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

After mining ceases, the pumps will be shut off and the mine will refill. The
• applicant has predicted a maximum depletion of stream flow of 182 gpm. This -
rate is based upon the full development of the life of mine plan for both the-
No. 5 and No. 6 Mine. This flow equates to 0.4 cfs. The Colorado Department
of Health has predicted a low flow fora 7-day/10-year event of 25.9 cfs for
the Williams Fork River. A depletion of 0.4 cfs to this flow would be
insignificant.
The Eagle Mine Complex is presently permitted through the Colorado Department
of Health to discharge up to 4.48 million gallons per day or 6.93 cfs of mine
water from the Eagle No. 5 and No. 6 Mines. A minor flow is permitted from
the Williams Fork strip pit. No discharge has occurred to date from the Eagle
No. 6 Mine which is being developed in the E seam underlying the F seam of the
No. 5 Mine. However, a monitoring well placed in the E seam shows it to have
comparable water quality to the No. 5 Mine discharge water. The water is
typified as sodium bicarbonate with a mean concentration for the No. 5 Mine
discharge of sodium of 312 mg/1 and mean bicarbonate level of 772 mg/1. The
conductivity for the No. 5 Mine discharge has a mean of 1220 umhos/cm. The
iron content of the water averages approximately .3 mg/1. The sulfate level
is relatively low with a mean of 67 mg/1. The discharge point for this water
is into the Williams Fork River and lies between upstream and downstream
monitoring stations on the Williams Fork River. The water of the Williams
Fork River is of a sodium bicarbonate type. Dissolved solids concentrations
average 340 mg/1 at an upstream gauging site above the mine water discharge
point. The downstream site averages 350 mg/1. A higher proportion of sodium
is evident in the downstream Williams Fork site,.possibly a resul•
• discharges from the No. 5 Mine, previous discharges from the No. and
discharges from the Williams Fork strip pit. Due to dilution no ping
increase in sodium levels in the Yampa River is noted. The Yampa River both
upstream of the confluence of the Williams Fork and downstream is typified as
a calcium/sodium bicarbonate type. Dissolved solids levels of the Yampa River
are lower than in the Williams Fork with a mean fora downstream gauging
station below the confluence with the Williams Fork of 281 mg/1.
A comparison of the upstream undisturbed Williams Fork sampling site and the
downstream sampling site leads to a conclusion that significant degradation of
the stream water system has not occurred to date due to pumpage from the No. 5
Mine. The surface water monitoring system will remain in effect until mining
has ceased and the Division is able to find that no further potential impacts
to the surface water system from mining activities can occur, that the
operator has minimized disturbance to the hydrologic balance and that no
material damage has occurred.
The Williams fork alluvium through the mine facilities complex is monitored
for quality and quantity by three wells, one of which is upgradient of the
mine disturbance. No significant variation is noted in quality or quantity of
water between the sites. However, from 1982 through 1985, the conductivity of
all the wells has risen. Well AVF-3, for example, had a low conductivity of
less than 900 umhos/cm in 1982 and rose to a high of 1800 umhos/cm in
mid-1984. Because the upgradient unaffected well (AVF-6) also shows this
trend, the rise in conductivity is assumed to be a natural occurring
condition. The major chemical constituents creating the increased
•
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