The Roxborough Water and Sanitation District (RWSD) Wastewater Regionalization Project, located near the Denver Metro area, involved a large metropolitan sanitary sewer line system installed near the South Platte River that traveled through multiple parks, golf courses, and street crossings. RWSD encountered wastewater treatment challenges with its older facility and faced the decision to upgrade its existing wastewater treatment plant or to reroute its wastewater and partner with area wastewater treatment facilities. Partnering with the Littleton/Englewood Wastewater Treatment Plant (WWTP) — the state's third largest publicly owned wastewater treatment facility — would provide regionalization of the District's wastewater treatment, eliminating the need for using multiple domestic wastewater treatment plants.
Lockheed Martin Space Systems Co., one of the four major business divisions of Lockheed Martin, is located nearby and faced the same wastewater treatment challenges as Roxborough. It also chose to combine resources and reroute all of its wastewater.
A pipe system was needed to reroute the existing wastewater. TST Infrastructure LLC, an Englewood, Colo.-based consulting engineering company, designed a 14.2-mile-long sanitary sewer pipeline to bring flows from the two systems together and transmit them to the Littleton/Englewood WWTP. The design included 8.3 miles of forcemain and 5.9 miles of interceptor.
TST Infrastructure designed two lift stations to accomplish this. One was constructed on Lockheed Martin property and was designed to receive gravity flows from the domestic wastewater collection system and transfer the wastewater to the second lift station, located on Roxborough's existing WWTP site. The wastewater would then travel up and over the spillway at Chatfield Reservoir, crossing under State Highway C-470 and running along the South Platte River . Gravity would then keep the flow moving toward a connection with Littleton/Englewood's interceptor at Santa Fe Blvd and Belleview Ave.
With only a 110-foot drop over the gravity main's almost 6 miles, construction required setting the pipe at a very flat 0.3 percent average grade with minimum slopes as low as 0.09 percent.
“The design and construction of the interceptor portion of the project was critical due to the numerous utility crossings and the minimal vertical drop across the pipeline,” said Chris Manning, civil engineer with TST Infrastructure.
Because the pipe route was located near the South Platte River and low-lying wetlands, additional problems occurred with respect to groundwater. Working below the water table required pumps to dewater the trench and aggregate to stabilize the pipe foundation in the trench.
Multiple contractors worked on various stages of the project. American Infrastructure, Inc., constructed the interceptor. With such a minimal grade tolerance for the entire run of pipe, coupled with the high water table, a pipe with maximum stability was especially critical.
A-2000 PVC sanitary sewer pipe from CONTECH Construction Products Inc. was chosen for the job because it could adhere to the slope constraints and also had superior joint strength. The profile wall design of A-2000 was engineered to provide long-term service and performance as well as material cost savings compared with other conventional sewer pipes. Joints and gaskets were also designed to stay tight, controlling infiltration and root penetration.
CONTECH has sanitary sewer pipe solutions available in diameters ranging from 4 inches to 72 inches. To construct the sanitary sewer pipeline, A-2000 was chosen with 500 linear feet of 12-inch diameter; 600 linear feet of 18-inch diameter; 30,000 linear feet of 24-inch diameter; and 4,000 linear feet of 36-inch diameter.
During installation, A-2000 saved time because it has a lighter handling weight, an easy-to-stab joint, and could be installed with smaller-than-normal crews. The low installed cost of A-2000 PVC pipe in combination with its 46-pounds-per-square-inch stiffness, superior hydraulics, tight joints, and superior strength allowed a rapid and economic installation.
“The South Platte River crossing required the design and construction of an inverted siphon to carry the wastewater beneath the river while maintaining the necessary elevation drops to connect at the city of Littleton interceptor downstream,” said Manning. “Half the river was diverted at a time so the pipe could be constructed and encased in concrete. There were also balancing pressures to ensure that air-lock would not occur, preventing vacuum pressure on the pipe.”
A-2000 met the performance criteria of the inverted siphon on this project and provided the versatility and assurance needed.
To meet RWSD's delivery schedule, American Infrastructure started the project with three crews working in different areas. To keep the project moving on an accelerated schedule, TST Infrastructure provided full-time oversight and the project was completed approximately six weeks ahead of schedule.
Roxborough's connector contract demonstrates the environmental and financial benefits of the regional wastewater treatment concept. The pipeline allows better quality and more cost-effective treatment of Roxborough's wastewater because of Littleton 's advance treatment capability. It improved the wastewater treatment services to the community and stabilized the cost of wastewater treatment to the residents of the District. Eliminating the two wastewater treatment plants stopped the discharge of treated wastewater into the South Platte River from both locations, thus improving the water quality in the Chatfield Reservoir Drainage Basin. This wastewater regionalization project proved a beneficial solution for the community as well as for the environment.
Andrew Jenkins is the sanitary and irrigation market manager for CONTECH Construction Products Inc. He has 10 years of experience in the civil engineering and construction industry. He can be contacted at firstname.lastname@example.org .