten human populations across the globe. The spatial prediction of landslide susceptibility plays a significant role in assessing vulnerability and applying safety measures to reduce landslide risk. The arid and mountainous terrain of Peru experiences a diverse range of landslides, including rockfall, shallow landslides, and debris flows. This study implements an integrated approach of ensemble feature selection, machine, and deep learning (DL) models for accurate landslide susceptibility mapping and spatial risk zonation. The study site is situated in the Arequipa region of southwestern Peru. The area includes a few active volcanoes and experiences active seismicity that can trigger slope instability. We prepared a historical landslide inventory using high-resolution and temporal imageries from Google Earth. Several factors contributing to landslide occurrence, including topographical (elevation, slope, aspect, curvature, topographic position index, ruggedness index, convexity), hydrological (rainfall, drainage density, topographic wetness index, stream power index, stream transportation index), geological (lithology, soil type, lineament density, distance from faults, seismic zone, distance from volcanoes) and anthropogenic (land use/landcover, distance from roads, distance from settlements) factors, were derived with conjugate utilization of multi-sensor remotely sensed and secondary datasets. The geolocation of landslides was used to derive the training datasets and subsequently used in developing machine learning (support vector

machine and random forest), convolution and recurrent DL models with different architectures. Models were evaluated using performance metrics and field verification. A sensitivity analysis was performed to assess the impact of training data quantity on the performance of models. The developed models successfully produced accurate landslide susceptibility maps, which were further used in spatial vulnerability analysis to categorize areas as higher or lower risk by considering the locations of settlements and road networks. The susceptibility and risk zonation map can be used as valuable baseline data to develop strategies to mitigate landslide risk.

Equity and Inclusion as a Business Imperative: How One Firm Created Change from Within

Lawson, Masai, Gannett Fleming, Inc., mlawson@GFNET.com (TS #12) Tackling inclusion and diversity in a business can seem like too tangled a knot to untie. Some think they must be the CEO to make a difference in this realm, and others think it’s too large of an issue to affect change. Creating change is often a lonely endeavor. Those who take on this challenge are not only looking to create a culture of inclusion and harness the power of diversity, but they’re also trying to convert the nonbelievers. Every ounce of energy is worth the investment, not only because it’s the right thing to do, but also because the numbers don’t lie: diverse teams are nearly always more profitable—enjoying higher rates of retention and client satisfaction than homogenous teams. This, in turn, translates into stronger employee engagement and an improved company culture. Simply put, inclusive teams can propel your firm to success. But merely talking about diversity and inclusion doesn’t make it so. How can an engineering firm move from words to action? Successfully implementing change requires support at the executive level of the organization, as well as broad company awareness and education. It also requires both qualitative and quantitative ways to measure success. As individuals, we can all influence shifts in our firm’s culture, and we can all impact change, no matter our years of experience or role in a firm. Using specific tactics and strategies, my presentation will explore Gannett Fleming’s journey to elevate inclusion and diversity in the 105-year-old, 2,500-person firm.

Imaging and Mapping of Karst Features in Central Texas Using Geophysical Methods

Laymon, Doug, Collier Geophysics, LLC, doug@colliergeophysics.com; Juan Ortega (TS #14) Subsurface imaging and mapping investigations of karst features were completed in central Texas using geophysical methods. Karst features are prevalent in the central Texas region and are found predominantly in the Edwards Group and other similar limestone formations in the area. The Edwards is also a major aquifer in the region and much of the deeper karst features are water filled. However, depending on the location and depth, these features can be filled with air, sediment, water, or a combination thereof and will provide different geophysical responses. Additionally, some karst features in the central Texas area are home to several endangered species and provide an important component of their habitat. These karst features can also be a geohazard of concern in the region due to their potential effect on construction projects. These effects can be related to both pre and post construction subsurface structural features and the potential effect to critical habitats if present. Subsurface imaging using geophysical methods such as electrical resistivity tomography (ERT) and seismic refraction tomography (SRT) can be useful in mapping these features to address engineering and construction related concerns. Case histories are presented to support the use of geophysics for preconstruction characterization and mapping of karst features. Application examples of the use of geophysics for characterization of karst features include pre-drilling of a utility corridor near an artesian spring and critical habitat, additional mapping of a cave near an existing roadway, and preconstruction characterization of a tunnel route to limit potential risks to tunneling machinery due to the presence of karst.

Linking Subsidence to Changes in Stored Water in California’s San Joaquin Valley

Lees, Matthew, Stanford University, mlees@stanford.edu; Rosemary Knight, rknight@stanford.edu; Ryan Smith, smithryang@mst.edu (TS #6) 1D compaction models have provided critical insights into the nature of subsidence in clay-rich aquifer systems. However, they have not been applied to the problem of estimating the change in total stored groundwater ( Sgw). Sgw is a quantity of fundamental importance for many groundwater management decisions, yet it is seldom known with a high degree of confidence. In this presentation, we describe how we used a 1D compaction model to estimate the change in stored groundwater in the multi-layered aquifer system in California’s San Joaquin Valley. In our model, we took hydraulic head timeseries in the coarse-dominated aquifer material as inputs and solved the governing equations for the compaction of clay and sand layers. We validated our model with surface deformation data from interferometric synthetic aperture radar (InSAR) and levelling surveys. Our model directly solved for the compaction of sands and clays, which is one of the three storage components in an aquifer system. As a biproduct, the model also calculated the head within all sand and clay layers in the aquifer system. We used this head information to compute the two other components of storage: drainage of pores and expansion of water. We could thus accurately quantify the total storage Sgw. We applied our model in the San Joaquin Valley, where we found a total loss of storage of almost 5 m of water between 1990 and 2017. We found drainage of pores and compaction of clays provided approximately equal volumes of water, while expansion of water contributed only a small portion of the total. Our study demonstrates a method which can provide accurate estimates of ∅Sgw and which could be used around the Valley to provide critical information to support groundwater management decisions.

Beardsley Afterbay Dam Maintenance Project – Using Data and Evaluations to Revise Designs

Lewis, Scott, Condor Earth, slewis@condorearth.com; Andy Kositsky, akositsky@condorearth.com (Presented by Andy Kositsky) (TS #4) Beardsley Afterbay Dam is a 41-foot-high wood crib dam in the Sierra Mountains on the Middle Fork Stanislaus River in California. The dam impounds the afterbay below a hydroelectric plant at Beardsley Dam. Tri-Dam Project (TDP) owns the facility. California Division of Dam Safety (DSOD) and the Federal Energy Regulatory Commission regulate the facility. TDP completed Beardsley construction in the late 1950s with Beardsley Afterbay providing tailwater for a turbine. In the early 1980s, TDP began diverting afterbay water through a new tunnel to a lower hydroelectric plant. Recently, DSOD restricted the pool elevation in the afterbay because of potentially unsafe conditions caused by increasing seepage through the dam estimated at 77 cubic feet per second (cfs). The lowering had a significant negative effect on TDP power generation downstream of the afterbay. TDP retained engineering geologists/civil engineers at Condor Earth (Condor) to expeditiously investigate the seepage and design maintenance repairs. Condor performed pre-construction and during-construction investigations and found that significant seepage occurred through deteriorated abutment cutoff walls, deteriorated deck planking, and created erosion

holes in crib backfill and surrounding ground. We designed sheet pile walls, backfill, deck replacement and other measures to reduce seepage to be constructed during short annual outage periods when afterbay lowering was possible. Condor evaluated conditions for design, during construction and between construction phases. We revised the designs based on our data evaluations to effectively mitigate the seepage. TDP’s construction contractor successfully constructed the work, and the seepage rate reduced to 7 cfs. DSOD removed the restricted pool elevation and TDP resumed water diversion/power generation.

Sea Level Rise and Land Subsidence at Tide Gauge Galveston Pier 21, Texas

Liu, Yi, Morgan State University, yi.liu@morgan.edu; Jiang Li, jiang.li@morgan.edu; John Fasullo, fasullo@ucar.edu (TS #1A) Relative sea level rise at tide gauge Galveston Pier 21, Texas, is the combination of absolute sea level rise and land subsidence. Geologic type at the tide gauge location is classified for land subsidence type determination. Land subsidence at the tide gauge includes basement rock subsidence (tectonic or GIA and rock creep subsidence) measured by GPS, creep subsidence of unconsolidated and/or semi-consolidated aquifer systems, and consolidation subsidence due to subsurface fluid withdrawals from the aquifer systems. We estimate subsidence rates of 3.53 mm/a during 1909–1937, 6.08 mm/a during 1937–1983, and 3.51 mm/a since 1983. Subsidence attributed to aquifer-system compaction accompanying groundwater extraction contributed as much as 85% of the 0.7 m relative sea level rise since 1909, and an additional 1.9 m is projected by 2100, with contributions from land subsidence declining from 30 to 10% over the projection interval. We estimate a uniform absolute sea level rise rate of 1.10 mm ± 0.19/a in the Gulf of Mexico during 1909–1992 and its acceleration of 0.270 mm/a2 at Galveston Pier 21 since 1992. This acceleration is 87% of the value for the highest scenario of global mean sea level rise. Results indicate that evaluating this extreme scenario would be valid for resource-management and flood-hazard-mitigation strategies for coastal communities in the Gulf of Mexico, especially those affected by subsidence.

Consideration of Bedrock Characteristics in Estimating Grout Fill Volume: Historical Case Studies

Martin, Rebecca, Missouri University of Science and Technology, rmg6c@mst.edu (TS #7) The engineer’s best answer to permeable, porous, fractured, jointed, or faulted rock at a proposed dam site—short of selecting a different location—is often grout injection. Injection of grout into abutment walls and foundations can mitigate poor rock stability by filling fissures, decreasing permeability, and improving shear strength. However, because abutment rock is unexposed and has site-unique characteristics, predicting the volume of grout required and thereby generating an accurate project budget is challenging. Volumes of grout significantly exceeding expectations are at times demanded mid- or post-project if dam stability is to be assured. Recent studies of grout injection have focused primarily on such questions as rheology and filtration tendency, and there have been few comparative studies evaluating models of seepage and grout take in differing rock types and strata. This presentation reviews case studies of major mid-twentieth century dams located in rhyolite ashflows and karstic limestone on the Tennessee, Snake, and Teton Rivers, examining the abutment rock in question, the methods used for grout volume estimation, modes of correction, and effects on the overall success of the dam projects. Available estimation methods from the twentieth century, namely, Lugeon tests and test-grouting, are compared to popular statistical and computational estimation methods of the past two decades, and the accuracy of each is evaluated in varying unstable rock types.

50 Years of Paleoseismology

McCalpin, James, GEO-HAZ Consulting, Inc., mccalpin@geohaz.com (TS #11) In the early 1970s, engineering geology (EG) added a new field of endeavor to its portfolio—studies of active faults. This field complimented the existing field of observational seismology, which had no techniques to study “dormant” faults (i.e., not currently seismically active). The realization slowly dawned that: 1) many Quaternary-active faults had a recurrence interval much longer than the historic record in the USA, and 2) considerable hazard existed from faults which could generate earthquakes only up to the M6s and lay in/near urban areas; it wasn’t just the M7-8 faults we needed to worry about. To study dormant faults from geologic evidence, EG had to import scientists with experience in geomorphology, Quaternary stratigraphy, and soil stratigraphy. These were found in academia and became strange in-house bedfellows to the older, traditional engineering geologists. A collaboration began between the EG industry, USGS, and academia that continues today; it swept me up in 1976. Over the past 50 years paleoseismic data has become a necessary input for Seismic Hazard Assessment (SHA) of ground motions and surface faulting. The field experienced a stairstep evolution of rapid advances triggered by new data collection tools (lidar, optically stimulated luminescence), separated by plateaus in which the new techniques were applied to large geographic areas. Research funding was plentiful in the 1970s–80s, but by the mid-1990s was subsumed by the growing dominance of climate change funding. By the late 2000s leadership in the field passed to Europe and Asia, which provided more funding for national and global paleoseismic studies. But the United States remained the incubator of new ideas/techniques, such as lidar, luminescence and cosmogenic dating, and the most sophisticated codes for Probabilistic Seismic Hazard Assessment. Paleoseismic projects will be affected by the national transitions away from fossil fuel projects to renewable energy, and by increasing water supply projects.

The Challenges of Large-Scale Terrain Conductivity Mapping and Inversion for Shallow Bedrock Determination

McKinley, Kate, THG Geophysics, Ltd., ksm@thggeophysics.com; Alex Balog, axb@thggeophysics.com (TS #14) With the recent increase in utility-scale solar projects, engineers are faced with the challenge of determining the appropriate foundation design in geographic areas that are dominated by varying shallow subsurface conditions. THG Geophysics has assisted in mapping shallow bedrock on several projects, some exceeding 1,000 acres, by deploying a UTV mounted terrain conductivity meter. THG deployed a GF Instruments CMD Explorer, a 3-dipole tool, to collect datasets that could be inverted to obtain maps of varying apparent conductivity with depth. Using boring data, associations were derived between apparent conductivity and rock conditions. In all cases, inverting datasets from records that cover large tracts with variable geologic conditions introduces challenges in formulating an apparent conductivity model that fits site conditions. In karst-dominated regions, shallow, high-quality limestone often occurs alongside sporadic sand deposits and thick, conductive clays overlie deep, weathered bedrock. In developing a conductivity cutoff model to represent the transition from soil to bedrock across a site, discriminating between clay and competent limestone was often simple. However, weathered limestone bedrock often exhibited higher conductivities than sand deposits, generating a

map that overestimated the presence of shallow bedrock in those areas. Further, areas underlain by shale bedrock often exhibited apparent conductivities similar to that of soil, resulting in deeper modeled bedrock than was indicated in boring data. Evaluating the relative success of modeled bedrock depth required an iterative process of adjusting model cutoffs and comparing results against known boring data. Although this method is fast and efficient for assessing large areas of shallow rock, it requires intensive geologic assessment of the inversion residuals to quantify misinterpretations.

