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A. Area of aquifer expected to be affected by the infection operation. Several <br />commenters asked about the extent of the effect of injection within the Upper Fox Hills <br />Formation. <br />EPA Response: <br />The vertical extent of injection is expected to be contained within the A2 sandstone <br />aquifer. There are confinement zones of impermeable shales that will isolate the injection <br />activity to the A2 sandstone. One of the purposes of the aquifer-pump test is to verify that the <br />A2 sandstone is hydrologically isolated from other aquifers. <br />Powertech provided a report included in the Administrative Record that the injectate is <br />expected to travel less than 50 feet away from the injection well (see page 5 of the Petrotek <br />report). Petrotek based this conclusion on the anticipated volume of injectate and the volume of <br />open space within the A2 sandstone available for groundwater to flow through. A more detailed <br />description of Petrotek's process for determination is included in the Statement of Basis for the <br />UIC Class V Final Permit. <br />One factor that affects how far the injectate will travel from the injection well is the <br />volume of fluids to be injected. In the Class V permit application, Powertech estimated that <br />200,000 gallons of groundwater would be pumped from the A2 sandstone during the aquifer- <br />pump test. Since that time, Powertech has had opportunity for additional observation of the <br />aquifer properties. More recent estimations indicate that 43,200 gallons will be pumped from the <br />A2 sandstone during the aquifer-pump test. <br />B. Comments related to the potential of insufficient sampline and characterization <br />of aquifer water quality. Some commenters believe that additional water quality <br />characterization is needed to demonstrate protection of underground sources of drinking water <br />during injection. This information would include additional baseline data on the water quality of <br />both the injectate and the receiving formation and discrete vertical samples collected throughout <br />the entire thickness of the receiving aquifer to develop an accurate characterization of the water <br />quality in the area affected by the aquifer-pump test and injection. <br />EPA Response: <br />The UIC Class V Permit has been changed to require that groundwater samples be <br />collected from the pumping well and analyzed for Total Coliforms; Total Metals for arsenic, <br />barium, cadmium, chromium, lead, mercury, selenium, and silver; Volatile Organic compounds; <br />Semi-volatile Organic Compounds; and Total Petroleum Hydrocarbons. The analytical results <br />will be submitted to the EPA. The analytical results from these samples will be used for <br />comparison with the results of the injectate analysis discussed in Section 2A. <br />The water quality within the A2 sandstone varies due to the presence of uranium ore <br />bodies, because the groundwater within the ore bodies shows elevated levels of uranium, radium, <br />radon, and other associated constituents. It is true that the uranium ore bodies may not extend <br />the full vertical thickness of the A2 sandstone. Figure 1 shows the A2 sandstone portions of logs <br />from wells PWI, MM 1, MUI, and MUU1 located in Section 33, Township 10 North, Range 67 <br />Page 10 of 24