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Fourth Quarter 2001 Groundwater Monitoring and Sampling Report-CAO#5-00-707,Stockton,CA <br /> ]anuary 15,2002 <br /> Shallow and Deep Monitoring Well Hydrographs <br /> Figures 7 and 8 present hydrographs for selected shallow and deep groundwater monitoring wells These <br /> figures also indicate a reversal of groundwater flow direction during June 2000 when the RIW was <br /> formerly to operation <br /> TPH-G and Benzene Isoconcentration Maps <br /> Figures 9 and 10 present shallow and deep TPH-G tsoconcentratton maps for the site, respectively <br /> TPH-G were not detected in shallow zone wells during the December 2001 sampling event In the deep <br /> zone, the highest concentrations of TPH-G were in well MW-25D (29,000 parts per billion, or ppb) <br /> Figures 1 I and 12 present shallow and deep benzene tsoconcentratton maps for the site, respectively <br /> Benzene was not detected in shallow zone wells during the December 2001 sampling event The highest <br /> deep zone benzene concentration was in momionng well MW-1 1 at 5,300 ppb <br /> Analytical Testing Results <br /> No TBA, RIPE, ETBE, TAME, 1,2-DCA, or EDB above laboratory reporting limits, were detected in any <br /> of the groundwater samples MTBE was reported in wells MW-13, MW-21D, and MW-24D at <br /> • concentrations of 3 1, 3 8, and 1 8 ppb, respectively <br /> Similar to lower hydrocarbon concentrations were generally observed during this sampling event when <br /> compared to the prior quarters data <br /> Future Activities <br /> The next quarterly groundwater monitoring for the site is scheduled for March 2002 A report <br /> documenting results of the groundwater monitoring will be submitted to the RWQCB by April 15, 2002 <br /> Any additional work will be proposed by EAI <br /> LIMITATIONS <br /> GR has performed this groundwater monitoring and sampling event in a manner consistent with the level <br /> of care and skill normally exercised by members of the earth science, environmental, geologic, and <br /> engineering consulting professions currently practicing under similar conditions in the area This work <br /> was conducted according to the scope of work agreed upon with Unocal Where important, GR identifies <br /> the sources used for the facts presented in this report, and also notes any verifications from other sources, <br /> if such verification was deemed necessary GR recommends this report be used only for the purpose <br /> intended at the time the report was prepared Any use of the information provided in this report by third <br /> parties shall be at their own risk <br /> 240022 01-001 5 <br />