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CvvATC • A S S O C I A T E S i y C These vaults were located along the eastern side of the property adjacent to large walnut storage bins (Figure 2) Vaults 7 and 8 were constructed with poured concrete and lined with fiberglass and asphalt, and were used to store calcium chloride and sodium dichromate clull 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 buildung (Figure 2) All of the vaults were taken out of service and cleaned in June 1990 (Weiss Associates, April 1991) WA of Emeryville, Cahforrua conducted several phases of subsurface soil and groundwater investigation activities at the subject property since December 1988 In January 1991,three groundwater 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 mnumum of 56 feet and at a maximum of 89 feet below grade surface (bgs) On January 31, 1991, 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 GCX]D for ethylene and propylene glycol The water sample collected from MW-3, adjacent to Vault 8, was analyzed for total soluble chrornium, sodium and calcium (EPA method 6010), CrVI (EPA method 7196), and chlorides (EPA method 325 2) All constituents were detected below the California Maximum Contaminant Level (MCL) or below the EPA secondary standard (aesthetic) with the exception of total chromium (0 10 milligrams per liter [mgll]) and CrVI(0 11 mg/1)in well MW-3 In order to assess the vandity of the MW-3 results for chromium species, a verification round of sampling was performed in August of 1991 by WA Water samples were collected from monitoring well MW-3 and Stockton City supply wells WP-1 and WP-2 Each sample was analyzed for total chromium and CrVI by Clayton Environmental Consultants The results indicated samples collected from both City wells were below method detection hrmts for total chromium (0 05 mg/l) and CrVI (0 01 mg/1) However, total chromium and CrVI were detected in the water samples collected from MW-3 In October 1993, RESNA Industries Inc (RESNA) attempted to evaluate the extent of chronuum and CrVI 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 advanced nine soil borings Low concentrations of CrVI were detected in soil and groundwater samples collected during the investigation The highest concentrations of CrVI in soil were detected in the samples collected from off-site boring SB9 CrVI concentrations at this location were well below the concentrations previously detected in soil boring 138-A, which was advanced beneath Vault 8 CrVI was detected in groundwater at low concentrations in the samples collected from borings SBI, SB2, SB3, SB4, SB5, and SB9 Concentrations ranged from 0 5 to 5 1 micrograms per liter (ug/1) The reported concentrations were below the MCL for total chromium of 50 ug/l and well below concentrations detected m samples collected from monitoring, well MW-3, which have historically contained the lughest concentrations detected at the site These findings s lenvvonmental1625831reports\RevisedWKP-Bench test.doc 2 I