Search

In 2014 and 2015, the U.S. Geological Survey (USGS) sampled water wells in the Los Angeles Basin and southern San Joaquin Valley, California, and oil wells in the San Joaquin Valley for analysis of multiple chemical, isotopic, and groundwater-age tracers (fig. 1). The purpose of this reconnaissance sampling was to evaluate the utility of tracers for assessing the effects of oil and gas production activities on groundwater quality in California. The and George R. Aiken

Between 1974 and 2001 water from as many as onethird of wells in the Eastern San Joaquin Ground-Water Subbasin, about 80 miles east of San Francisco, had arsenic concentrations greater than the U.S. Environmental Protection Agency Maximum Contaminant Level (MCL) for arsenic of 10 micrograms per liter (μg/L). Water from some wells had arsenic concentrations greater than 60 μg/L. The sources of arsenic in the study area include (1) weathering of arsenic bearing minerals, (2) desorption of arsenic associated with iron and manganese oxide coatings on the surfaces of mineral grains at pH’s greater than 7.6, and (3) release of arsenic through reductive dissolution of iron and manganese oxide coatings in the absence of oxygen. Reductive dissolution is responsible for arsenic concentrations greater than the MCL. The distribution of arsenic varied areally and with depth. Concentrations were lower near ground-water recharge areas along the foothills of the Sierra Nevada; whereas, concentrations were higher in deeper wells at the downgradient end of long flow paths near the margin of the San Joaquin Delta (fig. 1). Management opportunities to control high-arsenic concentrations are present because water from the surface discharge of wells is a mixture of water from the different depths penetrated by wells. On the basis of well-bore flow and depth-dependent waterquality data collected as part of this study, the screened interval of a public-supply well having arsenic concentrations that occasionally exceed the MCL was modified to reduce arsenic concentrations in the surface discharge of the well. Arsenic concentrations from the modified well were about 7 μg/L. Simulations of ground-water flow to the well showed that although upward movement of high-arsenic water from depth within the aquifer occurred, arsenic concentrations from the well are expected to remain below the MCL.

The Sacramento–San Joaquin Delta of California was once a 1,400 square kilometer (km) tidal marsh, which contained a vast layer of peat ranging up to 15 meters (m) thick (Atwater and Belknap, 1980). Because of its favorable climate and highly fertile peat soils, the majority of the Delta was drained and reclaimed for agriculture during the late 1800s and early 1900s. Drainage of the peat soils changed the conditions in the surface layers of peat from anaerobic (having no free oxygen present) to aerobic (exposed to the atmosphere). This change in conditions greatly increased the decomposition rate of the peat, which consists largely of organic (plant) matter. Thus began the process of land-surface subsidence, which initially was a result of peat shrinkage and compaction, and later largely was a result of oxidation by which organic carbon in the peat essentially vaporized to carbon dioxide (Deverel and others, 1998; Ingebritsen and Ikehara, 1999). Because of subsidence, the land-surface elevation on farmed islands in the Delta has decreased from a few meters to as much as 8 m below local mean sea level (California Department of Water Resources, 1995; Steve Deverel, Hydrofocus, Inc., written commun., 2007). The USGS, in collaboration with the University of California at Davis, and Hydrofocus Inc. of Davis, California, has been studying the formation of the Delta and the impact of wetland reclamation on the peat column as part of a project called Rates and Evolution of Peat Accretion through Time (REPEAT). The purpose of this report is to provide results on the age of the remaining peat soils on four farmed islands in the Delta.

As a result of pumping and subsequent declines in water levels, chloride concentrations have increased in water from wells in the Eastern San Joaquin Ground-Water Subbasin, about 80 miles east of San Francisco (Montgomery Watson, Inc., 2000). Water from a number of public-supply, agricultural, and domestic wells in the western part of the subbasin adjacent to the San Joaquin Delta exceeds the U.S. Environmental Protection Agency Secondary Maximum Contaminant Level (SMCL) for chloride of 250 milligrams per liter (mg/L) (fig. 1) (link to animation showing chloride concentrations in water from wells, 1984 to 2004). Some of these wells have been removed from service. High-chloride water from delta surface water, delta sediments, saline aquifers that underlie freshwater aquifers, and irrigation return are possible sources of high-chloride water to wells (fig. 2). It is possible that different sources contribute high-chloride water to wells in different parts of the subbasin or even to different depths within the same well. Sources of High-Chloride Water to Wells, Eastern San Joaquin Ground-Water Subbasin, California

