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Close to each mine, there will be some impacts to the local hydrologic regime. Usually, these impacts will manifest themselves as increased levels of chemical constituents and total dissolved solids. Regionally, however, due to the aerial extent of the basin, and amount of water present in the basin as a whole, no cumulative impact to the system is anticipated. The impacts to the alluvial aquifer system near Seneca II-W Mine cannot be assessed on a basin-wide scale as this system is discontinuous throughout the basin. Near the Seneca II-W Mine, the alluvial aquifer system may be impacted by mining, but cumulative effects of mining will be negligible. Spoils aquifer discharge will eventually flow across Hubberson Gulch alluvium. Depending on the water table conditions in the gulch, this water will percolate into the alluvium, or recharge the creek as overland flow. When the spoils water enters the alluvium of Hubberson Gulch, or that of Dry Creek due to recharge from the creek itself, the alluvial water will have higher than baseline TDS, boron, iron and manganese values. A series of wells monitored for water quality in the Hubberson Gulch alluvium will identify any plume of spoils water in the alluvial aquifer. Due to the high water table identified at this site, and which is probably existent throughout the Hubberson and Dry Creek alluvial systems, it is felt that spoils discharge will be diluted to acceptable levels. The Seneca II-W Mine has been designed to minimize disturbance to the prevailing hydrologic balance. Furthermore, the Seneca II-W Mine will not contribute any cumulative hydrologic impacts to the local or regional ground water hydrologic systems. Surface Water In January of 1981, the Colorado District of the U.S. Geological Survey, Water Resources Division, was contracted by the Division to model the cumulative effects of all anticipated mining in the general area of the Foidel Creek Mine (U. S.G.S., 1983). The U.S.G.S. adapted an existing surface water quality model for use in this area, and calibrated the model using data from water years 1976 to 1981. The Division provided estimates of the short-term and long-term effects of mining which were added to the model to predict the cumulative effect of mining in the general area. Model output (monthly discharge, dissolved solids concentration, and dissolved salt load) was obtained for four geographical locations; lower Middle Creek, lower Fish Creek, lower Trout Creek, and the Yampa River at the Hayden gaging station. The effects of mining prior to 1981 were included in the U. S.G. S. data used to calibrate the model. Therefore, the effects of mining after 1981 needed to be estimated and specifically added to the model. These effects were estimated by the Division using information obtained from the mine permit applications on file with the Division. Scenarios were developed which included both the direct and indirect surface water effects (indirect surface water effects result from the interaction of surface water with affected ground water systems). -38-