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USGS1998

Water-quality assessment of the Central Arizona Basins, Arizona and northern Mexico – Environmental setting and overview of water quality

The Central Arizona Basins study area in central and southern Arizona and northern Mexico is one of 60 study units that are part of the U.S. Geological Survey's National Water-Quality Assessment program. The purpose of this report is to describe the physical, chemical, and environmental characteristics that may affect water quality in the Central Arizona Basins study area and present an overview of water quality. Covering 34,700 square miles, the study area is characterized by generally north to northwestward-trending mountain ranges separated by broad, gently sloping alluvial valleys. Most of the perennial rivers and streams are in the northern part of the study area. Rivers and streams in the south are predominantly intermittent or ephemeral and flow in response to precipitation such as summer thunderstorms. Effluent-dependent streams do provide perennial flow in some reaches. The major aquifers in the study area are in the basin-fill deposits that may be as much as 12,000 feet thick. The 1990 population in the study area was about 3.45 million, and about 61 percent of the total was in Maricopa County (Phoenix and surrounding cities). Extensive population growth over the past decade has resulted in a twofold increase in urban land areas and increased municipal water use; however, agriculture remains the major water use. Seventy-three percent of all water with drawn in the study area during 1990 was used for agricultural purposes. The largest rivers in the study area-the Gila, Salt, and Verde-are perennial near their headwaters but become intermittent downstream because of impoundments and artificial diversions. As a result, the Central Arizona Basins study area is unique compared to less arid basins because the mean surface-water outflow is only 528 cubic feet per second from a total drainage area of 49,650 square miles. Peak flows in the northern part of the study area are the result of snowmelt runoff; whereas, summer thunderstorms account for the peak flows in the southern part. Ground water is the primary water supply in most of Arizona and the only source of drinking water used by communities in the southern half of the study area. Years of overpumping have caused water tables in basin fill to drop below once-perennial streams leaving streambeds dry, water too deep to pump economically, pumping of poorer quality water with depth, and earth fissures resulting from subsidence after dewatering of sediments. Natural processes-such as leaching of trace elements and major ions from geologic formations-and human activities-such as mining, agriculture, and urban development-have major effects on the quality of surface-water and ground-water resources in the Central Arizona Basins study area. Surface-water quality standards in Arizona are based on the designated use of the water such as full or partial body contact, fish consumption, aquatic and wildlife uses, and agriculture. Maintaining the biological integrity (health) of surface waters in Arizona is an important part of ensuring that these waters are suitable for designated uses. Important water-quality issues for surface water that are somewhat unique to Arizona include: (1) streamflows and riparian environments sustained by effluent from municipal wastewater-treatment plants that contains high concentrations of nutrients, potentially toxic trace elements and organic compounds, and fecal bacteria; (2) industrial, mining, agricultural, and municipal sources of contamination from Mexico; and (3) unpredictable high flows from major summer thunder storms causing stream-channel changes; high suspended-sediment concentrations and loads; sewage overflows; and breaching, erosion, and washout of landfills and mining operations. The quality of water in aquifers that are protected for drinking- water use is subject to standards that are in most cases equal to or more stringent than the primary drinking-water regulations of the U.S. Environmental Protection Agency. The general che

Arizona↗

USGS1996

Seasonal fluctuations of water quality in San Francisco Bay during the first three years of the regional monitoring program, 1993-1995

The 1995 Regional Monitoring Program (RMP) Annual Report includes monitoring results from the Base Program, Pilot and Special Studies, and summary and perspective articles contributed by RMP investigators and other scientists. The purpose of the RMP is to provide information on the status and trends of contamination in San Francisco Estuary water, sediment, and bivalve tissue, and to assess the potential for biological effects from exposure to those contaminants. The objectives, background, and rationale for the RMP are described in the Introduction (Chapter 1). The 1995 RMP Base Program was essentially the same as in 1994. Water monitoring was conducted in February, April, and August at 24 stations throughout the Estuary. Aquatic bioassays were conducted in February and August at 13 of those stations. Sediment monitoring was conducted in February and August at all 24 stations, and sediment bioassays were conducted at 12 of those stations. Bioaccumulation of contaminants by transplanted bivalves was monitored at 15 stations during two 90 day sampling periods: January to April and July to September. Pilot Studies on benthic fauna and tidal wetlands were conducted and Special Studies on trends in trace elements and development of sediment indicators were also included.

California↗

USGS2012

Status of groundwater quality in the California Desert Region, 2006-2008: California GAMA Priority Basin Project

Groundwater quality in six areas in the California Desert Region (Owens, Antelope, Mojave, Coachella, Colorado River, and Indian Wells) was investigated as part of the Priority Basin Project of the Groundwater Ambient Monitoring and Assessment (GAMA) Program. The GAMA Priority Basin Project is being conducted by the California State Water Resources Control Board in collaboration with the U.S. Geological Survey (USGS) and the Lawrence Livermore National Laboratory. The six Desert studies were designed to provide a spatially unbiased assessment of the quality of untreated groundwater in parts of the Desert and the Basin and Range hydrogeologic provinces, as well as a statistically consistent basis for comparing groundwater quality to other areas in California and across the Nation. Samples were collected by the USGS from September 2006 through April 2008 from 253 wells in Imperial, Inyo, Kern, Los Angeles, Mono, Riverside, and San Bernardino Counties. Two-hundred wells were selected using a spatially distributed, randomized grid-based method to provide a spatially unbiased representation of the study areas (grid wells), and fifty-three wells were sampled to provide additional insight into groundwater conditions (additional wells). The status of the current quality of the groundwater resource was assessed based on data from samples analyzed for volatile organic compounds (VOCs), pesticides, and inorganic constituents such as major ions and trace elements. Water-quality data from the California Department of Public Health (CDPH) database also were incorporated in the assessment. The status assessment is intended to characterize the quality of untreated groundwater resources within the primary aquifer systems of the Desert Region, not the treated drinking water delivered to consumers by water purveyors. The primary aquifer systems (hereinafter, primary aquifers) in the six Desert areas are defined as that part of the aquifer corresponding to the perforation intervals of wells listed in the CDPH database. Relative-concentrations (sample concentration divided by the benchmark concentration) were used as the primary metric for evaluating groundwater quality for those constituents that have Federal and (or) California benchmarks. A relative-concentration (RC) greater than (>) 1.0 indicates a concentration above a benchmark, and an RC less than or equal to (≤) 1.0 indicates a concentration equal to or below a benchmark. Organic and special-interest constituent RCs were classified as “low” (RC ≤ 0.1), “moderate” (0.1 < RC ≤ 1.0), or “high” (RC > 1.0). Inorganic constituent RCs were classified as “low” (RC ≤ 0.5), “moderate” (0.5 < RC ≤ 1.0), or “high” (RC > 1.0). A lower threshold value RC was used to distinguish between low and moderate RCs for organic constituents because these constituents are generally less prevalent and have smaller RCs than inorganic constituents. Aquifer-scale proportion was used as the primary metric for evaluating regional-scale groundwater quality. High aquifer-scale proportion was defined as the percentage of the area of the primary aquifers with an RC greater than 1.0 for a particular constituent or class of constituents; percentage is based on an areal rather than a volumetric basis. Moderate and low aquifer-scale proportions were defined as the percentage of the primary aquifers with moderate and low RCs, respectively. Two statistical approaches—grid-based and spatially weighted—were used to evaluate aquifer-scale proportions for individual constituents and classes of constituents. Grid-based and spatially weighted estimates were comparable in the Desert Region (within 90 percent confidence intervals). The status assessment determined that one or more inorganic constituents with health-based benchmarks had high RCs in 35.4 percent of the Desert Region’s primary aquifers, moderate RCs in 27.4 percent, and low RCs in 37.2 percent. The inorganic constituents with health-based benchmarks having the largest high aquifer-scale proportions were arsenic (17.8 percent), boron (11.4 percent), fluoride (8.9 percent), gross-alpha radioactivity (6.6 percent), molybdenum (5.7 percent), strontium (3.7 percent), vanadium (3.6 percent), uranium (3.2 percent), and perchlorate (2.4 percent). Inorganic constituents with non-health-based benchmarks were also detected at high RCs in 18.6 percent and at moderate RCs in 16.0 percent of the Desert Region’s primary aquifers. In contrast, organic constituents had high RCs in only 0.3 percent of the Desert Region’s primary aquifers, moderate in 2.0 percent, low in 48.0 percent, and were not detected in 49.7 percent of the primary aquifers in the Desert Region. Of 149 organic constituents analyzed for all six study areas, 42 constituents were detected. Six organic constituents, carbon tetrachloride, chloroform, 1,2-dichloropropane, dieldrin, 1,2-dichloroethane, and tetrachloroethene, were found at moderate RCs in one or more of the grid wells. One constituent, N -nitrosodimethylamine, a special-interest VOC, was detected at a high RC in one well. Thirty-nine organic constituents were detected only at low concentrations. Three organic constituents were frequently detected (in more than 10 percent of samples from grid wells): chloroform, simazine, and deethylatrazine.

