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C itizen’s Gu i de to D e n v e r Basi n Grou n dwat e r This Citizen’s Guide to Denver Basin Groundwater (2007) is the seventh in a series of educational booklets designed to provide Colorado citizens with balanced and accurate information on a variety of subjects related to water resources. Copyright 2007 by the Colorado Foundation for Water Education. ISBN 978-0-9754075-6-1

Acknowledgements The authors and the Foundation are solely responsible for the contents of this Guide. Authors: Ralf Topper, Colorado Geological Survey Bob Raynolds, Denver Museum of Nature & Science Design: R. Emmett Jordan The Colorado Foundation for Water Education thanks the people and organizations who provided review, comment and assistance in the development of this Guide. The Foundation extends a special thank you to the Colorado Geological Survey, Colorado Water Conservation Board and Suncor Energy Inc. for their generous financial support that made this publication possible.

Colorado Foundation for Water Education 1580 Logan St., Suite 410, Denver, Colorado 80203 • 303-377-4433 •

Officers President: Diane Hoppe 1st Vice President: Justice Gregory J. Hobbs, Jr. 2nd Vice President: Matt Cook Secretary: Wendy Hanophy Assistant Secretary: Rita Crumpton Treasurer: Chris Rowe Assistant Treasurer: Ken Lykens

Board of Trustees Staff Steve Acquafresca Becky Brooks Rep. Kathleen Curry Alan Hamel Taylor Hawes Lynn Herkenhoff Sen. Jim Isgar Rod Kuharich Veva McCaig Margaret Medellin Dale Mitchell John Porter John Redifer Rick Sackbauer Robert Sakata Reagan Waskom

Don Glaser, Executive Director Jeannine Tompkins, Office Manager

Mission Statement The mission of the Colorado Foundation for Water Education is to promote better understanding of water resources through education and information. The Foundation does not take an advocacy position on any water issue.

Colorado Foundation for Water Education

About the cover: Inset above homes in Castle Rock, two men pose with their horse-powered well drilling rig. All photographs and illustrations are used with permission and remain the property of the respective photographers (©2007). All rights reserved. Denver Public Library Western History Collection–cover (top), p.1 (bottom), p.12 (top 2), p.15, p.21. Brian Gadbery–cover (bottom), p.10, p.22, p.24, p.28. Ruth Wright–p.1 (top). Emmett Jordan– p.2, p.16, p.17, p.18, p.28, p.29. Eric Wunrow–p.4. Bob Raynolds–p.6 (3), p.8, p.33 (background). iStockPhoto. com–p.32. Jim Richardson–p.33.

Foreword Recent archaeological investigations have unearthed ancient Puebloan

munity-wide water planning efforts proved vital to their success.

reservoirs within Mesa Verde National Park. To support a population

In the semi-arid west, water is viewed by some as an under-val-

that grew into the thousands, the ancestral Puebloans of south-

ued commodity for which our expectations should be modest and

western Colorado learned to plan, build, and operate public works

our willingness to pay, higher.

projects to collect and store water. Some evidence suggests that

Our modern society has more resources than the Puebloans

their disappearance by A.D. 1300 may have been in response to

and can better adapt to changes in the distribution of our natu-

decades of successive drought cycles

ral resources. The administration and

and the subsequent loss of their water

management of water for sustained

supply. Like our predecessors, we need

future growth will become increas-

to develop long-term water supply strat-

ingly complex. This will require more

egies to serve and sustain our growing

reliance on strategies such as aquifer

population. Fortunately, we have more

storage and recovery, conjunctive use

technical and physical resources avail-

of ground and surface water resources,

able to meet our water needs. The chal-

conservation and reuse, and controlled

lenge will be to develop and implement

groundwater pumping. Aside from these engineering and management

effective water supply strategies in a timely and responsible manner.

Excavation of Far View Reservoir, Mesa Verde National Park.

mechanisms, political, economic, and

Many residents of the greater Denver metropolitan area are

personal behaviors may also continue to evolve and our laws

relying on non-renewable groundwater from deep aquifers in

will continue to adapt in order to reflect the true value of safe

the Denver Basin for their water supply. Increased reliance on

and secure water resources for future generations.

this resource has resulted in significant water level declines in

This Citizen’s Guide explores the nature of groundwater in the Denver Basin from a geologic, hydrologic and a sociologic

some areas. Population growth and increasing prosperity result in in-

perspective. Particular attention is devoted to the area of south-

creasing municipal water demands. Projections from the State

ern Arapahoe County and northern Douglas County, commonly

Demographer suggest that 2.8 million new residents will call

referred to as the South Metro Area, because of its rapid growth

Colorado home by the year 2030. Approximately two-thirds of

and reliance on groundwater. Although much is known about

these new citizens will reside along the Front Range. Population

the nature of the Denver Basin aquifers, additional understand-

growth in Colorado will influence changes in lifestyles, land use,

ing is necessary to effectively and wisely use this water sup-

politics, personal values, and economics.

ply. This publication presents information regarding the history,

Perhaps we can learn from the early Puebloans whose com-

status and future of this important water resource. Cowboys water their horses at what was then known as Mummy Lake. Excavation revealed this site was part of an ancient reservoir system and is now known as Far View reservoir.

Citizen’s Guide to Denver Basin Groundwater


Table of C on t e n ts

Foreword............................................................................................................................ 1 Background........................................................................................................................ 4 Groundwater Basics.......................................................................................................... 6 Studying the Denver Basin............................................................................................... 8 The Geologic Story............................................................................................................ 9

How Geologists Read the Earth’s History from Rocks.......................................... 10

Aquifer Descriptions.............................................................................................. 11

Fountains of Water: Water Use and Regulation........................................................... 12

Denver Basin Groundwater Development............................................................. 13

On the plains, windmills (above, right), which pump groundwater (above) for livestock, are a common sight.


Colorado Foundation for Water Education

Widespread Use of Wells and Drought Conditions Require

Groundwater Management................................................................................... 14

Regulating the Denver Basin Aquifers................................................................... 16

The Denver Basin Rules......................................................................................... 17

How Much Groundwater is Left?................................................................................... 18

Water Level Trends................................................................................................ 19

How Long Will the Denver Basin Aquifers Last?................................................... 20

Dropping Artesian Pressure................................................................................... 21

Economic Considerations...................................................................................... 21

Regional Water Level Decline and Well to Well Interference................................ 22

Homeowners Hunt for Water.......................................................................................... 24 Population Growth and Development........................................................................... 25 Sustainability................................................................................................................... 26

Converting to Renewable Water............................................................................ 27

Regional Master Plan............................................................................................. 27

Looking for Renewable Water Supplies................................................................ 28

Alternative Management Strategies...................................................................... 29

Timeline of Colorado Groundwater Law....................................................................... 30 Glossary............................................................................................................................ 32 Additional Reading.......................................................................................................... 33

Citizen’s Guide to Denver Basin Groundwater



Water is the life-blood of civilization.


Colorado Foundation for Water Education

In semi-arid Colorado, we maintain a delicate balance between water supply and demand. Beneath the Denver metro communities lies a tremendous groundwater resource. This resource comprises aquifers that cover an area extending from Colorado Springs on the south to Greeley on the north and from the foothills of the Rocky Mountain foothills on the west to the eastern plains near Limon. This 6,700 square mile area is commonly referred to as the Denver Basin. In the Denver Basin, bedrock aquifers serve as a bank of stored water held in the pores of sandstones and siltstones that are more than 50 million years old. Studies show that it took tens of thousands of years or more for nature to fill this resource. Currently, many individuals and

Bac kground

municipalities in the Denver Basin rely on

flank of the basin near the foothills have

this groundwater for their primary water

already felt the adverse effects of the de-

• Rates of water withdrawal;

the aquifers;

supply, and in some places the decline in

clining levels. For some, the remedy may

• Location of future population growth

water levels is rapid.

be to drill deeper to extend the useful life

and development;

In the 1970s and 1980s when the state

of their wells. For others, this may not

began regulating the pumping of these

be a technically feasible or economically

aquifers, it recognized that they were finite

viable. In some cases, a deeper aquifer

• Aquifer storage and recovery projects;

and received virtually no recharge. In fact,

option may not exist. Still others have

• New regulations and legislation;

Denver Basin aquifer withdrawal results

recognized that they are going to have to

• Water conservation measures and

in mining of the aquifers that depletes the

replace their groundwater supplies with

• The economic value placed on the

water in storage and lowers water levels

renewable sources of water if they are

(pressure head) in wells.

to maintain a sustainable water supply in

Most wells that tap this resource are 500

• Alternate sources of water to meet demands;

the long-term.

water resources

This Citizen’s Guide to Denver Basin

to 2,000 feet deep. As water levels decline,

Eventually the water held in these

Groundwater explores the geology and

well production decreases and more wells

aquifers will be so depleted that addi-

hydrology of our underground water re-

may be required to meet the same demands.

tional pumping will become physically

source, the legal framework developed

Water level declines of more than 20 feet per

and economically impractical. While this

for its administration and management,

year have been observed in the primary aqui-

scenario may seem bleak, an informed

the current development of this resource,

fers used for public water supply in densely

populace can participate in the necessary

and its limitations and sustainability.

populated areas. Such dramatic declines are

long range planning required to assure a

The greatest impacts from increased

the response of confined aquifers to a fo-

sustainable water supply. Factors that will

pumping of these bed rock aquifers is occur-

cused pumping regimen. As pressure levels

influence our groundwater future in the

ring in the South Denver Metropolitan areas

are reduced, these rates of decline may not

Denver Basin include the following:

of southwest Arapahoe County and northern

be sustained into the future.

Douglas County. For this reason, they are an

Some wells located along the western

• The amount of water in storage in

emphasis of much of this document.

Citizen’s Guide to Denver Basin Groundwater


Grou n dwat e r Basi c s Throughout the Front Range metropolitan area,

luvial deposits, or in narrow crevices

both surface and groundwater are used for ag-

such as fractures and faults in crystal-

riculture, municipal, industrial, and domestic

line rocks. Humans have tapped these

use. Early settlers first diverted surface

water-filled pores and fractures since

water from streams, rivers, and lakes for

early civilization. Globally, groundwater

mining activities, then for irrigation and

accounts for the majority of fresh water

other farm related purposes. Surface wa-

on earth.

ter, with its ready access and storage ca-

Groundwater contained in deep sed-

pability, has historically provided about

imentary rocks such as those found in

80 percent of Colorado’s water supply.

the Denver Basin, has taken thousands

In contrast, groundwater refers to

of years to accumulate. Because of the

all water beneath the land’s surface.

inter-layered nature of the sedimentary

Because it is hidden from view, many

rocks that make up the aquifers, pre-

people think of it in the form of under-

cipitation infiltrating the soil does not

ground lakes, streams and veins. But

immediately impact the amount of wa-

most groundwater is located in very

ter in storage in these aquifers. Natural

small water-filled pore spaces between

recharge to the deeper bedrock aquifers

rock grains in sedimentary rocks, be-

of the basin is so slow that this ground-

tween sand and gravel particles in al-

water is essentially non-renewable.

Groundwater found in sedimentary rock (top) is slow to recharge, while alluvial groundwater quickly interacts with surface water (above).

Water supply wells of record with the State Engineer’s Office as of Feb. 2001.


