PUB00048

• Year: 1992
• Title: Systems Integration as a Water Supply Source for the Denver Metropolitan Area
• CWCB Section: Water Conservation & Drought Planning
• Author: Hydrosphere Resource Consultants
• Description: Overview of water supply alternatives and suggestion for process to address future water supply needs of the Denver Metro Area
• Publications - Doc Type: Historical

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DRAFT 8/24/92, Page 11

Issues to be addressed

The most difficult issue associated with the Green Mountain Exchange is the locatiun of
replacement storage reservoirs on the west slope. Many of the reservoir sites identified would
be politically controversial because of environmental problems associated primarily with loss
of big game winter range and loss of white water rafting opportunities on the main stem of the
Colorado River. Sufficient information to determine the feasibility of mitigation for these
impacts is not available. Additional issues include the following:

1. Green Mountain Reservoir was constructed by the U.S. Bureau of Reclamation in
1938 as a component of the Colorado-Big Thompson Project which serves the
Northern Colorado Water Conservancy District. A change in the purpose of Green
Mountain may require modification of Senate Document 80, which governs the use
of the reservoir and would require congressional action. There are conflicting legal
opinions regarding this issue, but at this time, the Bureau of Reclamation is taking
the position that congressional action would be required. Such changes could be
difficult, if not impossible, without nearly unanimous support.

2. Dillon Reservoir has been plagued by phosphorus loading which, if not adequately
controlled, could cause eutrophication of the reservoir. This could substantially
reduce the attractiveness of Dillon reservoir as a recreational facility and cause loss
of the fishery. Phosphorus concentrations in Green Mountain Reservoir are
generally higher than in Dillon and thus could further degradation of water quality
in Dillon. A possible solution to this problem, which required further
investigation, could be the direct discharge of the water pumped from Green
Mountain to the Roberts Tunnel.

3. The main stem of the Colorado River above Kremmling has already been
significantly dewatered by other trans mountain water diversions including the
Colorado-Big Thompson, the Windy Gap project, the Grand River Ditch, the
Moffat Tunnel Collection System, and the Robert Tunnel Collection System. One
of the main reasons for west slope opposition to Two Forks was the further
depletion of stream flows below Kremmling; Operational studies to determine the
severity and precise nature of these impacts have not been conducted for the Green
Mountain Pumpback and very little information is available regarding the
possibilities for mitigation.

There continues to be some west slope interest in this alternative because it may provide
an opportunity for development of some conditional west slope water rights. The possibility
for mitigation of stream flow impacts associated with the Green Mountain Exchange through
operational changes in the project, and environmental impacts associated with replacement
storage need further investigation.

B. Smaller New Storage Facilities

1. Gross Reservoir Enlarf!ement -- Gross Reservoir was built by the Denver Water
Department in 1954 to store water diverted from the Fraser and Williams Fork
basins via the Moffat Tunnel, as well as South Boulder Creek water. Enlargement
of the reservoir would increase the present storage capacity from 41,000 acre-feet to
113,000 acre-feet and would produce a firm annual yield of up to 21,000 acre-feet.
The annualized cost is estimated at $490 per acre-foot of yield. It may be possible
to further enhance the benefits of this alternative through cooperation with the
Northern District to allow joint use of the enlarged reservoir.