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San Joaquin County <br /> Environmental Health Department °!RE°T°R <br /> �,.•_,��• -p � Donna Heran,REHS <br /> z; ,Z 1868 East Hazelton Avenue <br /> -+ PROGRAM COORDINATORS <br /> Stockton, California 95205-6232 Robert McClellan,REHS <br /> • Jeff Carruesco,REHS,RDI <br /> •.cq :° Website: www.sjgov"org/ehd Kasey Foley,REHS <br /> Phone: (249)468-3424 Linda Turkatte,REHS <br /> Fax: (209) 464-0138 <br /> November 7, 2012 <br /> Messrs. Kirk Larson, PG, and Robert Trommer, CHG <br /> State Water Resources Control Board <br /> Division of Financial Assistance <br /> 1001 1 Street <br /> Sacramento CA 95814 <br /> Subject: 850 Milgeo Road, Ripon, CA <br /> Annual Five-Year Review Update Response CUF Claim # 9384 <br /> San Joaquin County Environmental Health Department (EHD) has received and reviewed the <br /> fifth annual five-year review update letter dated September 2012 from Kirk Larson of the State <br /> Water Resources Control Board (SWQCB) Cleanup Fund (CUF) for the above-referenced site. <br /> The CUF recommended that the EHD consider the site for closure. <br /> The EHD has reviewed the site data and notes that monitoring well MW4, screened 8 to 28 feet <br /> bsg, located in the source area, is screened too shallow to be sampled during periods of low <br /> groundwater elevation and also that there is a general positive correlation between increasing <br /> depth to water (DTW, declining groundwater elevation) and increasing contaminant <br /> concentrations. Graphs showing this relationship are attached. <br /> The EHD also notes that while the impact to groundwater is well characterized near monitoring <br /> well MW1 with MW7, further to the west shallow groundwater is not characterized. MW6, <br /> screened 45 to 59 feet below surface grade (bsg), has been significantly impacted compared to <br /> the similarly screen MW7 near the impacted MW1; however, there is no shallow zone <br /> monitoring well near MW6 to characterized the impact to groundwater in that area. A grab <br /> groundwater sample from 20 feet bsg collected from boring P6 was impacted by 850 <br /> micrograms per liter total petroleum hydrocarbon quantified as diesel (TPHd). This indicates that <br /> the stratigraphic interval between 20 feet bsg (P6) and 45-50 feet bsg (MW6) may be impacted, <br /> but is poorly characterized. The boring log for MW6 shows the unmonitored 25-foot interval to <br /> be comprised predominantly of sand, which can provide a porous, permeable migration pathway <br /> for impacted groundwater. While the predominant groundwater gradient is toward the northeast, <br /> groundwater flow is also controlled by permeable pathways and the impact in MW6 and P6 <br /> shows that significant migration toward the northwest has occurred. The EHD recommends that <br /> the monitoring gap in permeable strata near MW6 be monitored as well as the strata directly <br /> underlying MW4 before considering this site for closure. <br /> 2012 Five-Year Review Update Response CUF Claim No 9384.doc <br />