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Please remove these two sections. Remove also the reference to an ARAR <br /> waiver in Section 3.1.0.2. <br /> 8. Section 2.1.3.4 discusses vertical hydraulic conductivity. An aspect that should be <br /> evaluated during the ground-water modeling is the potential impact by the extraction <br /> system and injection system on the vertical gradient, and the potential impact that <br /> changes in the vertical gradient could have contaminant migration, both adverse and <br /> beneficial. <br /> The design criteria and ground-water modeling should address the potential <br /> impact on vertical gradients and possible effect on contaminant migration. <br /> 9. As identified in Section 2.1.3.8, the contaminant source loading rate to the ground <br /> water is a data gap. The TCE/PCE/DCE source definition (location and mass) needs <br /> to be defined during the site-wide RI/FS. Since these constituents have been identified <br /> as most critical, their source definition, and soil remediation, should have a high <br /> priority. Expeditious definition of the source could provide input that would make the <br /> solute transport analyses more reliable. More importantly, the continued presence of <br /> source material within the soil could obviously have adverse affect on the success of <br /> the ground-water cleanup program. <br /> Please clarify whether the site-wide RDFS will provide data on the <br /> TCE/PCE/DCE sources within the time-frame of the modeling study, or system <br /> design. (Is an interim investigation for the sources needed?) <br /> 10. Section 2.3.2.4 indicates that injection well depths will be partly determined from <br /> contaminant distribution. <br /> Please explain how the contaminant distribution will influence injection well <br /> depths. Does this refer to which horizon an injection well will be placed <br /> within to enhance the hydraulic control or flushing of the contaminants? <br /> 11. Section 2.3.2.5 addresses water quality of treatment plan effluent. Water quality <br /> parameters (inorganic chemistry and solids) may control the success of the injection <br /> wells, perhaps more so than further evaluation of the hydraulic parameters of the <br /> injection zone. Two aspects to be evaluated are (1) the characteristics of the treated <br /> water, and (2) the characteristics of individual aquifer zones. <br /> The well design criteria should clearly include an evaluation of the inorganic <br /> chemical characteristics of the aquifer zones and chemical compatibility with <br /> the treated water. The criteria should also include an evaluation of particle size <br /> limits for the injected water, especially if precipitation is a required treatment <br /> process. (The inorganic chemistry of the aquifer zones are addressed in Section <br /> 3.3.3.1 of the RDWP, but only in terms of hydraulic connection and <br /> EPA/11IAN94 3/6 <br />