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observed at the downstream site. An increase of 1,760 mg/l between 1981 and 2006 at the downstream site is likely attributable to mining. An increase in TDS from 600 mg/1 prior to mining in the Cow Camp Creek Drainage to approximately 4,055 mg/1 has been observed in monitoring data collected from 1981 to 2006. TDS in Bond Creek has risen from 550 mg/I in 1987 to 3,360 mg/1 in 2006. The operator has suggested that TDS levels in Bond Creek and Cow Camp Creek will stabilize after mining activities cease, as has been observed in the portion of the Grassy Creek drainage where mining has ceased. A prediction of TDS loading which could be expected to occur in both the Fish Creek and Grassy Creek basins during the months of June through September has been developed by the operator and included in the statement of probable hydrologic consequences. Mean monthly flow and maximum observed TDS concentrations from monitoring of spoil aquifer wells were used in the analysis. Predicted TDS concentrations for downstream locations on both Fish and Grassy Creeks were calculated usingthe mass-balance approach. Results of the analysis indicate that a maximum TDS of 2,341 mg/t would occur during September at a location below the mine on Grassy Creek. A corresponding flow of 0.84 cfs would result. Results of the analysis on Fish Creek predict a cumulative effect from the Cow Camp and Bond Creek drainages to result in an instream TDS concentration of 607 mg/I in Fish Creek below the mine during the month of July. This conclusion was based on assumed discharge of 0.2 cfs with a TDS concentration of 2,245 mg/1 from both Cow Camp Creek and Bond Creek. During August and September no flow in the tributaries is expected to reach Fish Creek as surface flow. There is no agricultural use of water immediately downstream of the Seneca II Mine on Grassy Creek. Due to the small quantity of flow contributed to the Yampa River by Grassy Creek, the increased concentration of TDS produced in the Yampa River would be minimal, and not preclude the beneficial uses of this water. An evaluation of the effect of increased TDS concentrations in Fish Creek is discussed in Section XIII ofthis document entitled Alluvial Valley Floors. Based on the foregoing analysis, the Division makes the finding that the Seneca II Mine site has been designed to minimize off-site surface water impacts. Ground Water Both consolidated and unconsolidated aquifer systems have been identified at and near the Seneca II Mine site. These aquifers may be affected by surface coal mining operations at this site. The Trout Creek Sandstone stratigraphicallyundeAies the Wolf Creek Coal by 70 feet. 25