Novel Asset Defect and Inflow & Infiltration Identification Techniques Used as Part of SF Bay Consent Decree Sewer Investigations

East Bay Municipal Utility District (EBMUD) owns and operates a regional Interceptor System that collects, conveys and treats municipal wastewater from seven Satellite agencies. The separated sanitary system, which treats wastewater from approximately 710,000 people, has an average dry weather flow of 52 million gallons per day (MGD). During medium sized storm events, the peak wet weather flows can exceed 700 MGD, representing a peaking factor of almost 14. The significant increase in flows requires the use of three wet weather facilities (WWFs) which perform primary treatment of the flows prior to discharge into San Francisco Bay. In September 2014, EBMUD and its seven Satellite members entered into a negotiated twenty-two-year Consent Decree. The Consent Decree has inflow and infiltration (I&I) reduction targets and prescribed work requirements designed to remove I&I, thereby reducing the number and frequency of sanitary sewer overflows as well as the frequency and volumes discharged from the three WWFs. Additionally, the Consent Decree requires EBMUD to implement a unique asset management-based program to identify specific sources of I&I throughout the regional collection system. This paper aims to describe how EBMUD has employed existing sewer investigation methodologies in novel ways to rapidly isolate the worse acting portions of a sewer subbasin at the few hundred-foot level and to locate specific sources allowing I&I to enter the system. The methodology to rapidly drill down within a subbasin to identify the portions of the contributing area which provide the most I&I is a wet weather flow isolation investigation. Flow isolation investigations take place immediately following a large rainfall event or series of rainfall events when soil saturation levels are elevated and occur between the hours of 12:00 AM and 5:00 AM. Since sanitary base flows are typically low during the investigation hours, flow that is observed in the system during this investigation period can predominantly be attributed to I&I. Flow measurements are taken at multiple locations within the investigation area during a short period of time. Additionally, a downstream flow meter is installed to record flows generated from the entire inspection area during the investigation period. The measured flows are then mass balanced (upstream flows subtracted from downstream flows) to determine which portions of the subbasin are contributing the most I&I during the investigation period. This methodology produces a subbasin wet weather heat map depicting the post-storm I&I rates in the project area, as demonstrated in Figure 1. The sewer assets in the heat map are color coded into normalized I&I color classes of gallons per day/inch diameter mile (GPD/IDM) ranges, indicating areas with low and high I&I contribution. These heat maps effectively demonstrate which areas are contributing the most I&I. For instance, in the project area shown in Figure 1, you can see that 85% of the total I&I generated in the subbasin was generated in just 8% (575 feet) of the total subbasin pipe length. This finding was confirmed during a late-night post-storm closed-circuit television (CCTV) investigation. During the wet weather flow isolation investigations, videos are taken at all maintenance holes (MHs) where active sources of I&I are observed. These videos have shown that many active sources of I&I are observed during wet weather that are not identified during a typical MH inspection. The method employed to identify specific sources of I&I includes utilizing smoke testing simultaneously with a CCTV inspection. This methodology visually locates and confirms the existence of a defect or other component in the sanitary sewer system allowing I&I to enter the sanitary system. This investigation type is performed as a follow-up to traditional sanitary sewer smoke testing and is utilized when smoke has been found to exit a storm water catch basin, indicative of a cross-connection of some type between the sanitary sewer and storm water systems. During the investigation, smoke is first blown into the sanitary sewer system until the smoking catch basin is activated. The smoke is then feathered down to a lighter density and a CCTV camera is inserted into the storm water sewer via either the smoking catch basin or a nearby connected maintenance hole (MH). The camera traverses the storm line until it captures the source of smoke as it enters the storm water pipe either by direct confirmation of a defect or by isolating the general location based on relative smoke density in the pipe. The smoke is then cleared and the CCTV camera is inserted into the sanitary sewer main at the identified general location in an effort to identify the discrete defect or other component that allowed the exfiltration of smoke. Typically, dye tests are performed as the go-to follow-up investigation to confirm a cross-connect between the two systems when a smoking catch basin is discovered during smoke testing. Dye test effectiveness is reduced when dealing with either elevated cross-connects between the two systems or 'indirect' connections. For elevated connections, sufficient dye must be introduced into the storm system to crest the invert and activate the connection. Dye test effectiveness is also reduced when the connection is 'indirect', such as offset joints in both the sanitary and storm water systems existing within close proximity of each other. With traditional dye testing source verification, EBMUD has had a positive source identification rate of just less than 25 percent. EBMUD has found that combination smoke/CCTV has proven to be a more efficacious and cost-effective follow-up method. As provided in Table 1, preliminary results to date of all completed investigations provide a 75% success rate at identifying a specific source allowing I&I into the sanitary system - a 300% improvement over traditional dye testing.