Laserfiche WebLink
RULE 2 - PERMITS <br />• t= x /(K -1/0) <br />= 10 ft / ( 0.0099 ft /d - 0.35 / 0.1) <br />= 29 days <br />Water entering the mine will be used consumptively for mine operation purposes such as dust <br />control. The quantity of inflow is expected to be small enough that mine - related water use will <br />consume all of the inflow. Groundwater pumped from the mine would have the potential to impact <br />the receiving surface drainage. These potential impacts are discussed in the sections on surface <br />water. <br />Changes in groundwater quality after mining is completed and groundwater flow through the area <br />has been re- established are not expected to affect present users of groundwater or surface water. <br />Typically, significant changes in groundwater quality occur when groundwater in the post- mining <br />environment is exposed to overburden materials that have collapsed into the mine void. However, <br />with the continuous mining method anticipated to be used in the PSCM, little to no subsidence is <br />expected. <br />The post- mining water quality that will result from flooding of the mine workings will undergo two <br />phases of development. Initially, groundwater filling the workings will be under oxidizing <br />conditions, and the quality of water refilling the mine will be a combination of the quality of water <br />from the adjacent overburden, coal and underburden, affected by the oxidizing conditions. The <br />• inflow will be derived from areas that are likely under reducing conditions, but the water quality in <br />the mine will change with exposure to the oxidizing conditions, much as occurs in surface -mine <br />spoils. Increased dissolved oxygen concentrations in the groundwater can lead to oxidation of pyrite <br />and reduction of pH, resulting in dissolution of carbonate minerals and consequent increases in <br />concentrations of calcium, magnesium, bicarbonate, sulfate and TDS. TDS concentrations in the <br />spoils aquifer at the Seneca II mine are as high as 4800 mg/L as a result of exposure to the rubblized <br />overburden material which constitute the spoils and the availability of a continuous supply of <br />oxygen. However, since little or no subsidence of overburden into the mine openings is expected, <br />exposure of the groundwater to overburden materials is not expected to increase beyond that of the <br />natural, pre- mining conditions, and the effect on groundwater quality refilling the mine workings is <br />not expected to be as pronounced as in a surface mine spoils setting. As the lowest - elevation <br />portions of the workings fill and the oxygen in the groundwater is consumed and not replenished, <br />the conditions will revert to the reducing conditions typically present at depth, which will limit <br />further oxidation of pyrite and the associated changes in pH, calcium, magnesium, bicarbonate, <br />sulfate and TDS. <br />A worst -case scenario for TDS increases in the mine area can be evalutated by assuming that the <br />water quality in the inflow will initially will be similar to that of the Seneca II spoils water (TDS = <br />4800 mg /L), that an oxidized, weathered area will develop around the mine workings and will have <br />chemical characteristics similar to the overburden rock that would comprise mine gob or spoils, and <br />that the quality of the groundwater passing through the weathered zone will change with time,as <br />observed at other mines producing coal resources from the Mesaverde Group in this geographic <br />area. For example, leaching tests performed on overburden material from the Eckman Park Mine <br />(as described in the PHCs section of the Foidel Creek Mine Permit (TCC, 1999) predicted that the <br />TDS concentrations in the groundwater flow through caved overburden would initially be elevated <br />and then would decrease with time. Two existing underground mines, the Eagle and the Foidel <br />PSCM Permit App. 2.05 -82 Revision 03/05/10 <br />