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USGS2016

Assessment of hydrogeologic terrains, well-construction characteristics, groundwater hydraulics, and water-quality and microbial data for determination of surface-water-influenced groundwater supplies in West Virginia

In January 2014, a storage tank leaked, spilling a large quantity of 4-methylcyclohexane methanol into the Elk River in West Virginia and contaminating the water supply for more than 300,000 people. In response, the West Virginia Legislature passed Senate Bill 373, which requires the West Virginia Department of Health and Human Resources (WVDHHR) to assess the susceptibility and vulnerability of public surface-water-influenced groundwater supply sources (SWIGS) and surface-water intakes statewide. In response to this mandate for reassessing SWIGS statewide, the U.S. Geological Survey (USGS), in cooperation with the WVDHHR, Bureau of Public Health, Office of Environmental Health Services, compiled available data and summarized the results of previous groundwater studies to provide the WVDHHR with data that could be used as part of the process for assessing and determining SWIGS. Existing geologic, hydrologic, well-construction, water-quality, and other related data and information from previous U.S. Geological Survey (USGS) hydrogeologic studies and the USGS National Water Information System (NWIS) database, in conjunction with data from the West Virginia Bureau for Public Health (WVBPH) Department of Health and Human Resources (WVDHHR) and the West Virginia Department of Environmental Protection database and files, were collected, compiled, and analyzed to help the WVDHHR to better assess public groundwater supply wells that may meet the definition of a surface-water-influenced- groundwater supply (SWIGS). In this study, measures of intrinsic susceptibility, which are characterized by the physical properties that affect the ease with which water moves through the unsaturated zone and, subsequently, into the saturated zone within an aquifer, showed that karst limestone aquifers are the aquifers most intrinsically susceptible to contamination within the State of West Virginia. Karst limestone aquifers are present within Cambrian- and Ordovician-age formations within West Virginia’s eastern panhandle and in Mississippian-age limestones within the Greenbrier River valley. Solution development within these limestone aquifers allows rapid recharge and flow of groundwater within the aquifer, both of which allow surface contaminants to easily enter the aquifer and travel long distances in a short period of time. Alluvial aquifers bordering the Ohio River in western West Virginia are also potentially highly susceptible to contamination because these alluvial aquifers can receive significant recharge from the adjacent Ohio River. Any potential contaminants that may be present in the river have the potential to enter the aquifer and contaminate wells completed within the sand and gravel alluvial sediments within which the wells are completed. These same alluvial sediments, however, help to retard the movement of bacteria and other potentially pathogenic organisms, such as Cryptosporidia and Giardia lamblia , into the aquifer. As a result, samples from alluvial aquifers bordering the Ohio River and elsewhere within the State do not commonly test positive for indicator bacteria, such as total coliform, fecal coliform, or Escherichia coli ( E. coli ). The alluvial sediments do not, however, provide assimilative capacity with respect to water soluble compounds such as nitrate and certain volatile and semi-volatile organic compounds. Therefore, the Ohio River alluvial aquifers are highly susceptible to organic compounds present in the river or on the land surface near a well. These aquifers are also susceptible to nitrate contamination from fertilizers, pesticides, and manure, which are commonly used on the fertile agricultural soils present on terraces along the Ohio River. Abandoned-coal-mine aquifers, which are typically used as a source of groundwater in southern West Virginia, are moderately susceptible to contamination. The vast network of voids from mine entries provide vast storage for groundwater in abandoned mine aquifers, and fracturing of overburden strata, which is common in areas of past or current mining, can allow rapid infiltration of contaminants to the aquifer. Where streams cross over below-drainage underground coal mines, there is an increased potential for contamination of coal-mine aquifers. As a result, above-drainage underground coal mines, those mines that are present at an elevation above local tributary drainage, are probably less susceptible to contamination than are below-drainage underground coal mines. Public groundwater supplies in abandoned coal mines need to be evaluated on a case-by-case basis to assess the potential for recharge of contaminated surface water to enter below-drainage underground coal-mine aquifers and to assess potential hydraulic conductivity to nearby surface-water bodies, such as lakes, ponds, rivers, or streams. Fractured-rock aquifers compose an additional major type of aquifer within the State of West Virginia. Owing to their low permeability and their typically small groundwater capture areas, fractured-rock aquifers within the State of West Virginia typically have low susceptibility to contamination. However, there are exceptions, and wells completed in fractured-rock aquifers that are in close proximity to streams may be adversely affected by induced recharge from the stream. Where such systems are present, frequent bacterial testing of the source water can be used to ascertain the potential for microbial contamination of the aquifer. Intrinsic susceptibility alone does not fully predict whether or not a well is vulnerable to contamination, only that the hydrogeologic terrain is suitable for rapid transport of pathogenic organisms or chemical compounds to and within the aquifer. However, contaminants may or may not be present in the recharge water to an individual well or well field. Therefore, an assessment of potential contaminant sources, such as nearby gas wells, landfills, underground storage tanks, above ground storage tanks, major transportation corridors, surface or underground coal mines, and flood plains, is needed to assess vulnerability. The assessments need to be conducted on a case-by-case basis or, as has been done in this study, by collecting and compiling the number of potential contaminant sources that may be present in the source-water-protection area for an individual public groundwater supply source. Groundwater public-supply systems in areas of high intrinsic susceptibility and with a large number of potential contaminant sources within the recharge or source-water-protection area of individual wells or well fields are potentially vulnerable to contamination and probably warrant further evaluation as potential SWIGS. However, measures can be taken to educate the local population and initiate safety protocols and protective strategies to appropriately manage contaminant sources to prevent release of contaminants to the aquifer, therefore, reducing vulnerability of these systems to contamination. However, each public groundwater supply source needs to be assessed on an individual basis. Data presented in this report can be used to categorize and prioritize wells and springs that have a high potential for intrinsic susceptibility or vulnerability to contamination.

