Raising Groundwater

Front Range cities ramped up groundwater pumping from the Denver Aquifer in the 1980s, figuring it would be a temporary water source until the Two Forks Dam and Reservoir Project was built on the South Platte River sixteen miles west of Castle Rock. But every fossil groundwater basin in Colorado, indeed throughout the world, is in decline. It is a story of a vanishing resource and a case study of mismanagement. And this might be the most important table in this book.

Figure 12.1 Colorado’s water balance

Two features stand out in this table. First, nearly all rain and snow falling on Colorado, 84 percent, never touches the ground. Instead, it evaporates and literally vanishes into thin air, a phenomenon that meteorologists call “virga.”[1] Second, we are using a million acre-feet more every year than ends up in rivers. We get this water by unsustainably mining our limited aquifers.

Of the 16 percent of precipitation that ends up in Colorado rivers, we have to deliver two-thirds of it to downstream states. That leaves only 5 percent for us. If temperatures continue warming and evaporation rises by only 1 percent from 84 percent to 85 percent, our share drops from 5 percent to 4 percent, a drop of 20 percent of our water supply. That is why global warming scares Colorado water planners so much.

The above table presents statewide averages, but it is higher in certain areas. For example, in mountainous areas of Jefferson County, evapotranspiration is 87 percent, and on the Eastern Plains it averages 98 percent! Hotter temperatures cause evapotranspiration rates to rise, and that could have dire consequences for river flows. The Bureau of Reclamation predicts that annual Colorado River flow will drop 12.4 percent by 2080 as the earth warms.[2] What the atmosphere gives in rain and snow it takes away in evapotranspiration.

Groundwater should be regarded as an emergency source of water. Instead, the state now relies on groundwater to supply nearly 20 percent of its overall demand. Andrew Stone, executive director of the American Groundwater Trust, said at a conference I attended in Denver in 2014, “When demands are met by depleting groundwater, the system is unsustainable. You have to define unacceptable consequences. This is where the politicians have to get involved.”[3]

So far, Colorado politicians have been unwilling to take a stand, instead permitting groundwater mining to occur at a rate that will deplete it within 100 years, by design.

Figure 12.2 Groundwater types

Water providers in Denver’s south metro area consider groundwater their ace in the hole. If reservoir levels drop and surface flows cease during droughts, groundwater can make up the slack. But discerning how much is left, or how fast we are depleting Colorado’s aquifers, is not adequately understood or documented. We pump 2,780,000 acre-feet a year out of the ground, and more than half (59 percent) comes from non-renewable aquifers whose recharge rate is miniscule.[4] Only a seventh of groundwater pumping is for municipal and industrial use; the rest is for agriculture. Nearly all groundwater pumped in Colorado is being used to grow corn and bluegrass.

Colorado has been doing this for decades. Thirty years ago, annual groundwater withdrawals statewide exceeded 2,500,000 acre-feet, compared to the 2,780,000 acre-feet pumped in 2013.[5] Not all of the fossil groundwater withdrawals are lost to the system since some percolates underground to recharge aquifers when farmers over-irrigate. I have struggled to determine how much groundwater mining is occurring, but that data is elusive.

At the 2014 groundwater conference, scientist Jeff Lukas of CU said that groundwater mining statewide totals at least 1 million acre-feet[BG1] [KR2] . Individual pumpers do not want this known[BG3] [KR4]  and state officials are reluctant to release the information as it could affect interstate compacts. Then state engineer Dick Wolfe said, “It’s not just about the science, it’s also about the rule of law, politics, and economics. We have to accommodate all of these.”[6] And economics professor Charles Howe of CU said “Groundwater presents classic economic problems—how should you be using a non-renewable resource over time? There’s no area where we can improve water management with greater social reward than in groundwater management.”[7]

The South Platte River basin has the highest population and consumes the most water of any basin in Colorado. On average, 1.4 million acre-feet of rain and snow fall on the basin each year, but farmers and cities divert about 4 million acre-feet each year from the South Platte River and its tributaries, reflecting how water is used and reused there. The South Platte basin adds another million acre-feet to this from groundwater mining and transbasin diversions.

Figure 12.3 South Platte Basin sources and uses of water

In all, the South Platte basin receives about 2.4 million acre-feet of water from precipitation, transbasin diversions, and groundwater mining, and sends 0.4 million acre-feet across state lines. Its total annual consumption is about 2 million acre-feet, nearly 40 percent of the total water consumed in Colorado each year. The South Platte basin is mining both the Denver Basin Aquifer and the Ogallala Aquifer. In Colorado, overzealous groundwater mining is occurring from the Front Range foothills to the High Plains along the border with Nebraska and Kansas.[8] But attempts to conserve it run head-on into the Colorado state constitution that says no diversion should ever be denied as long as water is being put to beneficial use. And it runs into the maxim held dear by many state water officials and irrigators that says any water that isn’t diverted, or pumped up to the surface, is being wasted.

The Denver Basin Aquifer sits beneath Weld County and most of Denver, Adams, Arapahoe, Douglas, Elbert and El Paso counties, basically the entire Denver metro area south to Colorado Springs. The geology of the Denver Basin Aquifer is daunting because it consists of four separate confined aquifers that lie at different depths, one beneath the other. It is confusing since one of the aquifers is called the Denver Aquifer. Because of this, I call the four aquifers together the “Denver Basin Aquifer System.” They are not connected to each other because they are separated by impervious layers of clay or shale laid down between 100 million and 37 million years ago. The lowest layers formed first when a great inland sea left behind sand, mud, and shale deposits. Later sedimentary layers formed as the Rockies rose and eroded gravel and silt onto the Great Plains. These aquifers are not connected to a river on the surface, and thus they are considered to be “fossil.”

Of the 15.9 inches of precipitation that falls each year on average on Denver, geologists estimate that only 1 percent, less than a quarter inch, recharges these aquifers. The rest is lost through evaporation or surface runoff into rivers like Cherry Creek or the South Platte. Since record-keeping began in 1983, the Arapahoe and Laramie Fox-Hills aquifers , the bottom two aquifers in the Denver Basin Aquifer System, have been declining as much as an inch a day, or 30 feet a year.

Figure 12.4 Aquifers in Denver area

Above is a cross-sectional view of the four aquifers that make up the Denver Basin Aquifer System, depicted 22 miles south of Denver. Each aquifer lies on an impermeable layer of rock, typically shale. By 2006, water levels had declined by 100 feet to 300 feet (30 to 90 meters) at various places in the Arapahoe Aquifer. Aquifer levels were declining ten feet to forty feet a year as late as 2006 and continue to decline between one and five feet a year today[BG5] [KR6] . Senate Bill 5, passed by the General Assembly in 1985, permitted annual withdrawals of 1 percent of the estimated aquifer, a rate that assumes a 100-year life. That’s already 40 years ago.

Based on the then-pumping rate, the USGS predicted in 2006 that the Arapahoe Aquifer will dry up around 2020 near Sedalia on the west side of the Basin.[9] I could not verify if this has occurred, but when the USGS monitored 36 groundwater wells in the Denver Aquifer between February 2012 and February 2019, the well with the largest decline was in the Arapahoe aquifer 6 miles northwest from Sedalia. It declined 2.26 feet per year, nearly 16 feet in all over the 7-year comparison period. The next largest annual decline was 0.92 foot per year, registered in wells in the Denver Aquifer. Of 13 wells monitored in the upper Dawson, lower Dawson, Denver, and Arapahoe aquifers, 12 showed declines.[10] The lowest aquifer in the Denver Aquifer, the Laramie-Fox Hills Aquifer, is estimated to contain 102 million acre-feet in a water-yielding bed that is rarely more than 200 feet thick. Well pumping levels in the Arapahoe aquifer, the most productive, have declined 125 feet in southeast Denver near Castle Rock and Parker, and by fifty feet at its northern edge near Brighton.[11]

These aquifers contain a lot of water but estimates of how much seem to drop with each new study. In 1985, the legislature assumed 467 million acre-feet were stored in the aquifer, with 295 million acre-feet available. In 1999, Leonard Rice Consulting Water Engineers, Inc., calculated that the Denver Basin Aquifer System contained 292 million acre-feet of theoretically available water, but current estimates are that about 200 million acre-feet are available.[12] That’s equal to about 820 times the volume of Dillon Reservoir.

