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N1. v kTC A S S O C I A T E S I N C . FVaults 1 and 5 had 1,200-gallon capacities and Vault 6 had a 500-gallon g capacity. These vaults were located along the eastern side of the property adjacent to large walnut storage bins (Figure 2). Vaults 7 and 8, which were constructed with poured concrete and lined with fiberglass and asphalt, E F contained calcium chloride and sodium dichromate chill water solution. Vaults 7 and 8 had 3,000 and 5,000-gallon capacities, respectively, and were located against the north wall of the processing F" building (Figure 2). All of the vaults were taken out of service and cleaned inn Ju e 1990 (Weiss Associates, April 1991). FSeveral phases of subsurface soil and groundwater investigation have been conducted at the subject property since December 1988. This work was performed by Weiss Associates (WA) of Emeryville, California. In January1991 three groundwater gr water monitoring wells were constructed to monitor the first encountered saturated zone, which was encountered at a depth of approximately 71 feet below grade in each boring. The wells were screened at a minimum of 56 feet and at a maximum of 89 feet below grade surface (bgs). On January 31, 1991, Weiss Associates (WA) personnel collected groundwater samples from each well. Samples collected from monitoring wells MW-1 and MW-2 (adjacent to Vaults 1 and 6, respectively) were analyzed by GC/F D for ethylene and propylene glycol. The water sample collected from MW-3, adjacent to Vault 8, was analyzed for total soluble chromium, sodium and calcium (EPA method 6010), hexavalent chromium (EPA method 7196), and chlorides (EPA method 325.2). All constituents were detected below the California Maximum F ` Contaminant Level (MCL) or below the EPA secondary standard (aesthetic) with the exception of total chromium (0.10 milligrams per liter [mg/1]) and hexavalent chromium (0.11 mg/1) in well F MW-3. In order to assess the validity of the MW-3 results for chromium species, a verification round of F sampling was performed in August of 1991 by WA. Water samples were collected from monitoring well MW-3 and City wells WP-1 and WP-2. Each sample was analyzed for total and hexavalent chromium by Clayton Environmental Consultants. The results indicated both City wells were below method detection limits for total chromium (0.05 mg/1) and hexavalent chromium (0.01 mg/1). However, total and hexavalent chromium were detected in the water samples collected from j Fwell MW-3. In October 1993, RESNA Industries Inc. (RESNA) attempted to evaluate the extent of chromium and hexavalent chromium in the soil in the vicinity of former Vault 8. Two soil borings, SBI and SB2 were advanced north of the former Vault 8. The results indicated that the soil impact was limited to the area occupied by former Vault 8, encompassing approximately 450 square feet. It was concluded that the soil impact extended directly beneath the former vault to the water table. The findings and results were presented in RESNA's report titled Additional Soil Assessment Report and Fourth Quarter Monitoring Report, Underground Storage Vaults, dated January 1994. In November 2001 and January 2002, ATC Associates advanced nine soil borings. 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 wAwordpro1625831reportsldeep well inst.doc 2