California↗

USGS2002

Reconnaissance-level assessment of water quality near Flandreau, South Dakota

This report presents water-quality data that have been compiled and collected for a reconnaissance-level assessment of water quality near Flandreau, South Dakota. The investigation was initiated as a cooperative effort between the U.S. Geological Survey and the Flandreau Santee Sioux Tribe. Members of the Flandreau Santee Sioux Tribe have expressed concern that Tribal members residing in the city of Flandreau experience more health problems than the general population in the surrounding area. Prior to December 2000, water for the city of Flandreau was supplied by wells completed in the Big Sioux aquifer within the city of Flandreau. After December 2000, water for the city of Flandreau was supplied by the Big Sioux Community Water System from wells completed in the Big Sioux aquifer along the Big Sioux River near Egan, about 8 river miles downstream of Flandreau. There is some concern that the public and private water supplies provided by wells completed in the Big Sioux aquifer near the Big Sioux River may contain chemicals that contribute to the health problems. Data compiled from other investigations provide information about the water quality of the Big Sioux River and the Big Sioux aquifer in the Flandreau area from 1978 through 2001. The median, minimum, and maximum values are presented for fecal bacteria, nitrate, arsenic, and atrazine. Nitrate concentrations of water from Flandreau public-supply wells occasionally exceeded the Maximum Contaminant Level of 10 milligrams per liter for public drinking water. For this study, untreated-water samples were collected from the Big Sioux River in Flandreau and from five wells completed in the Big Sioux aquifer in and near Flandreau. Treated-water samples from the Big Sioux Community Water System were collected at a site about midway between the treatment facility near Egan and the city of Flandreau. The first round of sampling occurred during July 9-12, 2001, and the second round of sampling occurred during August 20-27, 2001. Samples were analyzed for a broad range of compounds, including major ions, nutrients, trace elements, pesticides, antibiotics, and organic wastewater compounds, some of which might cause adverse health effects after long-term exposure. Samples collected on August 27, 2001, from the Big Sioux River also were analyzed for human pharmaceutical compounds. The quality of the water in the Big Sioux River and the Big Sioux aquifer in the Flandreau area cannot be thoroughly characterized with the limited number of samples collected within a 2-month period, and for many analytes, neither drinking-water standards nor associations with adverse health effects have been established. Concentrations of some selected analytes were less than U.S. Environmental Protection Agency drinking-water standards at the time of the sampling, and concentrations of most organic compounds were less than the respective method reporting levels for most of the samples.

South Dakota↗

USGS2021

Near-field receiving-water monitoring of trace metals and a benthic community near the Palo Alto Regional Water Quality Control Plant in south San Francisco Bay, California—2019

Trace-metal concentrations in sediment and in the clam Limecola petalum (formerly reported as Macoma balthica and M. petalum ), clam reproductive activity, and benthic macroinvertebrate community structure were investigated in a mudflat 1 kilometer south of the discharge of the Palo Alto Regional Water Quality Control Plant (PARWQCP) in south San Francisco Bay, Calif. This report includes the data collected by the U.S. Geological Survey (USGS) for the period January 2019 to December 2019. These data append to long-term datasets extending back to 1974. A major focus of the report is an integrated description of the 2019 data within the context of the longer, multidecadal dataset. This dataset supports the City of Palo Alto’s Near-Field Receiving-Water Monitoring Program, initiated in 1994. Significant reductions in silver and copper contamination occurred at the site in the 1980s following the implementation by PARWQCP of advanced wastewater treatment and source control measures. Since the 1990s, concentrations of these elements in surface sediments have continued to decrease, although more slowly. Silver appears to have stabilized at concentrations about twice the regional background concentration. Presently, sediment copper concentrations appear to be near the regional background level. Over the same period (1994–2019), sedimentary iron and zinc also exhibited modest declines. Sedimentary aluminum, chromium, mercury, nickel, and selenium have not exhibited any trend. Since 1994, concentrations of silver and copper in L. petalum have varied seasonally, apparently in response to a combination of site-specific metal exposures and cyclic growth and reproduction, as reported previously. Seasonal patterns for other elements, including chromium, mercury, nickel, selenium, and zinc, were generally similar in timing and magnitude as those for silver and copper. The annual growth and reproductive cycle explained a small amount of the variance in annual silver and zinc tissue metal concentrations. However, interannual trends are not apparent for any element. Biological effects of elevated silver and copper contamination at the Palo Alto site have been interpreted from data collected during and after the recession of these contaminants. Concentrations of both elements in the soft tissues of L. petalum declined with sedimentary copper and silver. This pattern was associated with changes in the reproductive activity of L. petalum , as well as the structure of the benthic invertebrate community. Reproductive activity of L. petalum increased as metal concentrations in L. petalum declined and presently is stable with almost all animals initiating reproduction in the fall and spawning the following spring. Analyses of the benthic community structure indicate that the infaunal invertebrate community has shifted from one dominated by several opportunistic species when silver and copper exposures were highest to one in which the species abundance is more evenly distributed, a pattern that indicates a more stable community that is subjected to fewer stressors. Importantly, this long-term change is unrelated to other metals and other measured environmental factors, including salinity and sediment composition. In addition, two of the opportunistic species ( Ampelisca abdita and Streblospio benedicti ) that brood their young and live on the surface of the sediment in tubes have shown a continual decline in dominance coincident with the decline in metals. Both species had short-lived rebounds in abundance in 2008, 2009, and 2010 and showed signs of increasing abundance in 2019. Heteromastus filiformis (a subsurface polychaete worm that lives in the sediment, consumes sediment and organic particles residing in the sediment, and reproduces by laying its eggs on or in the sediment) showed a concurrent increase in dominance and, in the last several years before 2008, showed a stable population. H. filiformis abundance increased slightly in 2011–2012 and returned to pre-2011 numbers in 2019. An unidentified disturbance occurred on the mudflat in early 2008 that resulted in the loss of the benthic animals, except for deep-dwelling animals like L. petalum . However, within two months of this event, animals returned to the mudflat. The resilience of the community suggested that the disturbance was not caused by a persistent toxin or anoxia. The reproductive mode of most species that were present in 2019 was indicative of species that were available either as pelagic larvae or as mobile adults. Although oviparous species were lower in number in this group, the authors hypothesize that these species will return slowly as more species move back into the area. The use of functional ecology was highlighted in the 2019 benthic community data, which showed that the animals that have now returned to the mudflat are those that can respond successfully to a physical, nontoxic disturbance. Today, community data show a mix of species that consume the sediment, or filter feed, those that have pelagic larvae that must survive landing on the sediment, and those that brood their young. USGS scientists view the 2008 disturbance event as a response by the infaunal community to an episodic natural stressor (possibly sediment accretion or a pulse of freshwater), in contrast to the long-term recovery from metal contamination. We will compare this recovery to the long-term recovery observed after the 1970s when the decline in sediment pollutants was the dominating factor.

