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Final Remediation Plan Page 9 <br /> Ranch Market 23569 South Santa Fe Road Riverbank CA February 28 2001 <br /> 4.0 EXTENT OF PETROLEUM HYDROCARBONS <br /> 41 Extent of Petroleum Hydrocarbons Adsorbed to Soil <br /> Referring to the Cross Sections A-A' and B-B'(Figures 5 and 6), the release of gasoline in the <br /> area of the former USTs appears to have migrated vertically downward to the groundwater, <br /> and then down gradient creating a 10 foot thick smear zone from 20 to 30 feet bgs (Table 2) <br /> The highest concentrations in soil of benzene, MtBE, and TPHg were found in the soil sample <br /> collected from AS-1 at 20 feet bgs, underlying the former UST pit The lateral and vertical <br /> extent of gasoline range petroleum hydrocarbons adsorbed to soil has been defined by the <br /> current data set (Figure 9) <br /> 4.2 Extent of Petroleum Hydrocarbons Dissolved in Groundwater <br /> The highest concentration of dissolved benzene, MtBE, TPHg, DIPE, EDB, TBA, and 1,2- <br /> DCA were found in the water sample collected from MW-1, located within the former UST <br /> pit (Table 3) Referring to Figure 10, the 1St quarter 2001 groundwater sample data define the <br /> lateral hn-uts of dissolved BTEX, and TPHg plume in groundwater With the exception of <br /> 0 63 ug/L MtBE reported in the upgradient well MW-6, the lateral limits of the dissolved <br /> MtBE, oxygenates, 1,2-DCA, and EDB plume in groundwater are defined <br /> Based on the water sample collected from MW-5D, a well screen from 65 to 70 feet bgs, the <br /> 1St quarter 2001 groundwater sample data defines the vertical limits of dissolved benzene and <br /> MtBE <br /> 4.3 Estimated Mass of Petroleum Hydrocarbons <br /> Using the soil sample analytical data in Table 1 and the third quarter 2000 groundwater <br /> analytical data in Table 3, SECOR calculated the estimated mass of hydrocarbons adsorbed to <br /> soil and dissolved in groundwater The assumptions and calculations used are presented in <br /> Appendix B <br /> The estimated mass of hydrocarbons adsorbed to soil was calculated for the vadose zone from <br /> 15 to 25 feet bgs and within the capillary fringe or smear zone from 25 feet to 35 feet bgs <br /> The area, thickness, and average concentrations used to calculate the mass of hydrocarbons is <br /> presented in Appendix B The following estimated mass and volume of gasoline range <br /> hydrocarbons are present at the site <br /> Petroleum Hydrocarbons As Gasoline Gallons Gasoline Pounds Gasoline <br /> Volume/Mass Adsorbed to Soil 3,638 25,464 <br /> Volume/Mass Dissolved in Groundwater 282 197 <br /> Total Mass Estimated Mass 3,920 25,661 <br /> File FRP-report doc SSCOR International Incorporated <br />