SUBSIDENCE

Surface subsidence could present a potential source of risk during all phases
of the project. If
subsidence would occur the effected area should be limited to the surface
area directly over an
adjacent to the mine. The two main processes of subsidence would be overburden
consolidation
rock failure within and around the mine. Evaluation of the mining methods
and studies on the
characteristics of the bedrock, backfill, and overburden indicate the maximum
possible surface
subsidence would be less than six inches. The predicted maximum possible
subsidence is within
allowable limit for conventionally designed buildings. There should be negligible
effect on topo
and land use considering the irregularity of the existing land surface and
variability in thickness
the glacial overburden. Thus, subsidence is viewed as a low risk event. If
significant subsidenc
would occur such that surface impacts result, the affected area would be
reclaimed in accordax
with section NR 132.08, Wisconsin Administrative Code.

LEACHING FROM THE ABANDONED MINE

After mining, salvageable and potentially toxic material would be removed
from the undergroi
workings. Groundwater interceptor drillholes, backfill delivery boreholes,
and fuel supply pipeiq
would be grouted. Following these activities, the mine would be allowed to
flood.

Under different geologic conditions, such as those encountered in southwest
Wisconsin, floodi
abandoned mine and the surrounding areas could result in groundwater contamination.
Ground
quality and flow data collected during baseline studies, however, indicate
there is only a very
vertical hydraulic interaction between the orebody and the overburden. This
situation is not
expected to change significantly after mining, since the mining process would
not result in ma,
bedrock fracturing or leave large unfilled areas after mining. Thus, the
post-mining groundwa4
regime should be essentially similar to pre-mining conditions. Contamination
of the glacial a
not expected to present a risk. However, if contamination would result from
the mine, the a
specified in the groundwater contingency plan would be followed and the appropriate
remedial
would be developed and implemented.

TAILING PIPELINE FAILURES

A buried high density polyethylene (HDPE) pipeline would be used to transport
tailings slurry
MWDF. In determining the appropriate pipeline specifications, the physical
properties of HO
as resistance to corrosion and abrasion, friction pressure loss and installation
methods were
evaluated. The pipeline is designed to operate for the duration of the project
without replace
These design considerations combined with the proper installation, flow pressure
monitoring,
periodic inspections should limit leakage and allow rapid identification
of leaks. Damaged se,
pipline would be excavated, contaminated soil would be removed and new sections
of pipe wo,
installed. If a leak would occur, the impacts should be confined to the area
immediately aro
leak. Therefore, the risk of a significant failure of the tailings pipeline
is judged to be low.

MINE/MILL FIRES

Operation of the mine requires the use and storage of certain combustible
materials. Unlike
other sulfide mines, there is no potential for combustion of the ore, waste
rock or backfill.
Therefore, fires which might occur underground should be of short duration
and confined to
areas. Based on records from all types of copper, lead, and zinc mines, it
is estimated that t
maximum frequency of mine fires is 0.2 fires per year or one fire every five
years.  : f

In accordance with Mine Safety and Health Administration requirements, appropriate
precau
and mitigation measures would be incorporated into the planned mine operation.
Installation
suppression systems, widespread distribution of fire extinguishers, availability
of larger fire
units and employee safety programs should minimize the risk and provide a
rapid response to
extinguishing the fire.



Mill fires also could occur, but the risk of a major fire are judged to be
low. The probability l
unanticipated surface fire is less than one fire over the life of the project,
and the duration &
fire would be less than four hours. An on-site fire control vehicle using
Exxon personnel wou
used to contain or extinguish small fires. To control a large fire outside
assistance might be
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