As Castle Rock, Colo., progresses toward its goal of 100% renewable water by 2065, the Plum Creek Water Purification Facility (PCWPF) is undergoing a $68-million expansion to double the processing capacity from 6 million gallons per day (MGD) to 12 MGD. Not for nothing, this expansion plan includes some of the most advanced, PFAS-targeting treatment tech in the country.
Like other communities, Castle Rock has been faced with important questions about its own water supply.
Historically, the town’s only water source was deep aquifers. However, an increasing awareness that these aquifers are a nonrenewable source, coupled with droughts and a growing population that has drastically increased demand, led to the development of a comprehensive plan released in 2006 to ensure a more sustainable future.
Photo: Emily Howard“One thing that we know is the deep groundwater that most of the Front Range is using is not renewable. Eventually, all those straws that are in the ground are going to dry them up. So a lot of communities are starting to move,” says Roy Gallea, engineering manager.
A big part of this plan has included transitioning from strictly groundwater use to a multisource approach using renewable sources like surface water, reused water, and alluvial wells, reserving the aquifers for times of severe drought.
“We had alluvial wells that we could tap into, but the water quality was closer to surface water. They identified early in Castle Rock that if we wanted to use our alluvial wells, that we would have to treat for surface water,” says Tim Lambert, plant superintendent.
Even though a shift of this magnitude required planning and additional costs, the droughts affecting Colorado in the early 2000s were influential in gaining strong support for the transition from officials and residents alike. It became widely understood that investing in long-term sustainability was necessary.
This investment in infrastructure, combined with sourcing new renewable water and local conservation efforts, will greatly improve the water availability for generations. The transition is long and expensive and requires some of the most inquisitive and creative minds to carefully plan and execute each step toward success.
Building the infrastructure
Today, the PCWPF is bustling with innovation and activity. It has broken ground on a new building that will mimic the current pretreatment facility, including a floc basin, sedimentation, and Biological Activate Carbon (BAC) filtration.
Mitch Horner, a water treatment operator, sits in the PCWPF control room keeping a watchful eye not only on the processes at this facility but on all the different sources supplying water to the growing town.
These sources have been growing since the construction of the facility in 2013, which was the first surface water treatment plant serving Castle Rock.
“With the ability to treat a renewable water source that we could take off East Plum Creek, we could just keep moving from there,” says Walt Schwartz, project manager.
The facility’s original pretreatment area had rapid mix flocculation, sedimentation, and green sand filters. The water then flows into membrane filtration racks. “That’s micro-filtration. Each of the 4,000 straws is 1 ten-thousandth of a millimeter worth of filtrate that’s getting rid of all those pathogens and microorganisms. That really cuts down on our Total Organic Carbon (TOC) count, which then lowers the disinfection byproducts we add,” says Horner.
Photo: Emily HowardIn 2022, advanced treatment processes were added. A raw water blending tank was introduced so different sources of supply from surface water, reused water, and alluvial wells could be blended before entering pretreatment.
“Green sand filters were converted to BAC filters, which we pump in through a PALL membrane system. Then it goes into the advanced treatment building, which has oxidation with ozone and hydrogen peroxide followed by granular activated carbon (GAC) and then ultraviolet disinfection,” says Schwartz. “Finally, we have a high-service pump station where we disinfect with sodium hypochlorite and add ammonia chloramines for our disinfectant residual distribution system.”
In preparation for the full-scale project, Castle Rock conducted a pilot project to evaluate the best advanced treatment processes that would allow them to create high-quality drinking water from wastewater. As a result, when that advanced water purification facility came online, it was one of the most advanced in the country, meeting regulations that hadn’t been written and addressing problems before they arose.
“When you look at the design these guys have brought forward, we not only meet regulatory requirements, we exceed them,” says Tim Lambert, plant superintendent. “Speaking as an operator, it definitely makes our life much easier. We have so many tools.”
One of the many tools added was the GAC filters. These massive cylinders have activated carbon that absorbs a range of organic contaminants. “The plant was specifically designed to be able to treat water for direct potable reuse (DPR), and GAC was a critical process for this capability,” says Sandra Sandman, Castle Rock Water’s Customer Relations Program Manager.
But the GAC filters were not only helpful in meeting DPR standards, they helped filter out Chemicals of Emerging Concern (CECs) such as pharmaceuticals and PFAS.
