"This is a commitment point (on the project)," Marty Hanneman, the town's project manager for the facility, told the council.
Council members asked for at least one more month to make their decision.
While council members said they still like the idea of sending cleaner water to the Bay, they are being pressured by local residents who say they fear the project would damage the park and question whether Atherton's runoff water is really that dirty to start with. Residents also questioned how much flood protection the project would offer.
Chad Helmle of Tetra Tech, the consultants designing the project, told the council the proposed facility would have prevented Atherton's worst flooding downstream of the park in the past 15 years: the 2014 over-topping of the Atherton Channel on Marsh Road.
But Atherton officials said they think only about a dozen homes, at most, were affected by that event.
"This project to me is so worrisome on so many levels," said Julie Quinlan of Maple Avenue, mentioning possible problems with the underground structure in an earthquake, costs to the town at the end of the facility's life, and the impacts of construction going on while the civic center is being built and Caltrain is electrifying its train service.
"I believe the downsides by far outweigh the benefits," Quinlan said.
Atherton resident and former Park and Recreation Committee member Sandy Crittenden said he thinks the annual operating costs, estimated by the consultants as $72,621 a year, would be much higher. The underground water storage vaults would be a breeding ground for mosquitoes, he said.
"Do we want our children to play in a park like this?" he asked.
Laurie Thomas, who lives in the nearby Menlo Park neighborhood of Felton Gables, said she worried about numerous potential dangers from the facility. "I don't know that we can guarantee that some child isn't going to find his way in through a manhole cover," she said.
Council members, who often meet in a nearly empty room, have had residents turn out by the dozens for at least three meetings on the project and also have been flooded with emails and phone calls.
"Why has no one supported this project?" asked council member Rick DeGolia. "No one has come to us and pounded the table for why this is an important project."
Council member Bill Widmer asked to have all possible locations for the facility researched. "It would be nice if we could understand that we have (eliminated) every location other than the park," he said.
"I haven't been convinced that we need it," said council member Elizabeth Lewis. "I think more public outreach and more education needs to be conducted."
But Mayor Cary Wiest reminded everyone about why the town is looking at the project in the first place: the $13.6 million in funding from Caltrans, which is building a number of such facilities around the state to meet its obligations to clean up water that flows from roadways it controls.
"There's 13 million reasons to look at this project," Wiest said. But he questioned whether Atherton was contributing the toxins that need to be cleaned out of the water.
"We want to make the right decision, the informed decision," Wiest said.
In the end, the council voted to continue the discussion to its May 16 meeting, have the Park and Recreation Commission provide a recommendation, and get more information about alternative locations and the amount of toxins in Atherton runoff water.
One of the consultants at the meeting, Richard Watson of Watson and Associates, said the town may be able to retain the Caltrans funding if it only removes trash and particles from the runoff water without filtering for toxins such as mercury and PCBs.
Speakers have expressed major concerns about concentrating such toxins in a facility in the park, although the consultants have said that anything filtered from the water would be considered ordinary trash, not toxic waste.
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