What to Look for in an Inclusive Company

Moe, Minda, Arcadis U.S., Inc Minda.Moe@arcadis.com (TS #12) This presentation will summarize important facets of an LGBTQ+ inclusive workplace that job seekers may look for, and which companies can use to improve their own policies. Internal structures and policies which helped Arcadis achieve a perfect score in the Human Rights Campaign’s 2021 Corporate Equality Index, including its corporate DE&I support and local Employee Affinity Groups structure, will be showcased.

Empirical Analysis of Landslide Runout in Glacial Strata in the Salish Lowland, Washington

Molinari, Mark, GeoEngineers, mmolinari@geoengineers.com; Carla Woodworth, cwoodworth@geoengineers.com; Cody Gibson, cgibson@geoengineers.com; Michelle Deng, mdeng@geoengineers.com (TS #5) This study developed empirical relationships to estimate potential landslide runout for slopes in Salish Lowland river valleys draining the North Cascade Mountains in western WA. There are multiple published studies relating landslide runout parameters of length (L), height (H), reach angle (), deposit area (A) and volume (V) using linear or log regressions. Most data sets include varying landslide types and sizes, geology, and geographic locations and/or are for large, long runout debris flows, lahars, and rock avalanches. River valleys in the eastern Salish Lowland are well suited for regional empirical study because of available high-quality lidar, numerous Holocene landslides, and slopes with relatively consistent topography and geology of glacial and interglacial deposits with underlying weathered rock on some lower slopes. Our data set consists of 160 landslides mapped in three river valleys: Cedar, North Fork Stillaguamish, and Skagit. The data includes H and L for debris slides/avalanches (120), debris flows (12) and flow and long runout (>3000 ft) landslides (28). Debris slides, avalanches and flow slides have unconstrained or partially constrained flow paths between the source area and valley floor, whereas debris flows have constrained flow paths. The failure H minimum is 34 ft and maximum is 955 ft, with 130 slides ranging in H from 100 ft to 600 ft. Runout lengths range from 127 ft to 5,998 ft. Analysis results indicate good correlations (R2 = 0.61 to 0.75) for regressions of H vs. L for the total data and subsets by landslide type. V vs. A data from the Cedar River valley also had good correlations; however, unlike some prior studies, relationships using or tan as a parameter have very poor correlations. Uncertainties in the source parameters and the equations can be used to assess a range of probabilities for future landslide runout risk assessment.

Pennsylvania State Route 26 – Emergency Landslide Mitigation

Morris, Matthew, Gannett Fleming, Inc., mmorris@gfnet.com; Joseph Krupansky, jkrupansky@gfnet.com (TS #10) Throughout Appalachia, Departments of Transportation (DOTs) are impacted by slope stability issues affecting their roadways and infrastructure. These slope failures commonly occur in an unpredictable manner and location, prompting the DOT to mobilize quickly to evaluate and mitigate the failure impacting the roadway. On April 26, 2020, a significant landslide slide occurred on State Route 26 near the town of Riddlesburg in Bedford County, Pennsylvania. The slide extended laterally 300 feet along the road and upslope approximately 100 feet above the roadway grade. The soil and rock that mobilized downslope completely covered SR 26 in tens of feet of soil and rock. The Pennsylvania Department of Transportation (PennDOT) engaged Gannett Fleming through an existing engineering agreement to evaluate the slide conditions, develop a mitigation plan and prepare contract bid documents. PennDOT set a goal of awarding the project to a contractor within three weeks, ultimately opening the roadway to traffic no later than July 4th weekend, as the road provides critical access to a popular recreational area. This presentation will cover the slide evaluation, development of the mitigation concept, plan and specification preparation, bidding processes, and construction consultation required to remove 15,000 cubic yards of soil and rock, stabilize the slope, and restore functionality of the road. The goal of the presentation is to show a landslide case history commonplace throughout Appalachia, and to educate the audience on the processes that PennDOT used to streamline the mitigation design and construction activities. Special emphasis will be placed on the innovative investigation methods used to evaluate the slide and adapting to unforeseen conditions revealed during construction.

Pyrite and Construction: Evaluating Pre- and Post-Failure

Murdock, Kathryn, Exponent, Inc., kmurdock@exponent.com (TS #15) Since the 1950s, the destructive potential of pyrite and related sulfide minerals to structures has been observed across four continents. The two manners by which iron sulfide minerals typically cause construction issues are: incorporation of soluble sulfate minerals into concrete mixes thus causing degradation from within the structure, or the presence of those minerals in fill or surrounding native soils which then through chemical interactions ultimately cause heaving of the nearby structures. Both processes are highly dependent on oxygen, iron sulfide, and carbonate availability, however the oxidation reaction of iron sulfide minerals is cyclic and will continue once oxygen has been introduced to the system. Increasingly, iron sulfide minerals have been identified as the causes of concrete degradation in homes and other structures in the northeast United States, leading to interest in mitigation of this hazard as the effects of iron sulfide-induced structural failures can appear years to decades after initial oxidation. Regulations as to the amount of acceptable iron sulfides vary by country and there is no universal standard. For example, Ireland has a maximum allowable sulfate of 0.2% in an acid soluble test, but this test does not measure the amount of pyrite, only the soluble sulfate, which is a byproduct of pyrite oxidation. The European standard EN 12620:2008 requires total sulfur content to be less than 0.1% if pyrrhotite is detected, or 1% if only other iron sulfides are present. Canada and Japan have also determined acceptable amounts of sulfate or total sulfur allowed in concrete, but a national standard has not been created for the United States. Identification of localized geology is paramount to preemptively reduce the risk of iron sulfide-induced damage. Once structural failures occur, visual, geochemical, and geophysical methods are available to evaluate if the cause is related to iron sulfides.

The Future of Tailings Management

Nelson, Priscilla, Colorado School of Mines, pnelson@mines.edu (TS #7) The global industry currently anticipates annual production rates of billions of tons of mine tailings and waste rock, with increases in the future expected due to the higher utilization of lower-grade ores. There is an increasing concern worldwide for the potential consequences from tailings dam seepage and failure due to the combination of unprecedented tailings production and the possibility of more extreme weather events associated with global climatic change that can adversely affect tailings disposal facilities. The mining industry must address and mitigate these risks by considering the continuity of materials flow and the integrated value chain. Holistic tailings management, including integrated selection of physical + geometallurgical + chemical + biological processes (sequenced here in general chronological order of involvement) is needed to achieve sustainable extraction (including remining, reprocessing, and recycling) and minimized tailings volume, with the attending positive social and environmental benefits. The value chain includes the ore body itself (characterization and modification of ore and gangue), excavation, transport, mineral processing, and tailings management/disposal/storage. Intervention can be designed to occur at any step in the value chain.

Resilience and the Urban Underground

Nelson, Priscilla, Colorado School of Mines, pnelson@mines.edu (TS #2) The underground construction industry has consistently provided the nation with needed infrastructure, meeting schedule, cost, and scope goals. Population growth will continue, and much of this growth will happen in our cities. Future urban development requires increasing and intensive planned use of underground space, but in order to make better decisions concerning the underground, the functions and operations of the human and physical infrastructure systems must be understood under normal operations and under extreme events as integrated systems with common and meaningful metrics and representations. This presentation introduces a framework for infrastructure analysis that can include all urban sectors—physical, social, and environmental.

Application of the Dam Site Exploration Framework for the Parish Camp Saddle Dam Raise – More Than Meets the Eye

Nichols, Holly, DWR, holly.nichols@water.ca.gov; Nicholas Hightower, nicholas.hightower@water.ca.gov; Joseph Mason, joseph.mason@water.ca.gov (TS #7) Parish Camp Saddle Dam is a 27-foot-high earthen embankment dam that is part of the Oroville Dam facilities in California. The dam was constructed in 1967 and is located about ten miles northwest of Oroville Dam. As a result of a comprehensive assessment of the vulnerabilities of the Oroville facilities, the Department of Water Resources Dam Safety Services Office created a dam safety project to raise Parish Camp Saddle Dam as much as 5 feet. This dam raise would lower the risk of overtopping failure during PMF-type flood events. The preliminary design consists of a full downstream overlay and dam raise, possibly steepening the uppermost portion of the upstream side of the dam. As part of the design process, the geology team was consulted to evaluate the need for additional geologic exploration. To develop the exploration workplan, the geology team utilized the exploration framework presented by Morley et al. (USSD Conference Proceedings, 2020). This dam site exploration framework ensures that the following five components have been considered: understanding the site geology, informing potential failure modes (both current and future), answering design questions, evaluating constructability, and supporting construction management. As could be expected, when the geology team delved into each of these topics, the need for more and more explorations became apparent. This presentation will discuss the evolution of this site exploration plan and how it was presented (and accepted) by the project team.

Changing the Bureaucracy – Advances in the California Department of Water Resources’ DEI Culture and Policy

Nichols, Holly, California Department of Water Resources, holly.nichols@water.ca.gov; Hilary Garibay, hilary.garibay@water.ca.gov; Tim Ross, timothy.ross@water.ca.gov (TS #12) Diversity, equity, inclusion, and social justice are important topics being discussed nationally, if not globally. Many employers are taking actions to help support diverse workforces, provide opportunities equitably, and create an inclusive working environment. The California Department of Water Resources has strived to create a trusting and welcoming workplace where employees embrace diverse viewpoints and treat each other with civility and respect. Within DWR, the geology community regularly meets to discuss DEI topics as they specifically relate to our profession. This presentation will discuss the actions being undertaken by DWR as a whole, but also within the subset of the geoscience community, including our bi-monthly diversity, equity, and inclusion roundtable discussion.

Geology of a Tuolumne River Crossing in the Poopenaut Valley of Yosemite National Park, California

Nielson, Dru R., McMillen Jacobs Associates, nielson@mcmjac.com; Su Soe, soe@mcmjac.com; Jon Burgi, burgi@mcmjac.com (TS #1B) The 306-foot-deep Hetch Hetchy Reservoir was formed in 1923 by construction of the 400-foot-tall O’Shaughnessy Dam across the Tuolumne River in Yosemite National Park, California. The dam spans a 900-footwide gap formed within an assemblage of granitic plutons that partition the Tuolumne River into upper and lower reaches. Prior to construction of the dam, the Upper Tuolumne River meandered through the nowflooded wide and expansive Hetch Hetchy Valley while the Lower Tuolumne River was, as it is today, confined in the narrow and steepsided Poopenaut Valley. The evolution of the landscape now occupied by the river and associated valleys included: 1) plate subduction–related volcanism and ancestral mountain range development rooted in Mesozoic plutons of the Sierra Nevada batholith; 2) erosion of the ancestral mountains exposing their granitic basement by the middle Cenozoic; 3) tectonic uplift, brittle jointing, and stream downcutting of V-shaped valleys of the modern Sierra Nevada by the late Tertiary; 4) several episodes of Pleistocene glaciation that resulted in the development of U-shaped and hanging valleys, roches moutonnée, moraines, and polishing striations of the basement bedrock; and, most recently, 5) renewed stream downcutting and scour, rockfalls, and forest-fire-influenced mass wasting. Collectively, these elements influence siting and design of civil structures in one of the most environmentally protected, pristine, and scenic natural landscapes of North America. This presentation summarizes the results of a geotechnical investigation of a bridge crossing of the Tuolumne River in Poopenaut Valley. The investigation included geologic field mapping of stream deposits, artificial fills, glacial signatures, granitic bedrock types with their associated sills and dykes, and discontinuities; seismic refraction surveys; bedrock coring; and a review of previous reference studies, published geologic maps, and historical aerial photographs and topographic maps. Data from the investigation were used to evaluate foundation characteristics and potential channel scour.

More Accurately Measuring Well Efficiency: A Step toward Better Design and Evaluation of Relief Wells

Niemann, William L., US Army Corps of Engineers (USACE)-CELRH, William.L.Niemann@usace.army.mil; Andrew M. Keffer, Andrew.M.Keffer@usace.army.mil; Kenneth K. Darko-Kaga, Kenneth.Darko-Kaga@usace.army.mil; Erich D. Guy, Erich.D.Guy@usace.army.mil; Trevor T. Deere, Trevor.T.Deere@usace.army.mil (TS #1B) Relief wells are used worldwide to reduce uplift pressures at dams and levees. Accurate measurement of well efficiency (Ew) is critical in the design and evaluation of these wells. This paper presents a detailed analysis of Ew for a US Army Corps of Engineers (USACE) relief well at the Magnolia (Ohio) Levee based on step-drawdown pump test data. The analysis entailed multiple recognized methods to quantify individual components of the total well losses at the design discharge. Such an approach is necessary to compute true Ew, and in a form that can be used to project uplift pressures against the blanket layer overlying the project foundation. Relating Ew to well losses is preferred to other measures such as specific capacity (discharge per unit drawdown) and the Lp of Driscoll (1986), which is the ratio of aquifer head loss to total head loss. We show how the step-drawdown test data used in this study is key in isolation of the individual components of the total well losses. In addition, we discuss challenges to data interpretation including geologic heterogeneity and partially penetrating wells.

