2022-09-06_REPORT - C1982056 (3)

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Foidel Creek Mine C-82-056 2021 Annual Hydrology Report Alluvial wells are monitored quarterly for water level and field parameters and semiannually for water quality parameters (except the Jones well which is monitored annually). Field parameters include pH, temperature, and conductivity. Water quality parameters include TDS, dissolved calcium, dissolved magnesium, dissolved sodium, bicarbonate, carbonate, sulfate, dissolved cadmium, dissolved lead, dissolved mercury, dissolved selenium, dissolved iron, dissolved manganese, dissolved molybdenum, nitrate and nitrite, ammonia and orthophosphorus. Alluvial groundwater in the Twentymile Park Basin exists under unconfined conditions within the alluvial materials underlying the major surface drainages of the area and backfilled areas of adjacent surface mined areas. Stream flows are the primary source of recharge to the alluvial aquifers. Alluvial deposition is limited in areas where stream gradients are relatively steep and in areas where the stream channel has eroded to or intersects resistant bedrock. Consequently, the alluvial deposits do not tend to be continuous. Shallow wells completed in these deposits indicate that they are usually less than 20 feet thick and the depth to groundwater is typically less than 10 feet. The limited extent of the Foidel Creek alluvial deposits, and the lack of base flow in the creek indicates that these deposits are relatively insignificant to the areas groundwater hydrologic system. Alluvial deposits containing groundwater are monitored in the Foidel Creek, Fish Creek, Trout Creek and Middle Creek drainages. In the Foidel Creek drainage, sites both upstream and downstream of the TC portals and support facilities are monitored. In the Fish Creek Drainage, sites upstream and downstream of the Mine 2 area and the Fish Creek Borehole dewatering facility are monitored. Foidel Creek Alluvial Groundwater: There are four Foidel Creek alluvial wells, 009-S-10, 001-S-5, 008-AV-1, and 008-AV-2. Water levels at the four Foidel Creek alluvial wells in 2021 remained consistent with established ranges and typical seasonal fluctuations, with elevated water levels occurring in the spring in response to recharge from the snowmelt season. Although conductivity within the Fish Creek alluvium has generally increased since monitoring was initiated, it's important to note that this trend has also been observed at upgradient well 009-S-10. Conductivity measured at all four wells in 2021 remained within the historic range of concentrations. TDS concentrations at point of compliance 13