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QUARTERLY GROUNDWATER MONITORING REPORT <br /> 4445 Pershing Avenue Stockton California <br /> I 1 0 INTRODUCTION <br /> This report documents the results of quarterly groundwater monitoring conducted by <br /> Aegis Environmental, Inc (Aegis), on April 21, 1992, at the Shell Oil Company (Shell) <br /> service station located at 4445 Pershing Avenue in Stockton, California (Figure 1) The <br /> monitoring included collection of depth-to-groundwater measurements and water samples <br /> from the four existing wells, MW-1, MW-2, MW-3, and MW-4, located on site (Figure 2) <br /> This report is based, in part, on information obtained by Aegis from Shell and Emcon <br /> Associates (Emcon) of Sacramento, California, and is subject to modification as newly <br /> Iacquired information may warrant <br /> 2 0 SITE DESCRIPTION <br /> The site is located on the southwest corner of the intersection of Rose Marie Lane and <br /> Pershing Avenue in Stockton, California The site is located within a <br /> commercial/residential area The facility is an active service station that retails unleaded <br /> gasolines <br /> 30 BACKGROUND <br /> Shell removed the underground storage tanks (UST) and associated piping, and installed <br /> a new double-wall fiberglass UST system in June 1990 Regulatory tank closure sampling <br /> was performed by Aegis, and reported to Shell in a "Tank Closure Report," dated <br /> June 14, 1990 Laboratory analysis indicated concentrations of benzene ranged from <br /> below detection limit (BDL) to 10 ppm Subsequent to the UST replacement, Aegis <br /> installed, developed, and sampled three groundwater monitoring wells, MW-1, MW-2, and <br /> MW-3, and installed two vapor extraction wells, VEW-1 and VEW-2, in July 1990 The <br /> results of the July 1990 investigation were reported to Shell by Aegis in a "Monitoring Well <br /> Installation Results Report," dated March 5, 1991 Laboratory analysis of groundwater <br /> samples indicated benzene was BDL at the time of the initial monitoring well installation <br /> Aegis has collected quarterly groundwater samples since the wells were installed in <br /> July 1990 Depth-to-groundwater measurements were collected by Aegis on a monthly <br /> r basis from July 1990 through July 1991 Subsequent depth-to-groundwater <br /> r measurements are collected on a quarterly basis coincident with groundwater sampling <br /> Prior sampling events were conducted in October 1990, January, April, July, and <br /> October 1991, and January 1992 <br /> i <br /> .19Z6Jk OMR y <br /> I <br />