2011-01-03_GENERAL DOCUMENTS - P2008043 (2)

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stated that the EPA should review these documents before issuing the Class V Final Permit. One comment also raised concerns that the proposed aquifer-pump test and subsequent injection activity might create the potential for contaminants from the Upper Laramie Formation to enter the Laramie-Fox Hills aquifer. EPA Response: The EPA has determined that the results of the aquifer-pump test will provide more definitive information about the integrity of the confinement zones above and below the A2 sandstone than the plugging and abandonment information for the historic exploration drill holes. The basic question that needs to be addressed is: "Has the integrity of the confinement zones been compromised by the presence and closure methods of the historic exploration boreholes?" The Statement of Basis for the UIC Class V Final Permit provides a detailed discussion of the aquifer-pump test procedure and explains why the results are a more effective means to answering this question than examination of these historical records for the purpose of issuing the Class V Final Permit. The permit requires Powertech to provide EPA with the results of the aquifer-pump test before any subsequent injection is authorized. The test results will serve as an indicator of the integrity of the confinement zones. The aquifer-pump test results will indicate if there are any breaches in the confinement zones above and below the proposed injection zone caused either by natural discontinuities in the confinement zones, improperly constructed or abandoned wells that penetrate the confinement zones, or improperly abandoned historic exploration bore holes that penetrate the confinement zones. The aquifer-pump test will include the measurement of water levels in observation wells completed in the same aquifer as the aquifer-pump test well, in this case the A2 sandstone. The test will also include the measurement of water levels in observation wells completed in aquifers above and below the aquifer being pumped. Monitoring changes in water levels in observation wells completed in the same aquifer as the pumping well can determine if there are any discontinuities in the confinement zones above or below the aquifer. The water level in observation wells completed in aquifers above and below the pumped aquifer should not show any change in water level during the aquifer-pump test, if the confinement zones are impermeable. If the water level in one of these observation wells should decrease, it would be an indication that water is being pulled from the aquifer through a breach in the confinement zone, into the aquifer being pumped. Injection activity under the Class V permit will be of short duration; the injectate is not expected to travel more than 50 feet from the injection well, and the groundwater will not be injected under pressure. Given these conditions, EPA has determined that the aquifer-pump test results will provide information adequate for evaluating the integrity of the confinement zones surrounding the proposed injection well. The proposed aquifer-pump test and subsequent injection activity will not create the potential for contaminants from the Upper Laramie Formation to enter the Laramie-Fox Hills aquifer. All wells related to this aquifer-pump test are cemented through the Laramie Formation, except for the wells that are screened within the sandstone within the Laramie Formation. The Page 8 of 24