Pond 7 of the old Cargill Salt Co. plant between Napa and Sonoma is an improbable sight: a lifeless salt flat spreading across more than 300 acres along the edge of the San Pablo Bay.
The surface is a twisted mass of filthy salt crystals, devoid of plants and avoided by the migratory birds that inhabit nearby marshes.
As long as the pond remains in this state, officials say, it poses a threat to the ecologically sensitive bay: should a rain storm flood the pond and breach the dirt banks, it could wash salt into the open water in concentrations high enough to kill fish and other wildlife.
But finally, two decades after the salt pond was abandoned, there is hope for safely returning it to productive use.
The Sonoma County Water Agency is in the final days of building a $10 million, 3.4-mile pipeline to bring recycled water from the nearby Sonoma Valley sewage treatment plant to the former salt plant, now owned by the state and known as the Napa-Sonoma Salt Marsh.
The agency plans to hold a ceremony Friday to mark the completion of the pipeline, including elected officials and representatives from the local, state, and federal agencies involved in the long-term salt marsh restoration effort.
By this fall, the agency hopes to use the water to help dilute the excessively salty water in a nearby pond, known as Pond 7a. By sometime next year, depending on when the Army Corps of Engineers can complete a separate portion of the project, the agency plans to use the water to dilute the salt pan in Pond 7, releasing it little by little into the bay in safe doses.
The restoration project may take as long as 10 years because of the need to dilute and discharge the salt residue, known as "bittern," slowly and carefully.
The project to restore Pond 7 and several other parts of the old salt plant has been in the making more than 15 years. It has involved a variety of agencies, including the state Department of Fish and Wildlife, which owns the land; the Army Corps of Engineers, which is doing much of the infrastructure work; and the state Coastal Conservancy and federal Bureau of Reclamation, which are providing money and technical expertise.
"We underestimated how long it would take to do this and how many agencies, how many partners" it would require, said Grant Davis, general manager of the water agency, as he stood last week at the end of the recycled water pipeline, next to Pond 7.
About $7.5 million of the pipeline cost was paid by the Sonoma Valley County Sanitation District, which is operated by the water agency. The rest was paid by various state and federal grants, including money from the Coastal Conservancy and Bureau of Reclamation.
If this pipeline "didn't bring fresh water down," Davis said, gesturing at the moonscape of Pond 7, "this would have been left here as a liability for a long time."
Pond 7 is one of a series of ponds along the edge of the bay that have been restored over the past decade, perhaps the largest wetland restoration effort in the state. The ponds were created by farmers in the 1850s for cattle and to irrigate crops.