While arguments centered on the clamor from off-loading barges, the larger debate played out over environmental-vs.-development considerations that could determine the fate of Dutra Materials' proposal.
Both sides were out in force.
Petaluma residents who said the plant will harm wildlife and air quality in addition to people's ears carried signs and wore stickers urging the commission to reject the proposal.
Heidi Rhymes, a member of the opposition group Moms for Clean Air, said the difference was huge between the county noise limit and what the plant will produce. She said the county shouldn't bend its rules for the plant.
"You can't fit a circle into a square," Rhymes said. "If it doesn't fit, it doesn't fit."
Asphalt plant backers, including developers and organized labor representatives from as far as San Francisco, wore their own stickers.
Cynthia Murray, president of the North Bay Leadership Council, said the county needs the jobs and inexpensive road material promised by the plant.
"This is something that will definitely improve the community," said Murray, a former Marin County supervisor who now lives in Petaluma.
After hearing from about 45 speakers -- both pro and con -- planning commissioners postponed a decison until May 21.
At that time, they will make a recommendation to the Board of Supervisors on whether to amend the county's noise limit.
All plant operations are within noise specifications or have been modified to meet standards except barge off-loading, which on the average would emit sound comparable to ordinary conversation. At its peak, it would put out an average of about 67 decibels.
Although the county is requiring Dutra to build soundwalls along a portion of the plant, enclose a burner and attach noise deadening blankets to a rock crusher, there is no practical way to avoid the din of off-loading barges, planner Steve Padovan said.
He's recommending relaxing the county standard, which the barges could exceed by about 14 decibels.
"We tried to reduce it but there's no way to get within the tables," Padovan said.
Supervisors, who took a 4-1 straw vote in favor of the project in February, will make a final decision in June. The date for that meeting has not been set.
Dutra is seeking a new use permit for its asphalt production plant, which would be relocated from a spot in use until several years ago on the river.
The company has said the plant would provide a consistent source of material for road and building construction and would help disperse aggregate production away from Forestville's two rock quarries.
But many residents, including the Petaluma City Council, say it's not a good fit for the area. Fumes and noise would outweigh benefits, they said.
Critics told county planning commissioners the noise from rock being unloaded from barges would drive off wildlife and tourists at Shollenberger Park, about 150 feet across the river.
But plant supporters said the noise would pale in comparison to the roar of traffic from nearby Highway 101, which they said doesn't seem to faze birds or deer.
Petaluma retiree and park regular Monty Chipman, who spoke in favor of the plant, said animals now seem to stick around despite the drone of power boats and the rumble from an existing gravel plant.