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<br />0022~8 <br /> <br />Durango Pumoing Plant - Stage 1 <br /> <br />D. Computer modeling of the groundwater regime was performed to determine effects <br />caused by the construction and operation of the pumping plant. The modeling indicates <br />that the pumping plant will affect up-gradient groundwater flow and levels during <br />construction. The affect on groundwater flow down-gradient in the Menefee Formation <br />is minor. The flow and levels can be restored to near existing conditions by including an <br />underdrain system in the plant design. The computer models are presented in detail in the <br />Hydrogeochemical Site Characterization report. The computer model has been updated <br />with current monitoring wells, readings and current technology, and is described in the <br />2002 addendum. <br /> <br />E. The original computer model predicted a total inflow of approximately 3 gallons per <br />minute into the excavation under steady state conditions with a flow of approximately 10 <br />. gallons per minute to dewater the. excavation over 25 days. Initial inflow of25 to 30 <br />gallons per minute may be possible as the surrounding materials dewater. Actual <br />groundwater inflow, particularly from the direction of the Animas River, may <br />significantly increase due to opening of joints and fractures during drill and shoot <br />excavation. <br /> <br />F. Water quality at the site is also discussed in detail in the site characterization report and <br />addendums. Very little groundwater contamination from the raffinate ponds remains at <br />the site following cleanup of surficial materials. <br /> <br />G. Monitoring over the last ten years indicates the groundwater on the north side of the fault <br />(pumping plant location) is similar to the background levels found in wells upgradient <br />from the site (DH-1l4 and DH-115) and are relatively uncontaminated compared to the <br />groundwater in the fault and on the south side of the fault. Water within the fault zone is <br />the most contaminated at the site. Samples analyzed from drill hole DH-llO, located in <br />the fault zone, indicates the groundwater in the fault has the highest levels of dissolved <br />uranium. Median radium 226+228 levels are similar to other monitoring wells in the <br />area, including background wells. <br /> <br />H. Monitoring of groundwater quality, both from monitoring wells and frorn groundwater <br />flowing into the excavation, will be required during pumping plant construction as part of <br />the Site Monitoring Plan. Current water quality data indicates that extensive water <br />treatment facilities will not be required during construction. A large portion of the water <br />coming into the excavation will be from the up-gradient side and is generally <br />uncontatninated and will pass current water quality standards. This water, along with <br />water entering from the direction of the Animas River will naturally serve to dilute the <br />much smaller quantity of potentially contaminated water which will enter the excavation <br />from the direction of the fault. <br /> <br />1.06 GEOLOGY OF PUMPING PLANT AND INLET CHANNEL <br /> <br />A. Exploration around the anticipated excavation (shown on the Drawing No. 69-529-5, <br />Surface Geology, Location of Exploration and Geologic Sections) includes drill holes <br />DH-107, -108, -Ill though -115, -119 through -122, and -126, and test pits TPDPP-lOl <br />through -103 and -106. Monitoring wells which were installed by the DOE are also <br />shown on the drawing. <br /> <br />Geology <br />00320.16 <br />