1. INTRODUCTION

1.1 STUDY PURPOSE

The City of Millbrae (City) is preparing a Specific Plan for its El Camino Real and Downtown Area (Specific Plan). The Specific Plan Area includes the Millbrae Priority Development Area (PDA), an area within the City that has been identified as a future infill development opportunity area. The Specific Plan Area encompasses a slightly larger area than the PDA and excludes the area within the adopted Millbrae Station Area Specific Plan (MSASP). The Specific Plan Area includes the El Camino Real (State Route 82) corridor, which spans from Victoria Avenue to the south and the City limits to the north. The Specific Plan Area also encompasses the City’s Downtown, which spans from Victoria Avenue to the south to Meadow Glen Avenue to the north. Many residential areas surrounding these commercial corridors are also included. It is anticipated that there will be an intensification of land use within the Specific Plan Area, with more mixeduse type development and higherdensity residential development. West Yost was retained to prepare this Infrastructure Report. The report identifies the potential impacts of the planned land use in the Specific Plan Area on the City’s water, sewer collection, and storm drainage infrastructure. The Infrastructure Report provides a capital improvement plan identifying recommended water, sewer collection and stormwater infrastructure needed for the Specific Plan Area, along with planning-level costs. The City will use this information to develop a financial plan and development impact fees for water, sewer collection and stormwater systems within the Specific Plan Area.

1.2 AUTHORIZATION

This work was authorized with a contract between West Yost and Mintier Harnish on April 30, 2021. Mintier Harnish is the consultant leading the Specific Plan effort.

1.3 REPORT ORGANIZATION

This report includes the following chapters following this Introduction chapter:

• Chapter 2: Specific Plan Land Use, Demands and Sewer Flows. Describes the Specific Plan Area and proposed intensification of land use. Presents projected water demands and sewer collection system flows associated with the intensification of land use.

• Chapter 3: Water System Analysis. Presents the analysis of the City’s water system to identify infrastructure needs and associated planning-level costs associated with the Specific Plan.

• Chapter 4: Sanitary Sewer Collection System Analysis. Presents the analysis of the City’s sanitary sewer collection system to identify infrastructure needs and associated planning-level costs associated with the Specific Plan.

• Chapter 5: Storm Drain System Analysis. Presents the analysis of the City’s storm drain system to identify infrastructure needs and associated planning-level costs associated with the Specific Plan.

1.4 ACKNOWLEDGMENTS

The development of this study would not have been possible without the key involvement and assistance of City staff. City staff provided data on existing systems, participated in project meetings to review land use and development assumptions, and provided input on report evaluation and findings.

The following West Yost team members contributed to the project:

• Elizabeth Drayer, Principal-inCharge, QA/QC

• Polly Boissevain, Project Manager

• Amy Kwong, Land Use, Demand and Supply Lead

• Megan McWilliams, Water System Lead

• Chris Pittner, Water System Analysis

• Patrick Johnston, Sewer Collection System Lead

• Youssif Hussein, Sewer Collection System Analysis and Storm Drain System Analysis

• Austin Oerding, Sewer Collection System Analysis

• Michele Miller, Storm Drain System Analysis Lead

• Lucas Russell, Storm Drain System Analysis

• Jean Bolger, Report Production

Page intentionally left blank.

2. SPECIFIC PLAN

LAND USE, WATER DEMANDS AND SEWER FLOWS

2.1 SPECIFIC PLAN OVERVIEW

The City’s El Camino Real and Downtown Specific Plan Area (Specific Plan Area includes the El Camino Real (State Route 82) corridor, which spans from Victoria Avenue to the south and the City limits to the north. The Specific Plan Area also encompasses the City’s Downtown, which spans from Victoria Avenue to the south to Meadow Glen Avenue to the north. Many residential areas surrounding these commercial corridors are also included. Figure 2-1 shows the Specific Plan Area and the proposed parcels that will be redeveloped as part of the Specific Plan. The figure includes the different land use types and the land use block numbers (e.g., CMU6, RMU13) used to summarize parcel specific future land use statistics.

2.2 EXISTING LAND USE

Per the City’s current General Plan Land Use Diagram and Official Zoning Map (October 2009), the existing land use within the Specific Plan Area ranges from commercial, residential (single family and multifamily), and office to parcels for planned development. While land uses within the Specific Plan Area are not expected to significantly change, uses are anticipated to intensify, with more mixed-use projects and higher-density residential projects.