Test wells drilled near Castle Rock in 1987 and near Kiowa in 1999 gave public agencies considerable aquifer data for the first time, and they produced well yields that were significantly lower than the values assumed in 1985. Water declines are largest in the west-central side of the Denver Aquifer and have decreased in Castle Rock by up to 180 m (nearly 600 feet!) since 1990. The Denver and Arapahoe aquifers show the largest groundwater storage losses, with the highest rates of loss occurring in the 1990s. In 2016, 29,284 wells existed in the Denver Basin Aquifer System. The fastest rate of well construction was between 1993 and 2007 when over 18,000 wells were drilled.

A 2019 study suggests that 12 million acre-feet have been mined, a rate of 461,077 acre-feet per year, from 1990 to 2016, nearly half of the 1 million acre-feet of groundwater mining that Jeff Lukas said occurs in Colorado each year. The cumulative total of 12 million acre-feet amounts to about 6 percent of available water in the Denver Basin Aquifer System, but the study cautions that “it is possible for storage depletion to be much less or much more.” Groundwater-level declines since 1990 are much more severe in the west-central areas” of the aquifers ranging from Arvada to Castle Rock.[13] Since 2007, the Colorado Foundation for Water Education has reported that the recoverable water stored in the Denver Basin Aquifer System may only be two-thirds of what was thought.[14]

Relying on gross comparisons like this—that we’ve only mined 6 percent of the aquifer system—can be misleading. The Arapahoe Aquifer is the primary and often sole source for municipal water for communities between Denver and Colorado Springs. Much of the Denver Basin Aquifer System is much farther east and the water is far deeper, making it cost-prohibitive to pump. This recoverable reserve is only a theoretical upper limit since wells are mechanically incapable of completely draining an aquifer. The cost of pumping, which is powered by electricity, will also limit actual recoverable water. Some soils are so dense that little groundwater transmits through them, and surface tension causes water to cling to soil particles so that it cannot be pumped. Other water is of poor quality. Time will tell how much water is recoverable.[15]

Why is it so difficult to predict how long groundwater will last? First, we lack wells whose function is solely to monitor water tables. Many of the monitoring wells are also producing wells, so the wells affect groundwater levels as they pump water, thereby distorting data. Second, since underground rock layers are not visible, scientists cannot see the features that divert or concentrate water into pockets or the underground passageways that connect them. Producing wells may be sucking water from other parts of the aquifer and not represent the actual water available.

The Colorado legislature regularly revisits this issue. In 1973 the legislature adopted a prior appropriation system for groundwater withdrawals. Administered by the state engineer, it was designed to ensure the groundwater supply would last 100 years. This was challenged by water users citing the 1876 Colorado Constitution, “The right to divert . . . shall never be denied.”[16] The Colorado Supreme Court sided with the legislature, holding that it had a rational basis to limit to water consumption in the state, and a 100-year useful life was deemed rational. In 1985 a commission convened by Governor Richard Lamm concluded, “Decreased yields could cause serious social and economic problems, but this should not prohibit development of the Denver Basin Aquifers.”[17] They reaffirmed the 1 percent rule: pumping was permissible as long as it did not deplete more than 1 percent of the total estimated recoverable groundwater each year. Again, this presumes a 100-year life, plus whatever percolates down to recharge the aquifer, but we know the replenishment rate is miniscule.

Figure 12.5 Confined and unconfined aquifers

The Arapahoe Aquifer is the main and best water source in the Denver Metro area, and particularly for the South Metro communities of Highlands Ranch and Castle Rock. It was expected to become an unconfined aquifer by 2020[BG7] [KR8] , and to see production drop by 85 percent by 2050.[18] Robert Raynolds of the Dept. Earth Sciences at the Denver Museum of Nature and Science reported that the transition has already begun to unconfined status in a report at a 2013 Geological Society of America meeting in Denver. He says that a confined aquifer becomes unconfined when, paradoxically, its annual water level declines level off. “It was predicted that the transition [from confined to unconfined status] would take place between 2004 and 2014 in the Castle Rock area,” Raynolds reported. “Data reported in 2012 indicates the prediction to have been optimistic with many wells having transitioned in 2005-2006. A diminished rate of fall (from 10’s of feet per year to single digit feet per year) and diminished well yields characterize the transition.”[19]

“Confined aquifers” are penned in by an impermeable upper rock layer so that water percolating down and into the aquifer creates hydrostatic (or artesian) pressure that forces water up into wells that are drilled into it. By contrast, an “unconfined aquifer” has the same pressure that water has on a lake surface—that is, atmospheric pressure. Water does not rise up into a well that is drilled into an unconfined aquifer; it must be pumped. Engineers know when an aquifer becomes unconfined because hydrostatic pressure declines and well yields decline. They also need more energy to pump it up. Eric Hecox, then executive director of the South Metro Water Supply Authority and now senior vice president of operations at Shea Properties, once said the Authority’s biggest fear is that the Arapahoe Aquifer becomes unconfined.

In all, Denver suburbs are withdrawing about 70,000 acre-feet a year from the Denver Basin Aquifer System. Another 300,000 acre-feet is being withdrawn from other designated groundwater basins in the Front Range.[20] The South Metro Water Supply Authority is a consortium of thirteen water providers in Douglas, Arapahoe, and Elbert counties that formed in 2004, providing water to Centennial, Highlands Ranch, Parker and Castle Rock. It committed in 2006 [BG9]  to eventually reduce its groundwater withdrawals from 111,000 acre-feet to 15,000 acre-feet. These providers know that the Arapahoe Aquifer is finite. Still, these same cities between Denver and Colorado Springs plan to be among the fastest growing in the nation, expecting to double their population in the next several decades.

One of the hardest things about being a lawyer is figuring out what’s not in a contract. That’s an apt metaphor for trying to find how much water is being withdrawn from the Denver Basin Aquifer System. In 2005, 57 percent of the South Metro Water Supply Authority’s water supplies, about 30,000 acre-feet, came from non-renewable sources—i.e., the Denver Basin Aquifer. The South Metro’s service area is huge, nearly as large as the Denver and Aurora service areas. Its 2016 master plan, recognizing that the Denver Basin Aquifer system receives very little recharge and is non-renewable, focuses on municipal conservation, stating, “Our region averages about 120 gallons of water use per capita per day, one of the lowest per capita rates in the state.” At that rate, an acre foot serves three households. It’s laudable, and is the lowest water consumption target I’ve ever seen a Colorado water provider commit to.

By 2013, South Metro boasted it was receiving less than half its water from non-renewable aquifers, but it still did not say how much it was withdrawing from the Denver Basin Aquifer System. The only clue I found was the graph reproduced below from its master plan. The orange bar at the bottom, labeled “Non-Tributary Groundwater,” is the Denver Basin Aquifer System, and it verifies that the South Metro Authority considers the aquifer a permanent water supply. It plans to keep growing, eventually delivering 110,000 acre-feet each year, enough water for over 800,000 residents using 120 gallons per person per day. It still expects to be withdrawing 18,000 acre-feet of Denver Basin Aquifer water in 2065 when fully built out. It will get about two-thirds of its water, nearly 75,000 acre-feet, from surface water supplies which can only come from drying up farms or diverting still more water from the Western Slope, and from recycling water it is already using.[21]

While members of the South Metro Water Supply Authority are trying to limit their groundwater pumping, billionaire Philip Anschutz, through one of his companies, Sun Resources, is building wells that could pump another 15,000 acre-feet of water per year from the Denver Basin Aquifer System.[22] A 1995 water-court decision established rights to 1.5 million acre-feet of water under the Greenland Ranch, a 21,000 acre ranch covering nearly 33 square miles between Denver and Colorado Springs. It is the oldest operating cattle ranch along Colorado's Front Range. Douglas County purchased 4,000 acres of Greenland Ranch with sales tax revenue and funds raised from Great Outdoors Colorado lottery ticket sales in what is billed as “one of the state’s biggest conservation success stories.”[23] But the open space acquisition did not include the water rights underneath. Anschutz acquired those rights in 2011 from the Gaylord family of Oklahoma. A 2009 “water right offering” estimated the groundwater could generate $370 million in revenues from growing communities including Castle Rock. The proposed pipelines run north and south of Greenland as far as 25 miles. We will keep still sticking straws into the aquifer until it is all captured.

The prior appropriation system governs surface water law in Colorado—whoever first puts water to beneficial use controls it—but Colorado decided that this doctrine would not work for deep basin groundwater. How could one determine, in a bowl with 10 or 100 straws, which straw was draining another’s well? Instead, fossil groundwater is governed by the “rule of capture”—anyone who drills into the aquifer can take whatever water they can pump to the surface.