Shallow Foundation Load-Settlement Behavior Assessed from Surface Geophysical Data

Norris, Gary, University of Nevada, Reno, norris@unr.edu; Sherif Elfass, elfass@unr.edu (TS #14) Given soil data from the Soil Conservation Service (USDA NRCS) and the shallow geophysical test shear or P wave record, the following method and spreadsheet provide the means for undertaking a preliminary evaluation of the load-settlement response of a shallow foundation at the prospective site. From the shear wave velocity (Vs), the initial shear modulus (Go) and then initial Young’s modulus (Ei) at the level of geophysical test field strain (1 x 10-6) is assessed. The Young’s modulus (E) at a specified stress level (SL) is then determined from a modulus reduction relationship. From the Schmertmann et al. (1978) relationship between Young’s modulus E and the cone penetration test point resistance, qc, and the Robertson and Campanella (1983) relationship [qc/N60= f(D50)], the standard penetration blow count N60 is determined. From the corrected blow count, N1,60, the soil friction angle (f) is obtained from the Florida DOT (2004) modified Peck, Hanson and Thornburn curves. The net bearing capacity, qnet, is then assessed knowing c (assumed) and f of the soil and the soil’s unit weight. The mobilized bearing pressure, qnet,m, and the strain (e = SL EXP(3.707 SL) e50/l ; e50, the strain at 50% SL (provided from a supplied figure) at the specified stress level (SL) and the settlement (= e B for a square footing from the Schmertmann triangle of strain beneath the footing) follow. The preceding method is for a c-f soil. A separate method is provided for the immediate load-settlement response of a c soil (saturated clay). Those who email me (norris@unr.edu) can get a gratis copy of the spreadsheet.

Practical Applications of Time Domain Reflectometry for Landslide and Slope Monitoring

Paulose, Presty, KANE GeoTech, Inc., presty.paulose@kanegeotech.com; Brian Forsthoff, brian.forsthoff@kanegeotech.com (TS #10) Time Domain Reflectometry (TDR) has been around for decades and is widely used for monitoring and diagnostic purposes in various fields. For geotechnical applications, TDR is used to detect and locate subsurface movement by installing and sealing coaxial cables in boreholes. The electrical properties of the TDR sensor cable change as it deforms. TDR sends an electrical pulse along the cable, and then the changes in that pulse are measured. Rapid data collection and simple installation methods make TDR a cost-effective solution to slope monitoring over other popular methods such as inclinometers. This methodology has been successfully implemented on infrastructure projects, including railways, pipelines, and dams in North America. TDR systems are configured for manual readings or remote monitoring. Manual readings routinely take less than a minute. In remote monitoring, alerts such as emails and text messages, notify key personnel of critical activity. It is possible to monitor dozens of installations from one location. Sensor cables are either installed horizontally or vertically. For example, in Tennessee an approximately 4,000-ft-long horizontal TDR sensor cables were installed along a potentially liquefiable dam embankment. In California, vertical TDR sensor cables were implemented to alert gas company personnel of landslides that could damage pipelines. One drawback of inclinometers is that they are unusable once the casing has deformed, and reliable readings are unobtainable. Since the TDR cable is smaller and more flexible, the sensor cable conforms to the deformations in the inclinometer casing. By retrofitting unusable inclinometer casing with TDR sensors in a California landslide, the life of existing monitoring systems was extended. This presentation describes the goals, design, construction, and challenges involved in implementing TDR systems with linear infrastructure applications.

Litho-mineralogic Analyses Applied to Paleoflood Investigations for Dam Safety Risk Assessments

Pearce, Justin, USACE Risk Management Center, justin.t.pearce@usace.army.mil; Bryan Freymuth, bryan.s.freymuth@usace.army.mil (Presented by Bryan Freymuth) (TS #7) A paleoflood investigation is being conducted along part of the Arkansas River to better characterize overtopping risk-driving failure mode for John Martin Dam in southeastern Colorado. One approach used in our paleoflood analysis is evaluating slack water deposits (silts and fine sands) found within arroyos tributary to the mainstem Arkansas River. A crucial uncertainty using this approach involves determining the provenance of the sediment—did the fluvial sediment interpreted as slack water deposits within Mud Creek arroyo originate from flood flows emanating from the tributary arroyo watershed or from large floods along the Arkansas River creating backwater inundation into the tributary arroyo watershed? Geomorphic and stratigraphic field evidence were equivocal; that is, onlap relationships and orientation of laminae and ripple marks were not fully sufficient to clearly demonstrate the fluvial origin. However, because the Arkansas River watershed headwaters contain volcanic rocks that are not present within the Mud Creek watershed, a litho-mineralogic approach was developed to semi-quantitatively assess the provenance of the flood deposits. Sediment samples from the flood deposits were hand processed and reviewed under optical microscopy. Results of the analysis determined the presence of minerals endemic to the Arkansas River watershed (e.g., olivine, topaz, beta-quartz) in each of the horizons sampled. Based on the results

the analysis, the slack water deposits were assessed as originating from backwater flooding into the Mud Creek arroyo from large rare past floods on the Arkansas River. This in turn permits the slack water flood deposits to be analyzed as a paleostage indicator for Arkansas River flood flows. This litho-mineralogic approach demonstrates a useful geologic tool to support paleoflood analyses in watershed tributary to mainstem rivers.

Comparing the Scoop3D and the GIS-TISSA Models for Slope Stability Analysis in Idukki, Kerala, India

Pikul, Stepan, Department of Geological and Mining Engineering and Sciences, Michigan Technological University, spikul@mtu.edu; Thomas Oommen, toommen@mtu.edu; K.S. Sajinkumar, sajinks@keralauniversity.ac.in (Presented by Thomas Oommen) (TS #13) Landslides are the most destructive hazard in the mountainous Idukki district in the State of Kerala, India. Therefore, evaluating the possible occurrence of landslides and analyzing the factors that trigger failure is an essential part of a reliable landslide assessment. Physics-based models are commonly used to determine potential landslide susceptible areas in terms of Factor of Safety (FS). Recent years have seen the use of physics-based methods for regional-scale landslide susceptibility analysis using geospatial tools. In this study, we compare two physics-based models using the same data from Idukki. The two models are the Geographic Information System-Tool for Infinite Slope Stability Analysis (GIS-TISSA) that utilizes the infinite slope stability analysis, and the Scoops3D algorithm that uses limit-equilibrium analysis. The significant difference between these two physics-based models is that the GIS-TISSA assumes a shallow failure surface parallel to the slope angle. In contrast, the Scoops3D evaluates deeper rotational failure surfaces. The results from these two physics-based landslide models are critically evaluated with the existing landslide database to verify the validity of these methods for Idukki.

Revisiting the Forgotten Volcano: Volcanic History and Hazards of Mount Adams

Pope, Isaac, Centralia College, isaac.pope@student.centralia.edu (TS #5) Reaching nearly 3000 meters above southwest Washington, Mount Adams is the second most voluminous stratocone along the Cascade Magmatic Arc. Sporadic eruptions over the past 520 ka have built the edifice of modern Mount Adams in three concentrated periods (about 520 ka, 350 ka, and between 40 to 10 ka), but despite its complex history, Mount Adams has largely been ignored in the literature. With an estimated postglacial output less than its rival Cascade stratocones (Hildreth and Fierstein, 1997), Mount Adams has been viewed as practically dormant, yet a reanalysis of the volcanic history suggests a different story. Based on lidar and field data, Pope (2020) argued that a lahar from Mount Adams deposited poorly sorted gravels along terraces over 30 m above the current Cispus River. Over 0.31 km3 in volume, this postglacial lahar likely destabilized slopes and triggered landslides (Pope, 2021). Furthermore, the Cispus River lahar likely originated from a large scarp on Mount Adams’ western slopes, suggesting that it may have been triggered by an eruption. Not only has the main stratocone been more active than previously thought, but the neighboring parasitic cones have produced a network of nearly twenty lava flows. Lidar analysis by Pope (In Preparation) revealed that most flows formed between 14 to 11 ka and 7 to 4 ka, showing that long distance flows are common and are potential hazards. This research indicates that Mount Adams has played a far greater role in the evolution of southwest Washington than previously believed and suggests that the current quiescence is temporary. Continued research will reveal interactions between Mount Adams and the surrounding volcanic complexes and illustrate the range of volcanic hazards to provide a better understanding of such hazards in locations characterized by volcanic features.

Lidar Analysis of Sector Collapses and Lahar Paths at Mount Adams

Pope, Isaac, Centralia College, isaac.pope@centralia.edu (Poster) As the second most voluminous Cascade stratocone, Mount Adams in southwest Washington has produced a variety of debris flows and sector collapses in the past 15 ka. Vallance (1999) conducted the most detailed analysis of lahar deposits in the White Salmon River flowing from Mount Adams’ southern flank towards the Columbia River. All three flows were triggered by debris avalanches on Mount Adams’ southwest flank, the oldest (Trout Lake Lahar) occurring about 6.0 ka ago and measuring over 0.07 km3. In each case, however, these flows occurred irrespective of any volcanic activity, leaving little incentive for further research on volcanic hazards. Even so, Pope (2020) identified deposits resulting from a lahar along the Cispus River over four times larger than the Trout Lake Lahar, suggesting the potential for eruption-induced flows. To ascertain the laharic history, Lidaranalysis was conducted of the Mount Adams stratocone. Along the western flank, a scarp measuring 20 km2 resembles major eruption induced sector collapses on other Cascade Volcanoes. At the headwaters of Adams Creek leading to the Cispus River, this scarp provides a likely source for the Cispus Lahar, but such major sector collapses appear to be the least frequent. Several slump blocks occur along the eastern rim of the peak where past glaciation remains particularly evident. Downstream the slump blocks are a highly aggraded stream bed with sparse vegetation between two lateral moraines, indicating that the slump blocks may have reactivated in the recent past to produce debris flows. Similar stream beds have been identified in the northeast and southeast quadrants draining into the Klickitat River to the east, as well as in the southwestern quadrant leading to the White Salmon River. The identification of such youthful sector collapses and flow paths suggest Mount Adams remains far more active than previously thought.

Active Faulting in the South Granite Mountains Fault Zone: Reactivated Compressional Faults Vs. Extensional Overprinting

Potter, Michael, University of Missouri Columbia, mrp4dd@umsystem.edu; Sean Polun, polunsg@missouri.edu; Francisco Gomez, fgomez@missouri.edu (Poster) Quaternary faulting in and around Wyoming’s Wind River Basin may pose a moderate earthquake risk for dams and other infrastructure within the region. The South Granite Mountains Fault Zone, located adjacent to the Wind River Basin, is one of several Quaternary faults in the region. The South Granite Mountains formed during the Late Cretaceous Laramide orogeny (75-45 Ma). Subsequently, during the Eocene, the extensive downfaulting and downfolding caused the Precambrian mountain core to collapse forming the Sweetwater Graben. Recent Quaternary deformation is expressed as fault scarps along the north side of the Granite Mountains. These features were originally studied in the 1980s but have received little attention since. In particular, the nature and style of faulting of this recent deformation was previously undocumented, and prior age estimates were broad. Recent data collected from the Quaternary faults in the northern Wind River Basin suggests active faulting occurs along reactivated Laramide thrust planes, this may also be true for the Granite Mountains region. This study applies new methodologies to assess the active tectonics and earthquake potential of the South Granite Mountains Fault Zone. Low-altitude aerial surveying using drones facilitate the measurement

and analysis of fault scarp morphology. Shallow seismic reflection profiling (planned for summer 2021) will used to image the fault geometry to depths of approximately 400–500 meters, thus providing critical constraints on the geometry of the active fault. Application of scarp degradation models, in addition to new age constraints from pending results using terrestrial cosmogenic nuclides, will improve the estimation of the Quaternary slip rate along the South Granite Mountains Fault Zone. A final component of this study involves the kinematic analysis of mesoscopic faults in the bedrock, along strike with the faulted Quaternary scarps.

The Latest Rate, Extent, and Temporal Evolution of Ground Deformation Over the Gulf Coast of United States by InSAR

Qu, Feifei, Department of Earth Sciences, Southern Methodist University; Zhong Lu, zhonglu@smu.edu; Jin-Woo Kim; Michael J Turco (Presented by Zhong Lu) (TS #6) Land surface deformation has occurred in many parts of the Gulf Coast. Complicated geological composition and high intensity of exploitation of underground fluids along the Gulf Coast have changed the aquifer system, reactivated faults, generated fissures, and caused damages to infrastructures. We investigated land surface deformation development of Gulf Coast using multi-temporal InSAR technique with 33 paths of L-band ALOS PALSAR images from 2007 to 2011, a dozen paths of Sentinel-1A/B during 2015 and 2019, as well as hundreds of Envisat, ALOS2 and COSMO-SkyMed scenes. We produced, for the first time, yearly displacement maps over the Gulf Coast from Texas to northern Florida. Deformation velocities from all tracks were mosaicked together to produce seamless maps of land displacement over about a wide area of ~500,000 km2, with a measurement precision of ~0.8 cm/year. Generally, the Gulf Coast is fairly stable except for the broadscale subsidence, such as Houston region (up to 4 cm/yr) and New Orleans (about 2 cm/yr), and some localized uplift/subsidence associated with water disposal/injection, oil/gas production and salt mining. Comprehensive ground stability analysis using InSAR measurements and other observations will continue to enhance our understanding of the deformation history, processes, and mechanisms, thereby further distinguishing the anthropogenic deformation from natural processes.

