View looking west from I-25 near E. Lincoln Ave. on December 23, 2020 in Lone Tree, Colorado. (Kathryn Scott, Special to The Colorado Sun)

This story first appeared in a Colorado Community Media newspaper. Support CCM’s neighborhood news.

On an average day, 25 people move to Douglas County. Each one needs to drink, shower, water their lawn and wash their dishes.

The full impact of that growth is difficult to see, but it’s easy to understand: More people need more water. And in a county where thousands of homes rely on a limited supply of underground aquifers, water providers are constantly working to shift to more sustainable resources before they run out.

Some aquifers deep under Douglas County have lost 2 to 6 feet in depth of water. Local water providers have noticed their supply wells aren’t producing like they once did.

“It’s like sucking water out of the bathtub with a straw,” said Rick McLoud, water resources manager for Centennial Water & Sanitation. “There’s only so much water in the bathtub and the sooner you suck it out with a straw, the sooner it will be gone.”

Centennial Water, which provides water to about 100,000 customers in Highlands Ranch and the Mirabelle neighborhood, is one Douglas County provider noticing declines in well production.

The water they’re pulling to the surface is depleting. And it’s not replenishing itself.

Growth is expected to continue in the county, with nearly 60,000 more people projected to move to the area by 2030, according to the state’s demography office. That means the community’s thirst is only going to increase.

To meet those demands, water providers are planning a mix of conservation efforts, wastewater projects and new infrastructure for renewable resources of water. The county government is also looking at how to bring in more water and is considering spending a portion of its $68 million in federal funds from the American Rescue Plan Act on the issue.

Over-reliance on groundwater

As Douglas County’s development has surged since the 1990s, many of the largest communities, such as Parker and Castle Rock, have relied on groundwater to fill residents’ bathtubs and sinks, said State Engineer Kevin Rein.

In Colorado, the Office of the State Engineer administers water rights, manages wells and their permits and monitors water use, among other water-related duties.

Groundwater from aquifers makes up about 65% of the water used by Parker Water and Sanitation, which is the provider for Parker and parts of Lone Tree and Castle Pines, and by Castle Rock Water. Centennial Water uses about 20% groundwater. Those ratios can change depending on drought conditions.

According to the state engineer’s office, Douglas County has about 440 municipal wells, which are used to draw water from the aquifers.

The state water engineer’s office estimates there are about 440 municipal wells in Douglas County drawing water from deep underground aquifers that are not recharging. (Screengrab)

“Douglas County is unique in that its over-reliance on groundwater in some ways has spoiled it in the sense that we’re not as subject to the hydrologic cycle as other areas are,” said Brock Smethills, president of Sterling Ranch Development Company and a board member of Dominion Water and Sanitation, which serves northwest Douglas County.

That’s because areas relying on renewable surface water and snowmelt will feel the impacts of a drought year more acutely.

A simulation produced by the United States Geological Survey shows that from 1880 to 2003, about half of the water removed from the Denver basin aquifers was drawn from the south Denver metro region, said Suzanne Paschke, the associate director for hydrologic studies for the Colorado Water Science Center in the USGS.

“That is where most of the storage depletion is occurring in the basin, according to our simulations,” Paschke said.

Rueter-Hess Reservoir, which was completed in 2012, is owned and operated by Parker Water and Sanitation. It has a capacity of 75,000 acre-feet.

Aquifer is depleting

Since 1996, the state engineer’s office has been advising those using wells in the Denver basin to be aware that the aquifers contain a finite amount of water, Rein said.

“We recognize the non-renewable nature and we have advised … that anyone using this resource should recognize that it’s non-renewable and it may not even last for the 100 years it’s allocated on,” Rein said.

In 2003, news reports said the aquifer was in such decline that some areas of the county could run dry of groundwater in 10 to 20 years.

Studies completed by the United States Geologic Survey in 2011 and 2019 showed that aquifer declines were continuing but stopped short of giving predictions on the amount of time until they’re empty.

“We can pull out less now than we used to when we first started,” said McLoud with Centennial Water. “We’re feeling its finiteness.”

Mark Marlowe, the Castle Rock water director, said many of the city’s wells have seen declines in water levels, though he added it’s difficult to determine how widespread that withdrawal is within the basin.

“There’s a big supply but it is going to become more difficult to extract that supply over the long term,” Marlow said. “Quite frankly, we want to protect that supply for periods when surface water is not available.”

That added difficulty comes because as the water level in the aquifer decreases, more wells must be drilled to maintain the same amount of production, causing increases in costs.

Castle Rock is currently working with Colorado State University to study their deep groundwater, Marlowe said.

“There’s still a lot to know and learn about the Denver basin groundwater in terms of how long it will be sustainable as a resource,” he said.

Ron Redd, the district manager of Parker Water and Sanitation, said from their well monitoring, they’ve also seen declines in multiple aquifers.

“On average we can see a 2- to 6-foot decline,” he said.

Douglas County sits on a layer of several aquifers, including the Arapahoe, Denver, Dawson and the Laramie-Fox Hills aquifers. Most major water providers use the water in the Arapahoe and Denver aquifers, which reach depths of 1,700 and 600 feet beneath the ground, respectively.

“While the aquifers are thicker there, I think there’s so much use that it’s heavily impacted,” Pashcke said.

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Elliott Wenzler wrote about politics, water, housing, and other topics for The Colorado Sun from October 2022 through September 2023. She has covered community issues in Colorado since 2019, including for Colorado Community Media. She has been...