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Section 1.0 Introduction Ara 1.1 General This report presents the results of the geotechnical and environmental studies performed by Camp Dresser&McKee Inc. for a proposed new south wall for the �- Brookside Pump Station located in Stockton,California (Figure 1). The scope of services conducted by CDM is in accordance with the City-approved Scope of Work and subsequent Notice to Proceed dated February 27,2001. 1.2 Project Background The City of Stockton (City) plans to replace a deteriorating wall on the south side of the existing Brookside Pump Station(Site). The wall,part of the existing wet well,is Ar failing due to corrosion of the reinforcing steel and degradation of the concrete. As an Irinterim repair to prevent further degradation and failure, the City has installed a temporary support system within the wet well consisting of timbers. r M1 The City is planning to construct a new concrete wall immediately outside the pump station south of the existing south wall (Figure 2). The plans indicate the existing wall t is 24 feet long and extends to a depth of 29 feet below existing ground surface (bgs) or about Elevation 57 feet'. The new 18-inch-thick wall will be of similar length and depth. Construction of wall is complicated by the presence of an 8-foot-diameter wet pit and E multiple shallow and deep sanitary sewer and stormwater lines located at the south }. end of the pump station as shown on Figure 2. The wet pit is located about b feet + south of the south wall. We understand that its walls are 12-inch-thick reinforced concrete. The base of the wet pit is at Elevation 58 feet, about one foot higher than the base of the south wall. Two b-inch-diamter steel pipes are located at about EIevation 59 feet,connecting the wet pit with the pump station. These two pipes must remain �. in service during construction. We discussed construction of the new wall using an open excavation with the City. Due to the presence of the adjacent structures and pipes, and a known shallow water table, an open excavation was not considered practical. Therefore, the project will require in situ wail construction or conventional construction with temporary excavation support. The construction is also possibly complicated by the presence of soil or groundwater i, contamination. Historically,the City has documented a release of raw sewage and chromium VI, sodium hypochlorite and hydrogen peroxide at the site. an. All elevations in this report are referenced to the finish floor elevation of the pump station and are in feet. The stated finish floor elevation is 87 feet(Figure 2),presumed to be based on a sea level datum. CDM cap & ice -� ~ Q;I25oM20248-GEo-T4.ReportiBiookside Pump Station.doc