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1 1 <br /> I <br /> 20 June 1995 <br /> AGE-NC-95-4111 <br /> ` Page 3 of 3 <br /> Theground water gradient was calculated to be 0 004 ft/ft directed N 47° E (Figure 3) The ground <br /> water gradient in the vicinity of MW-1 and MW-2 appears to be mounding with a northwest- <br /> southeast trend However, the gradient decreases near the north end of the site, adjacent to Grant <br /> Line Road Overall, the gradient is consistent with local trends and previous gradient calculations <br /> I4 2 PETROLEUM HYDROCARBON-IMPACTED GROUND WATER <br /> TPH-g and TPH-d were detected in MW-4 at 4,500 µg11 (parts per billion ppb) and 4,500 ppb, <br /> respectively TPH was not detected in any other well at the site Benzene, ethyl benzene and xylenes <br /> were detected in wells MW-2 and MW-4 at concentrations of 0 79 ppb to 500 ppb Toluene was not <br />' detected during the March 1995 sampling event <br /> Petroleum hydrocarbons were not detected in MW-1 or MW-3 The analytical results are summarized <br /> on Table 2 The laboratory report and chain-of-custody are included in Appendix D <br /> 5.0. CONCLUSIONS AND RECOMMENDATIONS <br /> Based upon analytical results of the ground water samples, it appears that the hydrocarbon plume has <br /> migrated northeast of MW-4, beyond the property limits An additional ground water monitoring <br /> well has been proposed for installation along the north side of Grant Line Road, northeast of MW-4 <br /> AGE is presently obtaining the proper permits for installation of the well within the City of Tracy <br /> right-of-way We anticipate installation of the well during July 1995 <br /> We recommend scheduling the next quarterly monitoring at the site after the proposed'momtonng <br /> well (MW-5) has been installed off-site Due to the potentially off-site migration of dissolved <br /> hydrocarbons, we also recommend the initiation of a"pump and treat" system to rmrarmze further <br /> Imigration <br /> 6.0. LEAffATIONS <br /> Our professional services were performed using that degree of care and skill ordinarily exercised by <br /> environmental consultants practicing in this or sinular localities The findings were based upon <br /> analytical results provided by an independent laboratory Evaluations of the geologic/hydrogeolooc <br /> conditions at the site for the purpose of this investigation are made from a limited number of available <br /> data points(i a monitoring wells) and subsurface conditions may vary away from these data points <br /> No other warranty, expressed or implied, is made as to the professional recommendations contained <br /> in this report <br />