California↗

USGS1955

A reconnaissance for uranium in carbonaceous rocks in southwestern Colorado and parts of New Mexico

Coal and carbonaceous shale of the Dakota formation of Cretaceous age were examined for radioactivity in the Colorado Plateau of southwestern Colorado and northwestern New l1exico during the summer of 1953. Older and younger sedimentary rocks and some igneous rocks also were examined, but in less detail, Weak radioactivity was detected at many places but no new deposits of apparent economic importance were discovered. The highest radioactivity of carbonaceous rocks was detected in black shale, siltstone, and sandstone of the Paradox member of the Hermosa formation of Pennsylvanian age. A sample collected from this member at the Bald Eagle prospect in Gypsum Valley, San Higuel County, Colo. contains 0.10. percent uranium. Carbonaceous rocks were investigated at several localities on the Las Vegas Plateau and the Canadian Escarpment in Harding and San Miguel Counties, northeastern New Mexico. Carbonaceous sandstone and siltstone in the middle sandstone member of the Chinle formation of Triassic age contain uranium at a prospect of the Hunt Oil Company southwest of Sabinoso in northeastern San Miguel County, N. Mex. A channel sample across 3.2 feet of mineralized rocks at this locality contains 0.22 percent uranium. Weak radioactivity was detected at two localities in carbonaceous shale of the Dakota and Purgatoire formations of Cretaceous age.

Trace Elements Memorandum↗

USGS1980

Geochemical-exploration studies in the Coeur d'Alene district, Idaho and Montana

The principal ore deposits in the Coeur d'Alene district are lead-zinc-silver replacement veins in Precambrian rocks of the Belt Supergroup. The main ore minerals are galena, tetrahedrite, and sphalerite. The host rocks are mainly quartzite, siltite, and argillite. Cretaceous quartz monzonite locally intrudes the Beltrocks. The geochemical investigations reported here were carried out to determine if geochemical methods would be useful in the search for concealed ore deposits. About 8,700 soil samples and 4,000 rock samples were collected from a 300-square-mile (780 square kilometer) area for this study. The samples were analyzed for 35 elements. Antimony, silver, lead, manganese, and copper form dispersion patterns and halos that are related to many of the ore deposits within the district, and these same elements were found to be most useful in delineating the known mineral belts that contain most of the orebodies. The dispersion patterns are probably primary, having only minor modifications due to secondary redistribution of the ore-forming elements. The mineral belts and geochemical-dispersion patterns have been laterally offset, perhaps as much as 16 miles (26 km), by postore faulting. Prefault dispersion patterns can be restored by adjusting the geochemical maps along the postore faults to match the dispersion patterns across the fault trace. The reconstructed dispersion patterns of antimony, arsenic, lead, sulfur, and the ratio of cadmium to zinc form concentric halos around the restored position of the Gem stocks. Most of the Coeur d'Alene ore has been mined from this halo. It appears that the geochemical exploration methods reported here successfully delineate the major mineral belts and indicate unexplored areas in which to search for new deposits.

Idaho, Montana↗

USGS2015

Status and understanding of groundwater quality in the Cascade Range and Modoc Plateau study unit, 2010: California GAMA Priority Basin Project

