GENERAL44216

• Permit No: C1981044
• IBM Index Class Name: General Documents
• Doc Date: 12/11/2001
• Doc Name: Page 33 through OSM Mine Plan Approval
• Permit Index Doc Type: Other Permits
• Media Type: D
• Archive: No

• There are no anticipated secondary impacts of the future mine discharge~pn the
quality of water in the bed rock aquifers. The Trout Creek and Middle
sandstones subcrop in the Williams Fork Valley upstream from the point of
discharge of the mine water. Although subcrop of the Twentymile sandstone is
downstream from the discharge point, the potentiometric data and map of the
aquifer indicate the probability of its discharging into rather than being
recharged by he impacted Williams Fork River. The characteristics of water
from the Twentymile sandstone and that of the Williams Fork River are so
similar that no clear demonstration of their discharge/recharge relationships
can be made on a quality basis. Such relationships might be clearer should a
greater difference develop between the two waters, eq. by future quality
deterioration of the river as the volume of mine water discharge increases.
At present, however, and based on the potentiometric relationships within the
aquifer, recharge by the impacted river and, therefore, degradation of the
quality of water in the Twentymile sandstone is believed unlikely.
The White Sandstone does not subcrop beneath the Williams Fork Valley. Its
subcrop underlies the Yampa River and its alluvium, upstream from the
confluence of the Yampa and Williams Fork Rivers. Asa result, the White
Sandstone will show no secondary impact on its water quality as a result of
being recharged by river and alluvial water impacted through discharge of the
No. 5 and No. 6 Mines. Strangely enough, the chemical character of water
sampled from certain of the White Sandstone monitoring wells has a greater
resemblance to that presently being discharged from the mine than has the
water from any of the other major sandstone aquifers.
• Following closure of the mines, it is estimated by the applicant that the
combined Eagle No. 5 and No. 6 Mine workings will take up to 16 years to
flood. Reportedly, the mines will have the potential to discharge from the
No. 5 portal toward the end of flooding. With the filling of the mine
cavities, the rate of inflows will decrease as the differences in static heads
are reduced between the mine and rthe sources of the inflow. This reduced rate
of inflow will increase the residency time of the mine water within the mine
cavity and thus allow for an increased chemical reaction time. The likely end
result is the development of increased total dissolved solids concentrations
and of potential acid, alkaline, or toxic mine discharges. Since the
applicant is required to properly seal mine openings to prevent gravity
discharges of mine waters, direct degradation of surface water by the escape
of this mine water through the mine portal will be eliminated.
Water from the flooded mine, however, also has some potential to contaminate
overlying and underlying aquifers. This contamination of ground water in
adjacent aquifers requires that; 1) there be a connection between the mine
workings and the aquifer; and 2) there be greater hydrostatic head in the mine
workings than in the aquifer so that mine water can be driven into the
aquifer. There is little likelihood of mine waters moving downward against
generally greater hydrostatic heads in underlying aquifers. Overlying
aquifers, however, may be impacted given the development of positive
differences in hydrostatic head and a hydrologic connection such as faulting,
or natural and/or subsidence fractures.
•
-35-