Geotechnical and Geologic Investigations to Support Evaluations of Liquefaction-Induced Lateral Spreading

Rathje, Ellen, University of Texas, e.rathje@mail.utexas.edu (TS #11) Liquefaction-induced lateral spreading is a major co-seismic geohazard and often the primary cause of damage to infrastructure; however, the geological and geomorphic controls responsible for triggering and controlling the extent and magnitude of lateral spread are poorly characterized. We explored lateral spreading along the Avon River in Christchurch, New Zealand from the 2011 Christchurch earthquake using a variety of methods including optical image differencing displacement maps, shear wave velocity profiles, boreholes, cone penetration (CPT) soundings, and paleoseismic trenching with accompanying radiocarbon dating. The geotechnical investigations indicated liquefaction and lateral spreading would be expected along the Avon River, although the observed magnitudes and lateral extents (i.e., horizontal distance from the free face/active river channels) of lateral spread displacement were under-predicted by the geotechnical lateral spread models. Lateral spreading recurrence was investigated using paleo lateral spread features, and the lateral extent of the spreading was significantly controlled by geologic conditions that can be identified by geomorphic mapping. Surface displacements terminate at points inward from the river at what we call paleo lateral spreading headscarps (PLSH), which look like fluvial terrace risers and are coincident with surface cracks due to lateral spreading. Trenching of these features indicated multiple paleo lateral spread events occurred in the last 600 years. The integration of geotechnical and geologic investigations at potential lateral spread sites can provide a more thorough evaluation of the magnitude and lateral extent of lateral spreading displacements.

Paleoseismic Study of the Gales Creek Fault, Oregon

Redwine, Joanna, Bureau of Reclamation, jredwine@usbr.gov; Ralph E. Klinger, rklinger@usbr.gov (TS #11) We undertook a multi-year, phased approach to study a local fault source in northwestern Oregon, to evaluate its impact on (or input or effect on?) a site-specific probabilistic seismic hazard analysis. The impetus for this study was the recognition that the Gales Creek fault zone (GCFZ), a major fault not known to be active, was mapped through a critical structure that lies less than 200 km east of the Cascadia Subduction Zone (CSZ). We took an iterative approach in evaluating the relative contributions to the seismic hazard in order to focus our efforts on the most important aspects. The first order question was whether the GCFZ is active. Long-term right-lateral strike slip displacement along the GCFZ was mapped and interpreted from displaced folded Eocene and Miocene-aged strata (Wells et al., 2020). Our evaluation of lidar imagery and field reconnaissance identified tectonic geomorphic features strongly suggesting active faulting. Based on that assessment, three trenches were excavated across the fault near the critical structure to definitively assess if the fault was active. The trenches exposed disrupted loess, colluvial, and waterlain sediments that were deposited throughout the past several hundred thousand years and indicated multiple surface-rupturing earthquakes occurred throughout the Pleistocene and Holocene. IRSL analysis of windblown quartz and feldspar and radiocarbon analysis of charcoal provide numerical age constraints on the timing of earthquakes. Our results demonstrated the GCFZ is an active strike-slip system with recurrence rates on the order of 2–3 kyr. Hazard assessments using those preliminary results show this local fault source does affect the seismic hazard at the site, even within ~180 km of the CSZ. To confirm our initial results and reduce uncertainty in segmentation models, four trenches were excavated across two fault segments, all exposing similar rupture histories. Segmentation models still include a range of uncertainty.

Assessing Construction Risk of Proposed High Hazard Dam Modifications – A Case History at Red Rock Dam

Richards, Kevin, USACE, kevin.richards@usace.army.mil (TS #7) The US Army Corps of Engineers (USACE) has been using Risk Registers for many years to evaluate economic risks during preparation of cost estimates for complex construction projects. This practice has improved the management of cost-related risks associated with construction cost growth and has become a routine activity on all major projects. However, construction at high hazard dams can also pose a different set of risks that are related to life-safety. Recent emphasis on the use of risk informed decision making has led to improvements in managing risk during all stages of a project where life-safety risk is paramount, including dam modification construction. Red Rock Dam is on the Des Moines River, southeast of Des Moines, Iowa, and is operated by USACE. The Federal Energy Regulatory Commission (FERC) issued a license in 2011 to develop a 36.39 MW hydropower plant at Red Rock Dam. The plans and specifications for this addition were reviewed by USACE in 2012 as part of an Agency Technical Review (ATR), which is a peer review that was done in typical fashion as if the project were being designed and built internally. FERC and USACE incorporated a semi-quantitative risk assessment (SQRA) as

part of the ATR, with the purpose of the risk assessment being threefold for USACE: 1) to inform the Section 408 modification request, 2) to ensure the completed modification would meet USACE dam safety criteria, and 3) to ensure the modification would not impose an unacceptable level of life-safety risk during construction. A number of potential failure modes were evaluated during the SQRA with a few being notable in terms of the potential for risk management measures. Risk management considerations prior to construction offer options that normally cannot be considered for an existing dam, such as: revising construction phases, modifying or supplementing design details, the addition of contingency planning, or reconfiguration. Based on the results of the SQRA, a design modification consisting of extending a cutoff wall into the embankment section was incorporated to address concerns of the potential for concentrated leak erosion (CLE). CLE was thought to be a potential risk driving failure mode due to anticipated relaxation of the temporary braced structures and planned steepening of the wrap-around section that would occur during construction. Although the amount of deformation in the wrap-around section was larger than anticipated, the recommended risk management measures performed well during construction and allowed the construction to continue without unnecessary delays or increased life-safety risk.

Rock Scour of the Unlined Lewisville Dam Spillway Channel: A Probabilistic Approach for Risk-Informed Design

Ring, Caleb, BGC Engineering, CRing@bgcengineering.ca; Michael George, mgeorge@bgcengineering.ca; Bradley Clark, bradley.d.clark@usace.army.mil (TS #7) The Lewisville Dam, owned and operated by USACE, provides flood control, drinking water, and recreation for the Dallas, Texas region. The dam releases flood flows through an uncontrolled ogee crest spillway with a concrete apron that discharges into an unlined bedrock channel. Since completion of the dam in 1955, seven flood events have discharged through the spillway resulting in scour of the Eagle Ford Shale bedrock. The shale is subject to slaking from alternating drying-wetting periods between discharges, which has resulted in channel degradation during spill events. Continued degradation of the unlined channel increases potential for scour immediately downstream of the concrete apron resulting in potential damage to the apron, and in the worst case, breach of the reservoir due to head-cutting erosion. As such, USACE is evaluating spillway modifications within a risk-informed design (RID) framework to reduce risk at the site associated with the spillway. This consists of modification to the concrete apron as well as addition of a turndown wall immediately downstream of the apron to limit head-cut erosion potential. To inform the turndown wall design, a probabilistic rock scour study was completed immediately downstream of the apron. A key challenge was the continued degradation of the downstream channel which influences the hydraulic flow regime at the end of the apron and the ultimate scour depth. Ultimate scour depths were estimated for multiple discharges up to the probable maximum flood for both current and possible future channel conditions based on observed channel degradation. A key finding was that lower return period flood discharges yielded some of the largest estimates for the ultimate scour depth over the anticipated design life of 50 to 100 years. USACE incorporated these results in the RID framework to select an appropriate design for the turndown wall.

Control of Artesian Pressures When Drilling Dams and Levees

Rogers, Gary D., Schnabel Engineering, grogers@schnabel-eng.com; Victor de Wolfe, victor.dewolfe@deereault.com; Sampson Ash, sash@schnabel-eng.com; Hawkins Gagnon, jgagnon@schnabel-eng.com; Susan M. Buchanan, sbuchanan@schnabel-eng.com (TS #4) Flowing artesian conditions may occur at dams and levees, both at the ground surface and when drilling in galleries of concrete dams. Once started, flow is difficult to control and can lead to movement of particles or interconnections in the subsurface which can endanger the dam or levee. Prior knowledge of potential artesian conditions, planning based on this information, and application of specific drilling techniques are critical to preventing uncontrolled flow from drill holes. Multiple techniques are available for preventing and controlling artesian pressures. First, and critical to preparedness, is the recognition that flow may occur and understanding the range of artesian pressures that may be encountered. Drilling and sampling under artesian conditions in a controlled manner requires prevention of flow by methods such as using weighted drilling fluid in mud rotary holes, using a viscous organic polymer drilling fluid, increasing the height of the casing above ground surface, and/or use of stuffing boxes to isolate artesian pressure. If flow does occur, the primary protective measure is a steel surface casing, installed prior to encountering the artesian conditions, that is securely embedded in a clay layer or, for concrete dams, in a concrete structure. Having this casing in place allows for flow to be sealed off with a valve at the top of the boring, protects against uncontrolled flow up the outside of the casing, and gives the team time to think about the situation and plan for resumption of drilling. Inflatable or mechanical packers can also be used to stop flow at depth and allows for placement of fresh drilling mud or installation of other flow prevention techniques. Instrumentation can be installed in borings under artesian conditions. Open standpipe piezometers, vibrating wire piezometers, and other instrumentation have been successfully installed and generally require no flow conditions during placement.

Landslide Dams and Historic Outbreak Flood Events, Community of Montecito, Southern Santa Barbara County, California

Rogers, J. David, The Project for Resilient Communities (TPRC), rogersda@mst.edu; Larry D. Gurrola, lg@larrygurrola.com (TS #5) (Presented by Larry Gurrola) Erodible Tertiary sedimentary rocks combined with high uplift rates create steep terrain that is conducive to bedrock landslides and landslide dams in the Santa Ynez Mountains. A study funded by TPRC was initiated following the January 9, 2018, debris flows to identify sites for debris catchment basins along the principal watercourses. Methodologies include historic fire, flood, and landslide research; aerial photographs, field mapping; lidar, geomorphologic and hydrologic analyses. Bedrock landslides mantle the slopes of the watersheds above the community of Montecito, many of which have formed landslide dams that normally overtop within 12–24 hours producing outbreak floods. Some of these landslides blocked channel flows with slide debris forming temporary lakes that temporarily store water up to 40 feet above the creek beds. Geomorphologic evidence includes landslides that pinch channels, deflected flow paths, and coincident knickpoints. Evidence of nine outbreak flood events were reported over the last 160 years, an average recurrence of once every 18 years. The earliest slide dam was in 1861 and again in 1911, which triggered warnings to downstream residents. One of the largest landslides mapped in this study was reported in 1909. Its toe diverted Cold Springs Creek approximately 200 feet, forming one of several landslide dams in the 1914 debris flow event. The 1914 event described a downstream

sequence of collapsing dams creating an amplified and cascading flood wave that caused severe destruction to the community of Montecito. Active undercutting and channel incision often expose basal slip surfaces priming slides for re-activation and increasing the likelihood of forming multiple dams over time. The potential for catastrophic outbreak flood waves appears to promote subsequent outbreak floods, which are more easily triggered under post-fire conditions. Landslide dams also increase the peak flows and volume of mobilized debris and elevate the flood hazard to downstream communities.

Highly Variable Subsurface Conditions at the New SDSU Mission Valley Campus & Football Stadium Site, San Diego, California

Sanders, James, Group Delta, jims@groupdelta.com; Christopher K. Vonk, chrisv@groupdelta.com; Charles Robin (Rob) Stroop, robs@groupdelta.com (TS #11) San Diego State University has started construction on the $2B redevelopment of the existing 170-acre former National Football League stadium site into a state-of-the-art new west campus with a 35,000-seat football stadium and mixed-use development that will include 1.6 million square feet of new office/innovation/research and development space, hotel & conference center, 4,600 residential units, and a 34-acre River Park. The site is located within the San Diego coastal plain and is underlain by Eocene-age nonmarine and near-shore sedimentary deposits of lagoonal sandstone, siltstone, and claystone. The west-flowing San Diego River has incised a broad (up to 3/4-mile-wide) river valley into the underlying Eocene sedimentary rocks and deposited thick sequences of poorly consolidated, coarse-grained cobble, gravel, and sand on the erosional surface. Sea level transgressions in recent millennia have backfilled the older San Diego River channel with finer grained alluvial deposits. Fill from prior aggregate mining and site development covers the site. Detailed geologic analyses of subsurface explorations revealed the presence of a San Diego River paleochannel across the site which causes the thickness of the underlying soils to vary substantially over relatively short horizontal distances within the proposed football stadium footprint. A high potential for earthquake induced soil liquefaction exists at the site and the complex zones of liquefiable soils vary significantly inside and outside of the paleochannel. The site lies just 7 kilometers east of the active (MW 7.0) Rose Canyon fault zone. This paper summarizes the highly variable subsurface geology encountered at the site, the exploration and data collection techniques utilized to overcome the difficult drilling and sampling conditions, and the integrated structural and geotechnical design approach developed to mitigate differential settlements on the planned stadium and critical infrastructure for the site.

