WCW Conference & Trade Show ▪ Winnipeg ▪ September 20 - 23 ▪ 2009
Infrastructure Serving Dawson City, Yukon – The New Klondike Gold Ken Johnson ABSTRACT Dawson City’s water and sewer services are provided by a buried, insulated high density polyethylene pipe (HDPE) utility system which was completed around 1980. The water and sewer infrastructure is reasonably complex in both its construction and operation. Beyond the piping systems that are associated with the infrastructure, there are 12 facilities that are an integral part of the infrastructure. The facilities handle approximately 850,000 cubic metres (190 million Imperial gallons) each of water and sewage in a year. Freeze protection for the water system is needed during the winter; the water in the pipes cools as it flows through the distribution piping, therefore additional heat is required to prevent the water in the pipes from freezing. The water is also re-circulated by pumping to confirm the water temperature in the pipe, and provide additional freeze protection. Subsoil conditions in Dawson City typically consist of organic silts, and silts, and this layer has an ice content varying from zero to greater than 50 percent excess ice content. This area is in the widespread discontinuous permafrost zone, with mean ground temperatures in the range of -1.5 C, which is considered to be “warm” permafrost. Problems with respect to water and sewer systems in these soil conditions have caused ground subsidence due to thaw of the ice rich permafrost, seasonal frost heave of buried foundations and utility pipes, or groundwater conditions. The soil conditions in Dawson City have required the development of unique and expensive water and sewer piping materials and installation techniques. The installation of the pipe requires consideration of the permafrost conditions to ensure that the area around the excavation is not significantly disturbed, particularly in areas where the permafrost has a lot of ice lensing. Dawson City continues to incrementally address the challenges of operating and maintaining a water and sewer facilities in the heart of Klondike. Bleeder reduction has been a priority over the past several years and water metering has been implemented to reduce water down in the range of 500 litres/capital/day from winter extremes of 1500 litres/capita/day. A comprehensive water and sewer facility assessment was completed in 2006, which has provided Dawson with the framework for system improvements over the next 20 years. The most significant infrastructure improvement in the next several years will be an upgrade in the sewage treatment system, which will cost approximately $25 million.
Page 1 of 7
WCW Conference & Trade Show ▪ Winnipeg ▪ September 20 - 23 ▪ 2009
Introduction Dawson City owns and operates water, sewage and drainage infrastructure which serves the residents, and businesses of the community. This infrastructure is reasonably complex and requires a dedicated staff of 5 individuals to operate and maintain. A lot has changed for the infrastructure in Dawson over the past 4 decades; as recently as the mid 1970’s, the community was still using wood stave pipe for the delivery of potable water (See Figure 1).
Figure 1. Installation of wood stave pipe in Dawson City (circa 1975) Beyond the piping systems that are associated with the infrastructure, there are 12 facilities that are an integral part of the infrastructure (See Figures 2 and 3). These facilities include:
Water well vaults (two) Well supply control building Backup well supply and building Water treatment and distribution pump house Valve chamber building Sewage lift stations (5) Sewage treatment plant
The facilities handle approximately 850,000 cubic metres (190 million Imperial gallons) each of water and sewage in a year (2005 estimate).
Page 2 of 7
WCW Conference & Trade Show ▪ Winnipeg ▪ September 20 - 23 ▪ 2009
Figure 2. Dawson City water infrastructure The age of these facilities ranges from approximately 15 years to almost 50 years, with the majority of the facilities being almost 30 years old (1979 construction). From a facility “lifespan” perspective, facilities that are over 25 years old are generally considered to be approaching the end of their service life. This is not to say that the facility needs to be replaced, but rather that the facility needs to be assessed, and major improvements may be required. Description of Facilities Water System Dawson City’s water system facilities consist of the water source, the water storage, and the water treatment and distribution (See Figure 2). The water source consists of a series of four wells located along the river bank, beside Front Street, at the junction of the Klondike and Yukon Rivers. The wells were drilled to depths of approximately 23 metres (80 feet), and each well is equipped with a 22 kilowatt (30 horsepower) submersible pump. One original well was installed in 1959 on Front St. and Craig St., near the power plant, and three additional wells were installed in 1991 on Front
Page 3 of 7
WCW Conference & Trade Show ▪ Winnipeg ▪ September 20 - 23 ▪ 2009
St. and Church St. to provide additional capacity. The newer wells are situated in concrete access vaults with an adjacent well control building. The original well is situated in a wooden building, and is generally used only as an emergency back up supply. The water storage consists of two insulated steel reservoirs located on 5th Ave and Dugas St., beside the water treatment and distribution building. The two reservoirs have a combined storage of approximate 1300 cubic metres (290,000 Imperial gallons), which provides storage for drinking water supply and fire protection. The water treatment and distribution consists of a building which contains various chemical, heating, pumping, electrical and piping systems for water treatment, freeze protection for the system, and water distribution. The water treatment consists of controlled chlorine gas injection into the water prior to distribution into the buried water systems; the chlorine provides disinfection to the water from the wells and a “residual” level of disinfection as the water is distributed throughout the community. Freeze protection for the water system is needed during the winter; the water in the pipes cools as it flows through the distribution piping, therefore additional heat is required to prevent the water in the pipes from freezing. Heat from several oil fired boilers is injected into the water to maintain the water supply several degrees above zero. The water is also re-circulated by pumping to confirm the water temperature in the pipe, and provide additional freeze protection. The pumping of water into the distribution piping systems utilizes 100 kilowatts (130 horsepower) of electric pumping capacity. An additional 100 kilowatts (130 horsepower) of diesel pumping capacity is available to provide fire flow to the distribution system. The water distribution system itself consists of 16 kilometres (10 miles) of insulated, buried water main, which has sizes between 150 millimetres and 250 millimetres (6 inches and 10 inches). The distribution system includes approximately 700 service connections to buildings and 85 on-line fire hydrants (See Figure 3). The system also includes a valve chamber building for controlling the flow of water. Figure 3. On-line hydrant in Dawson City Page 4 of 7
