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SECTIONEIGHT Conclusio>l~ and Recommendatlons <br />1 <br />8.1 CONCLUSIONS <br />The following conclusions were made based on results of this investigation: <br />1. It is feasible to capture tailing-affected groundwater seepage by installing and operating an <br />extraction well system along the north access road. <br />2. Wells completed in the alluvial aquifer will likely have specific capacities ranging from 0.5 <br />1 to 0.9 gpm/ft, and be capable of pumping rates as high as 7 gpm. <br />3. An extraction well system consisting of 17 wells spaced an average of 50 feet apazt and <br />' completed to the top of the Troublesome Formation would be needed to captwe a majority of <br />groundwater flowing through the alluvium. The wells installed as part of this investigation <br />can be used as extraction wells, so a total of ]4 new wells would be needed. <br />' 4. Each well should be designed and equipped to operate at an average rate of about `~ gpm. <br />5. The alluvial aquifer in the vicinity of the newly installed wells has a transmissivity ranging <br />' from 3,000 to 50,000 gpd/ft, hydraulic conductivity ranging from 15 to 238 ft/d, and a <br />storage coefficient ranging from 0.01 to 0.05. The most representative values for <br />transmissivity, hydraulic conductivity, and specific yield are 15,000 gpd/ft, 70 ft/d, and 0.03, <br />respectively. However, these values could be higher or lower depending upon location <br />within the alluvial aquifer due to variations in grain size and sorting. <br />6. The hydraulic conductivity of the Troublesome Formation may be as high as about 3 ft/d. <br />' However, additional hydraulic testing of wells completed in this formation would be needed <br />to obtain a better estimate of hydraulic conductivity for this formation. <br />7. Groundwater preferentially flows through the thickest portion of the alluvial aquifer in the <br />area between the extraction well and monitoring well HMMW-02. This conclusion is <br />supported by results of groundwater chemical analysis. <br />' 8. The groundwater in the alluvial aquifer has the potential for causing well screen plugging due <br />to precipitation of iron and/or manganese oxides. <br />' 8.2 RECOMMENDATIONS <br />The following are recommendations for extraction well system design criteria and additional data <br />collection activities: <br />1. The extraction well screens should be constructed with relatively large slot size and relatively <br />coarse filter pack gradation to increase pumping efficiency and reduce the potential for <br />capacity reduction due to iron and/or manganese oxide precipitation. <br />2. The extraction wells should be rehabilitated at ]east once per year, or more frequently <br />depending upon future operational experience. Well rehabilitation should, at a minimum, <br />include bailing, swabbing, and chemical treatment to remove mineral deposits from the well <br />screens. <br />' 3. The extraction well system should be installed in phases and tested to verify capture. <br />1(1~` \~.pI~IIFILE\~E1R~PROJERS69,v5W.11E,DERSOR_MNLFEA41l1A_OPIO_PRa 0E1.MREYISED TEQ1 YEAbRf.DO(.11Mn 31l PY O-1 <br />~/-YI <br />