A series of storms beginning before Christmas 2005 and ending after New Year’s Day 2006 produced significant runoff over much of northern California. The storms resulted in an estimated $300 million in damages and Federal disaster declarations in 10 counties. Several precipitation stations in the Sierra Nevada had precipitation totals greater than 20 inches for the period December 24 through January 3, and several stations in the Coastal Range had precipitation totals greater than 18 inches. The peak stream discharges resulting from the storms in the north coast area generally had recurrence intervals in the 10to 25-year range, although the recurrence interval for peak discharge at one station on Sonoma Creek near Agua Caliente was greater than 100 years. In the San Francisco Bay area, peak discharges also generally had recurrence intervals in the 10to 25-year range. Further south along the central coast and in southern California, peak discharges had smaller recurrence intervals, in the 2to 5-year range. Upper Sacramento River tributaries draining from the west had peak flows with recurrence intervals in the 2to 5-year range, whereas upper tributaries draining from the east side had recurrence intervals in the 5to 10-year range. Further south, Sacramento River tributaries such as the Yuba and American Rivers had peak discharges with recurrence intervals in the 10to 25-year range. On the east side of the central Sierra around Lake Tahoe, peak discharges had recurrence intervals in the 10to 25-year range. Further south in the Sierra, streams draining into the San Joaquin River Basin had flows with recurrence intervals ranging from 2 to 5 years. Introduction A series of storms beginning before Christmas 2005 and ending after New Year’s Day 2006 produced significant runoff over much of northern California, including the north coast and the Sierra Nevada. There were localized evacuations and flooding, some slope failures, and road closures. An estimated $300 million in damages were attributed to the storms (California Office of Emergency Services, 2006). Ten counties subsequently were declared Federal disaster areas: Contra Costa, Del Norte, Lake, Marin, Mendocino, Napa, Sacramento, Siskiyou, Solano, and Sonoma (Federal Emergency Management Agency, 2006). Major flood damages were concentrated primarily in the Napa and Russian River Basins in Napa and Sonoma Counties. The flooding was widely compared by the media to the floods of 1986 and 1997, although the stream discharges generally were significantly smaller than those of the earlier floods. A storm on January 1 had been predicted to cause problems in southern California also; however, that storm did not develop as predicted. Nevertheless, the storm did manage to rain on the Rose parade for the first time in 51 years. Summary of Major Storms On the basis of provisional data obtained from the National Weather Service, California–Nevada River Forecast Center (2006), storm totals recorded by automated rainfall recorders at several precipitation stations on the western slopes of the Sierra Nevada during the December 24–January 3 period were greater than 20 inches. In addition, recorders at several stations at the headwaters of the Russian and Napa River Basins in the Coast Range had storm totals greater than 18 inches. Storm totals at two selected stations in the Coast Range (Willits Howard RS and Venado) and at two selected stations in the Sierra Nevada (Brush Creek and Girard) are presented in table 1. The 3 days of the 7-day period with the most intense precipitation were December 28, December 31, and January 2. Daily precipitation totals were for a 24-hour period 4:00 a.m. to 4:00 a.m. Precipitation was as much as 4.68 inches on December 28 at the Willits Howard RS station. On December 31, the day of most intense rainfall over most of northern California, more than 5 inches were recorded at all sites, and the Venado and Willits Howard RS stations recorded 6.81 and 7.12 inches, respectively. Although rainfall intensity on January 2 generally was less than on December 28 and December 31, as much as 3.84 inches was recorded at Venado. Figure 1 shows the areal distribution and amounts of daily rainfall throughout northern California on December 28, 31, and January 2. Storms and Flooding in California in December 2005 and January 2006—A Preliminary Assessment By Charles Parrett and Richard A. Hunrichs

Field and laboratory studies were conducted to determine the effects of pesticide mixtures on Chinook salmon under various environmental conditions in surface waters of the northern Central Valley of California. This project was a collaborative effort between the U.S. Geological Survey (USGS) and the University of California. The project focused on understanding the environmental factors that influence the toxicity of pesticides to juvenile salmon and their prey. Samples were collected to characterize dissolved pesticide and dissolved organic carbon concentrations, and aquatic toxicity, associated with winter storm runoff concurrent with winter run Chinook salmon out-migration. Sites were selected that represented the primary habitat of juvenile Chinook salmon and included major tributaries within the Sacramento and San Joaquin River Basins and the Sacramento San Joaquin Delta. Water samples were collected daily for a period of seven days during two winter storm events in each year.

