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New Source of Dilution Waters?
When Cargill's former North Bay salt ponds became part of the Napa-Sonoma Marshes Wildlife Area, state wildlife managers and environmentalists were thrilled: this would be the largest wetlands restoration project in the state. But Cal Fish & Game, low on funds to restore the ponds, is in a dilemma over how to dilute the saltiest 700 acres - especially 300 acres of bittern - without negatively impacting the Napa River or the Bay. The Sonoma County Water Agency thinks it has an answer, one that could also help it meet its goal of zero summer discharge into the Bay and offer agricultural users a more environmentally responsible water supply than their current instream diversions. The water agency has proposed building a pipeline to link its treatment plant with at least one other North Bay water agency (Petaluma or Napa) - and preferably both - to deliver reclaimed water to the wildlife area, which is less than a mile from its own facilities.
The maximum amount of water that two agencies could deliver would be around 6,700 acre-feet per year, says Sonoma's Sean White. With that amount of water, restoration, and dilution of the bittern, could take between 10 and 13 years, since the diluted water would have to be released into the Napa River gradually to match the river's background salinity levels and avoid harming aquatic species. "You've got to remember that these bittern ponds are the industrial by-products of 50 years of salt harvesting," says White. "They're the most concentrated of the salt concentrate." By adding reclaimed water from a third water agency, the process could be shortened by at least a few years, says White.
When and how to discharge the diluted pond water are also questions. Under current regulations, summertime discharges are not allowed, but it would be easier to match background salinities then, when the river is saltier. Assuming that regulatory hurdles could be overcome, the diluted bittern would not simply be discharged all at once, says White, but probably through some type of continuous process incorporating a pipeline feeding reclaimed water to the site, a blending mechanism, and a real-time monitoring device to ensure a match with background salinities. The last hurdle would be cost. To build the infrastructure needed to deliver the water and link the three plants would require close to $20 million, says White. The agency is investigating possible sources of funding, including CALFED.
While enthusiastic about using reclaimed water, Fish & Game's Jim Swanson says there are many possible mechanisms for restoring the ponds, including first mixing the bittern with the "pickle" (slightly less salty) ponds and then adding that water to progressively less salty ponds. Even using reclaimed water, they will probably still need to use some river water too, he says. Swanson is concerned about nutrient loads in Sonoma's secondary-treated water, since nutrient loads in some of the ponds are already high. Upgrading the water agency's facilities to tertiary treatment would add to the overall cost but might be necessary, he says.
Swanson was also concerned at first that Fish & Game would be required to accept deliveries of reclaimed water for longer than needed. But he says the water agency's idea of delivering large volumes of reclaimed water for the first few years and then tapering off and selling more water to ag users makes sense.
Meanwhile, the Army Corps is studying the Sonoma water agency's reclaimed water proposal as one alternative for overall ecosystem restoration of the wildlife area's 7,000 acres of ponds. Swanson is hopeful that restoration, and neutralization of the bittern, can begin within the next few years, despite the Army Corps' notorious lack of speed. The ponds were acquired six years ago but only one has since been restored.
Restoration will most likely begin on ponds other than the bittern. Swanson hopes the refuge will benefit from more input from the various agencies examining the issues. "It'll probably take a little longer this way, but we'll end up with a better project than we could do on our own."
Contacts: Sean White (707)547-1908; Jim Swanson (707)944-5528
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