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The design of the off-channel water infiltration pit is included as Attachment C. The excavated portion of <br />the pit will totally contain a maximum volume of 190,384 gallons of water. Preliminary hydrogeologic <br />modeling suggests that a desired aquifer response will occur after 144 hours of pumping at 20 gallons per <br />minute, for a total water production value of 172,800 gallons. These water production calculations result <br />in the proposed excavated portion of the pit being fully adequate to contain all produced water. <br />Excavated subsoil will be utilized to construct a 5.5 foot tall berm around the entire perimeter of the <br />excavated pit to provide additional freeboard, and to account for potential water inputs from unusually <br />high-intensity storm events. It should also be pointed out that a moderate percentage of water discharged <br />into the pit will be lost to infiltration and evaporation during the course of the pump test. <br />For reclamation and surety bond calculations, Attachments C and D show the total surface disturbance <br />that will take place during the construction and utilization of the off-channel infiltration pit, as well as <br />other site specific information such as pit location photographs. Following utilization of the constructed <br />facilities, the pit will be filled back in with excavated backfill material and topped off with the segregated <br />topsoil. Powertech will comply with DRMS requirements related to the sampling of mud pits during <br />reclamation activities associated with the off-channel infiltration pit. <br />These requirements state: <br />o The concentration of radium-226 or radium-228 in soil may not exceed the background <br />level by more than 5 picocuries per gram (pCi/g) or 0.185 becquerels per gram (Bq/g), <br />averaged over the first 15 centimeters (cm) of soil below the surface; and <br />o The concentration of natural uranium in soil, with no radioactive decay products present <br />may not exceed the background level by more than 30 pCi/g or 1.11 Bq/g, averaged over <br />the top 15 cm of soil below the surface; and 150 pCi/g or 5.55 Bq/g, average <br />concentration at depths greater than 15 cm below the surface, so that no individual <br />member of the public will receive an effective dose equivalent in excess of 100 mrem per <br />year or 1 millisievert (mSv) per year. <br />The DRMS will require test results demonstrating that these limits have not been exceeded; the <br />tests are to be conducted during or immediately following the reclamation of the mud pits. If <br />these limits are exceeded, DRMS may require appropriate off site disposal of mud pit contents. <br />Following the backfilling of the pit with excavated material, the area will be graded to conform to the <br />original topography and re-seeded to the specifications outlined in the NOI application for this <br />modification. <br />At the request of DRMS, also included in this modification proposal as Attachment E are groundwater <br />quality analytical results from the target sand unit (A2 Sand - Sample IS-003T) in which the pump test <br />well will produce from, as well as from the uppermost aquifer below the ground surface (Upper Laramie <br />Formation - Sample IS-003Ta). In addition, Attachment E includes a groundwater chemical mixing <br />analysis for several constituents, with a particular interest in uranium and radium concentrations, which <br />are slightly elevated within the aquifer from which the pump test well will produce water. It should be <br />noted that the sample analytical results provided in this report are not from wells planned to be used <br />during the pump test, but are from wells located about 500 feet away. During the pump test, water quality <br />samples will be obtained from the produced water. <br />The Laramie Formation aquifer is the uppermost aquifer below the ground surface where the off-channel <br />infiltration pit is located. Groundwater within the Laramie occurs about 100 feet below the ground <br />surface, and the lowermost contact of the Laramie Formation with the Upper Fox Hills Formation exists <br />at about 434 feet below ground surface. Attachment E includes a dilution chemical mixing analysis that <br />quantifies the resulting water quality when mixing the discharged pump test water volume with the <br />uppermost Laramie Formation aquifer utilizing 2 separate dilution factors. As can be seen from the <br />results of the dilution mixing analysis, in the unlikely event that the dissolved chemical constituent <br />P-2008-043 Mod #2