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to the reoi ientation of the hydrocai bon plume as depicted in Figure 4 Neither MTBE nor any of the <br /> other oxygcnates veie detected b) method 8260 but the laboratory was unable to teach the <br /> standard reporting limit of I ppb due to interfeienec from other gasoline compounds (Appendi" B) <br /> The reporting hinit for the analysts was 10 ppb for four of the five oxygenates, and 50 ppb for <br /> Tertiary Butanol (Table 2) <br /> Gasoline Loricentiations also decreased in GT-1, and are now below the detection limit T its further <br /> supports the interpretation that the contaminant glume has migrated northward since the first <br /> quarter <br /> 4.0 RECOMMENDATIONS <br /> The direction of giound-vkater flow appears to vary more at this site than it does at rtost sites <br /> Quarterly mapping of the gradient does not seem to yield predictable, easily understood results <br /> Therefore, we iecomniend measuring water depths on a monthly basis during the third and fourth <br /> quarters of 1999 in oidet to better establish the rate of change in the flow direction and correlate the <br /> changes with causative factors, such as agricultural pumping Groundwater sampling should <br /> continue on a quarterly basis <br /> In order to petit} the laboratory result for the Gillt�!s domesttc well, we recommend san pling this <br /> well again titthtn ZO days This could be done in conjunction with the monthly measurement of <br /> water depths We also recommend analyzing the sample for gasoline and BZ EX <br /> In the First Quartet Report we recommended pet forming an aquifer pumping test of well GT-10 in <br /> July or August of this )car and perform ing pilot tests of two water treatment methoc s ex-situ <br /> btoreactoi and carbon canister The report was submitted less than one month ago and is still being <br /> reviewed by San loaqum County P14S/1-HD but in the meantime Nye have begun a cost cstimate to <br /> ptepate a work plan for these tasks Unless directed otherwise by PHS/EHD in early July, we intend <br /> to prepare the wort plan in the middle of Jul; and submit it for approval so that testitis could be <br /> pertormed in mid-Au4Must before the water le-,el drops below the contaminated zone <br /> 4 <br />