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The gasoline range hydrocarbon plume associated with this site is declining in concentration and <br /> should continue to do so with the removal of the source in the soils beneath this site. With continued <br /> vapor recovery, the bio-venting of MW8 and MW 12 and the commencement of sparging at MW2 <br /> and MW13, the reductions in groundwater concentrations should continue to decline at MWS and <br /> effects should be seen at MW12 during the January-March, 1998 Quarterly sampling. <br /> RECOMMENDATIONS <br /> 1. Continue to air sparge MW2 and MW13. When groundwater elevations are high (between 35 <br /> and 40 feet below top of casing) sparge both MW2 and MW13, when groundwater elevations are <br /> Iow (lower than 40 feet below top of casing) vapor extract from MW 13. <br /> 2. Using LTT vacuum pump system, sample all wells for TPHg, BTEX using 8020 method during <br /> the March 1998 quarterly sampling to confirm that the elevated results found during the <br /> December 1997 sampling was due in part by cross contamination using the Grundfos pump. <br /> 3. This site has been shown not to contain the Oxygenants with only occasional amounts of MTBE <br /> being found in offsite wells. Discontinue analysis for the Oxygenants. <br /> 4. Source removal has been accomplished and documented in the soils beneath this site with <br /> documentation borings S134, SB5, SBC and SB7. The soil contamination for this site should <br /> be considered remediated with no further action needed. <br /> LIMITATIONS <br /> The information presented in this report is based on the following: <br /> 1. The observations and data collected by field personnel. <br /> 2. The result of laboratory analyzes performed by a state certified analytical laboratory. <br /> 3. Our understanding of the regulations of San Joaquin County, the City of Stockton and the <br /> State of California. <br /> 4. References reviewed for this report. <br /> Changes in groundwater conditions can occur due to variations in rainfall, temperature, local and <br /> regional water use and Iocal construction practices. In addition, variations in the soil and <br /> groundwater conditions could exist beyond the points explored in this investigation. <br /> State Certified Laboratory analytical results are included in this report. This laboratory follows EPA <br /> and State of California approved procedures; however, WEGE is not responsible for errors in these <br /> laboratory results. <br /> The services performed by Western Geo-Engineers, a corporation under California Registered <br /> Geologist #3037 and/or Contractors License #513857, have been conducted in a manner consistent <br /> with the level of care and skill ordinarily exercised by members of our profession currently <br /> 7 R603 Update#50 12/97 <br />