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Mr. Travis Marshall <br />August 18, 2008 <br />Page 2 of 5 <br />intends to assess hydrologic characteristics of the water-bearing strata of concern by <br />conducting single-hole and multi-hole tests in the Phase I monitoring wells specifically <br />designed and installed for hydrologic testing and groundwater monitoring. <br />AMSO will evaluate the need to conduct long-term pumping tests after initial hydrologic <br />testing has been completed at the Phase I monitoring wells. Corehole CH-01 would be used as <br />a monitoring point during such long-term testing if the hole has been reconditioned and <br />completed to support monitoring of one or more of the water-bearing strata of concern. <br />All of the tomography holes (TM-1 through TM-4) will be cased (10 3/4 inch) to the top of the <br />illite-rich zone and then drilled using air-mist through the illite-rich zone below the casing. <br />The internal 4 %2 inch casing will be installed in the TM holes near the end of Phase I. Hole <br />TM-1 will be drilled first while monitoring the pressure head in existing well MWP 1-L3. As <br />each subsequent hole is drilled in Phase I (including the TM wells), pressure head monitoring <br />will occur in each previously drilled hole. If following this initial hydrologic testing it is found <br />that additional testing is needed to confirm initial results or to further assess hydrologic <br />properties within the illite-rich zone, withdrawal or injection testing will be considered using <br />two or more of the tomography holes before inner casing installation. The duration of such <br />additional testing will be determined on the basis of the water yield observed within the illite- <br />rich zone. <br />2. The NOI states that if drill holes are to remain open for more than 30 days after completion of <br />drilling; a packer seal will be placed in the hole to prevent aquifer cross-contamination <br />Based on DRAB knowledge of the movement of groundwater in the Piceance Basin, there is <br />significant concern about cross-contamination of aquifers. Please demonstrate that a <br />maximum of 30 days of the open hole condition provides an adequate margin of safety against <br />cross-contamination? Additionally, please indicate measures to provide a contingency plan <br />that will be implemented should aquifer cross-contamination be identified <br />AMSO Response: <br />AMSO understands that the route of cross-contamination of concern within the Piceance <br />Creek Basin is the migration through an open borehole of lower quality water within the lower <br />aquifer to the better quality waters comprising the upper, protected aquifer. AMSO has no <br />intention of leaving any drill hole open following the completion of drilling such that lower <br />aquifer groundwater may migrate to the upper aquifer. The tomography holes and monitoring <br />wells will be fully cased to the top of the designated testing(monitoring interval during drilling <br />operations. Corehole CH-01 will be drilled using drilling mud, and a positive head of drilling <br />mud will be maintained in the borehole through completion of downhole logging. The suite of <br />downhole logs that will be run on the Corehole requires that water-bearing zones within the <br />borehole remain isolated from one another from the beginning of drilling through completion <br />of logging. Upon completion of logging, corehole CH-01 will either be plugged and <br />abandoned, or cleaned/reconditioned to support hydrologic testing as discussed in Item 1 <br />above. If for any unforeseen reason the reconditioned hole must remain temporarily uncased <br />through the upper and lower aquifers, additional downhole logging (e.g., spinner, heat pulse, <br />temperature) will be performed to verify a downward pressure gradient exists between the <br />upper and lower aquifers. If the additional logging indicates consistent downward gradient <br />from the upper to the lower aquifer, no seal will be required to prevent borehole cross- <br />contamination of the aquifers. If the results do not indicate consistent downward flow between <br />the aquifers, AMSO will ensure the aquifers remain isolated during the time the hole is left <br />110 East 3 Street, Suite 201 P.O. Box 1470; Rifle, CO 81650 Phone: 970-625-4324 Facsimile: 970-625-4318