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{ <br /> ' 1444 MARIPOSA ROAD <br /> WKA No 2938 06 <br /> • September 6, 2000 <br /> ' Page 18 <br /> Based on results of laboratory analysis of soil samples obtained from the soil borings and low to <br /> nondetectable concentrations of petroleum hydrocarbons and oxygenates in groundwater,it is our <br /> opinion that subsurface soil poses no significant threat to groundwater quality onsite or offsite <br /> ' We base this opinion on historical groundwater concentration data obtained from the wells and <br /> mass volume calculations of petroleum hydrocarbons remaining in soil and groundwater beneath <br /> the site <br /> Recent past groundwater samples obtained from the wells indicate that petroleum hydrocarbons <br /> ' are essentially nondetectable in all wells with the exception of low concentrations of TPH as <br /> gasoline detected in well MW4 Low concentrations of MTBE(0 78 µg/l)was detected only in <br /> ' well MW2 since the latest sampling event performed on April 18, 2000 Benzene has not been <br /> detected in the water samples since June 16, 1999 <br /> ' Based on results ofoundwater les obtained over several past quarterly sampling events, <br /> g�' samples <br /> the plume does not appear to be migrating and that as a result, some degree of natural attenuation <br /> of the contaminant plume is most likely occurring beneath the site <br /> ' Potential sensitive receptors in the form of offsite wells will likely not be impacted by <br /> contaminated groundwater beneath the site based on the removal of the former ti STs and <br /> ' contaminated soil,historical groundwater flow direction and gradient data, and the attenuation of <br /> dissolved-phase petroleum hydrocarbons in groundwater <br /> ' of contamination remaining Craven the relatively low concentrationsg in the soil beneath the site, <br /> the low concentrations of TPH as gasoline in well MW4 and trace concentrations of MTBE in <br /> well MW2, and furthermore,based on the likelihood that sensitive receptors will not be <br /> impacted, we recommend that SJCPHD require no further action as related to the underground <br /> storage tanks at this site Furthermore,we recommend that the CVRWQCB be notified of our <br /> findings Upon concurrence for site closure by the SJCPHS and the CVRWQCB, we <br /> ' recommend that the seven groundwater monitoring wells be abandoned in accordance with <br /> County and State regulations and purged groundwater currently stored be removed from the site <br /> WALLACE KOHL <br /> Renledpapc. &ASSOCIATES INC <br />