To keep their fields from becoming waterlogged, growers installed drainage pipe systems. And the Bureau of Reclamation built the Orlando and Solano Projects to intercept water from streams tributary to the Sacramento River. As the Sacramento Valley has more rainfall, soils have not accumulated toxic amounts of trace elements to the same degree as in the San Joaquin Valley. However, irrigation throughout the Central Valley has clearly mobilized more salts, trace elements, and fertilizer and pesticide residues, than would occur under natural conditions. Substances of Concern in Drainage Salts Salt management is an inevitable chore of irrigated agriculture.
Salts occur naturally as rock weathers and forms soil.
While California's rainfall is enough to dissolve bits of rock into salts, it's sometimes not enough to remove them, so they build up in the soil. Irrigation causes still more salt accumulation, because surface water diverted to irrigate fields already contains salts in solution. The CVP and SWP import about 1,600,000 tons of dissolved salts into the San Joaquin Valley every year. Salts accumulating in the root zone make it harder for a plant to absorb the water it needs. Beyond a certain point, which varies for different species, the plant wilts and dies.