SITE INFORMATION AND CORRESPONDENCE

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Soil and Groundwater Investigation Report Mountain House Development Site#6 February 25,2010 4. FINDINGS 4.1 SUBSURFACE CONDITIONS Sediments encountered in soil borings SB-30 to SB-44consisted of laterally discontinuous strata of clay, silt, sand, and gravel; these observations are consistent with the previous investigation. Field indications of hydrocarbons (including visual, odor, and PID) indicated affected soil in SB- 39, SB-41, and SB-43 at depths ranging from 14.5 to 25 feet bgs. Small amounts of separate- phase oil (SPO) were observed in these borings between 17 and 24 feet. To delineate the vertical extent of affected soil, samples were collected from beneath the affected soil interval from SB-39 at 26 feet bgs, and from SB-41 and SB-43 at 29 feet bgs. Groundwater-level observations indicated that depth to first-encountered groundwater was between 6 to 10 feet bgs at the time of drilling. The groundwater appeared to occur under unconfined conditions based on soil moisture observations and static water-level measurements. Groundwater samples were collected from SB-35, SB-37 through SB-44 (using a temporary, pre- packed well screen), and the Foster Well. Groundwater samples collected from SB-42 and the Foster Well were also analyzed for General Minerals and TDS to evaluate the suitability of the groundwater for drinking-water use. Determination of the groundwater flow direction and gradient was not a component of this investigation; however, as noted in section 2.4, groundwater flow direction is inferred to be toward the northeast. Boring locations are depicted on Figure 2. The boring logs,which describe USCS soil classifications, PID readings, and observations of hydrocarbon-affected soil and/or groundwater, are provided in Appendix D. Boring locations were surveyed for longitude and latitude coordinates within a 5-foot range using a Global Positioning System with reference to the World Geodetic System 1984 coordinate system and datum. 4.2 SOIL ANALYTICAL RESULTS Soil analytical results, RSLs, and ESLs for the crude-oil constituents are summarized in Tables 1 and 2. Soil analytical results and the extent of affected soil are shown on Figure 3. A data usability discussion is included as Appendix E.1, and copies of the soil sample laboratory analytical reports are included as Appendix E.2. Section 5.1 compares the soil analytical results to the RSLs and ESLs to assess the extent of affected soil, and whether any further soil characterization is appropriate. 4.3 GROUNDWATER ANALYTICAL RESULTS The groundwater analytical results, ESLs, and WQOs are summarized in Tables 3 and 4. A map showing the concentrations of the dissolved crude-oil constituents in groundwater is provided on Figure 3. A data usability discussion is included as Appendix E.1, and copies of the groundwater sample laboratory analytical reports are included as Appendix E.2. Section 5.2 compares the groundwater analytical results to the ESLs and WQOs to assess the extent of affected groundwater, and whether any further groundwater characterization is appropriate. 4.4 DATA USABLITY SUMMARY SAIC-Benham performed a data usability evaluation to determine whether the data could be used for the intended purposes (i.e., delineation, risk evaluation, remediation). The evaluation 6 Front Science to Solutions