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groundwater sample collected from MW-3 (i.e., adjacent to Vault 8), was analyzed for total soluble chromium, sodium and calcium, hexavalent chromium, and chlorides. All constituents were detected, but were below the California Maximum Contaminant Level(MCL)or below the EPA secondary MCL(aesthetic) established at that time with the exception of total chromium (0.10 milligrams per liter [mg/L]) and hexavalent chromium (0.11 mg/L). It should be noted that neither an established MCL nor Action Level for hexavalent chromium had been established at that time. To validate the January 1991 chromium results in MW-3, Weiss collected a round of verification groundwater samples in August 1991. Water samples were collected from monitoring well MW-3 and from two of four municipal water supply wells located at the corners of the facility (WP-1 and WP-2). All three samples were analyzed for total and hexavalent chromium, and the results indicated both municipal wells were below method detection limits for total chromium and hexavalent chromium. However, total and hexavalent chromium were detected in the water samples collected from well MW-3, both at a concentration of 0.7 mg/L. In October 1993, RESNA Industries Inc. (RESNA) was retained to evaluate the extent of total and hexavalent chromium in soil in the vicinity of former Vault 8. Two soil borings, SB1 and SB2,were advanced north of the former Vault 8. The laboratory analytical results of soil samples obtained during this investigation indicated that soil impacts were limited to the area occupied by former Vault 8 and encompassed an area of approximately 450 square feet. Based on the results of this investigation, it was concluded that total chromium and hexavalent chromium in soil impacts extends from directly beneath the former vault to the water table (RESNA, 1994). In November 2001 and January 2002, ATC Associates Inc. (now Atlas) advanced nine soil borings (SB1 through SB9) at various locations on and adjacent to the site. Low levels of hexavalent chromium were detected in soil and groundwater samples collected during the investigation. The highest concentrations of hexavalent chromium in soil were detected in the samples obtained from off-site boring SB9, installed within East Worth Street, immediately north of the property boundary. Hexavalent chromium was detected in grab groundwater samples obtained from borings SB1, SB2, SB3, SB4, SB5, and SB9 at concentrations ranging from 0.0005 to 0.0051 mg/L. The laboratory-reported concentrations of total chromium were below the California Primary MCL of 0.05 mg/L. In addition, the concentrations of total chromium detected in these groundwater samples were well below concentrations previously detected in monitoring well MW-3, which historically contained the highest concentrations of total chromium in groundwater at the site (ATC, 2002a). In September and October 2002,cone penetration testing(CPT)borings CPT1 and CPT2, Geoprobe(direct push) borings CPT1 a and CPT2a, and groundwater monitoring wells MW-4 through MW-8 were installed at the site. CPT1 and CPT2 borings were advanced to 120 and 139 feet bgs, respectively, to provide continuous stratigraphic definition in the borings. Discrete groundwater samples were collected from CPT1a and CPT2a at depths of 109 and 114 feet bgs, respectively. Groundwater monitoring wells MW-4 through MW-8 were installed to total depths of approximately 65 feet bgs and constructed with screened intervals extending from approximately 45 to 65 feet bgs (MW-4, MW-5, and MW-6) or 50 to 65 feet bgs (MW-7 and MW-8). Hexavalent chromium was not detected in the soil samples collected during the installation of groundwater monitoring wells MW-4 through MW-8. Hexavalent chromium was detected in discrete groundwater samples collected from borings CPT1a and CPT2a at concentrations of 0.170 and 0.012 mg/L, respectively. It should be noted that these discrete groundwater samples were obtained from the deeper water-bearing zone at depths of 109 and 114 feet bgs, respectively. Total chromium was detected in the water samples collected from all the wells, including the facility supply well, with the maximum concentration (6.2 mg/L) observed in the groundwater sample collected from monitoring well MW-3. The discrete groundwater samples collected from CPT1a and CPT2a were not analyzed for total chromium (ATC, 2002b). On April 29 and 30, 2003,ATC supervised the advancement and construction of deep monitoring well MW- 9. The soil boring for MW-9 was advanced to approximately 113 feet bgs, and the well was completed with a screen interval extending from approximately 103 to 113 feet bgs. This groundwater monitoring well was 2 1 P a g e