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STATE OF CALIFORNIA --,,GEORGE DEUKMEJIAN, Governor <br />CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD— <br />CENTRAL VALLEY REGION <br />3443 ROUTIER ROAD PERIAT; SEWIC"E S <br />SACRAMENTO, CA 95827-3098 <br />29 September 1989 <br />Ms. Diane Hinson, Registered Sanitarian <br />Environmental Health Division <br />San Joaquin County Public Health Services <br />P.O. Box 2009 <br />Stockton, CA 95201 <br />ROBERTS PETROLEUM SERVICES, 930 VICTOR ROAD, LODI, JULY QUARTERLY GROUND WATER <br />MONITORING REPORT <br />We have reviewed the 7 September 1989 quarterly ground water monitoring report <br />prepared by Ensco Environmental Services, Inc., for this site. The report <br />provides the analytical results for samples obtained from the on-site ground <br />water monitoring wells on 18 July 1989. <br />No hydrocarbon contaminants were detected in the ground water samples during <br />this round of sampling. However, hydrocarbons were detected in samples <br />obtained from the on-site wells during the 13 January 1989 round of sampling. <br />In addition, MW -1 which contained free -phase hydrocarbon product during <br />previous investigations, is now dry. <br />Although the analytical results for two consecutive rounds of sampling have <br />shown no detectable levels of hydrocarbon contamination, we are concerned that <br />the free -phase hydrocarbons, previously detected in MW -1, may be migrating. <br />Therefore, we recommend that MW -1 be replaced. This replacement well should <br />be constructed with nominal 4 -inch diameter or greater casing and well screen <br />so that it may be used for extraction well in the event that ground water <br />remediation is necessary. <br />We also note that ground water samples obtained on 18 July 1989 were analyzed <br />on 1 August 1989. Therefore, the allowable holding time for these samples may <br />have been exceeded. To assure reliable analytical results, we request that <br />ground water samples obtained during future rounds of sampling be analyzed <br />more promptly. <br />If you have any questions, please call me at (916) 361-5731. <br />THOMAS D. PELTIER <br />Engineering Geologist <br />TDP/tdp <br />