S8_11-15-04

• Basin: Statewide
• Title: SWSI Phase 1 Report - Section 8 Options for Meeting Future Water Needs
• Date: 11/15/2004
• Author: CWCB
• SWSI - Doc Type: Final Report

Section 8
Options for Meeting Future Water Needs
not designed or constructed to current engineering
standards. Upgrading the existing facilities to be
compatible with an enlargement may not be cost-
effective.
8.2.4 Conjunctive Use of Surface Water
and Groundwater
Colorado's groundwater supplies are abundant but are
limited in many areas by physical or legal availability or
economic feasibility issues. Physical limitation affects the
reliability and sustainability of groundwater as a source of
supply. Physical availability measures the amount of
water an aquifer can produce, both in the short- and
long-term, and primarily affects the sustainability of the
resource. Legal availability relates to the amount of water
that can be extracted from an aquifer under the water
rights administration system that exists in a particular
area, and can affect the reliability of the supply.
In the context of water supply, aquifers can be
categorized as being renewable or non-renewable.
Aquifers that are located adjacent to rivers in the alluvial
floodplain deposits usually have a hydrologic interaction
with those rivers, and dynamically get water from or
discharge water to the rivers throughout their reaches.
Aquifers of this type are referred to as tributary aquifers.
They usually are unconfined aquifers that are relatively
shallow. Tributary aquifers are considered to be a
renewable source of water since they are hydrologically
linked to renewable supplies such as precipitation and
infiltration of surface water.
The other category of aquifer, non-renewable, is one that
is not replenished from renewable sources such as rivers
or infiltration of rainfall. Non-renewable aquifers generally
are located deep below the land surface, in consolidated
bedrock deposits, and would be classified as confined
aquifers. A non-renewable aquifer may be capable of
producing water reliably under varying climate conditions
(wet and dry years); but it may only last 50 to 100 years
and would therefore not be considered a sustainable
resource. Recharge of non-renewable bedrock aquifers
is very slow and withdrawal rates usually exceed
recharge. As water levels decline in a non-renewable
aquifer additional wells would be required to maintain a
given pumping rate. These non-renewable aquifers are
unreliable as a permanent, sustainable water supply.
Conjunctive use of surface water and groundwater can
maximize the benefits and reliability of both surface
water and groundwater sources of supply. In its simplest
form, conjunctive use involves using surface water when
surface supplies are ample, such as during average to
above average runoff conditions, and recharging aquifers
with available surface water. When surface water
supplies are in short supply, such as during below
average runoff conditions, groundwater supplies would
be used to a larger degree to meet demands. Both
bedrock and alluvial aquifers can be used in a
conjunctive use water supply operation by serving as a
water storage bank. Deposits are made in times of
surface water supply surplus and withdrawals occur
when available surface water supply falls short of
demand.
8.2.4.1 Bedrock Aquifer Conjunctive Use
Bedrock aquifer conjunctive use involves capturing and
using surplus surface water supplies for immediate use
or injecting these surplus surface water supplies into the
bedrock aquifer through wells. The intent is to extend the
life of non-renewable groundwater sources.
The benefits of bedrock aquifer conjunctive use storage
and recovery include:
^ Maximizes the benefits of bedrock aquifers and
extends their long-term reliability. The use of surplus
surface water supplies can reduce the need to
withdraw non-renewable groundwater. The recharge
of the aquifer extends the life of the groundwater
reserve.
^ Evaporation is minimized. Once the water has been
recharged, there is no additional evaporation as
compared to surface water storage.
^ There may be fewer environmental impacts than
surface reservoir storage.
^ Requires less surface area for water storage.
^ The permitting process is simpler than for developing
surface water storage.
^ Existing infrastructure designed for peak demands
can be used during non-peak demand periods.
Existing wells developed to meet peak demands can
be used as injection wells during non-peak periods.
^ Potable quality water can be withdrawn. Most bedrock
aquifers are of potable water quality and do not
require water treatment except for disinfection.
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