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GROUNDWATER MONITORING WELL INSTALLATION <br /> Western Lift <br /> 3430 South El Dorado Street <br /> ' Stockton, California <br /> INTRODUCTION <br /> At the direction of Mr. John Urrutia of the Bank of Stockton, <br /> Geological Audit Services, Inc. (GeoAudit) has supervised the <br /> installation of two monitoring wells and collection of soil and <br /> water samples at the referenced property (the site) . <br /> ' This report describes the installation procedures and presents the <br /> results of the soil and water sampling. The project background, <br /> procedures, findings and conclusions are contained in the following <br /> sections. <br /> BACKGROUND <br /> The site is located in a flat industrial area south of Stockton <br /> Fi ure 1 - Location Map, 7.5 Minute Stockton West Quadrangle,le, USGS g P g <br /> Topographic Map Series, 1976) . The facility consists of a large <br /> warehouse and adjoining office, and exterior fenced <br /> parking/delivery area (Figure 2 - Site Pian) . <br /> Three underground tanks were removed from the delivery area in June <br /> ' of 1991. Gasoline contamination was detected in three of the seven <br /> soil samples collected from the excavation, indicating that an <br /> unauthorized release of hydrocarbons had occurred and that an <br /> assessment of the site was required. Sample results were summarized <br /> in the Site Contamination Workplan submitted by GeoAudit to San <br /> Joaquin County public Health Services - Environmental Health <br /> Division (PHS/EHD) or. 24 July 1991. <br /> Initial assessment of the site was performed in two phases. Each <br /> phase consisted of overexcavation followed by the collection and <br /> analysis of soil samples from the walls and floor of the <br /> excavation. The excavation and sampling are described in the <br /> Preliminary Investigation and Evaluation Report (PIER) submitted to <br /> the PHS/EHD on 11 December 1991. <br /> The excavation was backfilled to grade with pea gravel and will be <br /> ' paved with asphalt to match the surrounding surface. Backfilling of <br /> the excavation was completed on 1 May 1992. <br /> Further site assessment began on 1 June 1992, when a groundwater <br /> ' monitoring well was installed immediately north of the former tank <br /> excavation. This location is in the down-gradient direction from <br /> the former tanks (see Figure 2 -- Site Plan) . This well was required <br /> by PHS/EHD because of the presence of volatile aromatic <br /> hydrocarbons in soil samples collected near the seasonal high <br /> groundwater depth of 35 feet. A water sample was collected from <br /> this well on 4 June 1992, and analyzed for TPH as gasoline, TPH as <br />