The town had advertised the meeting via a postcard mailed to all town addresses, but many at the meeting said they did not receive it.
The town has been talking about the project for more than a year, since it was offered $13.6 million through the California Department of Transportation (Caltrans) to build the underground facility.
Caltrans is being required by the state water board to reduce the amount of pollutants in runoff water near its roadways, so it has offered to pay for a number of such facilities throughout the state.
But speakers said that the town's timeline, which requires a council decision by June, is too short.
A resident of nearby Maple Avenue said the town has "a lot of outreach that has to be done before they make a decision."
"This seems like that's an awful short time to do this," he said, adding that the park was given to be used for recreational purposes.
"I think we should use it for what it was meant to be, which is recreational purposes," he said to general applause.
Atherton and other local entities have similar mandates from the regional water board.
Initial plans to put the structure under playing fields at Las Lomitas Elementary School fell apart after the City Council said it couldn't accept the district's terms, especially one asking the town to agree not to back out of the project once it was started.
Council members said they want the option to back out of the project once the design is far enough along that they can estimate what the annual maintenance costs will be, as the Caltrans agreement allows. The school district said it couldn't allow that because of its construction schedule.
Caltrans allowed the town to move the project site to Holbrook-Palmer Park, which had been identified in a drainage master plan as one of three possible locations for a storm water detention basin. The other locations were the Las Lomitas School campus and the privately owned Menlo Circus Club.
The drainage master plan envisions large, slightly depressed grassy areas where water could be diverted in flood conditions. The facility Caltrans has offered to pay for is much more elaborate, diverting and possibly storing the water deep underground, and would require much less above-ground land area.
Threat of lawsuits
More than one speaker said the town could face lawsuits if the project is approved in the park. "I think there's a high likelihood of lawsuits opposing this," said one neighbor. "This is going to be a very high-profile project in a very central part of town."
Others suggested alternative sites such as under the new civic center or under the playing fields at Menlo College.
City Council member Rick DeGolia, who is the liaison to the Park and Recreation Committee, said the project is still a long way from being approved. "We're looking at it. We haven't made any commitment to doing this," he said. Only after looking at "what all the potential impacts are, what all the potential benefits are" will a decision be made, he said.
The council does need to make a decision by June in order to continue the agreement with Caltrans.
Six feet under
Engineers at the March 7 meeting described the facility as an underground concrete structure about 11 feet deep, buried under 6 feet of soil, that could hold about 9 acre-feet of water. The drainage plan indicated that a holding area for 10 acre-feet of water would help the town avoid the size of flood predicted to occur once every 10 years.
Consultants at the meeting said the ability to divert that much water could protect from flooding both downstream and upstream from the park, and also in Redwood City, where the Atherton Channel ends up.
A rubber dam would divert water and debris to the underground facility after suspended debris was removed. The collected debris would be trucked off about four times a year, the consultants said.
While the engineering is still in preliminary stages, representatives of Tetra Tech, an international engineering firm that has designed a similar facility in Southern California, said they are looking at three possible park locations under grass fields and a parking lot. The construction would probably require a new bridge into the park, which could also be used by fire trucks, the consultants said.
Almost the entire facility would be underground, unless the town decides it wants to be able to use the collected water for spray irrigation. That would require treatment tanks, which would probably be placed in the corporation yard where park equipment is stored.
Cap on costs
The consultants also said that the project will not be built if it costs more than the amount Caltrans has agreed to pay. The town is responsible for the annual maintenance costs, which won't be known until the design is further refined.
Matt Fabry from San Mateo County's City/County Association of Government's storm water pollution prevention program said pollutants at the levels that would be collected by the system would not be considered toxic waste. "The levels of mercury and PCBs (polychlorinated biphenyls) ... that are going to be coming into any project in the park are going to be low levels," he said.
City Manager George Rodericks confirmed that in a similar Southern California project the town examined, the waste products from the facility go into a regular landfill and do not require any special treatment.
If the project is approved by the City Council, which is expected to vote on it by June, construction is scheduled to start in July 2019 and take 20 months to complete.
This timeline, which overlaps the town's construction of a new civic center, also raised some opposition. "Are you going to consider the impact on the people, the organizations," that use the park? one speaker asked. "We're going to be in a terrible situation with (the disruptions from) the new town center," he said. "Our only refuge is this park."
A consultant said the town would receive a number of benefits in addition to the flood control the project would provide. When the project is completed a new irrigation system, sod and pathways would be installed and, if the council approves, a new source of irrigation water would be available.
At is.gd/HP_water find the meeting presentation and other information about the project on the town's website.
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