Dames & Moore, 1999 - USDA Forest Service

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6.5.1 Air and Water Movement Associated with the Honeymoon Heights and Mine Support
Areas
The Honeymoon Heighti and Mine Support areas include the underground mine, waste rock piles,
abandoned mill building and maintenance yard. Each source area is described below.
6.5.1.1 Underground Mine Processes
Air Movement
The underground mine contains specific physical features which control the weathering and leaching of
surfaces within the mine (Figure 6.5-1):
Several portals are partially open to open (300-, 1 loo-, 1500-level main, and 1500-level
ventilator); however, only the lowest portal (1500 level main) is discharging water on a
year round basis.
No major vertically-oriented surface openings such as "glory holes" (openings to the
ground surface) or shafts exist.
The mine is flooded below the 1500 level, and the majority of the stopes below the 1500-
level have been backfilled.
All of the stopes above the 1500 level are not backfilled.
An important feature of the underground mine is that it was reported to have a consistent internal
temperature of 50°F (McWilliams, 1958), likely due to the geothermal gradient. This is an important
factor to the availability and supply of oxygen for oxidation in the underground mine.
In the summer, it has been observed that air both enters and exits the mirie at the 300-, 1 loo-, and 1500-
level portals. This is likely due to the sinking of cool, dense air in the mine when the outside temperature
is above 50°F, an effect resulting in air being drawn into the mine at other locations (i.e., 300-level), and
rising of less dense air when the outside temperature is below 50°F. Air flow through the mine is also
assumed to be caused by changes in barometric pressure. The air movement probably leads to
oxygenation of relatively near surface workings as shown in Figure 6.5- 1.
Winter is the likely time of relatively high air movement in the underground mine due to the significant
temperature difference between the external environment and the mine (Figure 6.5-2). The average
difference is estimated to be 30°F. As a result, warm air in the mine rises drawing air in through the
lower portals and causing venting from the upper part of the mine. These conditions allow oxygen to
penetrate into the workings resulting in oxidation of sulfide minerals and accumulation of weathering
products through the winter. Stopes farther back within the mine probably experience relatively stagnant
air conditions with relatively low oxygen concentrations and thus limited oxidation of sulfide minerals.
Flooded stopes below the water table remain permanently inaccessible to oxygen.
In the spring, airflow reduces as external temperature increases and the external temperatures and mine
temperatures are within 10°F (Figure 6.5-3).
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17693405-01 9Udy 27,1999;4: 11 PMDRAFT FINAL RI REPORT