Droughts in Colorado over the past century can be discerned by the ebb and flow of water legislation. The state created the CWCB and President Franklin Delano Roosevelt approved[BG10] [KR11]  federal funding for the Colorado Big Thompson project in 1937 as the Dust Bowl dragged on. In 1957, in the midst of a decade-long drought, the legislature began requiring permits for groundwater pumping. Following the 2002 drought, the legislature and courts finally required aquifer pumpers in the South Platte basin to augment stream flows—to replace water they were pumping from the ground.

In 1965 the legislature created the Colorado Ground Water Commission to regulate fossil groundwater. Since fossil groundwater has no discernable connection to surface streams, it recharges extremely slowly. The 1965 legislation established two precedents. First, it nullified prior appropriation, stating the doctrine had no place in governing groundwater withdrawals. Second, it wrested control away from the courts—today the Commission regulates fossil ground water mining free from court oversight. The legislature and courts perpetually wrangle over who controls water in Colorado, and this time the legislature won. The Ground Water Commission issues pumping permits to surface owners upon request, but it does not establish the permissible pumping rate until a well is drilled. Based on how much the well produces, the Commission estimates the size of the underground reservoir and limits annual pumping to 1 percent of that estimate. There are no guarantees—if the water supply does not last, so be it. It is all but inevitable that underground fossil water supplies will be exhausted since they took much longer than 100 years to accumulate.

Guaranteed or not, Colorado is heavily dependent on its dwindling groundwater supplies. In 1995, Colorado’s total groundwater withdrawal was 2.5 million acre-feet, the vast majority of which was for agriculture.[24] Fossil groundwater mining constitutes 18 percent, nearly a fifth of all water consumed in Colorado.[25]

Figure 12.6 Map of designated ground water basins in Colorado [26]

Eight “designated groundwater basins” on the Eastern Plains are depicted in the map above. Note that these do not include the Denver Basin Aquifer System, which is regulated separately by Senate Bill 5, passed in 1985. The two largest designated groundwater basins are the Northern and Southern High Plains Aquifers, our local name for Colorado’s share of the Ogallala Aquifer. The Republican River Basin has the same shape as the Northern High Plain Aquifer on the map, not surprising since the Republican River Basin occupies 80 percent of the Northern High Plain Aquifer. All wells in the Republican River Basin must be metered, meaning that farmers must report[BG12] [KR13]  how much water they pump each year. During 2012, Republican River basin farmers were pumping more than their maximum annual appropriations from at least forty large capacity wells. They claimed the excess pumping was necessary to finish out their crops.[27] The state engineer knew about the over-pumping but was powerless to prevent it until the end-of-year reports were due. When it comes to water, everything is political in Colorado, right down to the date reports come due.

Some members of the South Platte Roundtable bemoan that 109,000 acres of the 550,000 irrigated acres in the Republican River basin must be taken out of production, [BG14] but the eventual total is likely to be far greater. At current pumping rates, the Northern and Southern High Plains aquifers will be dry within an estimated 25-to-75 years, with the southern aquifer drying up first since it is shallower. Wells in the Southern High Plains Aquifer do not even have to be metered, meaning they can pump without limitation.

The Republican River Basin

The Republican Basin is a case study for what is likely to happen throughout the West as we grapple with higher temperatures and declining water supplies.

The Republican River, named after a branch of Pawnee Indians that early explorers called “Republicans,” drains a 24,000 square mile basin. It starts in eastern Colorado halfway between the South Platte and Arkansas rivers before coursing into Nebraska and Kansas. About a third of the basin is in Colorado, an area that was ground zero for the Dust Bowl. It was first settled in the 1870s just after the 1862 Homestead Act passed. Colorado, Nebraska, and Kansas signed the Republican River Compact in 1943 to allocate 11 percent of the Republican River flow to Colorado, 40 percent to Kansas, and 49 percent to Nebraska. The Compact allocates a “virgin water supply” of 478,900 acre-feet to the three states, equivalent to a year-round flow of 682 cfs. It’s not a big river, especially in relation to the 24,000 square-mile area it drains

The Republican River’s water politics are complicated since it lies above the Northern High Plains Aquifer. In 1966 the Colorado Ground Water Commission designated the Northern High Plains Ground Water Basin and started monitoring the increasing irrigation.[28] There are six geologic layers in the basin, including the familiar Niobrara, Dakota, and Morrison formations, but nearly all groundwater is in the Ogallala-Alluvium layer. The Ground Water Commission estimated the annual recharge, the precipitation replenishing the aquifer, was 423,500 acre-feet, about 0.4 percent of the estimated 96 million acre-feet in the Northern High Plains Aquifer. The Ground Water Commission also estimated that ground water use in 1966 was 331,360 acre-feet, or 0.3 percent of the total aquifer. At that rate of pumping, the aquifer would theoretically last forever since the replenishment rate exceeded withdrawals.

But that didn’t last long.

Beginning in the mid-1960s there was a rapid expansion of irrigated farmland, as high capacity wells increased from about 400 in 1960 to eventually 4,400. High capacity wells produce enough water to irrigate a quarter section of land, 160 acres, the typical green circle we see from the airplane flying east from Denver. In Denver, the typical suburb has five houses per acre, or about 800 houses on 160 acres.

In 1989 the Colorado legislature asked the state engineer to estimate depletion in the Northern High Plains Aquifer. There are 700 monitoring wells in the 7,000 square mile area, and the Colorado Division of Natural Resources measures well depth every winter, so they have a good record of the aquifer decline. From 1965 to 1989, the state engineer estimated the recoverable water in the aquifer had declined 17 percent to 101 million acre-feet, down from the 118 million acre-feet the geologists estimated was in the aquifer in 1965 (revised upward from the Ground Water Commission’s 1966 estimate of 96 million acre-feet). The aquifer was declining 0.6 percent per year, about 1 foot per year between 1965 and 1989. At this rate of decline, the aquifer would be down to 80 million acre-feet in 2025, and 51 million acre-feet by 2100.

 The Ogallala Formation is near the surface and consists of debris eroding from the Rocky Mountains. It sits above several layers of impermeable shale that keep the water from percolating further down. It is a “poorly consolidated alluvial deposit consisting of clay, silt, sand and gravel,” which means it resembles a river bed.[29] As the alluvium washed over the plains, it was thicker where it filled in canyons and shallower where it washed across flat terrain, as would happen if it filled in the undulating arroyo landscape we see today in eastern Colorado. The canyons that filled in have thicker deposits of alluvium and more water than adjacent regions where the alluvium is shallower. As the alluvium collected, water saturated it during the Pleistocene age, from about 2.5 million years ago to only 12,000 years ago, when wooly mammoths roamed. The Ogallala Alluvium is overlain by dune sand and loess, wind-blown dust that accumulated over time from the winds that still sweep eastern Colorado daily today. If you live east of I-25 on the Front Range and dig a hole to plant a tree, you’re digging into the dune sand and loess that overlies the aquifer.

This means that some of the high capacity wells have a lot more pumping capacity because they’re in thicker formations than neighboring wells. The 1989 report described 11 different wells that were in gravel beds ranging from 65 to 273 feet in thickness. Overall, the average thickness of the Northern High Plains Basin was 137 feet in 1965, and 117.7 feet in 1989, dropping 16 percent overall. While wells in beds 273 feet thick may last for hundreds of years, others in beds 65 feet thick could be dry within a few decades.

In 1940 there were an estimated 30,788 acres of irrigated land in the basin. Irrigated land increased nearly 8 percent per year for sixty years after the Dust Bowl, to 1,263,809 acres by 1970 and 2,757,110 acres by 2000.[30] If it weren’t for the Ogallala Aquifer, 30,788 acres is probably the sustainable irrigated agriculture, since that was the amount under cultivation before large scale pumping began. The USGS says the 2000-2009 Republican River Basin water level declines were nearly one-half of the declines of the entire Northern High Plains Aquifer, an area covering 174,000 square miles and seven times larger than the Republican River Basin.[31] In terms of aquifer decline, eastern Colorado is ground zero, just as it was in the Dust Bowl.

