SITE INFORMATION AND CORRESPONDENCE

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Mr. Sam Chamberlain - 2 - • 14 June 2006 Groundwater Flow The groundwater flow direction at the Pioneer site within the Upper and Middle Horizons has been toward the northeast, as shown by the flow maps presented in the Semi-Annual Monitoring Report. The groundwater flow direction at the DDJC-Tracy site in these horizons has also been toward the northeast as shown by the Upper Hydrologic Zone flow maps in Figures 5.3-1A and 5.3-1 B, pages 5-41 and 5-42 of the DDJC-Tracy 2005 Annual Monitoring Report. The groundwater flow direction at the Pioneer site within the Lower Horizon has not been defined because only one well is screened within this horizon. However, the groundwater flow direction within this horizon has been established by DDJC-Tracy, as shown by the Middle Hydrologic Zone maps in Figures 5.3-2A and 5.3-213, pages 5-43 and 5-44 of the DDJC-Tracy 2005 Annual Monitoring Report. These maps show flow across the Pioneer site has been toward the north. Apparently, groundwater extraction within the Middle Hydrologic Zone (Pioneer's Lower Horizon) at the DDJC-Tracy site has established a capture zone that locally influences groundwater flow direction. During periods of pumping of extraction wells EW024B and EW025B at DDJC-Tracy, the natural northeast direction of flow beneath the Pioneer site is diverted towards the north. Extent of Carbon Tetrachloride in Groundwater The lateral extent of carbon tetrachloride (CTCL) migration in the Upper Horizon and possibly the Middle Horizon appears to have been defined at the Pioneer site. The CTCL plume emanates from the Pioneer site and has migrated towards the northeast. For the most part, CTCL at DDJC-Tracy does not occur in these horizons (DDJC-Tracy's Upper Hydrologic Zone). The lateral extent of CTCL in the Lower Horizon is not currently monitored by the Pioneer well network. Well MW-15 is the only well screened in this Horizon and it is located northeast of the Pioneer site. DDJC-Tracy assessment and remediation activities have identified the presence of carbon tetrachloride (CTCL) in this Horizon. The Maps in Figures 4.'-JA, 4.3-713, and 4.3-7C, pages 4-44, 4-45, and 4-46 of the DDJC-Tracy 2005 Annual Monitoring Report present the distribution of CTCL detected in monitoring wells, extraction wells, and private wells between the 4th quarter of 2004 and the 3rd quarter of 2005. Almost all of the detections of CTCL have occurred in the wells completed within the DDJC-Tracy site Middle Hydrologic Zone (Pioneer's Lower Horizon). Also, these detections were in wells located north of the Pioneer site. A source for the CTCL has not been found on the DDJC- Tracy site. However, the Pioneer site to the south of the CTCL detections could be a source. The CPT investigations performed by Secor in 1999 and 2000 acknowledged that CTCL had migrated north — northeast in the Lower Horizon. In fact, the Secor Groundwater Investigation Report, dated April 2001 documents CTCL in the Lower Horizon approximately 4,000 feet north — northeast of the Pioneer site on November 16, 2000. Figure 9-1 of the Secor April 2001 report incorrectly shows that CTCL was not reported by the laboratory at boring location CPT-C. However, the laboratory reported CTCL at 0.5 micrograms per liter in that well. Two other CPT borings drilled west and southwest of CPT-C showed that CTCL was not present at or above the reporting limit at those times and places. That was