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Adit Discharge Summary for the Elkhorn and Charter Oak Mines, MT
Constituents—Constituents are chemical elements and complexes dissolved in the water. These include major cations such as calcium, magnesium, and iron; major anions, such as sulfate, chloride, and nitrate; “trace” metals, such as copper, lead, and zinc; and semimetallic materials such as arsenic.
Diurnal Fluctuations—Air temperature and plant activity, which are influenced by sunlight, can influence the chemistry of surface waters. Specific conductance and pH will show a regular pattern of fluctuations through the day and night to changes in air temperature and plant activity in response.
Flume—A flume can be placed at the outlet of a dam to capture all of the stream flow. The height of the water flowing through this specially constructed channel is used to calculate the discharge.
Ground Source Control Methods—Methods to limit the water that would normally enter the water table and eventually percolate into the mine. Ground source control methods could include regrading the land around the mine to reduce potential sources of moisture.
Ground-Water Recharge and Discharge System—The entire ground-water flow system associated with a mine is composed of the recharge area, the path of ground-water flow into the mine opening, and the “plumbing” system created by the underground workings.
Grouting—Most underground mines extracted ore from fractured bedrock. The fractures can transmit large amounts of water. Grouting entails pumping semiliquid material into the fractured rock around the mine. The grout is designed to withstand the pressure of the ground water to prevent water from flowing into the workings where acid mine drainage is generated.
Mineralization—Mineralization refers to the emplacement or formation of minerals that are economically valuable.
Plugging—If the rock in which the mine was constructed has sufficient strength, it may be possible to plug the portal or opening of the mine to prevent water from discharging. The mine fills with water. After a period of time, the water in the workings returns to a quality similar to that before mining.
Recharge Area—The recharge area is where surface water enters the ground water. This can be a pond, lake, or stream that is “leaking” water to the ground, or it can be an area where rain or snowmelt enters the ground water. For small, shallow mines, the recharge area for ground water near the mine may be just a few acres within a few hundred feet of the mine. For mines that are deep with extensive workings, the recharge area may be several square miles, up to several thousand feet from the mine.
V-Notch Weir—The weir is a plate or dam with a V-shaped notch in the center that captures all of the stream flow. The discharge of the stream can be calculated based on the height of the water flowing over the notch. A water-level recorder can record the water height over an extended period.
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