When the City of Ames (Iowa) and its engineering partner were designing a new lime softening water plant, there was no doubt it would be a major step-up in sustainability.

The old plant, operating since 1924, had been expanded many times to increase its capacity from 2 to 12 mgd. The new plant would have 15 mgd capacity and would include more efficient lighting and indoor temperature controls, better water efficiency, better training facilities, better on-site stormwater management and more.

Just before the start of design in 2012, the Iowa Department of Natural Resources made grant money available if the plant could qualify for Leadership in Energy and Environmental Design certification from the U.S. Green Building Council.

At the time, there were no LEED-certified water plants in Iowa; the grant could be worth $6.5 million, nearly 10% of the $70 million project. Ames officials and consultants at FOX Engineering decided to apply for the grant, raising the bar for sustainability improvements.

“A lot of the elements of LEED certification were the sorts of design criteria we normally would have incorporated in managing stormwater and things like that,” says John Dunn, director of Ames Water & Pollution Control. “But there were some credits we went after that did require us to make some design changes.”

The plant opened in 2017; and in March of 2019, the city learned it had been LEED-certified, achieving 43 points — three more than the minimum. It received the grant in the form of forgiveness against a loan from the state revolving loan fund.

Keeping it cool

Among changes in the plans prompted by LEED were a white membrane for the roof instead of a black rubber membrane, and an additive to make the concrete parking lot a brighter white instead of gray. Both changes help reduce the heat-island effect, the warming of urban areas compared to the surrounding areas. The U.S. EPA says heat islands can increase peak energy demand in summer and raise air conditioning costs.

The planners also looked at using source water for heating and cooling. “We’ve got 55-degree-F water coming through the plant every hour of every day,” Dunn says. “As part of our HVAC system, we installed essentially a geothermal well heat exchanger, so we could get some free heating and cooling from the groundwater we were paying to pump into the facility.”

The LEED application also affected stormwater management, according to Lance Aldrich, a FOX engineer and project manager for the plant design. Some retaining ponds required by the city code were redesigned to be rapid-infiltration ponds.

“That is a unique thing we normally wouldn’t do,” Aldrich says. “The water is held with the idea that you percolate it down, so it doesn’t run off. You dig a little deeper and replace that soil with a sand and soil mix, and you have plantings in it. It lets the water percolate in a lot faster.”

Under the river

The new plant is almost next to the old one, but it is on the other side of the Skunk River. That created an engineering challenge because waterlines had to go under the river so that the wells drawing water from underground could still be used. The storage infrastructure, high-service pumping and water mains were near the old plant, so the finished water also had to be delivered back across the river to take advantage of the existing facilities.

Because the city had experienced a broken waterline during a flood in 2010, Ames officials were worried about burying the waterlines under the river. “That was a big concern,” Aldrich says. “They wanted to make sure that what we did would be good for a long time, so we went deep. We went way underneath the river using directional drilling.”

Four waterlines were bored under the river: a raw waterline and a finished waterline at the north end of the property and a raw waterline and a finished waterline at the south end.

“The city wanted to separate them by quite a distance, in case something unexpected would happen with the river,” Aldrich says.

Moving lime sludge

The new plant, like the old one, uses lime in the softening process. The ponds for storing lime sludge are next to the old plant, so the sludge has to be pumped back across the river. That presented another problem. “The sludge doesn’t act like water,” Aldrich says. “It can get thick. It can be like toothpaste. We spent a lot of time researching the best way to do that.”

The sludge-moving system was designed to maximize flexibility for the staff. “We put in two pipes under the river, all the way from the plant to the lime ponds,” Aldrich says. “They were set up so they could pump down one of the lines or the other or both at the same time. The pumps have very big motors with variable-speed drives. They can pump at different flow rates by varying the speed of the pumps and whether they use one or both lines.”

Another issue presented by moving the sludge a long distance is that lime tends to deposit on the sides of the pipe. To counteract that, the system is designed to allow flushing of the pipes with water.  

Better work environment

The new plant, on the site of a former U.S. Department of Agriculture property where hogs were raised for research, is a big improvement in terms of working environment, Dunn says. Six people on the Water & Pollution Control administration staff work in the building along with 13 who work in the treatment plant.

“We have a pretty sophisticated lighting control system,” Dunn says. “It’s motion activated. The HVAC system has a sophisticated control scheme. In the old plant, a lot of people used to have space heaters. We don’t have to deal with that anymore. We’ve got good comfort levels.”

The new plant is also more efficient, although it takes more energy to run than the old one because it is bigger. “We’re able to run a much larger facility without having to increase staffing levels,” Dunn says. “That’s because of the automation built into the plant.”

The new plant is designed to be expandable from 15 to 20 mgd and again to 25 mgd, all within the initial footprint. “This was built with the expectation that it would have a 100-year life,” Dunn says. “It will serve four to five generations of Ames residents.”

The Ames plant is not the only LEED-certified water plant in Iowa. There now are smaller LEED-certified plants in Humboldt and Shenandoah, also designed by FOX.