Groundwater quality in the Cascade Range and Modoc Plateau study unit was investigated as part of the California State Water Resources Control Board’s Groundwater Ambient Monitoring and Assessment (GAMA) Program Priority Basin Project. The study was designed to provide a statistically unbiased assessment of untreated groundwater quality in the primary aquifer system. The depth of the primary aquifer system for the Cascade Range and Modoc Plateau study unit was delineated by the depths of the screened or open intervals of wells in the State of California’s database of public-supply wells. Two types of assessments were made: a status assessment that described the current quality of the groundwater resource, and an understanding assessment that made evaluations of relations between groundwater quality and potential explanatory factors representing characteristics of the primary aquifer system. The assessments characterize the quality of untreated groundwater, not the quality of treated drinking water delivered to consumers by water distributors. The status assessment was based on water-quality data collected in 2010 by the U.S. Geological Survey from 90 wells and springs (USGS-grid wells) and on water-quality data compiled from the State of California’s regulatory compliance database for samples collected from 240 public-supply wells between September 2007 and September 2010. To provide context, the water-quality data discussed in this report were compared to California and Federal drinking-water regulatory and non-regulatory benchmarks for treated drinking water. Groundwater quality is defined in terms of relative concentrations (RCs), which are calculated by dividing the concentration of a constituent in groundwater by the concentration of the benchmark for that constituent. The RCs for inorganic constituents (major ions, trace elements, nutrients, and radioactive constituents) were classified as “high” (the RC is greater than 1.0, indicating that the concentration is above the benchmark), “moderate” (the RC is from 1.0 to greater than 0.5), or “low” (the RC is less than or equal to 0.5). For organic constituents (volatile organic compounds and pesticides) and special-interest constituents (perchlorate), the boundary between moderate and low RCs was set at 0.1. All benchmarks used for organic constituents were health-based. For inorganic constituents, health-based and aesthetic-based benchmarks were used. Constituents without benchmarks were not considered in the status assessment . The primary metric used for quantifying regional-scale groundwater quality was the aquifer-scale proportion—the areal percentages of the primary aquifer system with high, moderate, and low RCs for a given constituent or class of constituents. The study unit was divided into six study areas on the basis of geologic differences (Eastside Sacramento Valley, Honey Lake Valley groundwater basin, Cascade Range and Modoc Plateau Low Use Basins, Quaternary Volcanic Areas, Shasta Valley and Mount Shasta Volcanic Area, and Tertiary Volcanic Areas), and each study area was divided into equal-area grid cells. Aquifer-scale proportions were calculated for individual constituents and constituent classes for each of the six study areas and for the study unit as a whole by using grid-based (one well per cell) and spatially weighted (many wells per cell) statistical methods. The status assessment showed that inorganic constituents were present at high and moderate RCs in greater proportions of the Cascade Range and Modoc Plateau study unit than were organic constituents. One or more inorganic constituents with health-based benchmarks were present at high RCs in 9.4 percent, and at moderate RCs in 14.7 percent of the primary aquifer system. Arsenic was present at high RCs in approximately 3 percent of the primary aquifer system; boron, molybdenum, uranium, and vanadium each were present at high RCs in approximately 2 percent of the primary aquifer system. One or more inorganic constituents with aesthetic-based benchmarks were present at high RCs in 15.1 percent of the primary aquifer system and at moderate RCs in 4.9 percent. Manganese, iron, and total dissolved solids were present at high RCs in approximately 12 percent, 5 percent, and 2 percent, respectively, of the primary aquifer system. Organic constituents were not detected at high or moderate RCs in the primary aquifer system, and one or more organic constituents were detected at low RCs in approximately 40 percent of the primary aquifer system. Two classes of organic constituents were detected in more than 10 percent of the primary aquifer system: trihalomethanes (chloroform only) and herbicides. The special interest constituent perchlorate was not detected at high RCs, but was detected at moderate RCs in approximately 2 percent of the primary aquifer system. The understanding assessment relied on statistical tests to evaluate relations between concentrations of constituents and values of potential explanatory factors representing geology, land use, well construction, hydrologic conditions, groundwater age, and geochemical conditions. The majority of the high and moderate RCs of arsenic, boron, molybdenum, uranium, and total dissolved solids were in samples from the Honey Lake Valley groundwater basin study area. Groundwater mixing with hydrothermal fluids present in the study area, evaporative concentration of groundwater in the Honey Lake playa, presence of uranium-bearing sediment derived from the adjacent Sierra Nevada, and release of arsenic and other trace elements from sediments under high pH and low dissolved oxygen conditions all appeared to contribute to these elevated concentrations. Thermal springs are in many parts of the Cascade Range and Modoc Plateau study unit and could account for locally elevated concentrations of arsenic, boron, molybdenum, and total dissolved solids in samples from the other study areas. Vanadium concentrations were greater in oxic samples than in anoxic samples, but were not correlated with pH, contrary to expectations from previous studies. Organic constituents were not detected at high or moderate RCs, and the occurrence of low organic constituents at low RCs ranged from 27 percent to 73 percent of the primary aquifers system in the six study areas. The Shasta Valley and Mount Shasta Volcanic study area had significantly greater occurrence of low RCs of herbicides compared to all of the other study areas, which could reflect the greater prevalence of modern groundwater in the Shasta Valley and Mount Shasta Volcanic study area and the presence of potential sources of herbicides, including applications to timberlands and roadside rights-of-way. The Eastside Sacramento Valley study area had the greatest occurrence of low concentrations of chloroform, and chloroform occurrence was most strongly associated with the combination of septic-tank density greater than two tanks per square kilometer and urban land use greater than 10 percent within a radius of 500 meters of the well. These conditions were most prevalent in the Eastside Sacramento Valley study area. The detection frequency of low concentrations of perchlorate was consistent with the probability of occurrence expected under natural conditions, except in the Eastside Sacramento Valley study area, where detection frequencies were much higher than expected and could not be explained by known anthropogenic sources of perchlorate.

California↗

USGS2005

Mass loading of selected major and trace elements in Lake Fork Creek near Leadville, Colorado, September-October 2001

A mass-loading study of Lake Fork Creek of the Arkansas River between Sugarloaf Dam and the mouth was completed in September-October 2001 to help ascertain the following: (1) variation of pH and aqueous constituent concentrations (calcium, sulfate, alkalinity, aluminum, cadmium, copper, iron, manganese, lead, and zinc) and their relation to toxicity standards along the study reach; (2) location and magnitude of sources of metal loading to Lake Fork Creek; (3) amount and locations of metal attenuation; (4) the effect of streamside wetlands on metal transport from contributing mine tunnels; and (5) the effect of organic-rich inflow from the Leadville National Fish Hatchery on water quality in Lake Fork Creek. The study was done in cooperation with the Bureau of Land Management, U.S. Department of Agriculture Forest Service, and U.S. Fish and Wildlife Service. Constituent concentrations and pH showed variable patterns over the study reach. Hardness-based acute and chronic toxicity standards were exceeded for some inflows and some constituents. However, stream concentrations did not exceed standards except for zinc starting in the upper parts of the study reach and extending to just downstream from the inflow from the Leadville National Fish Hatchery. Dilution from that inflow lowered stream zinc concentrations to less than acute and chronic toxicity standards. The uppermost 800 meters of the study reach that contained inflow from the Bartlett, Dinero, and Nelson mine tunnels and the Dinero wetland was the greatest source of loading for manganese and zinc. A middle section of the study reach that extended approximately 2 kilometers upstream from the National Fish Hatchery inflow to just downstream from that inflow was the largest source of aluminum, copper, iron, and lead loading. The loading was partially from the National Fish Hatchery inflow but also from unknown sources upstream from that inflow, possibly ground water. The largest sources for calcium and sulfate load to the stream were the parts of the study reach containing inflow from the tribu-taries Halfmoon Creek (calcium) and Willow Creek (sulfate). The Arkansas River and its tributaries upstream from Lake Fork Creek were the source of most of the calcium (70 percent), sulfate (82 percent), manganese (77 percent), lead (78 percent), and zinc (95 percent) loads in the Arkansas River downstream from the Lake Fork confluence. In contrast, Lake Fork Creek was the major source of aluminum (68 percent), copper (65 percent), and iron (87 percent) loads to the Arkansas River downstream from the confluence. Attenuation was not important for calcium, sulfate, or iron. However, other metals loads were reduced up to 81 percent over the study reach (aluminum, 25 percent; copper, 20 percent; manganese, 81 percent; lead, 30 percent; zinc, 72 percent). Metal attenuation in the stream occurred primarily in three locations (1) the irrigation diversion ditch; (2) the beaver pond complex extending from upstream from the Colorado Gulch inflow to just downstream from that inflow; and (3) the stream reach that included the inflow from Willow Creek. The most likely attenuation mechanism is precipitation of metal oxides and hydroxides (primarily manganese), and sorption or coprecipitation of trace elements with the precipitating phase. A mass-balance calculation indicated that the wetland between the Dinero Tunnel and Lake Fork Creek removed iron, had little effect on zinc mass load, and was a source for, or was releasing, aluminum and manganese. In contrast, the wetland that occurred between the Siwatch Tunnel and Lake Fork Creek removed aluminum, iron, manganese, and zinc from the tunnel drainage before it entered the creek. Inflow from the National Fish Hatchery increased dissolved organic carbon concentrations in Lake Fork Creek and slightly changed the composition of the dissolved organic carbon. However, dissolved organic carbon loads increased in the stream reach downs

