Laserfiche WebLink
RULE 2 - PERMITS <br />feet. Because of the increasing distance between the spoils aquifer and the mine workings, the flow <br />to the mine workings in this area would also be affected by the natural hydraulic gradient and <br />groundwater flow in this area. Consequently, potential inflow to the mine from the spoils aquifer <br />would likely be diluted by inflow of groundwater from other areas to the south. However, the <br />maximum potential inflow from the spoils aquifer to this part of the mine workings can be <br />calculated by ignoring the influence of groundwater flow from the other areas. To facilitate the <br />calculations, the 6,000 feet of mine workings was divided into six segments of 1,000 feet each, and <br />the flow equation was applied using the hydraulic gradient for each segment. The result is: <br />Q=T'Z(I <br />= (0.006 to 0.026feld)• [ (0.25 +0.25 +0.25 +0.25 +0.25 +0.17+ <br />0.16 + 0.14 + 0.12 + 0.11) - 1,000 ft] <br />= 12 to 51 ft' /d <br />= 0.06 to 0.26 gpm <br />Thus, the maximum total inflow derived from the spoils aquifer at the reclaimed Seneca II Mine <br />would range from approximately 0.06 gpm to approximately 1.8 gpm. <br />Neither of the above calculations considers groundwater velocity and the time it would take for <br />groundwater from the spoils aquifer to reach the PSCM workings. Consequently, the calculations <br />can be somewhat misleading in terms of predicting potential changes in mine inflow water quality. <br />The portal and north main areas are the part of the mine workings closest to the spoils aquifer and <br />would therefore receive groundwater inflow from the spoils aquifer in the shortest time. The time <br />calculated from the groundwater velocity and the distance predicts the arrival of the mid -point of <br />the plume of spoils groundwater, where the concentration of spoils water is at its maximum. <br />However, due to dispersion, the lower - concentration, leading edge of the plume travels faster than <br />the average groundwater velocity and arrives sooner. <br />Ignoring dispersion, the calculated travel time (Freeze and Cherry, 1979) is: <br />t= x /(K•I /0) <br />where: t = travel time <br />x = distance <br />K = hydraulic conductivity <br />I = hydraulic gradient <br />0 = effective porosity <br />The distance (x) is approximately 10 to 150 feet, the average gradient is 0.35, the effective porosity <br />is assumed to be 0.1 (10 %), and the tange of hydraulic conductivities of the overburden and the <br />Wadge coal are 0.00013 ft` /d and 0.00022 to 0.0034 ft /d, respectively. The underburden is not <br />considered because the gradient is upward from the underburden to the Wadge coal, so flow from <br />the spoils to the mine workings through the underburden would therefore not occur. The shortest <br />calculated travel time would result from the shortest travel distance (10 feet) and highest hydraulic <br />• conductivity (0.099 ft/d). Substituting these values into the equation and rounding to appropriate <br />significant figures gives the shortest time at which water derived from the spoils would begin to <br />enter the mine workings: <br />PSCM Permit App. 2.05 -81 Revision 03/05/10 <br />