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THRIFTY OIL GO . <br /> January 7, 1999 <br /> Mr Michael J Infurna Jr <br /> Senior REHS <br /> Site Mitigation Unit IV/LOP <br /> 304 East Weber St , Fifth Floor <br /> Stockton, CA 95202 <br /> RE Thrifty Oil Co. Station #171 <br /> 1250 North Wilson Way <br /> Stockton, CA 95205 <br /> 4th Quarter Monitoring Report, 1998 <br /> Dear Mr Inf ima <br /> Presented herein is the 4th Quarter 1998 Monitoring Report prepared for Thrifty Oil Co Station <br /> 4171 located at 1250 Wilson Way, Stockton, California(Figure 1) Presented in this report are the <br /> results of the quarterly groundwater monitoring program conducted on November 10, 1998 This <br /> report presents data collected during the period from November 10, 1998 Thrifty Oil Co has <br /> retained the services of Earth Management Company (EMC) to conduct quarterly monitoring and <br /> sampling activities at this site The data is reported by Thrifty's in-house environmental staff <br /> GROUNDWATER MONITORING <br /> Depth to groundwater is measured in each monitoring well on a quarterly basis Gauging data <br /> obtained from November 1992 through November 1998 is presented in Table 1 In general, <br /> groundwater occurs under water table conditions beneath the station at depths ranging from 46 50 <br /> feet below surface grade (bgs) in monitoring well MW-4 to 54 10 bgs in monitoring well MW-6 <br /> A groundwater elevation contour map based upon November 10, 1998 data is presented as Figure <br /> 1 A groundwater mound is present in the vicinity of monitoring well MW-4 The general direction <br /> of groundwater flow is toward the southeast with a gradient ranging from 0 03 to 0 13 feet/foot <br /> QUARTERLY GROUNDWATER SAMPLING <br /> As part of the groundwater monitoring program, groundwater samples were obtained from <br /> monitoring wells MW-3R, MW-4, MW-5, MW-6, TB-I, TB-7, TB-8, and TB-10 Groundwater <br /> samples were obtained by EMC and delivered in a chilled state in an ice chest following strict Chain- <br /> of-Custody procedures to a state certified laboratory and analyzed for volatile aromatic compounds <br />• �of benzene, toluene, ethylbenzene, xylenes, and MTBE by EPA method 8020, and total petroleum <br /> U-7 <br /> ��7 13539 E Foster Rd, Santa Fe Springs, CA 90670-0138•(562)923-9876 <br />