SITE INFORMATION AND CORRESPONDENCE

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Mr. Denis Brown v Page 2 of 3 2320 N. EI Dorado St, Stockton, CA 10 December 2009 sample from MW-6 (maximum concentration was 0.041 mg/Kg 1,2-DCA). Groundwater sampled from the wells have either been 'non-detect' for the CDCs, or have had low concentrations of TPHg, MTBE, PCE and/or TCE. Additional soil and groundwater samples were collected from cone penetration testing (CPT) borings advanced in 2008; the soil samples were generally "non-detect" for CDCs, except for six soil samples collected from CPT-1 and/or CPT-2 at depths ranging between 35 feet bsg and 80 feet bsg; the samples were impacted by low concentrations of PCE and/or TCE. The concentrations of the detected compounds ranged from 0.0052 mg/Kg TCE to 0.016 mg/Kg PCE. Discreet grab groundwater samples collected from the CPT borings were variously impacted by TPHg, BTEX, TBA, 1,2-DCA, PCE and/or TCE. The most impacted grab groundwater sample collected was the 64-foot sample from CPT-3, which contained 16,000 micrograms per Liter (Ng/L) TPHg, 720 pg/L benzene, 120 pg/L toluene, 1,300 pg/L ethylbenzene, 269 pg/L total xylenes, 9.2 PCE and 41 pg/L TCE. The other grab groundwater samples, much less intensely impacted, variously contained TPHg, 1,2-DCA, PCE and TCE, but no detectable BTEX. CRA concluded that: • Impacted soil and groundwater has been sufficiently delineated laterally and vertically, • The dissolved plume was contracting areally and had declining concentrations of COCs; • MTBE is the only COC not delineated down-gradient of MW-5, but CRA states that additional assessment is not needed as the concentrations are declining in MW-5; • The high concentration of TPHg and BTEX encountered in the grab groundwater sample collected from CPT-3 at 64 feet bsg was part of the release from the 2315 N. EI Dorado Street site, • The PCE and TCE detected in groundwater samples and in soil samples collected beneath the water table were derived from a previous on-site dry cleaning operation and were not part of the UST release; previously CRA had attributed the PCE and TCE to release(s) on the 2315 N. EI Dorado Street site, • Additional site assessment was not necessary; • No active remediation of impacted groundwater or soil has been conducted; • There are no water supply wells within 1,200 feet of the site; • A risk assessment for the site has not been completed; • Analysis for PCE and TCE in groundwater samples should be discontinued; and • A site closure summary report should be prepared. Based on this review of the SCM and site data derived through previous investigations of the site, the EHD agrees that the plume of impacted soil has been adequately delineated, as has the dissolved TPHg plume, and that the BTEX chemicals are not significant CDCs for this site. The contaminant impact to the CPT-3 64-foot grab groundwater sample better fits the profile of the impact on the 2315 N. EI Dorado Street site than it does that of the subject site and may be related to the unauthorized release up-gradient of the subject site. The SCM presented by CRA, the COCs monitoring history on the subject site, and the unlikely potential for impacting a sensitive receptor in the foreseeable future leads the EHD to agree that SCM, QM, NFAR Comment Letter 1210