By Peter Chawaga, Associate Editor, Water Online
Sometimes, the best laid plans go awry.
Aurora, CO, a municipality just East of Denver, had designed a water system to withstand the worst drought it had seen in recent history, a two-year period of water scarcity lasting from 1952 to 1954. But then it was hit with the drought of 2002 to 2004 and its reservoirs dipped down to 26 percent capacity, a mere nine-month supply that forced the community to rethink how it secured its supply.
“Aurora Water looked at 54 scenarios to meet water demand for the future, including growth,” said Gregory Baker, the manager of public relations for the utility. “Potable reuse was the most expeditious, economical, and meaningful in capacity.”
Aurora found that 95 percent of its water, which comes from a combination of three local basins, is reusable. But it only operated a small reclaimed water facility, used for municipal irrigation. With the early 2000s scare and further water stress looming, Aurora decided to change that.
“Water staff was charged by City Council with expanding and hardening our supply before the next big drought, which typically come on a 10-year cycle in Colorado,” Baker said. “After identifying the reusable supplies that were going to be recaptured, a location for diversion was identified in the South Platte River downstream of the regional wastewater facility.”
The South Platte River offered a chance to recapture the water that residents were using for washing, showering, and lawn watering. But relative to the mountain water that Aurora was used to, this source was of dubious quality. So, Aurora Water worked with technology providers to develop a series of treatment processes to bring it up to snuff. It retained CH2M in 2005 as the engineer to lead the project, broke ground in 2007, and brought the initiative, deemed “Prairie Waters,” online in 2010.
Through The System
Bringing together the worlds of natural cleansing methods and state-of-the-art technology, the Prairie Waters system delivers up to 12 MGD. It starts with riverbank filtration through 23 alluvial wells, which are spaced 50 to 100 feet from the South Platte River. It can take from seven to 10 days for water from the river to reach the wells, with biological constituents in the alluvium providing pretreatment.
The pretreatment is enhanced as the water is pumped through a series of football-field-sized basins, which contain more alluvial material. The water is pumped to the center of these basins and then out to their edges, taking another 20 or 30 days and removing more persistent substances.
After that, the water travels 34 miles through three pump stations to Aurora’s Peter D. Binney Water Purification Facility. There, the water travels over a series of concrete steps to precipitate out any manganese and iron. The water is then softened and injected with hydrogen peroxide, then passed through a series of high-intensity ultraviolet advanced oxidation generators, meant to destroy the cohesive bonds of any remaining contaminants.
Lastly, the water is passed through a biologically-activated carbon filter and blended with conventionally-treated mountain water. It’s a process that the utility believes to be effective against a particularly pervasive category of contaminant and at a relative bargain.
“This multibarrier process has been extremely effective in removing pharmaceuticals and personal care products,” said Baker. “As far as we know, this is the only water treatment system in the nation that was designed and built specifically to mitigate these contaminants. Prairie Waters cost $638 million, well below its projected $753 million proposed price tag.”
A Secure Supply
Because the system has been successful at removing contaminants, it has met Aurora’s goal of providing more drought security. The thinking is that with more access to water, there is more water available for reuse.
“Prairie Waters is resilient due to the fact that anytime you use water, you have water to reuse,” said Baker. “In a water-constrained area like Colorado, it will help meet our growth challenges. Aurora is projected to double our population from 360,000 today to over 740,000 in 2040. Full utilization of our current water supply will help meet that growth challenge.”
Though it is expensive to pump this alternative supply, it has already proved crucial to meeting local needs.
“We use Prairie Waters primarily in the summer to help meet higher demands,” Baker said. “We have also recently started using it during our low-demand seasons to supply water to neighboring communities that are dependent on nonrenewable deep aquifers. Called the ‘WISE Partnership,’ this is a cooperative arrangement between Aurora Water, Denver Water, and the South Metro Water Supply Authority to help these communities develop a sustainable and renewable supply.”
Overall, it’s a project that is leading an initiative Aurora would like to see more utilities around the country join.
“Potable reuse is being embraced by many communities as a sustainable and environmentally-friendly means of meeting water demand,” Baker said. “It’s really one of the most effective conservation efforts. Potable reuse provides very high-quality water that can be widely accepted by the community.”
Image credit: "Longs Peak," Ross Michaels, 2011, used under an Attribution 2.0 Generic license: https://creativecommons.org/licenses/by/2.0/