City of Tacoma

Tacoma, Washington, United States

Wastewater, Surface Water, and Solid Waste Cost of Service Study 

Raftelis was assisted the City of Tacoma Public Works Department (City) with a cost of service study for wastewater, surface water, and solid waste utilities. The study involved developing user-friendly cost of service models for all three utilities, training City staff on the use of the models, and developing a manual on the use of the models. One of the features of the models is to integrate the data from the City’s mainframe system directly into the models so the models can be easily updated. The models will also be capable of comparing actual and budgeted revenues and expenses so the City can take corrective action if needed. 

The cost of service analysis for the solid waste utility incorporated changeover from weekly collection to bi-weekly collection and accounted for the corresponding potential reduction in revenues. Surface water analysis included credits for properties that have direct discharge, revised rates for the incorporation of the open space program, and considered peaking factors. The wastewater cost of service analysis  included a review of the strength cost allocation parameters to ensure greater equity. All three utilities also had discounts for low-income customers, which would continue in this analysis. 

Water Demand Forecasting 

In another study, Raftelis worked with Tacoma Public Utilities (TPU) to develop water demand and production forecasts. Utilizing rate category econometric models developed in SAS based upon annual historical demand data from TPU’s water billing system, SAP, and numerous independent variables such as weather and economic indicators, the demand forecast predicted 10 years of water demand. The production forecast predicted 60 years of daily production values based upon decades of historical daily data including daily weather conditions. These forecasts were created to support planning activities at TPU by supplying inputs for the cost of service model as well as for assisting with infrastructure master planning needs.