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October 11, 1996 STTI_�',COR . Cosioco Inc Internattonal Incorporated P O Box 2197 Room PO - 3038 Houston, Texas 77252-2197 ATTENTION Ms Kim Burns Project Manager - Remediation Technology SUBJECT: Quarterly Monitoring Report, July - September 1996 Former Econo Gas Station 4325 East Washington Street Stockton, California Ms Burns This report presents the results of quarterly groundwater monitoring and sampling conducted at Conoco Inc 's former Econo Gas Station, located at 4325 East Washington Street, Stockton, California (the site) on August 29, 1996 This report also summarizes the status of soil remediation at the site for the period between July 1 and September 30, 1996 GROUNDWATER MONITORING AND SAMPLING Groundwater monitoring and sampling were conducted to evaluate the groundwater gradient and to collect representative samples. Prior to sampling, depth to water in each groundwater monitor well was taken and subjective analyses performed The subjective analyses consisted of purging E approximately 4 to 10 volumes of water using hand bailing methods or until groundwater parameters of pH, temperature, and conductivity stabilized as measured by portable meters calibrated to a standard buffer and conductivity standard Groundwater samples were then collected by lowering a clean disposable bailer into the well and collecting a representative sample of the formation water If the well was slow to recover, the sample was not collected until the water level approached 80 percent of its initial level The groundwater sample was slowly transferred to laboratory-cleaned sample containers, sealed with Teflon lined caps, and transferred to cooled storage Groundwater samples were submitted, under appropriate chain-of-custody to Quanterra Environmental Services Laboratory in Austin, Texas for analysis of total petroleum hydrocarbons as gasoline (TPHg), benzene, toluene, ethylbenzene, and xylenes (BTEX), and methyl tert-butyl ether (MTBE) i using the U S Environmental Protection Agency Method 80201G i i Groundwater Elevation Data A summary of data regarding groundwater levels through August 29, 1996 is presented in Table A Since the last quarterly monitoring event, groundwater elevations have decreased approximately 1 1 ' feet across the site The groundwater flow direction is generally toward the southeast at an approximate gradient of 0.001 ft/ft (Figure 1). I SECOR international,Inc CONOCO, Inc ConocoU0700-019\Stockton 396 October 11, 1996 1787 Tnbute Road, State C, Sacramento, CA 95815-4404 (916)648-9160 (916)648-8052 FAX 3