Colorado Foundation for Water Education

Finding Water The Denver Basin is a structural sedimentary basin that underlies the Denver metropolitan area from the foothills to the eastern plains. This layered, multi-aquifer system is recognized nationally as a major aquifer. Geologic units underlying the Denver Basin aquifer are also rich in mineral fuels with active production of oil and gas. Historically, coal has been produced from the Laramie Formation of the aquifer system. The structural depression referred to as the Denver Basin extends north and eastward outside of Colorado’s boundaries. This larger basin accumulated sediments as the Western Interior Seaway retreated and the Rocky Mountains rose. However, when the state was called upon to determine how the basin’s water should be used, it mapped out a smaller administrative area where it would focus its efforts. This administrative area covers 6,700 square miles extending into Weld County on the north; El Paso County on the south; Jefferson County on the west; and the eastern portions of Adams, Arapahoe, and Elbert Counties on the east. The thickest portion of the basin lies just west of the town of Parker, where the LaramieFox Hills aquifer is approximately 3,000 feet below the surface. The Denver Basin bedrock aquifer system consists of water-yielding strata, predominantly sandstones and siltstones, of Tertiary- and Cretaceous-age sedimentary rocks deposited 65-70 million years ago. The northern part of the Denver Basin aquifer system underlies the alluvial aquifer of the South Platte River, and is hydraulically connected to that unconsolidated aquifer over part of that area. Structural Sedimentary Basin — A topographically low area in the Earth’s crust in which sediments have accumulated by transport via streams from the adjacent hills.

This electron micrograph (left) shows rock grains and the small pore spaces that provide groundwater storage in the Arapahoe aquifer. The scale bar is equivalent to .5mm (thinner than a fingernail).


Studying t h e D e n v e r Basi n Denver Basin groundwater refers generally

water in each of Colorado’s major river

las County Water Resources Authority par-

to groundwater within the Dawson, Denver,

basins. The South Platte Decision Sup-

ticipants, Denver Water, and the Colorado

Arapahoe, and Laramie-Fox Hills aquifers. This

port System is currently being developed.

River Water Conservation District.

groundwater has a special classification

In addition to looking at the river system,

This study concluded that water lev-

under Colorado water law. The Colorado

this model also evaluates the Denver Ba-

els will continue to decline in response

legislature exercises absolute authority

sin bedrock aquifers as they interact hy-

to projected pumping rates even with ex-

over how the Denver Basin bedrock aqui-

drologically with the South Platte River

panded conservation and reuse by water

fers are allocated, whereas surface water

alluvial aquifer.

providers. The study further indicated that

and tributary groundwater are subject to

As part of this Decision Support Sys-

continued pumping of the Denver Basin

the Colorado constitution’s prior appro-

tem, the U.S. Geological Survey is develop-

aquifers will produce significant losses to

priation doctrine.

ing a new multi-layered numerical model of

well production, even with the majority of

Our understanding of the hydrogeol-

the Denver Basin. This model will enhance

water still in storage, due to well-to-well

ogy and water availability of the Denver

groundwater administrators‘ and scien-

interference. Well-to-well interference oc-

Basin is still evolving. Many organizations,

tists’ understanding of the impacts of well

curs when densely clustered wells com-

from federal scientific agencies to indi-

pumping, changes in storage and stream

pete for the same stored water.

vidual water districts, have studied this

depletion. Studies by the Denver Museum

In the southern portion of the basin,

aquifer system. During the late 1960s and

of Nature & Science in the late 1990’s, sup-

the El Paso County Water Authority has

early 1970s, geologists with the Colorado

ported by the National Science Founda-

recently prepared a water report to assist

Division of Water Resources and the U.S.

tion, indicated the geological framework of

its members in meeting year 2020 water

Geological Survey began to study the for-

the aquifers was significantly different than

demands. The water report suggests that

mations of the Denver Basin and map the

previously anticipated, resulting in reduc-

“The concept that housing developments

distribution of the aquifers. These efforts

tions in estimates of stored water.

could be initiated with Denver Basin aqui-

continued into the 1980s and resulted in a number of publications.

Recognizing that the depletion of the

fer water and generate sufficient rev-

Denver Basin aquifers is a regional issue,

enues to purchase renewable water as a

In the early 1990s, the Colorado Wa-

individual water suppliers that help serve

long-term water supply solution does not

ter Conservation Board and the Division

the metro area have funded cooperative

acknowledge the complex political, envi-

of Water Resources began funding data

studies to investigate alternatives for meet-

ronmental, and water availability issues

collection and the development of com-

ing future water demands. The South Metro

associated with the development of re-

puter-aided modeling tools called Deci-

Water Supply Study completed in February

newable water resources.” Individual wa-

sion Support Systems, to help administer

2004 was a joint effort between the Doug-

ter districts are also conducting their own investigations in developing their Denver Basin groundwater supplies. Most recently, the Colorado Geological Survey has been conducting detailed hydro-geologic mapping to complement its current surface geologic mapping along the western margin of the Denver Basin. The survey is refining interpretations of the Denver Basin aquifers in the Dawson Butte and Castle Rock South USGS 7.5 minute quadrangles south of Castle Rock. This area includes significant new commercial and residential developments that rely on Denver Basin groundwater, which are on the western margin of the basin where impacts from regional water level declines are currently most severe. This mapping effort will provide important information in support of critical future water management decisions.


Colorado Foundation for Water Education

Th e Ge ol o g i c Story Groundwater is in rocks. It is not in subterranean pools or in underground rivers. It occurs inside rocks, within pore spaces and between mineral grains. Porous rocks are the storage vessels for groundwater; when these rocks are water-saturated they become aquifers. Have you ever seen the rain “wet” a rock? Once water saturated, many rocks appear darker. Even if the surface water is wiped off, the rock remains damp. A rain100 million years ago

70 million years ago

wet rock provides an illustration of water seeping into the pore spaces of the rock. It is easier to extract or drain water out of coarse-grained rocks like gravels or sandstones, because the pore spaces tend to be large and well connected. The rock is said to have high porosity and permeability. By contrast, fine-grained rocks like mudstones, clays and shales yield water at much lower volumes and slower rates, because the smaller less-connected pore spaces drain less efficiently. Fine-grained

66 million years ago

65 million years ago

rocks yield little water and may even produce impermeable or confining layers separating aquifers. The rocks that make up the groundwater aquifers in the Denver Basin are sedimentary rocks, deposited as beaches and river channel sands as an ancient sea retreated and the Central Rocky Mountains rose. The rocks occur in logical patterns that reflect how and where they were deposited. Because the rock types influence groundwater yield, these depositional patterns directly influence the aquifer’s

55 million years ago

37 million years ago

behavior. These many-million year old beaches and deposited river channel sands create the geologic formations that geologists have labeled, in descending order, the Dawson, Denver, Arapahoe and Laramie Formations, and the Fox Hills Sandstone.

These paintings at left depict Ancient Denvers, scenes from the Front Range as they may have appeared over the past 100 million years. Images from the Denver Museum of Nature & Science. 34 million years ago

16,000 years ago

Citizen’s Guide to Denver Basin Groundwater


How Geol o g i sts R e a d t h e E a rt h ’ s Hi story To place the groundwater resources of the

years, more than a mile of marine shale,

uplift. The Arapahoe tends to be gravel-rich,

Denver Basin into perspective, it is best to start

rich in sea shells and fossil fish, accumulat-

particularly in the western part of the basin.

with the container—the rocks. Come along, it’s

ed on top of these sediments. These fossils

Detailed mapping and correlation of

a fun story.

are easy to find on the edges of the Denver

data from water wells show that the Arap-

Basin and are on display in museums, such

ahoe Formation was, in part, deposited by

as Denver’s Museum of Nature & Science.

rivers as a giant apron or fan of debris that

The geologic history of Colorado is eloquently written in the rocks beneath our feet. Geologists learn to read this writing,

As the ocean retreated over the next

came out of a vanished canyon located

and they deduce the history of the Earth

million years, a geological layer known as

from clues we can all see.

Fox Hills Sandstone accumulated on top

Over geologic time, these deposits

west of Castle Rock.

Core samples taken from well bores

of the marine shale. Immediately over this

were buried and eventually subsided to

tell geologists that the Denver Basin aqui-

sandstone layer, another geological layer

depths of 2,000 feet or more, where they

fers are curved and layered one on top

full of coal beds, sandstone, shale and

make up the water-saturated sandstone

of another, like a stack of bowls. In some

mudstone beds soon accumulated, repre-

beds of the Arapahoe aquifer. This is one

areas, these rocks are found in thick lay-

senting a swamp-like environment. This is

of the most important aquifers in the basin

ers far underground. At the margins of the

called the Laramie Formation.

and is the major source of groundwater for

basin the layers outcrop, giving scientists

The porous units of these two forma-

a great opportunity to determine what the

tions make up the oldest and deepest of

municipal water users in Douglas County. The Denver and Dawson formations

rocks of the Denver Basin look like under-

the Denver Basin aquifers—the Laramie-

overlie the Arapahoe Formation and in-

ground, and how the aquifers formed.

Fox Hills Aquifer.

termingle with one another. The Dawson

In the Denver area, for example, the

Some 68 million years ago, the Central

tends to be rich in granite fragments,

steeply tilted sandstone ridge west of town

Rocky Mountains were being uplifted by tec-

while the Denver is rich in volcanic com-

at Dinosaur Ridge, near Red Rocks Park,

tonic forces. Tumbling wild from the moun-

ponents. The diversity of the geologic

reveals dinosaur bones and foot prints,

tains came rivers full of the ingredients for a

environments at the time of deposition

ripple marks, and fossil plants. Remains of

series of rock layers that spread across and

results in variable quality aquifers de-

mangrove-type swamps and tidal estuar-

filled the Denver Basin. This variable debris

pending on location within the Denver

ies can be seen on the rocky ridge.

was the genesis for the most water-rich rock

Basin. Generally, the western portion of

Knowing what modern beach and

layers of the Denver Basin. Over the years,

the aquifers are better water producers

near-shore systems look like, geologists

geologists have named these rocks from

than their equivalent units in the central

can deduce that the Dinosaur Ridge out-

older to younger—the Arapahoe, Denver

or on the eastern side of the basin. The

crops are the remains of 100 million year-

and Dawson Formations.

location of a well with respect to the

old shoreline landscapes. Throughout the ensuing 30 million

The Arapahoe Formation is older, representing the onset of significant mountain

ancient sediments is critical to its water producing potential.

Visitors to Dinosaur Ridge near Morrison view 100 million year old Iguanadontid footprints.

10 |

Colorado Foundation for Water Education





Aquifer D e s c ri p t i on s


In the 1980s, when the State Engineer’s Office was asked to

analogy accurately represents the stacked geologic unit/aquifer

classify the aquifers in the Denver Basin in order to regulate

concept, the basin has an asymmetrical bowl shape in cross-

their use, it divided these sedimentary layers into four aqui-

section that is approximately one-half mile thick and 70 miles

fers: the Dawson, Denver, Arapahoe and Laramie-Fox Hills. The

wide. The asymmetry is expressed by low-angle dips of the

5000 4000

Fox Hills

4 Miles


aquifer units imperfectly mimic the distribution of the geologic

aquifers along the northern, eastern, and southern margins and

formations of the same names. The four Denver Basin bedrock

high-angle dips along the western margin. For administrative

aquifer layers are stacked like the layers of an onion. The up-

purposes, their boundaries are defined by the Denver Basin

permost aquifer covers the smallest area. Successive under-

Rules promulgated by the State Engineer in 1985. From the top

lying aquifers cover larger and larger areas. While the onion

down they are:

Rock Names


East 4 Miles

West Dawson Butte

Elevation (feet)

Dawson Aquifer

Vertical Exaggeration Approximately 20x


Denver Aquifer

Arapahoe Aquifer

6000 5000 4000

Laramie/Fox Hills Aquifer




Laramie-Fox Hills

This shallow uppermost aqui-

Underlying the Dawson aqui-

The Arapahoe aquifer includes

The Laramie-Fox Hills aqui-

fer covers an area of approxi-

fer, the Denver aquifer extends

rock units on the west side of

fer underlies the entire 6,700

mately 1,400 square


further north, east, and south

the basin deposited near the


in Douglas County, northern

and covers an area of approxi-

mountains by an ancient river

area of the Denver Basin. It is

El Paso County, and western

mately 3,500 square miles. It

fan system. These units possess

made up of both the beach

Arapahoe and Elbert counties.

typically contains fewer sand-

splendid aquifer characteristics.

sandstones of the Fox Hills and

This aquifer is most commonly

stone beds than the Dawson

This aquifer underlies an area

the overlying river sandstone

tapped by shallow domestic

aquifer because the ancient

of approximately 4,700 square

beds in the lower Laramie For-

wells. Water is found in discon-

meandering rivers were less

miles. Deep municipal wells

mation. Coal beds commonly

tinuous lens-shaped sandstone

common, and mudstone beds

along the I-25 corridor are often

occur in the lower part of the

beds deposited by ancient me-

often predominate. Sandstone

drilled in this aquifer and good

Laramie Formation and water

andering rivers. The rocks are

and pebble compositions are

quality wells yield up to 800 gal-

from this aquifer can be high

typically gravel-like and com-

typically volcanic. Wells com-

lons per minute. The aquifer also

in sulfur. Well yields of 350

posed of weathered granite

monly have yields of between

includes rocks deposited farther

gallons per minute are typi-

with typical well yields up to

50-150 gallons per minute. Ap-

east (away from the mountains)

cal. As the deepest of the four

300 gallons per minute. There

proximately 800 high-capacity

but their fine-grained nature re-

aquifers, it is often considered

are approximately 1,900 high-

wells have been completed in

sults in less productive wells, as

to be the aquifer of last resort

capacity wells completed in the

the Denver aquifer with total

found in eastern Elbert County.

for drinking water supplies.

