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

The metro Denver water community's interest in conjunctive use as a potentially large
scale water supply source has its roots in Denver's long-standing plans to build Two
Forks reservoir and in the more recent development of municipal wells in the Denver
Basin aquifers.

In the early 1980's Two Forks was seen as the answer to Denver's future water supply
needs. Over 100,000 acre- feet per year of storable flows remained in the South Platte
above Denver and in the Blue River at Dillon and Two Forks was thought to be the
perfect storage site for capturing these flows. While the project would have evaporation
losses, would have major environmental and recreational impacts and would require more
than 1,000,000 acre-feet of storage capacity to develop less than 100,000 acre-feet of
yield, Two Forks was seen as the only way to effectively capture these flows.

The U.S. EPA's rationale for veto of the project in 1990 was based on EPA's beliefs that
the project caused unacceptable environmental impacts and that practicable alternatives
with less adverse impacts existed. Use of Denver Basin groundwater as a supply to be
used in coni unction with surface supplies was one of the alternatives mentioned by EPA.

Development of Denver Basin groundwater began in earnest in the 1980's with the rapid
growth within southern Arapahoe and Douglas Counties, For many water providers in
this region, the Denver Basin represented the only available major water supply. Wells
could be easily developed into plentiful aquifers. The State's newly enacted SB5
regulations clarified ownership issues and facilitated well development by water districts
in the area. As growth continued in the region, Denver Basin groundwater became the
principal water supply.

However, many of these providers were concerned about relying on Denver Basin
groundwater as an exclusive supply over the long term. Natural recharge to the aquifers
was assumed to be quite limited. Providers were concerned that water levels in wells
would decline over time, leading to higher pumping costs, the eventual need for
additional wells and reduced supplies.

In the early 1990's, Arapahoe and Douglas County providers recognized the desirability
of using excess "wet year" surface supplies to meet their demands and to recharge
aquifers, thereby augmenting their groundwater supplies and substantially prolonging the
life of their groundwater resources (Mulhern, 1993). Thus the concept of conjunctive use
in a metro Denver setting was born. The most obvious source of these "wet year" surface
supplies would be the storable flows that remained in the South Platte above Denver and
in the Blue River at Dillon,

More recently, the City of Aurora has become interested in the potential of conjunctive
use as applied to local aquifers in mountain settings as a way to regulate runoff supplies
available to junior water rights. Aurora has filed water rights applications for the Eagle
River and South Park conjunctive use projects.

Conjunctive use was therefore identified early on in the MWSI as a major area of interest
on the part ofTAC members.

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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