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• Board Meeting Date: 5/21/2008
• Description: ISF Section - Injury with Mitigation - Case No. 5-07CW210; Application of Vail Associates, Inc. and the U.S. Forest Service
• Board Meetings - Doc Type: Memo

Linda J. Bassi April 29, 2008
Page 3
The actual start and finish dates and hours of pumping forsnowmaking operations would
vary from year to year depending upon when air temperatures become consistently cold
enough for snowmaking operations. Under optimal conditions, allowing well pumping to
occur for 10 hours per day, the desired snowmaking would be completed in a period of
about 36 days. Under normal operating conditions, it is likely that there will be
intermittent 1 to 3 day periods of sub-optimal conditions when no pumping would occur,
allowing the streamflow to recover to near natural conditions. As described below under
the Hydrologic Analysis, the potential reduction to the ISF would fluctuate from
approximately 0.009 cfs to 0.019 cfs, which would result in a 2% to 4% reduction of the
estimated dry year natural flow in Two Elk Creek below the Tea Cup Bowl Well at the
upperterminus of the CWCB 4 mile ISF reach.
The one acre-foot of water pumped from the Tea Cup Bowl Well is assumed to be 100%
consumptive to Two Elk Creek and the Eagle River at the time of diversion, with 80% of
the snowmaking diversions returning to Two Elk Creek and the Eagle River during the
ensuing spring and summer. During winter snowmaking operations, it is expected that
there will be a small amount of return flows to Two Elk Creek, which are not included in
this analysis.
Hydrologic analysis showing why full ISF protection is not possible
Based upon an evaluation of alternative water supply sources for snowmaking at the
base area around the Tea Cup and Skyline Express Lifts, it was determined that the
development of an alluvial well, tributary to Two Elk Creek, would be the most practical
and environmentally sound option. The potential hydrologic impacts of the proposed use
of the Tea Cup Bowl Well for snowmaking were evaluated using the Glover Parallel
Drain Analytical Solution of Groundwater Returns (Glover 1977). The Glover method
determines stream depletions from well pumping in an idealized stream-aquifer system.
The Parallel Drain method provides a mathematical solution for the stream depletion
pattern as a percentage of the pumping rate. The result of the Glover approach is a
daily time series of the depletive effect of well pumping on Two Elk Creek.
streamflows in Two Elk Creek were estimated based upon correlation with measured
flows in Wearyman Creek at the gauging station (USGS 09063200 Wearyman Creek
near Red Cliff, CO) for the period of record 1964 through 2005. Low-flow conditions
were then adjusted based upon several actual Two Elk Creek flow measurements
conducted in January of 2007.
Data required to use this method include the boundaries of the alluvial aquifer, the
saturated thickness, hydraulic conductivity, and aquifer specific yield. The boundaries of
the alluvial aquifer can be roughly estimated based upon topographic mapping of the
area. Because there are no other known wells in the Two Elk watershed, there are no
boring logs available that would provide site-specific information regarding the
characteristics of the aquifer and the alluvium. Based upon well completion reports for
wells in the Gore Creek and Eagle River alluvium and geologic mapping of the area,
reasonable ranges of conditions that are likely to be present in the vicinity of the
proposed well site can be estimated.
Well pumping would result in a small reduction to streamflows in Two Elk Creek. The
impact on streamflows in Two Elk Creek during continuous well pumping would increase
AMEC Earth and Environmental, Inc.