The Only Constant is Change: A Better Collection System Model for Capital Savings

This manuscript will summarize the positive change in collection system modeling used by Citizens Energy Group to support its wastewater program as a large wastewater utility under a consent decree with a commitment to efficiently provide sewer service to its ratepayers. The manuscript will emphasize Citizens’ lessons learned in refining the model while its wastewater program is in progress.The lessons are as follows:Leveraging recent improvements in GIS data and automated tools to construct a high-resolution hydraulic model;Using a dynamic approach to simulating inflow and infiltration (I/I) as groundwater;Integrating updated interceptor basins into Citizens’ base model; andEffective outreach to the internal stakeholders of Citizens’ modeling staff.Citizens’ System Modeling utilizes the ICM model for a variety of applications including design support, regulatory reporting, capacity assessments, operational troubleshooting, and master planning (Rubchinskaya et. al, 2015). Citizens had recently completed a sanitary sewer master plan update (Ranck et. al, 2016) that recommended a combination of storage, conveyance, and rehabilitation to achieve the targeted level of service. As Citizens was considering a different balance of capital projects and rehabilitation, System Modeling was progressing on a significant expansion of the collection system model to include all 12” pipes and transition the representation of I/I to a groundwater-based process (Gheith, 2014).Since the implementation of the master plan was ongoing, System Modeling developed an approach to expand and calibrate individual interceptor basins, then integrate them into Citizens’ base model for immediate application to support the planning efforts. The first priority basin was the Williams Creek interceptor basin, where storage and pumping alternatives were being considered to achieve the level of service, with a potential capital cost of $10 million.