Poisoned Lands, Polluted Water
Since the late 1960s the federal Central Valley Project, and later the State Water Project, supply irrigation water to growers irrigating approximately 1.3 million acres of drainage-problem lands on the west side of the San Joaquin Valley and Tulare Lake Basin.
These lands are naturally contaminated. They formed as an ancient seabed. As the muds and wetlands of the time dried up, metals such as selenium, boron, molybdenum, mercury, arsenic, and various other salts and minerals concentrated heavily in the soils and rocks that formed.
When irrigation service began in the Delta-Mendota Service Area and the San Luis Unit of the Central Valley Project, and in the Kern and Tulare regions served by the State Water Project, drainage water from the fields concentrated and mobilized these contaminants leading in 1983 to the poisoning of Kesterson National Wildlife Refuge.
The chemical problems of these lands have been known since the 1950s, and the state of California committed initially to providing drainage service to these lands as part of the electorate's approval of the State Water Project in 1960. However, eventually the state could not provide the service, and the federal Bureau of Reclamation was given responsibility for drainage service when Congress authorized the San Luis Unit (which contains Westlands Water District, and other smaller irrigating areas).
Irrigation of this land with water exported from the Delta adds enormous amounts of salt to the already-saline soils of the western Valley, as much as 4,000 tons of salt daily (the equivalent of 40 railroad cars). Only 1,700 tons of salts leave the basin daily in runoff and drainage to the San Joaquin River.
Plants naturally take up irrigation water, leaving salts to build up in the soil. To continue farming in these areas, up to one-half an acre-foot of water per acre (about 160,000 gallons of water per acre) must be added to the land just to leach salts out of the root zone (a process called "pre-irrigation"). This process also mobilizes selenium, molybdenum, arsenic, chromium and other toxins in the soils there.
This irrigation drainage water percolates down hill and towards open waterways like wetlands, the San Joaquin River, and its tributaries. Further down in the soils, there is an impermeable clay horizon called the "Corcoran Clay" where the percolating water collects and rises back up into the root zone if it's not managed otherwise. Left alone, the land would permanently salinize and become intolerable for most vegetation and unsuitable for farming, which would be an economic and environmental disaster for California.
In other areas of the San Joaquin Valley where the Corcoran clay is absent, contaminated drainage water percolates into aquifers that provide drinking water to many Valley residents.
Initially the Bureau and the State planned to build a San Luis Master Drain to the Bay-Delta estuary near Antioch, but construction of the drain was stopped after 93 miles were completed to the Kesterson Reservoir near Los Banos. In 1983, birds and other wildlife were found to have been poisoned with high levels of selenium. Bird embryos were deformed and dead.
The US Geological Survey estimated in 2006 that even if the San Luis Drain were completed, irrigation of the San Luis Unit (including the Westlands Water District) of the Central Valley Project were halted, and 42,500 pounds of selenium a year were discharged into the Delta, it would take 65 to 300 years to eliminate the selenium already built up in Valley groundwater.
Farmers and water districts throughout the western San Joaquin Valley try to reduce their drainage water. They recycle, blend, drip irrigate, and reuse their delivered water, and are successful in some cases in reducing selenium, salt and other discharges that have polluted the San Joaquin River. However, retiring these lands from irrigated agriculture remains by far the most cost-effective and reliable method to eliminate harmful drainage discharges to the river, the wetlands, and aquifers of the San Joaquin Valley.
The Westlands Water District has already retired 100,000 acres of land once irrigated with federal water. Any long-term solution to the western Valley's drainage problem must focus on larger-scale land retirement from irrigated production, improved irrigation practices, and application of new technologies where appropriate. Any approach not founded on land retirement will ultimately continue to store and concentrate toxic selenium and salts in the shallow aquifers where they may be mobilized by flood events or groundwater percolation.