Colorado↗

USGS2025

Chemostratigraphy of the Cretaceous Hue Shale in Arctic Alaska: Exploring paleoceanographic controls on trace element enrichment, organic matter accumulation, and source-rock evolution

We document chemostratigraphy in an outcrop of late Albian to early Campanian (∼103–82 Ma) marine source rocks to better understand paleoenvironmental controls on trace element (TE) enrichment and organic matter accumulation in the distal Colville foreland basin of Arctic Alaska and how those drivers are linked to arc volcanism and successions of Cretaceous oceanographic and climatic biogeochemical events. This unique, 113-m-thick section of Cretaceous Hue Shale deposited during a series of previously undocumented Arctic Cretaceous oceanic anoxic events (Lease et al., 2024) is the only known exposure of thermally immature (0.48–0.52% R o , random vitrinite reflectance) Hue Shale in Arctic Alaska. Strata comprise mainly clay-rich mudstone with elevated total organic carbon (TOC) and hydrogen index values reaching 26.3 wt% (mean = 7.5 wt%) and 689 mg hydrocarbon (HC)/g TOC (mean = 385 mg HC/g TOC), respectively. Maceral composition consists predominantly of fluorescent amorphous organic matter, with abundant brightly fluorescent alginite, including Tasmanites , acritarchs, and Leiosphaeridia . Discrete layers of volcanic ash (preserved as bentonite) are present throughout the section and provide quantitative age control based on U–Pb dates. Chemostratigraphic trends are investigated to advance our understanding of local oceanographic conditions and controls on stratigraphic and temporal heterogeneity of Brookian source rocks. Concurrent sedimentary enrichment in Mo, U, V, Pb, and Cu across the Albian–Cenomanian boundary of the exposed basal gamma-ray zone, may reflect anoxic to euxinic benthic redox conditions favoring organic matter accumulation and preservation. Fluctuating degrees of anoxia-euxinia are inferred throughout the overlying Hue Shale succession, reflected by varying patterns of TE enrichment and TE–TOC covariation. Elevated C org /P molar ratios (>250) across most of the section, with several values exceeding 690, signify that enhanced biological productivity is sustained throughout deposition. Enhanced productivity, recorded by both C org /P and excess Ba, also parallels increases in source rock richness (elevated TOC and S 2 values) during the late Albian–early Cenomanian and late Cenomanian – Turonian. Enhanced productivity and variations in oceanic circulation/stratification likely both drove changes in benthic redox conditions that favored organic carbon accumulation and preservation. Increased continental arc volcanism (e.g., Okhotsk–Chukotka volcanic belt) and High Arctic Large Igneous Province magmatic eruptions throughout the Cretaceous, inferred to have influenced nutrient cycling and local aqueous nutrient availability, also have been invoked as potential drivers of organic carbon burial and source-rock development across the sedimentary sequence. Results presented here document the organic-rich and oil-prone source-rock quality of the Hue Shale in the distal part of the Colville foreland basin and bolster the potential for a Cretaceous petroleum system beneath the eastern North Slope.

Alaska↗

USGS1971

Chemical compositions of rock types as factors in our environment

The types of rocks that form geologic units in the Earth’s crust supply most of the raw materials from which soils are formed and from which water derives its inorganic constituents. The compositions of what we eat and drink thus depend in part upon the compositions of the source rocks. Igneous rocks are formed by crystallization and solidification of a rock melt. Metamorphic rocks are formed by recrystallization of both igneous and sedimentary rocks caused by heat and pressure within the Earth’s crust. Sedimentary rocks are formed chiefly by the deposition in water of weathering and erosion products of pre-existing igneous, metamorphic, or other sedimentary rocks. The compositions of metamorphic rocks are generally similar to the compositions of the rocks that were metamorphosed, and only igneous and sedimentary rock compositions are considered here. Igneous rocks range in SiO 2 content from about 40 to nearly 80 percent, and other constituents increase in amount as SiO 2 decreases. The changes in the other constituents are not large, however, except for the quantitatively unimportant least silicic rocks; these contain conspicuously more magnesium and less aluminum than the other kinds of igneous rocks. Sedimentary rocks range in SiO 2 content from nearly zero for the carbonate rocks to almost 100 percent for quartzite and pure sandstone. Shale and clay contain intermediate amounts of SiO 2 and as much as 25 percent AI 2 O 3 , more than any of the igneous rocks. Carbonate rocks are composed mostly of calcium and magnesium carbonates. The contents of individual trace elements vary widely with rock type. Chromium, titanium, nickel, and cobalt are conspicuously concentrated in low-silica igneous rocks that are quantitatively unimportant. Arsenic, iodine, molybdenum, and selenium are conspicuously concentrated in shale and clay. In addition, most other elements occur in largest amounts in shale and clay compared to other sedimentary rocks, and in amounts nearly equal to those in igneous rocks. Soils derived from different kinds of igneous rocks do not differ from each other as much as do soils derived from different kinds of sedimentary rocks. This is partly because igneous rocks generally are more resistant to weathering than sedimentary rocks that were deposited in water. Some of the important constituents of sedimentary rocks have been precipitated from solution, which makes them more susceptible to weathering and re-solution. Similarly, sedimentary rocks have a greater effect than igneous rocks on the composition of ground water. Determination of areal variations in composition should be more detailed than normal petrologic investigations if the results are to be usable for environmental studies. Statistical principles should be used in planning the sampling, analysis, and interpretation of results.

Book chapter↗

USGS2017

Near-field receiving water monitoring of trace metals and a benthic community near the Palo Alto Regional Water Quality Control Plant in south San Francisco Bay, California; 2016

