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20 October 1995 <br /> AGE-NC Project No 95-0111 <br />' Page 3 of 4 <br /> hydraulic gradient flattens (decreases) slightly near the north end of the site, between MW-1 and _ <br />' MW-4 However, overall, the gradient is consistent with local trends and previous gradient <br /> calculations at the site <br /> 4 2 PETROLEUM HYDROCARBON-ROPACTED GROUND WATER <br />' TPH-g was detected in MW-1, MW-2 and MW-3 at concentrations of 620lag/l (parts per billion <br /> ppb), 130 ppb and 8,000 ppb, respectively TPH-d was detected in samples from MW-2 and MW-4 <br />' at concentrations of 73 and 3,400,000 ppb, respectively Laboratory notations for the sample from <br /> MW-4 indicated a high concentration of emulsified free product <br />' BTE&X were detected in samples from MW-1, MW-2 and MW-4 at concentrations ranging from <br /> 0 70 ppb (ethyl benzene in MW-2) to 800 ppb (xylenes in MW-4) Toluene was also detected in the <br /> sample from MW-3 at a concentration of 0 73 ppb Analytical results of the ground water samples <br />' are summarized in Table 2 The laboratory report and chain-of-custody are included in Appendix B <br /> 5.0. CONCLUSIONS AND RECOMMENDATIONS <br /> Based upon analytical results of the ground water samples, the down-gradient lateral extent of <br />' dissolved hydrocarbons has not been identified It appears that the hydrocarbons plume extend off- <br /> site to the northeast Furthermore, free product was encountered in well MW-4, located near the <br /> 1 north end of the site, suggesting that significant ground water and/or capillary fringe contamination <br /> may exist offsite <br />' Installation for an additional ground water monitoring well north of the subject site, across Grant Line <br /> Road, has been recommended by AGE in previous reports AGE is presently obtaining encroachment <br /> permission from the City of Tracy to install a monitoring well within the sidewalk along the north side <br /> of Grant Line Road Installation procedures are scheduled for late October or early November 1995 <br /> 1 <br /> We reconrimend scheduling the next quarterly monitoring at the site after the proposed monitoring <br />' well(MW-5) has been installed off-site After monitoring results have been obtained, initiation of a <br /> "pump and treat" system in the vicinity of MW-4 may be necessary to minimize further migration <br /> 1 <br />