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<br />SUMMARY (Continued) <br /> <br />. <br /> <br />anticipated effects of deep-well injection into the Coconino Sandstone <br />are described in the following section, "Surface and, Ground Water". <br />Surface facilities at Hanksville Salt Wash would interfere with develop- <br />ment of mining claims. If, after testing the injection formations, an <br />adverse effect was expected for claims and leases in the unit area, <br />Reclamation would notify the appropriate claim holders and lessors. The <br />relatively low earthquake activity in the area, the operation of deep- <br />well injection below formation fracturing pressure, and the lack of any <br />major faulting within 25 miles of the proposed injection well sites make <br />the risk of inducing significant seismic activity low. <br /> <br />Surface and ground water <br /> <br />Under the no-action alternative, salinity contributions from the two <br />salt washes are expected to continue as at present. The surface water <br />quality of the Colorado River would improve under the recommended plan <br />because of the deep-well injection of 20,900 tons of salt per year, <br />including 14,300 tons at Hanksvi1le Salt Wash and 6,600 tons at Emery <br />South Salt Wash. This reduction in salt would reduce the salinity at <br />Imperial by a mean 1.7 mg/L!/ and a maximum annual range of 0.8 to 2.3 <br />mg/~/ in any 1 year of operation. The reduction in total flow at Muddy <br />Creek would be 2.75 cfs, including 2.5 cfs at Hanksville Salt Wash and <br />0.25 cfs at Emery South Salt Wash. <br /> <br />. <br /> <br />The saline water would be injected in the Coconino Sandstone, which <br />has highly variable formation water quality ranging from 650 to 39,400 <br />mg/L total dissolved solids (TDS). Local formation water quality is <br />estimated to be 7,900 mg/L TDS based on sample data from local wells. <br />The formations above and below the injection zone are thought to have <br />competent barriers to vertical movement of water. The closest outcrop <br />of the formation is 7 miles from the proposed injection well in Hanks- <br />ville Salt Wash and is 11 miles from the proposed injection well in Emery <br />South Salt Wash. After 50 years of injection, the front of the saline <br />plume is expected to be 0.65 and 0.25 mile away from the injection wells <br />in Hanksville Salt Wash and Emery South Salt Wash, respectively. No <br /> <br />1/ The formula used for estimating the mean annual salinity reduc- <br />tion in mg/L at Imperial Dam is presented in Quality of Water, Colorado <br />River Basin, Progress Report No. 12 (U.S. Department of the Interior, <br />January 1985) and is based on the level of development anticipated to <br />occur by the year 2010. Based on this formula, the salinity at Imperial <br />Dam decreases 0.91 mg/L for each 10,000 tons of salt removed and increases <br />1.07 mg/L for each 10,000 acre-feet of depletion upstream of Imperial Dam. <br />2/ Maximum annual range of salinity impact at Imperial Dam based <br />on equations developed using the Colorado River Simulation System (CRSS) <br />computer model developed by the Bureau of Reclamation. The range of <br />effects considers the uncertainty of the hydrosslinity analysis as well <br />as a wide range of hydrologic and development conditions. The maximum <br />annual range represents the widest variation in salinity impacts possi- <br />ble by a project in any 1 year of operation. The average impact would <br />fall approximately midway between these extremes. <br /> <br />. <br /> <br />S-17 <br /> <br />002326 <br />