APPCOR11820

• Permit No: C1981034
• IBM Index Class Name: Application Correspondence
• Doc Date: 10/8/1982
• Doc Name: GRAND MESA GROUND WATER FINDINGS
• From: MLR
• To: DAN MATHEWS
• Media Type: D
• Archive: No

• -4- •
There is also the potential for the water quality in the three aquifers to
be impacted as a result of the proposed mining. In fact, this has already
occurred in some of the old workings near the existing E seam mine.
Water in these old workings have been found to have a TDS concentration
of about 10,000 mg/1. This is extremely poor quality water. It is not
known why the water quality in the old mine workings is so poor. However,
it is possible that the water quality in the new mines will be equally
as bad when mining is completed. Once the coal seam aquifers are
reestablished, discharge will probably again be to the glacial/alluvial
aquifer through the coal seam subcrop. The applicant has calculated that
the flow through the glacial/alluvial aquifer is about 1.53 cfs. Assuming
that the discharge from the coal aquifers is equal to the mine Inflows,
about 0.11 cfs will be discharging from the two coal seams into the
glacial/alluvial aquifer.. According to this scenario, the discharge
from the two coal seams represents about 70 of the total flow in the
glacial/alluvial aquifer. Amass balance analysis conducted by the
Division predicts that the resultant post-mining TDS concentrations in
the glacial/alluvial aquifer would be about 900 mg/1. The pre-mining
TDS concentration in the aquifer averaged about 330 m_q/1. This increase
of 570 mg/1 is probably a worse case. The assumptions and variables used
in the analysis are the same as those used by the applicant to predict
post-mining water quality in Ward Creek (see page 6B of the application,
September 9, 1982, addendum). This change in water quality will affect
water use patterns in the vicinity of the mines. A TDS of 900 mg/I
is in excess of EPA domestic water quality standards. According to the
applicant, there is little domestic use of ground water in the area
anyway. Most domestic water users obtain their water supply from the
Colby municipal water line. Other uses of water (stock, irrigation, and
industrial) should not be significantly affected by the predicted water
quality change. Ground water monitoring will be required to verify these
predictions.
The applicant proposes to place mine development waste on the existing
refuse pile (see Map 2.05.3(2)(b)-1 of the permit application). The
existing refuse pile is largely located in old abandoned strip mine pits.
Some additional disturbance is proposed. The refuse pile will be completely
underlain by bedrock and not the unconsolidated glacial/alluvial material.
The applicant has determined that significant vertical permeabilities
do not exist in the strata near the mine (see pages 20-35 of the application
addendum). Therefore, vertical infiltration of leachate into underlying
aquifers should not be a significant problem. Upon final reclamation,
the potential for hydrologic impact should actually be less because the
old strip mine pits will be reclaimed.