SITE INFORMATION AND CORRESPONDENCE

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Mr. Joe Hofbauer • - 2 - Y • 2 February 20071 Pioneer Americas LLC wells as the preferred remedial option for the Facility. Implementation of MNA included installation of seven additional groundwater monitoring wells down-gradient of the Facility. Wellhead treatment of the two water supply wells was not initiated because laboratory chemical analyses of water samples from the Reed well have not reported contaminants of concern and water from the Pombo well was not being used. However, as of early 2005, water from the Pombo well is again being used. In lieu of providing wellhead-treatment, Pioneer has been supplying the Pombo residence with drinking water through a private contractor. The Regional Water Board issued a draft MRP on 20 May 2005 for the Facility. Pioneer responded to the draft MRP by providing comments in a letter prepared by Secor, dated 17 June 2005. Also on 20 May 2005, the Regional Water Board directed Pioneer to complete a draft Cleanup Plan. In June 2006, following completion of the down-gradient monitoring wells and collection of approximately four years of monitoring and sampling data by Pioneer, Regional Water Board staff conducted a thorough review of the Facility groundwater monitoring data. This included the down-gradient water quality data collected by Pioneer subsequent to approval of the September 2001 Feasibility Study. In a letter dated 14 June 2006, the Regional Water Board concluded that the groundwater monitoring well network did not adequately monitor the Lower Horizon beneath the Facility. The Lower Horizon has been defined by Pioneer as an interval below 60 feet below ground surface (bgs). In the 14 June letter, Regional Board directed Pioneer to submit a work plan for monitoring wells to define the extent of the Lower Horizon plume of carbon tetrachloride (CTCL). This is the horizon in which the Defense Agency has reported CTCL in its groundwater monitoring wells to the north of the Facility. Only one Pioneer groundwater monitoring well is currently screened in the Lower Horizon. On 30 June 2006, Pioneer submitted a Draft Cleanup Plan, prepared by Secor. The Draft Cleanup Plan summarized activities associated with the release of volatile organic compounds, and the extent of primary contaminants of concern (COCs) in soil and groundwater. The primary COCs at the site are CTCL and chloroform. Also, the Draft Cleanup Plan evaluated remedial alternatives and proposed MNA as the alternative of choice. Groundwater Monitoring and Reporting Program 1 . Pioneer proposed to include Defense Logistics Agency monitoring wells LM177B and LM 151 B to establish the extent of CTCL contamination and groundwater flow direction in the Lower Horizon. These wells have been included in Pioneer's final Monitoring and Reporting Program. 2. The Pioneer proposal to add its water supply well AP-2 to the MRP could assist in establishing the extent of CTCL and chloroform contamination, and groundwater flow direction in the Lower Horizon. This well is included in the revised MRP. However, if the following procedures are not practical or possible, this well may not be adequate or acceptable for groundwater monitoring: the well should not be used for water