Napa Sanitation District Project Will Reduce Wet Weather Sewer Flows

May  30, 2014

Napa Sanitation District is breaking ground on a project to reduce wet weather sewer flows in an area of southwest Napa. This area, bounded by Oak Street to the north, Pine street to the south, Brown Street to the east and California Boulevard to the west, is a portion of a larger area that the District refers to as “Basin L”. Basin L was identified in the District’s Collection System Master Plan as an area with significant inflow and infiltration.  A portion of the Basin L #3 project lies within the City’s 5-year paving plan and construction of this project will be completed prior to the City’s paving.

Inflow and infiltration (I&I) is water that flows into sewer pipes from groundwater and stormwater. Groundwater (infiltration) seeps into sewer pipes through holes, cracks, joint failures, and faulty connections. Stormwater (inflow) rapidly flows into sewers via roof drain downspouts, foundation drains, storm drain cross-connections, and through holes in manhole covers. Most I&I is caused by aging infrastructure that needs maintenance or replacement.

The Basin L #3 Pipeline Rehabilitation Project comprises sewer main pipe in roadways and public lateral lines that run from the sewer main to the property line, which will be rehabilitated primarily by utilizing trenchless methods called pipe bursting and cured in place pipe (CIPP) lining. Pipe bursting is accomplished by using a breaking device called an expander head that is pulled through the defective pipeline from a launching pit. As it travels through the pipeline toward the receiving pit, the expander head breaks the pipe into many small pieces, pushing the pieces into the surrounding soil. New pipe is attached to the back of the expander head, replacing the line immediately.  CIPP lining is a method where a resin-impregnated flexible tube is inserted through the existing host pipe using an inversion method, inflating it to the inside diameter of the existing host pipe, and allowing the pipe to cure and harden to the required strength. 

The Basin L #3 project also includes the installation of new manholes and rebuilding of existing manholes, as well as sewer main sag repairs. “The flow reduction achieved by this project will reduce the chance of sewer overflows in the area, and decrease impacts to the treatment plant,” explains Tim Healy, District General Manager. 

The District received four bids for this project; Ranger Pipelines’ bid came in the lowest at $2,684,415. Construction is expected to take place from June through November 2014. Post-construction flow monitoring will be performed to evaluate the success of the project. 

Napa Sanitation District (NSD) provides wastewater collection, treatment, and disposal services to the residents and businesses in the City of Napa, Silverado Country Club, the Napa County Airport and several adjacent unincorporated areas. NSD also provides recycled water service to portions of southern Napa County. Covering 20 square miles, NSD has been serving the community since November 1945. For further information about the District, please see


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