GENERAL50259

• Permit No: C1981028
• IBM Index Class Name: General Documents
• Doc Date: 11/11/1986
• Doc Name: Proposed Decision & Findings of Compliance for RN1
• Permit Index Doc Type: Findings
• Media Type: D
• Archive: No

The applicant has also addressed the changes in ground water quality due to
the proposed mining operations. When water passes through spoil piles the
potential exists for changes in the water's quality. Studies on the Williams
Fork and Fort Union formations have shown that effluent water will contain
dissolved solids concentrations ranging from 1 to 2 times that of saturated
overburden extracts. The applicant prepared saturated extracts from composite
grab samples taken from 3 cores in the Laramie formation, The results of the
saturation extracts revealed an acreage TDS concentration of 450 my/1. From
that we would predict the spoil water quality to be 1-2 times this, or 4500 =
9000 my/l. Baseline water quality data for the overburden aquifer revealed a
TDS concentration of 7,000 my/1. Actual spoils water quality data collected
in Decerr~er of 1985 revealed a TDS concentration of 6900 nU'/l. This indicates
that the spoil water TDS concentration is similar to baseline and about 1.5
times the concentration predicated by the saturation extract. THis°shows that
spoil water will not degrade Ennis draw above baseline levels.
The final impact considered by the applicant was the potential for changes in
the recharge capacity of the Laramie overburden. The baseline investigation
of recharge capacity revealed that very little recharge to the Laramie occurs
at the mine site. This can be attributed to the water holding capacity of the
thick layer of overlying blow sands. Although the hydraulic properties of the
spoil are difficult to predict, the high clay content of the Laramie formation
suggests that the hydraulic conductivity of the spoils will be close to
baseline conditions. The effect of replacing only 4 feet of sand over the
reclaimed areas may suggest that an increase in recharge will occur. However,
the soil studies in Appendix L display field studies that show a 1'.9 inch
rainfall event only penetrated 28 inches into the sand. Based on the above
facts and predictions, the Division finds that the recharge rate will not be
significantly changed by the operation. Any potential increase in the
recharge rate should not significantly affect the hydrologic balance provided
the water quality predictions are sound. The ground water monitoring program
is designed to verify the hydrologic projections and identify any unforeseen
impacts to the hydrologic balance.
Monitoring:
The Coors Keenesburg Mine has collected extensive baseline water quality and
water quantity data since 1978. These baseline data are used to compare with
present day impact assessment monitoring. The overburden, coal, Laramie-Fox
Hi11s, Aeolian and Ennis Draw aquifers are monitored on a regular basis,
Currently 9 wells are monitored in these aquifers. With the exception of one
well, all are monitored for field and full suite parameters at regular
intervals. Water monitoring and analysis procedures are discussed on pages 56
and 57 bb of the permit application.
Sampling proceaures at this mine have been observed to be of high quality.
Water level measurements are accurately taken. Wells are evacuated at least
one volume with a submersible pump before a sample is taken and samples are
refrigerated and transported to a lab within 2 days.
The original permit approval contained a stipulation which required the
submittal of an annual hydrologic report. The Division believes that analysis
of the collected monitoring data is necessary to determine the extent of
impacts of mining on the hydrologic balance.
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