SITE INFORMATION AND CORRESPONDENCE_2005-2014

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Peter MacNicholl January 28, 2005 Page 3 of 5 contaminant level (MCL) for PCE of 5 micrograms per liter (Ng/L). Historical results for wells PW020 and PWO06 show that concentrations of TCE have remained relatively stable, below the MCL for TCE (5 pg/L). The GSU questions whether the relatively stable levels of PCE and TCE encountered in the public water supply wells may indicate an ongoing contribution from the overlying PCE and TCE plumes emanating from the Site. If so, then the contaminant plumes may not be adequately captured, and optimization of the remediation system may be necessary. Recommendation The GSU recommends revising the Draft 2004 Annual Progress Report to include a discussion of the relevance of the persistent presence of TCE and PCE in public water supply wells PW006, PW020, and PW021. 2) Figure 4.3-10 (Cross-Section B-B'): As illustrated here, there was a detection of TCE (1.0 pg/L) in well MW-522C during the 3Q04. This detection of TCE is bounded by non-detects (ND) in the two wells located above well MW-522C (MW522A and MW52213). However, there is no deeper well in this well nest and so currently there is no definition of the bottom of the TCE plume in this area. If additional data (e.g., HydroPunch data) in this area are available to define the vertical extent of the TCE plume it should be included in this discussion. Recommendation The GSU recommends revising the Draft 2004 Annual Progress Report to include a discussion of the vertical extent of the TCE plume in the area of well nest MW522, and the potential that a data gap exists in this area. 3) Figure 4.3-10 (Cross-Section B-B'): As illustrated here, the vertical extent of the TCE plume in well nest MW-439 is not defined. TCE was detected in well MW-339CD at a concentration of 2 pg/L during 3Q04. Hydraulic gradients between MW-3398 and MW-339C are upwards, however, there is no hydraulic gradient information for the area between wells MW-339C and MW-339CD. The vertical extent of the TCE plume is bounded further northwest (hydraulically [laterally] downgradient) in wells MW456C, MW438CD, and MW439D. It is possible that a TCE plume could extend vertically beyond well MW-439CD and could have moved below and beyond well MW456C. The GSU realizes that this scenario is possible, but believes it unlikely due to the influence of pumping from nearby groundwater extraction well EWNCR2 and the likelihood that groundwater in the area is directed towards this extraction point. Sharpe_U RS 112204_FFAAnnualReport.doc