A comprehensive DNR report ensures that the mine will meet environmental standards.
In “Four key questions about PolyMet” (March 17), concerns were raised about health, water modeling, financial assurance and duration. These questions can be addressed using information taken directly from the Supplemental Draft Environmental Statement (SDEIS) prepared by the Department of Natural Resources, the U.S. Forest Service, and the U.S. Corps of Engineers. The process took almost 10 years and cost more than $50 million. The full 2,169-page report can be found on the DNR website.
According to the commentary, some medical professionals have stated that the PolyMet mine would “increase Minnesotans’ exposure to five of 10 chemicals that are major concerns to public health.” The SDEIS does not indicate such exposure, but it does describe elemental results in water studies (page 110). Water-quality models for groundwater and surface water considered 28 solutes (dissolved elements) in 29 locations. Only two solutes, aluminum and lead, will exceed allowable levels, and the exceedances are minor and infrequent. These concentrations were higher due to less dilution from rainwater that was captured in the tailings pond instead of running off. Based on the SDEIS, there will be no increase in the chemicals.
The second question stated that tribal leaders are concerned that water model data are insufficient, and “one” DNR hydrologist questioned the Partridge River flow volumes. Other DNR representatives probably have a better understanding of the whole picture, because they oversaw the studies and approved them. Also, a more sophisticated model was used in the SDEIS than in an earlier draft. This model shows that the water flows downstream of the project are environmentally safe.
The third question is about adequate financial assurances. The SDEIS stipulates that financial assurances will be required, but it does not suggest an amount. The amount will depend on reclamation costs and on estimated water-treatment costs after closure. The mining plan uses progressive reclamation, where waste rock from one pit will fill another to reduce final reclamation costs. A highly effective water-containment system and a reverse-osmosis treatment system will already exist, so no additional capital costs will be needed for those. After the mine is closed, sealed and vegetated, the only ongoing cost will be for operating the treatment plant and monitoring. Adequate financial assurances will be established to sustain the monitoring and treatment for as long as necessary without affecting taxpayers.
The final question is the duration of monitoring and treatment, which is a concern for many. The SDEIS does not indicate exactly how long water treatment would be required after closure, but the signed DNR cover sheet does say, “Monitoring and water treatment would continue until it is no longer required in order to meet environmental standards and permit conditions” (page 2). Water-quality modeling was extended for hundreds of years, but monitoring and treatment will be based on actual results and will probably be much shorter, because the mining and closure plans are excellent.
Waste rock containing some sulfides will be reburied in a 600-foot-deep solid rock mine pit far below the water table. The water flow rate through solid rock (hydraulic conductivity) is as low as 1 foot/year (page 379). In other words, leakage though the pit walls and floor is insignificant. The waste rock will be covered with clean backfill, and a new wetland will be created above that. Waste rock can be safely stored there forever, and water slowly seeping from this wetland will not be contaminated by any rock stored far below.
Fine rock tailings will be pumped to a bentonite clay lined basin after most of the sulfides have been removed by chemical flotation. Five years of testing has shown that these tailings will not generate acids. At closure, more bentonite clay and vegetation will be added to convert the basin into a clean pond and the only new water entering the pond will be from rain. Water stored in the pond will not contact the tailings, so it should require little or no treatment. Water seeping through the tailings and captured by the containment system will require treatment if it dissolves elements of concern from the fine rock surfaces. These elements could be depleted relatively fast, but it is hard to predict how long the depletion will take.
Empty mine pits gradually fill with clean water to form a new lake. Some towns, such as the neighboring town of Aurora, use these lakes for a municipal water supply. Treating water from the clear water pit is in the closure plan, but the duration could be short, because only elements on the “surface” of the solid rock might be released. Also, the pit water volume is huge compared with the surface area of the rock pit, so concentration amounts will be low.
The DNR has done an outstanding job in assuring that PolyMet’s operating and closure plan will meet all environmental standards. The environmental risk is small, and problems can be mitigated without taxpayer involvement. Some concerned citizens and groups were strongly against the mine long before the SDEIS was even released, because “other” mines that were poorly designed had issues. Going forward, I hope that the permitting agencies judge PolyMet based on its own merits, which are many.
Mining is the most viable industry on the Iron Range, and there are no other good economic opportunities in the area. The PolyMet mine is environmentally safe, and it would restore prosperity and provide jobs for citizens who badly need them.
Dennis A. Helander, of White Bear Lake, is a retired engineer.
The Opinion section is produced by the Editorial Department to foster discussion about key issues. The Editorial Board represents the institutional voice of the Star Tribune and operates independently of the newsroom.