Water is an essential — and closely regulated — component of every mining operation. From access to process and potable water to the safe discharge of wastewater, mining facilities face often rigorous state and federal requirements and guidelines for water management and treatment. One such requirement is the National Pollutant Discharge Elimination System (NPDES) permitting program, administered by each state, for constituent limits in wastewater discharge to any body of water.
Once a mining operator receives an NPDES permit to discharge wastewater, the facility must report its wastewater constituent data for each outfall monthly in a discharge monitoring report (DMR). Established in 2015, the NPDES eRule required facilities to report DMR data electronically for the first time, making electronic DMR data available for download and analysis from the Enforcement and Compliance History Online website. A review recent DMR data highlighted some potential issues for mining operations. Thousands of NPDES permit violations were reported in this dataset of mining facilities, with the most common constituent exceedances reported for nonmetals like total suspended solids, nitrogen-ammonia, biological oxygen demand, coliform, and pH. The most common metal constituents were aluminum, iron, selenium, copper and zinc — in general, products not being mined for profit.
The interpreted conclusion from this data analysis shows that mining facilities are successfully recovering valuable metals from their water discharge — gold, silver, lithium, etc. — but losing ground on the high concentration of ancillary constituents resulting from the mining process. This oversight can lead to ongoing operational difficulties if violations continue to add up. Frequent permit exceedances will lead state Environmental Protection Agency (EPA) offices to level fines and demand treatment solutions to prevent future violations. This headache can be made even more detrimental to operations if a state EPA office denies the renewal of a facility’s permit or drastically reduces the permit limit values for compliance.
Fortunately, the industry is flush with treatment methods and technologies to treat constituents in wastewater and achieve permit compliance. For example, suspended solids can be treated with coagulation and flocculation, followed by settling in a pond or clarifier. Nitrogen-ammonia can be treated with breakpoint chlorination that converts and removes the ammonia, or membrane-based degasification can strip off ammonia.
Most technologies for metals removal are similar, using heavy metals reduction through softening to precipitate out metal hydroxides or two-state softening with an organo-sulfide feed to precipitate out metal sulfides. Selenium reduction can be accomplished through activated carbon, reverse osmosis, ion exchange, evaporation or even biological treatment.
With so many solutions available, finding the most effective and budget-friendly combination of technologies to treat a facility’s unique constituent mix can be daunting. The challenge is exacerbated when each state’s permit limits vary dramatically. By partnering with an experienced firm, like Burns & McDonnell, mining operators can unearth an economical answer to achieve permit compliance.
Balancing large water requirements against water scarcity and quality is vital for mining operators to maximize efficiency and minimize water-related impacts to the bottom line. Discover an effective water management strategy to avoid operating issues and keep business impacts at bay.
