In 2004, the San Francisco Regional Water Quality Control Board (SFRWQCB) indicated its intent to implement new regulations to uniformly monitor sanitary sewer overflows. Also envisioned was some type of collection system planning document, which all agencies would be required to produce.
The Bay Area Clean Water Agencies (BACWA), with a broad base of collection system management experience, elected to work collectively with the Regional Board to develop a system which would meet the needs of the Regulators, while retaining a common sense and practical approach to collection system management. Oro Loma staff actively participated on the BACWA collections sub-committee charged with developing the core details of the plan. Each element is the result of detailed negotiations with the SFRWQCB. On December 30, 2005, each District in Region II received a 13267 Letter outlining the agreed upon SSMP template and reporting requirements. The District first published its SSMP ahead of the requirement on January 28, 2005.
While BACWA was working with the SFRWQCB to develop the SSMP, the State Water Resources Control Board developed a similar requirement for the state which would supersede the Regional Board agreements. On May 2, 2006, the State issued a Waste Discharge Requirement (WDR) requiring all collection systems to comply with State SSMP regulations. Actual “on line” implementation for the San Francisco region began May 2, 2007.
During the past decade, the District has successfully developed, refined and implemented numerous processes and procedures which mirror the elements of the SSMP. The actual processes and procedures would fill volumes. Therefore, in developing its SSMP, the District has summarized its activities and pre-existing core documents as they relate to each topic required by the State SSMP.
Oro Loma Sanitary District was formed in 1911 and remained relatively rural until experiencing significant residential growth following the end of World War II. As of 2014, there are 272 miles of public sewer, 32,000 building service connections and 6,088 manholes. There are also 14 remote lift stations and 54 critical structures such as diversion boxes, aerial sewers, and siphons. Average rainfall within the service area is 19 inches and generally occurs between November and April.
As of January 2014, the average age of the collection system is 58 years. The pipes are predominantly vitrified clay pipe (VCP) with cement mortar joints. For new pipes installed today, the standard is 8” PVC. For rehabilitated pipes, the typical replacement is with 8” HDPE. Approximately 97% of the VCP sewers were installed prior to the introduction of modern pipe joints such as compression gaskets, which were not available until the 1960’s. Additionally, more than half of the collection system was already in place before the introduction of improved VCP manufacturing standards, which began in the mid- l950’s. Notwithstanding this, video inspection indicates that the overall condition of the District Collection System is very good.
The District has had an active sewer system management program since 1988, and has experienced very few line stoppages in recent years. Overflows are even less frequent. Stoppages and overflows have been on a steady decline since 1992 when the District focused its efforts on aggressive line cleaning, continuous video inspection, and dedicated funding to repair or replace every line defect which could result in a service interruption.
Historically, roots and debris together caused about 50% of District stoppages, and the remaining 50% was from “other causes”. Vandalism in remote areas had caused over 50% of overflows in excess of 1000 gallons. There have been no stoppages or overflows caused by system deterioration or pipe collapse on the gravity system. However, the District experienced three separate pipe breaks on an 8” pump station force main first constructed in 1995. After the first break, the piping was evaluated by independent engineers who determined that the pipe was adequate to meet design and pressure specifications. Subsequent failures prompted further analysis, which indicated that transient water surges (water hammer) within the pipeline were creating forces which exceeded the pipe’s capacity. In fall 2004, the portion affected by the transient water surges (approximately 75%) was replaced with butt-fused HDPE. Additionally, surge tanks were installed to reduce the surges on the system. There have been no subsequent failures.
The District is situated along the San Francisco Bay and about two-third’s of the District is close to or within a flood plain elevation with correspondingly high levels of ground water, particularly during the rainy season. In fact, many of the original sewers are thought to have been installed at or below groundwater tables. I/I contribution measured at the treatment plant typically does not exceed two and one half times the plant’s ADWF of 12.0 MGD. However, during an exceedingly wet weather period in February 1998, the plant recorded a one-day flow of 75.3 MGD. Interestingly, this was not one of the eleven highest-recorded storms since 1950 that have approached the intensity of the District’s 10-year “Design Storm.”
As a final note, Castro Valley Sanitary District owns 25% of the District’s treatment plant and independently transports their sewage to a joint interceptor system located one and one half miles east of the Plant.