By: Brian Skeens, CH2M Principal Technologist
The vibrant City of Fresno, California (City), provides water services to approximately 513,000 residential customers and 35,000 commercial and industrial accounts. For decades, the City relied on groundwater for nearly 90 percent of its water supplyâ€”meaning the City pumped more water from the ground than it was able to restore each year, causing groundwater levels to rapidly decrease at a rate of one foot annually.
Each year, the Cityâ€™s meets their water demands with 88 percent of groundwater and 12 percent treated surface water. Despite the Cityâ€™s development of an advanced surface water treatment facility and aggressive groundwater restoration efforts, it continues to face declining groundwater levels. In response to this challenge, the City has embarked on a major capital improvement program (CIP) that utilizes surface water allocations to reduce its groundwater reliance from 88 percent to 36 percent.
Through its Recharge Fresno program, the City is improving its pipelines and water system facilities to capture, treat and deliver surface water to Fresno homes and businesses. CH2M is collaborating as Program Manager with the City to construct the new 80 million gallons per day (MGD) Southeast Surface Water Treatment Facility (SESWTF) to treat surface (river) water to drinking water standards and diversify the Cityâ€™s water supply. Raw water from the Kings River will be delivered to the SESWTF through a proposed 13-mile long pipeline. Drinking water from the SESWTF will be delivered to the Cityâ€™s customers through a network of large diameter pipelines called Regional Transmission Mains (RTMs) that will be connected to the existing distribution system.
In an effort to reduce overall costs of constructing the RTMs, CH2M and the City worked on an optimization study. The RTM system initially included 25 miles of pipelines to essentially circle the southern half of the City and connect to existing grid mains and distribution piping. Schematic design of the initial route for these and other alternative pipeline routes was completed concurrent with the optimization study. The approach to the optimization study was to take the information developed during schematic design, including costs for various sizes and pipe production rates, and perform hydraulic modeling through the use of optimization algorithms to determine the lowest cost alternative. In addition, operating criteria were established for the hydraulic modeling, such as minimum and maximum pressures and target velocities. In the event operating criteria were violated, penalty costs were incurred for that modeling scenario. Additional costs penalties were assigned for typical non-cost evaluation criteria such as impacts to public at schools or hospitals, additional permitting and six other factors. The optimization model also used pumping energy costs combined with capital costs to yield an overall life cycle costs for comparison.
The initial construction budget for the RTMs was estimated at about $88 million and included 25 miles of 48-inch to 24-inch pipe. After completing in excess of 600,000 model runs, the optimized solution resulted in about 13 miles of 66-inch to 24-inch pipe with an estimated construction cost of $47M.Â The reduction in the amount of RTMs constructed will not compromise the ability of the system to deliver the necessary amount of drinking water, while allowing the City to reduce groundwater pumping. Â The total cost to perform this optimization was about $150,000 and resulted about $41M in cost savings without compromising service level objectives.
CH2M has been working with clients, like the City of Fresno on innovative solutions to solve water challenges across the globe for more than 70 years. We were pleased to share many of these solutions and technologies at this yearâ€™s AWWA ACE.
Brian Skeens is a Principal Conveyance Technologist in CH2Mâ€™s Water Business Group, out of the firmâ€™s Atlanta, Georgia office. He has more than 17 years of experience in water and wastewater projects for municipal water systems. Brian has served as technical and task leader on water conservation projects for cities and counties, as well as state and regional government entities to help make the most efficient use of water, and plan appropriately for and extend the life of current water supplies and other capital infrastructure.