ARCHIVED REPORTS_REPORT SUMMARIZING INSTALL OF MONITORING WELLS MW4,MW5,MW7,MW8 & SOIL BORING RDM1 & 4TH QTR 2013 GROUNDWATER SAMPLING

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s Ms. Angela Lee Huntbrook Holdings,LLC February 12, 2014 Page 11 Approximately 155 gallons of groundwater were generated during the well development (125 gallons) and initial sampling (30 gallons) of monitoring wells MW-4, MW-6, MW-7 and MW-8 during the • fourth quarter 2013. The water was transported under non-hazardous manifest to Instrat's treatment and disposal facility in Rio Vista,California. Copies of the disposal manifests are included in Enclosure O. Conclusions/Recommendations Based on the laboratory analytical results for the initial groundwater samples collected from monitoring wells MW4, MW-6, MW-7 and MW-8 on December 3, 2013, it appears that the lateral extent of dissolved petroleum hydrocarbon constituents and TCE in groundwater have been adequately assessed at this time. Concentrations of BTEX, fuel oxygenates (MTBE, ETBE, DIPE, TAME and TBA), and naphthalene in groundwater were all below the laboratory's reporting limit. The absence of volatile constituents in groundwater is consistent with an old fuel release as is suspected at the subject property. Low levels of TPHg were reported in monitoring wells MW-6 and MW-7 at concentrations of 77 and 220 pg/L, respectively. The TPHg reported in MW-6 was noted by the laboratory as being primarily compounds not found in typical gasoline, and after further discussion with lab personnel, is most likely a result of the TCE and PCE which fall into the reporting range for TPHg. In the future, RDM will request the laboratory to report both TPHg and Gasoline Hydrocarbons in order to differentiate between what is actually gasoline and TCE/PCE. Following silica gel cleanup, TPHd was only reported in • monitoring well MW-4 at a concentration of 84 µg/L, and was noted by the laboratory as being higher boiling point hydrocarbons, not typical of diesel. The highest concentration of TCE was reported in monitoring well MW-6, at a concentration of 4.6 µg/L, which is below the California Drinking Water Maximum Contaminant Level(MCL)of 5.0 µg/L. Dissolved tetrachloroethene (PCE) was reported in one offsite monitoring well sample at a concentration that exceeds the California Drinking Water MCL of 5 µg/L. PCE was reported in monitoring well MW-6 at a concentration of 36 gg/L. This well (MW-6) is located hydraulically crossgradient to downgradient (depending on the time of year) from the subject property. The PCE concentration reported in offsite monitoring MW-6 is significantly greater than any concentration reported in the onsite monitoring wells. The highest concentration reported onsite was in monitoring ti well MW-3 at a concentration of 9.0 µg/L on September 17,2013. It is RDM's opinion that the elevated PCE concentration reported in monitoring well MW-6 is most likely attributed to an offsite source such as an old dry cleaning facility. There are many well documented cases of impacts to sanitary sewers from historic illegal discharges of dry cleaning solvents. Before doing any further groundwater assessment for PCE, RDM recommends conducting a records review to identify any potential historic dry cleaners within the vicinity of the subject property and the location of the sanitary sewer along East • Main Street. The lateral and vertical extents of petroleum hydrocarbon and VOC constituents in soil onsite have been adequately assessed. Based on the previous consultant's soil data(Enclosure C)and RDM's results for boring RDM-1 (Table 1), the majority of the residual impact (secondary source) appears to remain in . the northeast corner of the site, in the vicinity of the former fuel island and UST(that was located on the east side of the former station building), at depths beginning at approximately 12 to 16 fbgs and extending down to the water table (48 to 52 fbgs). In soil boring RDM-1, the highest benzene concentration was detected at 3.3 mg/kg at a depth of 38 fbgs and the highest TPHg concentration was detected at 2,260 mg/kg at a depth of 18 fbgs. These results are similar to the previous consultant's results for soil boring SB-4(Figure 2). •