SITE INFORMATION AND CORRESPONDENCE

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Jbe Lentini • - 3 - 2 February 2010 Former Pipelines, Tracy in the Central Valley Region. The Basin Plan assigns drinking water as a potential beneficial use (BU) of to all groundwater underlying the Central Valley. As such, cleanup standards must be derived pursuant to drinking water standards. The Basin Plan states that groundwater shall not contain taste- or odor-producing substances in concentrations that cause nuisance or adversely affect BUs. The Central Valley Water Board's July 2008 A Compilation of Water Quality Goals may be used to assign numerical values that implement the narrative objectives. If background concentrations are below WQOs, the cleanup goals for COPCs in groundwater are set by background concentrations. Cleanup levels for soil and soil vapor are not set by any specific set of screening levels in the Central Valley. They are site specific and are determined by the maximum concentrations that prevent the degradation of groundwater quality and risk to human health. Soil cleanup levels that are protective of groundwater quality may be calculated using the Central Valley Water Board's June 1989 Designated Level Methodology for Waste Classification and Cleanup Level Determinations (DLM). Cleanup levels for soil vapors may be evaluated using modeling software, such as VLEACH, which is available on the internet at http://www.epa.gov/ada/csmos/models/vleach.html.. 2. Shell is free to perform the proposed risk assessment, but Central Valley Water Board staff will require Shell to clean up soil and groundwater pursuant to the requirements of the Basin Plan, not to the screening levels proposed to the RA Work Plan. If Shell chooses to proceed with the RA, the cleanup goal for each affected media would be the most stringent concentration of either the Basin Plan WQOs or the RA in order to protect both water quality and human health. 3. The RA Work Plan also proposes to conduct soil vapor sampling from permanent soil vapor probes. It is unclear whether permanent soil vapor probes have already been installed at the site or if Shell intends to propose their installation. 4. Page 2 of the Addendum states that soil and groundwater samples will be collected from the two deepest borings and provides a description of the proposed laboratory analytical suite. We understand that selected soil samples will be also be analyzed for geotechnical parameters including hydraulic conductivity, pore fluid saturation, porosity, bulk density, moisture content, organic content, and grain size. Neither the MW Work Plan nor the Addendum clearly define the criteria that will be applied to select the soil samples that will be submitted for laboratory analysis. In addition, in response to our 28 January2010 emailed inquiry requesting clarification on the sampling plan, CRA indicated that groundwater sampling for laboratory analysis will be restricted to the sentinel boring. It is unclear from which borings soil and groundwater samples will be sent for laboratory analysis. Soil and groundwater data from both deep borings may be essential to whether there is a nexus between the former pipeline and any potential groundwater contamination below 150 feet bgs. In addition, geotechnical data may be needed from more than one location to be representative of actual site conditions. Shell needs to submit the criteria, in writing, that will be used to determine which soil samples will be submitted for laboratory analysis and specify the minimum number of soil and groundwater samples that could be submitted for analysis.