PROJ00335

• Contract/PO #: C153512
• Contractor Name: Summit County
• Water District: 64
• County: Logan
• Bill Number: XB 99-999
• Loan Projects - Doc Type: Feasibility Study

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Small Reservoir Feasibility Study

S-9

Reservoir Levels

Dillon Reservoir levels are unchanged between Scenarios II and III, but are lowered
by negligible amounts during runoff months by the increased Peru Creek operations
depicted in Scenario IV,

Peru Creek Reservoir remains substantially full in many years (those when few
releases are required) and fills in two out of every three years, The maximum annual release
over the study period was 2200 AF, indicating that a facility smaller than 4650 AF could be
considered, Average annual evaporation is approximately 70 AF for the 4650 AF facility.

Exnort Levels

Levels of transmountain diversion are unchanged in Scenarios III and IV from those of
the baseline scenarios,

CONCWSIONSAND RECOMMENDATIONS

The following general conclusions can be drawn from the baseline analyses carried
out in the basin study:

1. With respect to water supply, most County water users appear
to have adequate water rights and augmentation plans to
meet their projected ultimate demand levels. Strict
interpretation of and adherence to the USBR's Green
Mountain minimum storage targets could induce some
shortages in augmentation releases from the Sales Pool and a
few users show ultimate demands slightly in excess of their
decree limits. Although substantial shortages are indicated at
the Climax mine, their use of recycled water from tailings
ponds was not modeled so shortages there may be
overstated, Minor shortages to snowmaking demands on the
Snake River and West Tenmile Creek are induced by instream
flow requirements, Straight Creek will not be able to provide
the entire ultimate water supply demand of Dillon and Dillon
Valley.

2, With respect to instream flows, the negotiated agreements
generally appear adequate to protect minimum stream
conditions without significant impact on other water users,
Flows on the Snake River below the North Fork are routinely
below the 6 cfs decreed instream flow under ultimate
demand conditions, During the fall and winter and flows
below Dillon fall below 50 cfs about once every 6 years,
Deficiencies below Dillon in the fall and early winter are
exacerbated by exchanges for upstream snowmaking use,
The use of a monthly time step in the basin model masks
instream flow deficiencies of less than a month's duration,