2012-01-05_REVISION - C1980005 (8)

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the undisturbed site. As the alluvial /colluvial water quality closely mirrors the quality of the stream, a degradation (i.e. increase in TDS) is observable in alluvial monitoring wells down - gradient of the mine site. Wells in the alluvium of Bond Creek show that high -TDS water from mining activity has not yet migrated very far beneath the creekbed. Water from the well in Bond Creek has not shown TDS levels elevated much beyond their historic values, near 5000 mg/I. When Seneca Coal Company can demonstrate that the reclaimed lands meet the Phase II bond release criteria, it is assumed that the majority of baseflow to Bond Creek will be contributed by spoil aquifer discharges to the surface system. In the Bond Creek drainage, Wadge spoils aquifer discharges will contribute flow to these tributary creeks and eventually to Fish Creek. During the months of June and July, Bond Creek sustains flow its entire length to Fish Creek. During this period, the creek contributes water to the associated alluvial aquifer. The spoils spring discharges are sufficiently diluted by snowmelt runoff to preclude degradation to the quality of the alluvial aquifers in the drainage. (See the Surface Water section of this Probable Hydrologic Consequences statement for further discussion regarding surface water impacts.) Information supplied by Seneca Coal Company indicates that at its confluence with Fish Creek, Bond Creek does not support flow during the months of August and September. It is assumed that during this period of time, Bond Creek flows for about 2 miles beyond the disturbed area boundary before becoming ephemeral. At the point where the stream becomes ephemeral, it is assumed, for purposes of this discussion, that the flow in the drainage is 0.2 cfs with a TDS concentration of 2,500 mg /l. Assuming that the alluvial water in Bond and Cow Camp Creeks is tributary to that of the Fish Creek alluvium, Seneca Coal Company performed aquifer tests on the Cow Camp Creek alluvial aquifer to obtain a travel time estimate for the potential salt plume through the alluvial aquifer. These tests resulted in an estimated transmissivity value of 4.1 to 5.6 ft /day. Based upon this value, a hydraulic conductivity (K) value of 0.32 feet /day was derived. Using the derived K value, and an assumed effective porosity of 0.30, it was determined that flow velocities within the Bond and Cow Camp Creek alluvial aquifers are 0.15 ft /day and 0.13 ft /day, respectively. Based upon these calculations, it is thought that travel time to Fish Creek within the Bond Creek alluvial body is 200 years. It would appear that the transmissivity range of 4.1 to 5.6 ft /day and the calculated travel times are extremely low for an alluvial system. To verify these calculations and assumptions, Seneca Coal Company placed a monitoring well in both the Cow Camp (GW -S69) and Bond Creek (GW -S68) drainages. These 20