Memorandum To: Jaime Johnson (ArcelorMittal Minorca Mine Inc.)

From: Dan Engel, Mark Jacobson

Subject: Survey of Material Deposition at Upland Tailings Basin

Date: May 13, 2014

Project: 23691439.00

On April 7, 2014, ArcelorMittal Minorca Mine Inc. (ArcelorMittal) discovered a washout of the access

road and main perimeter dam along the west abutment of the Upland Tailings Basin (Basin). Upon

discovery, actions were immediately implemented to: (1) minimize the impact of the release from the

washout material (material), (2) investigate the cause of the washout, (3) repair the perimeter dam, (4)

evaluate the potential extent of impact to the surrounding property caused by the washout, and (5) contact

the relevant regulatory authorities. Based on the investigation into the cause of this incident, it has been

determined that a failure occurred at the main perimeter dam along the west abutment. The discharge

from the decant tower typically flows northeast, which is directed by the decant diversion ditch. During

this incident, water flow from the decant tower was redirected due to ice blockage. As a result, water

levels rose until a portion of the dam failed, causing a washout. Aerial photographs (Attachment 1)

preliminarily confirmed that this breach did not cause any tailings material impact outside of the

ArcelorMittal property boundaries. In order to confirm the extent of impact, Barr Engineering Company

(Barr) was immediately contracted to perform a site evaluation. The purpose of this memorandum is to

summarize the results of that investigation.

On April 9 through 11, Barr visually mapped the extent of material deposition, measured the thickness of

material deposition, and evaluated the potential for erosion and transport of material downstream. Figure

1 shows the general location of the area potentially impacted by the event and the Public Waters

Inventory. Figure 2 shows the lateral extent of potential impacts from this event based on a visual

evaluation. Figure 2 further indicates the estimated thickness of material deposited based on

measurements obtained during the field investigation activities.

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Impacted Area Description

The impacted areas are located west of the Basin in Section 15 of Township 59 North and Range 17 West

(Figure 1). Wetlands along the west edge of the Basin are part of a larger wetland. No channels have been

observed within the wetland complex that could drain northward into the unnamed stream located nearly

one mile downstream, which eventually drains into Sand River, part of the Vermilion River Watershed in

the Rainy River Basin (Figure 1).

Field observations

When the Basin overflowed, the water traveled northward along the perimeter road, washed out a portion

of the road, and exited the road in two distinct lobes (Figure 2). Washed out material in the south lobe

traveled approximately 1,000 feet from the road edge. Washed out material in the north lobe traveled

approximately 375 feet from the road edge. Based on the field investigation, none of the material left

ArcelorMittal property nor did it reach any waters listed on the Public Waters Inventory, which is shown

on Figure 1. It is believed that all of the material was deposited into wetland areas. A return site visit

during the growing season is recommended in order to confirm documentation of affected wetlands.

The material is composed of a mixture of fine tailings, coarse tailings, and overburden soils that were

used to construct the dam and roadway. The material was saturated with water in most areas and dark

gray in color. Deposition thickness ranges from 18 inches at the road edge to one inch at the farthest

extents of the impacted areas. The coarser material was deposited immediately, while finer material

traveled the farthest away from the breach.

The percentage of material covering the ground surface was also estimated. The material flowed around

(and not over) some micro-topographical features such as senesced vegetation, tussocks, stumps, and

boulders. Ground surface coverage ranged from 50 to 95 percent. The ground surface was still frozen at

the time of the survey, and snow depth ranged from 8 to 18 inches at the site. Snow texture was icy and

granular, and turbid water was visible under the snow surface. Further field studies and evaluation will be

necessary once the snow has melted and the growing season has begun in order to evaluate overall

impacts of the incident.

Field observations were mapped using a Trimble GeoXH 6000 Global Positioning System (GPS) Unit,

capable of recording positions with sub-foot horizontal accuracy. Photographs were collected with a

Ricoh GPS camera (Attachment 2). The field data were mapped using ArcView 10.2.1 mapping software.

The total footprint of the deposition was subdivided into multiple polygons, each assigned an average

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thickness and percent ground surface coverage. Figure 2 shows the footprint of the impacted area,

categorized by thickness, including the acreage of each specific depositional lobe. Table 1 provides an

estimate of the area of each thickness depositional range.

