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Peter MacNicholl <br /> January 28, 2005 <br /> Page 4 of 5 <br /> Recommendation <br /> The GSU recommends revising the Draft 2004 Annual Progress Report to include <br /> a further discussion of the vertical extent of the TCE plume in the area of well <br /> nest MW-439. <br /> 4) Figures 4.3-7 and 4.3-8 (TCE, and PCE, Comparison Map 2000-2004, respectively): <br /> A comparison of the TCE and PCE plumes between 2000 and 2004 appear to show the <br /> plumes to be relatively stable overtime. The USACOE attributes this to hydraulic <br /> capture as well as attenuation (page 5-4, Section 5.3.2.2). The GSU would suggest that <br /> attenuation is likely a large factor, especially given the noted absence of hydraulic <br /> capture in the North Balloon area in both the A and B-Zones as discussed in Section <br /> 5.8.1 of the Draft 2004 Annual Progress Report. Also, as discussed below in Comment <br /> Nos. 5, 6, and 7, the GSU believes there may be other areas within DDJC-Sharpe <br /> which do not exhibit adequate hydraulic capture. In addition, another influencing factor <br /> in the depiction of the plumes may be inadequate characterization, i.e., groundwater <br /> monitoring wells may not be appropriately located to characterize the full extent of the <br /> plumes. <br /> Recommendation <br /> The GSU recommends revising the Draft 2004 Annual Progress Report to include <br /> a discussion of the relative importance of attenuation in the apparent lack of <br /> contaminant plume migration overtime. In addition, the GSU recommends <br /> including a discussion of the adequacy of plume characterization, i.e., whether <br /> there are an adequate number of wells, and whether wells are appropriately <br /> located, to characterize the vertical and lateral extent of each plume and to <br /> monitor plume migration. <br /> 5) Figure 5.3-1a (A-Zone 3Q04): There does not appear to be hydraulic capture of the <br /> northwest extent of the Central Area TCE plume (in the area of MW507A). In addition, <br /> there does not appear to be hydraulic capture of the northwest extent of the North <br /> Balloon PCE plume near (northwest) of EWNA8 and EWNA6. However, during 3Q03, <br /> hydraulic capture of the A-Zone in both the Central Area and the North Balloon appears <br /> to have been adequate <br /> Recommendation <br /> The GSU recommends further monitoring the effectiveness of hydraulic capture <br /> in the A-Zone in both the Central Area and the North Balloon plumes. Additional <br /> extraction wells may be necessary in these areas if hydraulic capture is shown <br /> not to be complete. <br /> Sharpe_U RS 112204_F FAAnnualRepo rt.doc <br />