Dawson aquifer that have been

annual permitted withdrawals

The State Engineer’s Office has

The Laramie-Fox Hills aquifer

permitted to withdraw 30,800

of more than 72,600 acre feet.

issued permits for more than

has seen the development of

1,000 high-capacity wells in the

490 high-capacity wells with

Arapahoe aquifer with maxi-

a permitted cumulative maxi-

mum total annual withdrawals

mum withdrawal of 51,600

of more than 168,700 acre feet.

acre feet.

acre feet annually.

Citizen’s Guide to Denver Basin Groundwater



| 11

Fountain s of Wat e r : Wat e r Use a n d R e g u l at i on Colorado’s early water development history is tied to the need for irrigation in a semi-arid climate. The diversion of river water for irrigation was first practiced in the mid1800s by two groups of settlers—Hispanic settlers in southern Colorado and pioneers from the eastern states and northern Europe who settled in the South Platte and Arkansas River basins. Legal rights to use water diverted from the rivers and creeks of Colorado became codified into territorial law. Ultimately a system of prior appropriation was devised to govern the use of all surface water in the state, and this concept was included in Colorado’s 1876 Constitution. A simple way to explain this system is “first come, first served,” that is, whoever diverts unappropriated water first for beneficial use, has a senior right. A majority of the laws regarding the use and development of water in Colorado are based on this system of prior appropriations for protection of water rights in order of their priority dates. When many of these laws were created, groundwater use was minimal in most areas. Wells were generally shallow and hand-dug. Windmills dotted the landscape, particularly on the high plains, and pumped limited quantities of groundwater for livestock and homesteads. Almost a century would pass before groundwater pumping would increase dramatically, and require extensive regulations to govern its use. Colorado water law has largely been

Artesian wells were found in many places in Colorado, including this well near Montrose (top). Pressure from artesian wells in Denver (right) were used, among other things, to operate the organ bellows in Trinity Methodist Church (above).

developed through the interaction between water users, water officials, the legislature and the judiciary. Judicial rulings have frequently identified and highlighted emerging groundwater issues. Rules governing the use of Denver Basin groundwater have evolved over time as our understanding and use of these

Artesian well or artesian spring — A well or

aquifers has increased.

spring that taps groundwater under pressure such that the water rises above the top of the aquifer, but may not come to the surface, without pumping. If the water naturally rises above the surface, it is known as a flowing artesian well. 12 |

Colorado Foundation for Water Education

D enver Basi n Grou n dwat e r D ev e l op m e n t Colorado Scientific Society members researched

funds from the Department of the Interior.

The fabulous artesian pressures from

and documented the artesian wells of Denver

In 1873, this study became known as the

these wells were put to many innovative

as early as 1884. According to historical ac-

United States Geological and Geographi-

uses. They helped produce the decorative

counts, R. R. McCormick was boring for

cal Survey of the Territories, or the “Hayden

fountains at Union Station, provided a pow-

coal in a ravine by St. Luke’s Hospital in

Survey.” His work showed artesian ground-

er assist for the elevators at the Brown Pal-

north Denver, when he struck the first arte-

water to be common along the western

ace Hotel, and operated the organ bellows

sian water. Due to its purity and superiority

edge of the Denver Basin from the towns

at the Trinity Methodist Church. By 1895,

over the water furnished from the South

of Marshall (near Boulder) to Sedalia, in

nearly 400 wells had been drilled in the vi-

Platte River by the Denver Water Company,

areas well known for their tilted sandstone

cinity of Denver and surrounding areas.

his discovery soon led to more interest in

outcrops. The outcrops measured 200 to

But they soon began to play out. By

widespread groundwater development.

600 feet higher than the City of Denver, and

the mid-1890s considerable pressure

Much discussion ensued in the scien-

were thought to be areas of aquifer recharge

losses had already been observed in the

tific and business community about the

whose elevation could account for the pres-

city wells and official investigations began

potential source of this gushing water.

sure in the artesian wells of Denver.

as to its cause. To some, this free-flowing

Many thought the water was derived from

By 1890, numerous artesian wells

water was being wasted by extravagance

seepage from reservoirs nearby, but other

had been drilled in the area. At the

and ignorance, and there was talk of new,

scientists correctly asserted this water was

lowest elevations in the basin, artesian

special legislation to prevent its waste.

artesian–emanating from deep sandstone

pressure pushed water more than 100

However, it would not be until the 1950s

layers under considerable pressure.

feet above the ground. Two main wa-

that new technology, population growth

The geology of the countryside around

ter-bearing sandstone layers had been

and drought would combine to push the

Denver was first described and mapped

identified at depths of 375 and 600 feet

state’s first set of extensive groundwater

by Ferdinand V. Hayden in the 1870’s with

in downtown Denver.

regulations into place.

Confined or Artesian Aquifers

The term water level ( ) is used in this document in reference to a completed well, whether it is the water table of an unconfined aquifer or the artesian head of a confined aquifer.

Confined or artesian aquifers are completely saturated geo-

hundred feet higher in elevation than most of the basin. Over

logic units in which the water is under pressure (artesian

most of the basin, the Denver, Arapahoe, and Laramie-Fox Hills

head) as a result of an overlying low permeability confining

aquifers are confined such that water levels in wells rise above

layer that prevents the free movement of air and water. As the

the top of the aquifer. The water produced from wells drawing

early geologists surmised, the Denver Basin aquifers were un-

on the artesian head represents a very small amount of the total

der artesian pressure because the recharge areas were several

water in storage as the aquifer is not being physically drained.

Citizen’s Guide to Denver Basin Groundwater

| 13

Widespre a d Use of We l l s a n d D rou g h t C on ditions R e qu i re Grou n dwat e r M a nag ement Although groundwater use in Colorado dates

realization that the Ogallala aquifer, in

face streams. Creating the category

back to the late 1800’s, it was not until the

particular, was being mined well be-


1950s that well drilling became widespread.

yond its recharge capacity. In 1957, the

first statutory departure from the “all

The loss of surface water supplies during

General Assembly created the Colorado

groundwater is tributary to streams”

the drought of the 1950s, together with

Ground Water Commission for the pur-

rule recognized by the Colorado Su-

expansion of rural electric co-ops and the

pose of examining and possibly regulat-

preme Court to protect appropriators

development of vertical turbine pumps,

ing critical groundwater areas. In 1965,

of natural stream waters.

led to expanded groundwater pumping

it gave the Commission authority to des-

Unlike tributary groundwater or sur-

east of the Continental Divide between

ignate groundwater basins where the

face water, designated groundwater is

1943 and 1969.

principal reliable source of water supply

regulated by the Ground Water Commis-

is groundwater with little connection to

sion and is not subject to court adjudi-

surface water.

cation. The Ground Water Commission

Existing vested surface rights holders in the South Platte and Arkansas river basins




became concerned that un-administered

The Commission has established

uses a modified appropriation system

diversion of tributary groundwater through

eight designated groundwater basins

to allocate designated groundwater out-

wells could be intercepting water needed

in eastern Colorado, four of which (Lost

side of the Denver Basin on a permit by

to fulfill senior surface water rights. This

Creek, Kiowa Bijou, Upper Big Sandy,

permit basis. But, the General Assembly

led to statutes and court decisions in the

and Upper Black Squirrel Creek) cover

has directed that designated groundwa-

1950s and 1960s requiring the State Engi-

the rural eastern 47 percent of the Den-

ter within the Denver Basin shall be al-

neer to administer tributary groundwater

ver Basin. By establishing the designat-

located to the owners of the overlying

under the doctrine of prior appropriation.

ed basins, the State General Assembly

land, based on the hundred year pump-

In the high plains area of Colorado,

acknowledged that some groundwater

ing regime that applies to the four aqui-

intensified irrigation pumping led to a

had little or no connection to the sur-

fers of the Denver Basin.




supplement to any significant degree

The Two Main Types of Groundwater

continuously flowing surface streams.

It is important to understand the two

It is regulated by the Colorado Ground

main categories that are used to talk

Water Commission.

about groundwater: Tributary and

natural conditions does not recharge or

Non-tributary. Tributary groundwater is hydraulically connected to a surface stream and can influence the amount or direction of flow of water in that stream. Water in sand and gravel alluvial aquifers adjacent to major rivers is an excellent example of tributary groundwater. Non-tributary groundwater is typically produced from aquifers geologically confined such that they have little physical connection to surface waters. With the exception of the Colorado Designated Groundwater Basins

uppermost portion of the Dawson aquifer, groundwater contained under confined conditions in the Denver Basin aquifers is considered to be non-tributary.

14 |

Colorado Foundation for Water Education

Deep Groundwater Gets a

and set criteria for the State Engineer to

100-Year Minimum Aquifer Life

follow in issuing well permits in these

Between 1965 and 1973, many new wells

bedrock aquifers.

were being drilled into the deep bedrock

For the first time, the general assembly

aquifers of the Denver Basin. This includ-

spelled out that landowners had the right

ed areas in the South Platte River basin

to develop deep non-tributary groundwa-

and in the south Denver metro area.

ter underlying their property. To set a limit

Concern over the amount of water

on pumping rates, the legislature adopted

being pumped and the life of these aqui-

a 100-year pumping regime. Regulations

fers led to Senate Bill 213 passed in 1973.

were implemented that allowed landown-

This legislation established how water

ers to withdraw water at the rate of one

pumped from deep and potentially non-

percent of the aquifer resource under

renewable aquifers should be managed

their property per year.

Does a Well Permit Guarantee a 100-year Water Supply? A Denver Basin well permit does not guarantee a 100-year water supply. Actually, the well permit gives a person the legal right to drill for water. Even when water is encountered, an estimate of available water is made, and a one percent withdrawal rate determined. Because of the uncertainty of available water estimates, the supply may last more or less than 100 years.

A group of Montrose, Colorado, citizens (circa 1885) pose in front of equipment used to drill an artesian well in Montrose County.

