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., ,... ,... l\:> CD ~ ~,~ j::; ".:. '~"~ " , NPDES;Permit No. CO-0042161 Salinity Control Study Twentymile Coal Company 3.0 Options for Reduction or Elimination of Salt Discharge Discharge occurs at Point 001 (Station 115) to mine dewatering at the Fish Creek Borehole. Average )nonthly flows range fromO to 0.9 cfs~ although instantaneous flow as high as L8cfs has been :measured; flow commonly ceases when pumps are not active. Treatment or containment options which would eliminate or reduce salt discharge from the mine discharge are developed below. These options include complete salt elimination by deep well inj~ion of all pumped water (Option 1), partial salt removal by reverse osmosis (Option 2), and partial salt reduction by deep well injection (Option 3). The conceptual details for these iopdons are developed further in this Section. 3.1 Option 1: - Deep Well Injection Elimination of Sait Discharge Deep well injection and eVapOration pond treatment were initially considered for complete salt elimination. It was concluded that an evaporation pond would not be suitable for treatment of this disc~arge because there is no place to locate an evaporation pond large enough to treat this relativel)\ large and nearly continuous flow. Thus the only practical option for complete elimination of salt discharge would be deep well injection. Based on the report "Reconn.issance of Ground-Water Resources in a Part of the Yampa River Basin Between Craig anJI Steamboat Springs, Moffat and Routt Counties, Colorado" (Brogden and Giles, 1977), tile shallowest formation which would appear to be suitable for deep well injection is the Dakola Sandstone, at a depth more than 6000 feet below surface. ' , ' In this conceptual evaluation, it is assumed that two deep injection wells would be required to accomm4date the entire discharge. These injection wells would be installed at two different locations; each approximately 1,000 feet from the existing sedimentation pond. Ideally, each injection, well should be capable of injecting flows up to 500 gpm so that each well cOuld accomm4date most discharges and both wells would have sufficient capacity for the higlJ.est discharg4 measured during the 1990 through 1994 record of 800 gpm. This would permit pne well to treat normal discharge in the event that the other well was out of service for repair or maintenance, It would also provide additional injection capacity in the event that mine ' discharg~ rates were to increase. ' The existing sedimentation pond would remain to facilitate removal of particulates but would be expanded and upgraded to provide storage and surge capacity in this option. The primary outlet wOuld be closed. The emergency outlet would discharge only under upset or by-pass conditions such as plugging Qt: the injection wells, equipment failure, or extreme storm events. , 1 , ';]' >1 " , ) .' , . AHA Fdc:name: 14S~Nl.DOC Page 14 2:52 PM 09129/95 j