2010-02-09_PERMIT FILE - C1982056A (6)

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monitoring well down gradient of the 1983 mine plan area. The fact that the well did not show effects from • mining indicate that drawdown from the mine is limited in areal extent. A potentiometric map for 1985 would not show any differences from the 1983 map and therefore was not constructed. The direction of ground water movement in the Wadge Overburden is generally towazds the center of the Twentymile Park Basin, as shown by the configuration of the potentiometric surface for this unit (Map 13, Twentymile Pazk Hydrology). Rechazge occurs along the outcrop of the sequence where unconfined ground water conditions exist locally. The water quality data from Wadge Overburden wells prior to 1979, or from wells which aze not directly down gradient from mining activities, indicates that ground water in this aquifer is characteristically asodium bicarbonate type with relatively low concentrations of calcium magnesium and sulfate ions, as depicted graphically in Figure 4-a, Ground Water Quality Data. Total dissolved solids concentrations are typically in the range of 400 - 3000 mg/1. Concentrations of trace elements are typically very low. For example, iron concentrations aze usually less than 0.4 mg/1, and manganese concentrations aze usually less than 0.2 mg/I. Ground water data from the Wadge Overburden prior to 1983 represent "baseline" conditions for the Foidel Creek Mine. Examination of water quality data from certain wells directly down gradient from the adjacent surface mined areas indicate that recharge of the Wadge Overburden through backfilled areas has caused changes in the natural quality of the Wadge Overburden. Backfill water quality is typically much higher in total dissolved solids and is dominantly a calcium, magnesium, sulfate type. The 009-79-4 well data (Table 8, Ground Water Data) shows an increase in most major solute concentrations, particularly sulfate, after 1982 when mining operations became active upgradient of the mine area. Water quality data from well TW-1, directly downdip from old reclaimed backfilled areas, also indicates significantly high than average concentrations of TDS and sulfate. Water quality changes in wells further downdip from the existing operations have not been detected to date (1983). • The influence of recharge of higher TDS water from upgradient spoils adjacent to the Eckman Park operation is also indicated from examination of electrical conductivity data collected from inflows into the Foidel Creek mine. An examination of electrical conductivity (EC) values from the 1985 inflow survey (Map 35, 1985 Water Inflow Survey) shows a regulaz trend of decreasing values form the updip spoils. The data indicates that significant increases above baseline EC levels exist up to 2500 feet from the spoils. Ground water inflows further downdip from. the old spoil areas have EC values which aze characteristic of the natural Wadge Overburden water quality. The recognition of the effects of previous mining activity on overburden water quality is significant because it strongly suggests that the quality of ground water inflows into the vast majority of the underground mine workings will be of much better quality than is presently observed. This is discussed in some detail in the Probable Hydrologic Consequences section of this permit application. Water level fluctuations in Wadge Overburden wells reflect some seasonal influence, particularly following spring snowmelt when the majority of bedrock recharge is believed to occur. Seasonal variation in water quality during the baseline period is not evident from the data, although some variation in parameter values occurs. A 15 foot-thick clay was placed between the old spoils and the old surface mine highwall near the portal entries of the Foidel Creek Mine prior to the initiation of mining to try to minimize recharge to the undisturbed overburden form the spoils. The effectiveness of the liner is apparently limited since bypass appears to be indicated by the inflow of ground water with TDS levels of up to 4000 mg/l, which is typical of spoils water. However, much of the recharge from the spoils to the undisturbed Wadge Overburden may have occurred prior to emplacement of the liner. • The undisturbed Wadge Overburden permeability is very low, in the range of 0.01 to 0.1 ft/day. The clay liner would be expected to have permeability in the order of 0.001 ft/day. Given that the clay liner probably has permeability at least an order of magnitude lower than the natural permeability of the undisturbed overburden, is probably does offer some resistance to flow. However, the limited extent of the liner, and the fact that the integrity PR 03-06 2.04-22 05/07/03