More Than One Way to Allocate Flow: EBMUD Develops Alternatives for Satellite Peak Flow Limits to Help Solve a Regional I/I Problem

摘要

The East Bay Municipal Utility District (EBMUD) provides water and wastewater services to customers in the East Bay region of San Francisco Bay, California. EBMUD conveys and treats an annual average daily flow of approximately 66 million gallons per day (mgd) [2.9 m~3/s] of wastewater generated by seven “Satellite” agencies (six cities and one special district). Each Satellite agency owns and operates its own sanitary sewer system that collects wastewater generated from homes and businesses in its respective community. EBMUD currently operates three Wet Weather Facilities (WWFs) with a combined capacity of over 300 mgd [13.1 m3/s]. During wet weather, infiltration and inflow (I/I) into the East Bay collection system can cause flows to multiply by ten or more times the dry weather average. In 2009, EBMUD was issued a National Pollutant Discharge Elimination System (NPDES) permit prohibiting discharges from its three WWFs, along with a Cease and Desist Order. EBMUD was also issued a Stipulated Order for Preliminary Relief (SO) outlining tasks EBMUD must complete to begin reducing discharges from the WWFs and assess alternatives for further reducing I/I in the East Bay collection system. A key component of the SO is the Flow Monitoring/Data Assessment Program, which includes requirements for EBMUD to develop a comprehensive program comprising flow and rainfall monitoring, hydraulic and hydrologic modeling, and stakeholder participation. The SO also requires EBMUD to develop alternative sets of Capacity Flow Limits (CFLs) on discharges from the Satellite agency collection systems that would enable EBMUD to cease discharges from its three WWFs. This paper explores in detail the intricacies of applying technical monitoring and modeling to a regional I/I problem that has potential for significant political and economic impacts. Topics include an overview of the extensive flow monitoring and modeling performed, technical considerations in developing flow limits with specific examples, and key considerations for the development of various alternative sets of CFLs. EBMUD’s experience in implementing an extensive flow monitoring and modeling program can provide useful insight to other agencies seeking to develop monitoring programs involving 100 or more flow meters. Additionally, the paper examines the numerous potential implementation issues related to a flow limits-based program.