Napa Salt Pond Complex

Nine thousand acres of solar salt evaporation ponds were created in the 1950s, replacing wetlands that had been operated as duck hunting clubs for several decades. Even the duck clubs were not natural. They had been converted from the original tidal marshes of the Napa Creek estuary.
Cargill Salt Company, the owner of the Napa salt pond complex, sold it to the State of California in 1994. The State planned to restore wetlands on the property. Construction in three of the ponds, Ponds 3, 4 and 5, commenced in 2006, carrying out a plan to restore 3,000 acres of tidal wetlands. That phase was completed in 2009, and is now fully reconnected to the tidal regime of the Napa Creek estuary. Additional work is pending.
One of the challenges yet to be addressed is the high concentrations of residual salt in five of the ponds. Their containment levees cannot be breached nor the ponds reconnected to the open waters of the estuary until the salt concentration inside the ponds is reduced, lest the hypersaline conditions harm aquatic life.
After the commercial sodium chloride is removed from Bay water through the process of evaporation, many salts still remain in the waste water. Over the life of the complex, these residual salts were stockpiled in large ponds at the northern end of the complex.
These ponds were called “bittern” ponds, after the waste fluid that remained once the sodium chloride was removed. The bittern ponds are typically inundated with rain water during winter and spring, but dry out during the summer, revealing the salt-encrusted bottom of the ponds. The bittern ponds have such elevated levels of residuals salts that nothing can live in them, summer or winter. They are sterile wastelands, a far cry from the rich tidal marshes from which they were created.

The Bay Institute works to promote regional funding to support this restoration project.