NO SMOKING!

by Mike Perricone

Fermilab's pond system uses evaporation for efficient cooling, and for a friendly site.

When founding Director Bob Wilson put his stamp on the original design and development of Fermilab, he wanted the site to be open to the sky, with only clouds altering the vista.

He ruled out the big, industrial-strength, plume-producing cooling towers that remain the norm for most industrial facilities, and he was aided by the scope of the 6,800-acre site. The natural open terrain made it possible to install the series of artificial ponds that contribute to the character and attractiveness of the Lab as a welcoming area for recreation.

After all, how many scientific or industrial facilities have a working cooling system that can also provide visitors with a day fishing?

"We have by far one of the most complex industrial pond systems anywhere. People who look at our set-up say they’ve never seen anything so integrated on this scale,” said Steve Krstulovich, whose engineering duties in the Lab’s Facilities Engineering Services Section involve overall responsibility for the system—and whose history includes the development in 1990 of the computerized water management program to keep that system working smoothly.

With supplementary cooling towers located only atop the Central Utility Building (and those essentially used only in summertime), the Lab’s complex system of interconnected ponds supplies the cooling water for the Wilson Hall high-rise, for the accelerators, for the detectors, for the outlying industrial buildings, and for the fire protection system.

"Cooling towers take a lot of maintenance,” Krstulovich said. "They create solid waste and disposal problems. Cooling towers would create huge plumes of vapor, and that’s all you would see around Fermilab. Instead, the ponds create a friendly environment that also serves the community with recreation, fishing, and an overall pleasant atmosphere.”

With their large surface areas, water volumes and flow rates, the ponds use the natural (and invisible) process of evaporation to shed the heat picked up from equipment throughout the site. Annual rainfall is insufficient to replace all the water lost through evaporation, and the deficit is made up by pumping in water from the nearby Fox River—about 250 million gallons of it each year, along with an incidental supply of fish eggs that helps keep the Fermilab ponds well stocked.

The catch is that the Lab can’t tap the Fox River in times of drought, when pumping would be most desirable. Under Illinois conservation standards, the Lab can only bring in water when the river’s natural flow exceeds 275 cubic feet per second.

The ponds act as reservoirs to keep a sufficient supply of water on the site. The system is designed to provide enough water to keep the site running for 83 days, based on a survey of weather conditions over the last 25 years.

Casey’s Pond, in the northeast corner of the site, is the oldest and one of the largest ponds, holding 36 million gallons of water. The adjacent Six-Acre Pond was recently dug to add another 12 million gallons to the site supply, and to pre-cool water recirculating back to Casey’s Pond.

Casey’s Pond is the heart of the Lab’s water supply, feeding the fire protection system and the three main cooling pond systems: the accelerator cooling system, the Central Utility Building system, and the Industrial Cooling Water system. In the earliest days of the Lab’s construction, Casey’s Pond originated as a "borrow pit” for earth needed around the site. The resulting hole was filled with water for a fire protection system, then was tapped for the ICW system and some additional cooling uses. When the Lab is operating full tilt, Casey’s Pond can pump out as much as 12,000 gallons per minute.

Lake Logo, in the middle of the Main Ring where the Tevatron is located, was another original pond, and the source of a stream that led off the eastern end of the site. Damming that stream produced the eastern ponds, Lake Law, AE Sea, named for the Atomic Energy Commission (AEC), and Dusaf Pond, named for the architectural and engineering firm that built Fermilab.

Water circulating through the CUB system undergoes the most thorough treatment with bromine solution to kill algae and bacteria. Since 1992, the site-wide system has been treated with annual flushes to clear out debris from the water lines to prevent blockages and to keep runoff water to offsite creeks within Illinois environmental standards. The Lab acts as a watershed for three offsite systems: Indian Creek to the west, Ferry Creek to the east, and Kress Creek to the north.

What appears to be a moat around the Main Ring is actually an interconnected series of 26 cascading ponds, containing a total of 39 million gallons of water. Each pond is about four feet deep, and keeps water flowing around the ring at about 1,000 gallons per minute during the hot weather. Water leaving the accelerator equipment generally enters a cooling pond with a temperature of around 94 degrees Fahrenheit, and leaves with a temperature around 87 degrees.

As part of the Lab’s management plan, measurements of a column of air in the sump at the Casey’s Pond pumping station link the pond level to possible emergency action at the Lab. The column is normally about 126 inches. If it drops to 90 inches, the Lab plans shutdowns to reduce the cooling load. At 75 inches, the plans begin to take effect. If the level reaches 12 inches, the Lab stops using the ponds for cooling, to conserve water for fire protection.

"That’s only happened once,” Krstulovich said, adding that the recent wave of 100-degree temperatures had no serious effect on the Lab’s water supply. "That would happen only with a prolonged drought over several months. We noticed pond temperatures going up somewhat, but all in all, the system was working very well.”