2008-04-15_REVISION - M1980244 (325)

Home Browse Search

28 Grassy Valley hydrologic conditions water in these wells indicates that the underlying granite is saturated and receives only limited recharge from the alluvium because of its low permeability. i~ Alluvial wells above the diatreme are generally dry or fluctuate seasonally. Dry wells may indicate that the alluvial water has become bedrock recharge. • Groundwater levels in the granites, which show little seasonal variation, indicate that they are generally saturated and that recharge and groundwater flow within them are very limited. • No pattern of groundwater flow in the Grassy Valley feeder diatreme is clearly discernable indicating that the system is dominated by fracture flow and is compartmentalized. • Limited and localized recharge to the diatreme feeder is indicated by seasonal variations in some deep bedrock wells. • Paired diatreme wells show vertical gradients indicating slow vertical recharge and a compartmentalized system. • The vertical gradient between the Grassy Valley diatreme feeder and the main diatreme to the south indicates that there may be a significant permeability contrast between the two diatreme bodies and, together with structural geological data, indicates that the system is compartmentalized. It also indicates that the limited groundwater flow within the Grassy Valley diatreme feeder will likely be towards the main diatreme. 4.3.6_ Groundwater chemistry Groundwater samples have been collected for chemical analysis from the following monitoring wells: CAM 1A, CAM 1 B, COB 1A, COB 1 B, GVMW 1 B, GVMW 2A, GVMW 26, GVMW 3B, GVMW 4A, GVMW 5A, GVMW 7A, GVMW 7B, GVMW 8A, GVMW 8B, GVMW 10 AND WL 1A. The period of record, water quality statistics, water level and field parameter data summaries have been compiled for these wells and are provided in Tables C4 through C19 (Attachment C), respectively. Development of the WHEX portion of East Cresson surface mine will remove several monitoring wells as shown on Figure 4.1. The major ion chemistries of the average groundwater data for selected wells in Grassy Valley are presented in Figures 4.4 through 4.7. As shown in these figures, groundwater samples are generally characterized as calcium-magnesium waters and range between sulfate and bicarbonate type waters. Average groundwater field pH measurements range between 5.9 and 7.7 su, with the slightly acidic pH readings in the deeper bedrock wells GVMW-2A AND GVMW-5A. Average sulfate concentrations in the groundwater samples ranged from 6 to 582 mg/L. Nitrate concentrations ranged from 0.03 to 10.7 mg/L, with the higher concentrations. detected in the deep bedrock wells GVMW-2A and GVMW-5A, and the shallow well GVMW 26. These wells will be removed by the WHEX surface mine. 4.4 Grassy Valley water balance modeling The dynamic systems modeling code GoldSim (version 9.60) (www.aoldsim.com) was selected as the primary tool for construction of the water balance model of current and post closure conditions in Grassy Valley. GoldSim is a graphical program for performing dynamic, deterministic, or stochastic simulations to support management and decision-making. For 2736 Cripple Creek & Victor Gold Mining Company Water Management Consultants