Citizen’s Guide to Denver Basin Groundwater

| 15

R egul ati n g t h e D e n v e r Basi n Aqu i f e r s In the late 1970s, groundwater speculation as

In the mid-1980s a separate “Blue

well as large new housing developments that

Ribbon” committee was also convened

applied for groundwater permits precipitated

by Gov. Richard Lamm to develop a set

Statutory Groundwater Definitions

concerns about sustainable water supplies for

of recommendations to the legislature

Designated Basin Groundwater—Desig-

the Front Range.

regarding the future management of

nated groundwater is water that under

this resource. Among their findings are

natural conditions would not recharge or

the following:

supplement continuously flowing surface

The state legislature and Denver Regional Council of Governments created

streams. It is specific to deep groundwa-

a groundwater task force charged with making recommendations about pump-

• The prior appropriation doctrine

ter underlying the eight “designated basin”

ing water from the area’s deep aquifers.

does not work for deep non-tribu-

areas created by the Colorado Ground

The following were among the panel’s

tary groundwater. Preventing injury

Water Commission, located on Colorado’s

main conclusions:

to senior water rights is central to

eastern plains. This is considered non-

the prior appropriation system.

tributary and is regulated under specific

However, the interdependent and

designated basin rules.

• The bedrock aquifers underlying the

Tributary Groundwater—Water hydraulically

greater metro area contained large

artesian nature of the Denver Basin

amounts of water that could be a

aquifer system makes that protec-

connected to a surface stream that can

great asset to supplement water

tion impossible if the resource is to

influence the amount or direction of flow

supplies for the Front Range;

be developed. After the first well

of water in that stream. It is regulated by

starts pumping, all subsequent

the prior appropriation system, like other

at the edge of the Denver Basin,

wells will naturally deplete that first

surface water rights.

where the aquifers are thin, may be

well’s original artesian pressure.

depleted, need to be re-drilled, or

Protecting “senior” rights from any

pumping of which in 100 years will not

depletion just isn’t possible.

deplete the flow of a natural stream at

• Artesian wells and wells drilled

run dry before others; • Economics would likely be the

• Deep bedrock aquifers should be

Non-Tributary Groundwater—Water the

an annual rate greater than 1/10th of one

deciding factor in limiting this water

pumped with special care, because

percent of the annual rate of withdrawal


they are essentially non-renewable, or

from the well.

renew over very long time frames.

• Decreased yields could cause seri-

Not-Nontributary Groundwater—Denver Basin groundwater that is connected with

ous social and economic problems,

• No groundwater is completely non-

but this should not prohibit develop-

tributary and if it does adversely

surface streams or the deeper aquifers

ment of the Denver Basin aquifers.

affect surface streams, water rights

where they outcrop. If pumped, these

holders should be compensated by

withdrawals would deplete the flow of a

returning some water to the stream.

natural stream at an annual rate greater

• The interests of overlying landowners should be clarified.

Augmentation plans are court approved plans under the priority system to protect senior surface rights and are generally developed by engineers, lawyers, and other consultants. They allow for out-of-priority diversions by replacing water in the stream that junior users consume.

16 |

Colorado Foundation for Water Education

than 1/10th of one percent the annual rate of withdrawal from the well.

The D env e r Basi n Ru l e s

Areas along the South Platte River contain not-nontributary groundwater. In 1985, complex legislation commonly known

overlying streams, and were actually not

Senate Bill 5 required that the Denver

as Senate Bill 5 took into consideration the rec-

non-tributary. Unfortunately, the confus-

Basin aquifers be evaluated for their po-

ommendations of the “blue ribbon” committee.

ing wording “not-nontributary” stuck dur-

tential hydraulic connection to surface

Specific statutory language and definitions were

ing the rule-making process and is still

water. This was accomplished by the

developed to address the allocation of the Denver

used today.

State Engineer’s Office through model-

Basin and Dakota aquifers, as well as all other

Not-nontributary groundwater refers

ing. To avoid having to evaluate how to

non-tributary groundwater statewide. Senate

to those parts of the Denver Basin aqui-

replace this water on a case-by-case ba-

Bill 5 also required the State Engineer to

fers which are in some way connected to

sis, a blanket strategy for replacing water

promulgate rules and regulations govern-

surface streams or the aquifers where they

potentially removed from local rivers by

ing the withdrawal of groundwater from

outcrop. Examples that contain not-non-

well pumping was implemented. The leg-

the Denver Basin aquifers by December

tributary groundwater are areas along the

islation required judicial approval of plans

31, 1985. These became know as The Den-

South Platte River or the various streams

for augmentation at different standards

ver Basin Rules. While this legislation did

within the basin such as Monument Creek,

of four percent of withdrawals or actual

not specify how groundwater in the basin

Plum Creek and Cherry Creek.

depletions depending upon the aquifer

should be managed over the long-term,

For parts of the Denver Basin not within

and the distance from the stream contact.

it did provide a basic legal framework for

a designated basin, the water court has ju-

These replacement requirements do not

how the groundwater of the Denver Basin

risdiction to enter decrees for the use of

apply to groundwater within the desig-

should be allocated.

water. In the designated parts of the Den-

nated basins.

By enacting this legislation, the Gen-

ver Basin, the 1/100th per year pumping

eral Assembly agreed that it was accept-

rule applies and the Ground Water Com-

Municipal Rights to

able to mine the Denver Basin aquifers

mission makes all determinations regard-

Denver Basin Groundwater

by taking out more water than was being

ing the allocation and use of water.

As development of the Denver Basin aquifers progressed, cities and water districts

replaced. This was allowable even though reduction in the artesian head or water

Replacing Depletions from Streams

wondered what rights they have to develop

levels in the aquifers would occur, and

Though the General Assembly defined

groundwater beneath their communities.

some wells might be impaired.

non-tributary groundwater as not con-

Initially, water was allocated to the

The legislature also clarified that non-

nected to surface water, they realized

overlying landowner at the rate of one

tributary groundwater is “water which in

some hydrologic connection may be evi-

percent of the aquifer resource per year.

100 years will not deplete the flow of a

denced over very long timeframes. Con-

Landowner consent is normally required

natural stream at an annual rate greater

sequently, Senate Bill 5 provided that not

to extract Denver bedrock water from un-

than 1/10th of one percent of the annual

all the water withdrawn from the non-trib-

der a person’s property.

depletion from the well.” This definition

utary Denver Basin aquifers could be con-

SB 5 clarified that municipalities and

applies primarily to the Denver, Arapahoe

sumed; two percent had to be replaced.

water districts by implied consent may

and Laramie-Fox Hills aquifers.

The State Engineer generally assumes

utilize the Denver Basin groundwater re-

that this provision is met by return flows

sources within their boundaries, if they

from outdoor watering or other sources.

provide a reasonable alternative water

The legislature also recognized that some of the deep Denver Basin aquifers were not completely dissociated from

The not-nontributary designation in

supply to the land owners.

Citizen’s Guide to Denver Basin Groundwater

| 17

How Muc h Grou n dwat e r i s L e f t ? Current estimates are that the basin contains

has become a significant input of water

aquifer is used as a municipal water supply

over 200 million acre feet of recoverable water

for portions of these two aquifers and

in the southeast Denver metropolitan area,

in storage. Since most of the water produc-

may account for some of the observed

resulting in localized water-level declines of

tion to date is from the artesian portion

water level increases.

up to 125 feet in the past decade.

of the aquifers, we’ve used less than one

Water level trends in the dominant mu-

Annual water level changes for the

percent of the water in storage. Yet, in the

nicipal water supply aquifers, the Arapa-

Denver, Arapahoe, and Laramie-Fox Hills

most heavily developed aquifers water

hoe and Laramie-Fox Hills, are not favor-

aquifers are shown in the sidebar on

levels (artesian pressures) are declining

able. Over the past 10 years, water levels

page 24. These patterns emphasize that

at rates of one inch per day (30 feet per

have declined throughout the Arapahoe

in areas of high demand along the Front

year). More important than how quickly

aquifer. Between 1990 and 2000, develop-

Range, groundwater resources are being

they are dropping is how long it will be

ment in the south Denver metro area of

withdrawn from the Denver Basin bedrock

economically feasible to continue signifi-

northern Douglas County and southern

aquifers at rates in excess of recharge, re-

cant pumping of these resources.

Arapahoe county has resulted in declines

sulting in a mining condition that depletes

Each year, groundwater measure-

from 100 to almost 300 feet. With local de-

the groundwater in storage and lowers

ments from select wells in the Denver

cline rates of up to 40 feet per year, the fu-

water levels in wells.

Basin are published by the Colorado Divi-

ture prospects for this aquifer are of great

sion of Water Resources. The validity of

concern to water managers.

By contrast, in certain areas in the central and eastern portions of the aqui-

these data is sometimes questioned be-

Annual decline rates of this magni-

fer, water levels are either stable or may

cause the wells measured are not dedicat-

tude were simulated by computer models

ed monitoring wells and vary significantly

as part of the 2004 South Metro Water

It is important to note, however, that

in age and how they are pumped, among

Supply Study—a joint effort between the

the hydrogeological characteristics of the

other differences. However, consistent

Douglas County Water Resources Author-

Denver Basin aquifers localize the effects

annual trends in the data allow engineers

ity, Denver Water and the Colorado River

of pumping. Pressure changes are not

and hydrologists to infer the gain or loss

Water Conservation District to look at al-

being felt over the entire basin as con-

of water storage in these aquifers.

ternative sources of water supply.

ventional theory would predict. The sedi-

be rising.

The data indicate that depending on the

Model results predicted the Arapahoe

mentary rock formations that hold water

aquifer and the well’s location, water levels

aquifer in southern Arapahoe and northern

in these aquifers do not allow significant

in the Denver Basin aquifers are either rela-

Douglas counties along the I-25 corridor

groundwater movement laterally across

tively stable, declining, or even rising.

will become unconfined by the year 2020,

the basin over short periods.

or sooner. This means that the artesian

This means that even if groundwater

Water Level Trends

pressure head of the aquifer will have been

levels are not dropping in the eastern

For the shallower Dawson and Denver

drawn off, and wells will begin physically

portion of the basin, in terms of human

aquifers, water level data show both rises

draining the pore space of the aquifer.

life-spans, those portions of the aquifer

and declines depending upon location.

Throughout the past 10 years water lev-

cannot compensate for the significant wa-

With the housing development boom of

els in portions of the Laramie-Fox Hills aqui-

ter draw downs created by the pumping

the last decade, lawn irrigation recharge

fer have also declined. The Laramie-Fox Hills

stresses of the south metro area.

18 |

Colorado Foundation for Water Education

In t roduction 5 66 03 nwsene - 28491F 6000




31 ft/yr

5 67 20 nenwsw - 17421F 6000

4500 20 00

19 95

Water Level Changes in the Arapahoe Aquifer 1983-2006

19 90

20 00

19 95

19 90

19 85



19 85


6 66 17 nwse - Stonegate 6000


24 ft/yr

19 95

19 90

20 00

19 9

30 ft/yr

19 85

4500 19 95

4500 0


19 85


20 00


6 66 34 nenesw - 29735

5 67 34 sese - 7729F 6000


26 ft/yr




19 95

19 85

00 20

19 9

19 95

4500 0

4500 19 85



20 ft/yr


19 9


7 67 21 sene - 29574F

6 68 01 nenesw - 21905F 6000


28 ft/yr



20 00

19 95

19 85

20 00

19 9

19 95

4500 0

4500 19 85


19 90

28 ft/yr 5000

8 66 09 nenesw - 25602F

6 67 20 swswsw - 22189F 6000


20 00

19 95

19 90

19 85


8 67 08 swsw - 25601F 6000

48 ft/yr




19 95



4500 20 00


43 ft/yr


19 95

23 ft/yr

Graphs illustrating the falling water levels/artesian head in municipal water wells in the Arapahoe aquifer as reported by the Colorado State Engineer. Each graph shows the elevation (in feet) of the water level plotted against time, and each represents a well located at the spot indicated by the arrow to the map. The red line is the best fit line showing the long term rate of fall. As water level data is not reported systematically, some wells have more measurements than others.