Geophysical Imaging of Critical Zone of Trinity/Edwards Aquifer over Haby Fault of Balcones Fault Zones, Texas

Saribudak, Mustafa, Environmental Geophysics Associates, mbudak@pdq.net (TS #1B) Regionally, the Haby Crossing fault zone is characterized as a lateral barrier to groundwater flow between Edwards and Trinity Aquifers. However, results from our geophysical investigation demonstrate that karstification along the fault plane may have created conduits for preferential lateral flow between the Edwards and Trinity Aquifers. Twodimensional images of electrical resistivity tomography data were used to map the hydrogeologic and structural features within the study area. The contact between the Edwards and the Trinity Aquifers is located on the upthrown side of the Haby Crossing fault. The Trinity Aquifer units appear to be folded upwards near the fault. However, away from the fault, in the northwest direction, the resistivity data shows that the boundary is smoother and is about 75 m deep. Magnetic and ground conductivity data confirm the locations of the structural features. The fault zone on each profile contains fault-related folding, faulting, and tilting. The Haby Crossing fault is a low resistivity feature indicating a high clay content in the brecciated fault material however, self-potential data identified multiple karst features within this fault zone indicating that it is permeable enough to allow ground-water flow along the fault plane. Location of karstic features, such as caves, voids, or sinkholes (conduits) determined by this study may identify areas of groundwater communication between the Trinity and Edwards Aquifers. The results also can help choose an area where groundwater tracer studies be performed to better understand the groundwater flow paths and cross aquifer communication.

Geophysical Mapping of Mt. Bonnell Fault of Balcones Fault Zone, Central Texas

Saribudak, Mustafa, Environmental Geophysics Associates, mbudak@pdq.net (TS #9) Integrated geophysical surveys (resistivity, self-potential, conductivity, magnetic, and ground penetrating radar) were conducted at three locations across the Mt. Bonnell fault in the Balcones Fault Zone of Central Texas. This normal fault has hundreds of meters of throw and is the primary boundary between two major aquifers in Texas, the Trinity and Edwards Aquifers. In the near-surface on the Edwards Plateau, the fault juxtaposes the Upper Glen Rose Formation, which consists of interbedded limestone and marly limestone, against the Edwards Group, which is mostly limestone, on the eastern down-thrown side (coastal plain). The Upper Glen Rose member is considered to be the Upper Trinity Aquifer, and also a confining zone underlying the Edwards Aquifer. Geophysical results indicate not only the location of the fault but additional karstic features on the west side (Upper Glen Rose Fm.) and on the east side (Edwards Group) of the Mt. Bonnell fault. Resistivity values of the Glen Rose and Edwards Group do not appear to have significant lateral variations across the fault. In other words, the Mt. Bonnell fault does not appear to juxtapose different resistivity units of the Edwards Group and Upper Glen Rose member. Thus, the fault may not be a barrier to groundwater flow. With the abundant karstic features (caves, sinkholes, fractures, collapsed areas) on both sides of the fault, as determined by the geophysical data, one can conclude that lateral intra-aquifer groundwater flow between the Edwards Aquifer and Upper Trinity is likely.

Subsurface Structure of Pilot Knob Submarine Volcano (Austin, Texas) imaged using Resistivity and Magnetic Methods

Saribudak, Mustafa, Environmental Geophysics Associates, mbudak@pdq.net (TS #11) Pilot Knob represents an extinct submarine volcano in a shallow sea that had a brief period of eruptive activity during the Upper Cretaceous time. The Pilot Knob is located in south Austin and is part of the Balcones Magmatic Province (BMP), which includes approximately 200 occurrences of igneous rocks emplaced during the deposition of the Austin Chalk (limestone) Formation. Pilot Knob, however, is the best exposed volcanic marine eruptive center in the BMP of Texas. Several resistivity imaging and magnetic surveys, two of which cross the entire apex of the volcano, indicate significant information about the internal structure of the volcano. These findings are: 1) several dikes and eruption centers (craters), 2) a buried volcanic core overlain by layers of low resistivity basaltic flow and resistive Austin Chalk layers, 3) scattered, slumped and rotated Austin Chalk blocks through the volcanic matrix of the volcano, especially near the apex of the

volcano, 4) a huge volcanic eruption center cutting through the tuff units in the west part of the volcano, 5) horizontal basaltic flows in the northern and southern part of the volcano, and 6) long resistivity and magnetic profiles crossing the volcano helped define the buried boundaries of the basaltic eruption centers and tuff units (pyroclastic). One of the striking results of this study is that magnetic and resistivity data indicate peculiar low magnetic and low resistivity values, respectively, across the majority of the Pilot Knob volcano. This could be due to the extensive alteration of volcanic rocks, which formed almost entirely beneath the sea level.

Mountain Tunnel Access Roadway Improvements

Schick, Jamie, McMillen Jacobs Associates, schick@mcmjac.com; David Tsztoo, dtsztoo@sfwater.org; Joe Buitrago, jbuitrago@sfwater.org (TS #5) The Mountain Tunnel is a significant route for the San Francisco Public Utilities Commission to deliver water from Hetch Hetchy Reservoir into the Priest Reservoir. McMillen Jacobs Associates is the lead design firm for the improvements project that will ensure the reliability of daily water delivery to customers and provide continued capacity for future demands. A critical project component is the improvement of three roadways that lead to access portals along the tunnel. These roads were initially constructed to provide construction access and have used for years for facility access. Roadway improvements will provide tunnel access resiliency for inspections, maintenance, and repairs, and accommodate heavy truck and construction equipment during the six years of construction. Proposed improvements include road widening and shoulder stabilization, rockfall mitigation, and drainage improvements. This paper will discuss McMillen Jacobs’ investigation to identify and characterize rockfall and landslide hazards along the roadway and develop slope mitigation strategies. Mitigation alternatives were identified through a combination of visual observation and input from owner maintenance personnel. Rockfall hazards were addressed through a combination of approaches ranging from draped doubletwisted wire mesh cable net systems to attenuator systems and pattern rock bolting. Significant reaches of these roads will require scaling and rock doweling to reduce rockfall hazards along the corridor. Over 30 rockfall mitigations were developed for the roadways. Debris flow hazards were addressed with a combination of shoulder improvements using pinned gabion wall systems and concrete decks supported by micropile foundations. Roadway construction is scheduled for spring and summer of 2021. McMillen Jacobs is providing engineering support during construction and this includes oversight of the scaling and rock doweling as well as drapery system installation. This work is considered critical path for completion of underground improvements.

Summary of ASCE/EWRI Land Subsidence Task Committee Report and Plans for Development of Standard Guidelines for Assessment and Mitigation of Land Subsidence Caused by Groundwater Withdrawals

Sheng, Zhuping, Sheng Engineering PLLC; zhuping.sheng@sheng-eng.com; Conrad Keyes, Jr., cgkeyesjr@q.com; Jiang Li, jiang.li@morgan.edu; Yi Liu, yi.liu@morgan.edu; Devin Galloway, dlgallow@usgs.gov; Dora Carreón Freyre, freyre@geociencias.unam.mx; Pietro Teatini, pietro.teatini@unipd.it; Earl Burkholder, eburk@globalcogo.com; Ahmed Elaksher, elaksher@nmsu.edu; Dana J. Caccamise II, dana.caccamise@noaa.gov; Van Kelley, vkelley@intera.com; Tianliang Yang, sigs_ytl@163.com; Ben Willardson, ben.willardson@uvu.edu (TS #6) Hydrogeologists and engineers recognize land subsidence caused by groundwater removal from aquifer systems as a major geologic hazard that can lead directly to structural damage of built infrastructure and indirectly damage land and ecosystem resources related principally to increased inland and coastal flood susceptibility. In response to growing water demands worldwide, increasing groundwater withdrawals from aquifer systems typically lowers groundwater levels, depletes groundwater storage, and causes land subsidence in many susceptible aquifer systems. Some of these affected aquifer systems artificially store and recover water as a component of managed aquifer recharge projects, which further complicates assessment and mitigation of land subsidence. Over the past several decades, new technologies and approaches have been developed to detect, monitor, and control land subsidence. Water managers and planners, hydrogeologists, and engineers need current guidelines to better manage groundwater resources and reduce land subsidence risks under various, often complex groundwater development scenarios. The Land Subsidence Task Committee was established within the American Society of Civil Engineers – Environmental and Water Resources Institute (ASCE/EWRI) to summarize worldwide land subsidence caused by underground fluid withdrawal, principally groundwater overdraft, and evaluate progress in applying new technologies and approaches to subsidence assessment and mitigation. We will present a summary of the committee report, as well as plans for developing ASCE/EWRI standard guidelines for mitigating land subsidence due to overdraft of susceptible aquifer systems. These guidelines will be a valuable tool for water-resources project planners and resource-management professionals.

Recurrence of Large Upper Plate Earthquakes in the Salish Lowland, Washington State

Sherrod, Brian, USGS, bsherrod@usgs.gov; Richard Styron, richard.h.styron@gmail.com; Stephen Angster, sangster@usgs.gov (TS #11) Paleoseismic studies documented 27 paleoearthquakes from observations of postglacial deformation at 63 sites on 13 shallow fault zones in the northern Cascadia fore arc. These fault zones were created by northward fore arc block migration manifested as a series of bedrock uplifts and intervening structural basins in the Salish lowland between the 49th parallel and Olympia, Washington, to the south, bounded on the east and west by the Cascade Mountains and Olympic Mountains. Estimates of paleoearthquake magnitude range from M~6.5 to ~7.5. For each paleoearthquake, we use published ages to calculate earthquake-timing probability density functions (PDFs); for some events broad PDFs reflect earthquakes constrained by only minimum or maximum limiting ages. The earthquake record starts shortly after glacier retreat ~16ka BP. Earthquakes prior to the mid-Holocene were apparently scarce, with only a handful of older earthquakes identified

throughout the lowland. The paleoseismic record picks up in earnest ~4000 yrs BP, with 21 of the 27 paleoearthquakes on faults throughout the Salish lowland. A cluster of earthquakes started about 2500 yrs BP and lasted until about 900 yrs BP on faults located in the central and northern lowland. A Monte Carlo approach was used to calculate the recurrence intervals and rates for earthquakes on individual fault zones as well as on the regional fault network as a whole. Thousands of samples drawn from each earthquake age PDF were sorted (following stratigraphic ordering where possible) and differenced, yielding distributions for inter-event times that reflect the uncertainty in the radiocarbon ages. For the Puget Lowland as a whole, the postglacial mean recurrence interval is ~400 years, with a median of ~175 years and a mode of ~20 years. These results are suggestive of earthquake clustering, and that a large earthquake may be followed soon after by additional large earthquakes on regional faults.

Seismic and Electrical 3D Geophysical Imaging for Landslide Remediation Wolf Creek Pass, Colorado

Sirles, Phil, Collier Geophysics, LLC, phil@collierconsulting.com; Khamis Haramy; Marilyn Dodson; Todd Schlittenhart (TS #10) Seismic and electrical geophysical investigations were performed using 3D acquisition, processing and presentation imaging techniques on two active landslides in southwestern Colorado. The slides are actively moving and are under ongoing active remediation. The translational East Fork Landslide terminating in the East Fork of the San Juan River reactivated in 2008, with a 600-foot wide by 2,000-foot upslope disturbance, displacing a roadway about 150 feet. The rotational Jackson Mountain Landslide terminating in the San Juan River reactivated in 2009, with a 2,000-foot wide by 2,500-foot upslope disturbance, closing US 160. Both damaged a major gas line. Seismic and electrical 3D geophysical methods were used to determine subsurface characterization and assess bulk material properties on a selected portion of each slide. These new approaches could be used on landslides to optimize subsurface volumetric evaluation of the site and to augment the conventional geotechnical field investigation methods for landslides. These slides had existing information which was used in the geophysical analyses to aid in determining the effectiveness, benefits, and limitations of performing 3D geophysical surveys on ‘active’ landslides. While the geophysical data (acquisition methods, interpretation, and presentation of geophysical results) may be useful for future design and remediation efforts, the primary purpose was to evaluate the value of using these wide-area geophysical surveys to better characterize translation and rotational landslides. The results indicated that volumes of higher electrical response are present at bedrock depths under the Jackson Mountain Landslide and outside the most recent movement on the East Fork Landslide. Anomalies with low resistivity also correlated with areas of higher water content, which can be useful for remediation through drainage. The 3D seismic imaging provided volumetric subsurface images rather than singular point measurements to delineate shear zone depth.

3D Geophysical Investigations to Evaluate Risk at Karstic Wind Turbine Foundation Sites

Sirles, Phil, Collier Geophysics, LLC, phil@collierconsulting.com; Roy Bowling Roy@CollierGeophysics.com (TS #14) Geotechnical site characterization for proposed wind turbine foundations, located in known karst terrain, requires a broader evaluation of the risk. Both the dissolution of gypsum or anhydrite in evaporite formations, or fracture-widening and void/cave development in soluble limestones cause the scope of investigation to be wider beneath very specific turbine foundation design and loading conditions. One-dimensional borehole information is necessary, but it cannot resolve the largescale risk of karst. Additionally, due to the amorphous nature of karst, traditional 2D geophysical investigations often cannot accurately assess the karst condition due the physics of the method. As such, threedimensional 3D geophysics is necessary to provide a true volumetric foundation assessment of the bedrock. 3D geophysical case histories from western Oklahoma’s Permian- and Pennsylvanian-age evaporite formations, and also central Oklahoma’s Ordovician-age folded and faulted limestone, will show why different approaches are necessary to evaluate the large-scale subsurface conditions. Since the geophysical data are but one data set to assess the rick of karst, the case histories will demonstrate how all the available data are used in an integrated approach to assign a risk factor at each proposed foundation. Both 3D seismic and 3D electrical resistivity methods, used in the different geologic setting, will be presented; and, how they correlate with borehole information, lidar data, and site geologic observations. The combination direct (intrusive) borehole data with the indirect (non-invasive) 3D geophysical measurements is critical to provide confidence in the risk for safe foundation construction, and that the structure will remain resilient for its design life. Additionally, the presentation will show how the risk of positioning the large cranes (used in construction), or the crane-paths between foundation sites, can also be assessed from the geophysical 3D data. Unconventional 3D data visualization techniques are paramount for everyone on the geotechnical team.

