His gun locked and loaded, an employee of MP Industries wove his waythrough a maze-like ditch at the Patuxent Waste Water Treatment Plant.
When, at the signal from the platform high above, he fired a sustained burst of dry ice pellets, the fecal matter hit the man. And the woman. And everyone else standing on the platform.
A cloud of dust -- the freeze-dried remnants of fecal matter thata moment before had been glued to the side of the concrete ditch -- engulfed the platform. Eventually, a gentle breeze cleared the air, revealing a wall now clean and white.
Anne Arundel County Department of Utilities officials were showing off Tuesday a new technology being used to repair one of two oxidation ditches at the plant, which serves Crofton, Millersville and Odenton.
After discovering that the concrete had begun to corrode, the Utilities Department hired MP Industries to clean and paint the interior walls. The freeze drying -- the object of yesterday's show -- came no extra charge.
Richard Bowen, the project manager for Anne Arundel County, said officials decided to paint the ditch, where toxics and harmful nutrients are removed from waste water, after discovering that something in the treatmentprocess is eating away at the concrete.
Ordinarily, engineers would expect the concrete at the 4-year-old, $25 million plant to last about 30 years, he said.
But, "we noticed the concrete was startingto corrode and get soft," Bowen said. "We're investigating now as towhy."
In the meantime, Bowen hopes a coal-tar coating will protect and preserve the concrete.
Before the concrete can be painted, the walls must be scrubbed clean, Bowen said. Officials expected to have to water- or sandblast, which might further damage the concrete ordelay work as painting crews wait for the water to dry, he said.
But MP Industries, the low bidder for the project at $200,000, had a different idea: they proposed blasting the walls clean with dry ice pellets that evaporate on impact.
"The pellets, which look exactly like rabbit food, are pulverized," said Chris Rufolo, an inspector with Datanet Engineering, which is overseeing the MP Industries contract. "Basically, all you have left are freeze-dried contaminants falling to the floor."
If successful at Patuxent, the county will clean and paint the Broadneck Waste Water Treatment Plant this summer, Bowen said.