ARCHIVED REPORTS XR0009820 - Laserfiche WebLink

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• INTRODUCTION ' In accordance with a request from Mr. William Stewart, Geological Audit Services, Inc. (GeoAudit) has performed quarterly monitoring procedures at 515 West Eleventh Street In Tracy, California (the ' site) . The proaect background, procedures, findings and conclusions are presented in the following sections. The site location is presented 1n Figure 1. A plan of the site is presented in Figure 2 . ' BACKGROUND ' The site is located in a relatively flat business and residential area of Tracy, California (Figure 1 - Location Map) . The site was formerly a Beacon Gasoline Station. ' Three underground storage tanks were removed from the site in 1988 . Hydrocarbon contamination was discovered in the soil and groundwater following the tank removal. Subsequent assessment ' activities included the installation of three on-site groundwater monitoring wells 1n June 1988 (Figure 2 - Site Plan) . M A passive monitoring program was conducted between the second quarter of 1990 and the first quarter of 1991. During the monitoring program, contamination levels showed considerable fluctuation. Based on information from the existing assessment/ ' monitoring reports, the depth to ground water is approximately 8 to 12 feet with the gradient directed to the north or northwest. Contamination is directed primarily to the north. ' PROCEDURES ' On 24 February 1993, representatives from Geological Audit Services, Inc. visited the site. Depth to groundwater was measured for each well. An oily substance was observed in monitoring well #1 ' (MW #1) during bailing, and 1t was determined that an interface meter should be obtained to determine the thickness of this layer. ' Geological Audit returned to the site on 5 March 1993 . An interface meter was used to determine the thickness of the substance in MW #1, and the depth to water in each well was measured relative to the top of the casing. The oily substance in MW #1 was found to be ' a film, and not significant for depth to groundwater measurements. The hydraulic gradient and flow direction were determined from this data (see Table 1 below) . After water levels were measured, a three-stage submersible purge pump was used to purge the standing water from each well. Approximately 8 to 10 gallons of water were removed from each well to stabilize temperature, pH and conductivity (Table 2) . The water was placed in DOT approved 55-gallon drums and stored on-site. Water samples were then collected using disposable plastic bailers.