The Specific Plan Environmental Impact Report (EIR) includes an existing conditions baseline. The existing baseline includes existing conditions plus ‘Pipeline Projects’ which are approved development projects and development projects that have been submitted for City review at the time of the issuance of the Notice of Preparation for the EIR (December 3, 2021). The City provided a list of the Pipeline Projects that are assumed to be a part of the existing land use for the purposes of this evaluation. Table 2-1 summarizes the Pipeline Project land use and Figure 2-2 shows the Pipeline Projects in relation to the Specific Plan Area. The location of the Pipeline Projects was determined by using the list of Assessor’s Parcel Numbers (APNs) provided by the City for each Pipeline Project. The Pipeline Projects consist of general commercial, hotel, office, restaurant, and residential land uses, and include the following developments:

• Serra Station (Transit Oriented Development 1 [TOD1])

• 480 El Camino Real

• Moxy Hotel

• 130 – 140 El Camino Real

• 959 El Camino Real

• 1100 El Camino Real (Anton)

• 1301 Broadway

FIGURE 2-1. PROPOSED LAND USE

San Francisco International Airport

Proposed Land Use

ELCAMINO REAL be developed per WRT Design but are shown to remain consistent with land use file provided.

2. Although the MSASP is within the El Camino and Downtown Specific Plan area, infrastructure improvement needs were already identified for the MSASP in the Millbrae Station Area Specific Plan Technical Reports (West Yost, 2015). This report assesses infrastructure needs for the remaining areas within the Specific Plan.

Symbology

0 750 375 Scale in Feet

Commercial Preference Area

Residential Mixed Use (RMU)

Residential (R)

Corridor Mixed Use (CMU)

Neighborhood Commercial Mixed Use (NCMU) Downtown Mixed Use (DMU)

Specific Plan Boundary

MSASP Boundary

BART Tracks San Francisco Bay Millbrae City Limits

Notes:

1. The parcels identified as ‘Residential’ are not expected to be developed per WRT Design but are shown to remain consistent with land use file provided.

2. Although the MSASP is within the El Camino and Downtown Specific Plan area, infrastructure improvement needs were already identified for the MSASP in the Millbrae Station Area Specific Plan Technical Reports (West Yost, 2015). This report assesses infrastructure needs for the remaining areas within the Specific Plan.

Figure 2-1

Specific Plan

Proposed Land Use

City of Millbrae

Downtown and El Camino Specific Plan Infrastructure Report

TABLE 2-1. PIPELINE PROJECTS LAND USE SUMMARY

Source: Millbrae Pipeline Projects for GP-SP EIR_rev 11-3-21 spreadsheet provided by WRT on November 4, 2021

(A) Square footage for residential units not provided. Units are shown as net new units.

FIGURE 2-2. PIPELINE PROJECTS

2.3 PROJECTED SPECIFIC PLAN LAND USE

WRT, the community design consultant for the Specific Plan, provided West Yost with the proposed land uses within the Specific Plan Area. The proposed land use includes estimates of residential and nonresidential building square footage and residential dwelling units for the following land uses:

• Residential Mixed Use

• Residential

• Corridor Mixed Use

• Neighborhood Commercial Mixed Use

• Downtown Mixed Use

Table 2-2 summarizes the overall proposed land use in the Specific Plan Area. Table 2-3 details the land uses by block number corresponding to Figure 2-1 and summarizes the estimated water use and wastewater base flows that are discussed in subsequent sections. The parcels identified as ‘Residential’ are not expected to be developed per WRT but are shown to remain consistent with the land use file provided.

TABLE 2-2. SPECIFIC PLAN LAND USE SUMMARY AREA, SQUARE FEET RESIDENTIAL DWELLING

TABLE 2-3. ESTIMATED WASTEWATER BASE FLOW AND WATER DEMAND BY LAND USE BLOCK

Source:CityofMillbrae2015WSAandMillbraeCapacityStudyspreadsheet(providedtoWestYoston11-4-2021)

(a)Non-residentialwastewaterbaseflowisestimatedbyusingthesewergenerationrate,0.1gpd/SF,whichisforoffices,retail(store),orindustriallanduses.Therestaurantsewergenerationrateisestimatedas0.3gpd/SFandisbasedon2019waterusedataforrestaurantsalongElCaminoReal.

(b)The2015MillbraeWSAdidnotprovideasewergenerationrateforresidentiallanduse.Thewaterdemandwasestimatedfirstusingtheresidential(multi-family)waterdemandfactor,138.41gpd/unit,listedinthe2015MillbraeWSA.Thewastewaterbaseflowratewasestimatedbydividingbyafactorof1.15(equivalenttoapproximately85%water tosewerconversionrate).Thisisthesameconversionratethe2015MillbraeWSAusedfornon-residentiallanduse.

2.4 WATER USE FACTORS AND SEWER GENERATION RATES

To estimate the water use and sewer flows for the proposed land use within the Specific Plan Area, water use factors and sewer generation rates from the City’s 2015 Water Supply Assessment (WSA) were used for all land use types except for restaurants, as further discussed below. Table 2-4 summarizes the sewer generation rates and water use factors used to calculate the average dry weather sewer flow and average day water use for the Specific Plan. The 2015 WSA provided sewer generation rates and multiplied those by 1.15 to estimate water use. The sewer generation rates and water use factors are multiplied by the planned non-residential developed square footages or the number of residential units or commercial hotel rooms to calculate sewer flows and water use.

Subsequent evidence has shown that the restaurant sewer generation rate listed in the 2015 WSA, 2.78 gallons per day per square foot (gpd/SF), was higher than the amount actually used by restaurants. West Yost used 2019 water consumption data provided by the City and building square footages for restaurants along El Camino Real to confirm the sewer generation rate.

