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"';- " NPDES (permit No. CO-0042161 Salinity Control Study Twentymile Coal Company ~ ~ w::.. ..... 4.2 Feasibility and Cost Evaluation 'of Options 4.2.1 E1limination of Salt Discharge - Option 1 The consmtction of two injection wells for this option is technically feasible. An injection well penjlit would be required from EFA. It is uncertain whether this permit could ,be obtained ~d whether the Dakota Sandstone would prove suitable for injection. Furthermore, the depletion of water by deep well injection may require a surface water right. Since the surface water rights in the vicinity are connected with flood irrigation in the valIey, if is possible t)1atTwentymile Coal Company could be prohibited from injecting, the discharge if water depletion results in material damage to the quantity of water supplying a designated Alluvial Valle)' Floor. Cost estif\lates for Option' 1 were based on estimates from drillers and in-house experience at installing i deep, large diameter wells (12-incb. diameter injection well to a d\l\)th of approxim4tely 6,000 feet, with stainless steel screen and pressure we\\ heads). Costs eStimates for transfer pumps were obtained from vendors, Piping cost was determined for two injection wells eaqh approximately 1,000 feet from the pump station adjacent to the existipg sedimentation pond. Other costs were calculated using estimating methods outlined in cOst estimatio~ haildbookS and design texts. References included Means Site Work & L\\rtds~ve Cost Datt 12th Ed.,R.S, Means Co. Inc., 1993. The capital cost of Option 1 is $4,793,000 with annuM operating costs of $106,000. Capital and operating costs are itemized in Table 6. ' Option 1 lvould eliminate salt loading by mine dewatering by an average of 1.83 tons per day or 668 tons/year, at a capital cost of $7,176 per ton over one year's operation and an annu,'al operating :cost of $159 per ton. ' Since the injection system is designed to remove the entire discharge !up to 1,000 gpm, the flows in Fish Creek would be reduced accordingly. The salt loads and! TDS in Fish Creek would be reduced measurably during low' flows but not measurably at high flows, The feasibility of permitting two deep injection wells to dispose the entire disqharge is uncertain as would be the actual capacity of these injection wells. ^:\ ~ 1 ,'.\ 1 ., . A I , j " 1 J AHA F'.tleoame::t4SALCNl.DOC Page 26 11:59 AM 09n9195 1