1,4-Dioxane in Groundwater: Emerging Contaminant Concerns

Smith, William (Gary), WGS Consulting, wgsconsulting@hotmail.com (TS #8) 1,4-Dioxane (DXA) is a likely human carcinogen and has been found in groundwater at sites throughout the United States (US) and worldwide. The physical and chemical properties and behavior of DXA create challenges for characterization and treatment in the environment. It is highly mobile, does not readily biodegrade, and is completely miscible in water. It is unstable at elevated temperatures and pressures and may form explosive mixtures with prolonged exposure to light or air. DXA is a likely contaminant at many sites contaminated with chlorinated solvents because of its widespread use historically as a stabilizer for those compounds (particularly 1,1,1- trichloroethane [TCA]). DXA is a by-product present in many goods, including paint strippers, dyes, greases, antifreeze, and aircraft deicing fluids, and in some consumer products (deodorants, shampoos, and cosmetics), and as a purifying agent in manufacture of pharmaceuticals. It is a by-product in the manufacture of polyethylene terephthalate (PET) plastic. Traces may be present in some food supplements, food residues from packaging adhesives, or on DXA-containing pesticides applied to food crops.1 DXA is considered an emerging organic contaminant in the environment due to the above widespread uses, and investigative difficulty in detecting low DXA concentrations in groundwater plumes. It is typically found at low ppm or ppb concentrations in groundwater but may be found at high ppm concentrations at DXA manufacturing sites. One of the last US manufacturers of DXA shut down in 2019 and moved production to European operations due to increasing regulatory scrutiny and perceived environmental risk.2 DXA remediation has become a priority at many sites in the USA due to status as a likely human carcinogen. As of 2016, DXA had been identified at more than 34 USEPA National Priorities List (NPL) sites; it is likely present at many other USA governmental and industrial sites.3 Remediation focus on DXA is typically on groundwater that may be used as a potable source, and ongoing risk assessments by federal and state agencies have increasingly lowered the acceptable risk level to low ppb concentrations (typically <5 ug/L). (1,4) This presents an issue for both remediation technology efficiency, and the ability to detect DXA at allowable

groundwater concentrations in groundwater. DXA does not bind to soils and migrates preferably to groundwater pore spaces where it may migrate much more rapidly than co-contaminants such as chlorinated solvents. Thus, it is often found at the leading edge of groundwater plumes that exhibit multiple co-contaminants.3,4 This presentation summarizes the state of the art in DXA remediation of contaminated groundwater, including references to several ongoing successful remedial sites around the world.

References

1. US Environmental Protection Agency (USEPA), Office of Land and Emergency Management (Nov 2017) Technical Fact Sheet – 1,4-Dioxane, EPA 505-F-17-011, 8 p. 2. Editorial Staff, WAFB Television Baton Rouge Louisiana Video News (15 January 2019) BASF Chemical Plant in Zachary, LA to Shut Down in April 2019, TV Video. 3. Agency for Toxic Substances and Disease Registry (ATSDR) (2012. “Toxicological Profile for 1,4-Dioxane.” www.atsdr.cdc.gov/toxprofiles 4. USEPA (2006) Treatment Technologies for 1,4-Dioxane: Fundamentals and Field Applications, EPA 542-R-06-009, web address: cluin.org/download/542r06009/pdf.

1,4-Dioxane in Groundwater: A Worldwide Technology Survey

Smith, William, WGS Consulting, wgsconsulting@hotmail.com (TS #8) DXA remediation in groundwater may be designed for either ex situ or in situ application. In practice, in situ methods are typically designed to transport contaminated groundwater to the location of remedial technologies that are more typically used ex situ, such as funnel & gate or French drain extraction. With several US DXA remedial projects having now been operating for years, effective remedial technologies have increasingly been narrowed to those capable of destroying DXA, either chemically or thermally. For this reason, in situ chemical or biochemical remediation are much more difficult to design for low acceptable residual DXA concentrations in potable groundwater supplies. Currently, effective remedial technologies applied for DXA in the USA include: 1) Advanced Oxidation Processes (AOP), or, 2) adsorption or ion exchange (IEX) materials (e.g., AmbersorbTM), used in combination with thermal regeneration of granular activated carbon (GAC). Treated groundwater can be reinjected or directed for additional residual treatment in Wastewater Treatment Plants (WWTP), prior to surface water discharge. Because DXA and similar contaminants must be treated to essentially non-detect concentrations (<1 ug/L), proprietary AOP technologies have been developed specifically for DXA These include peroxide/ozone oxidation – prominent examples licensed as HiPOxTM technology by APTWater5 and photocatalytic oxidation - licensed as PhotoCatTM technology by Purifics6. These technologies have been proven to be effective for DXA remediation at multiple sites, down to low ppb or ppt levels, even from initial high ppm-level (>100 mg/L) concentrations using multiple pass technology. These technologies are typically applied for ex situ pumping and recovery of DXA contaminated groundwater, and treated groundwater can be reinjected to improve hydraulic transport and recovery efficiency of contaminated groundwater. Filtration or membrane technologies may be used ahead of AOP methods to avoid solids issues with AOP equipment when necessary. IEX methods for DXA remediation using AmbersorbTM or similar resins typically operate at lower contaminated groundwater influent concentrations (<1 mg/L) but can achieve nondetect levels (<1 ug/L) on a continuous basis. These methods depend on IEX regeneration, typically aligned with a second phase of concentrated DXA adsorption on GAC, followed by GAC thermal regeneration, that results in total DXA destruction.7 Additional destruction technologies are being developed at demonstration levels currently, including electrochemical destruction at high temperatures for concentrated DXA or PFAS type emerging contaminants8. Residual low ppb levels of DXA after remedial treatment can be reinjected, to assist in contaminated groundwater transport and recovery, or, discharged to WWTPs that achieve residual destruction by biochemical or physical/chemical methods. Traditional UV/peroxide technology is not likely to be effective for DXA in a low ppb or non-detect remedial setting.

References

5. APTWater, Long Beach, CA (2009) HiPOx Case Study: US Air Force Plant 44, 2 p. 6. Purifics, London, ON, Canada (2013) Groundwater Remediation Case History: Chemical Free 1,4-Dioxane Purification, Sarasota Florida, 2 p. 7. Woodard, S., ECT2, Whittier, CA (2016) Optimized Treatment of 1,4Dioxane in Extracted Groundwater with Reinjection for Aquifer Replenishment, 2016 Emerging Contaminants Conference, Westminster, CO, PPT presentation, 21 p. 8. Linked News - Australia, “AECOM announces first demonstration of DEFLUORO electrochemical remedial technology for emerging contaminants,” May/Jun 2021.

1,4 Dioxane – In Consumer Products, Landfill Leachate and Surface Water

Smyth, Joan, Smyth Gardner, Inc., joan@smithgardnerinc.com (TS #8) This presentation will follow the path of 1,4 Dioxane in our environment from initial synthesis to post-disposal. Details will be presented of synthesis and usage of 1,4 dioxane during consumer product production and will summarize concentrations in consumer products over time and regulations limiting 1,4 D in consumer products. The presentation will follow the disposal of consumer products in landfills and will summarize concentrations of 1,4 dioxane in landfill leachates in the United States and globally. Since most landfill leachates are disposed at wastewater treatment plants, this presentation will also summarize data from surface water studies pf 1,4 dioxane in wastewater treatment plant discharges as well as surface water sampling locations to evaluate the potential impact of landfill leachates on surface water. As a point of comparison, limited information regarding concentrations of 1,4 D in septic system effluent will also be presented to give a more comprehensive picture of how 1,4 D is entering our environment from consumer product usage and disposal.

Assessing Karst Hazard for a Proposed Nuclear Power Plant Site in the Valley and Ridge of Tennessee

Sowers, Janet, FUGRO, j.sowers@fugro.com; David Fenster, rockpic001@gmail.com (TS #9) Federal guidelines for the siting of nuclear power plants require thorough evaluation of geologic hazards, including focused investigation and assessment of hazards judged to have the greatest potential to impact the site. The proposed site was the subject of an extensive karst hazard evaluation conducted as input to an Early Site Permit (ESP) application. Karst features can impact foundation stability and the nature of groundwater flow and, therefore, the modeling of any accidental radionuclide releases. Steps in the karst hazard assessment included: 1) data collection and characterization, 2) development of a karst model, and 3) hazard evaluation. Karst was characterized by an initial review of regional and local karst literature and data, followed by collection of new data for the site area and the site itself. Mapping of sinkholes, depressions, springs, and caves within a five-mile radius of the site was based on interpretation of lidar topographic data and field reconnaissance. Depression density was found to strongly correlate to lithology. Site exploration documents the stratigraphic sequence of limestone units of the Chickamauga Group dipping 57 degrees to the east. Dissolution cavities were logged in many of the boreholes. The karst model for the site is based on the following

concepts and observations: the bedrock surface beneath residual soil is irregular due to dissolution from penetrating rainwater; dissolution features occur both in the vadose zone from downward percolating water, and in the phreatic zone from flowing groundwater; the dominant orientation of dissolution pathways is strike-parallel and is constrained by low-carbonate units; and the thicker and purer carbonate beds have larger and more numerous cavities and sinkholes. Potential hazards to the nuclear island due to subsurface dissolution are foundation settlement or collapse and enhanced contaminant migration. Hazard mitigation measures will be addressed.

The 1811–1812 New Madrid Earthquakes: Then & Now

Steckel, Phyllis, Earthquake Insight LLC, psteckel@charter.net (TS #9) The 1811–1812 New Madrid earthquakes, the largest earthquakes ever felt east of the Rockies in historic times, were centered in the mid-Mississippi Valley. The sparse population and their simple structures, as well as the natural land surfaces near the epicenters were devastated. Farther out, small frontier settlements (St. Louis, Louisville, and Natchez) had significant damage. Many of the residents of the established cities along the Atlantic coast (Washington DC, New York, Charleston, and Norfolk) were alarmed by the earthquakes, which awoke President James Madison as he slept in the White House and caused some damage in those locations. Through the research of many geoscientists over many years, the 1811–1812 earthquakes have become better understood: the New Madrid seismic zone is active; the largest events on the New Madrid usually occur in a series of three or more, followed by many thousands of aftershocks; the thick, loose sediments of the Mississippi Embayment and the Mississippi and Ohio river floodplains greatly amplify and prolong ground-shaking; and the area is especially vulnerable to landslides, lateral spreading, and liquefaction. In the 210 years since these earthquakes, tens of millions of people and many trillions of dollars are at risk in private and public infrastructure of national importance. Several pillars of the national economy as well as national security are at risk in the event of a repeat of the 1811–1812 New Madrid earthquakes including bulk storage and transport, steel production, aluminum smelting, pipelines, parcel delivery, agriculture, and port and multi-modal facilities.

Evaluating Potential Hazard from Faulting and Induced Seismicity at the U.S. NRC for a Proposed Nuclear Power Plant Site

Stirewalt, Gerry L., U.S. Nuclear Regulatory Commission, gerry.stirewalt@nrc.gov (TS #11) Nuclear Regulatory Commission (NRC) geologists considered two potential hazards at the proposed site of V.C. Summer Nuclear Station (VCSNS) Units 2 and 3, located in South Carolina adjacent to VCSNS Unit 1 that began operation in January 1984. The hazards were induced seismicity related to filling of a water supply reservoir for Unit 1 and faults in foundation bedrock of proposed Units 2 and 3. NRC geologists re-evaluated data associated with reservoir-induced seismicity (RIS) previously collected for licensing Unit 1 and evaluated new data related to faulting in excavations for safety-related engineered structures at VCSNS Units 2 and 3. The need to re-evaluate RIS data arose because NRC geologists needed to confirm that RIS events did not define fault trends at the site location that were unrecognized in the excavations for Units 2 and 3. Data reviewed by NRC geologists showed RIS started with filling of the reservoir in 1977 and dropped to pre-impoundment background levels after filling. Maximum magnitude of RIS events was 2.8 so well below the seismic design basis for safetyrelated structures at Units 2 and 3 related to the Charleston and New Madrid seismic zones. RIS events did not delineate any unexpected fault or fracture trends and negligible hazard existed from RIS for VCSNS Units 2 and 3 due to the small magnitudes of the events. Radiometric ages on fault displacements acquired by the applicant and field observations of relative age relationships of faulting by NRC geologists revealed that faults mapped in the excavations were not younger than Mesozoic so posed negligible hazard from fault displacement at the site. NRC geologists confirmed that the applicant completed geologic site characterization activities necessary to satisfy all regulatory requirements and that neither RIS nor faulting required the applicant to plan for mitigation of such hazards at the site.

