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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 4
gradually until it reaches the actual rate of pumping. The hydrologic analysis using the
Glover approach was based upon the following data inputs:
Distance from well to Two Elk Creek: 120 feet
Distance from the aquifer no flow boundary to Two Elk Creek: 150 feet
Aquifer Hydraulic Conductivity: 150 feet per day
Aquifer Saturated Thickness: 50 feet
Aquifer Specific Yield: 0.2
Under these assumptions, after well pumping is initiated, the impact on streamflows
would reach about 47% of the amount being pumped after 12 hours, and 72% with one
day X24 hours) of continuous pumping, as shown in Figure 2. When pumping is
terminated, however, any impact on streamflows in Two Elk Creek would begin to
diminish at approximately the same rate that occurred during pumping until the alluvial
aquifer fully recovers from the well pumping. When the aquifer fully recovers, the
streamflow would return to the natural pre-pumping flow.
While the impact of pumping at the rate of 15 gpm X0.033 cfs) is less than the 0.04 cfs
flow reduction that would typically be considered de minimis by the CWCB, the impact
on the actual flow would potentially be greater because winter flow conditions in Two Elk
Creek are considerably less than the 4.0 cfs ISF water right. This impact would be
mitigated through the delayed impact of well pumping on streamflows and the use of
intermittent rather than continuous pumping to reduce streamflow depletion rates. For
example, assuming well pumping fora 10 hour period, the impact on streamflow would
reach 57% of the amount being pumped after 3 days of pumping, as shown in Figure 3.
AMEC Earth and Environmental, Inc.
Figure 2. Hourly percentage impact of continuous pumping on streamflow.