When the Republican River Compact was signed in 1943, there was little groundwater pumping, but today about 4,000 high capacity wells irrigate 600,000 acres in the Republican River Basin in Colorado.[32] All those pumps create zones of depression—as the well sucks the local soil dry, water is drawn from adjacent soil in the alluvium—and that has caused the Republican River to decline. Kansas sued Nebraska in the US Supreme Court in 1998, and again in 2010 when it also joined Colorado in the suit, because Kansas wasn’t receiving the 190,300 acre-feet it was supposed to receive in the 1943 Compact. Kansas’ problem is it’s downstream, like the last farmer on the irrigation ditch. The problem with “compacts is that they tend to be very prescriptive in who gets how much water,” CSU professor John Tracy, director of the Colorado Water Center, said in a 2023 podcast. “[T]he climate has changed, and the predictability of river flows has really gotten difficult. Telling either an upstream state or a downstream state that you get so much water when you’re relying on an unreliable climatological system has become problematic.”[33]

In each case the Supreme Court appointed a special master to propose a settlement, which the Supreme Court essentially followed. That alone has caused concern among the states, fearing that if a special master could decide their fates, essentially an outsider chosen to rule like Solomon, they may as well reach agreement among themselves.[34] After the Special Master held in 2000 that the Republican River and the underlying groundwater were connected hydrologically, the Colorado legislature created the Republican River Water Conservation District to bring Colorado into compliance. From 2003 to 2007, Colorado irrigators continued pumping 10,000 acre-feet over their allocation each year. When Kansas joined Colorado in a second US Supreme Court case in 2010, Colorado settled by agreeing to retire 25,000 acres from irrigation by 2030. The Republican River Water Conservation District website keeps a running tab, and by October 28, 2024, 17,066 acres had been taken out of production, about two-thirds of what’s eventually required.[35]

John Tracy, the professor in the Department of Ecosystem Science and Sustainability at CSU University, says there’s only one answer: to irrigate less. It’s comforting to say, “Well, we’ll just be more efficient without water. But the reality is the amount of water being used for agricultural production is the evapotranspiration from the crop being grown. If you actually want to save the water you have to retire the land. Everything else is smoke and mirrors,” Tracy said.[36] If Colorado does not take 25,000 acres out of production, then the state engineer may need to essentially turn off all the wells in the Republican Basin, some 3,000 and counting.

Administration is complicated because the state engineer administers surface rights on the Republican River and its hydrologically-connected groundwater sitting beneath the river. But the Colorado Ground Water Commission has jurisdiction over the Northern High Plains Aquifer, which basically encompasses the entire Republican River basin, and it regulates wells further away from the river. Do the wells further out from the Republican River suck up water that impacts the groundwater directly beneath the Republican River? Yes, but that means two state agencies with different rules and bureaucracies have to solve Kansas’ problem. One affected irrigator complained, “[The State said] “We are going to adopt basin rules and if you don’t get into compliance with these basin rules, we will shut you down. We will start with the wells within one mile [of the river], three, 10, 15, then we will take up the rest of the basin.”[37]

The solution in the Republican River Basin has been to retire farmland. The Republican River Water Conservation District levies an assessment on each irrigated acre, and uses the money raised to buy out irrigated farm land. Or, irrigators can enroll land into the Conservation Reserve Program. The Farm Service Agency, a USDA agency, pays farmers to retire acreage from irrigation and to restore the native grasses, trees, and riparian buffers that existed when the buffalo roamed. The USDA in October 2014 issued $2.1 billion to reclaim 1.7 million acres, amounting to $773 per acre. Payments typically last for 10 to 15 years, hopefully enough time for significant environmental benefits to accrue. There are currently 26 million acres enrolled, and Colorado has the most acres enrolled of any state, at 2,978,741 acres. Five states that overlie the Ogallala Aquifer including Colorado, South Dakota, Nebraska, Texas, and Kansas, together account for 12 million acres enrolled, about half of all acres funded by the Conservation Reserve Program.[38]At water meetings it is dismaying to hear the stories told by Republican Basin irrigators about the decline to their way of life. About 90,000 people live in the three states overlying the Republican River Basin, a density of about one person per 190 acres. But the declining water table is also an opportunity, as the residents can take their payments and practice agriculture elsewhere.

Not Non-Tributary?

In 2010 the Colorado legislature amended the 1965 Groundwater Management Act, taking away the right of surface water right holders to claim that groundwater pumped in “designated groundwater basins” was interfering with their surface water rights.[39] That had been a feature of the Groundwater Management Act since it was passed in 1965. The 2010 amendment permits these designated groundwater basins to be enlarged, reflecting the political clout of groundwater pumpers on the Eastern Plains. Through 2012 the state engineer approved 6,857 wells in these designated basins, with over three-fourths located in in the Northern and Southern High Plains aquifers, which are both part of the Ogallala Aquifer.[40]

Non-tributary groundwater is a legal definition that implies that the groundwater is not connected to a surface stream. Senate Bill 5 mathematically defines this, stating that if groundwater pumping does not cause a stream flow to decrease by one-tenth of a percent, the water is non-tributary and not connected to the stream. It is easy to see why engineers are needed to interpret this law. Hydrology engineers soon pointed out that Monument Creek, Plum Creek, and Cherry Creek in the Denver metro area were being depleted by more than 0.1 percent per year by groundwater pumping. That led to the creation of another category of groundwater, “Not Non-Tributary Groundwater.”

It is confusing, but in the end rather simple, as almost all legal concepts are once you strip away the jargon. “Not non-tributary groundwater” refers to water pumped from the deep Denver Basin Aquifer System that actually does affect surface stream flows and is therefore connected to them. Another name for it would be “tributary groundwater.”

The following table summarizes these categories.

Table 12.1 Five Types of Non-tributary Groundwater in Colorado

The Five Types of Non-tributary Groundwater in Colorado

Non-tributary groundwater

Groundwater that has no discernable connection to a surface stream. Also called fossil water.

Denver Basin groundwater

Fossil groundwater stored in four aquifers below Denver, in order of highest to deepest: the Dawson, Denver, Arapahoe, and Laramie Fox Hills aquifers.

Designated Groundwater Basins

Eight fossil groundwater basins on the Eastern Plains that are governed by the Colorado Groundwater Commission, not by water court. The two largest are the Northern and Southern High Plains aquifers, comprising Colorado’s share of the Ogallala Aquifer.

Not non-tributary groundwater[41]

Groundwater in the Denver Basin that is actually connected to a surface stream. This is legally proven when it is demonstrated that a stream flow declines by more than 0.1 percent per year as a result of groundwater pumping. It refers to tributary groundwater that enters the Denver Basin Aquifers.

Tributary groundwater

Groundwater that is obviously connected to a stream, so that pumping has a discernable effect on stream flow. Also known as alluvial groundwater, it is most prevalent in the South Platte and Arkansas river basins.

One takeaway from this table is that there isn’t all that much water in Colorado. If there was, we wouldn’t we splitting hairs like this.

“Tributary groundwater” is water that seeps from rivers into the ground. Until 2003, tributary groundwater was also governed by the rule of capture—whoever pumped it got it. Today, groundwater pumping from the alluvium along the South Platte and Arkansas rivers on the Eastern Plains is governed by the prior appropriation system. It took nearly eighty years before the state finally required groundwater pumpers to compensate for the impact their pumping had on surface river flows. But the burden of proof still lies with the state to demonstrate a well is impacting surface river flows.

Well drillers have long known that the first place to drill for water is in canyons or other land surface depressions because water tends to flow underground in the same patterns it flows above ground. They know that ground and surface water flows are connected. Convincing lawyers and politicians of this connection is a study of human denial throughout the West, as each state has gone through bruising political battles trying to establish the link between ground and surface water. Colorado is no exception. Groundwater pumping began in the Depression when pumps and rural electricity became commercially available, but it wasn’t until 1957 that Colorado began requiring permits for groundwater wells. Still, anyone could drill for alluvial groundwater once a permit was obtained, which the state engineer could not deny. After the 2002 drought, the state engineer and water court finally began requiring groundwater pumpers to augment surface flows that were obviously dropping because of groundwater pumping. Today it is difficult to obtain a permit to drill into an alluvial system without augmenting the groundwater with water from someplace else.[42]

Groundwater pumpers augment their pumping by purchasing water stored in reservoirs to replace their groundwater withdrawals, or by digging “recharge reservoirs” on their farms. These are shallow reservoirs that are filled by diverting water from the South Platte during high runoff periods when the river is running high and “free.” As a sign of increasing scarcity, there was less water available for recharge reservoirs along the South Platte River in 2008 than there was in 2007, even though the snowpack was better in 2008. The South Platte Roundtable states, “There is little unappropriated water to develop in the South Platte River,” even in high flow years when the river is free.[43] 2009 through 2011 were better snow years, and residents in Sterling along Highway 76 and in Gilchrist and LaSalle along Highway 85 south of Greeley started complaining their basements were flooding. In places the water table was rising to within five feet of the surface. Reagan Waskom, the now former director of the Colorado Water Center at Colorado State University, was tasked by the legislature in 2012 to study this.[44] He said there were three causes: improving rain and snowfall since the 2001-2008 drought; reduced pumping by farmers who could not augment their groundwater withdrawals; and 500 new recharge ponds that were dug. The basement flooding upset legislators in Weld and Logan counties. Senator Vicki Marble, a Republican from Weld County, said, “Gilchrist and La Salle farmlands are being destroyed by salt buildup because they aren’t allowed to pump. Each basin has its own problems, and the more government gets involved, the worse it gets. I’m not a fan of water court. Government isn’t seeing this the way the people are.”[45] Waskom cautioned that “local problems should not get global solutions.”[46] There are 18,600 points of diversion on the South Platte River. The South Platte is a large, complicated basin, and when asked whether we are augmenting too much, Waskom replied, “it depends on the timing and drought cycles.”

