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CLOSURE REQUEST REPORT Section No 3 0 Former American Forest Products Company 07/31/01 2801 West Lane Page 3-6 Stockton,California i TPHd has been reported in groundwater samples at a maximum concentration of 440 micrograms per liter (ltg/L) (DMW-6, 1115/00) Positive identification of diesel has been Iimited to samples collected at DMW-6, based on laboratory comparison with diesel standard chromatograms Unknown hydrocarbon has been reported sporadically at all seven monitoring wells at concentrations up to 780 µg/]L Analytical laboratories have attributed the unknown hydrocarbon to weathered diesel, primarily for samples from DMW-7 and DMW-6 At other wells, the detections of unknown hydrocarbon have been attributed to naturally-occurring organic compounds In order to investigate the nature of the unknown hydrocarbon, a split sample from DMW-3 was analyzed in November 1999 using the silica gel cleanup method, which can eliminate non-petroleum hydrocarbons The original sample from DMW-3 analyzed with EPA Method 8015M without the silica gel cleanup had a reported concentration of 170 pg/L No hydrocarbons were reported in the same sample analyzed with the silica gel cleanup method, suggesting that a significant portion of the hydrocarbons reported in groundwater at the site may be derived from naturally-occurring hydrocarbons, unrelated to the TPHd impacts The effects of well screen depths have been assessed using two sets of well clusters DMW4/DMW-7, and DMW-5/DMW-6 The new wells were installed immediately adjacent to the corresponding wells to allow for the collection of groundwater samples from the water table interface, and from the depths below the water table surface The sampling was required due to rising water levels that submerged the well screens in the original wells Comparison of results for the clustered wells suggests that samples . collected from below the water-table interface have lower TPH concentrations, indicating that groundwater impacts are concentrated at the interface, and that dissolved TPH impacts are minimal Monitoring wells DMW-6 and DMW-7 were installed near the centers of the soil impacts Therefore, TPHd concentrations would be expected to be highest at these wells Analytical data from these two wells indicates that diesel (primarily weathered) is present in groundwater collected at the water-table interface TPH is consistently detected, but concentrations are variable and range from 74 }tg/L to 780 lam Groundwater monitoring for TPHd has not indicated the presence of a well-defined plume that can be consistently mapped between sampling events Time-series graphs presenting concentrations of TPHd over time for site monitoring wells are included in Appendix B These graphs were prepared to evaluate temporal trends in the TPHd concentrations Increasing or decreasing TPHd concentrations correlating to rising groundwater levels are not apparent The single TPH detection prior to 1998 was reported at DMW4 in 1995 (180 pg/L) The highest TPH concentration reported at DMW-4 after 1998 is 190 Lig/L, indicating that an increase in groundwater TPH concentrations due to rising groundwater levels is not apparent In addition to TPHd, groundwater samples have also been analyzed for TPHg, BTEX, VOCs, SVOCs, and fuel additives Results indicate that groundwater has not been impacted by TPHg, BTEX, or SVOCs VOCs detected are limited to 1,2-DCA, carbon tetrachloride, and chloroform Repeated analysis for 1,2- DCA indicates that it is only present in a localized area centered at DMW-5 and DMW-6, and extending to DMW-2 Groundwater samples were collected and analyzed for fuel additives in August and November 2000 Fuel additives included ethanol, methanol, t-butanol, 1,2-DCA, tert-amyl methyl ether, tert-butyl ethyl ether, isopropyl ether,and methyl tert-butyl ether The only fuel additive detected was 1,2-DCA K 18401%fp`afp_closure_rpt doc