West Virginia↗

USGS2017

Groundwater quality in the Western San Joaquin Valley study unit, 2010: California GAMA Priority Basin Project

Water quality in groundwater resources used for public drinking-water supply in the Western San Joaquin Valley (WSJV) was investigated by the USGS in cooperation with the California State Water Resources Control Board (SWRCB) as part of its Groundwater Ambient Monitoring and Assessment (GAMA) Program Priority Basin Project. The WSJV includes two study areas: the Delta–Mendota and Westside subbasins of the San Joaquin Valley groundwater basin. Study objectives for the WSJV study unit included two assessment types: (1) a status assessment yielding quantitative estimates of the current (2010) status of groundwater quality in the groundwater resources used for public drinking water, and (2) an evaluation of natural and anthropogenic factors that could be affecting the groundwater quality. The assessments characterized the quality of untreated groundwater, not the quality of treated drinking water delivered to consumers by water distributors. The status assessment was based on data collected from 43 wells sampled by the U.S. Geological Survey for the GAMA Priority Basin Project (USGS-GAMA) in 2010 and data compiled in the SWRCB Division of Drinking Water (SWRCB-DDW) database for 74 additional public-supply wells sampled for regulatory compliance purposes between 2007 and 2010. To provide context, concentrations of constituents measured in groundwater were compared to U.S. Environmental Protection Agency (EPA) and SWRCB-DDW regulatory and non-regulatory benchmarks for drinking-water quality. The status assessment used a spatially weighted, grid-based method to estimate the proportion of the groundwater resources used for public drinking water that has concentrations for particular constituents or class of constituents approaching or above benchmark concentrations. This method provides statistically unbiased results at the study-area scale within the WSJV study unit, and permits comparison of the two study areas to other areas assessed by the GAMA Priority Basin Project statewide. Groundwater resources used for public drinking water in the WSJV study unit are among the most saline and most affected by high concentrations of inorganic constituents of all groundwater resources used for public drinking water that have been assessed by the GAMA Priority Basin Project statewide. Among the 82 GAMA Priority Basin Project study areas statewide, the Delta–Mendota study area ranked above the 90th percentile for aquifer-scale proportions of groundwater resources having concentrations of total dissolved solids (TDS), sulfate, chloride, manganese, boron, chromium(VI), selenium, and strontium above benchmarks, and the Westside study area ranked above the 90th percentile for TDS, sulfate, manganese, and boron. In the WSJV study unit as a whole, one or more inorganic constituents with regulatory or non-regulatory, health-based benchmarks were present at concentrations above benchmarks in about 53 percent of the groundwater resources used for public drinking water, and one or more organic constituents with regulatory health-based benchmarks were detected at concentrations above benchmarks in about 3 percent of the resource. Individual constituents present at concentrations greater than health-based benchmarks in greater than 2 percent of groundwater resources used for public drinking water included: boron (51 percent, SWRCB-DDW notification level), chromium(VI) (25 percent, SWRCB-DDW maximum contaminant level (MCL)), arsenic (10 percent, EPA MCL), strontium (5.1 percent, EPA Lifetime health advisory level (HAL)), nitrate (3.9 percent, EPA MCL), molybdenum (3.8 percent, EPA HAL), selenium (2.6 percent, EPA MCL), and benzene (2.6 percent, SWRCB-DDW MCL). In addition, 50 percent of the resource had TDS concentrations greater than non-regulatory, aesthetic-based SWRCB-DDW upper secondary maximum contaminant level (SMCL), and 44 percent had manganese concentrations greater than the SWRCB-DDW SMCL. Natural and anthropogenic factors that could affect the groundwater quality were evaluated by using results from statistical testing of associations between constituent concentrations and values of potential explanatory factors, inferences from geochemical and age-dating tracer results, and by considering the water-quality results in the context of the hydrogeologic setting of the WSJV study unit. Natural factors, particularly the lithologies of the source areas for groundwater recharge and of the aquifers, were the dominant factors affecting groundwater quality in most of the WSJV study unit. However, where groundwater resources used for public supply included groundwater recharged in the modern era, mobilization of constituents by recharge of water used for irrigation also affected groundwater quality. Public-supply wells in the Westside study area had a median depth of 305 m and primarily tapped groundwater recharged hundreds to thousands of years ago, whereas public-supply wells in the Delta–Mendota study area had a median depth of 85 m and primarily tapped either groundwater recharged within the last 60 years or groundwater consisting of mixtures of this modern recharge and older recharge. Public-supply wells in the WSJV study unit are screened in the