Courtesy of Jon M. Dinges

The U.S. federal government and multiple states have been tightening water discharge standards over the past few years. Today, many jurisdictions are developing numeric nutrient criteria for nitrogen and phosphorous. With this in mind, mining operations need to update their water management plans to meet these new standards once they are issued.

The National Pollutant Discharge Elimination System (NPDES) permit program in the U.S. regulates the discharge of pollutants into surface waters. Delegated to most states, the program establishes total maximum daily loads (TMDLs) for pollutants for surface water bodies to help determine whether waters are either meeting their standards or are impaired for certain pollutants.

Most regulated pollutants are quantitative – for example, no more than 3.7 micrograms per litre of copper in a body of water. But historically, water quality criteria for nutrients such as nitrogen and phosphorous have been governed by regulations that state that entities “cannot discharge nitrogen or phosphorous in amounts that will cause an imbalance in flora and fauna in the water body.”

Unsurprisingly, this has made it difficult to determine discharge levels and resulting impairment. To address this, the federal U.S.  Environmental Protection Agency (EPA) promulgated the National Numeric Nutrient Criteria Strategy, and plans to work with states to develop specific numeric criteria for nutrients in water bodies.

Understanding numeric nutrient criteria

Although nitrogen and phosphorus occur naturally in aquatic ecosystems, elevated levels can cause massive algal blooms that threaten water quality and impact streams, rivers, lakes, bays and coastal waters, resulting in serious environmental, economic and health issues.

Numeric nutrient criteria targeting nitrogen and phosphorus pollution are an important tool for protecting these water bodies, as the criteria can enable effective monitoring, facilitate the development of NPDES discharge permits, and simplify TMDLs for impaired waters.

Related: Monitor, share, innovate, reduce and repeat. This is the new water cycle for mines.

Today, it is critical for states to work with the EPA to determine nutrient limits in discharge, to help water bodies move from impaired status to meeting water quality standards. The issue crosses international borders as well. To help combat the toxic algal blooms that plague the Great Lakes, Canada and the U.S. entered into the 2012 Great Lakes Water Quality Agreement, which established phosphorous reduction targets for Lake Erie. The two nations are working together to outline strategies for meeting the new targets.

Case study: phosphate mining in Florida

According to the U.S. Geological Survey (USGS), the U.S. is the world’s third-largest producer of phosphate after China and Morocco/Western Sahara. Although Canada has not yet produced notable amounts of phosphate to date, significant igneous occurrences are located throughout the country, and in 2015, Quebec approved Arianne Phosphate’s $1.2-billion Lac à Paul phosphate mine in the Saguenay-Lac-Saint-Jean region, expected to be the largest in Canada near an inhabited area.

In the U.S., phosphate mining is well-established in central and north-central Florida, where it has been a key economic driver for decades. The case study involves a large phosphate mine in Florida that operates in a very sensitive environment.

The nearby river is nutrient impaired, and the surrounding area is a designated water resource caution area, meaning water supplies are insufficient and water quantity is a concern. The Florida Springs Initiative is actively working to restore natural artesian springs across the state. Many springs are present in the area, requiring the mining company to be extremely cognizant of how they operate to avoid impacting those resources.

The mining company, the Florida Department of Environmental Protection and the Suwannee River Water Management District came together to develop a unique US$3.6-million project.

They developed a solution that relied on a pump station and a pair of pipelines to redirect water from the point of discharge back to the mine to be reused in the mine’s surface water operations. The goal was to reuse discharge water, reduce mine discharge and associated nutrient load, and reduce groundwater pumped from the Floridan aquifer system, which feeds the natural springs in the area.

The project successfully reduced phosphorus by about 110,000 pounds per year, nitrogen by about 140,000 pounds per year, and groundwater use by about 20 million gallons.

Getting ahead of regulations

Proactive, forward-thinking mining operations are committed to sustainable practices as they work to maintain their social licence to operate. Numeric nutrient criteria will continue to develop across the United States, greatly affecting how mines operate and discharge. Mining operations that have the foresight to cooperate with states proactively will benefit. For while the cost of compliance can be fairly significant, the cost for noncompliance is far more damaging.