2016-06-15_REVISION - C1982056 (8)

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6/16/2016 State.co.us Executive Branch Mail - Fwd: Twentymile Coal -Use of Flocculant to Settle Coal Fines Prior to Discharge to Fish Creek We have an existing water treatment facility on Fish Creek that has been used for years to treat mine water prior to discharge in order to meet the effluent limits and requirements of our Colorado Discharge Permitting System (CDPS) industrial discharge permit. Originally, this facility used sodium -hydroxide (caustic soda) to change the pH of the mine water discharge, causing iron and other suspended solids to agglomerate and drop-out in a three cell (in series) settling pond system prior to discharge. Sodium hydroxide is a strong alkaline material with certain handling hazards, and the system was fairly expensive to operate, so in 2006 Twentymile converted our treatment system to an electro- coagulation system, where the mine water is directed over a series of charged electric plates causing suspended solids in the water to pick-up an electrical charge, adhere to other particles, and drop-out in the settling pond system prior to discharge. While this system remains in-place, we have not used it for a number of years because our extensive mine water recycling system has allowed us to balance mine water use with mine inflow and recycling such that both our water withdrawals and discharge have been minimal. We are moving into a new coal seam which is underneath the previously mined seam. In order to safely develop and mine this lower seam, we need to drain some of the water which has accumulated in the previously mined and sealed areas of the upper seam. This additional water volume means that we need to discharge some of the water. The water that we need to discharge has elevated coal fines from pumping operations, elevated iron, and elevated electrical conductivity (EC). In consultation with water treatment professionals, we have determined that the coal fines and iron can most effectively be treated with a polymer flocculant. The flocculant would be metered into the flow stream in the existing Electro -Coagulation Building prior to a mixing tank, with the discharge into the first cell of the three -cell settling pond system, and progressive movement through the pond system to the discharge point. The selected flocculant (SOLENIS Amerifloc 490 — Safety Data Sheet attached) is approved for use in drinking water systems, and at the proposed feed rate of 20 mg/I will be consumed in the reaction with suspended solids, with little or no residual in the discharge to the stream. The SDS sheet (Section 12) indicates an LC50 for Daphnia magna (most sensitive aquatic species) of 10 — 100 mg/I, with an exposure time of 48 hours. Based on this information, our testing, and the consultants recommendations, we are confident that we can meet our permit effluent limits (which include WET testing) while using this treatment method. Consistent with past practice, we propose to limit discharge to high flow periods (typically during spring runoff) in order to take advantage of the resulting mixing and dilution so that we can meet a relatively stringent EC limit. We have applied to the Colorado Division of Reclamation, Mining, and Safety for a permit revision to allow use of this additional treatment method, and they have requested consultation with Colorado Parks and Wildlife. Given that we are already into the runoff season, we would like to process this request as soon as possible in order to discharge this year, so we would very much appreciate your timely consideration and response. I have attached a sample CPW consultation letter as a template to facilitate your response. Please feel free to contact me with any questions, or to discuss. Thanks for your consideration and assistance — Best regards, Jerry Jerry M. Nettleton Manager Environmental Affairs Twentymile Coal, LLC 29515 RCR27 https:Hmail.googl e.com/m ai I/u/0/?ui=2&i k=e29129fcb5&view= pt&search=i nbox&th=155594daebO563cl &si m l=155594daebO563cl 2/3