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installed in order to further assess groundwater quality within the deeper groundwater-bearing interval in the vicinity of CPT1. Hexavalent chromium was detected in the groundwater sample collected from well MW9 at a concentration of 0.0049 mg/L (ATC, 2003). In May 2003, ATC conducted an additional subsurface investigation at the site that included completion of a video log survey of the facility well (FW) located inside the facility building. The well was located within a concrete below-grade vault below a concrete floor. The vault was rectangular and has dimensions of approximately 5-feet by 5-feet by 6-feet deep. The wellhead was mounted flush to the bottom of the vault. The total depth of the facility well borehole was observed to be 133 feet below top of casing. The bottom 25 feet of the borehole was open. Based on observations from the bottom 25 feet of the boring,the borehole diameter was estimated to be 18 to 24 inches. The well casing was constructed of steel pipe with a diameter of approximately 1 foot and extended to a depth of 108 feet from the top of casing. The well was vertically perforated beginning at a depth of 67 feet below top of casing and extended to the bottom of the casing. Diamond Foods indicated that there were no plans to utilize the well;therefore, ATC recommended that the FW be properly destroyed. The construction details of the FW, as observed on the video log, indicate that it appeared to be screened across more than one water-bearing zone and was a potential conduit for migration of groundwater between shallow and deeper groundwater bearing intervals. On October 13, 2004, a geologist from ATC supervised the advancement of two soil borings, SB10 and SB11, to collect soil samples for use in a bench scale test. Soil boring SB10 was advanced at an approximate 35-degree angle from vertical in a southerly direction, beneath the cooling unit. Soil samples were collected at three different depths in order to assess the potential presence of hexavalent chromium. Assuming drilling angles and using trigonometric functions,the soil sampling intervals correspond to vertical depths of approximately 13.6 to 17.3 feet bgs, 23.3 to 27.1 feet bgs, and 33.4 to 37.3 feet bgs, respectively. Soil boring SB11 was advanced vertically in the vicinity of MW-7 to an approximate depth of 39.5 feet bgs and soil samples were collected to further assess the lateral extent of hexavalent chromium impacted soil in the vicinity of MW-7. SB11 is located hydraulically crossgradient with respect to Vault 8 and the cooling unit. Soil samples were collected from SB11 at vertical depth intervals of 15 to 19.5 feet bgs, 25 to 29.5 feet bgs, and 35 to 39.5 feet bgs. The soil samples collected from SB11 were visually inspected to ensure the lithology was similar to that of the samples collected from SB10. The purpose of soil sample collection from S1311 was to provide non-impacted control samples or samples representative of background concentrations for baseline characterization and bench scale testing. The concentrations of hexavalent chromium detected in the soil samples collected from beneath the chiller unit were low and were comparable to the concentrations detected in the soil samples collected from beyond the known extent of hexavalent chromium impacted soil. It was concluded that it was possible that previously impacted soil beneath the cooling unit has been flushed over time by cooling water leaching into the subsurface, resulting in low concentrations of hexavalent chromium in the soil. Due to the production of elevated manganese concentrations, bench scale testing of zero valance nano-scale iron was recommended. This material was shown to reduce hexavalent chromium to trivalent chromium and may have less propensity to produce high manganese concentrations as a secondary affect to groundwater(ATC, 2005a). On August 1, 2005, the facility well (FW)was permanently abandoned. FW was destroyed by using a Mills Knife to perforate the entire length of the well casing. The perforating tool was removed from the well and a cement and sand mixture (10 sack) was pumped into the well under pressure using tremmie pipe that was placed at the bottom of the well and raised as the cement and sand mixture rose to the top of the casing. The vault was filled with the cement and sand mixture to within approximately one foot of the top of the vault (at grade). Approximately 13.5 cubic yards of the cement and sand mixture were pumped into the well and vault(ATC, 2005b). Groundwater monitoring and sampling has been conducted quarterly following the installation of each monitoring well in accordance with MRP R5-2004-0840. In August 2011, ATC requested a reduction in frequency and analyses. The CVRWQCB issued a revised MRP (No. R5-815-2011) which reduced the frequency of groundwater monitoring and sampling from quarterly to semi-annual and reduced the laboratory analytical regime. This sampling schedule has been followed until the present. 3 1 P a g e