SITE INFORMATION AND CORRESPONDENCE

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M. Scott Mansholt -2 - 18 November 2005 Chevron-Pombo Property NFA Request Approval • A narrative describing potential exposure pathways for residential receptors considered for the risk assessment as described in the Human Health Risk Screening Evaluation was provided. The Hazard Index and Risk values derived by the earlier human health risk assessment were described in the revised report. The DTSC determined the total hazards index was 0.1; the total risk was 2 X 10-6, with potential future groundwater exposure contributing a risk of 2 X 10"6, and potential soil exposure contributing a risk of 2 X 10-7. • Review of the Risk Evaluation by DTSC staff determined that the risk values are acceptable if the land use remains non-residential. Consequently, since the land is developed as commercial, is zoned as General Highway Commercial by the City of Tracy, and provided this designation is not changed or modified, a land-use deed restriction is not necessary. According to the findings provided in site characterization reports and in conjunction with the results of the Risk Assessment review by DTSC, Regional Board staff concur that the extent of impacted soil has been delineated and is limited to the eastern portion of the site and a small area near the western boundary where affected soil was previously removed. Based on the investigative results, the extent of impacted groundwater is limited, has been delineated, and concentrations are attenuating. Review of the data indicates that residual petroleum hydrocarbons in soil at the site do not result in a significant source of TPH constituents to groundwater. DTSC staff has determined that risk at the site, based on the Risk Assessment data, is acceptable provided the land use remains as commercial. Since the use of shallow groundwater wells in the Tracy area is prohibited for domestic or municipal use by the City of Tracy municipal Code, for administrative reasons unrelated to petroleum impacts from the OVP, the use of groundwater at the property does not present an environmental concern. According to the field investigative data and information, coupled with the DTSC's findings, and with the provisions that the information provided was accurate and representative of site conditions, no further action is required. If existing, additional, or previously unidentified chemical constituents at the site cause or threaten to cause pollution or nuisance or are found to pose a threat to public health or water quality, then 1)nothing in this determination is intended or shall be construed to limit or preclude the Regional Board or any other agency from taking any further enforcement action, and 2) this letter does not relieve Chevron of any responsibilities mandated under the California Health and Safety Code and the California Water Code. Nothing in this determination shall constitute or be construed as a satisfaction or release from liability for any conditions or claims arising as a result of past, current, or future operations at this location.