SITE INFORMATION AND CORRESPONDENCE

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i 1 Mr. Maurice Benson - 2 - 25 November 2008 Defense Logistics Agency In 1993, soil samples were collected from three borings within the UST excavation area. The highest concentration of TPH in the diesel range detected by laboratory analysis was 18,200 mg/kg. BTEX concentrations were also detected. In addition, laboratory analysis of a groundwater sample collected by HydroPunch detected TPH in the diesel range at a concentration of 478,000 micrograms per liter (µg/L). This sample was collected approximately 25 feet northeast of the former UST location, in the downgradient groundwater flow direction. No other groundwater samples were collected during this event. In 1998, soil samples were collected from six borings south, east, and north of the former tank excavation. The highest concentration of TPH in the diesel range detected by laboratory analysis was 17,000 mg/kg. Ethylbenzene and total xylenes concentrations were also detected. Nine HydroPunch groundwater samples were collected. Laboratory chemical analyses detected TPH in the diesel range at concentrations up to 650,000 µg/L. That result was obtained from a shallow sample collected approximately 50 feet northeast of the former UST location. DDJC submitted the Draft UST Program Preferred Alternatives Report in May 2002. That report recommended remedial alternatives for the USTs at the DDJC Site, including UST 25. Continued groundwater monitoring was recommended for UST 25. In a review letter dated 18 September 2002, the Regional Water Board made the following comment on Section 5.11.7 of the draft report: The extent of the UST Site 25 groundwater plume is not defined north (downgradient) of Building 255, but this section proposes installation of only one monitoring well in this area. It is unclear whether one monitoring well is adequate for monitoring the downgradient edge of this plume. This section should recommend a limited CPT investigation to: 1) define the extent of the plume, 2) determine the number of downgradient wells needed to monitor the plume, and 3) optimize placement of the monitoring wells. DDJC prepared their response to the Regional Water Board comment after they conducted an additional sampling event in 2003. The DDJC response to comment is presented below: The additional investigation at UST Site 25 collected two downgradient groundwater samples to fully delineate the extent of the plume. That event included the collection of shallow HydroPunch groundwater samples approximately 40 feet to 220 feet downgradient of the former UST location. Also, soil samples were collected from one boring at the northeast corner of the former UST excavation. The results of laboratory chemical analyses on the soil and groundwater samples were presented in the October 2003 Final UST Program Preferred Alternatives Report. However, groundwater monitoring wells were not proposed or recommended.