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FORMER AMERICAN FOREST PRODUCTS FACILITY f Section No.4.0 + Additional 1,2-DCA Investigation and Site Conceptual Model February 2005 4 And Second Quarter 2004 Quarterly Monitoring Report Page 4-2 The plots of water-level elevations versus time show a response to cycles of wet and dry years. Water levels rose approximately 30 feet between the early 1990s and 1998. Since 1999, the trend has reversed, and water levels have declined approximately 15 feet. Second quarter 2004 water level measurements i (dune 14) show that water levels lie approximately 46 to 47 feet bgs, and that the groundwater gradient is f ` to the north at approximately 0.10 foot per foot. A comparison of water-level data for the two deeper wells, DMW-7 and DMW-8, screened to depths of 109.5 and 90 feet bgs, respectively, to the remaining ! wells that are screened to depths of 60 to 70 feet bgs, shows no significant difference. Thus,there appears ` to be a negligible vertical gradient within the shallow groundwater zone penetrated by the site wells. 43 GROUNDWATER ANALYTICAL RESULTS i A historical summary of analytical results for groundwater samples collected through June (second quarter) 2004 is included in Table 3. Results for PCE and 1,2-DCA are also presented on Figure 5. Isoconcentration contours of 1,2-DCA are presented in Figure 6. 17, 4.3.1. TPH-D TPH-D was not reported in samples from any wells for the second quarter of 2004. Unknown hydrocarbon (UH), was identified in the groundwater sample collected from one well, DMW-6, at a concentration of 61 micrograms per liter(µglL). The UH is interpreted as weathered diesel. 4.3.2 Volatiles and Oxygenates by EPA Method 8260B 1 1,2-DCA was reported in samples collected from DMW-2 (2.8 µg/L), DMW-3 (160 µg/L), DMW-6 (27 µg/L), and DMW-9 (10 µg/L). These results are either lower or within the range of previously reported results for the respective wells. Chloroform was reported only in the sample collected from -� DMW-1 1.5 ° ( µg/L), which is lower than for any previous quarter. PCE was reported in the sample , collected from one well,DMW-9, at a concentration of 9.0µglL. [ ,�. M t> � 4.3.3 Lateral Distribution of 1,2-DCA with Time Isoconcentration contours of 1,2-DCA for four quarters from September 2003 through June 2004, are presented in Figure 6. These figures show a limited lateral distribution of low concentrations of 1,2-DCA in groundwater. The concentrations of 1,2-DCA during the period range downward from 31 µg/L, within a plume with a radius of 60 feet or less. ' t. f KAWprocess\22736\American Forest\Well Installation Report revOl.doe 14