Addressing Nitrate in California’s Drinking Water with a Focus on Tulare Lake Basin and Salinas Valley Groundwater

University of California, Davis (UC Davis) | March 1st, 2012

In 2008, Senate Bill SBX2 1 (Perata) was signed into law (Water Code Section 83002.5), requiring the State Water Resources Control Board (State Water Board), in consultat

In 2008, Senate Bill SBX2 1 (Perata) was signed into law (Water Code Section 83002.5), requiring the State Water Resources Control Board (State Water Board), in consultation with other agencies, to prepare a Report to the Legislature to “improve understanding of the causes of [nitrate] groundwater contamination, identify potential remediation solutions and funding sources to recover costs expended by the State to clean up or treat groundwater, and ensure the provision of safe drinking water to all communities.” The University of California prepared this Report under contract with the State Water Board as it prepares its Report to the Legislature.  This executive summary focuses on major findings and promising actions. Details can be found in the Main Report and eight accompanying Technical Reports. Technical Report 1: Project and Technical Report Outline (Version July 2012) Technical Report 2: Nitrogen Sources and Loading to Groundwater (Version July 2012) Appendix, Technical Report 2: Appendix Figures to Technical Report 2 (Version July 2012) - 84 MB (large file) Technical Report 3: Nitrogen Source Reduction to Protect Groundwater Quality (Version July 2012) Technical Report 4: Groundwater Nitrate Occurrence (Version July 2012) Technical Report 5: Groundwater Remediation and Management for Nitrate (Version July 2012) Technical Report 6: Drinking Water Treatment for Nitrate (Version July 2012) Technical Report 7: Alternative Water Supply Options for Nitrate Contamination (Version July 2012) Technical Report 8: Regulatory and Funding Options for Nitrate Groundwater Contamination U.C. Davis Groundwater Nitrate Project links and updates

California Natural Resources Agency Annual Report on the Salton Sea Management Program

California Natural Resources Agency (CNRA) | March 25th, 2024

Significant, measurable progress continued at the Salton Sea (Sea) over the last year. The largest restoration project in the Sea’s history neared completion, suppressi

Significant, measurable progress continued at the Salton Sea (Sea) over the last year. The largest restoration project in the Sea’s history neared completion, suppressing dust and restoring habitat across thousands of acres at the south end of the Sea. In other areas along the Sea, hundreds of acres now host native vegetation recently planted to suppress dust over coming decades. These plants have taken root, are growing and are beginning to serve their purpose. This year also witnessed the first major investment by federal agencies to stabilize the Sea; the U.S. Bureau of Reclamation (Reclamation) granted $70 million to accelerate local restoration projects.

California regulation of agricultural runoff

American Bar Association (ABA) | November 1st, 2017

Agriculture in California is a multibillion dollar industry that produces more than half of the nation’s fruits, nuts, and vegetables. But this comes at a cost. Agricul

Agriculture in California is a multibillion dollar industry that produces more than half of the nation’s fruits, nuts, and vegetables. But this comes at a cost. Agriculture is the primary source of water pollution, with irrigation and rainfall sweeping excess fertilizers and pesticides off the fields into adjoining waters and, over time, leaching into groundwater. As a result, waterbodies—spanning roughly 8,000 miles of rivers and streams and 300,000 acres of lakes, bays, and wetlands—are impaired.

Comparing imidacloprid, clothianidin, and azoxystrobin runoff from lettuce fields using a soil drench or treated seeds in the Salinas Valley, California

Environmental Pollution (Elsevier) | October 10th, 2022

Neonicotinoid insecticide use has increased over the last decade, including as agricultural seed treatments (application of chemical in a coating to the seed prior to pla

Neonicotinoid insecticide use has increased over the last decade, including as agricultural seed treatments (application of chemical in a coating to the seed prior to planting). In California, multiple crops, including lettuce, can be grown using neonicotinoid treated seeds or receive a direct neonicotinoid soil application (drenching) at planting. Using research plots, this study compared pesticide runoff in four treatments: (1) imidacloprid seed treatment; (2) clothianidin seed treatment; (3) imidacloprid drench and an azoxystrobin seed treatment; and (4) a control with no pesticidal treatment. Neonicotinoid and azoxystrobin concentrations were measured in surface water runoff during six irrigations events in the 2020 growing seasons. Results showed runoff concentrations up to 1308 (±1200) ng L−1 for imidacloprid drench treatment, 431 (±100) ng L−1 for clothianidin seed treatment, 135 (±60) ng L−1 for imidacloprid seed treatment, 13 (±10) ng L−1 for azoxystrobin seed treatment (treatments averaged). The percent of applied mass in runoff over the entire sampling period varied by compound; the imidacloprid seed treatment and drench were similar (0.015 and 0.019%, respectively) to the clothianidin seed treatment (0.036%) while the azoxystrobin seed treatment was much higher (15%). Although the proportion of imidacloprid in runoff was similar for imidacloprid treatments, the mass applied during soil drench was > 4x the amount applied from the imidacloprid seed treatment. Surface soils were collected before planting and at the end of the trial. The neonicotinoids were detected in soil throughout the study and average maximum concentrations were 9–13 ng g−1; azoxystrobin was detected in only two soils at concentrations up to 0.57 ng g−1. These results elucidate the comparative mass runoff resulting from planting treated seed and soil drench applications and highlight the value of additional work to characterize off-site transport from the many commodities that may be utilizing treated seeds.

