Rehabilitation of a Large Semi-Elliptical Sewer

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ABSTRACT
The Sanitation Districts of Los Angeles County (Districts) own, operate, and maintain a wastewater treatment and collection system that includes approximately 1300 miles of sanitary sewers ranging from 6 to 144 inches in diameter. A portion of the Districts’ Joint Outfall “A” Trunk Sewer was constructed of cast-in-place reinforced concrete having a semi-elliptical cross section and included an interior lining of vitrified clay tiles for corrosion protection. This paper describes the rehabilitation of approximately 15,200 feet of 114- and 126-inch semi-elliptical sewer using a flexible and spiral wound polyvinyl chloride (PVC) liner embedded in a structural grout.

The 114- and 126-inch semi-elliptical Joint Outfall “A” Trunk Sewer was constructed in the late 1920s. The sewer is located immediately upstream of the Districts’ Joint Water Pollution Control Plant in the City of Carson, California and conveys a peak flow of 100 cfs. Over the years, the majority of the vitrified clay tiles above the low flow level became dislodged and allowed debris to accumulate in the sewer to depths of approximately two to four feet, significantly reducing the capacity of the sewer. Moreover, physical inspections of the sewer and manholes indicated that the exposed concrete had corroded up to four inches at some locations.

An $8.5 million contract to rehabilitate 6500 feet of 114-inch and 700 feet of 126-inch semielliptical sewer was awarded in May of 2001. Construction of this contract was successfully completed in October 2003. A second contract for $12.6 million to rehabilitate 8000 feet of 114-inch semi-elliptical sewer was awarded in March 2005. One-half of the lining on the second contract has been completed and it is anticipated that the remaining work will be completed by October 2006. Both contracts specified the rehabilitation system to be installed by person-entry methods and the selection of the contractor was based not only on the overall bid price, but also on the contractor’s proposal and approach to the project.

INTRODUCTION
The County Sanitation Districts of Los Angeles County (Districts) are a confederation of 24 independent sanitation districts that serve the wastewater treatment and solid waste management needs of approximately 5.1 million people in Los Angeles County. The Districts’ service area covers approximately 800 square miles and encompasses 78 cities and unincorporated areas within the county. The Districts own, operate, and maintain more than 1300 miles of main trunk sewers ranging from 6 to 144 inches in diameter that convey approximately 510 mgd of wastewater to 11 wastewater treatment plants.

Seventeen of the sanitation districts are signatory to a Joint Outfall Agreement, which provides for a regional system of interconnected facilities known as the Joint Outfall System (JOS). The JOS service area encompasses 670 square miles of unincorporated territory and 73 cities, including some portions of the City of Los Angeles. The JOS includes six upstream water reclamation plants and the Joint Water Pollution Control Plant (JWPCP), located in the City of Carson. These plants together treat approximately 475 mgd of wastewater.

The backbone of the JOS consists of nine joint outfall sewers, which are shown in red on Figure 1. The 17 sanitation districts party to the Joint Outfall Agreement proportionately share the ownership, operation, and maintenance of the 450-mile network of joint outfall sewers. These sewers typically carry wastewater generated from more than one sanitation district. Individual sanitation district sewers, which are shown in blue on Figure 1, only carry flow from one particular district. Connector sewers, which are not shown on the figure, are owned and operated by local jurisdictions.

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