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ENIVIR01dMENTAL HEALTh <br /> PI RMIi SERVICE KAPREALIAN ENGINEERING <br /> I N C O R P O R A T E D <br /> 44 DEC IS PM 2, 13 <br /> December 9 , 1994 <br /> Unocal Corporation <br /> 2000 Crow Canyon Place, Suite 400 <br /> P.O. Box 5155 <br /> San Ramon, California 94583 <br /> Attention: Ms. Tina Berry <br /> RE: Former Unocal Service Station #5098 <br /> 5606 Pacific Avenue <br /> Stockton, California <br /> Dear Ms. Berry: <br /> Kaprealian Engineering, Inc. (KEI) has received MPDS Services, <br /> Incts. Quarterly Data Report (MPDS-UN5098-04) dated October 18, <br /> 1994, for the above referenced site. Based upon review of the MPDS <br /> report, KEI recommends a modification to the current ground water <br /> monitoring and sampling program. <br /> The analytical results of the most recent ground water samples <br /> collected from monitoring wells MW12 through MW15 on September 14 , <br /> 1994 , showed no detectable concentrations of all EPA method 8010 <br /> constituents. In addition, the ground water samples collected from <br /> monitoring wells MW12 and MW13 during the past five consecutive <br /> quarters of sampling (September 1993 - September 1994) have shown <br /> no detectable concentrations of all EPA method 8010 constituents. <br /> Therefore, KEI recommends that the EPA method 8010 analysis be <br /> discontinued for wells MW12 through MW15. <br /> The ground water samples collected from monitoring wells MW10 and <br /> MWil during the past seven consecutive quarters of sampling (March <br /> 1993 - September 1994) have shown no detectable concentrations of <br /> all EPA method 8010 constituents, except for 1, 2-dichloroethane <br /> (1, 2-DCA) . During this time period, the maximum concentration of <br /> 1, 2-DCA detected in well MW10 was 2 . 9 ppb, and the concentration of <br /> 1, 2-DCA detected in well MW11 consistently ranged from 77 ppb to <br /> 310 ppb. Therefore, KEI also recommends that the frequency of the <br /> EPA method 8010 analysis for wells MW10 and MW11 be reduced from <br /> quarterly to annually. <br /> In summary, future ground water samples collected from monitoring <br /> wells MW12 through MW15 will no longer be analyzed for EPA method <br /> 8010 constituents, and future ground water samples collected from <br /> monitoring wells MW10 and MW11 will be analyzed for EPA method 8010 <br /> constituents on an annual basis. <br /> 2401 Stanwell Drive,Suite 400 <br /> Concord,California 94520 <br /> Tel:510.602.5100 Fax:510.687.0602 <br />