Outside of Colorado, the state engineer could permit farmers to pump more or relax river calls so farmers can fill their recharge reservoirs, but that is not feasible in Colorado because water courts adjudicate augmentation plans that must be followed.

The problems on the South Platte points to the constant tug-of-war between the legislature, water courts, and the state engineer’s office over water administration. The decisions that courts make don’t always square with the problems on the ground. Waskom suggests the state’s division engineers could play a larger role, and not be as quick to order downstream farmers to stop pumping. Or they could refrain from placing administrative calls on the river so that recharge reservoirs can fill. He believes these could be tested in pilot projects. Waskom concludes, “The HB 1278 study has revealed that the existing groundwater monitoring data collection network is irregular and incomplete but could rather easily be substantially upgraded. Additionally, water management organizations in the basin should be strongly encouraged to share data and collaborate on data collection.”[47]

Maybe what we don’t know can hurt us.

More alarming is the number of wells we are drilling into the Denver Aquifer. In 1985, 12,000 wells withdrew 36,000 acre-feet from the Denver Basin Aquifers. By 2001, the number of wells had nearly tripled to 33,700. In 1995, nearly 445,000 acre-feet was withdrawn in Adams, Arapahoe, Denver, Douglas, and Elbert counties, a 12-fold increase from the 36,000 acre-feet withdrawn only ten years earlier when Senate Bill 5 was passed.[48] Despite the new wells, aquifer withdrawals by 2006 [BG15] had declined to 350,000 acre-feet.[49] Groundwater pumping from the Denver Basin Aquifer System is a losing game that will only get worse as we keep mining it.

Between 2011 and 2021, wells show considerable variability in how much water levels have changed. The Colorado Division of Water Resources reported well depths at 71 wells across the Denver Basin Aquifer System, and while two wells show water levels have actually risen closer to the surface, I calculate the weighted average decline has been 17.5 feet over all wells in all the different aquifers, with the steepest average decline being 47’ registered at 23 wells in the Denver Aquifer. This is more evidence of the continuing decline of the aquifers.[50]

Figure 12.7 Wells drilled into the Denver Aquifer

Each new well drilled into an aquifer creates another “zone of depression,”. That impacting existing wells that are already pumping the adjacent water. As the wells produce less water, new wells must be continually drilled, an increasingly expensive process. Over 200,000 permits have been issued for producing wells in Colorado, and the state engineer continues to receive over 4,000 ground water well drilling applications each year.[51]

The Colorado Foundation for Water Education provides an example showing that, at a drilling cost of $500,000, the first well can deliver 30 acre-feet of water for a cost of $267 per acre-foot. As newcomers add wells, the provider must add additional wells to keep delivering 30 acre-feet a year. Eventually, by the time the provider has added a sixth well to continue delivering 30 acre-feet each year, the cost has risen to $13,500 per acre-foot.[52] The example assumes a 2006 cost of $500,000 to drill a well. By 2014[BG16] , the cost to drill a well into the Denver Aquifer was closer to $1 to 1.5 million.[53] One result (and cause) of the near tripling in the number of wells is a 50 percent increase in the Front Range population between 1980 and 2000.[54]

When the General Assembly passed Senate Bill 5 in 1985, legislators demonstrated some concern for the future by requiring that 2 percent of water pumped from the Denver Aquifer had to be replaced, implying that 98 percent of the groundwater mining was acceptable.[55] The state engineer assumes that lawn overwatering, responsible for most of the recharge in the Denver and Dawson aquifers in the Denver Basin Aquifer, satisfies this 2 percent replenishment requirement.[56] Ironically, the more that people over-water their lawns, the more these underground aquifers get recharged, yet another factor playing into the South Platte Roundtable’s resistance to high municipal conservation targets. This cynical arrangement appears to be a losing game because the same water that recharges the aquifer was pumped out of the aquifer. But that is not true if the water was pumped from the Arapahoe or Laramie-Fox Hills aquifers and ends up in the higher Dawson and Denver aquifers. That process transfers water from one aquifer to another, and different parties have different wells drilled into these aquifers. This is one more facet of Colorado’s incredibly complex, and political, water law.

Boulder attorney David Harrison said in 2006, “I do not think Senate Bill 5 was intended as a groundwater management act. It is a groundwater allocation act. There is no management of the Denver Basin right now. Somewhere along the line we will make an economic decision not to use it (nonrenewable groundwater) very much anymore, except in emergency situations.”[57]

The question we are not addressing in Colorado is whether it is wise to pump ancient water supplies up to the surface to grow bluegrass or corn for a few more decades. El Paso, Adams, Weld and Arapahoe counties are projecting they will add 850,000 new residents and be among the fastest growing counties in Colorado between 2025 and 2050.[58] Groundwater pumping may not be an option for these counties, so they will either have to purchase agricultural water rights or divert still more water from the Western Slope. Assuming the new residents use 164 gallons per day in 2050, the conservation target the South Platte roundtable recommends, the projected 850,000 new residents in these counties will need 156,000 acre-feet a year.[59] If they use the more responsible 130 gallon per day target set by the Denver Metro roundtable, the counties will still need another 125,000 acre-feet.[60] Some of that need will be met by bringing water over from the Western Slope and storing it in underground aquifers. The South Platte and Metro roundtables say their plans to store water underground is eco-friendly since it avoids having to build new dams and because there will not be any evaporation losses from the underground aquifers.[61] But it takes energy to pump the water into and back out from the aquifer, which today is still obtained primarily by burning CO2-emitting coal. And Western Slope river health will continue to decline if still more water is diverted to the Front Range. The Colorado Roundtable has never signaled its willingness to increase Colorado River diversions so they can be stored underground on the Front Range.[62]

Colorado citizens may ultimately have to decide whether it makes sense to further destroy the health of our alpine rivers so we can continue growing bluegrass. Water providers like Denver Water, Northern Water, the South Metro Water Supply Authority, Colorado Springs Utilities, Aurora, and the Southeastern Colorado Water Conservancy District, all want to divert more water from the Western Slope. And nearly all of that water will be consumed by bluegrass lawns. Rather than transferring water from the Western Slope to recharge the aquifers, geologists at the USGS and the Denver Museum of Natural History recommended the fixes listed below in 2007 to stop mining the Denver Basin aquifers. The current system, a myriad of small water managers pursuing their individual interests, will almost certainly mine the aquifers out of existence.[63] One recommendation that has been followed is recharging water into the Denver Aquifer in high water years, which Highlands Ranch has been doing. But ten years later most of the USGS recommendations are still not being implemented. [64]

Table 12.2 Recommendations to reduce use of groundwater, and likely objectors

USGS recommendations to

reduce groundwater mining.

Who will object

More observation wells should be drilled so we can monitor how much the aquifers are declining.

Parties who rely on groundwater but do not want their pumping or the extent of groundwater mining made public. They will mask this concern by saying it is too expensive to drill observation wells.

Reduce lawn watering.

South Platte Roundtable.

Include warnings in home sale contracts that the water supply is limited.

Real estate brokers.

Increase tap fees for water connections.

Developers.

Recharge aquifers when excess surface water is available in Front Range tributaries in storm events.

Water right holders who claim they own the water under prior appropriation.

Recharge aquifers by diverting water from the West slope.

West slope.

Reuse water rather than letting it flow down the South Platte and Arkansas Rivers to farmers lower in the basin.

South Platte roundtable.

The Ogallala Aquifer

Groundwater mining is an international problem. The journal Nature produced a comprehensive report of groundwater declines across the globe in January 2024, and the first of its 14 maps of a declining aquifer was the Ogallala Aquifer. It reported that there were 45,911 monitoring wells in aquifers with at least five monitoring wells across the globe with sufficient data to calculate the change between 1980-2000 and 2000-2020. It concludes, “Our results indicate that twenty-first century realities—including climatic trends, hydrogeologic conditions, groundwater withdrawal rates, land uses and management approaches—have resulted in widespread, rapid and accelerating groundwater-level declines.” In maps of aquifer declines around the world, it colored aquifers in deep red that were “deepening during 1980-2000 and faster deepening post-2000.” The most conspicuous and largest deep red area on earth was the Ogallala Aquifer, confirming it was among the fastest declining aquifers on earth.[65] The article concluded that when declining groundwater levels were slowed, it was due to the “implementation of regulatory measures.”[66] No surprise there—the only way to regulate human activities is to regulate human activities.

