The Mill Creek Watershed collection system is one of the larger systems operated by Johnson County Wastewater (JCW).  The watershed is currently just 60% developed but significant growth is expected to occur, which will increase wastewater flows beyond the capacity of existing infrastructure.  JCW chose the team of WCS Engineering and HDR to develop an optimized and prioritized capital improvement plan to meet the needs of expected long-term growth in the watershed.

Using extensive inflow and infiltration (I/I) pilot project results obtained by JCW, the team used the system hydraulic model and the optimization software OptimizerTM to determine the cost-effective balance between I/I reduction, conveyance, storage, and treatment alternatives.  Sensitivity analyses were then performed on potential storage sites and I/I reduction alternatives to gain further confidence in the solutions.

The Cost-Effective Analysis Curves below show solutions for the interim and ultimate population growth scenarios for conveyance-only alternatives, all alternatives (“optimized solution”) and discharge to the treatment plant influent pump station (IPS) constrained to the existing pump capacity.  The optimization scenarios for interim and ultimate population growth were used to phase the capital improvement plan sequence of implementation and maximize return on investment.