PUB00084

• Year: 2004
• Title: Artificial Recharge of Ground Water in Colorado -- A Statewide Assessment
• CWCB Section: Administration
• Author: Colorado Geological Survey
• Description: This study was a special assignment to the CGS from the DNR Executive Director. The tqask was to assess the underground water storage options potentially available in our state.
• Publications - Doc Type: Tech Report

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Artificial recharge technologies are broadly grouped according to whether water is recharged at
the surface or underground, and then by whether water is recharged into the unsaturated zone or
directly into the saturated zone of the aquifer.
. Surface infiltration is the impoundment of water at the ground surface for the purpose of
infiltration to the underlying near-surface, unconfined aquifer.
. Subsurface infiltration is the application of water below the ground surface for
infiltration to the underlying unconfined aquifer.
. Direct injection differs from infiltration systems by recharging water directly into the
saturated zone of the aquifer.
. Aquifer storage and recovery (ASR) wells are wells through which water is injected into
aquifer storage during times of low demand and high surface-water supply and
subsequently recovered by pumping at a later date when demand exceeds surface supply.
. Modification of natural recharge involves man-made changes to the land surface or
hydrogeologic conditions to increase the amount of recharge from natural and local
sources.
. Underground (non-aquifer) water storage technologies apply to storage and retrieval of
water in natural or manmade voids in the subsurface, such as abandoned mines or natural
caverns.
The selection of a particular technology requires detailed site investigation and depends on the
hydrogeologic setting of the target aquifer, land availability and uses, and the project objectives.

Artificial recharge is being used in at least 32 states in the U.S. and at least 26 countries
worldwide. The methods used span the entire spectrum of known technologies, but the dominant
methods are injection wells and infiltration basins. The larger scale projects are generally located
in drier areas of the U.S. (i.e., the west and southwest), or areas in which the growing population
has overtaxed the available water supply (e.g., California, Florida, New Jersey, New York).

An inventory of artificial recharge projects within Colorado identified 19 active operations
including:
. Augmentation in the lower South Platte River basin,
. Seasonal storage as part of conjunctive use of ground water and surface water in the San
Luis Valley,
. Direct injection at two water districts in the Denver Basin,
. Regulation of water supply and water quality at several smaller municipal water systems.

The occurrence and distribution of Colorado's water resources are inherently linked to the state's
geography and underlying geology. As a result of Colorado's complex geology, a multitude of
aquifers in various areas ofthe state are suitable for artificial recharge projects. The geologic
units containing these aquifers can be broadly classified as unconsolidated sediments, poorly
consolidated sediments, or consolidated rock. The amount of storage available in an aquifer is
dependent upon the aquifer's (1) storage coefficient (storage ability), (2) areal extent, and (3)
freeboard (amount the water level could rise above present water level). In general, unconfined
aquifers have smaller areal extent, 10' s of feet of freeboard, and a high storage coefficient.
Confined aquifers, on the other hand, often have a large areal extent and 100's of feet of
available freeboard, but a very low storage coefficient.