Keeping the Water Moving: Solving Pressure Problems with Multiple Constraints in Stillwater, Oklahoma

The City of Stillwater (City) has experienced explosive growth in the southwest portion of the City’s service area. The service area includes a wide range of development, from areas within the City to a large portion of City owned rural service areas and wholesale customers. This growth combined with prolonged drought led to operational water pressures of 6 pounds per square inch (psi) at customer meters during peak demands of 2011. This area of the city includes more than 9 square miles of land and six different pressure zones due to significant changes in terrain. The City envisioned a delivery program, “Water 2040,” to not only deliver water supply at the required pressure to meet current demands, but also to address the needs of customers through the year 2040. The City’s multiple objectives and constraints were established as: (1) ensure minimum pressure of 45 psi at all locations from 2015 through 2040; (2) limit phasing to $30 million (M) per loan to satisfy a Trust Indenture Limitation, with projected total program cost of $93.2 M; (3) maintain water quality throughout all phases; (4) incorporate risk and resiliency planning while limiting oversizing; (5) meet average day, maximum day, and fire flow (where applicable) requirements; (6) increase system storage from 0.5 million gallons (MG) to 2.5 MG; (7) meet Oklahoma Department of Environmental Quality (DEQ) consent order deadlines for water pressure improvements and unpermitted facilities. To identify the optimal approach for efficiently delivering the Water 2040 Program, the City incorporated all of the objectives and constraints into a decision matrix that was fueled by hydraulic modeling and prioritization. The City identified the phasing and has successfully constructed 3 pump stations, 9 miles of pipe, and 2 elevated water storage tanks to meet the goals of the Water 2040 Program. The program will continue to deliver an additional 7 mi of pipe and a new water treatment plant (WTP) finished water pump station.