• Evaluation of Ambient Water Quality in Urban Ground-Water Systems
• Transport of diazinon and chlorpyrifos in the lower San Joaquin River Basin during the dormant spray season in 2000 and 2001
• In-season monitoring of diazinon and chlorpyrifos in the lower San Joaquin River Basin, April through August 2001
• Evaluation of nutrients and oxygen-demanding substances in the San Joaquin River Basin upstream of Vernalis during summer and fall of 2000 and 2001
• Assessment of organic carbon loads from the upstream watersheds to the Sacramento-San Joaquin Delta for water years 1980 to 1999
• Evaluation of pesticide distribution and bioassessment in the San Joaquin River Basin, 2001 and 2002
• Selenium and sediment loads in storm runoff in Panoche Creek, California, February 1998

The USGS has participated on a multi-agency team with the State Water Resources Control Board, Department of Health Services, Department of Water Resources, and Lawrence Livermore National Laboratory to assess the occurrence and concentrations of low-level volatile organic compounds (VOC) and ground-water age (using tritium-helium) in public-supply wells in urban areas across the state. As part of this program, 40 ground-water samples were collected during 2001 in Modesto in the eastern San Joaquin Valley. This program may be extended to other cities in the San Joaquin Valley in the near future.

For more information see: http://ca.water.usgs.gov/projects02/ca576.html

Transport of diazinon and chlorpyrifos in the lower San Joaquin River Basin during the dormant spray season in 2000 and 2001
Cooperative study with the California Department of Pesticide Regulation

The USGS, with funding from the California Department of Pesticide Regulation and sampling support from the Central Valley Regional Water Quality Control Board, sampled several sites in the lower San Joaquin River Basin in January and February during 2000 and 2001 for diazinon and chlorpyrifos and 45 other dissolved pesticides. Sampling frequency ranged from weekly during non-storm periods to every four hours for several days during storm runoff. The data is being used by the Regional Board in the development of a Total Maximum Daily Load (TMDL) for diazinon and chlorpyrifos. In addition to surface-water sites, the sampling in 2001 included urban storm runoff in Modesto and rainfall sampling in the Modesto urban area and surrounding agricultural areas. The data collected in 2000 and 2001 showed a much smaller load of diazinon was transported in the lower San Joaquin River than during USGS sampling in 1993-95. This was probably due to the greater than 80-percent reduction in diazinon application since the 1993-95 period. Precipitation was a significant contributor to the diazinon and chlorpyrifos loads in the urban storm runoff in Modesto.

Kratzer, C.R., Zamora, Celia, and Knifong, D.L., 2002, Diazinon and chlorpyrifos loads in the San Joaquin River Basin, California, January and February, 2000, U.S. Geological Survey Water Resources Investigations Report 02-4103, 38 p.

Zamora, C., Kratzer, C.R., Majewski, M.S., and Knifong, D.L., 2003, Diazinon and chlorpyrifos loads in precipitation and urban and agricultural storm runoff during January and February 2001 in the San Joaquin River Basin, California: U.S. Geological Survey Water-Resources Investigations Report 03-4091, 56p.

The USGS, with funding from the California Department of Pesticide Regulation and sampling support from the Central Valley Regional Water Quality Control Board, sampled 12 sites in the lower San Joaquin River Basin on a weekly basis for diazinon and chlorpyrifos and 45 other dissolved pesticides. This data is also being used by the Regional Board in the development of a Total Maximum Daily Load (TMDL) for diazinon and chlorpyrifos. Most of the sampling effort on diazinon and chlorpyrifos during the past decade in the lower San Joaquin River Basin has concentrated on the dormant spray season. This study provided an extensive database on in-season loads and sources of diazinon and chlorpyrifos.

Dissolved oxygen levels in the San Joaquin River near Stockton frequently drop below the water quality objective for the protection of aquatic life during July through November. Among other adverse impacts to aquatic biological communities, these relatively low dissolved oxygen levels could be inhibiting the upstream movement of spawning salmon. An initial assessment by the Technical Advisory Committee (for the development of a TMDL) indicated that a significant portion of the problem was originating from the San Joaquin River Basin upstream of Vernalis.

The objective of this project was to collect data that would help to better define the sources of nutrients (nitrogen and phosphorus) and oxygen-depleting substances in the San Joaquin River Basin upstream of Vernalis. The project built on previous work conducted by the USGS during the San Joaquin NAWQA. The monitoring was coordinated with ongoing and related monitoring in the area by the University of California, Davis and by Lawrence Berkeley Laboratory.