Groundwater mining is a national problem. In 2015 the USGS studied withdrawals from principal aquifers in the United States and reported the Ogallala Aquifer was the most heavily pumped aquifer in the nation.[67] And by far the dominant use, 90 percent or more, is agriculture. As with the Nature article, the first aquifer mentioned by the USGS was the Ogallala.

Estimates vary on when the Ogallala Aquifer will be dried up. The Ogallala Aquifer stretches from North Dakota to Texas, and it underlies 14 percent of Colorado along its eastern border with Kansas and Nebraska border. It is responsible for nearly all irrigated agriculture in the Great American Desert, but it is quickly disappearing.. The useful life keeps changing because we cannot see how much water is underground. We are only going to know how much water is left when it runs out. States keep their pumping rates close to the vest. No one wants to be the first to use less, and no state wants the others to know how much it uses. If they admit that underground supplies are ample, others will join them in extracting it. If they announce that supplies are low, cities or legislators might restrict pumping. It is in every state’s interest to say as little as possible about known supplies. In Texas, where Ogallala groundwater levels are dropping the fastest, the High Plains Underground Water Conservation District recently set pumping caps.

Figure 12.8 Ogallala Aquifer estimated storage

The USGS estimates that in 1980 the aquifer contained about 3.25 billion acre-feet of drainable water The USGS estimated there was 2,980 million acre-feet in the Ogallala Aquifer in 2000, and 2,910 million acre-feet in 2019.[68] [BG17] [KR18] Over two-thirds of that water is in Nebraska. Only 60-80 percent is likely available for large-scale pumping, and these estimates are already more than 15 years old.[69] Former Colorado state engineer Dick Wolfe estimated that Colorado is depleting 850,000 acre-feet from the Ogallala Aquifer every year. At this rate, the aquifer would run dry in Colorado between 2070 and 2095, or sooner if it is uneconomical to pump. Parts of the aquifer would undoubtedly dry up sooner because it is shallower at the edges. There are two ways to look at Colorado’s tiny 3 percent share of the Ogallala Aquifer—use it up as fast as possible before it disappears due to pumping by other states, or use it as sparingly as possible to preserve it for future uses that may be more valuable that growing corn. Guess which approach Colorado has been pursuing.

Figure 12.9 Ogallala Aquifer declines

The Ogallala Aquifer has declined in every state since pumping began (except for a slight increase in Nebraska), based on numbers the USGS compiled in 2000[BG19] . In Colorado, the average area-weighted aquifer decline was 2.7 meters (nine feet) through 2000, and 4.2 meters (14 feet) by 2019. It was worse in Kansas (27 foot decline) and Texas (44 foot decline).[70] Nationally, the USGS estimates that through 2000, Ogallala aquifer levels had declined 3.6 meters (12 feet), irrigated acreage declined 16.5 million acres (15 percent of the 174,000 square miles now being irrigated), and total aquifer storage declined by 197 million acre-feet.[71] Using USGS’ updated amounts, the entire High Plains aquifer had declined 16.5 feet through 2019. Water in the aquifer typically lies 100 to 400 feet below the surface, which is how deep wells have to be drilled to reach it. It covers 174,000 square miles across eight states, almost double Colorado’s land area. Nebraska, Kansas, and Texas account for 88 percent of all Ogallala Aquifer withdrawals.[72] In Texas, the aquifer yields about two-thirds of all groundwater pumped in the state.[73] In 1980 about 170,000 wells were pumping 18 million acre-feet a year across the entire Ogallala Aquifer, more than the Colorado River’s annual flow, to irrigate over 13 million acres. For comparison, the Ogallala Aquifer was irrigating only 2 million acres in 1949.

The USGS determined that the Ogallala Aquifer was discharging maybe 3 million acre-feet a year into springs and rivers before pumping began. This is therefore the sustainable yield from the aquifer. The 2000 pumping rate was seven times greater, 21 million acre-feet a year. As of 2005, hydrologists estimated 253 million acre-feet had been depleted from the aquifer, about 9 percent of the 2,950 million acre-feet the USGS estimates is available.[74] Michael Wines, a reporter at The New York Times, wrote in 2013, "Vast stretches of Texas farmland lying over the aquifer no longer support irrigation. In west-central Kansas, up to a fifth of the irrigated farmland along a 100-mile swath of the aquifer has already gone dry."[75]

In most areas the aquifer water table has dropped between ten and fifty feet since groundwater mining began in the 1950s, with drops of over 100 feet recorded in several agricultural regions. The quality of the Ogallala groundwater is also declining. Arsenic, radon, chloroform and pesticides are all listed in the Safe Drinking Water Act for causing adverse health effects, and all are present in the Aquifer at rates exceeding EPA guidelines.[76] Richard Cowen, a retired geology professor at the University of California at Davis, said in 2008, “The Ogallala water is fossil water that will run out, within a few decades at present rates of withdrawal. That in itself is not necessarily the kind of news that makes people stop pumping.” Cowen continued, “’I should get mine while it's going,’ is a typical response that makes sense when one considers that corn or cotton generates much more money than dry farming, and that everyone else has their well down there sucking the water out of the aquifer. If A doesn't pump it out, then B will, because the water law of the West says that the water in an aquifer cannot be owned by anyone: it's yours if you can pump it. How would any individual farmer gain (or even break-even) by refraining from pumping water from the Ogallala?” [77] One way to delay draining the Ogallala is to use drip irrigation since it is so much more efficient. Ninety percent of the water is taken up by crops with drip irrigation, compared to 75 percent with sprinklers, and 25 percent with flood irrigation.[78] In Deming, New Mexico, an agricultural region along Interstate 10 between Tucson and El Paso, farmers now use drip irrigation for 90 percent of all irrigated land in Luna County, using furrow flood-irrigation for the remaining 10 percent.

I learned about Deming, New Mexico, when I met Dee Greeman at the 2014 groundwater water conference in Denver. He is an irrigation consultant and president of the San Luis Valley Conservancy District in Colorado’s Rio Grande Basin. Greeman says that farmers in Deming have saved their aquifer by converting to drip irrigation. In Deming the annual rainfall is 7 to 9 inches, mostly falling during the summer monsoon season. Deming farmer Don Hartmann says his chili yields increased from 15 to 20-25 tons when he converted to drip, while the water he needed to grow his chili crop declined from 36 inches to 30 inches per season.[79] By spoon-feeding liquid nitrogen and phosphoric acid fertilizer through the drip tape, he cut fertilizer use by about 50 percent. By not wetting the soil surface, fewer weed seeds germinated. The cleaner fields require less cultivation, time, labor, and diesel—that means Hartmann spends fewer hours in the tractor cultivating the fields. Fields irrigated with drip are also warmer, which means plants grow faster compared to furrow-irrigated fields that cool down when they are flooded. When I asked Greeman how they pulled that off, he credited “the local NRCS agent who really got behind drip irrigation and urged and showed local farmers how to install it.”[80] Federal EQIP grants from the Natural Resource Conservation Service help pay for the $2,500-per-acre drip installation cost, which is typically recouped in about 5 years. It often takes a very dedicated, passionate individual who sparks change. I wish I had been able to locate a Colorado community for this story.

Drying up the Ogallala Aquifer is national policy, as evidenced by all the subsidies going to farmers who suck water up from it. No other conclusion can be drawn from the graphs below.

[81]

One reason Colorado is not conserving the Ogallala Aquifer is because eight states withdraw water from it. It won’t help if Colorado is the only state that aggressively pursues drip irrigation. Meanwhile, the huge oasis that the Ogallala Aquifer has enabled is gradually disappearing, perhaps never to be seen again. Our kids will think it was only a mirage.

Figures

Figure 12.1 Colorado’s water balance

Figure 12.2 Groundwater types

Figure 12.3 South Platte Basin sources and uses of water

Figure 12.4 Aquifers in the Denver area

Figure 12.5 Confined and unconfined aquifers

Figure 12.6 Map of designated ground water basins in Colorado

Figure 12.7 Wells drilled into the Denver Aquifer

Figure 12.8 Ogalla Aquifer estimated storage

Figure 12.9 Ogallala Aquifer declines

Figures 12.10 Value of irrigated versus dry land

Notes

[1] Jeff Lukas, speech given at the Colorado Groundwater Conference, Denver, December 4, 2014. Lukas works for the Western Water Assessment and is the lead author of Climate Change in Colorado, 2d Ed., 2014, a report commissioned by the Colorado Water Conservation Board, in August 2014.

