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Cumulative Hydrologic Impact Statement The most recent cumulative hydrologic assessments for the basins germane to Meadows No. 1 were updated in January, 1987 for the ground water basin associated with the Hayden Gulch mine and in October, 1987, for the Yampa River Surface Water basin associated with the Eckman Park Mine (see Figure 4). These assessments considered short-term and long-term effects of mining to the surface water and ground water hydrologic systems. These CHIS's are available for review at the Division's offices, 1313 Sherman St., Room 215, Denver, Colorado 80203. The following paragraphs summarize the projected impacts in these basins. Mining in the Hayden Gulch Syncline will affect the quantity and quality of localized aquifers in the Mesa Verde formation. Water quality and quantity in the regional Tow Creek, Trout Creek and Twentymile Sandstone aquifers are not expected to be impacted by mining. A decrease in the water levels of the Wolf Creek, Wadge and Lennox coal-overburden aquifers is expected. The water levels will decrease adjacent to the mine pits during mining. The water levels will rise after the backfilled mine pits resaturate to an equilibrium level approximating the pre-mine water levels. The reduction of ground water levels will be insignificant due to the short-term duration and the negligible impact to existing supply wells. Ground water contributions to streams from the aquifers are not expected to decrease because of the large distance from the affected recharge area and the discharge area of the aquifers and the long travel time required for ground water to travel from the recharge to the discharge areas. The long-term effects of surface mining will be the development of spoils aquifers and associated spoils springs in the backfilled mine pits and the degradation of water quality in the backfilled spoils. Spoils aquifers may develop in the backfilled mine pits and may provide recharge to the local coal-overburden aquifers present in the downdip mine highwall. Excess spoils water which does not recharge the bedrock will discharge at the surface as spoils springs. The poor quality spoils water that infiltrates the bedrock aquifers will move down-gradient in the bedrock. Impacts to these aquifers on a regional scale is expected to be minimal because dilution of the effluent plume will occur as the affected ground water moves down gradient. Excess spoils water that does not recharge the bedrock aquifers will discharge at the surface as spoils springs. The addition of this lower quality water to the surface water system will result in increased flow and salinity in the streams, predominately during the six-week period following snowmelt. Spoils water quality will return to background levels as water flushes salts from the spoils materials. Estimates on the length of time required to flush backfilled spoils to background salinity levels range from several hundred to a few thousand years. -9-