What is Mining-Influenced-Water?
During the mining period in Park City’s history, drainage tunnels were constructed at the lower elevations of the mine works to keep water within the mountain from interfering with the mining operations. These drainage tunnels, which contain trace metals from the natural soils and mining operations, discharged directly to the environment. Over the course of Park City’s history, these waters have been used for various purposes such as drinking water, irrigation, and snowmaking. The water which exits existing mine tunnel entrances (portals) are referred to as Mining-Influenced-Water (MIW).
Why Treat Mining Influenced Water?
Metals in waste streams don't naturally degrade and are toxic to aquatic life, even at low concentrations. As part of the EPA’s Clean Water Act, it has established that cleanup of mining-influenced-waters, such as those being discharged from the tunnels, is a significant environmental benefit. In 2014 the Utah Division of Water Quality (DWQ) and Park City entered into a Stipulated Compliance Order (SCO) which contained major milestones for treatment compliance and requirements on pollutant loadings related to the water discharges from the Judge and Spiro mine tunnels. Non-compliance with the terms of the SCO can lead to:
Characteristics of MIW Treatment Design
Water treatment design is a process in which the raw water is analyzed and, based on the receiving water characteristics (stream designation by the DWQ) and the discharge requirements for the treated effluent (water to be discharged from the plant), the treatment process is established. The design is highly site specific and focuses on treatment efficiency, reliability, cost-effectiveness, and minimalizing such items as energy use, traffic impacts, maintenance, and personnel.
Characteristics of the tunnel water must be taken into consideration in terms of physical, chemical and biological characteristic. Sizing of the M-I-W treatment plant depends upon the flows collected within each drainage tunnel. Tunnel flows change from year to year and vary significantly from season to season. The new water treatment plant process has been developed through substantial studies, which included a year-long pilot-scale study to establish the treatment process and prove its effectiveness in removing metals in the tunnel raw water and a thorough evaluation of life-cycle cost and benefit.
The selected process is considered a multi-barrier approach and includes pre-oxidation, rapid mix/flocculation/ sedimentation (to remove specific particulate metals though precipitation), granular media filtration (to further remove iron and manganese from the water which may cause aesthetic water quality problems such as reddish and/or blackish staining of sinks/bathtubs or laundry), post-filter adsorption (where specific medias are used to remove targeted dissolved metals), and disinfection (for drinking water use).