WCW Conference & Trade Show ▪ Winnipeg ▪ September 20 - 23 ▪ 2009
Sewage System Dawson City’s sewage system facilities consist of the five lift stations, and the sewage treatment plant (See Figure 4). The sewage collection system itself consists of 16 kilometres (10 miles) of insulated, buried sanitary sewer, which has sizes between 150 millimetres and 250 millimetres (6 inches and 10 inches), and approximately 3.5 kilometres (2 miles) of buried force main from the lift stations. The collection system includes approximately 700 service connections to buildings. Figure 4. Dawson City sewage infrastructure. The sewage lift stations generally consist of submersible pumping systems in wet wells, with control buildings either on top of or adjacent to the wet wells. Four of the lift stations may be considered “small” facilities, and the remaining facility may be considered a medium sized facility. Four of the lifts stations collect sewage from the developments along the Klondike Highway up to the Callison development. The force main from these lift stations discharges into a manhole at the top of Craig St. The sewage treatment facility consists of a primary screening operation using two 0.75 millimetre mesh rotostrainers controls, and backup power. The building has three levels; the upper level is at the ground elevation and provides space for the heating and ventilation equipment. The middle level provides space for the screening operation, and an adjacent operating area. The lower level provides space for the inlet and outlet pumps and piping. The sewage discharges into the Yukon River, mid-channel 200 metres (650 feet) west of dyke for flood protection. Concerns with Facilities With the age of these facilities ranging from approximately 15 years to almost 50 years, and the majority of the facilities being almost 30 years old, there is a concern that the facilities
Page 5 of 7
WCW Conference & Trade Show ▪ Winnipeg ▪ September 20 - 23 ▪ 2009
may be at the end of their service life. This concern is supported by the corrosion that may be observed in many of the facilities. The facility operating staffs have been undertaking incremental measures to replace badly corroded components with new stainless steel components. This has been undertaken on a limited basis with the available human and financial resources. The age of the facilities also suggests that improvements may be necessary so that the facilities are operating within the current applicable building and related codes. Of particular code related importance in the current operation water and sewage facilities is the “confined space” ventilation, which applies to chlorination of drinking water and processing of sewage (pumping, and screening); odour control is also another issue. Challenges of Dawson City Water and Sewage System Subsoil conditions in Dawson City typically consist of a surface layer of common road fill 0.6 to 0.9 metres in thickness, underlain by organics, organic silts, and silts to a depth of 3 to 5 metres. This layer of silt and organic silt has an ice content varying from zero to greater than 50 percent excess ice content. Beneath this layer of organic silt, a layer of alluvial gravels has been deposited by the Yukon River; these gravels are relatively dense and thaw stable. This area is in the widespread discontinuous permafrost zone, with mean ground temperatures in the range of -1.5 C, which is considered to be “warm” permafrost. Since the permafrost temperature is just below freezing, the permafrost may thaw or degrade very easily from disturbances such as the installation of underground utilities. Problems with respect to water and sewer systems in these soil conditions have caused ground subsidence due to thaw of the ice rich permafrost, seasonal frost heave of buried foundations and utility pipes, or groundwater conditions. In a two year period, in the mid 1980’s over 225 metres of polyethylene sewer pipe failed by ovalling or collapsing. The problems due to frost action in the soils were compounded in the vicinity of hydrants, vertical risers and service connections because a vertical restraint is imposed on the piping system. At service connection locations, there were numerous examples of service risers causing a local collapse of the main because of the vertical load on the horizontal sewer main. Adjacent to hydrants and valves, pipe failures occurred at fusion weld joints because of bending or torque along the connecting pipe. The unique soil conditions in Dawson City have required the development of unique water and sewer piping materials and installation techniques. Several studies in the late 1980’s compared pipe and bedding configurations, and developed the corrugated cover on insulated HDPE piping that is the pipe standard for Dawson City today (See Figure 5). The installation of the pipe requires consideration of the permafrost conditions to ensure that the area around Page 6 of 7
WCW Conference & Trade Show â–Ş Winnipeg â–Ş September 20 - 23 â–Ş 2009
the excavation is not significantly disturbed, particularly in areas where the permafrost has a lot of ice lensing.
Figure 5. Insulated piping in Dawson City with corrugated metal cover. Future Water and Sewer Improvements Dawson City continues to incrementally address the challenges of operating and maintaining a water and sewer facilities in the heart of Klondike. Bleeder reduction has been a priority over the past several years and water metering has been implemented to reduce water down in the range of 500 litres/capital/day from winter extremes of 1500 litres/capital/day. A comprehensive water and sewer facility assessment was completed in 2006, which has provided Dawson with the framework for system improvements over the next 20 years. Dawson is putting considerable effort into the operation and maintenance of its ground water supply system to ascertain if the wells are under the direct influence of surface water, and to characterize the ground water in regard to aggressive activity in metal pipes. The most significant initiative in recent years has been the upgrading of the preliminary treatment system with a mechanical sewage treatment system. The process selection for the mechanical system applied a design/build competition, and the recommended process is a deep shaft activated sludge configuration. This process is somewhat unique; however a similar process has been operating successfully in Homer, Alaska for the past 16 years. The capital cost for the deep shaft technology will be approximately $25 million, with an estimated annual operation and maintenance cost of less than $300,000. With the high cost of infrastructure in Dawson City, the new gold in the Klondike may be associated with water and sewer not the nuggets of yellow metal. Page 7 of 7