Best Management Practice Taconite Tailings Road Aggregate
MnDOT has prepared this guidance document to provide its internal procedures and requirements for work performed on MnDOT Right of Way, including MnDOT-owned facilities. This document should not be construed as a full description of all regulations pertaining to the subject matter. Contact the Regulated Materials Unit (RMU) in the MnDOT Office of Environmental Stewardship for additional information or legal requirements.
Background
MnDOT’s current Standard Specification for Construction Manual allows taconite to be used in bituminous mixtures obtained from processed ore mined westerly of a north-south line located east of Biwabik, Minnesota (R15W-R16W) or from ore mined in southwestern Wisconsin. Starting in the 1950s, MnDOT constructed roadways in northern Minnesota using taconite tailings for aggregate in road base and bituminous, however, no records were kept documenting the origin of the taconite. Many of these roadways now require reconstruction which requires excavation of taconite tailings.
Sample testing conducted by MnDOT and others indicates that taconite tailings do not meet the regulatory criteria for ACM and so are not subject to asbestos regulations. MnDOT has produced this best practice for management of tailings used in highway construction, recognizing that even though taconite tailings are not subject to regulation, some reasonable handling techniques are prudent because a fraction of the minerals found in taconite could have an asbestos-like form. This best practice is based on MnDOT sampling and studies conducted by others.
Management Practice of Roadway Taconite Tailings
Future MnDOT highway construction contract special provisions will inform potential bidders of the presence of known taconite tailings in road sections used to construct the roadway.
Every effort will be made to leave taconite tailings on-site within the project limits. If the tailings are remaining within the project limits, no testing of the tailings is required, but the safety precautions described below must be followed.
If the tailings must be removed from the project limits, notify RMU to assess the material for asbestos using Polarized Light Microscopy (PLM) methodology. Based on previous research done on tailings from Minnesota mines and previous testing completed on taconite in MnDOT roadways, it is unlikely that testing will reveal that tailings should be considered asbestos containing material (ACM). However, to provide due diligence that MnDOT is not moving taconite that tested positive for ACM to a new location, PLM testing will be completed if tailings will be removed from the project limits.
If test results indicate the taconite tailings are not ACM, the tailings can be removed off-site for use on another MnDOT project. The safety precautions described below must be followed.
If test results indicate taconite tailings are ACM, all taconite tailings disturbed will be managed as asbestos containing waste materials (ACWM). Contact RMU for assistance.
Excavated taconite tailings will be re-used on the current project or tested non-ACM on another MnDOT project as part of road base, fill areas (such as berms) or fill slopes. All reused taconite tailings will be covered with either pavement or a minimum of six inches of soil.
Safety Precautions for Handing Taconite Tailings
- The MnDOT District Safety Administrator located in the district where a highway project with suspect or known taconite tailings is located will provide awareness training for all MnDOT project personnel regarding proper safety and industrial hygiene practices to follow when working with taconite tailings.
- Safety and industrial hygiene best practices, such as wetting active work areas, will be used when handling taconite tailings to minimize the generation of respirable dust.
- Temporary stockpiles of taconite tailings will be covered with minimum 10 mil reinforced plastic or wetted to minimize generation of respirable dust.
- If taconite will be transported off-site, dust emissions must be minimized. The taconite tailings will be covered during transportation and wetted during loading and unloading operations.