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CLOSURE REQUEST REPORT Section No 4 0 Former American Forest Products Company 07/31/01 2801 West Lane Page 4-2 Stockton,California Tabulated soil analytical results are presented in Table 3 Groundwater analytical results for the site are presented in Tables 4, 5 and 6 Groundwater analyses include the March 2001 confirmation round of sampling 8. Concentration contours of contaminants found and those remaimng in soil and groundwater, both on and off site, including: lateral extent of soil contamination; vertical extent of soil contamination; lateral extent of groundwater contamination; and vertical extent of groundwater contamination. The lateral and vertical extent of residual soil impacts are presented in Figures 9 through 14 The lateral extent of TPH impacts in groundwater for the most recent sampling events during November 2000 and March 2001 are presented in Figures 15 and 16 Groundwater data from clustered wells suggests that the TPH impacts are concentrated at the water-table interface, and deeper, dissolved impacts are limited 9 Zone of influence calculated and assumptions used for the subsurface remediation system and the zone of capture attained for the soil and groundwater remediation systems. No active remediation system was constructed at the site 10 Reports/information including unauthorized release report, quarterly monitoring reports; problem assessment report; final remediation plan, well and borings logs; and other. An unauthorized release report does not appear to have been filed Section 6 0 presents a summary of important documentation regarding site investigation, feasibility studies, remedial action, and groundwater monitoring These documents have been submitted to the RWQCB, and to the PHS-EHD 11. Best Available Technology (BAT) used or an explanation for not using BAT. The technology used to remediate impacts at the site was excavation and removal of the fuel tanks, combined with the excavation and treatment of soil, and capping of the site using asphalt Remaining impacts to soil and groundwater appear to be undergoing passive biodegradation, as documented by the presence of weathered diesel in groundwater samples Detailed evaluations of remedial alternatives were presented in the FS/RAP (Dames & Moore, 1988), and the Technical Evaluation (Dames & Moore, 1994c) 12. Reasons why background was/is unattainable using BAT. The site remediation plan implemented in 1990 included the excavation and removal of soil with TPHd impacts greater than 10,000 mg/kg The approach implied leaving residual impacts below 10,000 mg/kg in place, and allowing natural degradation to continue, combined with surface capping to limit infiltration and leaching Background concentrations below detection limits may be obtainable using passive biodegradation over an extended period of time Enhanced biodegradation was considered in the Technical Evaluation, but reduction of TPH to concentrations below 500 to 1000 mg/kg in a short timeframe using this method was considered unlikely 13. Mass balance calculation of the substance treated versus that remaimng. A mass balance calculation has been performed using existing soil and groundwater data, and is included in Section 2 4 and Appendix C K 1840191afp1afp_ciosure_rpt doc