WATER TREATMENT PROCESS
Water pollution is not an option
As a mining company, we know our environmental footprint extends beyond our fence line. The most obvious example is water, which — if managed improperly — has the potential to harm the environment. Using state of the art water treatment, process control, testing, and water management capabilities we can eliminate that potential.
Early in project development, water balance models predict the amount of water necessary versus available. Process requirements, reuse opportunities, plus historical climate and hydrological data are all taken into account. The models serve as the foundation of a water management plan, which is an integral component of mine design, operation, and closure.
In an ideal situation, you would have just the right amount of water when it is needed. In Back Forty’s case, we have more water than we can use; therefore we need to collect, treat, and discharge excess water. That means our water management plan must be tailored to reflect the needs of both the facility and the community.
As a result, our plan promotes continuous improvement in the form of minimizing water loss, efficient water usage, in-process recirculation systems, and most importantly — effective water treatment.
Our mine features an on-site, state-of-the-art wastewater treatment plant (WTP) to ensure the treated water is safe for the environment, and even cleaner than the strict quality standards established in our NPDES permit. For example, our standard for mercury is 1.3 parts-per-trillion, or 0.0013 ng/L which much lower than the EPA safe drinking water standards and the average statewide observed concentrations in water bodies. The WTP is designed to treat up to 63,000 gallons of water per hour. The treated water will be reused in the mining process or discharged to the environment. The plant will begin operating during construction and continue into closure.
PROCESS DESCRIPTION
CONTACT WATER BASINS
Water that comes into contact with mining activities (e.g., mill process water, inflow to the open pit, tailings and waste rock facilities, runoff from snow and rain) will flow via gravity or pumps to lined Contact Water Basins (CWB). Design features of the CWBs include a maximum capacity of roughly 161M gallons, ability to contain a 100-year/24-hour storm event, a composite liner system, and emergency spillway to the open pit. From the CWBs, water will be pumped to the WTP to begin the treatment process.
PRECIPITATION
Treatment starts with a series of reactor tanks to remove as many dissolved solids as possible from the water. A chemical reaction within the tanks causes very fine particles to bind together to form larger particles for easier removal in the following steps.
CLARIFICATION
Here the particles, or solids, settle to the bottom of the tank. The solids are pumped to the mill to be combined with thickened tailings and sent to the tailings management facility. The water above flows to the filtration process.
FILTRATION
The water will travel through a sequence of filters to remove any fine particles remaining after the clarifier.
The first is a multimedia filter composed of elements such as sand, activated carbon, and gravel to remove solids from the water. Multimedia filters help remove suspended solids similar to how a coffee filter traps coffee grounds and allows water to pass.
Next, the water passes through a 0.1 micron cartridge filter. For a sense of scale, a human red blood cell is about 7.5 microns wide. The tiny holes in this filter allow water to move through and stop unwanted particles from continuing.
From here, water passes through another filter with adsorbent pellets designed to collect dissolved mercury. The water we discharge to the Menominee River is required to meet the quality standard of 1.3 parts-per-trillion — try to imagine a single drop in 10 million gallons of water.
Finally, water will pass through a 0.5 micron cartridge filter to prevent any remaining particles from leaving the system. From here the water is sent to the treated water tank.
TREATED WATER
The treated water storage tank will hold the water until it is reused in the mining process or discharged to the environment. Our permit allows for the release of up to 1.52 million gallons of treated water per day. The actual amount discharged will vary by the amount of water the plant receives. We will only discharge water that meets quality standards to the Menominee River. If water does not meet permit conditions, we will return it to the CWBs for re-treatment.
An on-site laboratory will analyze water quality data necessary for both operations and process control. A third-party accredited laboratory will confirm compliance with permit requirements.
MONITORING
For more than a decade, we have been studying the regional groundwater and surface water conditions. Simultaneously, we have managed a regional hydrology survey to define surface water conditions in the surrounding rivers and lakes.
Existing groundwater and surface water monitoring programs extending beyond the mine site will continue throughout operations and after mine closure. Monitoring includes water quality and the aquatic ecosystem both upstream and downstream of the discharge point to the Menominee River. Michigan Department of Environment, Great Lakes, and Energy, U.S. Environmental Protection Agency, and
Wisconsin Department of Natural Resources all determined that the conditions in our water discharge permit will protect the health of the community, wildlife and the environment — including the river.
Throughout the life of the mine, we will continue to look for ways to reduce our environmental impact. If you have additional questions or concerns, you can reach us by clicking on the Contact tab at the top of the page.
