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No Further Action Request • Section 10 Former American Forest Products Facility 2/16/2006 URS Project No 17322736 Page 1-2 County Public Health Service, Environmental Health Division (SJCPHS-EHD) approved the work plan in a letter dated April 15, 2002, with the following conditions • Groundwater should be sampled from a permeable zone below 80 feet below ground surface (bgs) representing historic low groundwater levels in order to define the vertical extent of groundwater contamination, and • Monitoring well samples would potentially be required to demonstrate stability of the 1,2- DCA plume and decreasing concentrations with time The following conclusions were drawn from the 2002 1,2-DCA investigation (URS, 2002a), based on six samples collected from five direct-push sampling locations • The lateral distribution of 1,2-DCA was limited to a small area (approximately 60-foot radius) in the vicinity of the northeast corner of the former maintenance facility building • Concentrations of 1,2-DCA decline with depth • Detections of tetrachloroethene (PCE) (not previously reported in site groundwater samples) were limited to the northern perimeter of the site and are apparently unrelated to the source of the 1,2-DCA Due to site conditions limiting direct-push penetration, the maximum sampling depth was 65 feet bgs While the data collected provided good lateral delineation of the extent of 1,2-DCA groundwater impacts, data demonstrating the stability of the 1,2-DCA contaminant, its occurrence within the zone of historic low groundwater levels, and variations in its concentration with time were incomplete These data gaps were identified in a letter from the SJCPHS-EHD commenting on the 2002 1,2-DCA investigation (SJPHS-EHD, 2003) A follow-up work plan (URS, 2003) was prepared to collect data demonstrating the stability of the 1,2- DCA contaminant plume, its occurrence within the zone of historic low groundwater levels, and variations in its concentration with time As directed by that work plan, URS installed two additional groundwater monitoring wells, DMW-8 and DMW-9, downgradient of the source area, sampling of these wells began with the first quarter 2004 URS presented the investigation results in February 2005 (URS, 2005a) and incorporated a closure request in the Third And Fourth Quarter 2004 Groundwater Monitoring Report (URS, 2005b) Data presented in those reports showed that concentrations of 1,2-DCA in downgradient well DMW-9 had varied between 10 micrograms per liter (µg/L) and 31 µg/L during the four rounds of quarterly sampling since the well had been installed Based on the sporadic, low detections of total petroleum hydrocarbons (TPH), the low concentrations of 1,2-DCA, and the declining or level trend in 1,2-DCA concentrations after four quarters of sampling from monitoring wells DMW-8 and DMW-9, URS recommended the site be considered for closure (URS, 2005b) In its comments on the investigation report and closure request , SJPHS-EHD agreed that concentrations of total petroleum hydrocarbons as diesel (TPH-D) had decreased to below detection in all wells, but disagreed with URS' request for site closure based on the downgradient detections of 1,2-DCA (SJPHS- ED, 2005) The SJPHS-EID comment letter dated May 5, 2005, (Appendix A) required that a work plan be prepared to further assess the downgradient extent of the 1,2-DCA, and further directed satisfactory completion of a survey of existing water supply wells within a 2,000-foot radius of the site E VPro1ectslURS\AFP\2005 DCA InvestigationlHP Investigation ReportlAFP 2005 Report WP-TE-Rev02 doe