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David Wang, P.E. , Chief <br /> Page 3 <br /> 1.5, 1991 <br /> It is estimated that the treatment system will be in operatiom for <br /> sixteen plus years. <br /> GENERAL COMMENTS: <br /> The Department does not dispute the selection of the air stripping <br /> technology. Rather, our comments reflect information gaps not <br /> included in the FFS. Closing these gaps is importan to <br /> understanding the selection process. <br /> GENERAL REPORT CONTENTS: <br /> 1) Data gaps exist in the RI/FS documentation for the ce tral <br /> area IRM. Elements that need to be submitted include the risk <br /> assessment and treatability studies. Performance data from <br /> the North and South Balloon air strippers could possibly be <br /> substituted for all or part of the treatability studies <br /> 2) RECOMMENDED REMEDIAL ACTION: Section 6 provides an excellent <br /> discussion regarding the differences between the diff rent <br /> technologies under consideration. However, the rationale used <br /> in selecting the air stripping technology was not incl ded. <br /> Without a discussion of the reasons the stripping technology <br /> was chosen, the reviewer can not construe why the selection <br /> was made. We recommend a narrative be drafted that outLines <br /> the thought process that was used to select the air stri ping <br /> technology. <br /> HYDROGEOLOGY: Hydrogeologic comments are of a limited natur , as <br /> a thorough hydrogeologic review was conducted on a RI sub mitt d in <br /> November 1990. <br /> 3) OTHER CONTAMINANTS: The FFS only discusses TCE. Other VOCs <br /> and hydrocarbons have been detected in the ground water. The <br /> Department questions why these contaminants were not factored <br /> into the selection process. The Department' s concern centers <br /> around how the stripper' s performance and maintenance will be <br /> affected by compounds other then TCE. As two other strippers <br /> are currently operating at DDRW Sharpe, this information <br /> should be available for presentation in the FFS. <br /> 4) PLUME DEFINITION: Vertical ground water gradients in the <br /> central area are intermittently affected by agricultural <br /> pumping. Additionally, the influence of the AB and CD zones <br /> is not fully understood. The Department recommends that <br /> additional effort be channeled into interpreting the <br /> influences of both the off-site pumping and the intermediate <br /> zones. Extreme care should be used in placing the extraction <br /> system, regulatory approval be obtained prior to placement. <br />