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1 5 0 CONCLUSIONS This report has presented the history, corrective action investigations, soil remediation and groundwater monitoring results from the former American Forest Products facility in Stockton, California Leaking underground storage tanks in the vicinity of the maintenance shop impacted soils with diesel fuel Early corrective action investigations included a preliminary site assessment and a soil and water investigation which were completed in 1985 and 1987, respectively Supplemental investigations in 1988 defined the lateral and vertical extent of the impacted soils A Feasibility Study/Remedial Action Plan for the site was reviewed by the San Joaquin PHS-EHD and the RWQCB This plan called for excavation and on-site treatment of soils with TPH/D concentrations exceeding 10,000 mg/kg The RWQCB requested a work plan for soil remediation and installation and sampling of four additional monitoring wells Dames & Moore submitted a work plan as requested in April 1990 The work plan was implemented in June 1990, and all soils above the target concentration were excavated and treated on-site After confirmational sampling was completed, the excavation was backfilled with clean soils, and repaved Impacted soils were treated on-site by bioremediation to reduce TPHID concentrations Following approximately five months, the 3,100 tons of excavated soil was disposed in a Class If landfill in December 1990 In January 1991, the San Joaquin PHS-EHD requested the removal of product lines associated with the 10,000-gallon UST A work plan was accepted in May 1991, and the removal and disposal of the underground pipe and pump island began in June 1991 After the pipe was removed, approximately 160 cubic yards of TPH/D-impacted soil was excavated, treated and disposed at Port Costa Materials, Inc After approximately 160 cubic yards of excavated soil was classified, soils at the floor of the excavation were resampled and found to contain less than 10 mg/kg TPH/D The excavation was backfilled with clean fill material and was repaved in August 1991 Groundwater monitoring has been conducted at the site since July 1987, when JHKA installed three monitoring wells, and sampled for TPH/D and volatile organic (BTXE) parameters in water samples Due to a large drop in groundwater level, four additional wells were installed and the three JHKA wells were abandoned From July 1987 to July 1991, groundwater gradients have been relatively flat (0 0015 to 00 019 linear feet/foot) and groundwater flow is in the north/northwest direction Since the initiation of groundwater sampling and analysis, no detection of volatile, semzvolatile, or other Ihydrocarbon constituent has been detected in any well downgradient of the impacted soils or USTs Given the corrective actions taken for soils, and the lack of impact to groundwater, American Forest Products Company requests closure of this site 5AC36 046 22