19 85




19 9

20 00

8 67 12 swne - 22664F

7 67 04 nese - 28858F 6000

19 9

4500 19 85

4500 19 95




19 85

23 ft/yr


24 ft/yr

19 9


8 67 14 nwse - 237969 6000


Citizen’s Guide to Denver Basin Groundwater

00 20

19 95

19 9

19 85

20 00

19 95

4500 19 90

4500 19 85



32 ft/yr 5000

| 1 9

How L ong Wi l l t h e D e n v e r Basi n Aqu i f e r s L ast? State statutes presume the productive life of the

in substantial revisions to estimates of the

at the State Engineer’s Office indicates ex-

Denver Basin aquifers to be at least 100 years,

amount of groundwater available for ex-

empt and non-exempt Denver Basin wells

and permit well pumping up to one percent of that

traction. In the late 1980s, the actual amount

are authorized to withdraw as much as

supply per year. But well permits do not guar-

of water stored in the Denver Basin aquifer

350,000 acre feet of groundwater per year

antee water will be available for a century

system—from the foothills to east Elbert

from all four aquifers. Assuming this rate of

or more. Well permits actually only grant

County—was estimated by the U.S. Geolog-

production is accurate and fixed, then 200

the right to drill for water and pump at the

ical Survey to be 467 million acre feet, with

million acre feet of water in storage could

stipulated rates.

269 million acre feet being recoverable by

last approximately 570 years.

Much time and money is spent trying

pumping. While gravity will help drain out

Although a 570-year aquifer life sounds

to understand how and when water sup-

much of the water, some will necessarily re-

promising, scientists and water managers

plied from the Denver Basin aquifers will

main in the rock clinging to particles. That

are concerned that these estimates may be

change from confined to unconfined con-

is why recoverable reserves are always less

misleading. Evaluating the recoverable stor-

ditions. These include extensive computer

than actual reserves.

age of these aquifers still assumes that the

models developed by the USGS, the Divi-

Today, new data indicates that actual

aquifers will be drained almost completely.

sion of Water Resources, and various aca-

aquifer yields may be one-third less than pre-

However, wells are physically incapable of

demic and consulting groups.

viously predicted. In 1999, a continuous core

draining an aquifer to that extent. In addi-

Such models were used when the regu-

drilled in the central part of the Denver Basin

tion, much of the estimated recoverable re-

lations allocating Denver Basin groundwa-

by the Denver Museum of Nature & Science

source is spread across the eastern part of

ter were first developed in the mid-1980s.

provided a series of geologic samples. Anal-

the basin, where demand is minimal and the

They estimated, for example, the amount of

ysis of these samples and other recent data

cost of extraction and conveyance is pres-

recoverable water from each aquifer.

have helped to refine estimates of recover-

ently prohibitive. Because of uncertainty in

able water. Current estimates are that about

the basin hydraulics there are many wells in

200 million acre feet may be recoverable.

the Denver Basin that may not have a 100-

Over the past decade, a somewhat refined understanding of the geological characteristics of these aquifers has resulted

Analysis of permitted wells recorded

year useful life.

Confined v. Unconfined Aquifers In certain locations on the edges of the Denver Basin, the aqui-

confining pressures.

fers outcrop to the surface. This connection to the surface, lack

Increased groundwater withdrawals from the Denver Basin’s

of overlying confining layers, and a water table that is directly

confined aquifers (the Denver, Arapahoe, and Laramie-Fox Hills

influenced by precipitation, creates what hydrogeologists call

systems) are beginning to convert these aquifers from confined

unconfined conditions along the edge of the basin.

to unconfined conditions.

This is in contrast to the majority of the Denver Basin where

As an aquifer becomes unconfined, it is no longer under pres-

aquifers that are buried deep underground, separated from sur-

sure and its water begins to drain from the pore spaces between the

face streams by intervening impermeable layers of shale and

rock grains. It is theorized the rate of water level decline in the aquifer

claystone. In these areas the aquifers are said to be confined as

should decrease as the previously confined aquifer goes unconfined.

the water level in a well rises above the top of the aquifer due to

It is also anticipated that well production rates will diminish.


20 |

Colorado Foundation for Water Education

D ropping A rt e sia n P re s su re Artesian pressures dropped in the Denver Basin

newable water resources. The acquisi-

aquifers as soon as widespread pumping began

tion of new water supplies is not simply

more than 100 years ago. And, it will continue

a financial transaction.

to happen in response to pumping because of the unique hydraulics of the basin.

It is likely that economics will prevent the Denver Basin aquifers from being com-

Back in the 1970s and 1980s when sci-

pletely exhausted. Over time, large-capac-

entists, engineers, lawyers and others were

ity pumping may become so expensive

struggling to come up with a set of rules to

that it simply becomes too costly to drill

regulate pumping in the Denver Basin, the

more wells or to keep pumping existing

drawdown of water levels (artesian head)

wells with diminishing returns.

Artesian pressures dropped in the Denver Basin aquifers as soon as widespread pumping began more than 100 years ago.

and potential injury to some wells owners was understood as inevitable. And over time, dropping artesian pres-

Cascading Reduction in Well Yield 80

sures has made extraction of water less efficient and more costly in some areas. Artethe total elevation the pumps must lift water. But with declining water levels, larger pumps

amount of water. This problem has already started to occur in some south metro areas of the basin that are being drawn down by municipal pumping. Economic Considerations At the end of the day, the amount of water available from the Denver Basin may be limited by economics, as much or more than by state regulations




7th Well 6th Well 5th Well

age will be required to produce the same


4th Well

and motors, as well as increasing energy us-


PUMPING RATE (in acre feet per year)

sian pressure assists well pumps by reducing


40 30

2 nd We ll

1st Well


3 rd

W el


10 0 0



or the amount of water in storage.





While it may seem that giving a re-

To illustrate the cascading reduction in well yield and requirement to drill more and more

source a 100-year or even 400-year life is

wells to maintain a specific production requirement, we reference an example from the US

short-sighted, some also see it as an impor-

Geological Survey.

tant compromise that allows development

Assume that well A produces 40 acre feet per year when initially completed,

of the south metro area, while buying time

and it experiences a fixed rate of water level decline that causes the aquifer to be

for those same developments to generate

dewatered in 100 years. If the required application needs 30 acre feet per year,

the revenues needed to acquire renewable

well A needs to be augmented in 25 years. So we drill well B, and the combined

water supplies—or encourage annexation

yield of both wells far surpasses our fixed yield, but the combined well yield

of developments by municipal providers.

decreases more rapidly. In another 27 years a third well (C) is required to maintain

This interim use/revenue generating

the required production capacity. With three wells operating we again exceed our

concept, however, does not necessarily

water need, but due to declining water levels and well-to-well interferences it will

factor in all the complex political, social,

only be 13 years before a fourth well is needed. You can see from the graph above

economic and environmental issues as-

that this sequence will continue at an ever increasing frequency even though the

sociated with the development of re-

water level is declining at a constant rate. In this example, if the cost of constructing and equipping each well is $ 500,000 then the water cost for the first well is $267 per acre-foot. Because of reduced total production as more wells are added, the water cost for the sixth well is $13,500 per acre-foot. This simple example does not include increased operation expenses. Clearly the economics of relying on non-renewable groundwater supplies as a primary resource are not favorable in the long-term.

| 21

Denver Aquifer

In Parker and Castle Rock where municipal wells are pumping large volumes of water, water levels are declining.

R e g i ona l Wat e r L ev e l D e c l i ne a n d We l l to We l l In t e rf e re nce Arapahoe Aquifer

Drilling more and more wells is not necessarily a

water, water levels are declining—in some

viable long-term solution. A pumping well pro-

cases quite dramatically. In areas where

duces a cone of depression in the ground-

there are fewer wells or production rates

water around that well. Cones of depression

are lower, such as in the majority of the

from multiple wells in a well field overlap

eastern half of the basin, water levels are

and accentuate each other resulting in a

falling more slowly or remaining stable.

greater regional water level decline.

Laramie-Fox Hills Aquifer

Annual rates of water level change in wells in the aquifers of the Denver Basin. More than -48 feet -48 to -40 feet -40 to -32 feet -32 to -24 feet -24 to -16 feet -16 to -8 feet -8 to 0 feet 0 to +8 feet +8 to +16 feet 22 |

The Denver Basin aquifers also differ

Computer modeling results from the

in physical character and water holding

2004 South Metro Water Supply Study

capacity from one side of the basin to

indicated that the combined effect of re-

the other. For example, the sandstones

gional water level declines and well-to-

within the Arapahoe aquifer are thick

well interferences may result in produc-

and have the best water storage prop-

tion loss of as much as 85 percent in the

erties near the mountains on the west

Arapahoe aquifer by 2050.

side of the basin. However, they become thin to nearly insignificant on the

Location, Location

eastern edge of the basin.

Determining how much water will be

The area “in the margin” or on the

available to current and future groundwa-

outer edges of the bowl—if one thinks of

ter users in the Denver Basin is dependent

the Denver Basin aquifer as a series of

on the aquifer tapped, and the location of

stacked bowls—are the most vulnerable

the well.

to dropping water levels. For example,

In high population areas such as Park-

some well users living on the western

er and Castle Rock where there are many

margin of the Denver Basin in Douglas

municipal wells pumping large volumes of

County, have already been forced to

Colorado Foundation for Water Education

Douglas County The orange area has been defined by Douglas County commissioners as Margin A, where dried up wells and lowered pressure have forced limits on development. The yellow area is in less danger but still faces problems.

Water table declines are so prevalent in some areas of Douglas County that the county has developed maps highlighting these areas, and requires developers in these areas to find renewable, sustainable water supplies. These regions are referred to as Water Supply Overlay District Margins A and B (see map). It is anticipated that at the current rates of decline, many of the well users in these areas may not have available groundwater supplies in 15 years. deepen their wells or pumps in an at-

have to deepen their wells, the sustain-

Basin aquifers for municipal water sup-

tempt to find more water.

ability of this resource is promising.

ply. As a consequence, its water levels

In contrast, outside of these marginal

It is important to note that vertical

are dropping the fastest, particularly in

areas, there are many well owners with

transmission of water between the Den-

the south metro area where high-vol-

shallow wells which tap Denver and Daw-

ver Basin aquifers is extremely slow. For

ume municipal wells are operating.

son aquifers that are not experiencing any

this reason, the deeper aquifers being

These wells are often 1,500 to 2,000 feet

water level declines. Most are relatively

tapped and depleted by municipal users

deep and can pump at rates of 700-800

shallow, low-yield wells drilled by indi-

are not drawing water in any meaningful

gallons per minute or more. Sustainable

vidual landowners or developers to serve

way from the overlying aquifers being

water supply strategies are being devel-

household needs or a smaller subdivi-

tapped by individual homeowners.

oped and implemented to maximize the

sion. Because the draw on these shallow

useful life of these wells. The strategies

aquifers is spread over large areas, and

Arapahoe Aquifer Dropping Fastest

include water conservation, conjunctive

extraction rates are lower, water levels

Efficient well production combined with

use of surface groundwater and ground-

in these aquifers are stable or falling at a

good water quality makes the Arapahoe

water recharge.

slower rate. Although homeowners may

aquifer the most desirable of the Denver

Citizen’s Guide to Denver Basin Groundwater

| 23

Homeown e r s Hu n t f or Wat e r Plum Valley Heights, a small subdivision of horse properties tucked in the foothills between Sedalia and Highlands Ranch, has just 29 homes and is still dependent on non-renewable groundwater. And it’s running out. For Jack McCormick and his neighbors, that spells problems in so many ways. They aren’t connected to a surface water supply, their aquifer levels are falling, Colorado water law doesn’t protect them, and other booming metro communities might or might not be amenable to helping. “It’s a crisis for us in the margin,” McCormick says one misty spring afternoon, as he speaks with visitors in his dining room. He’s got maps to show where the basins and urban areas are, as well as the small communities in the Chatfield area cut off from the urban infrastructure. “We’re in the most tenuous part of the county.” Plum Valley Heights is on the rim of the stacked and tilted bowls of the Denver Basin aquifers and is the first to feel the effects of a diminishing groundwater supply. McCormick’s first well was drilled 408 feet into the shallow Dawson aquifer. It initially produced 5 gallons a minute, but production finally dropped to a point where it was no longer useful. Next, McCormick drilled a new well into the lower Arapahoe aquifer. Since 1987, the well’s static level has dropped 7 to 10 feet a year. Four times since then the pump’s been lowered, chasing the dropping water table. He estimates the well’s life may be only 1015 more years, depending on technology. “Less than a half mile away, one of my neighbors has his pump as low as it can go,” McCormick says. “These folks up here,” he says pointing to a small enclave north of his property. “They’ve been hauling water for years.” “One of the things we need for certain is a remedy,” McCormick says. “I’d be hard pressed to prove Highlands Ranch is pumping our water. We need legislation that adequately defines injury.” McCormick and his neighbors have been “working the issue.” They aren’t rookies. The residents of Plum Valley and the surrounding communities have been talking to county commissioners, lobbying for legislation, searching for renewable water sources in conjunction with new developers, and teaming up with their 30,000 or so rural neighbors in Louviers, Chatfield Basin and Meridian to bring in a surface water supply. Plum Valley, McCormick says, is hanging some hopes on developers who are mulling plans for Sterling Ranch, a 2,000-acre tract immediately to the east. If the area is developed for housing, Plum Valley and its neighbors could tap into its infrastructure for surface water. They’re already saving money for the possibility. “We’re not looking for others to solve our problems,” McCormick says. “We want to come to the table and participate.”

