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Chevron#9-0557 June 2013 <br /> 139 Center Street South, Stockton <br /> Claim No: 5820 <br /> The affe,ted.groundwater is not currently being used as a source of drinking water, and it is highly <br /> unlikely that the affected groundwater will be used as a source of drinking water in the foreseeable <br /> future. Other designated beneficial uses of impacted groundwater are not threatened, and it is <br /> highly unlikely that they will be, considering these factors in the context of the site setting. <br /> Remaining petroleum hydrocarbon constituents are limited and stable and concentrations are <br /> decreasing. Corrective actions have been implemented and additional corrective actions are not <br /> necessary. Any remaining petroleum hydrocarbon constituents do not pose a significant risk to <br /> human health, safety or the environment. <br /> Rationale for Closure under the Policy <br /> • General Criteria: The case meets all eight Policy general criteria. <br /> • Groundwater Specific Criteria: The case meets Policy Criterion 1 by Class 4. The <br /> contaminant plume that exceeds water quality objectives is less than 1,000 feet in length. <br /> There is no free product. The nearest water supply well or surface water body is greater <br /> than 1,000 feet from the defined plume boundary. The dissolved concentrations of <br /> benzene and MTBE are each less than 1,000 pg/L. <br /> Vapor Intrusion to Indoor Air: The case meets Policy Criterion 2a by Scenario 3b. The <br /> maximum benzene concentration in groundwater is less than 1,000 pg/L. The minimum <br /> depth to groundwater is greater than 10 feet, overlain by soil containing less than <br /> '100 mg/kg of TPH. <br /> Direct Contact and Outdoor Air Exposure: The case meets Policy Criterion 3b. Although <br /> no document titled "Risk Assessment'was found in the files reviewed, a professional <br /> assessment of site-specific risk from potential exposure to residual soil contamination found <br /> that maximum concentrations of petroleum constituents remaining in soil will have no <br /> significant risk of adversely affecting human health. Residual contamination was removed <br /> by excavation. <br /> Objections to Closure and Responses <br /> According to GoeTracker, the County responded to the March 2013 Low-Threat Closure Request, <br /> and stared that before the County can complete the site closure consideration two items need to be <br /> addressed: <br /> o provide an explanation why contaminants of concern continue to increase in groundwater <br /> monitored by MW-15D. <br /> RESPONSE: Residual contamination is confined to the source area and the case meets <br /> Policy Criterion 1 by Class 4. <br /> • Provide the technical justification for the use of the geometric mean rather than the <br /> arithmetic mean when calculating the mass estimates of TPHg in soil and TPHd in <br /> groundwater; and clarify why the height (h) was multiplied by 0.8 to get a volume of <br /> 7,700,000 cubic feet when calculating the TPHd mass in groundwater. <br /> RESPONSE: Mass balance calculations are not required under the Policy. <br /> Determination <br /> Based on the review performed in accordance with Health & Safety Code Section 25299.39.2 <br /> subdivision (a), the Fund Manager has determined that closure of the case is appropriate. <br /> Page 2 of 11 <br />