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r <br /> r <br /> 23 May 1996 <br /> r AGE-NC Project No 95-0132 <br /> Page 4 of 5 <br /> rApril 1996, ground water flow direction at the site shifted 20° towards the west During the same <br /> period, ground water surface elevation rose an average 4 25 feet <br /> 4 2 ANALYTICAL RESULTS OF GROUND WATER SAMPLES <br /> rMTBE was detected in MW-1 at 0 51 µg/l (micrograms per liter or parts per billion ppb) Other <br /> petroleum hydrocarbons were not detected in samples collected from MWA or MW-3 Analytical <br />' results of ground water samples are summarized on Table 2 The laboratory report (CAL Laboratory <br /> I D Nos 720AW, 2W) and chain-of-custody form are included in Appendix B <br /> 5.0. CONCLUSIONS & RECOMMENDATIONS <br /> r Between January 1995 and April 1996, TPH-d has decreased in MWA It is possible that natural <br /> attenuation combined with the rise in ground water may have contributed to the decrease in <br /> hydrocarbon concentrations in MWA Furthermore, petroleum hydrocarbons have not been detected <br /> in samples collected from the up-gradient (MW-2) or down-gradient (MW-3) wells <br /> The City of Manteca Municipal Water Well No 13 is located approximately 120 feet down-gradient <br /> rof the former UST area On 20 January 1994 and on 18 May 1994, ground water samples were <br /> collected from the Well No 13 and were analyzed for volatile organics in accordance with EPA <br /> r methods 502 2 Volatile organics were not detected in either sample Copies of the laboratory reports, <br /> obtained from the City of Manteca, are included in Appendix C <br /> r We recommend preparation of a Closure Summary Report for the site Based upon current and <br /> historical analytical results of ground water samples collected from the site, we recommend <br /> discontinuing ground water monitoring at this time <br /> 1 <br /> 6.0. LIMITATIONS <br /> rOur professional services were performed using that degree of care and skill ordinarily exercised by <br /> environmental consultants practicing in this or similar localities The findings were based upon <br /> analytical results provided by an independent laboratory Evaluations of the geologic/hydro geologic <br /> conditions at the site for the purpose of this investigation are made from a limited number of available <br /> data points, and subsurface conditions may vary away from these data points and with time No other <br /> rwarranty, expressed or implied, is made as to the professional recommendations contained in this <br /> report <br /> r <br />