24 |

Colorado Foundation for Water Education

Popul ati on Grow t h & D ev e l op m e n t Denver Basin population by county from Colorado Dept. of Local Affairs


Total Housing Units by County







100000 50000 0



Douglas County has captured national headlines


















Adams Arapahoe Boulder Denver Douglas El Paso Elbert Jefferson Weld

Total Housing



would equate to a water demand of about

for being one of the most rapidly growing coun-

growth in the 1990s with influxes of peo-

ties in the nation. Between 1990 and 2000,

ple and a large construction boom that

Results from the recently complet-

its population grew by 191 percent and

created 10,000 new jobs each year. Ac-

ed Statewide Water Supply Initiative

local municipalities and water districts

cording to the Colorado Department of

indicate that Colorado’s population is

have worked hard to acquire new water

Local Affairs, each of the Denver Basin

expected to increase by 65 percent be-

sources to meet this growing demand.

counties experienced significant popula-

tween 2000 and 2030. An additional 2.8

tion increases since 1985 with resultant

million people are expected to call Colo-

increases in water demands.

rado home by 2030, with over 80 percent

Development has continued even in areas lacking a renewable and sustainable

467,000 acre feet per year.

water supply. Because groundwater has

Municipal water providers must secure

of these new residents living along the

been plentiful, is of good quality, and is

adequate supplies to meet peak demands

Front Range urban corridor. Planning of-

inexpensive to produce, development has

within their service area. Providers gener-

ficials in Douglas County have projected

used this resource as its primary source

ally plan on an annual water demand of

that their population will nearly double

of water supply. However, municipal wa-

0.6 acre feet per household. In 2004, El-

by the year 2025. Where will municipal

ter providers are beginning to recognize

bert, Douglas, Weld, Adams, El Paso, and

suppliers find a sustainable, renewable

that continued dependence on groundwa-

Arapahoe counties had approximately

water supply required to meet these in-

ter will come at an ever-increasing price.

778,000 housing units combined, which

creased future demands?

Fort Collins

These three maps show the increase in developed areas from 1957 to 1977 to 1997, respectively (United States Geologic Survey).


Citizen’s Guide to Denver Basin Groundwater

| 25

Sustainab i l i t y The sustainability of natural resources is diffi-

not a renewable resource, and could not

generally applies to private exempt do-

cult to quantify, but it is often generalized that

be expected to last forever.

mestic wells except for those located

we must meet the social, environmental, and

Although there is significant debate

economic needs of the present without compro-

regarding how much water is available

along the basin’s western margins. In contrast, municipalities like Castle

mising the ability of future generations to meet

in different parts of the Denver Basin, it is

Rock that are pumping from the deep

their own needs.

important to note that aquifer drawdown

Arapahoe aquifer have experienced an-

In some ways, this concept of sustain-

and a 100-year aquifer life are central

nual declines of 40 feet or more, and it is

ability appears to be at odds with Colorado’s

parts of how the state decided to allocate

anticipated that these wells will start to

own water resource doctrine: “The right to

this complex resource.

have diminished water flow rates within

divert the unappropriated waters of any

The result is that depending on loca-

‘natural stream’ to beneficial uses shall nev-

tion and the aquifer tapped, south metro

Rural well owners on the western mar-

er be denied.” The courts have determined

area businesses and homes may have seri-

gins of the Denver Basin between Denver

that maximum utilization of stream water is

ous water supply challenges to address in

and Colorado Springs are particularly at

implicit in the Colorado Constitution.

the near future. These challenges can be

risk. Not only are they in a clearly identified

framed with certain scientific evidence.

area of significant groundwater level de-

The problem is that maximum utili-

the next decade.

zation of groundwater resources in the

Current well logs and measurements

clines, but they must find their own solu-

Denver Basin is not sustainable. These

show that the Denver Basin aquifers are

tions, through the formation of rural water

ancient aquifers are a finite resource that

reacting variably to the pressures of

users associations, long-range planning or

replenishes only on the scale of hundreds

development. Where demand is mod-

resigning themselves to trucking in water.

or thousands of years. Yet by allocating

est and the resource large, the aquifers

this resource based on a 100-year life, the

show few declines and may provide

state legislature acknowledged this was

many decades of adequate supply. This

Aquifer volume drained by pumping

Saturated aquifer volume

We have previously stated that the estimated recoverable water supply of 200 million acre feet in storage could last approximately 400 years under the current maximum permitted rate of withdrawal. However, the estimate of the amount of water storage is based on an average value of water holding capacity (specific yield) for each of the four major aquifers. We have also stressed that this aquifer property is very location dependent being a function of geology. This graphic illustrates a simple conceptual model of the Arapahoe aquifer and the relation between geology and the amount of water recoverable. On the west side of the basin where the aquifer is dominated by sandstones, the amount of water physically capable of draining from the saturated pore spaces may be as much as 25 percent of the rock volume. The eastern portion of the aquifer volume may only yield 10 percent. With only two borings in the Denver Basin from which aquifer core samples have been recovered and analyzed, our knowledge and estimate of the average storage coefficient is limited.

Saturated aquifer volume

Aquifer volume drained by pumping


Volume of recoverable water

Volume of recoverable water

Arapahoe Aquifer WEST

26 |

EAST Colorado Foundation for Water Education

C onverti n g to R e n ewa b l e Wat e r Ron Redd is in his sixth year as utilities direc-

on new development to $19,500, from

tor for Castle Rock. Bisected by Interstate 25,

$11,500 for each new residential building

average of 170 gallons per day. In the meantime, Redd and his staff are

the former quarry town is one the Front Range’s

permit. The additional money raised will

developing strategies to invest in renew-

fastest growing communities.

help fund new renewable water sources.

able sources. Increasing and banking the

The 38,000-person town now depends

Their end goal is to provide a transi-

impact fees, along with pumping different-

almost entirely on non-tributary, non-re-

tion and “soft landing” for the town as it

ly to extend the aquifer’s life are two ways

newable groundwater from the Denver

moves away from the exclusive use of

to meet current and future water needs.

Basin aquifers. But faced with a build-out

non-renewable groundwater, and sus-

“We’re considering two dozen alterna-

population of some 104,000 people, the

tains itself through the integrated use of

tives for renewable sources,” Redd says.

town’s declining wells may be unable to

ground and surface water supplies. Part of

“Basically, we priced them all out, and

produce enough water. That’s why in the

the solution is water conservation.

they came in costing about $300 million.”

next 20-30 years Castle Rock plans to con-

Currently, the town’s water conserva-

Options include buying into the newly

vert to a water supply that is more than

tion target is to reduce per capita con-

constructed Reuter-Hess reservoir in Parker,

75 percent renewable water. Town plan-

sumption by 18 percent. Castle Rock is

pumping water from as far away as Sterling

ners estimate they will need an additional

already on its way toward that goal. So

or the Arkansas River, or buying into Denver

18,800 acre feet of water per year.

far, residents have decreased their aver-

Water’s Green Mountain pump-back water

In preparation, in early 2006 the town

age daily usage to 135 gallons per person

project for $25,000 to $30,000 per acre foot,

increased its water resource impact fees

per day, 35 gallons below the Front Range

among other scenarios.

R egional Wat e r M ast e r P l a n The South Metro Water Supply Authority

(long-term), and at buildout. The pro-

ity members include Arapahoe County Wa-

(SMWSA) adopted a Regional Water Master

jected demands take into account sav-

ter and Waste Water Authority, Castle Pines

Plan in June 2007. This plan will guide the

ings associated with current and antici-

Metropolitan District, Castle Pines North

participating water providers as they re-

pated water conservation programs.

Metropolitan District, Centennial Water &

duce their reliance on deep groundwater

The plan quantifies additional renew-

Sanitation District, Cottonwood Metropoli-

and expand the role of renewable water

able water supply goals. The goals are

tan District, East Cherry Creek Valley Wa-

supplies in meeting current and future

based on projected water demands less

ter & Sanitation District, Inverness Water &

water needs. Although they currently

projected available supply from current

Sanitation District, Meridian Metropolitan

hold non-tributary groundwater rights

and identified sources. The aggregate

District, Parker Water & Sanitation District,

for about 111,000 acre feet per year,

new renewable water supply goal in-

Pinery Water & Waste Water District, Rox-

the Authority’s members intend to re-

creases from an additional 4,000 acre

borough Park Metropolitan District, Stone-

duce their sustained use of non-tributary

feet per year in 2010 to 43,400 acre feet

gate Village Metropolitan District and the

groundwater to less than 15,000 acre feet

per year at buildout. An additional 10

Town of Castle Rock.

per year at buildout.

percent in renewable supply at buildout

The Regional Water Master Plan is avail-

is needed to address uncertainties and

able at the South Metro Water Supply Au-

potential future participants.

thority Web site

The plan identifies demands and provides strategies to meet water needs in 2010 (interim), 2020 (mid-term), 2030

Water Demands (AFY)

120,000 100,000 80,000

ACWWA CPNMD Castle Rock Centennial Cottonwood ECCV Inverness Meridian Parker Pinery Roxborough Stonegate

140,000 120,000 Supply by Source (AFY)


The South Metro Water Supply Author-

60,000 40,000

100,000 80,000

10% Additional Renewable (Uncertainty/Unincorporated) SMWSA Additional Renewable (Treated Demands) Reuse/Recapture of Return Flows Surface Water Rights (existing/identified) Alluvial Water Rights Non-tributary Groundwater 32,900 4,000





20,800 24,000




27,100 5,100

20,000 25,900






2030 (Long-Term)




2010 (Interim)

2010 (Interim)

2020 (Mid-Term)

2030 (Long-Term)

2020 (Mid-Term)


Total water demands (potable and non-potable) for each SMWSA provider.






Projected sources of supply, aggragated for all 12 SMWSA water providers.

