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Mr Jeffrey Wong <br /> C A M B R I A February 23, 2006 <br /> corresponding depths and soil types in boring SB-6 were significantly less This supports Shell's <br /> assertion that the MTBE most likely degraded and/or migrated through the soil since the <br /> January 1999 investigation and is no longer present at concentrations warranting additional SVE <br /> within the source area <br /> Shell installed wells MW-12, MW-13, and MW-14 to further assess the lateral extent of fuel <br /> oxygenates in groundwater near the site's perimeter and MW-15 to further assess the vertical <br /> extent of fuel oxygenates in groundwater downgradient of the USTs MTBE was not detected in <br /> MW-12 and was detected in MW-13 and MW-14 at concentrations of 44 and 25 ppb, <br /> respectively No other fuel oxygenates were detected in these wells The deeper well, MW-15 <br /> contained 52 ppb TPHg, 31 ppb MTBE, and 63 ppb TBA Shell recommends sampling these <br /> wells quarterly to establish a concentration trend <br /> Based on historical groundwater monitoring data, Shell recommends the following changes to the <br /> existing groundwater monitoring sampling schedule Shell recommends reducing the sampling <br /> frequency for wells MW-6 and MW-8 through MW-11 to annual (during the first quarter) and <br /> wells MW-1, MW-3, and MW-5 to semi-annual (during the first and third quarters) The <br /> remaining wells (MW-2, MW-4, MW-7, MW-12 through MW-15, P-1, and P-2) would continue <br /> to be sampled quarterly If SJCEHD concurs with this recommendation, the revised schedule <br /> would be implemented beginning with the second quarter 2005 sampling event <br /> Shell conducted bioparameter analyses in wells MW4, MW-7, and MW-8 for one year The <br /> decreasing MTBE concentration trend and nitrate, sulfate, and methane results suggest that <br /> bioremediation is likely occurring As originally proposed and discussed above, these analyses <br /> will be discontinued beginning with the first quarter 2006 sampling event <br /> Shell has operated a temporary GWE system since September 29, 2005, which is currently <br /> pumping from well MW-4 Shell will continue to operate the system and review field data, grab <br /> groundwater analytical data from wells MW-2 and MW-4, and groundwater monitoring data from <br /> all wells to assess its effectiveness <br /> 13 <br />