A Montgomery County judge ruled yesterday that prosecutors did not have enough evidence to convict a Rockville man and his concrete company of discharging polluted water into a tributary of Rock Creek.

After a four-day non-jury trial, Montgomery Circuit Court Judge Vincent E. Ferretti Jr. said he was not convinced beyond a reasonable doubt--the standard for a criminal conviction--that George E. Gregg, 68, or his company, Montgomery Concrete Inc., knowingly polluted the state waters.

Gregg faced up to one year in jail and a $25,000 fine on each of five counts after he and his Southlawn Lane company were charged with polluting state waters on four days in January and failing to report that his company had discharged contaminated water. The case is believed to be the first in which someone has been prosecuted on criminal charges in Montgomery County in connection with the alleged pollution of state waters.

Ferretti ruled that he did not hear any evidence that Gregg's concrete plant was operating on the days when county investigators said they found polluted water running from beneath a wall behind his property. The judge said he also was not convinced that any of the company's trucks dumped pollutants into a water-filled pit that investigators said could have leaked into the ground water.

"How do you show it's the operation of the plant that caused the pollution?" Ferretti said.

Assistant Montgomery State's Attorney Tom Eldridge argued that the contaminated water, which an expert testified came from concrete operations, couldn't have flowed from anywhere but the plant. The PH-level of the runoff water, Eldridge said, was "100 times stronger than Liquid Plumber."

"The circumstantial evidence is overwhelming that this pollution resulted from the activities at that plant," Eldridge said.

But Gregg's lawyer, Peter Davis, argued that there was no evidence that the water-filled pit on Gregg's property leaked. It was "pure speculation," Davis said, that the contaminated water came from the concrete plant rather than from rainwater running off other property in the industrial area.

"They were never able to trace the source of the water to any conduct on the part of the plant," Davis said.

David Weaver, a spokesman for Montgomery Executive Douglas M. Duncan (D), said county officials are still considering levying fines against Gregg and his company.

Ellen Scavia, a supervisor in the county's Department of Environmental Protection, said criminal charges are reserved for "recalcitrant" polluters who ignore notices of violation.

Gregg received two notices of violation from the county and was told by state investigators that his pit probably was leaking, but he did nothing about the situation, Eldridge said.