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i l FORMER AMERICAN FOREST PRODUCTS FACILITY Section No.5.0 Additional 1,2-DCA Investigation and Site Conceptual Model February 2005 And Second Quarter 2004 Quarterly Monitoring Report Page 5-1 l .ti 5.0 CONCLUSIONS AND RECOMMENDATIONS ' 5.1 CONCLUSIONS i s + Lithologic data from two new groundwater monitoring wells installed in March 2004, i DMW-S and DMW-9, corroborate data collected from previous borings and indicate sediments consisting of interbedded clays, silts, and fine sands. The fine sands are local and , discontinuous. + The groundwater gradient during the dry season is to the north at 0.010 feet per foot. During the rainy season,the groundwater gradient is irregular. + During the last four quarters of sampling, weathered diesel has been identified in five of the nine site wells at a maximum concentration of 2001tgft— + 1,2-DCA has been detected during the last four quarters in four monitoring wells, including DMW-9, the shallower of the two new downgradient wells installed in March 2004. The maximum 1,2-DCA concentration detected in any of these wells during thiU riod was_31 1.tgJI. in DMW-9 (March 2004). By the June 2004 sampling round, the 1,2-DCA concentra- tion in the sample collected from DMW-9 had dropped to 10 gg/L. + PCE was detected only in DMW-9,and not in samples collected from the wells in the vicinity 1, of the site source area, suggesting that this constituent may not originate on site. + Data from two quarters of sampling from the recently installed downgradient wells, DMW-S � and DMW-9, show low concentrations of 1,2-DCA and PCE in DMW-9, the shallower of the two wells. No detections of site constituents were reported for the deeper well, DMW-8, i indicating lack of vertical migration. r r 4 5.2 RECOMMENDATIONS Data from two quarters of groundwater monitoring incorporating the two new downgradient wells show low concentrations of site constituents and a lack of vertical migration. Based on communication with Mr. Jeffrey Wong of the San Joaquin Public Health Service, Environmental Health Division, four quarters of data from those wells showing low concentrations of site constituents that are either stable or declining k could form a basis for a request for No Further Action. Based on the data presented in this report, URS plans to present that request in the Fourth Quarter 2004 Groundwater Monitoring Report, which is in preparation and due to the agencies by February 15,2005. } 444 i i f KAWprocess1227351American ForesAWell Installation Report revol.doc t! M