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CLOSURE REQUEST REPORT Section No 5 0 Former Amencan Forest Products Company 07/31/01 2801 West Lane Page 5-3 Stockton California 11. An estimate of the amount (in pounds or gallons) of contamination remaining in the soil and/or in the dissolved phase may be substituted for a mass balance. Mass balance calculations have been completed using soil data and are included in Appendix C A total of 12,468 kg of TPHd is estimated to have been left in the subsurface, following completion of remedial action in 1990 12. Human-health based risk assessment. all input and output sheets must be submitted, including the risk calculations If the GSI ASTM RBCA is used, the following pathways must be evaluated. soil volatilizing to indoor and outdoor air, groundwater volatilization to indoor and outdoor air, soil leaching to groundwater In addition, if the 95% UCL is not used,justification must be submitted for using a lower UCL. Include. output tables; input tables; RBSL or SSTL results, baseline risk summary table; slope factors and MCLS; and COC concentrations. A risk assessment and fate and transport model were prepared as part of the FS/RAP ( Dames & Moore, 1988) Results indicated that downgradtent wells would not be impacted until after 200 years A cleanup level of 10,000 mg/kg was developed based on the transport of naphthalene,and the calculated exposure risk. Excavation and treatment of soil, combined with capping the site, was assessed to provide adequate protection to human exposure I An additional fate and transport model was run using VLEACH as part of the first closure request (Dames & Moore, 1994a) Naphthalene was selected as the most toxic compound associated with the TPH soil impacts Results of the modeling indicated that, given stable groundwater levels deeper than 35 feet bgs, naphthalene concentrations resulting from soil leaching would be below the naphthalene MCL A groundwater level of 35 feet bgs maintained over 25 years would theoretically result in naphthalene concentrations above the MCL However,naphthalene has not been detected in groundwater 13. Stratigraphic cross-sections shall depict- location and screened intervals of wells, and/or verification/confirmation borings with sample locations and concentrations. Lithologic cross-sections were constructed based on the results of soil borings and monitoring well installations Figures 5 through 6 present geologic cross-sections, including location and screened intervals of wells, and soil borings with sample locations and concentrations 14. If verification/confirmation borings were not advanced, the original data must be depicted on the cross-sections. Verification/confirmation borings were advanced as part of the soil remedtation, and data are depicted on the in Figures 9 through 14 15. Rising water levels may have influenced the ability of the momtoring network to assess contaminant migration. As stated in the PHS-EHD letter dated August 3, 1998, groundwater monitoring well screens have been submerged due to rising groundwater elevations The ability of the monitoring well network to accurately asses contaminant migration was questioned In order to address this issue, two monitoring wells were installed in 1998, and the screens were placed so as to allow for sampling from the water table interface The well locations were selected adjacent to existing monitoring wells on the downgradient margin of the K 1840191afp\afp_c1osure_rpt doc 07/31/01 3 24 PM