Project #4849

Exploring Cost-Benefit Analysis of Post Long-Term Control Plan Approaches to Wet Weather Management

Principal Investigator
Research Manager
Harry Zhang, PhD, PE
Carollo Engineers
Integrated Planning & Water Management
Combined Sewer Overflows (CSOs)
Green Infrastructure


For decades, municipalities and utilities with combined sewer overflows (CSO) have developed and implemented long-term control plans (LTCP) to reduce CSO events. As some LTCPs near completion, there is a national discussion about whether further CSO control actions are cost effective. This project has provided a comprehensive evaluation of experiences, best practices, and costs for CSO and wet weather management. The objectives of the study are to (1) evaluate the state of knowledge and research needs for a holistic approach to wet weather management and post-LTCPs for CSOs; (2) develop a robust database of practices, costs, and benefits of existing wet weather management strategies; (3) identify gaps in existing knowledge of CSO and wet weather management technology costs and benefits that will support future research needs; and (4) develop a practical guide focused on approaches to enhance post-LTCP wet weather management. Based on the results of the literature review, utility survey, and the two-day virtual workshop, this study has developed a set of actions that can be initiated by utilities, municipalities, and others. Published in 2023.