Water is one of Montana’s most essential natural resources and is a key element to all stages of any mining project. Historic impacts to water resources have left a legacy that Montana’s mining industry deals with on a daily basis. Understanding of and respect for this critical resource are essential to balance societies needs for both mineral and water resources.
Water Use and Water Rights
Water is required at all stages of mine development. In Montana, companies pursuing new mining projects must obtain water use permits from the Montana Department of Natural Resources and Conservation (DNRC) for any beneficial use including mining, milling, other consumptive uses and for produced water from a mining operation. Wells exceeding 35 gallons per minute (gpm) require permits from DNRC; wells less than 35 gpm (exempt wells) must be recorded with DNRC. Temporary Use permits for use of surface water resources may be obtained for temporary activities such as drilling or construction.
A new water right or modification of a historic water right (change of place of use or point of diversion) require submittal of an application to DNRC. DNRC’s permit process may take six months or more. Historic water rights attached to a property deed may or may not allow use of surface water, as Montana is in the process of adjudicating these historic rights and they may be denied if they haven’t been used for an extended period. A change of ownership of a water right must be disclosed in the realty transfer and recorded with the DNRC within 60 days of filing the deed.
Any water supply system that serves over 25 people is regulated as a public water supply by Montana Department of Environmental Quality. Designs for construction or alteration of public water supply systems including wells, connections, piping and associated waste disposal must be approved by DEQ. Operators of public water supply systems must be certified by the DEQ.
Historic impacts to water quality from some mine sites has focused attention on the mining industry. Acid mine drainage is a phenomenon that can occur when rock containing sulfide minerals is exposed to air and water. The water can become acidic and often carries elevated levels of metals. At elevated levels many common metals are toxic to wildlife and aquatic species. Sediment release in runoff from disturbed land, construction and roads is also a water quality concern associated with any large land disturbance. Sediment can affect aquatic life if it reaches streams or other surface water.
Water quality concerns occur not only during mine construction and operation, but may continue after mine closure. When mining is completed, dewatering pumps are turned off and groundwater may flow back into pits or underground workings where there may be continuing concerns about acidity and metals.
Changes in water quality can affect human health and the environment and are regulated by DEQ. Release of any water from a mine through a discrete conveyance (pipe, pump, ditch etc.) to surface water or discharge to groundwater requires a permit from Montana DEQ. Stormwater runoff from disturbances associated with mining activity also requires a permit from DEQ. These permits regulate discharges and set limits on the amounts of particular substances that can be discharged in water to protect public and environmental health.
Understanding water use needs and potential for mining activities to impact water resources are a key component to planning a successful mine operation. Mining companies use a variety of techniques to reduce, conserve, and recycle water from mining processes. When excess water must be discharged it may be necessary to treat it to meet permit limits. The logistical and financial requirements associated with water management are commonly a central component of the mine permitting process. Permit review typically includes:
- Testing to determine the potential for acid mine drainage from waste dumps, leach piles, and tailings
- Acquiring surface and groundwater data to establish baseline conditions
- Design of management strategies and technical solutions to prevent or control acid mine drainage and metal leaching. Detailed management plans aimed at mitigating and minimizing exposure to air and water of sulfide minerals in waste rock and processed ore are created by mining companies and reviewed and approved by regulatory agencies.
- Use of water treatment plants to treat excess water prior to discharge either to surface or groundwater