Background

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 that 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. This process was then again repeated for the 2012, and 2022 revisions to the Order. The District is now operating under Order WQ 2022-0103-DWQ Statewide Waste Discharge Requirements General Order For Sanitary Sewer Systems which was adopted December 6, 2022.

Over the last 20 years, the District has successfully developed, refined, and implemented numerous processes and procedures that mirror the elements of the SSMP. The actual processes and procedures include too many pages to incorporate into this document. 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.

System Overview

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 2023, there are 272 miles of public sewer, 32,000 building service connections, and 5,993 maintenance holes. There are also 12 remote lift stations and over 117 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 June 2023, 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 1960s. 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- l950s. Notwithstanding this, video inspection indicates that the overall condition of the District’s 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 that could result in a service
interruption.

Historically, roots and debris caused about 50% of District stoppages, and the remaining 50% was from “other causes.” Vandalism in remote areas had caused over 50% of the overflows in excess of 1,000 gallons. The District has taken action to identify locations to install locking maintenance hole covers in areas prone to vandalism (easements). There have been no stoppages or overflows caused by system deterioration or pipe collapse on the gravity system since the SSMP was approved.

The District is situated along the San Francisco Bay and about two-thirds 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. Inflow/infiltration contribution measured at the treatment plant typically does not exceed two and one half times the plant’s ADWF of 12.0 MGD.

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.

View full text of SSMP

View the Board action approving the SSMP

View Collection System Service Call Response