“When you look at the PCWPF, I have a conventional treatment system for my raw water that we feed into the membranes that then goes into advanced treatment through the GAC. When PFAS started to be a big issue, they [had] already designed the GAC filters that are knocking out the PFAS. If you look at the treatment train, I mean, it is comprehensive,” says Lambert.
Today the plant is designed to exceed the standards for direct potable reuse (DPR), though they are still doing indirect potable reuse. “We’ll see where we end up going with that. DPR would allow us to use more of our water rights because we wouldn’t lose any water to evaporation or transpiration, but it would come with increased testing and regulations,” says Gallea.
Expanding what’s working
The advanced purification and technological systems already in place are a badge of honor for Castle Rock Water, so this expansion, which will double its capacity, is proof that the plan created in 2006 and in execution for nearly 20 years is working as expected.
It also means that they have been successful in securing more renewable water to process.
Beginning in 2024, the expansion project is adding two additional buildings: one that will mirror the pretreatment area and one that will house 10 new GAC tanks.
Photo: Emily HowardTwo of the current buildings have enough space to expand most of the advanced treatment equipment within the existing footprint. Additional membrane system racks have already been added on an as-needed basis and three more will be added as part of the expansion. A new generator that can power the larger operation in an emergency also will be added.
The expansion is scheduled for completion in 2028.
“It’s going to give this man here [Mitch] more tools in his belt and another 6 million gallons he can push. We can rest wells if we’ve got water available in our reservoirs,” says Lambert.
Water users won’t notice a thing
Impeccable planning and preparation prior to this expansion ensured that the facility can sustain construction outages without any water interruption to the town.
Construction will only happen during the winter months, which require only one-quarter of the daily usage of the summer months. This allows more opportunities to draw from the vast sources they’ve been securing.
From the beginning, finding new sources of water that will run through the growing PCWPF have been a big piece of this puzzle
“Castle Rock Water had to develop existing water rights, plan for reuse of all reusable water supplies, purchase new water rights, and develop regional partnerships,” says Sandman.
Water Infrastructure and Supply Efficiency (WISE) is a critical component in bringing additional renewable water supply to Castle Rock—and many other areas. Under this partnership, South Metro water providers use shared infrastructure to enable the supply, offering economies of scale, and reducing the overall cost to customers.
“We’re heading further north and further east, following the river to find new sources of water rights that we can acquire. Then the problem is how we get it back to town,” says Gallea. “It’s a regional issue, so the WISE partnership has quite a few different municipalities that have pitched in.”
It takes a village
Meeting the 100% renewable goal will take more than simply being able to supply more water. Conservation is an important component of this plan, especially as the population grows with people who may not be used to the flora and fauna native to an arid, high-altitude environment.
Landscape choices are important in Colorado, as they have a huge impact on water usage. In fact, in Castle Rock, the water usage quadruples during the summer months mostly to accommodate lawns and landscapes.
“The biggest thing is lawns. Some grasses are native to Colorado, but Kentucky bluegrass and some of the other turfs that are out there were imported from other climates. It’s that American dream that everybody’s been sold on: You need to have that lush green grass. Some of the battle is trying to get the public to change their mindset and perspective,” says Gallea. “So many of the Colorado species are very beautiful and we are trying to get people to recognize that.”
Because of this, Castle Rock has put a ton of effort into eliminating water-loving landscapes and promoting a more water-wise approach.
“We did an ordinance back in 2023 trying to limit the amount of turf that new builds were putting in for single-family homes. We have eliminated turf in the front yard and limited turf in the back yard to 500 square feet,” says Sandra Sandman, Castle Rock’s Customer Relations Program manager.
ColoradoScape promotes water-wise landscaping. The program works to educate and inspire the community regarding native plants and drought-tolerant species. The town has even created a rebate program to help with the cost of transitioning to water-wise landscaping.
“A big project that we have right now is a turf removal rebate. It’s $3.25 per square foot that you remove and replace with ColoradoScape,” says Sandman. “We’ve had a phenomenal response. Those types of programs have really been monumental in moving that daily gallon per capita down.”
Castle Rock Water is currently running at 112-114 gallons of water per day per capita, and the goal is to get it down to 100.
As Castle Rock Water forges into the future, it stands as an excellent example of how innovative, forward-looking solutions can transform local water systems, creating a better outlook for generations to come.