Trace-metal concentrations in sediment and in the clam Macoma petalum (formerly reported as Macoma balthica ), clam reproductive activity, and benthic macroinvertebrate community structure were investigated in a mudflat 1 kilometer south of the discharge of the Palo Alto Regional Water Quality Control Plant (PARWQCP) in south San Francisco Bay, Calif. This report includes the data collected by U.S. Geological Survey (USGS) scientists for the period January 2014 to December 2016. These append to long-term datasets extending back to 1974. A major focus of the report is an integrated description of the 2016 data within the context of the longer, multi-decadal dataset. This dataset supports the City of Palo Alto’s Near-Field Receiving Water Monitoring Program, initiated in 1994. Significant reductions in silver and copper concentrations in sediment and M. petalum occurred at the site in the 1980s following the implementation by PARWQCP of advanced wastewater treatment and source control measures. Since the 1990s, concentrations of these elements appear to have stabilized at concentrations somewhat above (silver) or near (copper) regional background concentrations Data for other metals, including chromium (Cr), mercury (Hg), nickel (Ni), selenium (Se), and zinc (Zn), have been collected since 1994. Over this period, concentrations of these elements have remained relatively constant, aside from seasonal variation that is common to all elements. In 2016, concentrations of silver and copper in M. petalum varied seasonally in response to a combination of site-specific metal exposures and annual growth and reproduction, as reported previously. Seasonal patterns for other elements, including Cr, Ni, Zn, Hg, and Se, were generally similar in timing and magnitude as those for Ag and Cu. This record suggests that legacy contamination and regional-scale factors now largely control sedimentary and bioavailable concentrations of silver and copper, as well as other elements of regulatory interest, at the Palo Alto site. Analyses of the benthic community structure of a mudflat in south San Francisco Bay over a 40-year period show that changes in the community have occurred concurrent with reduced concentrations of metals in the sediment and in the tissues of the biosentinel clam, M. petalum , from the same area. Analysis of M. petalum shows increases in reproductive activity concurrent with the decline in metal concentrations in the tissues of this organism. Reproductive activity is presently stable (2016), with almost all animals initiating reproduction in the fall and spawning the following spring. The entire infaunal community has shifted from being dominated by several opportunistic species to a community where the species are more similar in abundance, a pattern that indicates a more stable community that is subjected to fewer stressors. In addition, two of the opportunistic species ( Ampelisca abdita and Streblospio benedicti ) that brood their young and live on the surface of the sediment in tubes have shown a continual decline in dominance coincident with the decline in metals; both species had short-lived rebounds in abundance in 2008, 2009, and 2010 and showed signs of increasing abundance in 2016. Heteromastus filiformis (a subsurface polychaete worm that lives in the sediment, consumes sediment and organic particles residing in the sediment, and reproduces by laying its eggs on or in the sediment) showed a concurrent increase in dominance and, in the last several years before 2008, showed a stable population. H. filiformis abundance increased slightly in 2011–2012 and returned to pre-2011 numbers in 2016. An unidentified disturbance occurred on the mudflat in early 2008 that resulted in the loss of the benthic animals, except for deep-dwelling animals like Macoma petalum . However, within two months of this event animals returned to the mudflat. The resilience of the community suggested that the disturbance was not due to a persistent toxin or anoxia. The reproductive mode of most species present in 2016 is reflective of species that were available either as pelagic larvae or as mobile adults. Although oviparous species were lower in number in this group, the authors hypothesize that these species will return slowly as more species move back into the area. The use of functional ecology was highlighted in the 2016 benthic community data, which showed that the animals that have now returned to the mudflat are those that can respond successfully to a physical, nontoxic disturbance. Today, community data show a mix of species that consume the sediment, or filter feed, have pelagic larvae that must survive landing on the sediment, and those that brood their young. USGS scientists view the 2008 disturbance event as a response by the infaunal community to an episodic natural stressor (possibly sediment accretion or a pulse of freshwater), in contrast to the long-term recovery from metal contamination. We will compare this recovery to the long-term recovery observed after the 1970s when the decline in sediment pollutants was the dominating factor.

California↗

USGS2018

Near-field receiving-water monitoring of trace metals and a benthic community near the Palo Alto Regional Water Quality Control Plant in south San Francisco Bay, California—2017

Trace-metal concentrations in sediment and in the clam Macoma petalum (formerly reported as Macoma balthica ), clam reproductive activity, and benthic macroinvertebrate community structure were investigated in a mudflat 1 kilometer south of the discharge of the Palo Alto Regional Water Quality Control Plant (PARWQCP) in south San Francisco Bay, Calif. This report includes the data collected by U.S. Geological Survey (USGS) scientists for the period January 2017 to December 2017. These append to long-term datasets extending back to 1974. A major focus of the report is an integrated description of the 2017 data within the context of the longer, multi-decadal dataset. This dataset supports the City of Palo Alto’s Near-Field Receiving Water Monitoring Program, initiated in 1994. Significant reductions in silver and copper concentrations in sediment and M. petalum occurred at the site in the 1980s following the implementation by PARWQCP of advanced wastewater treatment and source control measures. Since the 1990s, concentrations of these elements appear to have stabilized at concentrations somewhat above silver (Ag) or near copper (Cu) regional background concentrations. Data for other metals, including chromium (Cr), mercury (Hg), nickel (Ni), selenium (Se), and zinc (Zn), have been collected since 1994. Over this period, concentrations of these elements have remained relatively constant, aside from seasonal variation that is common to all elements. In 2017, concentrations of silver and copper in M. petalum varied seasonally in response to a combination of site-specific metal exposures and annual growth and reproduction, as reported previously. Seasonal patterns for other elements, including Cr, Ni, Zn, Hg, and Se, were generally similar in timing and magnitude as those for Ag and Cu. This record suggests that legacy contamination and regional-scale factors now largely control sedimentary and bioavailable concentrations of silver and copper, as well as other elements of regulatory interest, at the Palo Alto site. Analyses of the benthic community structure of a mudflat in south San Francisco Bay over a 40-year period show that changes in the community have occurred concurrent with reduced concentrations of metals in the sediment and in the tissues of the biosentinel clam, M. petalum , from the same area. Analysis of M. petalum shows increases in reproductive activity concurrent with the decline in metal concentrations in the tissues of this organism. Reproductive activity is presently stable (2017), with almost all animals initiating reproduction in the fall and spawning the following spring. The entire infaunal community has shifted from being dominated by several opportunistic species to a community where the species are more similar in abundance, a pattern that indicates a more stable community that is subjected to fewer stressors. In addition, two of the opportunistic species ( Ampelisca abdita and Streblospio benedicti ) that brood their young and live on the surface of the sediment in tubes have shown a continual decline in dominance coincident with the decline in metals; both species had short-lived rebounds in abundance in 2008, 2009, and 2010 and showed signs of increasing abundance in 2017. Heteromastus filiformis (a subsurface polychaete worm that lives in the sediment, consumes sediment and organic particles residing in the sediment, and reproduces by laying its eggs on or in the sediment) showed a concurrent increase in dominance and, in the last several years before 2008, showed a stable population. H. filiformis abundance increased slightly in 2011–2012 and returned to pre-2011 numbers in 2017. An unidentified disturbance occurred on the mudflat in early 2008 that resulted in the loss of the benthic animals, except for deep-dwelling animals like M. petalum . However, within two months of this event animals returned to the mudflat. The resilience of the community suggested that the disturbance was not due to a persistent toxin or anoxia. The reproductive mode of most species that were present in 2017 is reflective of species that were available either as pelagic larvae or as mobile adults. Although oviparous species were lower in number in this group, the authors hypothesize that these species will return slowly as more species move back into the area. The use of functional ecology was highlighted in the 2017 benthic community data, which showed that the animals that have now returned to the mudflat are those that can respond successfully to a physical, nontoxic disturbance. Today, community data show a mix of species that consume the sediment, or filter feed, have pelagic larvae that must survive landing on the sediment, and those that brood their young. USGS scientists view the 2008 disturbance event as a response by the infaunal community to an episodic natural stressor (possibly sediment accretion or a pulse of freshwater), in contrast to the long-term recovery from metal contamination. We will compare this recovery to the long-term recovery observed after the 1970s when the decline in sediment pollutants was the dominating factor.

