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i Working to Restore Nature ' September 1993 Quarterly Groundwater Sampling & Analysis December 1, 1993 Quik Stop Market No 132, Stockton, California F7132 93 ' Information obtained as of August 1991 indicated that the gasoline plume extends beyond the station boundary to the east In an effort to evaluate the extent of the plume RESNA requested permission to conduct investigations on the property to the east These requests ' were not successful and permission to enter this site, which is occupied by a Taco Bell restaurant, was not granted In August 1991, RESNA recommended and initiated quarterly pumping of monitoring well MW-5 This pumping was agreed upon with the SJCPHS in August 1991 as a temporary interim remedial activity pending receipt of permission to enter adjacent downgradient ' properties In this remediation, monitoring well MW-5 is pumped using a vacuum truck with a clean PVC-extension During the pumping, water in the well is kept at a low level by periodic pumping over a period of about 3 hours Previous measurements indicate that ' pumping for 3 hours removes approximately 200 gallons of groundwater Groundwater samples are obtained prior to and at the completion of pumping The groundwater samples are collected following the procedures outlined in the RESNA groundwater sampling protocol (Appendix C) The samples are transported to a state-certified laboratory and analyzed for TPHg and BTEX The results of these analysis are included in Table 1 In an effort to further delineate the off-site extent of the gasoline plume RESNA conducted a soil gas and shallow groundwater survey along the eastern side of the Taco Bell site and the portion of West Hammer Lane adjacent to the Taco Bell site This survey was tconducted on April 29, 1992, with a specially equipped van operated by Tracer Research Corporation (Tracer) of Tucson, Arizona, under the direction of a RESNA geologist The results of this survey indicated that the gasoline plume in the upper aquifer did not extend tinto the areas investigated in this survey (RESNA, July 1992) Based on the results of the Tracer Survey, RESNA recommended the installation of two groundwater monitoring wells on the Taco Bell property While RESNA waited for permission to install the two groundwater monitoring wells on the Taco Bell property, scheduled quarterly groundwater sampling and analysis were continued In our June 1992 quarterly report (RESNA, October 1992) RESNA recommended that on ' the basis of an established history of nondetectable TPHg and BTEX the sampling frequency for wells MW-3 and MW-4 be reduced from quarterly to semi-annually In a letter dated November 17, 1992, to Mr Jack Griffith of Quik Stop Markets the SJCPHS ' approved the semiannual sampling and analysis of these two wells In November 1992, with the assistance of the SJCPHS, RESNA was granted permission to enter the Taco Bell property and install 2 groundwater monitoring wells These monitoring wells, designated MW-6 and MW-7, were installed on December 9, 1993 Subsequent ' A-3