2015-08-18_PERMIT FILE - C1982056A (4)

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The water quality data from Wadge Overburden wells prior to 1979, or from wells which are not directly down gradient from mining activities, indicates that ground water in this aquifer is characteristically a sodium bicarbonate type with relatively low concentrations of calcium magnesium and sulfate ions, as depicted graphically by Figure 4- a, Ground Water Quality Data. TDS concentrations are typically in the range of 400 — 3000 mg/l. Concentrations of trace elements are typically very low. For example, iron concentrations are usually less than 0.4 mg/l, and manganese concentrations are usually less than 0.2 mg/1. 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 waters in the Wadge Overburden. Backfill water quality is typically much higher in TDS, 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 down -dip 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 historic surface operations have not been detected in the baseline. The influence of recharge of higher TDS water from up- gradient 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 regular trend of decreasing values form the up -dip spoils. The data indicates that significant increases above baseline EC levels exist up to 2,500 feet from the spoils. Ground water inflows further down -dip from the old spoil areas have EC values which are 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 the values for individual parameter occurs. A 15 foot -thick clay barrier 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 from the spoils. The effectiveness of the barrier is apparently limited since bypass appears to be indicated by the inflow of ground water with TDS levels of up to 4,000 mg/l, which is typical of spoils water. Much of the recharge from the spoils to the undisturbed Wadge Overburden may, however, have occurred prior to placement of the barrier. The undisturbed Wadge Overburden permeability is very low, in the range of 0.01 to 0.1 ft/day. The clay barrier would be expected to have permeability on the order of 0.001 ft/day. Given that the permeability of the barrier is at least an order of magnitude lower than the natural permeability of the undisturbed overburden, it probably offers some resistance to flow. The limited extent of the barrier, and the potentially significant head at the interface, probably results in a marginal difference from the hydrologic situation which would exist if there were no barrier. The existence of the liner is not believed to have caused the occurrence of the backfill discharge near the CYCC Sediment Pond F. This discharge occurs from a vertical culvert in the spoil which was used for wash down of trucks at the surface mine operation. The reason this discharge began to occur in 1984 is that pumping of the well, which had maintained the water level in the spoils below the ground surface, ceased at that time. The natural water level in the down -dip portions of the spoils is above the ground surface, as indicated by several existing backfill seeps and springs in the area, which are not up -dip from the liner. Spoils discharge at the ground surface results from recharge to the spoils at higher elevations and the lower permeability of the down -dip undisturbed bedrock, which results in pooling and elevated water levels in the vicinity of the old highwalls. TR13 -83 2.04 -22 11/03/14