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FORMER AMERICAN FOREST PRODUCTS FACILITY Section No. 1.0 Additional 1,2-DCA Investigation and Site Conceptual Model February 2005 And Second Quarter 2004 Quarterly Monitoring Report Page 1-2 Y L - Health Service, Environmental Health Division (SJCPHS-EHD) in their letter of April 15, 2002, which included 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 wells would potentially be required to demonstrate stability of the 1,2-DCA plume and decreasing concentrations with time. The 2002 work plan also provided for a cessation of quarterly groundwater monitoring while the results of the investigation were evaluated. The report of the 1,2-DCA investigation (URS,2002b)showed,based on six samples collected from five direct-push sampling locations,that: • The lateral distribution of 1,2-DCA was limited to a small area (approximately 60-foot AW radius)in the vicinity of the northeast comer of the former maintenance facility building; • Concentrations of 1,2-DCA decline with depth;and }� . 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 same source as the PCE. bp However, due to site conditions limiting direct-push penetration, the maximum sampling depth was (� limited to 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 IF incomplete. These data gaps were identified in a letter from the SJCPHS-EHD commenting on the 2002 1,2-DCA investigation (SJPHS-EHD, 2003). t 1.2 PURPOSE AND SCOPE The purpose of the work described in this report was to provide data demonstrating limited extent and stability of groundwater contaminants as a basis for site closure. The scope of work included reinstitution of quarterly groundwater monitoring and the installation of two additional wells.Lithologic and analytical data obtained from this new work have been used to update the site conceptual model, which includes a lithologic cross-section, groundwater elevation contour maps and flow direction, plots of groundwater elevation versus time, and isoconcentration maps. 1.3 REPORT FORMAT This report consists of six sections and four appendices. Section I summarizes site background { information and states the purpose and scope of this report. The scope and procedures of field activities L are described in Section 2.0. Section 3.0 reports the soil analytical results, and Section 4.0 presents the site conceptual model. Conclusions and recommendations are provided in Section 5.0, and references are i listed in Section 6.0. L Boring logs and well completion diagrams for DMW-8 and DMW-9, installed in March 2004, are f ..� included in Appendix A. Appendix B includes field documentation for water samples collected during the L * K:%Wprocess12273ri American Forest\Weil Installation Report revOI Am