“Just because it is written doesn’t make it true in the field.”

So says David Montgomery, treatment services superintendent of the Plum Creek Water Purification Facility in Castle Rock, Colorado, reflecting on the new advanced treatment processes in operation at the town’s 6 mgd plant.

Adds Tim Lambert, water treatment supervisor and operator in responsible charge, “Sample, test, verify and repeat, particularly with advanced processes which require draw-down testing, flowmeter verification and chemical dosing confirmations.”

Montgomery, Lambert and the Plum Creek team are successfully operating the new facility, designed for future direct potable reuse, but now operating as an indirect reuse plant. “Our team contributed by helping to design, construct and start up the advanced process, while flawlessly operating the existing surface water treatment plant,” says Montgomery.

“All this work was completed during the pandemic. The team learned how to operate the new processes without any noticeable impact on our customers.”

Boom town

The original water system in Castle Rock, just south of Denver, was made up of several small package pressure filter facilities. In the early 1980s, the town built a series of plants designed to remove iron and manganese from the raw water, which was pulled from multiple wells scattered across the area.

With the town growing rapidly, the Ray Waterman Regional Water Treatment Facility was built in 2006, using manganese oxide-greensand for iron and manganese removal. In 2013, the town started up the Plum Creek plant, the first surface water treatment plant ever owned by the town. “It enabled us to use local renewable water as a water supply,” says Montgomery.

Then, in 2020, with the advanced processes online, the Burns & McDonnell-designed Plum Creek plant began treating a blend of deep groundwater, raw water from Plum Creek, and indirect reuse water. 

“The plant is now designed specifically to enhance water quality and treat for Contaminants of Emerging Concern,” says Lambert “We’ll be able to handle direct potable reuse in the near future once the State of Colorado sets regulatory standards.” 

Advanced treatment

In the advanced process, raw water from wells and surface water is pre-ozonated using Primozone ozone generators before combining in a 1-million-gallon raw water mixing and equalization basin. The water passes through aerators, and ferric chloride and potassium permanganate are injected before the flocculator/sedimentation plate settlers (Parkson Corporation). The rapid mixers are Lightnin.

Clarified water travels to biologically active carbon filters (Calgon Carbon Corporation), recently converted from conventional anthracite gravity filters. The filtered water collects in a pre-membrane feed well, before being pumped through four racks of Aria Microza microfiltration membrane filters (Pall Water).

The water is re-ozonated, hydrogen peroxide is added and the water passes through granular activated carbon filters (also Calgon Carbon Corporation). From there, the water is UV disinfected (Trojan Technologies) and injected with sodium hydroxide (caustic) for pH adjustment. Sodium hypochlorite (bleach) is added before the water enters the clear well.

Liquid ammonium sulfate is added for chloramination before the water flows to the distribution system. Watson-Marlowe pumps are used for chemical feed throughout. Plant PLCs run Allen Bradley ControlLogix (Rockwell Automation). The human-machine interface is PlantPAx and FactoryTalk (also Rockwell Automation). Cartegraph supplied the computerized maintenance management system.

Staffing up

Staffing has matched the increases in treatment complexity at Plum Creek. In 2013, the operations staff consisted of one supervisor and five operators who ran the plant only during daylight hours.

Now, in addition to Montgomery and Lambert, the staff includes John Ferguson and Kevin Moore, operator supervisors; treatment operators Andrew Dieter, Lanre Ajayi, Ed Allbright, John Whitesel, Matt Arpaio, Alpha Camara, Randy Mullins, Brent Pickrell, Kristen Reaves, Joe Compton and Courtney Stoddard. Crew members work two shifts seven days a week.

Bringing a new plant online without disrupting service is always difficult, and that was no less so at Plum Creek. The town was moving from a small daytime operation to a complex plant requiring many more operators.

Lambert says that setting clear treatment goals helped in the transition. So did calling on the Texas AWWA for operator training assistance, and running a pilot study to determine treatment performance of the new processes.

“In order to get the treatment staff on board and organized to operate the advanced processes, the engineering group came up with a list of treatment goals, which provided a framework for the operators to follow,” says Montgomery. The goals listed water quality action levels for the raw water at each treatment step and for the finished water. The goals set standards that exceeded Colorado regulatory requirements.

Controlling TOC

Those goals surely helped as operators faced significant increases in TOC brought by accelerated pumping of raw water from Plum Creek. Precise TOC measurements are critical to helping operators understand changes in water quality and make informed decisions about TOC-related processes, Lambert says.

“At first our operators used a spectrophotometer for TOC analysis, but that was not ideal,” says Lambert. “It required a lot of prep work to set up the instrument with reagents. Samples needed to incubate for several hours before testing, and the entire process took over four hours to get a reading.”

Eventually the staff purchased a TOC analyzer (SUEZ), which provides real-time sample analysis. It includes a 63-vial auto-sampler, along with pre-cleaned and pre-tested sample vials. “Plant operators simply place a sample vial into the analyzer and results returned with 15 minutes,” Lambert says.

The operations staff made a number of other changes on their own. “The plant operates best using mid to high flows,” says Lambert. “Low-demand winter flows can be challenging. The staff developed a process flow calculator based on water quality, which helps to fine tune treatment based the raw water quality parameters. The calculator provides data that steers the staff to blend surface and groundwater to achieve the best ratio for water quality.”

At the intake

The staff also came up with ways to improve operations at the Plum Creek diversion pump station intake structure. “It was being overtaken by huge sand loads traveling down the creek bed,” Lambert says. “The staff designed and built new stop-logs that held back the sand and debris but allowed the water filter through screens.” The change has improved water quality and eased maintenance requirements.  

In another change for the better, the staff also purchased an excavator to dredge the creek directly in front of the intake structure, greatly improving the quality of water entering the raw water pump station.

The Plum Creek team also made major process adjustments to manage high total dissolved solids in the surface water, primarily inorganic salts and small amounts of organic matter. TDS can cause discolored water, hardness deposits on fixtures, and a salty taste. Staff members also had to fight through processing high levels of manganese that was binding the new GAC filters after overfeeding of peroxide and ozone.

But the biggest challenge has been keeping up with growth. “The team has managed to keep the wells repaired, drilled new wells, rehabilitated the treatment plants, started up the new surface water plant, and have kept growing, right along with the town,” says Montgomery.

“We’ve maximized the development of a renewable water supply, and we’ve passed the last three sanitary surveys with no deficiencies.”

Changing from daytime to around-the-clock operations has also been challenging, especially with increased staffing: “We restructured the staff working hours and hired additional staff. We try to have two operators on shift at all times, with one experienced operator and a less experienced operator on each shift for safety and training.”

People matter

While the technical successes at Plum Creek are noteworthy, Montgomery, Lambert and rest of plant management are proudest of achievements on the people side. Montgomery emphasizes “the trust and friendships that have been developed over the years with fellow operators are vital and the reason for our success.”

Safety is paramount. “We’ve not had a major injury over last 20 years,” says Lambert. “Considering the hazards the staff faces each day, like bulk chemical handling, working in ice and snow, in confined spaces, on slippery surfaces, around water, and automated electrically driven machinery, safety of our staff is the biggest achievement. The machines can easily be replaced, but well trained and dedicated professionals are hard to find and essential to keep.”