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  California Water Science Center

The USGS is currently is involved in several studies of water quality in the San Joaquin Valley. The studies described here include:

  1. Ground Water Ambient Monitoring and Assessment (GAMA)
  2. Transport processes of pyrethroid insecticides in streams and rivers of the San Joaquin Basin
  3. Development of a simulation/optimization model of the Modesto area ground-water basin for evaluation of water resource management alternatives

GAMA Studies:

The GAMA program is a comprehensive assessment of statewide ground-water quality. The program is designed to help better understand and identify risks to ground-water resources. Ground water is being sampled at many locations across California in order to characterize its constituents and identify trends in ground-water quality. The results of these tests are providing information for water agencies to address a variety of issues ranging in scale from local water supply to statewide resource management. The GAMA program was developed in response to the Ground-Water Quality Monitoring Act of 2001 (Sections 10780-10782.3 of the Water Code): a public mandate to assess and monitor the quality of ground water used as public supply for municipalities in California. The goal of the act was to improve statewide ground-water monitoring and facilitate the availability of information about ground-water quality to the public. The State Water Resources Control Board is implementing the GAMA Program in coordination with the U.S. Geological Survey and Lawrence Livermore National Laboratory. The GAMA program includes six study areas within the San Joaquin Valley: North San Joaquin Valley Basin, Central Eastside Basin, Madera Chowchilla Basin, Western San Joaquin Valley Basin, Southeast San Joaquin, and Kern Basin. Information on these basins and the overall GAMA program can be obtained at the following URL: http://ca.water.usgs.gov/gama/ . Publications on San Joaquin Valley study areas are listed in the Related Studies/Publications section.

Pyrethroid Insecticides in the San Joaquin River Basin:

Because of restrictions on the use of organophosphorus insecticides, such as diazinon and chlorpyrifos, increasing amounts of new insecticides are being used as replacements. One class of insecticide that is greatly increasing in use is the pyrethroid group of compounds. Unlike the organophosphorus pesticides that they are replacing in agriculture, these compounds are not effectively transported in water as dissolved constituents, but rather are strongly attached to sediment particles. The pyrethroid compounds have very high octanol-partition coefficients (Koc), and as a result are not dissolved in river water, but attached to particle surfaces. Toxicity to water column aquatic organisms has not been demonstrated, probably because the amount of suspended sediment is insufficient to result in toxicity. However, toxicity to benthic organisms has been observed. Because of this association with sediment, it is less likely that pyrethroid insecticide concentrations will be toxic to invertebrates or fish in the water column, however, little is known about the contribution to sediment toxicity of pyrethroid compounds, or the consequences of sudden mixing of bed sediment material to the water column, producing suspended sediment, such as what happens during storm events. Although suspended sediment from irrigation run-off will contribute to the overall accumulation of pyrethroid insecticides in streams, storm events will transport the greatest amount of new suspended sediment, eventually resulting in the deposition of this material in regions that may affect the benthic aquatic portion of the ecosystem.

The study of pyrethroid insecticides in the San Joaquin River Basin is a cooperative CALFED-funded study headed by Dr. Joe Domagalski of USGS. The study also includes scientists from UC Davis and UC Berkeley. The objectives of the study are:

  1. Determine the amount of pyrethroid insecticides transported with suspended sediments in representative streams of the eastern and western San Joaquin Valley and in the San Joaquin River, under storm water runoff conditions and during the irrigation season, and measure the accumulation of pyrethroid insecticides in the bed sediments of these streams during the irrigation season.

  2. Assess the amount of pyrethroid insecticides in recently deposited bed sediment in representative streams of the eastern and western San Joaquin Valley during the irrigation season (March through September)

  3. Assess the toxicity of the stream sediments at the beginning, middle and end of the irrigation season with respect to pyrethroid insecticides (Note: UC Berkeley task)

  4. Using the pesticide-use reporting of the California Department of Pesticide Regulation and various sources of publicly available soils data, develop a Geographic Information System (GIS) procedure that can be used to determine portions of sub-watersheds that are particularly prone to sediment transport with high levels of pyrethroid insecticides (Note: UC Davis task).

Model of Modesto-area ground water basin:

A description of this project is available at the following URL:


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