As part of a collaborative study involving the United States Geological Survey Toxics Substances Hydrology Project (Toxics Project) and the University of California Davis Bodega Marine Laboratory (BML) water samples were collected at three sites within the San Joaquin River Basin of California and analyzed for dissolved pesticides. Samples were collected during and immediately after the first significant rainfall (greater than 0.5 inch per day) following the local application of dormant spray organophosphate insecticides during the winters of 2000 and 2001. All samples were collected in conjunction with fish-caging experiments conducted by BML researchers. Sites included two locations potentially affected by runoff of agricultural chemicals (San Joaquin River near Vernalis California and Orestimba Creek at River Road near Crows Landing California and one control site located upstream of pesticide input (Orestimba Creek at Orestimba Creek Road near Newman California). During these experiments fish were placed in cages and exposed to storm runoff for up to ten clays. Following exposure the fish were examined for acetylcholinesterase concentrations and overall genetic damage. Water samples were collected throughout the rising limb of the stream hydrograph at each site for later pesticide analysis. Concentrations of selected pesticides were measured in filtered water samples using solid phase extraction (SPE) and gas chromatgraphy-mass spectrometry (GC/MS) at the U.S. Geological Survey organic chemistry laboratory in Sacramento, California. Results of these analyses are presented.

The San Jose 30 x 60-minute quadrangle straddles the California Coast Ranges southeast of San Francisco, and extends from west of the San Andreas fault near Santa Cruz on the southwest (long. -122°, lat. 37°) to the San Joaquin River in the Central Valley on the northeast (long. -121°, lat. 37.5°). The map is a new geologic compilation that is based on extensive previous work by many authors and a great deal of new mapping, largely at 1:24,000, much of which is previously unpublished. This report presents the preliminary geologic map of the San Jose 30 x 60-minute quadrangle at a scale of 1:100,000, and consists of a spatial database of nine layers, two colored map sheets (geologic map and correlation diagram), and a descriptive text.

Suspended sediment samples were collected in westside tributaries and the main stem of the San Joaquin River, California, in June 1994 during the irrigation season and in January 1995 during a winter storm. These samples were analyzed for 15 organochlorine pesticides to determine their occurrence and their concentrations on suspended sediment and to compare transport during the irrigation season (April to September) to transport during winter storm runoff (October to March). Ten organochlorine pesticides were detected during the winter storm runoff; seven during the irrigation season. The most frequently detected organochlorine pesticides during both sampling periods were p,p'-DDE, p,p'-DDT, p,p'-DDD, dieldrin, toxaphene, and chlordane. Dissolved samples were analyzed for three organochlorine pesticides during the irrigation season and for 15 during the winter storm. Most calculated total concentrations of p,p'-DDT, chlordane, dieldrin, and toxaphene exceeded chronic criteria for the protection of freshwater aquatic life. At eight sites in common between sampling periods, suspended sediment concentrations and streamflow were greater during the winter storm runoff - median concentration of 3,590 mg/L versus 489 mg/L and median streamflow of 162 ft 3 /s versus 11 ft 3 /s. Median concentrations of total DDT (sum of p,p'-DDD, p,p'-DDE, and p,p'-DDT), chlordane, dieldrin, and toxaphene on suspended sediment were slightly greater during the irrigation season, but instantaneous loads of organochlorine pesticides at the time of sampling were substantially greater during the winter storm. Estimated loads for the entire irrigation season exceeded estimated loads for the January 1995 storm by about 2 to 4 times for suspended transport and about 3 to 11 times for total transport. However, because the mean annual winter runoff is about 2 to 4 times greater than the runoff during the January 1995 storm, mean winter transport may be similar to irrigation season transport. This conclusion is tentative primarily because of insufficient information on long-term seasonal variations in suspended sediment and organochlorine concentrations. Nevertheless, runoff from infrequent winter storms will continue to deliver a significant load of sediment-bound qrganochlorine pesticides to the San Joaquin River even if irrigation-induced sediment transport is reduced. As a result, concentrations of organochlorine pesticides in San Joaquin River biota will continue to be relatively high compared to other regions of the United States.