Citizen’s Guide to Denver Basin Groundwater

| 27

Preserving the Aquifers In 1973, the General Assembly estab-

L o ok i n g f or R e n ewa b l e Wat e r S u ppl i e s

lished a minimum Denver Basin aquifer pumping life of 100 years. More recently, in an effort to promote a longer aquifer life, counties such as Elbert, Adams, Weld, and El Paso have enacted a 300-year rule. All new development in those counties must show they can provide a sufficient water supply to last at least 300 years. This means if a developer or overlying landowner is relying on groundwater, the total annual volume of groundwater available to them is 0.33 percent of the

Transferring water from agriculture (above), on a willing buyer-willing seller basis, is one of the most likely sources of new water for urban areas. Conservation measures include irrigating golf courses (right) and parks with treated, but non-potable water.

calculated water in storage. The assump-

In the long-term, sustainable solutions for wa-

even Denver’s renewable surface water

tion is that with reduced annual pumping,

ter supplies in much of the south metro area

supplies have their limits.

there will be less drawdown and less well-

will require at least a partial shift to surface

Transferring water from agriculture,

to-well interference, prolonging the life of

water resources. But in this day and age,

on a willing buyer-willing seller basis, is

the aquifer.

finding unclaimed surface water to divert

one of the most likely sources of new

on a reliable basis can be an expensive

water for these areas. Currently, agricul-

and challenging proposition.

ture accounts for more than 85 percent

It is important to note that the volume of total recoverable water is an estimate, a number that has been very hard to quantify.

28 |

To the west, additional renewable

of the water delivered for use in Colo-

supplies may be acquired through trans-

rado. While this option has historically

basin diversions, but the construction of

meant drying up irrigated lands, recent

storage, conveyance, treatment, and dis-

legislation has authorized interruptible

tribution facilities is expensive, difficult to

agricultural transfers and crop rotation

permit, and has potentially negative envi-

options. Any conversion of agricultural

ronmental ramifications. It would also be

water should be pursued in a thought-

unpopular in the basin of origin, an area

ful and respectful manner reflecting the

that may have its own water issues. Con-

importance of and need for continued

struction of additional storage projects

viable agriculture and the open space it

like the proposed Two Forks Dam on the

represents. In addition, water providers

South Fork of the South Platte River has

in the South Metro area are individually,

historically been unpopular.

or in partnership, developing local wa-

To the south, the over-appropriated

ter storage solutions. Although Rueter-

Arkansas River which supports both

Hess, the City of Parker’s new reservoir,

growing municipalities and existing

is the largest and most known, several

farm communities provides limited new

other storage alternatives are under

water for Front Range communities.

way. Centennial Water is adding over

To the east, very few significant sur-

6,200 acre feet of new surface storage

face water resources exist and data sug-

below Chatfield Reservoir. Also, a num-

gests that on the eastern edge of the

ber of the water suppliers in the South

Denver Basin the quality of the aquifer

Metro area are participating in the real-

is so poor that only limited amounts of

location of storage in Chatfield Reser-

water could be extracted and imported.

voir to provide for additional surface

To the north, it has been suggested

storage of domestic water. The future

that Denver Water might some day be

benefit of on-stream storage and the

induced to share water with the south

significant role it will play in managing

metro area. This is possible, but it was

future supplies of renewable water for

brought home by the 2002 drought that

the region is noteworthy.

A lternat i v e M a nag e m e n t St r at e g i e s Alternatively, water managers are looking at ways

of golf courses, parks and open-space.

In t roduction

and will require cooperation among many

to reduce groundwater demands, and to diversify

Conjunctive use manages surface

water districts and providers.

their options for managing existing groundwater

water and groundwater supplies jointly

Sustainable water management in this

supplies. A partial list of options includes:

to produce a larger, more reliable sup-

arid state relies on the ability to store water.

ply than either water supply could gen-

Storage projects involve the construction

• Water conservation;

erate alone. The goal is to allow water

of new reservoirs, conversion of storage

• Conjunctive use of surface water and

providers to extend the life of their aqui-

facilities, and enlargement or rehabilitation

fers while fully using their surface water

of existing reservoirs. The conversion of

rights, managing short-term shortages,

gravel pits to gravel lakes is another option

and minimizing the need for new, above

for development of new storage capacity.

ground storage reservoirs. For example,

However, limited surface water flows and

water providers like Centennial and East

protection of existing water rights in the

groundwater; • Potable and non-potable water reuse; and • Control of non-native phreatophytes, high water-use plants.

Cherry Creek Valley Water have contract-

Denver Basin make the construction of

Conservation programs have been

ed to purchase available surface water

new on-channel reservoirs difficult.

effective in both reducing water demand

from Denver, and only use groundwater

Off-channel reservoirs require the con-

through changes in consumer behav-

to augment their peak demands or in

struction of diversion and pumping facili-

ior and improving water use efficiency.

times of drought.

ties to deliver the water to storage. Parker

Tiered rate pricing and mandatory water-

Actively recharging aquifers is an

Water and Sanitation District is construct-

ing restrictions during the recent drought

emerging strategy to not only manage

ing the off-channel Reuter-Hess Reservoir

decreased Denver Water’s demand by

water supply, but also restore and protect

to hold water that may include a blend of

almost 20 percent. The town of Castle

aquifers. During wet years with above-

deep Laramie-Fox Hills groundwater, re-

Rock is hoping it can get its customers to

average precipitation and runoff, surface

cycled effluent and alluvial groundwater.

reduce their water use by 18 percent over

water is stored for later use by injecting

Communities around Parker are con-

the long-term. Parker Water and Sanita-

it into groundwater aquifers. In this sce-

sidering participation in the project, and

tion District has been very successful in

nario, a deep confined aquifer is used for

expansion of the reservoir is being con-

reducing demand through pricing and

storage in much the same way as a sur-

sidered even prior to its completion. The

conservation, reducing their water deliv-

face reservoir. A water management dis-

decade-plus permitting process required

ery to 0.4 acre feet per household.

trict might also direct water from streams,

for this construction project illustrates

Conservation can also be achieved

lakes, or reservoirs to permeable areas of

the time challenge of constructing major

through removal and control of non-na-

a groundwater basin where the water can

new infrastructure.

tive water-loving vegetation, or phreato-

infiltrate the soil through recharge ponds.

Individual homeowners will be able to

phytes, that consume water that could

In either case, the stored water can be

supply their water needs in areas where

otherwise be put to beneficial use. Tama-

withdrawn at some future point when

aquifers are thick by continuing to deep-

risk is an invasive plant species of partic-

surface sources are in short supply.

en their wells. However, those located

Centennial Water District has been im-

on the western fringe of the basin where

Reuse water may involve recycling re-

plementing an aquifer storage and recov-

aquifers are thin, may face the need to

turn flows after infiltration into the ground,

ery (ASR) project in the Denver Basin for

convert to alternate supplies.

or effluent from wastewater treatment

14 years. Direct injection through existing

Finally, some experts suggest that

plants. Many municipalities are reusing

production wells is a proven technology

changing the rates or spatial patterns of

treated but non-potable water for irrigation

for putting additional water in storage and

groundwater pumping can help extend the

restoring groundwater levels. They have

life of the aquifer. The development of sat-

23 wells permitted for injection into the

ellite well fields is proposed to reduce the

Denver, Arapahoe, and Laramie-Fox Hills

impact of high density, large capacity wells.

aquifers when surplus water is available.

Clearly, water providers in the Denver

ASR projects are also being implemented

Basin can not meet all of their objectives

by Consolidated Mutual Water Company

with a single water strategy. Sustainable

in the Lakewood area and by Colorado

solutions will require them to continue

Springs Utilities. To be effective in address-

to develop collaborative integrated use

ing declining water levels, aquifer recharge

strategies to meet the current and future

must be implemented on a regional scale

water needs of the basin.

ular concern in Colorado.

Citizen’s Guide to Denver Basin Groundwater

| 2 9

Timeline of C ol or a d o Grou n dwat e r L aw The following timeline sets forth, in summary

engineer, (3) a well permit “shall not

1968 Colorado Supreme Court states that

form, major events in the establishment of Colo-

have the effect of granting or conferring

“implicit” in the Colorado Constitution’s

rado groundwater law.

a groundwater right upon the user,” (4)

prior appropriation provisions are the

the priority date of a “groundwater ap-

propositions that: (1) “along with vested

1876 Article XVI, Sections 5 and 6 of the

propriation shall not be postponed to a

rights, there shall be maximum utilization

Colorado Constitution declare that

time later than its true date of appropria-

of the water of this state” and (2) admin-

the un-appropriated water of every

tion by failure to adjudicate the right in a

istration of water in the second century

“natural stream” is the property of the

surface water adjudication,” and (5) the

of prior appropriation law involves how

public dedicated to the beneficial use

newly-established Ground Water Com-

maximum utilization of surface water and

of the people of the state by priority

mission shall identify critical ground-

tributary groundwater can be integrated

of appropriation.

water areas that “have

into the law of vested rights, Fellhauer v.


reached or exceeded the normal annual 1903 Colorado General Assembly provides that any water right derived from

rate of replenishment,” 1957 Colo. Sess. Laws, Ch. 289, 863-73.

any “natural stream” is subject to court adjudication, 1903 Colo. Sess. Laws, Ch. 130, 297-98.

People, 447 P.2d 989, 995 (Colo. 1968). 1969 Colorado General Assembly adopts the Water Right Determination and Ad-

1965 Colorado General Assembly adopts

ministration Act of 1969 which, among

the Ground Water Management Act

other provisions, states that (1) tributary

that: (1) authorizes the Colorado Ground

groundwater and surface water shall be

Water Commission to create designated

administered according to the doctrine

term “natural

basins for groundwater that has little or

of prior appropriation, in order to maxi-

stream” subjects to the rule of prior ap-

no connection to a surface stream, (2)

mize beneficial use, (2) vested surface

propriation all sources of stream sup-

provides for the Ground Water Commis-

water and tributary groundwater rights

ply, including percolating groundwater

sion to allocate and regulate designated

shall be protected in order of their de-

that is tributary to a surface stream,

groundwater through a permit system

creed priorities, (3) wells that have not

German Ditch & Reservoir Co., 56 Colo.

on a modified prior appropriation basis

obtained adjudication of their priorities

252, 270-71 (1914).

for economic development through the

have a period of two years in which

1914 Colorado Supreme Court confirms that the constitutional

maintenance of reasonable pumping

to file for their original appropriation

1919 Colorado General Assembly pro-

levels, (3) authorizes the creation of lo-

date and, if not, their priorities shall be

vides that all claims to prior appropria-

cal groundwater management districts

postponed to other priorities that have

tion water rights shall be filed within

for regulation of designated groundwa-

been adjudicated by the courts, and (4)

two years; if not, their priorities shall

ter, (4) requires all new wells, wherever

augmentation plans may be decreed to

be postponed to those water rights

they may be located in the state, to

allow out-of-priority diversions that are

that are adjudicated by the courts, 1919

obtain a construction permit from the

not subject to state engineer curtail-

Colo. Sess. Laws, Ch. 147, 487-96.

state engineer, and (5) provides that a

ment, if sufficient replacement water

state engineer well construction permit

is provided to alleviate material injury

1951 Colorado Supreme Court holds that

“shall not have the effect of granting nor

to adjudicated water rights, 1969 Colo.

Colorado law includes a presumption that

conferring a groundwater right upon the

Sess. Laws, Ch. 373, 1200-1224.

all groundwater is tributary to and sub-

user,” 1965 Colo. Sess. Laws, Ch. 319,

ject to appropriation and administration


as part of the waters of a surface stream,

1973 Colorado General Assembly provides that non-tributary groundwater

unless a person proves by clear and sat-

1965 Colorado General Assembly, by a

outside of designated groundwater ba-

isfactory evidence that the groundwater

separate act from the Ground Water

sins shall be subject to state engineer

is not tributary, Safranek v. Town of Li-

Management Act, requires State En-

well construction permits and rules

mon, 123 Colo. 330, 333 (1951).

gineer to administer tributary ground-

that provide for overlying landown-

water in accordance with the doctrine

ers, or those acting with the consent

1957 Colorado General Assembly pro-

of prior appropriation that is applicable

of overlying landowners, to use this

vides that: (1) all users of groundwater

to the distribution of surface water, and

type of groundwater which underlies

must file a statement of use with the

adopt rules and issue orders neces-

their lands on the basis of a “minimum

state engineer, (2) new wells shall not be

sary to enforce this responsibility, 1965

useful life of one hundred years,” 1973

drilled without a permit from the state

Colo. Sess. Laws, Ch. 318, 1244-45.

