SITE INFORMATION AND CORRESPONDENCE

Home Browse Search

M. Scott Mansholt - 3 - 4 April 2008 Mountain House Site #2 SAiC stated that the future use of affected groundwater using new water supply wells is unlikely since the site is within the Byron Road easement ROW, is of poor quality, and in fine- grained soils that typically yield low flow wells. Considering that the site use will not likely change, SAIC conducted the environmental risk evaluation based on the most likely potential exposure - for a construction/trench maintenance worker. SAIC's environmental risk evaluation considered total petroleum hydrocarbons as crude oil (TPHc), PAHs, and BTEX component analytical results in soil. No BTEX compounds, with the exception of a single low detection of toluene, BTEX was not reported and thus not considered COPCs. The PAH results were compared to the ESLs for a construction/trench worker scenario to evaluate potential risk exposure at the site. Except for naphthalene at 3.9 mg/kg in a sample from 20-feet, PAH constituent concentrations did not exceed respective ESLs with results below the ESLs and/or were non detect (ND). Fuel fingerprint evaluation of soil concluded the residual hydrocarbon in soil is consistent with weathered San Joaquin Valley crude oil or bunker fuel. SAIC evaluated TPHc concentrations relative to the ESL using the U.S. EPA software, ProUCL (v.3), to establish a 95-percent upper confidence limit (UCL) for all TPHc data collected. The TPHc ESL for a construction/trench worker is 15,000 milligrams per kilogram (mg/kg); the calculated 95- percent UCL for the highest TPHc concentration exceeding the ESL was 12,000 mg/kg at 20-feet in a single boring. The calculated 95-percent UCL was 9,971 mg/kg, which is well below the 15,000 mg/kg ESL for TPHc. Thus, SAIC concluded the TPHc at the site does not pose a threat to human health for a construction/trench maintenance worker scenario. We previously concurred with Chevron that removal of impacted soil was not feasible since the bulk of the source occurs within and beneath the Byron Road easement, which also contains the two former OVP lines. SAiC previously assessed available technologies and review of various remedial alternatives for crude oil at the OVP/TAOC projects. The feasibility study determined that the residual crude oil is viscous and immobile, is within low permeability silty, clay soils, has been delineated, and with time natural attenuation will reduce petroleum hydrocarbons. Low permeability soil in the project area has limited the movement and migration of crude oil in the subsurface. Based on the technological feasibility evaluation, SAIC concluded there is no feasible cost effective means or easily implemented process to actively and/or effectively remove the petroleum hydrocarbons identified at the site. SAiC's report demonstrated that consistent with State Water Resources Control Board Resolution No. 92-49, a review of readily available cleanup technologies found that the options would not be effective or feasible and those options considered would be costly given that the affected area lies beneath Byron Road easement and the former OVP lines. According to the findings provided in site characterization reports and in conjunction with the results of SAIC's environmental risk evaluation, Regional Water Board staff concur that the extent of impacted soil and groundwater has been delineated and is limited to within the Byron Road easement ROW. Review of the data indicates that residual petroleum hydrocarbons in