REP40013 - Laserfiche WebLink

Home Browse Search

3.0 Hydrologic Consequences There is potential for dewatering of groundwater aquifers located within and above the Maxwell coal seam member of the Raton Formation. Previous studies included in the mine permit document project inflow of as much as 180 gpm and indicate an area of influence on groundwater up to 2.1 miles from the perimeter of the mine workings. The average discharge when discharge occurred from the mine at Pond 002 was 76 gpm. The maximum discharge from Pond 002 was 148 gpm. The workings are now flooding, which is resulting in changes in the potentiometric surface around the mine back to premining conditions. Localized dewatering was evident from the flow of groundwater (seeps, etc.) into the underground mine workings, and the pumping and discharge of these mine waters into surface flows. However, no loss of springs or impacts to existing adjudicated wells have been noticed to date. Relatively constant flows suggest a general low quantity of water within the formations, and retention of member integrity with retention of low vertical transmissivity of free water. There has been no noticeable impact on groundwater hydrology from the gradual flooding ofthe Golden Eagle Mine. The apparent low vertical transmissivity and integrity of the surrounding rocks might inhibit any effect of free water on the recharge of the overburden. Monitoring of the underground workings began in 1997 at GEM-1, GEM-2, and GEM-3. Rate of filling of the workings has been monitored through time and no effects have been identified. Table 3.1-1 presents the average water level data for the three wells. All data is presented in Appendix A. GEM-1 showed a slight rise in water level in 2004. GEM-2 had water for the first time in the fourth quarter of 2000 and the level rose approximately 13 feet in 2004. GEM-3 had water for the first time in first quarter of 2001 and the level rose approximately 13 feet in 2004. GEM-1 is the highest elevation of the mine floor of the three GEM wells. Water measured at this site is probably spilling to the north into the extensive area of longwall mining north of Highway 12. As measured, the current potentiometric surface of water in GEM-I, GEM-2 and GEM-3 is approximately 6814. At the current rate of flooding, al] areas of the mine appear to be in equilibrium. 3.2 WATER QUALITY PAW-6 documents an additional loading of dissolved solids greater than that observed at PAW-5, in that it detects mine water discharges. Solids levels in the PAW-6 sample taken in 2003 and 2004 show decreases from previous years which indicates that effects of mine water discharge are diminishing. Figure 3.2-1 shows water quality at the two PA W stations. However, the historic records of PRS-3 indicates little effect on stream quality from the local sources of alluvia] groundwater. Well CCAW-1 is located dawn gradient of the development waste storage area and shows elevated levels of dissolved solids (Figure 3.2-1). Basin monitored the overburden and the coal seams adjacent to the mine. The five overburden wells were completed in zones of elevated flow during drilling, and consequently reflect different strata. Two overburden wells located north ofthe workings, NM-20 and NM-22 exhibited very alkaline conditions (pH ranging from 9.9-11.85) and were sodium carbonate waters. They have moderate salinity with conductivities ranging from 400 - 504 mg/I. There are four coal wells associated with the monitoring program. Site NM-23, north of the Golden Eagle workings is a slightly acidic (pH 5.74 - 6.2), very saline (TDS of 2400 mg/1) sodium/iron chloride water. Previously this was an excessively alkaline (pH 9.4 - ] 1.46) sodium bicarbonate water. Again, there is some thought that the pump extraction process modified the chemistry of the water. This site has elevated iron concentrations, and levels of manganese and chloride which exceed ground water standards. No water quality samples were collected from deep wells during 2004 as a result of the new monitoring program. Water quality of the mine workings have been monitored as the mine is allowed to fill. Water samples have been collected at GEM-1 since 1999 and GEM-2 since 2002. The water is a sodium bicarbonate type with elevated salinity (TDS ranging from 1050 to 1540 mg/L). Figure 3.2-2 shows water quality at the two GEM stations. 292-34 Golden Eagle Mine Rpt (3.2.05) 3-3