ARCHIVED REPORTS_NOTICE OF INTENT FOR INSTALLATION, OPERATION AND MAINTENANCE OF AN OZONE INJECTION GROUNDWATER REMEDIATION SYSTEM

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' SITE GEOLOGY AND HYDROGEOLOGY ' The Site is located in the San Joaquin sub-basin of the Great Valley Sequence. The Great Valley is composed of a thick sequence of sedimentary formations derived from the erosion of the ancestral Sierra Nevada mountain range to the east. Geological maps from the United States Geological Survey show that the Site overlies alluvial soils associated with the Calaveras River from the Holocene and/or the upper Pleistocene. ' The site-related boring logs show silty sand with gravel fill covering the Site extending from the ground surface to between 1.0 and 1.5 feet. Alluvial soils consisting of moist, firm, clay and clayey silts underlie the fill to approximately 25 feet. From 25 feet to the deepest total depth explored of ' approximately 120 feet, discontinuous lenses of silty sand and sand are alternately developed within the clay and silty clay matrix. At least three sand lenses have been identified during investigations at the Site with monitoring wells completed within each of these zones. The shallow zone extends from approximately 25 feet to 60 feet; the intermediate zone extends from approximately 60 to 75 feet; and ' deep zone extends from approximately 110 to 120 feet. The readily available site-related boring logs are presented in Appendix A. The site-related groundwater monitoring wells are completed in at least two separate saturated sand lenses referred to in past documents as the shallow zone (MW-1 through MW-7, GWX-1 and VX-1), the intermediate zone (MW-8, MW-10 and MW-12) and the deep zone (MW-9, MW-11 and MW-13). ' Based on our review of the site hydrogeology, the intermediate zone is the same saturated sand lens as the shallow zone but with the wells screened at the base of the sand lens rather than across the top of the lens.The well construction details for the above listed wells are presented in Table 4. ' The Third Quarter—2009 groundwater elevation data show the groundwater flow in the shallow zone directed east-northeast at a gradient of 0.004, the groundwater flow in the intermediate zone directed ' east at a gradient of 0.006, and the groundwater flow in the deep zone directed east-northeast at a gradient of 0.005. These flow directions and gradients are generally consistent with past gradient and flow directions observed for the Site. ' NATURE AND EXTENT OF SOIL AND GROUNDWATER IMPACTS TPHg and BTEX are the primary residual constituents in the soil and groundwater beneath the Site. ' The cumulative soil analytical data for the Site are included in Table 1. These data show that the distribution of petroleum hydrocarbon soil impacts is primarily located between 30 and 50 feet, depths typically below the recent historical groundwater surface. Our recent SVE pilot testing confirmed the absence of vadose zone impacts at the Site. Therefore, this CAP is specific to the residual dissolved petroleum hydrocarbons in the groundwater beneath the Site. ' The cumulative historical groundwater analytical data are summarized in Tables 2 and 3. The monitoring well construction details are summarized in Table 4. The lateral distribution of the dissolved petroleum hydrocarbons in groundwater is limited to within no greater than 175 feet downgradient of the former onsite USTs as supported by the absence of TPHg in monitoring wells ' MW-5 and MW-6 over the past 8 years. The greatest dissolved concentrations remain onsite in the area of the former USTs in the vicinity of wells MW-1 and GWX-1 with order of magnitude lower, concentrations in cross-gradient wells MW-2 and MW-3. Vertically, the distribution of dissolved petroleum hydrocarbons is limited to the shallow and intermediate zone (the same sand lens). The approximate lateral and vertical distribution of the dissolved petroleum hydrocarbons in the groundwater beneath the Site are schematically depicted on the geologic cross-sections and conceptual ' site model included in Appendix B. ' Project No.S9183-06-02 -3- November 11,2009