Walls of Steel

Fisher Tank Co.

3131 W. Fourth St. * Chester, PA 19013

Phone 610/494-7200

www.fishertank.com

DSM Chemicals North America, Inc., had to make a decision fast. The company was about to open a new facility to recycle caprolactum from used carpeting when management realized their 10-year-old wastewater treatment plant could not handle the additional wastewater generated by the recycling operation.

"We needed to increase our treatment capacity very fast because we didn't want to block the recycling operation," said Reese Bridges, maintenance manager for Augusta Service Co., DSM's service organization.

One option was to erect another storage tank. Not only was the cost a deterrent, time was running out. A second option was to reactivate a 1.5-acre onsite lagoon, which had been formerly used for wastewater treatment.

The good news--it was big enough to do the job--260 ft diameter, 14 ft deep and a capacity of 10 million gallons. Moreover, all the ancillary pumps, piping and processing equipment was already there.

The bad news--the walls and bottom, lined with one-inch thick gunnite over a polyethylene liner had weakened. This was why the company, rather than risk a leak, had taken the lagoon out of service years earlier.

"We figured it would be much more cost-effective, saving perhaps as much as $1 million, to use the existing impoundment rather than build a new tank above ground," said Bridges.

To help them make a decision, DSM sought the opinion of the Fisher Tank Co., a builder of above ground steel storage tanks.

Management decided if the lagoon alternative were feasible, they insisted the walls and bottom of the earthen impoundment be covered with a leak-proof steel lining.

Steel belly

Contract Engineer Ron Liljegren and Operations Manager Jack Whiting journeyed from Fisher Tank to the site to size up the project. They worked out a budgetary price and, by the end of the week, Fisher Tank got the go-ahead to proceed on the $500,000 project.

Within days, FTC's Liljegren, who served as project supervisor, mobilized two, 10-man crews under foreman Tom Limperous. Working in two, 10-hour shifts, Fisher Tank personnel began lowering the 8 ¥ 20-ft carbon steel plates into the excavation and positioning them against the embankment walls. Because specs called for a liner that was 100% steel to guard against any possible leakage, Fisher Tank employed only continuous welding along the seams and vacuum.

The underlying gunnite, with its polyliner, remained in place, functioning as a secondary containment system in compliance with environmental regulations. In the unlikely event of a leak, the secondary system would drain the water through the bottom. For back-up protection, the entire liner was coated with an anti-corrosion epoxy.

"They met all expectations and validated our decision to use the old impoundment," Bridges said. "We haven't had any leaks at all and no liner problems."

With the steel-lined lagoon online, DSM almost doubled its treatment capacity.

Converting the impoundment increased the capacity by 4.5 million gallons, bringing the total at the site to more than 10 million gallons. The new facility, like the other two tanks, handles about 850,000 gallons of water each day.

The wastewater has a residence time of only one day throughout the plant before it is discharged it into a river, absolutely clean.