The City provided West Yost with 2019 water consumption data for 65 restaurants within the Specific Plan boundary. Of the 65 records, West Yost used water consumption data from 35 restaurants where the restaurant was a stand-alone building. West Yost determined the area of each restaurant building using a building footprint shapefile. The water use factors ranged from 0.01 gpd/SF to 1.68 gpd/ SF. The average water use factor was estimated as 0.34 gpd/SF. Using the potable water to sewer conversion rate, West Yost estimated the sewer generation rate to be approximately 0.3 gpd/SF.

TABLE 2-4. SUMMARY OF SEWER GENERATION RATES AND WATER USE FACTORS (A)

(A) Sewer generation rates and water use factors are multiplied by the planned non-residential square footage or the number of residential units or commercial hotel rooms to calculate sewer flows and water use.

(B) The sewer generation rates listed are from the City’s 2015 WSA. The sewer generation rate for restaurants was recalculated by West Yost using 2019 water consumption data for restaurants along El Camino Real within the Specific Plan Area.

(C) The residential water use factor is from the City’s 2015 WSA.

(D) The 2015 WSA provides sewer generation rates and multiplies those by 1.15 to estimate water use. The 2015 WSA did not provide a sewer to water conversion rate for residential land use so the same non-residential conversion rate was applied.

2.5 WATER USE

The following sections summarize the existing and projected water use within the Specific Plan Area.

2.5.1 EXISTING WATER USE

The existing water use is based on 2012 water consumption per the 2015 WMP. The existing demands were updated to reflect the Pipeline Projects.

Table 2-5 summarizes the estimated demands for the Pipeline Projects that are included as part of the existing system analysis. In the Specific Plan Area, the updated existing average day demand, including Pipeline Projects, is 0.5 million gallons per day (mgd) and the updated maximum day demand is 1.0 mgd.

2.5.2 PROJECTED WATER USE

The Specific Plan Area projected water use was estimated using the proposed building information (square footage and dwelling units) presented in Table 2-3 and the sewer generation rates and water use factors presented in Table 2-4.

Table 2-6 summarizes the buildout average day demand for the Specific Plan Area and buildout maximum day

TABLE 2-5. SUMMARY OF ESTIMATED WATER DEMAND FOR PIPELINE PROJECTS

(A) See detailed demand calculations by land use block in Table 2-3.

(B) Per the City’s 2015 WMP, maximum day peaking factor for both residential and non-residential land use is 2.0.

(C) Per the City’s 2015 WMP, hourly peaking factor is 1.66 for residential land use and 1.75 for non-residential land use.

(D) Non-revenue water is estimated to be 7.6 percent because it is the largest value reported in the City’s 2015 WMP.

demand and peak hour demand, using peaking factors from the City’s 2015 Water Master Plan (WMP). The estimated demand is calculated for the projected land use based on building square footage and residential dwelling units by land use block summarized in Table 2-3 and shown on Figure 2-1.

TABLE 2-6. SUMMARY OF ESTIMATED BUILDOUT WATER DEMAND FOR SPECIFIC PLAN AREA

(A) See detailed demand calculations by land use block in Table 2-3.

(B) Per the City’s 2015 WMP, maximum day peaking factor for both residential and non-residential land use is 2.0.

(C) Per the City’s 2015 WMP, hourly peaking factor is 1.66 for residential land use and 1.75 for non-residential land use.

(D) Non-revenue water is estimated to be 7.6 percent because it is the largest value reported in the City’s 2015 WMP.

2.6 WASTEWATER FLOWS

The following sections summarize the existing and projected wastewater flows for the Specific Plan Area.

2.6.1 EXISTING WASTEWATER FLOWS

The existing average dry weather sewer flows within the Specific Plan Area are based on 2011 water consumption records and 2011 flow monitoring data, per the 2012 Capacity Assurance Report. In the Specific Plan Area, the existing average dry weather sewer flow is estimated to be 0.47 mgd, including the Pipeline Projects.

Table 2-7 summarizes the estimated wastewater base flow for the Pipeline Projects which are included as part of the existing system analysis. The estimated wastewater base flow for the Pipeline Projects is 228,500 gpd, or 0.23 mgd.

TABLE 2-7. SUMMARY OF ESTIMATED WASTEWATER FLOWS FOR PIPELINE PROJECTS

TABLE 2-8. SUMMARY OF ESTIMATED BUILDOUT WASTEWATER FLOWS FOR SPECIFIC PLAN AREA

2.6.2 PROJECTED WASTEWATER FLOWS

Projected wastewater flows for the Specific Plan Area were estimated using the proposed building information (square footage and dwelling units) presented in Table 2-3 and the sewer generation rates and water use factors presented in Table 2-4. Table 2-8 summarizes the estimated wastewater average dry weather flow of the Specific Plan Area. The total is approximately 566,300 gpd, or 0.57 mgd.

Page intentionally left blank.