GENERAL55915 - Laserfiche WebLink

Home Browse Search

a 2. Effects on Groundwater During mining, the Canadian Strip Mine open pit received inflow from the Sudduth Coal seam, also from the adjacent underburden and overburden. The inflow to the pit from these sources was estimated to be less then two gallons per minute. This inflow has locally lowered, and may continue to lower the potentiometric surface in these units. It is estimated that this depletion of head will only have local consequences due to the somewhat impermeable nature of these units. A spoils aquifer will develop in the reclaimed No. 1 pit. A monitoring well has been installed to verify this. The sources of the water supplying this aquifer are: (1) infiltration of overland flow from upslope drainage; (2) inflow from undisturbed Sudduth Coal to the south, and from the adjacent under/overburden. Some amount of surface drainage will infiltrate the backfilled pit. Initially, the amount of infiltration will be greater than in undisturbed areas due to the depression formed by the pit reclamation. As the vegetative cover in the reclaimed area becomes established, it is thought that much of the summer surface runoff will be used by the vegetation, and eventually lost to evapotranspiration. Spring snowmelt runoff will likely add some amount of recharge to the spoils aquifer. The hydrologic consequences of the mining operation during the previous permit terms were small. Some inflow to the then open pit occurred, but due to the hydro- geologic characteristics of the Sudduth Coal and its under- and overburden, inflow was small. As no water supply wells are completed in these units, no affects to local water users have been observed. Also, no springs have been identified emanating from these units in the area of the mine. The pit is spatially removed from the Bolton Draw alluvium; therefore, no inflows from or depletion of this aquifer have occurred. As documented during the previous permit term, the volume of groundwater inflow to pit No. 1 stabilizes over time. The mine should not expect that any inflow conditions will change after the pit is backfilled. Therefore, the amount and rate of inflow from adjacent units shall not exceed approximately pvo gallons per minute. Inflow will stabilize when an equilibrium is reached between the spoil aquifer and the source of inflow, the most significant of which is the undisturbed Sudduth Coal seam. It is expected that the hydraulic equilibrium between the spoils aquifer and the Sudduth Coal seam will be exceeded for some period each year following spring snowmelt runoff. The snowmelt runoff will cause the spoils aquifer water table to Canadian Strip Mine, C-81-026 19 July 31, 1992