Alameda County is located at the northern end of the Diablo Range of Central California. It is bounded on the north by the south flank of Mount Diablo, one of the highest peaks in the Bay Area, reaching an elevation of 1173 meters (3,849 ft). San Francisco Bay forms the western boundary, the San Joaquin Valley borders it on the east and an arbitrary line from the Bay into the Diablo Range forms the southern boundary. Alameda is one of the nine Bay Area counties tributary to San Francisco Bay. Most of the country is mountainous with steep rugged topography. Alameda County is covered by twenty-eight 7.5' topographic Quadrangles which are shown on the index map (alq_quad or Sheet 2). The Quaternary deposits in Alameda County comprise three distinct depositional environments. One, forming a transgressive sequence of alluvial fan and fan-delta facies, is mapped in the western one-third of the county. The second, forming only alluvial fan facies, is mapped in the Livermore Valley and San Joaquin Valley in the eastern part of the county. The third, forming a combination of Eolian dune and estuarine facies, is restricted to the Alameda Island area in the northwestern corner of the county.

Contra Costa County is located at the northern end of the Diablo Range of Central California. It is bounded on the north by Carquinez Strait, through which flows 27 percent of California's surface water runoff. San Francisco Bay forms the western boundary, the San Joaquin Valley borders it on the east and the Livermore Valley forms the southern boundary. Contra Costa is one of the nine Bay Area counties with streams that are tributaries to San Francisco Bay. Most of the county is mountainous with steep rugged topography. Mount Diablo, in the center of the county, is one of the highest peaks in the Bay Area, reaching an elevation of 1173 meters (3,849 ft). Contra Costa County is covered by twenty-five 7.5' topographic Quadrangles shown on the index map (ccq_quad or Sheet 2). However, two of the quadrangles (Hayward and Petaluma Point) contain no Quaternary deposits in Contra Costa County, and so are not discussed herein. The Quaternary deposits in Contra Costa County comprise two distinct depositional environments. One, forming a transgressive sequence of alluvial fan and fan-delta deposits, is mapped in the western four-fifths of the county. The second, forming a combination of eolian dune and river delta deposits, is mapped in the San Joaquin Valley in the eastern part of the county.

From 1992 through 1994, the San Joaquin-Tulare Basins Study team of the USGS National Water Quality Assessment program investigated the occurrence and distribution of water quality constituents in shallow groundwater underlying two areas of different agricultural land uses: almond orchards and vineyards. The study was restricted to the alluvial fans of the eastern San Joaquin Valley, the area of most groundwater use in the valley. A geographic information system (GIS) was used to delineate the distribution of the two target land uses, to evaluate ancillary data, and to select candidate wells that fit prescribed criteria. Twenty domestic water supply wells were sampled in each of the two areas. In addition, pairs of observation wells were installed and sampled at five of the sites in each area to evaluate whether the water quality in the domestic wells reflects that of the shallow groundwater underlying the target land use. A preliminary evaluation of the results shows that nitrate concentrations in the shallow groundwater are significantly higher in the almond orchard areas than in the vineyard area (p=0.005). In contrast, concentrations of l,2-dibromo-3- chloropropane (DBCP) were higher in the vineyard area than in the almond orchard area (/?=0.032). The most frequently detected pesticides in groundwater underlying both areas were simazine, atrazine, and desethylatrazine (an atrazine degradation product). These observations are explained, in part, by differences in chemical application and hydrogeologic factors.

Specific objectives of the report are (1) to provide an overview of the nature and variability of the major-ion chemistry of ground water in the study area, (2) to examine the age and origin of ground water in different parts of the ground-water-flow system by using environmental isotopes and supporting major-ion chemistry, (3) to describe the distribution of selected trace elements in the ground-water-flow system in relation to the dominant factors and processes that affect them, and (4) to assess the relations among major ions and trace elements in ground water by using multivariate analyses and the consistency of these relations with the distributions of major ions and trace elements. The report focuses on the distribution of arsenic, boron, molybdenum, and selenium, the elements most likely to affect ground-water quality in the area.