[2] Reclamation concludes, “Across almost all research is the projection of continued and increased warming in the Basin and very likely increases in the severity of future droughts. However, the research suggests continued uncertainty in projections.“ See “Colorado River Basin Water Supply and Demand Study, Technical Report B – Water Supply Assessment,” February 2012 Update, US Bureau of Reclamation, pg. B-87. This projection is the midpoint of prior studies reviewed in the USBR report that predict runoff will be reduced by 4 to 20 percent; pg. B-8-9. See http://www.usbr.gov/lc/region/programs/crbstudy/Report1/Updates/TechRptB.pdf.

[3] Keynote address at the Colorado Groundwater Conference, Denver, Dec. 4, 2014, put on by the American Groundwater Trust.

[4] These figures are from a speech given by Dick Wolfe, Colorado State Engineer, on December 4, 2014, at the Colorado Groundwater Conference in Denver. The conclusions in this chapter are the author’s.

[5] 1995 groundwater withdrawals exceeded 2.5 million acre-feet. Groundwater Atlas of Colorado, Colorado Geological Survey, 2003, pg. 13.

[6] Dick Wolfe, see note 4 above.

[7] Speech given at the Colorado Groundwater Conference, Denver, December 4, 2014.

[8] Groundwater Atlas of Colorado, pg. 19.

[9] Moore J.E., Raynolds R.G., and Dechesne M., “Bedrock aquifers and population growth in the Denver Basin, Colorado, USA,” USGS, Episodes, Vol. 30, No. 2, 2006, pg. 118.

[10] Malenda H., Penn C., Groundwater Levels in the Denver Basin Bedrock Aquifers of Doublas County, Colorado, 2011-19, USGS, Scientific Investigations Report 2020-5076, 2020, pgs. 1, 11-13, 21, https://pubs.usgs.gov/sir/2020/5076/sir20205076.pdf.

[11] Groundwater Atlas of Colorado, Colorado Geological Survey, USGS, 2003, pg. 90. These figures are from 2003.

[12] Citizen’s Guide to Denver Basin Groundwater, 2006, Colorado Foundation for Water Education, pg. 20; Groundwater Atlas of Colorado, pg. 93.

[13] Ruybal C., Hogue T., and McCray J., “Assessment of Groundwater Depletion and Implications for Management in the Denver Basin Aquifer System,” Journal of the American Water Resources Association, 2019, pgs. 1, 12-14, 16-17.

[14] Citizen’s Guide to Denver Basin Groundwater, pg. 20; Groundwater Atlas of Colorado, pg. 87.

[15] Groundwater Atlas of Colorado, pg. 93.

[16] Colorado Constitution, Art. 15, Sec. 6.

[17] Citizen’s Guide to Denver Basin Groundwater, Colorado Foundation for Water Education, 2007, pg. 16, https://issuu.com/cfwe/docs/cg-groundwater.

[18] Id, pg. 18, 22.

[19] Raynolds R., “Conversion from Confined to Unconfined Conditions In the Critical Arapahoe Aquifer of the Denver Basin, Colorado,” Oct. 27-30, 2013, Paper No. 8.

[20] Wolfe, D., “Surface Water and Ground Water Administration in Colorado,” 2005, pg. 12, http://hermes.cde.state.co.us/drupal/islandora/object/co percent3A20403.

[21] South Metro Water Supply Authority, “2016 Regional Master Plan Update,” pgs. 7-8, downloaded October 27, 2024, https://southmetrowater.org/application/files/9615/7867/2371/MP-Publication-Final.pdf.

[22] Finley, B., “Aquifer wells in Douglas County challenge renewable-water strategies,” Sep. 13, 2012, The Denver Post, http://www.denverpost.com/2012/09/13/aquifer-wells-in-douglas-county-challenge-renewable-water-strategies/.

[23] While Bruce Finley’s article describes the Greenland Ranch as 7,640 acres, the Conservation Fund says it had 21,000 acres. “Greenland Ranch,” The Conservation Fund,” downloaded Dec. 8, 2016.

[24] Groundwater Atlas of Colorado, pg. 13.

[25] Groundwater Atlas of Colorado, pg. 18.

[26] Ground Water Atlas of Colorado, pg. 23 https://coloradogeologicalsurvey.org/water/groundwater/

[27] Memorandum from Keith Vander Horst, Designated Basins Team Leader, on Staff Activities from May 1 to July 31, 2012 to Dick Wolfe, Exec. Dir., Ground Water Commission (Aug. 17, 2012), pg. 4.

[28] In the Matter of the Proposed Designated Ground Water Basin of the Northern High Plains of the State of Colorado, Findings of Fact, Conclusions of Law, Final Order, Colorado Ground Water Commission, April 14, 1966.

[29] Id.

[30] Final Report of the Special Master, Supreme Court of the United States. (September 2003). Kansas v. Nebraska and Colorado, No.126 Original. Retrieved from:

http://www.supremecourt.gov/SpecMastRpt/Orig126_102003.pdf.

[31] Peterson, S.M., Traylor, J.P., and Guira, M., 2020, Groundwater availability of the Northern High Plains aquifer in Colorado, Kansas, Nebraska, South Dakota, and Wyoming: U.S. Geological Survey Professional Paper 1864, Figure 13B Inflows/outflows, 2000-9,pg. 1, https://doi.org/10.3133/pp1864

[32] Republican River Compact Administration, State of Colorado, downloaded October 28, 2024, https://republicanriver.org/the-states/state-of-colorado/#:~:text=Predominately%20agricultural%20economy,approximately%204%2C000%20high%2Dcapacity%20wells

[33] “If the wells run dry,” podcast by Stacy Nick, Sept. 28, 2023, https://source.colostate.edu/republican-river-compact-significance/

[34] “Lessons Learned from Colorado Experiences with Interstate compact Administrations,” Republican River Basin, Colorado Mesa University, pg. 21, https://www.coloradomesa.edu/water-center/documents/wc_lesssons-learned_2122_webversion.pdf

[35] Republican River Water Conservation District, downloaded Oct. 28, 2024, https://republicanriver.com/

[36] Id, footnote 30.

[37] Id, footnote 32.

[38] “USDA to Begin Issuing $2.14 Billion to Agricultural Producers through Key Conservation and Safety-Net Programs,” USDA Farm Service Agency, https://www.fsa.usda.gov/news-events/news/10-21-2024/usda-begin-issuing-214-billion-agricultural-producers-key-conservation

[39] CRS Section 37-90-106 established designated groundwater basins under the control of the state engineer’s office (SEO). Subsection 1(a) was amended in 2010 to provide that surface owners could no longer claim that pumpers in designated groundwater basins were depleting surface river supplies once the SEO issues a groundwater drilling permit (the "cut-off" date). The 2010 amendment states, "After this cut-off date has passed, any request to exclude wells that are permitted to use designated groundwater from an existing groundwater basin shall constitute an impermissible collateral attack on the original decision to designate the basin."

[40] Vanderhorst, Note 33, pg. 2.

[41] Nontributary groundwater is legally defined in CRS Section 37-90-103(10.5) and not nontributary groundwater is legally defined in CRS Section 37-90-103(10.7).

[42] The Yampa River basin is not under administration, shorthand for saying that nearly every river in the basin is free and not subject to regular calls. It might be one of the state’s significant exceptions, but it will likely be more strictly regulated in the future.

[43] Section 6.4.2, pg. 6-19 of the South Platte SWSI 2010 Basin Report (Final Draft, ~11 MB), South Platte Basin roundtable pg. maintained by the CWCB, downloaded August 23, 2014.

[44] House Bill 2012-1278 charged CSU to study the South Platte recharging and augmentation programs. Waskom, R., “Report to the Colorado Legislature HB12‐1278 Study of the South Platte River Alluvial Aquifer,” Dec. 31, 2013.

[45] Comments made on a legislative panel at the Colorado Groundwater Conference, Denver, Dec. 4, 2014.

[46] Speech titled “HB 1278 (South Platte Ground Water Study),” given at “Ground Water Regulation: History and Focus on Water Divisions 1, 2, and 3,” Colorado Legal Education, Oct. 30, 2013.

[47] See note 38, pg. 11.

[48] Groundwater Atlas of Colorado, pg. 95.

[49] Citizen’s Guide to Denver Basin Groundwater, pg. 20.

