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EPA COMMENTS DRAFT - WELL MONITORING PROGRAM, ANNUAL MONITORING REPORT, OCTOBER 1993 SAMPLING ROUND (Report dated April 1994) DDRW-TRACY Major Comment 1. Section 5 . 1. 1.3, page 5-2 The text on page 5-2 states that "TCE has migrated to the northeast beyond the limits of monitoring well coverage. . . " . This is also reflected in Figures 5-2 and 5-3 . • The monitoring system needs to be extended to adequately define the extent of the TCE plume. This will require installation of additional off-depot monitoring wells . Steps should be taken to begin the approval process for well installation. Other Comments 2 . Section 3 .2 . 6 .7, page 3-31 The text on page 3-31 states that " . . .very little seasonal change of groundwater elevations is seen in the Lower Horizon. " However, Figures 3-11 through 3-14 show that the Lower Horizon' s seasonal rise between March 1993 to July 1993 was similar to that of other horizons . Does the comparable change imply hydraulic connection between all horizons? if so, this would be inconsistent with the conclusions reached in Sections 3 .3 . 5 .4 and 3 .3 . 5 .5, which suggest that the Lower Zone is relatively isolated from overlying zones based on chemical data from Stiff diagrams . • The text should resolve the apparent inconsistency between the hydraulic data that appears to support that the Lower Horizon may be hydraulically connected and the chemical data that supports the Lower Horizon is not hydraulically connected. 3 . Tables 5-1, Summary of Background Reference Values for Metals No explanation is provided on apparent anomalous background results for some metals. For example, there is a two order of magnitude difference between the middle and upper horizons for total aluminum (381 versus 95, 321 µg/1) . • For background concentrations that differ by at least one order of magnitude between horizons, some explanation or recognition of such large differences should be provided EPA/R9 06j=94 l