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r April 22, 1996 SECOR International hiCoipoi ated Conoco Inc P O Box 2197 Room PO - 3038 Houston, Texas 77252-2197 ATTENTION: Ms. Linda S. Thompson Project Manager - Remediation Technology SUBJECT: Quarterly Monitoring Report, January - March 1996 Former Econo Gas Station 4325 East Washington Street Stockton, California Ms Thompson- 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 February 23, 1996. This report also summarizes the status of soil remediation at the Site for the period between January 1 and March 31, 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 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), and benzene, toluene, ethyibenzene, and xylenes (BTEX) using the Method 8020/G Groundwater Elevation Data A summary of data regarding groundwater levels through February 23, 1996 is presented in Table A Since the last annual sampling event, groundwater elevations have increased approximately 3 8 feet across the Site The groundwater flow direction is generally toward the south-southeast at an approximate gradient of 0 009 ft/ft (Figure 1) SECOR InteFwhonal, Inc „, Lr CONOCO, Inc' Con-o\N0700-009\Stockton 196 Apnl 22, 1996 17i°I irlhS/iot 5aun010110 ( 1 95S10-7004 (916) 150--1 ;3; (916),150-01101 11