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Fernando's Place • • September 2016 1201 South Center St., Stockton Claim No: 12186 Rationale for Closure under the Policy • General Criteria: The case meets seven of eight Policy general criteria. A conceptual site model that assesses the nature, extent, and mobility of the release has not been developed. • Groundwater Specific Criteria: The case does not meet the Policy Criterion for groundwater. The extent of the contaminant plume above water quality objectives is undefined. Benzene concentrations exceed 1,000 micrograms per liter(Ng/L). The plume appears to be expanding into deeper groundwater. There are three municipal supply wells within 1,000 feet of the Site. One of these wells is located 200 feet north of the site, the second municipal well is located 600 feet northeast of the Site, the third municipal well is located approximately 900 feet north of the Site. It is not known if the two closest wells are currently active (AGE, 2002). The third supply well is currently inactive. These wells are cross-gradient of the plume based on the dominant groundwater flow direction. No screen interval information is available for these wells on GeoTracker. • Vapor Intrusion to Indoor Air: The case does not meet the Policy Criterion for vapor intrusion to indoor air. Benzene concentrations are above 1,000 pg/L in groundwater. Depth to groundwater is less than 30 feet. Soil vapor samples have not been collected near the onsite buildings. • Direct Contact and Outdoor Air Exposure: The case meets Policy Criterion 3a. Maximum concentrations in soil are less than those in Policy Table 1 for Commercial/Industrial use, and the concentration limits for a Utility Worker are not exceeded. There are no soil samples results in the case record for naphthalene. However, the relative concentration of naphthalene in soil can be conservatively estimated using the published relative concentrations of naphthalene and benzene in gasoline. Taken from Potter and Simmons (1998), gasoline mixtures contain approximately 2 percent benzene and 0.25 percent naphthalene. Therefore, benzene concentrations can be used as a surrogate for naphthalene concentrations with a safety factor of eight. Benzene concentrations from the Site are below the naphthalene thresholds in Table 1 of the Policy. Therefore, estimated naphthalene concentrations meet the thresholds in Table 1 and the Policy criteria for direct contact with a safety factor of eight. It is highly unlikely that naphthalene concentrations in the soil, if any, exceed the threshold. Objections to Closure and Responses The Regional Water Board objects to UST case closure (LTCP Checklist dated February 17, 2016) because: The areal extent and depth of groundwater contamination have not been defined. RESPONSE: State Water Board staff agree. The plume has not been delineated in the downgradient direction. Recommendation The Fund recommends that the Regional Water Board direct the Responsible Party to define the downgradient extent of groundwater contamination, collect soil vapor samples from near the onsite buildings, and implement an effective soil and groundwater treatment technology to achieve Policy guidelines in a timely manner. Page 2 of 2