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Aquifer Storage and Recovery Study

Aquifer Storage and Recovery, or ASR, is the injection of treated drinking water into an aquifer for later recovery and use. An aquifer is an underground layer of sand, gravel or rock through which water can pass and is stored.

The concept of ASR is similar to a savings account at a bank — drinking water is injected (deposited) during wet years and stored indefinitely. During droughts, that same water is extracted (withdrawn) to supplement supplies.

Denver Water is exploring how ASR may contribute to delivering high-quality drinking water to our customers far into the future. To help with this study, we have secured access to several properties in the Denver metro area to drill exploratory boreholes and collect data on the underlying aquifer.

If Denver Water were to pursue ASR, wells would be drilled at strategic sites in and around Denver. Treated drinking water would be taken from water mains and injected into wells in the Denver Basin Aquifers (several permeable rock formations that underlie all of Denver and much of the Front Range region). The same wells would pump the water back up from the aquifers in times of need.

That's fracking, right?

Definitely not. The use of hydraulic pressure to increase the yield of a petroleum well (known as “fracking”) is as different from ASR as night and day. In fracking, petroleum wells are injected with a mix of water, sand and other materials and chemicals. ASR involves injecting only clean, treated drinking water into underground aquifers, which have the capability to hold water and are already used as a drinking water source for many communities along the Front Range. Local aquifers exist at depths ranging from 500 to 2,000 feet, while the depth of the average petroleum well is between 6,000 and 10,000 feet.

Why is Denver Water exploring the possible use of ASR?

Denver Water is responsible for securing reliable sources of water to meet our customers’ future needs. Experts say that ASR has advantages over traditional surface reservoir water storage, as it tends to be comparatively less costly, has no evaporation, has a lower impact to communities and the environment, and has fewer permitting challenges. Studying the feasibility of using ASR is part of our “all of the above” strategy — which includes conservation, expanding sources of supply and recycling water — to ensure our ability to meet future needs of customers in our service area.

Is it going to work?

The concept is proven and is working here in Colorado and at hundreds of sites across the country, but more study is needed to learn about the aquifers under our feet in Denver. Our study will help us determine if pursuing this is a smart investment on behalf of our ratepayers.

How will you find out?

Exploratory drilling for the ASR study began in September 2015 at this Northeast Denver site.

The study will be a multiyear effort. In late summer 2015, we started drilling exploratory boreholes on four sites across the Denver metro area. The geologic data we’re gathering will help us decide whether proceeding to the next step — developing an ASR pilot well site — is feasible. If so, we will develop a pilot well site to perform additional tests that will help us understand how well the aquifer is able to store water, what happens to water quality once injected into the aquifer, how easily water can be extracted once injected, and more.

Drilling these boreholes sounds like it will be disruptive.

While drilling these exploratory boreholes is likely to come in phases and will create noise, we have strategically selected sites that will provide reliable data with the least inconvenience to residential customers. We are working closely with the appropriate governmental entities to secure necessary permits and will perform our work under their regulation and oversight. In the case where an exploratory borehole may impact a residential neighborhood, we secured a variance for the Denver Noise Ordinance and are implementing mitigation strategies to minimize our impact on our neighbors. If, for any reason, noise levels exceed what is allowed, we can issue hotel vouchers where required by the ordinance.

What volume of water storage are we talking about here?

Again, that is one of the things our study is designed to help us understand. Our estimates indicate that one ASR site could store between 20 and 150 acre-feet of water per year. To give you some perspective, our smallest surface reservoir — Strontia Springs — has a capacity of 7,863 acre-feet. Several ASR wells would be needed to significantly increase water storage capabilities.

What happens to water that has been injected into an aquifer — does it come out at the same level of quality as it went in?

That’s one of the things we will determine later on if we pursue a pilot facility. No matter what, ensuring our customers receive the highest-quality water is our top goal. Water extracted from an aquifer would absolutely go through a water treatment process once more and meet or exceed state water quality standards before we provide it to customers for their use.

What is the budget?

We currently have $1.36 million total budgeted for the exploratory borehole project. Additional funds will have to be budgeted if/when we proceed to developing a pilot well site.

If it all goes according to plan, when do you expect the ASR program to come online and start benefitting customers?

We anticipate spending the rest of 2016 and into 2017 studying the feasibility of investing in a pilot well site. If results are positive, we still have many steps left, including developing the pilot site, working with regulatory agencies (the Environmental Protection Agency, Colorado Department of Public Health and Environment and others) for proper permitting and oversight approvals. At this point it is premature to speculate when ASR could be implemented.


Matt Wittern, Denver Water Public Affairs, 303-628-6304