California↗

USGS1994

Reconnaissance investigation of water quality, bottom sediment, and biota associated with irrigation drainage in the Owyhee and Vale Projects, Oregon and Idaho, 1990-91

A reconnaissance investigation was conducted during 1990--91 in the Owyhee and Vale projects in eastern Oregon and southwestern Idaho, as well as at a number of sites in the Snake River and tributaries to the Snake River in the area of study. The objective of the study was to determine if agricultural drainwater entering the study area was causing, or had the potential to cause, significant harmful effects to human health, fish and wildlife, or may adversely affect the suitability of water for beneficial uses. Approximately 153,000 acres of land are irrigated annually within the areas of the Owyhee and Vale projects. Large quantities of water are required because of the semiarid climate and relatively high evaporation rates. Several reservoirs in the area are filled annually during the wet, nonirrigation season to sustain irrigation during the dry summer months. During the irrigation season, this impounded water, along with direct diversions from the Malheur, Owyhee, and Snake Rivers, is transported to the irrigated areas through a series of diversion tunnels, siphons, canals, aqueducts, ditches, and drains. Major crops grown in the area include sugar beets, alfalfa hay and other hay crops, onions, and winter wheat. Minor crops include corn, potatoes, mint, various seed crops, and fruit. In 1987, it was estimated that the following amounts of pesticides were used in the project areas: 2,4-D (21,000 lbs [pounds]), chlorpyrifos (1,000 lbs), dacthal (40,000 lbs), dicamba (320 lbs), endosulfan (2,500 lbs), ethion (11,000 lbs), malathion (24,000 lbs), parathion (5,000 lbs), and phorate (11,000 lbs). Median concentrations and values for total dissolved solids, alkalinity, sodium adsorption ratio, and hardness in the Vale project area were greater than 1.5 times those values observed in the Owyhee project area or at other Snake River locations. During irrigation (August 1990), total dissolved solids, alkalinity, sodium adsorption ratio, and hardness values increased in a downstream manner. Constituent values at drainwater sites generally were comparable to concentrations below the irrigated ureas in the Owyhee and Vale project areas. The trace elements arsenic, boron, copper, molybdenum, vanadium, and zinc were detected in most water samples; cadmium, chromium, lead, and selenium were detected in some samples at concentrations generally near the analytical reporting limit; mercury was not detected in any samples. In some water samples, concentrations of arsenic, boron, cadmium, copper, and lead exceeded State or Federal water-quality standards or criteria. Most trace elements in bottom sediment were detected at concentrations within the expected 95-percent baseline range for soils from the Western United States. Concentrations that exceeded the 95-percent baseline range for study area soils were: (1) arsenic and lead in one sample from a site in the Vale project area; (2) mercury, lead, and tin in one sample from a site in the Snake River system; (3) manganese in two samples from two sites in the Snake River system; and (4) manganese from one sample from a site in the Vale project area. Fifteen pesticides and metabolites were detected in whole-water samples collected from sites in the study area. DDT, plus its metabolites (DDE and DDD), dieldrin, endrin, 2,4-D, dicamba, and dacthal were detected in samples collected from seven or more sites. Other pesticides detected included chlorpyrifos, endosulfan, ethion, malathion, parathion, phorate, and lindane. Most of the detected pesticide concentrations generally were largest in drainwater and at the most downstream sampling locations in the Owyhee and Vale project areas. Concentrations exceeded water-quality criteria established for the protection of freshwater aquatic life in 86 percent of the whole-water samples analyzed for DDT plus its metabolites, 71 percent of the dieldrin samples, 14 percent of the endrin samples, and 10 percent of the parathion samples. Eight pesticides and

Water-Resources Investigations Report↗

USGS2005

Questa baseline and pre-mining ground-water quality investigation. 5. Well installation, water-level data, and surface- and ground-water geochemistry in the Straight Creek drainage basin, Red River Valley, New Mexico, 2001-03

The U.S. Geological Survey, in cooperation with the New Mexico Environment Department, is investigating the pre-mining ground-water chemistry at the Molycorp molybdenum mine in the Red River Valley, northern New Mexico. The primary approach is to determine the processes controlling ground-water chemistry at an unmined, off-site, proximal analog. The Straight Creek drainage basin, chosen for this purpose, consists of the same quartz-sericite-pyrite altered andesitic and rhyolitic volcanic rock of Tertiary age as the mine site. The weathered and rugged volcanic bedrock surface is overlain by heterogeneous debris-flow deposits that interfinger with alluvial deposits near the confluence of Straight Creek and the Red River. Pyritized rock in the upper part of the drainage basin is the source of acid rock drainage (pH 2.8-3.3) that infiltrates debris-flow deposits containing acidic ground water (pH 3.0-4.0) and bedrock containing water of circumneutral pH values (5.6-7.7). Eleven observation wells were installed in the Straight Creek drainage basin. The wells were completed in debris-flow deposits, bedrock, and interfingering debris-flow and Red River alluvial deposits. Chemical analyses of ground water from these wells, combined with chemical analyses of surface water, water-level data, and lithologic and geophysical logs, provided information used to develop an understanding of the processes contributing to the chemistry of ground water in the Straight Creek drainage basin. Surface- and ground-water samples were routinely collected for determination of total major cations and selected trace metals; dissolved major cations, selected trace metals, and rare-earth elements; anions and alkalinity; and dissolved-iron species. Rare-earth elements were determined on selected samples only. Samples were collected for determination of dissolved organic carbon, mercury, sulfur isotopic composition (34S and 18O of sulfate), and water isotopic composition (2H and 18O) during selected samplings. One set of ground-water samples was collected for helium-3/tritium and chlorofluorocarbon (CFC) age dating. Several lines of evidence indicate that surface water is the primary input to the Straight Creek ground-water system. Straight Creek streamflow and water levels in wells closest to the apex of the Straight Creek debris fan and closest to Straight Creek itself appear to respond to the same seasonal inputs. Oxygen and hydrogen isotopic compositions in Straight Creek surface water and ground water are similar, and concentrations of most dissolved constituents in most Straight Creek surface-water and shallow (debris-flow and alluvial) aquifer ground-water samples correlate strongly with sulfate (concentrations decrease linearly with sulfate in a downgradient direction). After infiltration of surface water, dilution along the flow path is the dominant mechanism controlling ground-water chemistry. However, concentrations of some constituents can be higher in ground water than can be accounted for by concentrations in Straight Creek surface water, and additional sources of these constituents must therefore be inferred. Constituents for which concentrations in ground water can be high relative to surface water include calcium, magnesium, strontium, silica, sodium, and potassium in ground water from debris-flow and alluvial aquifers and manganese, calcium, magnesium, strontium, sodium, and potassium in ground water from the bedrock aquifer. All ground water is a calcium sulfate type, often at or near gypsum saturation because of abundant gypsum in the aquifer material developed from co-existing calcite and pyrite mineralization. Calcite dissolution, the major buffering mechanism for bedrock aquifer ground water, also contributes to relatively higher calcium concentrations in some ground water. The main source of the second most abundant cation, magnesium, is probably dissolution of magnesium-rich carbonates or silicates.

