A Method to Group Wastewater Collection Systems by Key Attributes to Evaluate Potential Impacts from Urban Water Conservation

In California, over 400 water supply agencies provide water to 36 million people living in cities and suburbs. The wastewater generated by homes, businesses, and industrial facilities is managed by hundreds of wastewater collection, treatment, reuse, and recovery systems. A procedure was developed to extrapolate modeled effects of water conservation from a sample of collection systems (50) to all potentially-affected systems throughout the state (over 300). An Excel-based model of wastewater collection system operations was developed to evaluate physical and chemical changes in pipes from lower flows. The model was run for fifty systems across the state of varying sizes and locations. Key impacts of corrosion, hydrogen sulfide production, sediment deposition, and use of added chemicals were evaluated based on changes in wastewater influent flow rates. To then extrapolate effects statewide, collection systems were grouped by the key characteristics that correlate with modeled impacts. The R code associated with this Hydroshare resource demonstrates how to use modeled results from the subset of collection systems to: 1) Identify key explanatory attributes of impacts using statistically-significant regression models, 2) Use the key explanatory attributes to identify non-geographic clusters of collection systems, and 3) Use the clusters to group systems for extrapolating effects. The modeling was used to support regulatory rulemaking for California’s “Making Water Conservation a Way of Life” associated with Assembly Bill 1668 and Senate Bill 606 (AB 1668-SB 606). Details of the model’s development and use were presented in public workshops in December 2021 and May 2022, which can be found at this link: https://www.waterboards.ca.gov/water_issues/programs/conservation_portal/regs/water_efficiency_legislation.html