SITE INFORMATION AND CORRESPONDENCE

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Doug O'Neal • • February 7, 2002 Page 3 - Although useful, the 1997 data from HydroPunch sample locations K-PIPP-1 and K- PIPP-3 (shown on Figure 1) did not evaluate VOC concentrations in the Upper Intermediate Zone. As stated in Dudek (1998), these samples were obtained from the Upper Zone. The lithology in which these samples were obtained is unknown. GSU urges caution if these data are used to design the off-site investigation and to select well locations. - The proposed spacing of wells should be based on pumping and non-pumping flow conditions. The spacing between the proposed well location and well KIA 2 (520 feet) is too large. ■ For the purposes of preparing a lithclogic log, the Workplan proposes to obtain samples at five-foot increments from 0 to 80 feet below ground surface (fbgs) and to obtain continuous samples from 80 to 125 fbgs. GSU notes that it is to the facility's advantage to maximize the amount of lithologic data obtained while conducting the off-site investigation. GSU recommends that, at a minimum, the Workplan be modified to state that if unexpected coarse-grained units are encountered between 0 to 80 fbgs, as determined by soil samples or drill rig behavior, continuous sampling will be conducted to evaluate the lithology. ■ GSU has the following concerns regarding the proposed monitoring well design: - The Workplan proposes two different screen lengths (20 feet on Page 4; 15 feet on Page 5 and Figure 10). GSU and DTSC guidance documents (Page 26 of DTSC 1995) recommend that the slotted screen length be no longer than 10 feet. A screen length of 15 feet may be considered in cases where the well is designed to screen across the water table. GSU recommends that DTSC staff be present on-site during the offsite investigation and that the well screened intervals be selected in consultation with DTSC. - The Workplan proposes a specific screened interval for the well. GSU recommends that the Workplan state that the actual screened interval will be selected in the field based on encountered conditions. Additional field screening tests, such as soil headspace measurements, should be conducted to determine the most appropriate screened interval. - GSU concurs that surging the filter pack after placement will promote better well performance. However, a filter pack that extends more than three to four feet above the top of the screen slots seems excessive. GSU recommends that the Workplan state that the filter pack will not extend more than three feet above the top of the screen and that the filter pack will not hydraulically connect the Upper Intermediate Zone and the Upper Zone. - GSU is concerned that the proposed annular seal (Volclay grout) will not provide a long- term seal for the monitoring well, particularly because portions of the seal will lie within the unsaturated zone. Instead, GSU recommends placement of a two-foot bentonite pellet seal above the filter pack followed by neat cement grout for the annular seal. The recommended grout mixture is: 5.5 to 5.8 gallons of potable water per 94-pound sack of Type I Portland cement. - The Workplan should justify the selected screen slot size and filter pack gradation.