ARCHIVED REPORTS_SITE CONCEPTUAL MODEL 2009

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amec�9 highest in shallow groundwater (with the highest TCE concentration at approximately 56 feet bgs (6,000 pg/L). TCE concentrations were much lower at greater depths (31 pg/L at 74 feet bgs; 6 —210 pg/L between approximately 88 and 186 feet bgs). Chloroform and 1,1-DCA were detected at concentrations of 90 and 40 pg/L, respectively, in the sample from 99 feet bgs. Cis-1,2-dichloroethene was reported at a maximum concentration of 30 pg/L in the sample from M-25C2 (approximately 176 — 186 feet bgs). Vinyl chloride was not detected in any of these groundwater samples. 3.4.2 Spatial Distribution of TCE in Site Groundwater B-zone The water table (B-zone) has been impacted by TCE near the former Decaffeination Building. During early investigations, TCE concentrations in samples from onsite B-zone monitoring wells (M-1 B and M-4, near the location of N-1) were less than 10 pg/L; greater concentrations were reported in samples from monitoring well M-313, approximately 100 feet southwest of the TCE storage tank area (up to 73 pg/L). In October 1987, groundwater samples were collected from B-zone vapor extraction wells near the former decaffeination and TCE storage tank areas (VE-1, VE-2, VE-3, and VE-4); the sample from VE-4 was reported to contain the highest TCE concentration (2,140 pg/L); although subsequent samples collected from this well were lower (378 pg/L in January 1994). Of the ten B-zone groundwater samples collected by Geomatrix in 2005, only one was reported to contain TCE at concentrations greater than 1,000 pg/L (at CPT-14, from a depth of approximately 40 feet bgs, approximately 30 feet north of M-1 B; Figure 7). TCE concentrations at M-1 B have been increasing since the 1990's, as illustrated by the May 2005 TCE concentration of 590 pg/L (Appendix C). This suggests that the highest TCE concentrations (210 — 2,500 pg/L) in the B-zone generally are located in the area between N-1, CPT-3 (approximately 150 feet south of N-1; Figure 7), and CPT-2 (approximately 70 feet east of CPT-3). Upper A-zone Seven Upper A-zone groundwater samples were reported to contain TCE concentrations greater than 1,000 pg/L. These sample locations lie within a triangular area approximately bounded by former supply wells N-3 and N-4, CPT-16 (near Industrial Avenue, approximately 200 feet west of N-4), and former supply well N-1 (approximately 200 feet north of CPT-16; Figure 8). The greatest TCE concentrations reported were 6,600 pg/L, 7,700 pg/L, and 7,800 pg/L from depths ranging from approximately 53 to 55 feet bgs at locations CPT-17, CPT-3, and CPT-2, respectively. These locations are no farther than 80 feet apart, and are directly beneath the former Boiler Room (CPT-17) or less than 40 feet north of it (CPT-2 and CPT-3). Concentrations of TCE for Upper A-zone samples from CPT-9 and CPT-10, AMEC Geomatrix, Inc. I:\Doc_Safe\9000s\9837.005\4000 REGULATORY\SCM_01.30.09\1_text\SCM Report Final.doc 19