Wastewater from the Rock Creek Mine would be required to pass though a treatment facility and a diffuser pipe prior to its discharge into the Clark Fork River. Montana Department of Environmental Quality describes the diffuser as "...a perforated pipe running transverse to the flow of the river anchored to the bed of the river. The proposed design calls for a diffuser extending the full width of the river (300 feet) in order to provide maximum dilution. Two-inch ports in the pipe would be spaced every ten feet.” Without this diffuser pipe to mix the mine effluent with river water, a concentrated plug of polluted water would enter the river with little mixing. As a result, migrating trout would be more likely to avoid this area of the river with its elevated metals.

Even after the complex water treatment process and dilution with the river via the diffuser, the discharge from the mine would still exceed acute aquatic life standards for copper, cadmium, lead and silver. It would require an additional 300 feet of mixing zone in the river to meet water quality standards for aquatic life. This discharge would also contain additional toxic metals such as mercury, arsenic, manganese, selenium and zinc. The complex system of treatment and discharge though the diffuser would need to be maintained and operated in perpetuity.

The efficiency of the water treatment and the quality of the effluent discharged into the Clark Fork River is based on information provided to Montana DEQ by the mining company and its consulting firm. Montana DEQ determined the limitations of the effluent and simply accepted the assurances from the mining company that the parameters would be met.

Revett’s approach to dealing with the mine tailings (waste rock removed from the mine) is fraught with problems.  The Rock Creek Mine would produce 100 million tons of tailings, creating a 325-acre mountain of toxic waste rock over a football field high (325 feet).  This  pile would be unlined and would sit adjacent to Rock Creek and  just a quarter mile from the Clark Fork River.   Of particular concern is the level of arsenic, a human carcinogen, and other heavy metals in the proposed pile.  In fact, the tailings would discharge 20 – 30 gallons per minute of contaminated water from the bottom of the pile  into the aquifer. That’s 43,200 gallons of water a day carrying arsenic, lead, copper, zinc and cadmium into the groundwater that recharges streams, rivers and wells. The U.S. Fish and Wildlife Service recognized the risks to Rock Creek and its bull trout from the tailings when they stated in the 2006 Biological Opinion that "groundwater filtration of metals from the tailings impoundment would risk contamination of Rock Creek."

The mining process would create massive underground rooms that would fill with water that has been diverted from the wilderness and surrounding area.  During mine production, the water entering these rooms would become contaminated and have to be pumped out to the treatment facility. The post-mining world beneath the wilderness would, however, be vastly different. When the lights have gone out, the machinery has been quieted, the mining company and those that permitted the mine are long gone, and the mine adit (opening) plugged, 2,046 gallons of water will continue to enter the mine every minute of every day. This water will collect forming a subterranean reservoir that will contain 207 million gallons of water, cover 64 acres and be 10 feet deep. It is likely that acid mine drainage and metals leaching will develop in this man-made cavern beneath the wilderness. The polluted water will escape into the wilderness ecosystem via springs and seeps, threatening the East Fork of Bull River, Rock Creek and other tributaries. Stemming the outward flow of contaminated water would be extremely difficult if not impossible.

Subsidence (cave-ins) is an inevitable consequence of underground mining—it may be small and localized or extend over large areas. It may be immediate or delayed for many years. But it can, and commonly does, impact streams, lakes and ponds above underground mining cavities.

"Subsidence can cause the formation of open cracks, fissures or pits, which, if connected either directly or indirectly to surface water (streams, lakes, ponds), may lead to partial or complete loss of water that is drained to lower strata or mine workings. Depletion of water resources in this manner can impact their suitability (quality and quantity) as well as impact aquatic life forms (SME, 1986) and other life, which may depend on surface water systems." (Excerpted from: Technical Report on Underground Hard-Rock Mining: Subsidence and Hydrologic Environmental Impacts by Steve Blodgett, M.S. and James R. Kuipers, P.E.)

Translation? Even though a mine may be 800 feet below the surface, it can have severe, repercussions on surface water. In the case of  the Rock Creek Mine, the ore body sits beneath alpine wilderness lakes and numerous creeks and streams. Cliff Lake sits above what would be the mine cavity and would be one of several alpine wilderness lakes at risk from draining due to the exposure or formation of mine related subsurface cracks and fissures. Cliff Lake also receives 90% of its recharge from groundwater and any "alteration of flow" would starve the lake, causing it to die a slow death.