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PUBL C HEALTH V L P-c�{R` ICES� <br /> Fl. <br /> SAN JOAQUIN COUNTY �' < <br /> JOG]KHANNA M.D..M.P.H. •.. ; <br /> Health Officer �`' •. �� <br /> P.O. Box 2009 • (1641 East Hazelton Avenue) •Stackton,California 9520'1 <br /> 4Cikoae► <br /> (Cal <br /> CLINT ROGERS <br /> CHEVRON USA, INC. MAR 2 S 1992. <br /> P O BOX 5004 i11F1 <br /> SAN RAMON CA 94583-0804 <br /> RE: Chevron Station ,#9-6465 SITE CODE:. 1786123 <br /> 5608 North Pershing,Avenue <br /> Stockton CA <br /> San Joaquin County Public Health Services, Environmental Health <br /> Division has reviewed the "Corrective Action Plan" dated February <br /> 20, 1992 , submitted by Groundwater Technology, Inc. and has the <br /> following comments. <br /> The corrective action alternative of verification monitoring <br /> chosen by Chevron seems to be warranted at this time. As <br /> mentioned in a previous letter from this office to Chevron dated <br /> June 24, 1991 and also in Chevron's corrective action plan, the <br /> decrease in the levels., of hydrocarbons found in the groundwater <br /> may be directly related to the drop in the water table. ' The <br /> hydrocarbons, therefore, may be "hung up" in the soil and may <br /> again impact the groundwater at the site should the water table <br /> rise. <br /> The Corrective Action plan mentions that "all perimeter,; <br /> monitoring wells were below the method detection limit indicating <br /> that the dissolved benzene, toluene, ethylbenzene and xylene <br /> plume has not migrated laterally beyond the boundaries of the <br /> Chevron property. " Monitoring well 8 and monitoring well 11, <br /> both located in the general downgradient direction from'�the site <br /> and on the perimeter of the property, have shown levelsof <br /> dissolved benzene, toluene, ethylbenzene and xylene on at least <br /> two sampling events. Although these levels were minimal they <br /> indicate that migration of the groundwater contaminant plume <br /> off-site has already occurred. The contamination may be°!hung up <br /> in the soil and may impact the groundwater again shout&the water <br /> table rise. <br /> Due to the above mentioned areas of concern, the decision to <br /> reduce the frequency of the groundwater monitoring events or the <br /> number of wells sampled should be dependent on site conditions, <br /> namely depth to water data in relation to the contaminant <br /> concentrations. Should the water table rise to previous levels <br /> and the concentrationslof contaminants remain at nondetectable <br /> levels a re-evaluation of the groundwater monitoring and possibly <br /> a request for closure can be made at that time. <br /> A Division of San Joaquin County Health fare Services 1( <br />