Comparison of potential drinking water source contamination across one hundred U.S. cities

Nature Portfolio (Springer Nature) | December 13th, 2021

Drinking water supplies of cities are exposed to potential contamination arising from land use and other anthropogenic activities in local and distal source watersheds. B

Drinking water supplies of cities are exposed to potential contamination arising from land use and other anthropogenic activities in local and distal source watersheds. Because water quality sampling surveys are often piecemeal, regionally inconsistent, and incomplete with respect to unregulated contaminants, the United States lacks a detailed comparison of potential source water contamination across all of its large cities. Here we combine national scale geospatial datasets with hydrologic simulations to compute two metrics representing potential contamination of water supplies from point and nonpoint sources for over a hundred U.S. cities. We reveal enormous diversity in anthropogenic activities across watersheds with corresponding disparities in the potential contamination of drinking water supplies to cities. Approximately 5% of large cities rely on water that is composed primarily of runoff from non-pristine lands (e.g., agriculture, residential, industrial), while four-fifths of all large cities that withdraw surface water are exposed to treated wastewater in their supplies.

Concentrations, Loads, and Associated Trends of Nutrients Entering the Sacramento–San Joaquin Delta, California

University of California, Davis (UC Davis) | December 15th, 2021

Statistical modeling of water-quality data collected at the Sacramento River at Freeport and San Joaquin River near Vernalis, California, USA, was used to examine trends

Statistical modeling of water-quality data collected at the Sacramento River at Freeport and San Joaquin River near Vernalis, California, USA, was used to examine trends in concentrations and loads of various forms of dissolved and particulate nitrogen and phosphorus that entered the Sacramento–San Joaquin River Delta (Delta) from upstream sources between 1970 and 2019. Ammonium concentrations and loads decreased at the Sacramento River site from the mid-1970s through 1990 because of the consolidation of wastewater treatment and continuously reduced from the mid-1970s to 2019 at the San Joaquin River site. Current ammonium concentrations are mostly below 4 µM (0.056 mg N L–1) at both sites, a concentration above which reductions in phytoplankton productivity or changes in algal species composition may occur. The Sacramento River at Freeport site is located upstream of the Sacramento Regional County Sanitation District’s treatment facility’s discharge point; nutrient water quality there is representative of upstream sources. Inorganic nitrogen (nitrate plus ammonium) concentrations and loading differed at both sites. At the Sacramento River location, concentrations decrease in the summer agricultural season, reducing the molar ratios of nitrogen to phosphorus. In contrast, inorganic nitrogen concentrations increase in the San Joaquin River during the agricultural season as a result of irrigation runoff, increasing the molar ratio of nitrogen to phosphorus. This increase suggests a possible nitrogen limitation in the northern Delta and a phosphorus limitation in the southern Delta, as indicated by the molar ratios of bioavailable nitrogen to bioavailable phosphorus. Planned upgrades to the Sacramento Regional Wastewater Treatment Plant (SRWTP) will reduce inorganic nitrogen inputs to the northern Delta. Consequently, the supply of bioavailable nitrogen throughout the upper estuary should diminish. Source modeling of nitrogen and phosphorus identifies agriculture, atmospheric deposition, and wastewater effluent as sources of total nitrogen in the Central Valley. In contrast, geologic sources, agriculture, and wastewater discharge are the primary sources of phosphorus.

Desalination Demonstration Report for Buena Vista Water Storage District

Buena Vista Water Storage District | December 1st, 2003

Saline agricultural drainage water within the Buena Vista Water Storage District is accumulating in shallow aquifers located below productive farmland. This saline water

Saline agricultural drainage water within the Buena Vista Water Storage District is accumulating in shallow aquifers located below productive farmland. This saline water has risen to elevations where it increases the soil salinity in crop root zones resulting in reduced crop productivity and in some areas of the District, lands have been taken out of production because of the high saline groundwater table. A reverse osmosis pilot plant was constructed to demonstrate the feasibility of desalting saline irrigation drainage water for use as a water supply for agricultural or municipal use. The demonstration plant was constructed in the Buena Vista Water Storage District northwest of Bakersfield, California. The plant operated during the irrigation seasons of 2000 and 2002.

Estuary News, August 2001

San Francisco Estuary Partnership (SFEP) | August 15th, 2001

Estuary News, August 2005

San Francisco Estuary Partnership (SFEP) | August 15th, 2005

Estuary News, August 2007

San Francisco Estuary Partnership (SFEP) | August 15th, 2007