[50] Groundwater Levels in the Denver Basin Bedrock Aquifers, 2022, Colorado Division of Water Resources, pg. 5. To do this weighted average calculation, I multiplied the number of wells in the statistics by the 10 year change in water table depth (the left- and right-most number columns), and then summed the products and divided by the 120 wells that were sampled.

[51] Stiller-Shulman, A., “No Seat At the Water Table: Colorado’s New Groundwater Basin Statute Leaves Senior Surface Rights In the Lurch,” Univ. of Colo. Law Rev., Vol. 84, 2013, pg. 826,http://lawreview.colorado.edu/wp-content/uploads/2013/11/12.-Stiller_For-Print_s.pdf; Wolfe, D., “Surface Water and Ground Water Administration in Colorado,” 2005, pg. 12; “Ground Water Administration and Well Permitting, Colo. Division of Water Resources; Marx, E, Wascom, R., Wolfe, D., “Private Wells for Home Use – 6.700,” CSU Extension, Dec. 2013,https://extension.colostate.edu/topic-areas/natural-resources/private-wells-for-home-use-6-700/#:~:text=Ground%20water%20wells%20are%20the,new%20permits%20are%20requested%20annually.

[52] Citizen’s Guide to Denver Basin Groundwater, pg. 21.

[53] Speech by Eric Hecox, Colorado Groundwater Conference, December 4, 2014, Denver. Wells cost more because they have to be drilled deeper and construction costs have risen since 2006.

[54] “Historical Census Population,” Colorado Dep't of Local Affairs (DOLA) , https://dola.colorado.gov/demog_webapps/hcpParameters.jsf.

[55] The legislature did not say the offending groundwater miner had to recharge the Denver basin aquifer with 2 percent of the water it was withdrawing; rather, the statute says the groundwater miner could not be required to “relinquish the right to consume . . . more than two percent of the amount of such groundwater which is withdrawn.” See, CRS Section 37-90-137(9)(b); Harrison, D., Sperling, V., Sims, S., “Intro to Ground Water Law in Colorado and Surface-Groundwater Conflicts In the South Platte,” 2006, pg. 4.

[56] Groundwater Atlas of Colorado, pg. 88.

[57] “Denver Basin Aquifers in Decline,” downloaded Dec. 10, 2016, Colorado Foundation for Water Education (CFWE).

[58] “Historical Census Population,” DOLA, https://dola.colorado.gov/demog_webapps/hcpParameters.jsf.

[59] South Platte Basin Implementation Plan, Volume 1, January 2022, pg. 46, Cooperative Growth gallons per capita per day for the Remaining South Platte River Basin, Table 2, pg. 46.

[60] Water demand is estimated by the following formula: # new residents x # gallons per day x 365 days / 325,851 gallons in an acre-foot.

[61] Colorado’s Water Plan, Final 2015 Draft, Chapter 3: Overview of Each Basin, pg. 3-14.

[62] On April 27, 2009, Arkansas Basin Roundtable chair Gary Barber asked the Colorado Basin Roundtable to help fund a $60,000 study to determine the feasibility of storing water from the Roaring Fork and Fryingpan drainages in aquifers in the Arkansas Basin. Arkansas basin roundtable members hope to divert more water in the Fryingpan-Arkansas Project during wet years, noting there is 218,000 acre-feet of storage available in these aquifers. Barber said the Arkansas Basin has fallowed 60,000 acres to reduce further depleting the Arkansas Basin aquifers. The Colorado Basin Roundtable declined to fund the study.

[63] Moore, J.E., et al, “Bedrock aquifers and population growth in the Denver Basin, Colorado,” 2007, pg. 118, https://pubs.er.usgs.gov/publication/70029731.

[64] “Bedrock aquifers and population growth in the Denver Basin, Colorado, USA,” USGS, Episodes, footnote 11.

[65] Jasechko, S., et al, “Rapid groundwater decline and some cases of recovery in aquifers globally,” Nature, January 24, 2024, Figure 3, Comparison of aquifer scale trends in depth to groundwater during the late twentieth and early twenty-first centuries, pg. 718.

[66]Id, pg. 720.

[67] Lovelace J., Nielsen M, Read A, Murphy C, and Maupin M., Estimated Groundwater Withdrawals from Principal Aquifers in the United States, 2015, USGS, Circular 1464, pgs. 1, 22-28.

[68] McGuire, R. L., et al, “Water in Storage and Approaches to Ground Water Management, High Plains Aquifer, 2000,” 2003, USGS, Circular 1243, pg. 25, http://pubs.usgs.gov/circ/2003/circ1243/pdf/C1243.pdf. High Plains Water-level Monitoring Study, USGS Nebraska Water Science Center, https://ne.water.usgs.gov/projects/HPA/index.html; Water-Level and Recoverable Water in Storage Changes, High Plains Aquifer, Predevelopment to 2019 and 2017 to 2019, USGS Scientific Investigations Report 2023-5143, pg. 1, https://pubs.usgs.gov/sir/2023/5143/sir20235143.pdf

[69] “Mission 2012,” Massachusetts Institute of Technology, downloaded Dec. 9, 2014, http://web.mit.edu/12.000/www/m2012/finalwebsite/problem/groundwater.shtml.

[70] Water-Level and Recoverable Water in Storage Changes, High Plains Aquifer, Predevelopment to 2019 and 2017 to 2019, USGS Scientific Investigations Report 2023-5143, pg. 9, Table 2, https://pubs.usgs.gov/sir/2023/5143/sir20235143.pdf

[71] Not all of Colorado’s decline in irrigated acres stems from aquifer dry-up; some has also resulted from water transfers off the farm to new development. See McGuire, note 52, pg. 32.

[72] “The Ogallala Aquifer and Its Role as a Threatened American Resource,” 2008, Asia-Pacific Economic Cooperation (APEC). This paper is at Chapter – Groundwater\Sources.

[73] Lesikar, B., “Questions about Texas Groundwater Conservation Districts,” 2002, Texas A&M Univ., pg. 2.

[74] “Ogallala Aquifer, last modified 24 Jan. 2017, Wikipedia.

[75] Wells Dry, Fertile Plains Turn to Dust, Michael Wines, The New York Times, May 19, 2013, http://www.nytimes.com/2013/05/20/us/high-plains-aquifer-dwindles-hurting-farmers.html?smid=pl-share&_r=0.

[76] See Mission 2012: Clean Water, Massachusetts Institute of Technology, downloaded December 9, 2014, http://web.mit.edu/12.000/www/m2012/finalwebsite/problem/groundwater.shtml.

[77] Cowen, R., "Mining Water," Sep. 14, 2008, UC Davis. An unexpected pleasure of writing this book was coming across Professor Cowen’s article on groundwater pumping from the Ogallala Aquifer and in Arizona. I attended the British-born Cowan’s geology course, “The History of Life,” in 1975 while attending Davis. His textbook by the same name is well received.

[78] Roberts, M., “Development of standardized methodologies to determine Historic Diverted Volume,” Sep. 13, 2012, Montana Dept. of Natural Resources, pg. 4.

[79] Blake, C., “Subsurface drip solution for frugal New Mexico farmer,” Nov. 22, 2010, Southwest Farm Press, Vol. 37 Issue 23, pg. 1..

[80] Conversation with Ken Ransford on December 4, 2014.

[81]

 [BG1]Didn’t we just cite a figure above of 2.78M? Is there a difference between “withdrawals” and “mining”?

 [KR2]Yes, mining means it isn’t being replenished. I interpret this to mean that 2.78m acre-feet is being withdrawn from the ground each year, and 1 maf is being mined, meaning permanently extracted from the system.

 [BG3]Do pumpers want to keep secret what they pump, or what the whole state pumps?

 [KR4]Probably both. If the public know about the loss statewide, the public might get alarmed and attempt to clamp down on this.

 [BG5]Can you define “today”?

 [KR6]Let’s have Bob (?) Raynolds, FN 19, review this chapter. He can likely fill in the data gaps.

 [BG7]Did it become an unconfined aquifer by 2020?

 [KR8]Yes, Bob Raynolds confirmed that it did.

 [BG9]Update from 2006

 [BG10]is “approved” correct?

 [KR11]See my change. You’re right, the fed gov’t authorized C-BT; Colorado authorized Conservancy Districts, which permitted Northern to come into existence and contract with the Feds to build C-BT. The CO legislature did not approve C-BT.

 [BG12]is this public?

 [KR13]The person who would know is the Division Engineer for Division 1, the So Platte Basin. To find out, we should call him.

 [BG14]from over-pumping, by the engineer?

 [BG15]Update from 2006.

 [BG16]Update from 2014.

 [BG17]Update from 2000.

 [KR18]Done

 [BG19]Update from 2000.