2001-12-11_REPORT - C1980007 - Laserfiche WebLink

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• IMPACT ASSESSMENT FOR THE PERMIT AREA AND ADJACENT AREAS .'.':l:io:l:'2Ys.2:::~):,."r::.:.`:sn'~.:'•w'.'.:i.'G`ri:•oy.'uS:OSfss'a`Xe:2Y'A`.yuv','h"YSOR2:YdR!'.':U.'aVi:ix::T'.`YS.^.L`M~^'B.:iNYCRY'1l Ab`::iSiL'~~'^.~M:14':.M''tlRYRA'.G".::`.J.`:S:S:i"".~.Y."'k.".Y.'~,iRY~Y:.' ~'!^~i'SY.q`::^:'S.'C/~~LY HYDROLOGIC DATA INTERPRETATION AND This section focuses on three areas. First, it analyz- es the hydrologic data gathered during water year 1989. Second, it assesses impacts of mining on the quality and quantity of water in surface streams, springs, groundwater aquifers, mine inflows, and mine discharges during water year 1989. Lastly, it estimates potential impacts of mining on these waters during water year 1990. Surface water, springs, and groundwater are consid- ered separately even though they are interrelated. The report attempts to show the interrelationships that are significant or could be expected. Because mine water and groundwater are so interrelated, they are discussed together. ASSESSMENT OF MINE WATER AND GROUNDWATER MINE WATER The underground room and pillar mining methods in use at the Mt. Gunnison No. 1 Mine can affect groundwater in essentially two ways. First, devel- opment mining in areas where groundwater is present in or near the coal seam can cause local- ized movement of this water into the mine work- ings. To dart, groundwater movements of this type have occurred in areas of low cover which are highly fractured (near outcrops and near stream channels) and where sandstone channels bearing water immediately overlie the coal seam. Secondly, retreat mining can cause, subsidence and the fracturing of overlying groundwater formations. Again, water usually moves into the mine work- ings. At the Mt. Gunnison No. 1 Mine, the perme- ability of the "F' seam and overlying strata is very low and the areal extent and quantity of water stored in these units are small. Gulch behaved similarly to previous years, relative to inflows. InBows occurred primarily from the roof in areas of low overburden and near the "F' seam outcrop. follow locations were essentially the same as previous years and are shown on Exhib- it If. The estimated (lows at these locations are also shown on Exhibit Ii. Separate estimates are provided for low Bow conditions and spring runoff conditions. Table 6 shows total estimated sustained mine inflows for the 1989 water year. The seasonal pattern of mine inflows observed at the main portal area and along Sylvester Gulch indicate that the colluvium, coal, and bedrock recharge locally. The area along Sylvester Gulch contains many naturally occurring fractures. Water moves down slope through the colluvium and fracture zones and discharges as springs and steps. Water inflows appear to be controlled by the amount of precipitation (mostly snowmelQ, depth of overburden, and location and extent of fracture zones and not by the extent of the underground workings. Mine water inflows [or the 1990 water year in the Sylvester Gulch and the main portal areas arc expected to be similar to those of the 1988 and 1989 water years. However, precipitation could have an impact on inflow rates if there is a dramat- ic change in 1990. Precipitation during 1989 was less than 1988. Mine water inflows for other areas of the mine are related to particular geologic and topographic features as well as water-bearing formations. These areas include the 1st West Submain, Panels 1W1S, 1W2S, IW3S, 1W4S, 1W55, 1W6S, the 1st East Submain, and the Northwest Submains. Because of these local features, each area is discussed sepa- rately. 1st West Submttin During 1989, the mine workings located near the The 1st West Submain was advanced two crosscuts . outcrop, the main portal area, and along Sylvester during 1989 to make roam for the 1W6S panel.