Emergency Response and Navigating Naturally Occurring Asbestos – Rockslide Mitigation on US-95 near Riggins, Idaho

Struthers, James, McMillen Jacobs Associates, struthersjr@gmail.com; Bradley Erskine, erskine.geo@gmail.com (TS #15) On July 3 and 10, 2020, two large sequential rockslides occurred near Riggins, Idaho on US-95, which is the major north-south artery for Idaho. Together the rockslides deposited about 20,000 cubic yards of rock on the highway but left a large unstable remnant block hanging above the road. These rockslides were the result of structurally controlled failures within the ultramafic rocks of the Jurassic to Permian-aged Riggins Group. Idaho Transportation Department (ITD) retained the services of McMillen Jacobs to provide geotechnical consultation during the mitigation efforts. Following contract development, ITD advertised the project and held a pre-bid meeting 21 days after the failure. Bid was, however, delayed because naturally occurring asbestos (NOA) was discovered at the rockslope; a first historic case for ITD projects. In response, ITD contracted a Subject Matter Expert (SME) to develop a contacting and mitigation strategy to advance the project. Based on guidance from the SME, we established a sampling protocol in seven distinct regions with the project limits. The majority of the sampling was conducted using roped-access techniques. Samples were sent to Asbestos TEM Laboratories of Berkeley, California for identification of potential asbestos mineral species and quantification of amount of each species present. Concurrently, we initiated the mitigation measures which included avoiding disturbance of areas with suspected NOA, dust control, air monitoring and personnel training. Analytical results and detailed mapping demonstrated that NOA was limited to shear zones and schistose areas within the lower zone portion of the rockslope, below the primary proposed area of disturbance. Most samples were less than 1% regulated NOA. However, one sample out of the excavation area displayed concentrations of NOA > 5%. The contractor was able to avoid this area and mitigate the large overhanging rock block by drilling and blasting.

W-6 Upper Segment: Hwy 90 to SW Military Drive Sewer Tunnel Project

Swartz, Jason, Black & Veatch, swartzj@bv.com; Gerardo Gomez, Gerardo.Gomez@saws.org (TS #2) San Antonio Water System (SAWS) entered into a Consent Decree with the United States Environmental Protection Agency (EPA) to rehabilitate portions of their wastewater collection system and reduce sanitary sewer overflows (SSOs). The Consent Decree required SAWS to remediate field confirmed capacity constraints according to an agreed and defined schedule. The W-6 project is a major component of the Consent Decree and eliminates a known capacity constraint by replacing approximately 19,000 LF of existing 54-inch sanitary sewer main that currently through Lackland Air Force Base. The replacement sewer main involves 29,000 LF of primarily 104” FRP gravity sanitary sewer pipe constructed by underground construction techniques. The tunnel project extends from a location east of Leon Creek along US Highway 90 (US90) to the intersection of US90 and West Military Drive, then heads southward along West

Military Drive to Pearsall Road. This alignment avoids Lackland Air Force Base and minimizes impacts to the local community by being constructed underground. The majority of the alignment is being constructed utilizing a 142-inch Lovat Dual Mode Tunnel Boring Machine. The project also includes nine shafts and multiple trenchless crossings to make near surface connections to the new works. This project is one of SAWS’s largest projects ever undertaken and was started in July 2020 and is expected to be completed the first half of 2023. This paper will discuss some of the construction challenges while tunneling over 100 feet below the surface within the Navarro Group geologic formation.

ALARP Design Considerations for Dams and Levees

Terry, Thomas, US Army Corps of Engineers, thomas.terry@usace.army.mil; John Kendall, john.r.kendall@usave.army.mil (TS #4) The presentation will begin with a short definition of what ALARP (As Low As Reasonable Practicable) is relative to life safety risk and how it applies to the design of new dam and levee facilities. The presentation will present various examples of how the authors have provided ALARP related recommendations to planning and design teams for projects based on qualitative risk assessments preformed at the planning (conceptual) stage of project development. The findings of these projects allowed life safety risk to inform the conceptual design of the projects, prior to seeking authority, and helped tailor the project such that they met the intent of risk ALARP as they enter the next phases of design and eventually construction.

Evaluation of Non-liquefiable Soil Layer Impact on Liquefaction Surface Manifestation in Dyer County, Tennessee

Tohidi, Hamed, The University of Memphis, htohidi@memphis.edu; David Arellano, darellan@memphis.edu; Chris Cramer, ccramer@memphis.edu; Roy Van Arsdale, rvanrsdl@memphis.edu; Renee Reichenbacher, renee.reichenbacher@gmail.com (TS #11) Liquefaction occurs predominantly in loose saturated sands because of the buildup of excess pore water pressure that occurs due to dynamic stresses from earthquakes. The excess pore water pressure results in a sudden decrease in effective stress that contributes to a decrease in shear strength. In the past century, and as a result of earthquakes all around the world, liquefaction has caused irretrievable damages to thousands of buildings, bridges, highways, and utilities. Thus, evaluation of the liquefaction potential of areas near major seismic zones is essential. Dyer County, Tennessee, is located within New Madrid seismic zone. The surface geology of the county is characterized by three geologic/geomorphic units: lowland (floodplain), intermediate (loess covered terrace and bedrock), and upland (loess covered terrace and bedrock). In this study, the liquefaction surface manifestation potential of Dyer County, Tennessee is evaluated based on two different approaches; Liquefaction Potential Index (LPI) developed by Iwasaki (1978–1982) and LPIISH framework presented by Maurer et al. (2015) based on Ishihara’s (1985) boundary curves. The key difference between these two methods is that LPI does not consider the impact of non-liquefiable soil layers on liquefaction surface manifestation while LPIISH does. The impact of non-liquefiable soil crust on liquefaction surface manifestation is assessed for 70 combinations of earthquake magnitude and peak ground acceleration (PGA). The results of this research are presented in a format of Liquefaction Probability Curves (LPCs), and liquefaction hazard maps. This study reveals non-liquefiable soil layers have a significant impact on liquefaction surface manifestation of liquefiable soil layers in all three geologic/geomorphic units. Not considering the effect of non-liquefiable soil layers on liquefaction surface manifestation can result in up to 50% overprediction of liquefaction probability for strong earthquake scenarios of lowlands which are the most susceptible geologic units to liquefaction.

The Science and Policy of Groundwater Regulation: A Comprehensive Approach to Protecting the Houston Region from Land Subsidence

Turco, Michael J., Harris-Galveston Subsidence District, mturco@subsidence.org; Ashley I. Greuter, agreuter@subsidence.org; Kelsey D. Seeker, kseeker@subsidence.org (TS #6) Since the development of the coastal areas near present-day Houston, Texas, subsidence has been a significant public policy concern. Concerns associated with subsidence in the Houston area include coastal inundation from storm surge, inland flooding, and critical infrastructure damage. Subsidence is caused by compaction of aquifer material due primarily to the extraction of groundwater from the Gulf Coast Aquifer System, shifting the primary source water from groundwater to an alternative source, such as surface water, has been a public policy priority for over four decades. The Houston area, until recently, has relied mostly on groundwater as the primary source water for municipal, agricultural, and industrial needs. In 1975, following decades of subsidence totaling over 10 feet, the Harris-Galveston Subsidence District was created to regulate groundwater withdrawal in Harris and Galveston counties to prevent subsidence. Leveraging the alternative surface water resources developed by the City of Houston in the 1950s, the Subsidence District’s regulatory framework focuses on spatial prioritization and the systematic conversion to alternative source waters. This comprehensive approach of enforcing attainable regulatory requirements, informed by local stakeholders, and based on the best available science, has resulted in a dramatic reduction in subsidence rates. Results from the Subsidence District’s monitoring program show that the implementation of the regulatory program has substantially slowed subsidence in areas where full conversion from groundwater to alternative water has been completed. Reasonable management of groundwater use in this region is vital for the longterm prevention of subsidence and increases the resilience of the entire region. An overview of the regulatory policy, subsidence monitoring program, and major infrastructure projects conducted by regional water providers to achieve conversion will be presented.

Addressing Uncertainty Through an Open, Collaborative Database of Liquefaction Case Histories

Ulmer, Kristin, Southwest Research Institute, kulmer@swri.org; Thomas Weaver, thomas.weaver@nrc.gov; John Stamatakos, jstamatakos@swri.org; Miriam Juckett, mjuckett@swri.org (TS #11) Seismic induced soil liquefaction has historically caused significant damage to engineering structures. If not addressed adequately, liquefaction may pose a significant risk to critical infrastructures, such as nuclear power plants, lifeline systems, and earthen dams. Liquefaction triggering evaluation methodologies over the past several decades allow engineers to assess if liquefaction is likely to occur at a site and, consequently, whether it poses a safety risk to infrastructure. These evaluations typically rely on triggering models that quantify a soil’s resistance against liquefaction based on field penetration tests. However, there is inherent uncertainty and a general lack of consensus on several key issues in the models developed to date. In addition, the case histories upon which these empirical models rely represent only a subset of the range of geologic conditions that may be applicable to critical structures. These uncertainties and lack of consensus were at the core of a recent National Academy of Sciences study, which highlighted the need for improved liquefaction triggering models based on an improved database of empirical

observations. The Next Generation Liquefaction (NGL) project aims to address this need by developing an open, collaborative database of case histories. This database provides access to objective data and allows users across the world to contribute additional data. This presentation highlights some of the ways that the NGL database can address uncertainty in liquefaction triggering evaluations. For example, data acquired from recent and future case histories could expand the parameter space so new models can be developed that are applicable to a broader range of geologic conditions. Increasing our understanding of and ability to quantify uncertainties will improve risk evaluations for critical infrastructure, including mitigation strategies for potential hazards. Improving risk evaluations will facilitate making better decisions that impact facility safety and project costs.

Innovative and Alternative Treatment Technologies to Mitigate 1,4-Dioxane Contamination in the Long Island, New York Water Cycle

Venkatesan, Arjun, Center for Clean Water Technology, Stony Brook University, arjun.venkatesan@stonybrook.edu (TS #8) 1,4-Dioxane is a probable human carcinogen and a widespread contaminant in Long Island water supplies, with some of the nation’s highest concentrations detected (up to 34 µg/L). Analysis of the Unregulated Contaminant Monitoring Rule 3 data from the USEPA revealed that 39 water districts/distribution areas in Long Island had detections of 1,4dioxane greater than the EPA’s cancer risk guideline level of 0.35 µg/L. Furthermore, recent studies have confirmed the presence of very high levels of 1,4-dioxane in several household products and thus domestic wastewater could potentially serve as an important and ongoing source of 1,4-dioxane pollution in the environment. Due to its environmental persistence, conventional water and wastewater treatment processes are not effective in removing 1,4-dioxane. A combination of concentrated onsite wastewater treatment systems, sole-source aquifer, and elevated background 1,4-dioxane levels in groundwater, as observed in Long Island, NY, presents a unique challenge to prevent further contamination via wastewater discharges. Research at the NYS Center for Clean Water Technology is focused on optimizing both drinking water treatment and onsite wastewater treatment to minimize 1,4-dioxane exposure and to control ongoing pollution of groundwater. This presentation will summarize i) recent data from a pilot-study of 1,4-dioxane treatment using four different Advanced Oxidation Process (AOP) technologies; ii) the performance of full-scale Nitrogen Removing Biofilters (NRBs) to remove 1,4-dioxane from onsite wastewater; and iii) treatment challenges and research needs. Results reveal that although all AOP systems are capable of removing 1,4-dioxane, UV/H2O2 and O3/H2O2 performed most efficiently with respect to cost and energy consumption. In NRBs, the majority of 1,4-dioxane removal (~80%) occurred in the top oxic layer, implying that the removal was likely driven by aerobic microbial degradation. The results also demonstrate that installation of NRBs can reduce 1,4-dioxane to levels even lower than the NY State drinking water standard of 1 µg/L.

The Dam is Growing?!?: A Case History of Fontana Dam

Walker, Scott, Tennessee Valley Authority, srwalker3@tva.gov (TS #4) The Tennessee Valley Authority’s Fontana Dam is a 2,365-foot-long concrete gravity structure located at River Mile 61.0 on the Little Tennessee River in western North Carolina. With a maximum height of 480 feet, it is the tallest dam in the eastern United States. Originally developed to help meet demand for electricity during World War II, the dam was constructed over a three-year period and placed into commercial operation in January 1945. Bedrock at the site is primarily feldspathic quartzite, graywacke, and phyllite of the Precambrian-age Smoky Mountain Group. Silica (such as the strained quartz present in the metasedimentary rocks quarried for concrete aggregate at Fontana) can react with Portland cement to form a hydrophyllic gel that causes the concrete to expand. This type of alkali-aggregate reaction (AAR) was first confirmed at Fontana Dam in 1974, and induced stresses and deformation of the mass concrete resulting from AAR have required various intervention and mitigation techniques over the years. This presentation will cover the history of the Fontana Project, including the logistical challenges associated with constructing a large dam in a remote location on an aggressive wartime schedule, design and construction challenges associated with foundation treatment due to geologic structure, and the ongoing challenges created by AARinduced “concrete growth”—including a decision to decommission and abandon the emergency spillway in 2003.

