2010-12-09_REVISION - C1982057 - Laserfiche WebLink

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precipitation, overland flow, and discharge from the Williams Fork formation overburden and the coal seams being mined. The backfilled pits in and of themselves will display unconfined conditions, however the pits will be surrounded on the sides and be underlain by relatively confining units. The underlying material will be even more confining than the sides. As water enters the reclaimed areas it will tend to migrate through the spoils toward the lowest point in the pit. While some of this water may be lost to the walls, the major portion of it will stay in the pit, as the permeability of this material is greater than that of either the walls or the floor. It is projected that the water quality of spoil aquifers at the Seneca II-W Mine site will approximate that at the nearby Seneca H Mine. The Seneca II Mine spoil aquifers exhibit elevated levels of total dissolved solids, magnesium, manganese, molybdenum, and sulfate. Complete water quality analyses of two spoils aquifer wells are published in the Seneca II Mine 1984 Annual Hydrology Report, Appendix B. As the aquifer is developing, the water will be of slightly poorer quality than the above assumptions, but as the more easily leached constituents are lost, the quality should approximate that at Seneca II Mine. Analysis of spoils water from the Seneca II Mine indicates that this magnesium-calcium sulfate water has elevated levels of sulfate and magnesium. TDS values vary between 2,200 and 4,000 mg/1. Eventually, water at Seneca II-W Mine will begin to discharge to the surface as the water elevation exceeds the ground level or when sufficient head is developed. The primary impact of Seneca II-W mining operations (including south extension operations) on surface water quality will be an increase in total dissolved solids (TDS) concentration resulting from the occurrence of spoil springs after backfilled spoil in the mine pits has become saturated. The projected impacts on each of the affected drainages near the permit area are summarized below. Hubberson Gulch Seneca Coal Company projects spoil springs in the Seneca II-W South Area will increase TDS in Hubberson Gulch upstream from the Pond 006 drainage from 676 mg/l to 1,787 mg/1. This prediction was calculated from mean discharges and mean TDS concentrations for June - September data for the entire period of record. This projection exceeds the Division's suspect level for material damage for water used to irrigate hay crops. SCC estimated production losses resulting from the increase in salinity. Based on the information provided by SCC, the Division finds that no material damage will occur. See Section B.XII of this document for additional details. Dry Creek Seneca II-W Findings Document 42 C1982057 Permit Renewal No. 5 December 9, 2010