TECHNICAL REPRINTS

Sacramento County Restores Sewer Service

by Norman Ainslie

Located 75 miles south of Sacramento, in the Sacramento River Delta, Locke, California, is the only remaining authentic Chinese village in the United States. Locke was founded in 1915 after a fire broke out in the Chinese section of nearby Walnut Grove, CA. Levee construction originally brought the Chinese to this area, but by the time Locke was built most of the work was in farm labor.

In the 1940's, restaurants, bakeries, herb shops, fish markets, gambling halls, boarding houses, brothels, grocery stores, a school, clothing stores, and the Star Theatre lined the bustling streets of Locke. On August 2, 1970, Locke was added to the registry of national historical places by the Sacramento County Historical Society because of its unique status as the only town in the United States built exclusively by the Chinese for the Chinese.

In 1983, the County of Sacramento Water Quality Division analyzed the existing sewerage system in the historic community of Locke. In the report summarizing this analysis, the combined sewer system was found to be a public nuisance, in danger of creating adverse health impacts and in desperate need of substantial improvements. The lack of a financial program prevented any resolution of the sewer problem for the next 13 years

The adoption of California Proposition 204 in November 1996 provided the potential to resolve this funding situation. Under Proposition 204, loans for water conservation, groundwater recharge, local water supply construction projects, and water conservation or groundwater recharge feasibility studies are made at half the interest rate the State of California pays on the bonds.

The existing sewage system was built in 1915 to serve only the historic community. The system was designed to flow by gravity to a septic tank that serves as a pumping station to pump sewage to three evaporation treatment ponds. The system was originally designed to have zero discharge from the ponds.

The existing system operated as a combined sewage and drainage system. Historically, it was continuously surcharged during heavy rains. The pumps at the septic tank could not adequately handle flows unless the force main was disconnected and virtually untreated combined sewage and storm water discharged directly onto an open field east of the community. In recent years, there was absolutely no evidence of any flow reaching the treatment ponds, even during wet weather. Residents complained of sewage smell and potential health hazards. The other properties within the project area utilized septic tanks with on-site disposal systems that directly discharge to the local high water table.

Experience with gravity sewers serving nearby Walnut Grove indicated that the constant motion of groundwater due to tidal influences in the Sacramento River delta had shifted the vertical alignment of some sewer lines making gravity flow difficult to maintain. The water table in the vicinity of Locke is approximately 1 ft below the ground surface, causing damage to any proposed gravity system due to tidal influences and increased inflow/infiltration.  

The age of the historic buildings in Locke and their close proximity to each other meant that any sewer system solutions include careful consideration of the construction impact on the community. The purpose of installing a new sewerage system was to provide reliable sanitary services to protect the health and welfare of the residents while allowing them to continue to enjoy the historic nature and lifestyle of the community.

Alternatives Proposed

The 1983 sewerage study proposed several collection system alternatives, including collection system rehabilitation/repair and collection system replacement. All the collection system alternatives proposed to connect the project area to the nearby Walnut Grove sewer system.

The first rehabilitation alternative involved installing a slip line inside the existing combined sewer and the second alternative suggested making structural repairs to the existing combined sewerage system.

Neither of these solutions addressed the problem of tidal influences on gravity system flow or groundwater infiltration. Furthermore, both alternatives involved heavy construction utilizing a backhoe or other excavating equipment to dig trenches two to three feet wide and six to seven feet deep. Due to the narrow and confined streets and alleyways of the historic community, these construction techniques were considered potentially too disruptive. Hand excavation, while reducing the disruption, would have greatly increase the cost and extend the installation period.

The first replacement alternative in the study proposed construction of a new gravity sanitary sewer system leaving the old sewer for storm drainage. This solution faced the same problems involving tidal influences and disruptive construction.

Making the Grade

The final alternative, which was selected for implementation, proposed construction of a new low-pressure-sewer (LPS) system. An LPS system begins with a closed grinder pump, smaller than a washing machine, that accepts wastewater, grinds its contents into a fine slurry, and transports it through small-diameter pipes, requiring no manholes. The elimination of manholes and operation as a pressurized system greatly reduces infiltration and inflow. Tidal influences on groundwater have no effect on an LPS system, which does not depend on gravity flow for effective operation.

Unlike conventional gravity central sewers, which use 24-inch pipe and require deep excavation, an LPS system is not destructive to the landscape's natural or built features and requires less maintenance. Also, the disruption from system failure is greatly reduced using an LPS system.

LPS System Construction

Recently, the Locke Sanitary Sewer Project received funding as the result of a grant by the United States Department of Agriculture (USDA) Rural Utilities Service. The Sacramento Housing & Redevelopment Agency (SHRA) provided additional funding for the balance of project costs.

"Bringing this project in on schedule, within budget, and with the least amount of disruption to the town and residents of Locke was of utmost importance to the Sanitation District," explained Sacramento County Supervisor Don Nottoli who represents the area and also sits on the District's Board of Directors.

Environment One (E/One), a pioneer in the manufacture and implementation of low-pressure sewer systems, was chosen as the vendor and construction of the new LPS sewer system began in February 2003 by Sacramento County Sanitation District 1.

Construction activities started with the installation of a pipeline connecting Locke's new sewer system with the Walnut Grove sewer system. The LPS system consists of approximately 1500 ft of 1-1/2" to 3"PVC pipe, 48 E/One GP 2010 individual grinder pumps, two E/One GP 2014 duplex grinder pumps, and connection of all existing services to the new system. Each pump is monitored for maintenance using E/One alarm panels.

"Residents of Locke were very excited about the project," said Connie King, long-time Locke resident and unofficial mayor.

"The construction caused very little disruption in the historic Locke community, because the LPS system is far less intrusive than a typical gravity system," said Michael Meyer, P.E., Project Manager for the Sanitation District. "The pipes are smaller and the trenches are shallower."

The permanently visible evidence of the E/One LPS system within the historic community consists of an alarm panel mounted to each pump station and the access lid. Where possible, the pumping units are installed under existing wooden walkways, using a hinged access through the walkway. In other locations, the units are installed in the back of the structure to minimize any aesthetic impact.

"We liked the modular design of the E/One grinder pump station and the instrumentation," said Meyer. "In addition, E/One pumps are designed to be replaced in the field, making maintenance easier."

Depending on which gravity sewer alternatives are compared, savings of $80,000 to $170,000 are estimated by the Sanitation District for the combined construction and maintenance for the E/One LPS system.