Salinity in the Central Valley: An Overview

The Central Valley is one of the most rapidly growing areas in the nation. Population in the Valley is anticipated to increase 39% by the year 2020. Industry and urbanization are taking place at an increasing pace, although agriculture is still a dominant economic force here, accounting for 57% of the $6.5 billion in sales of all agricultural products in California in 2002. The Central Valley is also home to wildlife and includes the largest contiguous wetlands area remaining in California. The warm, dry, Mediterranean climate and fertile soils have drawn agricultural users for over a century. The presence of transportation corridors and ready access to workers has enticed industry to move in, and the relatively cheap price of land has encouraged urban development. The open areas and wetlands provide vital habitat for many species, particularly migratory birds along the Pacific Flyway. But the very features that make the Central Valley desirable for wildlife, farmers, developers, industry and the general population also contribute to salinity problems.

When water is used, salts are left behind. Every time a farmer irrigates a field, every time a managed wetland is flooded, every time an industrial facility conducts some water-requiring process, and every time you or I take a shower, we contribute to the salinity problem because the water we use and release has a higher salinity concentration than what we started with. Sometimes this is because we add salt intentionally (home water softeners, plant fertilizers), but even when no salts are added to the system, evaporation and consumptive use act to concentrate unused salts. Additionally, salts move with water so salts originating in one basin will turn up in another. This is a significant problem when the receiving basin has no reliable way of disposing salt, as is the case in the Tulare Lake Basin; or has only limited capacity to discharge salt, which is the case in the San Joaquin River Basin.

We know today that salinity impacts are being felt in the Central Valley and that these impacts are increasing.

A very preliminary analysis of salt flux in the Delta, estimated that 700 thousand tons of salt flow into the Delta from the Bay annually and are imported into the State, federal, and other water supply projects.

The Tulare Lake and San Joaquin River Basins collectively receive over two million tons of salt annually through water taken in and distributed by state and federal water projects.

Because the Tulare Lake Basin is a closed basin with no reliable outlet for the discharge of salts, and there is no other viable option at this time, the majority of the salt imported into the basin from the state and federal water projects (over one million tons per year) is collecting in the basin and is migrating to the basin’s groundwater. For this reason, the Central Valley Regional Water Quality Control Board’s Tulare Lake Basin Plan assumes degradation by salt is occurring in the basin and contains a controlled degradation policy for groundwater.

A preliminary evaluation of salt migration to groundwater in the San Joaquin Valley estimated that over 400 thousand tons of salt per year were being added to the confined aquifer in the San Joaquin Basin.

In a current study, preliminary findings of a USGS investigation have shown chloride levels in the semi-confined aquifer near Stockton are increasing and have been found to be as high as 2,200 mg/l and EC as high as 5,930 ?S/cm

A simple analysis of groundwater data from 14 drinking water wells on the south side of Fresno has shown an average increase of 30 ?S/cm in the past 15 years.

Although this is not a radical increase, it does indicate that salt imported into the area may be impacting the drinking water aquifer.

The mean annual EC levels in the San Joaquin River near Vernalis have nearly doubled since the mid-1940s.

Because the San Joaquin River is limited in its capacity to assimilate salts safely, a Total Maximum Daily Load (TMDL) has been adopted for salt and boron. The Basin Plan for the San Joaquin and Sacramento Basins has been amended to include the TMDL.

The recently completed Draft Soil Survey of Fresno County, California, Western Part states that approximately 400 thousand acres of saline-sodic soils currently exist in the survey area. This acreage constitutes approximately 48 percent of the irrigated land within the boundaries of the survey area, up from approximately 33 percent of the irrigated saline-sodic land identified in 1985, an increase of approximately 120 thousand acres in 18 years.

There are currently 4470 acres of active evaporation basins in the Tulare Lake Basin, and this number may be increasing due to recent legislation allowing Integrated Farm Drainage Management Systems for individual farms in salt impaired areas. The Board has stated that evaporation basins are, at best, interim salt management tools, not a final disposal option.

Approximately 113 thousand acres on the west side of the San Joaquin Valley have been retired (permanently removed from irrigation) due to regional drainage problems (high salinity, shallow groundwater). More land retirement is anticipated.

Salinity problems are often complicated by the presence of other materials. Soils on the west side of the San Joaquin Valley are high in selenium, so any salt management program in the area must also address selenium management.

Approximately $40 million in both public and private funds has been spent (as of 2005) to manage salt and selenium problems in the Grassland Drainage Area alone.

Water providers are experiencing salinity impacts and costs are being incurred and are being passed on to customers to protect their systems from corrosion and provide the quality of water needed by their customers.

Agricultural, industrial, and municipal dischargers in the Region are spending increasingly greater resources on monitoring for, treating, controlling, and managing salt.

Over the years, the Central Valley Regional Water Quality Control Board has been aware of the growing problem of increasing salinity in the Central Valley, but many of the key decisions that must be made in order to control Valley salinity are outside of this Board’s jurisdiction. This report is a first step in opening a dialogue between the stakeholders and decision makers that will need to be involved in a comprehensive, sustainable, salinity management program for the Central Valley and for the State of California.