More and more people are moving to the state of Colorado and increasing the demand for water, while less and less water is available due to a sustained drought. The population has grown from 1 million in 1930 to more than 5 million today, and is expected to continue growing at an increasing rate.

In an effort to close the gap between water supply and demand, and to prevent a significant shortfall in the near future, the state has put together an aggressive plan, Colorado’s Water Plan, to conserve water more proactively than ever. One goal of the initiative is to increase water storage, and Denver Water, water supplier to Denver and its surrounding suburbs, is exploring the feasibility of storing excess water in the Denver Basin aquifer system during wet times to pull from during dry times.

Aquifer storage and recovery has been done in other places, but this is a first for Colorado’s oldest and largest water utility, which provides water to more than 1 million people.

“It’s pretty exciting because we’re kind of paving a new path for the utility by looking at this technique. It’s fun and it’s rewarding to be involved in that sort of a project,” says Bob Peters of Denver Water, who is serving as project manager of the aquifer storage investigation.

“I think it’s an awesome concept,” says John Taylor, who serves as a regional manager for Hydro Resources, a groundwater servicing specialist headquartered in Sugarland, Texas. Taylor works out of the Fort Lupton, Colo., branch and his crew was subcontracted by Leonard Rice Engineers to complete the exploration drilling for the project. He says the project is a unique one for Hydro Resources because of its scale and the media coverage it comes with.

“It’s not a new concept, but the biggest portion is Denver Water is, I believe, the largest water rights holder in the state,” says Jasen Decker, of Hydro Resources, who served as drilling manager. “If they were to go through with this, the potential for our business would be huge.”

“It’s pretty exciting because we’re kind of paving a new path for the utility by looking at this technique. It’s fun and it’s rewarding to be involved in that sort of a project.”

Decker oversaw the drilling of four 1,800- to 2,200-foot-deep small-diameter test boreholes that were geophysically logged. Cutting samples were taken every 5 feet, with an end goal of Leonard Rice Engineers examining the samples to determine the storage capacity of the aquifer at each point, and then reporting the findings to Denver Water. Decker’s three-man crew utilized a Midway 3500 carrier-mounted rig, 4½-inch drill pipe and 6-inch drill collars. Total time for the project, which spanned about 10 miles throughout Denver, lasted about 10 days. In the end, the boreholes were filled with cement and abandoned.

“What we’re looking at is the thickness of the sand beds that are in the Denver Basin, because those are the more productive parts of the aquifer, so how thick they are and what the permeability is of those sands,” Peters says.

While a lot of borehole logs have already been obtained from the Denver Basin, Peters says most of them are not from Denver, which is the area he is concerned with. The large amount of data gaps make for a lot of uncertainty with regard to productivity of the aquifer within the immediate Denver area, which is why the drilling of four boreholes by Hydro Resources was recently necessary.

Once Denver Water is presented with results of the analysis, they will be able to decide if more data is necessary, thus more test boreholes needed, or if moving forward with the installation of a pilot well facility is logical. Peters says he hopes to have results from the initial samples early this year.

The Denver Basin covers thousands of square miles and, theoretically, millions of acre-feet of storage of water exist within the aquifer, but, Peters says, it depends upon the productivity of the aquifer materials as to whether or not an aquifer storage and recovery would be a good option. He says a key factor is cost. “So, for example, if we’re trying to store 100 acre-feet underground, does that take 100 wells or does it take two wells? ... Wells are expensive to drill, so if it takes a lot of wells, then we might have to think twice about whether this would work for us or not.”

What makes aquifer storage more appealing than traditional above-ground reservoirs is the fact that less water is lost through evaporation, the building of a dam is not necessary and less land is used in an increasingly crowded area.

If the results were promising and aquifer storage and recovery were deemed feasible, the implementation of such a system would take years. The initial step would involve establishing a pilot well to demonstrate how it would work. It would connect to Denver Water’s potable redistribution system and the water would be injected underground using that well. If the pilot proved successful, an indeterminate number of wells would be installed across the city. They would be connected to the water system and inject water during wet years, when available, from the surface water system, Peters says. Then, during drought, the utility would flip a switch that would pump the water back up.

“I hope that we find that it’s feasible,” Peters says. “It could be an important supply option for us down the road. We’re getting to the limits of our water resources and we’re getting to the limits of our ability to impact public land and the environment, so it could be a very important supply project for us in the future.”