New Mexico↗

USGS2019

Near-field receiving-water monitoring of trace metals and a benthic community near the Palo Alto Regional Water Quality Control Plant in south San Francisco Bay, California—2018

California↗

USGS2003

Water quality at fixed sites in the Great Salt Lake basins, Utah, Idaho, and Wyoming, water years 1999-2000

The Great Salt Lake Basins (GRSL) study unit of the National Water-Quality Assessment program encompasses the Bear River, Weber River, and Utah Lake/Jordan River systems, all of which discharge to Great Salt Lake in Utah. Data were collected during each month at 10 sites in the GRSL study unit from October 1998 to September 2000 to define spatial and temporal distribution and variability in concentration of nutrients, major ions, trace elements, suspended sediments, and organic compounds. Water samples collected from rangeland and forest sites in the GRSL study unit generally contained low concentrations of dissolved solids. Median dissolved-solids concentration in water samples was highest at sites with mixed land uses. Dissolved-solids concentration in some parts of the Bear River during low flow exceeded Utah State standards for agricultural use. Total-nitrogen concentration in water samples from GRSL sites ranged from 0.06 to 11 milligrams per liter. Water samples from predominantly forest and rangeland sites generally had a low total-nitrogen concentration. Many samples from sites with a higher percentage of agricultural and urban land cover had higher concentrations of total nitrogen. Fifty percent of the samples collected at GRSL sites had total phosphorus concentrations that exceeded 0.1 milligram per liter, the recommended limit for the prevention of nuisance aquatic-plant growth in streams not discharging directly into lakes or impoundments. Concentration of most trace elements in water samples from the fixed sites generally was low; however, arsenic concentrations, as high as 284 micrograms per liter, sometimes exceeded aquatic-life guidelines. Forty-three pesticides and 35 volatile organic compounds were detected in water samples from three GRSL sites; however, the concentration of most was low, less than 1 microgram per liter. The herbicides atrazine and prometon and the insecticides carbaryl and diazinon were the most frequently detected pesticides. Chloroform and toluene were detected in more than 90 percent of the samples and were the most frequently detected volatile organic compounds. The concentration of carbaryl, diazinon, malathion, and toluene in water samples from GRSL sites sometimes exceeded aquatic-life guidelines.

Idaho,Utah, Wyoming↗

USGS2012

Status of groundwater quality in the Coastal Los Angeles Basin, 2006-California GAMA Priority Basin Project

Groundwater quality in the approximately 860-square-mile (2,227-square-kilometer) Coastal Los Angeles Basin study unit (CLAB) was investigated as part of the Priority Basin Project of the Groundwater Ambient Monitoring and Assessment (GAMA) Program. The study area is located in southern California in Los Angeles and Orange Counties. The GAMA Priority Basin Project is being conducted by the California State Water Resources Control Board in collaboration with the U.S. Geological Survey (USGS) and the Lawrence Livermore National Laboratory. The GAMA CLAB study was designed to provide a spatially unbiased assessment of the quality of untreated (raw) groundwater in the primary aquifer system. The assessment is based on water-quality and ancillary data collected in 2006 by the USGS from 69 wells and on water-quality data from the California Department of Public Health (CDPH) database. The primary aquifer system was defined by the depth interval of the wells listed in the CDPH database for the CLAB study unit. The quality of groundwater in the primary aquifer system may be different from that in the shallower or deeper water-bearing zones; shallow groundwater may be more vulnerable to surficial contamination. This study assesses the status of the current quality of the groundwater resource by using data from samples analyzed for volatile organic compounds (VOCs), pesticides, and naturally occurring inorganic constituents, such as major ions and trace elements. This status assessment is intended to characterize the quality of groundwater resources in the primary aquifer system of the CLAB study unit, not the treated drinking water delivered to consumers by water purveyors. Relative-concentrations (sample concentration divided by the health- or aesthetic-based benchmark concentration) were used for evaluating groundwater quality for those constituents that have Federal and (or) California regulatory or non-regulatory benchmarks for drinking-water quality. A relative-concentration greater than (>) 1.0 indicates a concentration greater than a benchmark, and a relative-concentration less than or equal to (≤) 1.0 indicates a concentration equal to or less than a benchmark. Relative-concentrations of organic and special-interest constituents [perchlorate, N -nitrosodimethylamine (NDMA), 1,2,3-trichloropropane (1,2,3-TCP), and 1,4-dioxane] were classified as "high" (relative-concentration>1.0), "moderate" (0.5 status assessment for evaluating regional-scale groundwater quality. High aquifer-scale proportion is defined as the percentage of the area of the primary aquifer system with a relative-concentration greater than 1.0 for a particular constituent or class of constituents; percentage is based on an areal rather than a volumetric basis. Moderate and low aquifer-scale proportions were defined as the percentage of the primary aquifer system with moderate and low relative-concentrations, respectively. Two statistical approaches-grid-based and spatially weighted-were used to evaluate aquifer-scale proportions for individual constituents and classes of constituents. Grid-based and spatially weighted estimates were comparable in the CLAB study unit (within 90-percent confidence intervals). Inorganic constituents with human-health benchmarks were detected at high relative-concentrations in 5.6 percent of the primary aquifer system and moderate in 26 percent. High aquifer-scale proportion of inorganic constituents primarily reflected high aquifer-scale proportions of arsenic (1.9 percent), nitrate (1.9 percent), and uranium (1.2 percent). Inorganic constituents with secondary maximum contaminant levels (SMCL) were detected at high relative-concentrations in 18 percent of the primary aquifer system and moderate in 47 percent. The constituents present at high relative-concentrations included total dissolved solids (1.9 percent), manganese (15 percent), and iron (9.4 percent). Relative-concentrations of organic constituents (one or more) were high in 3.7 percent, and moderate in 13 percent, of the primary aquifer system. The high aquifer-scale proportion of organic constituents primarily reflected high aquifer-scale proportions of solvents, including trichloroethene (TCE; 1.7 percent), perchloroethene (PCE; 1.1 percent), and carbon tetrachloride (1.0 percent). Of the 204 organic constituents analyzed, 44 constituents were detected. Eleven organic constituents had detection frequencies of greater than 10 percent: the trihalomethanes chloroform and bromodichloromethane, the solvents TCE, PCE, cis -1,2-dichloroethene, and 1,1-dichloroethene, the herbicides atrazine, simazine, prometon, and tebuthiuron, and the gasoline additive methyl tert -butyl ether (MTBE). Most detections were at low relative-concentrations. The special-interest constituent perchlorate was detected at high relative-concentrations in 0.5 percent of the primary aquifer system, and at moderate relative-concentrations in 35 percent. The special-interest constituent 1,4-dioxane was detected at high relative-concentrations, but an insufficient number of samples was analyzed to provide a representative estimate of aquifer-scale proportion.

California↗