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Ground Water Injection FS -2- 10 December 1991 <br /> Marley Cooling Tower Company <br /> (gpm) . It is unclear why the injection wells or more injection wells at the same rate <br /> or different rates were not considered for the FS. Marley has requested that the <br /> National Pollutant Discharge Elimination System (NPDES) permit be revised to allow <br /> flows up to 700 gpm, although average dry weather average flows may be significantly <br /> less than 700 or even 500 gpm. Therefore, it is unclear why only 500 gpm was selected <br /> as the injection rate for the evaluation. <br /> My detailed comments are discussed below. <br /> Page 3. The FS Report discusses the ground water quality in the different zones <br /> beneath the Marley site. The pH of the ground water is neutral to slightly <br /> alkaline (up to 9.0) It is assumed that some of these pH values may be <br /> representative of the ground water that has been impacted by the inorganic <br /> plume. The FS Report is unclear as to whether there are significant <br /> differences in pH in the different zones between the impacted an non- <br /> impacted areas of the aquifer. <br /> Specifically, the concentrations of general minerals may be higher in the <br /> area of the North Yard where the ground water may have been impacted by the <br /> plume. The Injection FS Report should have addressed whether there is a <br /> difference in pH and concentrations of inorganic constituents between the <br /> two proposed injection areas. If there are significant differences in pH <br /> between the different areas, the chemical compatibility with the treated <br /> ground water effluent could be affected. Therefore, if injection is <br /> pursued, the pH and concentrations of minerals in the "recipient" ground <br /> water may need to be considered further in selection of the injection site. <br /> Page 5. The results of common ion analysis of samples collected from the treatment <br /> influent and effluent are summarized in Table 2. However, concentrations of <br /> iron, copper, hexavalent chromium, total chromium and total dissolved solids <br /> (TDS) in the effluent from the electrochemical treatment system were not <br /> presented in Table 2. Some of these constituents are monitored and reported <br /> monthly as required in the NPDES permit (Waste Discharge Requirements <br /> (WDRs) Order 91-035) . Since January 1991, Marley has been monitoring the <br /> influent and effluent to the electrochemical treatment system, as well as <br /> the ion exchange system and has submitted this information in the monthly <br /> monitoring reports. Therefore, it is unclear why these data were not <br /> included in Table 2. <br /> Page 6. The FS Report states that scale deposits formed by the precipitation of <br /> inorganic compounds may be removed using a acidic solution accomplished <br /> through pH adjustment of the effluent prior to injection. Marley is <br /> currently using pH adjustment as part of the treatment of ground water, <br /> therefore pH adjustment prior to injection is feasible. Presumably, capital <br /> costs would be relatively low to implement a final pH adjustment. <br /> Page 6. The FS included an analysis of potential precipitation formation using <br /> different analytical models: the Langelier Saturation Index, the Stiff and <br /> Davis extension of the Langelier Index and the Ryznar Stability Index. <br /> These different analytical methods were used to evaluate four different <br /> mixtures: a 50/50 mix of the ion exchange treatment effluent combined with <br /> the electrochemical treatment effluent; a 50/50 mix of the ion exchange <br /> treatment effluent combined with ground water; a 50/50 mix of the <br />