SITE INFORMATION AND CORRESPONDENCE

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Ocampo Property September 2013 821 South Wilson Way, Stockton Claim No: 18916 Rationale for Closure under the Policy General Criteria: The case meets seven of eight Policy general criteria; the conceptual site model is incomplete because the extent of the groundwater plume is not adequately defined. • Groundwater Specific Criteria: The case does not meet Policy criteria because the extent of groundwater contamination is undefined east (downgradient) of the Site. • Vapor Intrusion to Indoor Air: This case meets Policy Criterion 2b. Although no document titled 'Risk Assessment' was found in the files reviewed, a professional assessment of site- specific risk from potential exposure to petroleum constituents as a result of vapor intrusion found there to be no significant risk of petroleum vapors adversely affecting human health. �N ,` The onsite building is an active facility with multiple rollup doors that would prevent the .I\ accumulation of soil vapors in the building. In addition, excavation was conducted to depth of 15 feet and nearly 8,258 pounds of TPHg was pulled from the subsurface by soil vapor extraction. Rebound test showed soil vapor extraction had reached asymptotic levels. • 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 sample 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 can be directly substituted for naphthalene concentrations with a safety factor of eight. Benzene concentrations from the Site are below the naphthalene thresholds in Policy Table 1. Therefore, the estimated naphthalene concentrations meet the thresholds in Table 1 and the Policy criteria for direct contact by a factor of eight. It is highly unlikely that naphthalene concentrations in the soil, if any, exceed the threshold. Recommendation The Fund recommends that the County direct the Responsible Party to define the extent of groundwater contamination and to implement an effective soil and groundwater treatment technology to achieve Policy guidelines in a timely manner. K' Larson, P.G. Date Robert Trommer, C.H.G. Date ngineering Geologist Senior Engineering Geologist Technical Review Unit Chief, Technical Review Unit (916) 341-5663 (916) 341-5684 Page 2 of 10