Neurodiversity: Challenges and Advantages of Autism in the Technical Workplace

Walker, Scott R; Tennessee Valley Authority, srwalker3@tva.gov (TS #12) Autism is a neurological condition that means the brain processes information differently from those who are “neurotypical.” It is estimated to affect 1 in 54 people born in the United States and is diagnosed in boys at a rate far exceeding that of girls. Although first described in 1943, autism was not formally recognized as a standalone diagnosis until 1980. The term Asperger’s syndrome was coined in 1981 to describe a form of “high functioning” autism often characterized by high intelligence, a focused interest in a particular subject, and difficulties with social interaction. The prevalence of autism in the children of engineers is double that of the general population, and (unsurprisingly) many “Aspies” gravitate toward careers in technical or analytical fields. However, statistics about autism in the workplace can be hard to quantify because it is officially characterized as a “disability” and requires self-identification, yet most Apies do not see themselves as disabled and many do not wish to be “labeled.” Because of the hereditary component and the timing (and evolution) of diagnostic criteria, parents whose children are diagnosed with autism may embark on a journey of self-introspection and find that they too share similar traits. In the technical workplace, the value found in strengths common to many Aspies (creative thinking, attention to detail, accuracy, and the ability to hyperfocus) can be overshadowed by difficulties with “soft skills.” Challenges related to neurodiversity in the workplace can manifest in hiring processes and performance reviews that are (unintentionally) inequitable, or when colleagues misinterpret actions or behaviors, leading to negative opinions or resentment. The Tennessee Valley Authority has established Inclusion as one of four core values, and TVA is working to increase neurodiversity by partnering with the University of Tennessee at Chattanooga to hire degree-seeking students on the autism spectrum as summer interns.

Thermal Imaging for Rockfall Detection

Wellman, Edward, University of Arizona, ecwellman@email.arizona.edu; Chad Williams, cpwilliams@arizona.edu; Brad Ross, bjr@arizona.edu (TS #5) Under a NIOSH research grant, the Geotechnical Center of Excellence is evaluating the capability and limitations of thermal imagers to detect rockfall events and the conditions that can lead to rockfall. This two-year study includes testing four different thermal imaging systems that will be used to detect man-made rockfalls and a longerterm surveillance test in a variety of mines and conditions. The surveillance test will determine thermal imaging’s ability to detect rockfall

events in a wide range of temperature, moisture, dust, distance, and humidity conditions. Four thermal infrared imagers were acquired for the project. Two medium resolution imagers, one high resolution, and one high-resolution imager with pan, tilt, and zoom capability were acquired. The imagers were installed on a mobile mine monitoring platform. The project aims to test thermal imaging cameras’ effectiveness to detect and record rockfall events and rockfall hazards in surface mining operations as a method to protect mine workers from the risks of rockfalls. One of the primary goals is to identify cost-effective off-the-shelf systems integrated with existing slope monitoring systems or mounted separately as a part of routine mine observations. This presentation will document early results from the project, with results from trials in Arizona, Colorado, and Washington.

Glauconitic Sand: A New Geohazard for Offshore Wind?

Westgate, Zack, University of Massachusetts at Amherst, zwestgate@umass.edu (TS #9) Glauconitic sand, otherwise known as “greensand,” is a challenging soil type that can pose significant risk to foundation installation and performance. This is due to its tendency to transform from a stiff, high permeability coarse-grained material to a weak, low permeability fine-grained material due to particle crushing. Glauconite is an iron potassium mica with a characteristically green color, often found in peloidal form. It forms under reducing conditions within shallow marine depositional environments and has been found in coastal regions of the United States including locations along the Atlantic outer continental shelf associated with offshore wind farm developments. Due to its friable nature, glauconite affects the geotechnical properties of the sediments in which it forms. Geotechnical laboratory tests performed on glauconitic sand samples reveal a wide range in particle size gradation, low particle crushing strength, high specific gravity, and variable cementation. Intact glauconitic sand exhibits high strength, but under moderate disturbance it is relatively brittle, similar to carbonate sediments found in tropical regions. Given its tendency to crush, in situ testing with cone penetrometers produces high tip resistance and high sleeve friction, limiting the usefulness of standard soil classification charts. This talk presents a review of the geological basis for glauconitic sand formation, describes its depositional environment and maturation process, and presents examples of its geotechnical characteristics. Insights into the impact of glauconitic sands on offshore foundation installation and performance are discussed. Guidance is provided to engineering geologists and geotechnical engineers for planning site investigations where glauconitic sands may be encountered in relation to nearshore and offshore infrastructure developments.

Projected Climate Change Effects on Post Wildfire Debris Flow Probability, Volume, Hazard, and Runout on the 2017 California Thomas Fire Area

White, Zane, Colorado School of Mines, zcwhite@mymail.mines.edu; Paul Santi, psanti@mines.edu (TS #9) The 2017 Thomas Fire near Montecito, California burned almost 282,000 acres and was followed by multiple debris flows in early January that killed twenty-three people and caused at least $177M in damage. These debris flows are noteworthy because they entered populated neighborhoods and were the focus of much news coverage. Consequently, this is an ideal event to extrapolate the potential differences expected due to climate change by predicting and modeling debris flow impacts if this event was to happen in years 2050 or 2075. We use climate model data that predicts changes in peak rainfall intensity and frequency of severe rainfall and enter these new values into standard US Geological Survey predictive equations to estimate the increase in probability and volume of debris flows. While the current design storm for debris flows in these watersheds is 40 mm/hr, the RCP 4.5 and 8.5 climate models predict 46 mm in 2050 and 47 to 50 mm in 2075. We then use other published climate studies to show increase in wildfire size and burn intensity. Wildfire sizes are expected to increase by approximately 50–65% by 2050 and 75–90% by 2075. Burn intensity for the area was conservatively assumed to maintain the same proportions as the 2017 fire: 11% unburned, 31% burned at low intensity, and 58% burned at moderate and high intensities. These proportions were scaled to the predicted larger burned perimeter in 2050 and 2075. Finally, we apply these changes to debris-flow runout models to show the expected increase in runout area and to demonstrate changing hazards. Runout is calculated for 14 high-hazard drainage basins across the fire area, and also for a cluster of 21 contiguous basins in a representative subarea within the fire perimeter.

To Boldly Go: Field Notes on Diversity in Planetary Science

Wyrick, Danielle, Southwest Research Institute, Space Science and Engineering Division, dwyrick@swri.org (TS #12) Planetary science has begun to examine the many structural boundaries that stand in the way of furthering the goals of diversity, equity, and inclusion. Due to its somewhat insular nature, this extraterrestrial geoscience field provides a microcosm within which to discover and test best practices in team innovation and impact through integration. This presentation will discuss the current research on diversity in planetary science, focusing on what we know of the systemic inequities that persist. More importantly, this talk focuses on what we can do as a community to foster best practices in practical ways to ensure the advancement of the next generation of geoscientists.

Using Drone Imagery to 3D Model and Aid in Remediation Design for an Emergency Landslip in Jefferson County, Ohio

Yeakley, Julia, Gannett Fleming, jyeakley@gfnet.com; Thomas L. Monaco, Tmonaco@gfnet.com; Yuru Zimmerman, Yzimmerman@gfnet.com (TS #3) In 2019, intense rainfall activated landslips along a county road in Jefferson County, rupturing two lanes of pavement and causing the popular route to close. This work involved coordination between Gannett Fleming, Jefferson County, the contractor, and ODOT under an Emergency Contract. The landslip consisted of multiple slips occurring in two directions, downslope and upslope of the road. The slip was in active movement as the project began and the initial scope consisted of monitoring the movement with inclinometers. However, the slide continued to move and widen at a dramatic rate and the inclinometers sheared within two weeks of installation. Due to the urgent circumstances and limited budget for survey, drone footage was utilized to create a 3D model. Using Bentley’s Context Capture editor program, we were able to create accurate cross sections and model the soil and rock profile for global stability analyses as well as design in Civil 3D and, ultimately, MicroStation. In July 2019 funding was found for the repair and Gannett Fleming led the design and remediation effort. From that point till the completion of construction in early October, Gannett Fleming delivered design services, temporary stabilization measures, contract drawing preparations, review of contractor’s submittals, and on-site consultation. The ultimate remediation was a 514-foot soldier pile and lagging wall downslope with a 344-foot plug pile wall with lagging extending above grade to capture debris upslope. This presentation will summarize how drone imaging and inclinometer data allowed the project to be substantially completed within three months of authorization.

Lateral Spreading in Balboa Boulevard (1994 Northridge): Suspected Mechanisms, Data, and Predictive Capabilities

Ziotopoulou, Katerina, University of California, Davis, kziotopoulou@ucdavis.edu; Renmin Pretell, rpretell@ucdavis.edu; Craig Davis, cadavisengr@yahoo.com (TS #11) The 1994 MW 6.7 Northridge earthquake led, amongst the many other failures, to the lateral spreading failure of Balboa Blvd. in the northern side of the San Fernando Valley. Damages observed at Balboa Blvd. include extensional and compressional failure zones, large displacements, and pervasive pipeline failures. The failure mechanism behind these observations has been investigated through the years but was never explicitly proven. The availability of subsurface data, ground displacement measurements, and ground motion recordings makes this case history well suited for the 1) numerical investigation of the failure mechanism leading to ground deformations at this site; 2) evaluation of the accuracy of adopted analysis methods and engineering procedures to reasonably capture the observations; and 3) identification of key factors leading to ground deformations. The geotechnical characterization of Balboa Blvd. was assessed based on field and laboratory data obtained from two investigation campaigns. Transitional probability geostatistics were used to develop stratigraphic models that capture the heterogeneity and the spatial variability patterns of sand-like and clay-like soils present at this site. The stratigraphic models were implemented in a finite difference software and the behavior of sand-like and clay-like soils was simulated using advanced constitutive models. Sensitivity analyses were performed to address uncertainties associated with the spatial variability of soils, the proportion of sand-like and clay-like soils within the soil deposit, and the strength properties of these materials. Results suggest that a compounded effect of both liquefaction of sand-like soils and cyclic softening of clay-like soils led to the excessive ground deformations. This study sheds light on the importance of using appropriate engineering procedures and numerical modeling protocols in the prediction of deformation patterns, the selection of key input parameters, and the necessity of adequate subsurface data such that rational hypotheses about suspected or expected failure mechanisms can be made.

New AEG Diversity Scholarship & Grants Program

Funded through the AEG Foundation

The AEG Diversity, Equity, and Inclusion Committee (DEIC) has recently begun a new program through the AEG Foundation. The Diversity Scholarship & Grants Program has two different functions. Both are to financially support new ways to introduce and attract students from diverse backgrounds to study geoscience and to consider it as a possible career path. AEG Chapters and members are urged to help get the word out about these two new diversity resources.

Diversity Scholarship for College or University Students

The scholarship will be awarded annually to one student who is a geoscience major in their sophomore, junior, or senior year at an accredited college or university. The successful applicant will have a GPA of 2.9 or better. This scholarship is in the amount of $5,000. It is not renewable, but those who have received it in previous years may reapply.

Diversity Field-Trip Grants

These grants are intended to help introduce middle-school and high-school students from diverse backgrounds to the geosciences as a possible career path. Middle school and high school Earth science and STEM teachers are invited to apply. The grants will pay for transportation, insurance, admission fees, and other direct expenses for five different school groups, from all over the US, to go on a geology-related field trip. The field-trip itineraries must include at least three different geology-related field stops. Each school group will receive approximately $1,000 to pay for field trip expenses. Grant applicants are encouraged to contact their local AEG Chapter, USGS office, college or university geology departments, college or university Geology Club, or local hobby groups such as cavers, mineral clubs, fossil hunters, etc. The field-trip grant applicants will receive a more favorable evaluation if they reach out to other geoscientists in their part of the country. Spread the Word…

AEG members should be aware of this new educational resource and actively invite eligible scholarship and grant recipients to apply. Hopefully, they will receive inquiries from various middle-school and high-school earth science teachers who would like some help in planning and leading their geoscience field trip. This incentive should result in AEG members being contacted by interested local teachers. It will encourage collaboration. And even if the grant application to AEG Foundation is unsuccessful, perhaps that AEG Chapter could help the field trip financially, or by meeting the group at a field site, or other proactive support. vv

For more information, please visit www.aegfoundation.org/diversity. For questions, please contact diversity@aegfoundation.org. To contribute to this new Diversity Scholarship Fund, please visit www.aegfoundation.org/donate.

Portland Marriott Downtown Waterfront – …for the 2023 Annual MeetingSave the Date

Portland, Oregon – September 19–24

The In-Person AEG 2020 Annual Meeting has been rescheduled for 2023. Portland, Oregon’s largest city, sits on the Columbia and Willamette rivers, in the shadow of snow-capped Mount Hood. It’s known for its parks, bridges, and bicycle paths, as well as for its ecofriendliness and its microbreweries and coffeehouses. The city hosts thriving art, theater, and music scenes. Surrounded by Portland hot spots, the Marriott Portland Downtown Waterfront hotel reflects the vibrancy of the city and is located directly on the waterfront in downtown, surrounded by more than 60 breweries. Wind down with friends by sampling some of the 150 types of whiskey at their on-site restaurant, Proof Reader. The hotel even helps you go green with complimentary car-charging stations, biodegradable straws and easy access to light rail from the nearby Morrison Subway Station. At night, retire to elevated guest rooms with 24-hour room service, waterfall showers, free Wi-Fi, premium channels and views of Portland. Don’t miss all of the exciting Field Courses, Guest Tours and the Special Event at the Oswago Hills Vineyard planned for this incredible Annual Meeting.