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ADDITIONAL GROUND WATER MONITORING WELL INSTALLATION AND <br /> QUARTERLY GROUND WATER MONITORING REPORT, FIRST QUARTER 1992 <br /> Exxon Station RIS 7-3708 <br /> 2705 Country Club Boulevard <br /> Stockton, Caldorrua <br /> Delta Project No 40-91-838 <br /> Page 4 <br /> ' Soil samples collected at 10 feet below grade from the borings of monitoring wells MW-4 through MW-6 <br /> did not contain detectable levels of petroleum hydrocarbon constituents 71m sail samples were not <br /> analyzed within the EPA r ended boldin time due to a laboratory login error The analyses of <br /> the soil samples were performed two days outside of the recommended EPA holding time; however, due <br /> ' to the field screening results and the laboratory analytical results,the presence of petroleum hydrocarbons <br /> in the soil is not evident Copies of the soil sample analytical certified reports are included in <br /> ' Appendix C <br /> 2.3 Ground Water Monitoring Well Construction <br /> Monitoring wells MW-4 through MW-6 are constructed of 4-inch diameter, flush-threaded, Schedule 40 <br /> ' PVC material installed to a depth of approximately 25 feet below grade The wells were screened with <br /> 0 01-inch-wide slots from 10 to 25 feet below grade The annular space in each well is filled with <br /> No 2/12 sand to approximately 3 5 feet above the screened interval A 2-foot thick bentonite seal was <br /> placed above the sand pack The remaining annular space in the well was filled with cement grout <br /> containing approximately 5 percent bentonite The top of the well casings contain locking water tight <br /> expansion caps and were completed at the surface with traffic rated well covers <br /> The well construction details for monitoring wells MW-4 through MW-6 are included in Appendix D <br /> ' Copies of the encroachment permits obtained from the City of Stockton and monitoring well construction <br /> permits obtained from the San Joaquin County Public Health Service are included in Appendix E <br /> ' 3.0 FIRST QUARTER 1992 MONITORING RESULTS <br /> ' 3.1 Ground Water Level Measurements <br /> Monitoring wells MW-1 through MW-6 were surveyed to determine the elevations of the riser pipes with <br /> ' reference to a California Department of Transportation bench mark (No 1618L) with an elevation of <br /> 0 728 feet above mean sea level (MSL) On February 11 and March 18, 1992, water levels were <br /> measured in monitoring wells MW-1 through MW{ <br /> ' RPT112 JDM <br />