Colo. Sess. Laws, Ch. 441, 1520.

30 |

Colorado Foundation for Water Education


acting with the consent of the over-

(4) injurious depletions not adequately

that the “tributary character” of water

lying landowners, to be extracted at

replaced shall result in curtailment of

that “takes over a century to reach the

a rate of no more than 1/100ths per-

the out-of-priority diversions, Empire

stream” is “de minimus” and is “not

cent per year, 1985 Colo. Sess. Laws,

Lodge Homeowners’ Association v.

part of a surface stream” as contem-

Ch. 285, 1160-69.

Moyer, 39 P.3d 1139, 1150 (Colo. 2001).

1974 Colorado



plated by the Colorado Constitution’s prior appropriation provisions, Kuiper v. Lundvall, 187 Colo. 40, 44 (1974).

1988 General Assembly clarifies that the

2002 Colorado General Assembly (1) au-

Ground Water Commission, when is-

thorizes State Engineer to approve

suing permits for the beneficial use

substitute supply plans for out-of-pri-

1977 Colorado General Assembly re-

of designated groundwater in the four

ority tributary groundwater diversions

peals legislation it had enacted in

Denver Basin aquifers, shall allocate

under limited circumstances while aug-

1974, 1974 Colo. Sess. Laws, Ch. 111,

this water on the same basis as provid-

mentation plan applications are pend-

440-42, that had allowed the State

ed in the 1985 act for non-designated

ing in the water court, and (2) approves

Engineer to approve temporary aug-

portions of the Denver Basin, namely

the Arkansas river basin amended rules

mentation plans while the water court

“upon the basis of ownership of over-

governing the diversion and use of trib-

was adjudicating applications for

lying land” and “an aquifer life of one

utary groundwater in that basin, 2002

augmentation plans, 1977 Colo. Sess.

hundred years,” 1988 Colo. Sess. Laws,

Colo. Sess. Laws, Ch. 151, 459-64.

Laws, Ch. 483, 1702-04.

Ch. 258, 1238. 2003 Colorado Supreme Court holds

1983 Colorado Supreme Court holds that:

2000 Colorado Supreme Court holds that

that proposed State Engineer 2002

(1) designated groundwater and non-

all water within Colorado constitutes a

South Platte Basin rules allowing out-

tributary groundwater are not subject

public resource consisting of: (1) wa-

of-priority diversions under replace-

to the prior appropriation provisions

ters of the natural stream, which in-

ment plans, in the absence of an aug-

of the Colorado Constitution, and the

cludes surface water and groundwater

mentation plan application pending in

General Assembly may use its plenary

that is tributary to the natural steam, (2)

water court, were contrary to statute

authority to decide how these public

designated groundwater, (3) nontribu-

and in excess of his authority, Simp-

waters shall be allocated and adminis-

tary groundwater outside of designated

son v. Bijou Irrigation Co., 69 P.3d 50,

tered, and (2) the 1969 Act applies only

groundwater basins, and (4) nontribu-

67 (Colo. 2003).

to surface water and tributary ground-

tary and not-nontributary Denver Ba-

water, State v. Southwestern Colorado

sin groundwater of the Dawson, Den-

2004 Colorado General Assembly al-

Water Conservation District, 671 P.2d

ver, Arapahoe, and Laramie-Fox Hills

lows South Platte tributary ground-

1294 (1983). The General Assembly

aquifers, Upper Black Squirrel Creek

water wells to operate out-of-priority

responds promptly with legislation that

Ground Water Mgmt. Dist. v. Goss, 993

under State Engineer approved sub-

(1) recognizes and enforces prior water

P.2d 1177, 1182 (Colo. 2000).

stitute supply plans, with provisos that (1) augmentation plan applica-

court decrees adjudicating nontributary groundwater outside of designated ba-

2001 Colorado Supreme Court holds that

tions must be filed in Division No. 1

sins and (2) allows the water courts to

through the 1969 Act (1) the General

Water Court by December 31, 2005,

adjudicate to overlying landowners the

Assembly created a new statutory au-

and (2) wells not included in an adju-

right to extract nontributary groundwa-

thorization for water uses that, when

dicated augmentation plan or State

ter outside of designated basins under

decreed, are not subject to curtailment

Engineer approved substitute supply

their lands, 1983 Colo. Sess. Laws, Ch.

by priority administration, (2) this statu-

plan shall be “continuously curtailed”

516, 2079-80.

tory authorization is for out-of-prior-

from operating out of priority, 2004

ity diversions for beneficial use that

Colo. Sess. Laws, Ch. 316, 1205.

1985 Colorado General Assembly pro-

operate under the terms of decreed

vides that nontributary and not-non-

augmentation plans, (3) plans for aug-

Timeline excerpted from “An overview

tributary groundwater in the Denver

mentation allow diversions of water

of Colorado Groundwater Law” pre-

Basin bedrock aquifers of the Daw-

out-of-priority while ensuring the pro-

pared by Justice Greg Hobbs for the

son, Denver, Arapahoe, and Laramie-

tection of senior water rights through a

Geological Society of America Sym-

Fox Hills formations shall be allocat-

replacement water supply that offsets

posium on Groundwater Mining and

ed to overlying landowners, or those

injurious out-of-priority depletions, and

Population Growth.

Citizen’s Guide to Denver Basin Groundwater

| 31

Gl ossary Alluvial aquifer An aquifer formed by geo-

Cone of depression The draw down of the

Specific yield Represents the volume of

logic sediments deposited in a stream

potentiometric surface due to the

water that can drain from a unit vol-

channel or on a floodplain.

pumping of a water well. The amount

ume of saturated material by gravity.

of draw down diminishes away from

The storage property of an unconfined

Aquifer Storage and Recovery Storage of

the well so that the resulting configu-

aquifer, whose value is often on the or-

water in a suitable aquifer through

ration of the modified groundwater

der of 0.15.

direct injection in a well when water

surface resembles a cone. Storage coefficient Represents the volume

is available and later recovery of the water from the same well when it is needed.

Confined aquifer An aquifer that is overlain by a confining bed.

of water yielded from the combined elastic properties of water and the aquifer skeleton, from a unit volume of

Artesian head The elevation, above the

Conjunctive use Coordinated use of surface

the aquifer. The storage property of a

top of the aquifer, to which water will

and groundwater supplies to meet de-

confined aquifer, whose value is often

rise in a well completed in a confined

mand so that both sources are used

on the order of 0.0001.

aquifer due to hydrostatic pressure. It

more efficiently. Structural sedimentary basin A topographi-

defines the potentiometric surface. Return flows Surface water or groundwa-

cally low area in the Earth’s crust in

Bedrock aquifer An aquifer within the solid

ter that returns to rivers and shallow

which sediments have accumulated

rock that underlies any unconsoli-

aquifers after being put to beneficial

by transport via streams from the ad-

dated sediment or soil.

use, such as irrigation. In river basins

jacent hills.

all around Colorado, the same water is

32 |

diverted and returned to the river and

Unconfined aquifer An aquifer having a wa-

shallow aquifers three to seven times

ter table, whose surface is at atmo-

or more before it leaves the state.

spheric pressure.

Colorado Foundation for Water Education

A ddi t i ona l R eading Alley, W. M., Reilly, T. E., and Franke, O.

Hobbs, G.J., Jr., 2004, Citizen’s Guide to

L., 1999, Sustainability of Ground-Wa-

Colorado Water Law: Colorado Foun-

ter Resources: US Geological Survey

dation for Water Education, 34 p.

Circular 1186, 79 p. Hobbs, G. J., Jr., 2007, The Public’s Water CDM in Association with Meurer & Asso-

Resource, Articles on Water Law, His-

ciates, 2007, Regional Water Master

tory, and Culture: Continuing Legal

Plan: South Metro Water Supply

Education in Colorado, Inc., 395 p.

Authority, 128 p. Available at www.

MacDonnell, L.J., 2000, Colorado

Topper, R., Spray, K.L., Bellis, W.H. Hamilton, J.L., and Barkmann, P.E., 2003,

Ground-Water Law, in Aiken and Colorado Foundation for Water Edu-

Ground-water Atlas of Colorado:

others, ed., Colorado Ground-Water

cation, 2004, Citizen’s Guide to

Atlas: Lakewood, Colorado, Colorado

Colorado’s Water Heritage: Colorado

Ground-Water Assoc., p. 121-122.

Foundation for Water Education, 34 p. Marstan, E., Noel, T. E. Sibley, G., Laflin, Colorado Water Conservation Board,

R., Werner, B., Hoyt, H.L., Smith, S.,

South Platte Decision Support

2005, Citizen’s Guide to Colorado’s

System Technical Memorandum for

Environmental Era: Colorado Founda-

Tasks 39, 42.2, 43.2, and 44.2: Avail-

tion for Water Education, 34 p.

Colorado Geological Survey Special Publication 53, p. 210 Woodard, L.L., Sanford, W., and Raynolds, R.G., 2002, Stratigraphic variability of specific yield within bedrock aquifers of the Denver Basin, Colorado: Rocky Mountain Geology, v.37, p. 229-236.

able on the CWCB’s web page. Raynolds, R.G., and Reynolds, M.L., Colorado Water Conservation Board,

2004, editors, A Special Issue on Bed-

Statewide Water Supply Initiative:

rock Aquifers of the Denver Basin:

Available on the CWCB’s web page.

The Mountain Geologist, v. 41, no. 4.

Cross, C.W., Chisolm, F.F., Chauvenet,

orado Water Conservation: Colorado Foundation for Water Education, 34 p.

Robson, S.G., 1987, Bedrock Aqui-

R., and van Diest, P.H., 1884, The

fers in the Denver Basin, Colorado

Artesian Wells of Denver: Colorado

— A Quantitative Water-Resources

Scientific Society, Proceedings, v.1,

Appraisal: U.S. Geological Survey


Professional Paper 1257, 73 p.

Emmons, S.F., Cross, C.W., and Eldridge,

Zeilig, Nancy, 2004, Citizen’s Guide to Col-

Robson, S.G., 1989, Alluvial and Bedrock

G.H., 1896, Geology of the Denver

Aquifers of the Denver Basin — East-

Basin in Colorado: U.S. Geological

ern Colorado’s Dual Ground-Water

Survey Monograph No. 27.

Resource: U.S. Geological Survey Water Supply Paper 2302, 40 p.

Frohardt, Paul D., 2004, Citizen’s Guide to Colorado Water Quality Protection:

Romero, J.C., 1976, Ground Water Resourc-

Colorado Foundation for Water Educa-

es of the Bedrock Aquifers of Denver

tion, 34 p.

Basin, Colorado: State of Colorado, Division of Water Resources, 109 p.

Grigg, N., 2005, Citizen’s Guide to Where Your Water Comes From: Colorado Foundation for Water Education, 34 p. Hobbs, G.J., Jr., 1997, Colorado Water Law: An Historical Overview, Univ. of Denver, Water Law Review, v.1, no.1.

Citizen’s Guide to Denver Basin Groundwater

| 33

Not that many years ago, settlers turned to water dowsers to find what they could not see, groundwater. Prosperity, if not survival, rode on a “sweet water” well. A “dry hole” could dash a homesteaders dreams. Science has replaced the dowser, but not lessened our dependence on groundwater. This Citizen’s Guide to Denver Basin Groundwater explores the geology and hydrology of our underground water resource, the legal framework developed for its administration and management, the current development of the resource, as well as its limitations and sustainability.

1580 Logan St., Suite 410 Denver, Colorado 80203 303-377-4433 •

Citizen's Guide to Denver Basin Groundwater  

This guide explores the geology and hydrology of the Denver Basin underground water resource, the legal framework developed for its administ...

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