PUB00053

• Year: 1999
• Title: Metropolitian Water Supply Investigation Final Report
• Author: Hydrosphere Resource Consultants
• Description: Metropolitian Water Supply Investigation Final Report
• Publications - Doc Type: Water Resource Studies

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Metropolitan Water Supply Investigation

MWSI Results

3.2.1.5. Analytical Approach

The MWSI analyzed an example conjunctive use project that focused on the southern
metro Denver area, involving DCWRA member providers and Denver Water. This
example was selected because of the importance of Denver basin groundwater use in the
southern metro Denver area, A large-scale regional example project was investigated
because of widespread interest in conjunctive use among DCWRA providers, and
because Denver Water's Resource Statement contained guidelines for cooperative actions
which encouraged the consolidation of water supply proposals at regional or sub-regional
levels. The MWSI's analysis focused on the physical water availability, operational,
facilities and potential yield aspects of a conjunctive use project It did not address in
detail the water rights, environmental impacts, facility costs or implementation aspects of
such a project

The central premise in the MWSI's example conjunctive use plan was that a new pipeline
from Denver's Conduit 26 could be used to deliver surface water to DCWRA
groundwater providers where it could be used directly, stored in new reservoirs, and
recharged into Denver Basin aquifers via well fields, The pipeline could also be used to
deliver surface water and groundwater back to Denver at the Foothills treatment plant
when needed, The surface water captured under this arrangement could provide water to
new development or could be delivered to existing users, thereby reducing existing levels
of pumping from Denver Basin aquifers.

Conjunctive use could be implemented with or without "borrowing" water from Denver's
reservoirs, Each of these two concepts can be explained and simulated via relatively
straightforward operating rules,

In the ''without-borrowing'' concept, surface water would be diverted from the river and
delivered to DCWRA providers only during high flow periods when Denver's unused
divertible supplies were directly available, During other periods, water would be
withdrawn from Douglas County reservoirs and pumped from Denver Basin wells to
meet demands,

In the "with-borrowing" concept, surface water would also be released from Denver's
Cheesman, Eleven-Mile and Dillon reservoirs ("borrowed") to meet additional demands,
to fill Douglas County reservoirs and to recharge Denver Basin aquifers, In this manner
additional space would be created in Denver's reservoirs to more effectively capture
surface flows in subsequent years. Borrowing from Denver's reservoirs would occur only
when Denver's reservoirs were above a specified "storage trigger" level, and the
cumulative amount borrowed ("the debt") would be tracked. If Denver's reservoirs
subsequently refilled completely, the debt to Denver would be erased. If Denver's
reservoirs only partially refilled, the debt to Denver would be the amount borrowed or the
reservoir capacity that was not refilled, whichever was less. If Denver's reservoirs fell
below the storage trigger, borrowing would cease and the debt to Denver would be paid
back with deliveries from Douglas County storage or from well pumping to Denver's
Foothills water treatment plant via the new pipeline within a specified "repayment

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Prepared for the Colorado Water Conservation Board, Colorado Department of Natural Resources by
Hydrosphere Resource Consultants, 1002 Walnut Street, Suite 200, Boulder, CO 80302