REDUCING SANITARY SEWER OVERFLOWS IN A LARGE COLLECTION SYSTEM

Located in Northern Virginia along the western bank of the Potomac River, Fairfax County is the largest jurisdiction in the Washington DC, metropolitan area with a population of over one million. With the service area of 234 square miles and over 850,000 customers, it has one of the nation's largest sanitary sewer system which include 3300 miles of sanitary sewer ranging from 8 inches to 60 inches, 64 pumping stations, and 53 permanent flow meters. The oldest sewers were installed in the 1940s and 1950s. Older lines were constructed using vitrified clay pipe. Lines installed between 1950 and 1970 were primarily concrete and lines installed after 1970 were made from PVC. Approximately 100 millions gallons of wastewater is conveyed daily to six treatment facilities.Although sanitary sewer overflows (SSOs) in Fairfax County were not excessive, these were also not within a generally acceptable range. Wastewater Collection Division (WCD) began tracking SSOs closely in 1995, when there were 128 occurrences. There were no known quality violations as a result of SSOs, and 22 sewer damage claims were paid to private property owners. WCD's primary reason for embarking on major operational and management changes was based on its desire to improve customer service and to prepare for the anticipated EPA SSO control regulations, which at the time were in the early stages of development. In an effort to reduce SSOs, a comprehensive approach was adapted which included, among others, the following initiatives: reorganization, employee participation, streamlining the workload, thorough investigation of all SSOs, sewer system rehabilitation/ replacement, purchase of new equipment and implementation of new business practices. This paper will discuss all these initiatives in detail to illustrate how their implementation, optimization and integration has resulted in very significant reduction in sanitary sewer backups in private properties and overflows in surface waters. The case study will also present the program results using statistical data collected over the course of several years.