Development of an SSO Mitigation Plan: Lessons Learned from the Field

Abstract

Wastewater collection and conveyance systems have long been a neglected component of many municipal wastewater systems, due to a lack of funding and management focus. Increased population growth has resulted in increased wastewater flows. Aging systems may not have the hydraulic capacity to receive the increased flows due to a large volume of Infiltration and Inflow (I/I) and lack of periodic maintenance. This may result in a Sanitary Sewer Overflow (SSO) to receiving waters. With the implementation of the Total Maximum Daily Load (TMDL) program and watershed protection programs, SSO events have received increased attention from regulatory agencies. Utilities are required to record the events and estimate the volume of the spills as they occur. The purpose of the evolving Capacity, Management, Operations, and Maintenance (CMOM) program is to minimize SSO events by requiring that each wastewater utility develop a comprehensive program. A response plan is still needed, however, to address the negative impacts of SSO events to receiving waters. Fulton County, Georgia (the county in which the bulk of the City of Atlanta is located), operates a 45 million gallons per day (MGD) wastewater system consisting of 16 sewersheds, 5 treatment plants, 45 pump stations, over 300 miles of pipelines, and over 42,000 manholes. The system primarily serves residents in the unincorporated portions of the County in areas to the north and south, effectively bisected by the city limits of Atlanta, which operates a separate system. The County is currently developing several action plans in response to CMOM requirements. Noted action plans include development of a comprehensive sewer collection system model and master plan, implementation of a comprehensive maintenance program, replacement or rehabilitation of key conduits, and upgrades at pump stations. It is the goal of the County to become more proactive, instead of reactive, in terms of its activities; however, again a response plan was needed, and in fact required for SSOs. MACTEC assisted Fulton County in developing a procedure for responding to SSO events in isolated waterbodies such as lakes and wetlands. This methodology uses a simple series of charts to simplify the calculation of carbonaceous and nitrogenous Biochemical Oxygen Demand (BOD). The process takes as an input the volume of the waterbody and the volume of the spill and estimates the size and schedule of run times for aeration equipment deployed in response to the SSO event. Several iterations of this procedure were developed to simplify the methodology applied in the field. MACTEC developed and conducted a series of training classes with Fulton County's sewer collection system personnel. Despite technological difficulties and a disparity between educational backgrounds, the sewer collection system personnel provided valuable feedback on the state of the system and the methodology applied. As the CMOM program evolves, it will be important to consider some of the lessons learned from operational personnel to ensure effective implementation.