USGS sampled four sites on the mainstem of the San Joaquin River, from upstream of the Merced River to Vernalis every two weeks. In addition to the four river sites, eight tributaries were also sampled (in 2001 only) every four weeks. At each sampling site, field-measurements were made of Secchi Disk transparency, specific conductance, pH, water temperature, dissolved oxygen, and alkalinity. Laboratory analyses included suspended sediment, volatile suspended solids, nutrients, major ions, dissolved and suspended organic carbon, bulk measures of organic carbon such as ultra-violet light absorption, chlorophyll-a and pheophytin-a, and isotopes of carbon, nitrogen, and oxygen.

Loading rates of nutrients and dissolved organic carbon increased in the San Joaquin River in the fall with the release of wetland drainage into Mud Slough and with increased reservoir releases on the Merced River. During August 2000 and September 2001, the chlorophyll-a loading rates and concentrations in the San Joaquin River declined and remained low during the rest of the sampling period. Other than Mud Slough, tributaries were minor sources of chlorophyll-a load, implying that most of the chlorophyll-a was growing in the San Joaquin River instead of entering from tributaries. Based on the carbon to nitrogen ratios and the d¹³C of particulate organic matter in the San Joaquin River and tributaries, the particulate organic matter in the river was mostly phytoplankton. The range of d¹⁵N and d¹⁸O values of nitrate in the San Joaquin River and tributaries suggest that animal waste or sewage was a significant source of nitrate in the river.

Kratzer, C.R., Dileanis, P.D., Zamora, Celia, Silva, S.R., Kendall, Carol, Bergamaschi, B.A., and Dahlgren, R.A., 2004, Sources and transport of nutrients, organic carbon, and chlorophyll-a in the San Joaquin River upstream of Vernalis, California, during summer and fall, 2000 and 2001: U.S. Geological Survey Water-Resources Investigations Report 03-4127, 113 p.

Organic carbon compounds are constituents of concern for drinking water taken from the Sacramento-San Joaquin Delta because of the potential for organic carbon to be transformed into trihalomethanes during water treatment. A preliminary assessment of source areas of organic carbon to the Delta system estimated that upstream watersheds contribute over half the load. Data on organic carbon and other constituents from the U.S. Geological Survey, U.S. Environmental Protection Agency, California Department of Water Resources, CALFED, and other readily-available computerized databases was retrieved and reviewed for water years 1980 to 1999. This data was used to determine loads and major source areas of organic carbon and other constituents, and to evaluate trends in concentrations and loads over the twenty-year period. The data also helped to identify data gaps and monitoring needs for organic carbon and other constituents in upstream watersheds.

USGS is providing assistance to the Central Valley Regional Water Quality Control Board with monitoring and assessments related to TMDL issues in the San Joaquin River Basin. This study includes an evaluation of in-season pesticide synoptics, an evaluation of wet and dry deposition of pesticides, and bioassessment of agriculturally-dominated streams in the San Joaquin River Basin.

Several reports are planned as part of this study.

Brown, Larry R., and May, Jason T., 2004, Periphyton and macroinvertebrate communities at five sites in the San Joaquin River Basin, California, during June and September, 2001, U.S. Geological Survey Scientific Investigations Report 2004-5098, 43 p.

Brown, Larry R., Panshin, Sandra Y., Kratzer, Charlie R., Zamora, Celia and Gronberg, Jo Ann M., Occurrence, distribution, instantaneous loads, and yields of dissolved pesticides in the San Joaquin River Basin, California, during summer conditions, 1994 and 2001, U. S. Geological Survey Scientific Investigations Report 2004-5083, 53 p.

Five to nine samples were collected per storm throughout the hydrograph of four storms in February 1998 at Panoche Creek at Interstate 5. Suspended sediment concentrations were highly variable during the storms, ranging from 32,900 mg/L to 251,000 mg/L with a median of 126,000 mg/L. Dissolved selenium concentrations in the storm samples ranged from 16 to 60 mg/L with a median of 30 mg/L. Total selenium concentrations in the storm samples ranged from 57 to 320 mg/L with a median of 115 mg/L.

No significant storm events occurred during the remainder of the study period (water years 1998 to 2000) and thus no additional storm sampling took place. Assuming that future sediment and selenium transport is similar to 1998, a reasonable estimate of loads can be calculated from the streamflow record at the Interstate 5 gage. Loading rate prediction equations were developed for suspended sediment, dissolved selenium, and total selenium as a function of streamflow at the I-5 gaging station. Additional storm sampling would improve these estimates and possibly allow for separate equations for the rising and falling limbs of storm hydrographs.