Salt of the Earth : It’s Harvest Time at Bay Area Ponds Where Nature Turns Water Into Brine

Creeping slowly down another arrow-straight row, the giant harvester deftly snatches the crop from the ground and spits it, two tons at a time, into a train of railroad hopper cars lined up alongside.

The sun is setting, but the harvest will continue--24 hours a day, seven days a week. As with many other crops, rain is the enemy here and forecasters warn of imminent showers.

But this is no ordinary crop of avocados or artichokes, zinnias or zucchini. The small army of seasonal workers is reaping a totally inorganic bounty: salt.

In one of the most unusual forms of “farming” in agriculturally diverse California, the Leslie Salt Co. pulls more than 1 million tons of salt each year from tens of thousands of acres of evaporation ponds along the southern and northernmost parts of San Francisco Bay.

In addition to accounting for about 5% of all U.S. salt production, the company’s evaporation ponds comprise an important habitat for birds and other animals that have been hurt by the loss of most of California’s wetlands to development and farming.

About 12,000 acres of the company’s 40,000 acres of ponds make up the bulk of the San Francisco Bay National Wildlife Refuge. With the varying salinity of the ponds supplying a variety of food, such as brine shrimp, the salt farm has become an important nesting area for the white pelican, Caspian tern, black-necked stilt and other species.

“As the salinity increases, different life forms take over the ponds,” said public affairs manager Lori A. Johnson. “At each stage, this attracts different bird species, many of which we wouldn’t find here otherwise.”

Leslie is the bigger of the nation’s only two remaining major “solar salt” producers--those who produce salt by evaporating sea water in open salt ponds using only the sun and wind. The other, Western Salt Co. near San Diego, produces a small fraction of the annual Leslie harvest.

“It’s a pretty simple process, probably the oldest method in the world for collecting salt,” said Johnson.

The process begins each summer, when the bay water is saltiest because fresh-water rivers and streams emptying into it are at their lowest flows. Thousands of acres of shallow, irregularly shaped ponds are flooded, and the sun and wind begin evaporating the water.

Over five years, the increasingly salty brine is transferred, mostly by gravity and some pumping, through a series of new ponds ever closer to processing plants in Newark and Redwood City and south of Napa.

When about 90% of the water has been removed, the resulting liquid, called “pickle,” is sent to several shallow, 40-acre crystallizer beds where the salt crystals grow on compacted-clay liners. In the fall, a 5- to 8-inch-thick crust of 99% pure salt lines the pits and the highly automated harvest begins.

Rain during the harvest months of September, October and November can dissolve the salt crystals, so the harvest runs nonstop.

Giant mobile harvesters--which look like grain harvesters and were built by Leslie employees--scrape the salt from the ground, grind it up to the size of pencil erasers and then pour it into miniature railroad hopper cars on movable tracks. The tracks are shifted every time the harvesters scrape a 12-foot-wide path through the rectangular crystallizer beds.

In the processing plant, the salt is briefly washed with brine to remove the pinkish stain left by microorganisms that flourish in the brackish pickle. The salt is then piped onto distinctive snow-white, 90-foot-high “stacks,” or piles, where it is left to dry for a year.

Other salt-production techniques--such as carving it from salt mines, dissolving underground deposits in water which is evaporated on the surface, or boiling it out of seawater in factories--produce salt that requires additional refining, Johnson said. Other big salt-producing states are Louisiana, Kansas, Oklahoma and New York.

Johnson said most of the 1.2 million tons of salt to be harvested from the bay each year requires no additional refinement because the solar process produces salt that is 99% pure. The raw salt is sold for such industrial uses as pulp- and paper-making, textile manufacturing and chlorine-bleach production, as well as salt licks for livestock.

The small fraction of salt used for food production--sold to canners, soup manufacturers, cheese makers, hospitals and restaurants--is refined to remove most of the 1% of metallic salts that remain in the crystals after they are harvested. Table salt, which accounts for only 3% of all production, is 99.9% pure sodium chloride, Johnson said.

Ohlone Indians drew salt from San Francisco Bay for centuries by evaporating bay water in natural tide pools, Johnson said. Commercial salt production did not begin until 1854, when a man named John Johnson (no relation to Lori Johnson) diked off a small part of the bay near Newark--on land still used for salt production by Leslie--and reaped a harvest he was able to sell for the then-lucrative price of $50 a ton.

Competitors soon followed Johnson in this profitable field, and increased production quickly dropped the price to $2 a ton. But the business persisted, and even though a series of mergers has left the bay with only one producer, it still pulls salt from the sea in basically the same way as the Ohlone.

“We prefer to think of it here as ‘harvesting’ salt rather than ‘mining’ because in mining you come in and take something that will never come back,” she said. “We really harvest a crop every year. When you take it from the sea, salt is a renewable resource.”