In 2023, engineering staff and reclamation crews at Coronado’s Greenbrier and Logan divisions set out to reduce iron concentrations in water discharge by use of a passive stone bed water treatment system. This system treats mine water discharge to compliant concentrations without introducing chemicals, which not only reduces treatment costs, but also limits potential environmental impacts due to chemical overtreatment.
Challenge
At times, mine water discharges require treatment to meet permitted effluent limitations. In some situations, such as alkaline iron discharges, treatment options other than the introduction of chemical additives are available.
Solution
The use of passive treatment facilities whenever possible not only provides economic benefit to Coronado, but also eliminates the use of potentially harmful chemicals, with the added benefit of a more natural looking aesthetic. Coronado has been able to achieve compliant discharge while significantly reducing treatment costs and minimising potential downstream environmental impacts.
Outcomes
Implementation of the stone bed passive water treatment system resulted in:
Logan Division: The site discharges approximately 50-150 gpm of 12 mg/l iron water. Prior to construction of the rock ditchline, the site was utilising 15,000 to 20,000 gallons of sodium hydroxide per month, resulting in an average cost of U$28,950 to US$38,600 per month. Following installation of the 2,200 linear foot rock ditchline, the iron concentration reduced by 99.5% which meets effluent limitations while not requiring the introduction of any sodium hydroxide.
Greenbrier Division: The abandoned underground mine holds approximately 50 million gallons of water that must be dewatered to release the permit. This water has an iron concentration of approximately 10 mg/l, which is significantly above effluent limitations. Rather than treating the water with sodium hydroxide to achieve permit limitations of the discharge, Coronado is constructing two 1000’ by 15’ iron staining beds. These beds are predicted to reduce iron concentrations by 99.9%. This system is estimated to result in cost savings of US$120,000 over the planned dewater period in chemical cost alone. The limestone bed construction will result in a total cost savings of approximately US$165,000.