Footprint and Volume of Material Release

Table 1 and Figure 2 provide details of the location, footprint, and volume of material deposited within

areas located outside of the Basin, but assumed to be wetlands. It is estimated that 114,565 cubic feet of

material was washed out of the dam and roadway and deposited over a total area of 5.88 acres, although

there is not contiguous cover of material within that area. Approximately 3.2 acres of the deposition area

is 4 inches in thickness or less and 2.68 acres contains deposits of 6 inches or more. At this time, it is

believed that most of the impacted area is predominantly coniferous and deciduous forest wetland

communities dominated by balsam fir, ash, speckled alder and willow. Other tree species present at the

site include black spruce, paper birch, white cedar, and aspen. A wetland delineation will be conducted

during the growing season to determine the extent of wetlands affected by the deposition.

Containment

The field investigation included an assessment of the potential for erosion and subsequent transport of

material. Based on that investigation, it was determined that the deposits are unlikely to migrate

downslope or enter any surface waters under conditions of normal precipitation. The affected wetlands

typically consist of shrub and forested plant communities in which hydrology generally ranges from up to

about 6 inches of inundation adjacent to the Basin to no standing water at the farthest extent of deposition.

The ground surface slope ranges from flat to 2 percent in the affected areas, so surface water flow

velocities are limited and the erosive potential for surface runoff is low. Natural ground surface roughness

(stumps, boulders, depressions, hummocks, and hollows) and vegetation also impede concentrated flow

of any surface waters, and naturally contain the material. The nearest surface water is an unnamed stream

(tributary to the Sand River) located approximately 4000 feet northwest of the affected areas (Figure 1).

In addition, no continuous surface water flow paths between the affected wetlands and downstream

waters were observed during the aerial imagery review or the on-site investigation. On the basis of the

aforementioned site observations, there is little potential for material to remobilize and reach any

downstream waters, and no containment measures (e.g. silt fence) appear necessary.

Conclusion

It appears that no wetlands were affected with perennial flow connection to downstream, navigable

waters. The material is confined to areas within approximately 1,000 feet of the Basin with no potential

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for further downstream transport. More detailed delineation of affected wetland areas will be conducted

during the growing season.

Table 1

Material Release Summary

ArcelorMittal Minorca Mine, Inc.

Average Material 

Depth (Wet)

Estimated 

Material 

Coverage* Area

Material Volume 

(Wet)

(in) (%) (ac) (cf)

North lobe 12 95 0.035 1,448

North lobe 8 95 0.048 1,314

North lobe 6 95 0.068 1,411

North lobe 1 50 0.216 376

North lobe 4 50 0.024 170

North Lobe Subtotals: 0.391 4,719

South lobe 8 95 1.693 46,242

South lobe 18 95 0.181 11,235

South lobe 12 95 0.221 9,137

South lobe 12 95 0.434 17,968

South lobe 2 80 0.448 2,500

South lobe 2 95 0.180 1,189

South lobe 2 50 0.572 1,992

South lobe 4 90 0.291 3,766

South lobe 4 75 1.467 15,817

 South Lobe Subtotals: 5.487 109,847

TOTALS: 5.878 114,565

*Less than 100% due to micro‐topographic features such as vegetation, stumps, and boulders.

Location

Plant Area

LaurentianPit

UplandTailings Basin

Release SiteSee Figure 2

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Vermilion River

Wou ri Creek

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Hay Lake Outlet

Vermilion River

Figure 1SITE LOCATION

APRIL 2014ArcelorMittal Minorca Mine

St. Louis County, MN

Barr

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Copyright:© 2013 ESRI, i-cubed, GeoEye

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Figure 2RELEASE AREAS

APRIL 2014ArcelorMittal Minorca Mine

St. Louis County, MN

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Ground Elevation (feet)IndexIntermediateRelease Flowpath

Material Thickness (inches)124681218

I0 300 600150

Feet

North Lobe0.39 acre footprint4,700 cubic feet (approx.)

South Lobe5.49 acre footprint109,900 cubic feet (approx.)

Location of overflow

Attachment 1

Aerial Photograph

 

Attachment 2

Site Photographs

 

 

 Photograph 4793 – Erosion of perimeter access road, immediately downstream of overflow 

 Photograph 4830 – North lobe of material deposition, extending northwest from access road 

 Photograph 4839 – Erosion of access road, immediately upstream of north lobe of deposition 

 Photograph 4888 – Material in shallow marsh community (south lobe) 

 Photograph 4918 – Undisturbed shallow marsh (near south lobe) 

 Photograph 4922 – Thick material deposit in forested wetland (south lobe) 

 Photograph 4937 – Thin deposit of fine material in shrub wetland (south lobe) 

 Photograph 4971 – Thick deposit of coarse material (north lobe) 

 Photograph 5052 – Thin deposit of fines (north lobe)