SITE INFORMATION AND CORRESPONDENCE_2006-2007

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9� LFR Third, stable to increasing concentrations documented in well CHMW-003A indicate that the Phase I IRA is working as designed and fits within the SCM. This well and others are located at or immediately upgradient from the extraction wells intended to capture affected groundwater at the Pacific Avenue boundary of Lincoln Center. Data at CHMW-003A is from a well located on the Chevron Gas station immediately downgradient from and within the groundwater flow path of the known HSA and is also located less than 35 feet from an active groundwater extraction well. Concentrations at this location have ranged between 360 µg/1 in 1997 to 15,000µg/1 in 2004, and most recently were at 13,000 µg/1 in December 2005 (see T/C graph for well CHMW-003A, attached). The concentrations in this well have been generally increasing with time. The observed increasing trend in this well was expected as the A- and-B zone groundwater extraction system on Pacific Avenue is designed to capture and remediate the higher VOC concentrations migrating (and indeed induced) toward it within the deeper and more permeable sand units known to exist in this area. The extraction system is performing as designed, and is actively remediating the PCE- affected groundwater that migrates toward it. Additionally, as the majority of the higher concentrations within this area are migrating preferentially within more conductive sands, the increasing trend is expected to reverse and begin decreasing in response to the Regional Water Quality Control Board-approved installation of the air/ozone sparging system within the boundaries of the HSA. All of the observations above fit into and lend support to the SCM. Lastly, well location MW-108A is located on the eastern and opposite side of Pacific Avenue from the other locations referenced in FA's letter. LFR and the Trust have discussed the persistent concentrations in this area with Lincoln Center on several occasions and had discussed the option of performing additional investigation and potentially remedial work in that area. This area is located downgradient from and to the east of the A- and B-zone groundwater extraction systems located on the western side of Pacific Avenue, and is interpreted to be located within the stagnation zone of the groundwater extraction system. LFR has recently proposed additional investigation ("Work Plan to Conduct a Focused Membrane Interface Probe Investigation, Lincoln Center, Stockton, California," dated April 27, 2006), which is designed to better assess lithology and concentrations within this area. Upon completion of the investigation, LFR is currently proposing an in situ injection pilot study in this area, which will be designed to address the relatively higher concentration observed in A-zone groundwater within this portion of the Site. In summary, as described in the Phase IV IRA Detailed Plan, relatively higher concentrations of VOCs are located at approximately 30 to 50 feet bgs within groundwater of the HSA, that were previously located above the water table. Due to the low permeability of these materials, these relatively higher concentrations of VOCs have been bound within these clay and silt sediments and continue to act as a source of relatively higher concentrations of VOCs to groundwater within and downgradient from the HSA. However, as noted in the Phase IV IRA Detailed Plan report, the higher concentrations within the HSA are primarily located within the tighter sediments and are not easily remediated. Multiple lines of evidence suggest that relatively higher concentrations emanating from the HSA are primarily confined to and migrating preferentially within, the more conductive sand lenses. These patterns and trends validate LFR's SCM for this area, and, by removing or destroying the VOCs within the HSA, the higher concentrations located downgradient Itr-Fart-FS-respoo -06750Am:lfr 4