SITE INFORMATION AND CORRESPONDENCE

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M. Scott Mansholt • ChevronTexaco -2 - Former 2 - Former Lyoth Loading Station 6 July 2005 (OEHHA) for review and comment. The using a residential land use (adult/child) sceenario aluated Gene alyt hemential s als Ofpotentetroleum ti 1 concern as ociated with petroleum hydrocarbons closely scrutinized b an and xylenes (BTEX) and polynuclear aromatic hydrocarbons include During the various site Y HRA' -benzene, toluene, ethylbenzene, investigations, low concentrations Of BTEX and PAH compounds s . just above the respective method detection limits (MDLs) were reported. Accordingto the the site was below he ' except for the two locations, beneath the large tank and the pipeline areas HRA, the theoretical excess cancer risk`s for described above. The risk estimated for those areas was 2 X 10-5 -6, respectively. "The excess lifetime cancer risk for carcinogenic compounds (the medium is soil, water, and air) is those compounds considered by CAL/EPA or USEPA to pose a carcinogenic risk to humans. This value represents the risk, or theoretical probability, of developing cancer from that chemical upon exposure to that medium. Consequently, in February 2002, at the request of OE soil analysis results for those onsite areas was submitted3 or furtherreview tof cono the e ntratti 99 ns of benzene Present and a change to the total risk based on a re-evaluation of the inhalation pathway. Subsequently, in an 18 April 2002 memorandum OEHHA stated that "...the risks in (the two onsite areas) are within acceptable range is a value judgment and that 10-6 to 10-4 is not necessarily an acceptable range. According to the National Contingency Plan, risks below 10-6 are generally acceptable. Risks greater than he generally require remediation, and between 10-6 and 10� are within the range of risk management, wherein other factors, along with risk,maybe used to evaluate acceptability of the risk". In addition, the HRA data submitted to OEHHA stated that the none cer health effects for both areas along the OVP do not exceed an acceptable hazard index (HI) of 1. "The hazard quotient (index) is the ratio of the estimated dose from exposure to compounds in a medium, eto a value, which is believed not to produce adverse health effects". Current Offsite Investigation Following review of the 2003 and 2004 semi-annual reports, Regional Board staff determined that the extent of impacted groundwater had not been delineated offsite downgradient(northeast) of wells MW-6, MW-7, and soil borings GMX-2 and 3. Consequently, Regional Board staff requested that additional borings be advanced downgradient. Regional Board staff approved a 22 September 2004 Workplan for the additional investigation, to define the extent of affected soil and groundwater downgradient of the site. In February 2005, SAIC conducted a soil and groundwater investigation and advanced three borings to collect soil and groundwater samples for analysis. A groundwater sample was obtained from each of the three soil borings at the first encountered groundwater; which was approximately 16- 18 feet. Total petroleum hydrocarbons as diesel was reported at 760, 3,600, and 87 µg/L, respectively in borings B-1, B-2, and B-3; BTEX compounds were not detected. Low concentrations at or slightly above the respective MDLs for four PAHs ranging between 0.04 µg/L to 0.07 gg/L were reported in groundwater. *1 -Cal-EPA,Preliminary Endangerment Assessment Guidance Manual,Department of Toxic Substances Control, 1994