Tulare Formation and zones above and below the Corcoran Clay Member are used. The Tulare Formation primarily consists of alluvial sediments derived from the Coast Ranges to the west, except along the valley trough at the eastern margin of the WSJV study unit where the Tulare Formation consists of fluvial sands derived from the Sierra Nevada to the east. Groundwater from wells screened in the Sierra Nevada sands had manganese-reducing or manganese- and iron-reducing oxidation-reduction (redox) conditions. These redox conditions commonly were associated with elevated arsenic or molybdenum concentrations, and the dominance of arsenic(III) in the dissolved arsenic supports reductive dissolution of iron and manganese oxyhydroxides as the mechanism. In addition, groundwater from many wells screened in Sierra Nevada sands contained low concentrations of nitrite or ammonium, indicating reduction of nitrate by denitrification or dissimilatory processes, respectively. Geology of the Coast Ranges westward of the study unit strongly affects groundwater quality in the WSJV. Elevated concentrations of TDS, sulfate, boron, selenium and strontium in groundwater were primarily associated with aquifer sediments and recharge derived from areas of the Coast Ranges dominated by Cretaceous-to-Miocene age, organic-rich, reduced marine shales, known as the source of selenium in WSJV soils, surface water, and groundwater. Low sulfur-isotopic values (δ34S) of dissolved sulfate indicate that the sulfate was largely derived from oxidation of biogenic pyrite from the shales, and correlations with trace element concentrations, geologic setting, and groundwater geochemical modeling indicated that distributions of sulfate, strontium, and selenium in groundwater were controlled by dissolution of secondary sulfate minerals in soils and sediments. Elevated concentrations of chromium(VI) were primarily associated with aquifer sediments and recharge derived from areas of the Coast Ranges dominated by the Franciscan Complex and ultramafic rocks. The Franciscan Complex also has boron-rich, sodium-chloride dominated hydrothermal fluids that contribute to elevated concentrations of boron and TDS. Groundwater from wells screened in Coast Ranges alluvium was primarily oxic and relatively alkaline (median pH value of 7.55) in the Delta–Mendota study area, and primarily nitrate-reducing or suboxic and alkaline (median pH value of 8.4) in the Westside study area. Many groundwater samples from those wells have elevated concentrations of arsenic(V), molybdenum, selenium, or chromium(VI), consistent with desorption of metal oxyanions from mineral surfaces under those geochemical conditions. High concentrations of benzene were associated with deep wells located in the vicinity of petroleum deposits at the southern end of the Westside study area. Groundwater from these wells had premodern age and anoxic geochemical conditions, and the ratios among concentrations of hydrocarbon constituents were different from ratios found in fuels and combustion products, which is consistent with a geogenic source for the benzene rather than contamination from anthropogenic sources. Water stable-isotope compositions, groundwater recharge temperatures, and groundwater ages were used to infer four types of groundwater: (1) groundwater derived from natural recharge of water from major rivers draining the Sierra Nevada; (2) groundwater primarily derived from natural recharge of water from Coast Ranges runoff; (3) groundwater derived from recharge of pumped groundwater applied to the land surface for irrigation; and (4) groundwater derived from recharge during a period of much cooler paleoclimate. Water previously used for irrigation was found both above and below the Corcoran Clay, supporting earlier inferences that this clay member is no longer a robust confining unit. Recharge of water used for irrigation has direct and indirect effects on groundwater quality. Elevated nitrate concentrations and detections of herbicides and fumigants in the Delta–Mendota study area generally were associated with greater agricultural land use near the well and with water recharged during the last 60 years. However, the extent of the groundwater resource affected by agricultural sources of nitrate was limited by groundwater redox conditions sufficient to reduce nitrate. The detection frequency of perchlorate in Delta–Mendota groundwater was greater than expected for natural conditions. Perchlorate, nitrate, selenium, and strontium concentrations were correlated with one another and were greater in groundwater inferred to be recharge of previously pumped groundwater used for irrigation. The source of the perchlorate, selenium, and strontium appears to be salts deposited in the soils and sediments of the arid WSJV that are dissolved and flushed into groundwater by the increased amount of recharge caused by irrigation. In the Delta–Mendota study area, the groundwater with elevated concentrations of selenium was found deeper in the aquifer system than it was reported by a previous study 25 years earlier, suggesting that this transient front of groundwater with elevated concentrations of constituents derived from dissolution of soil salts by irrigation recharge is moving down through the aquifer system and is now reaching the depth zone used for public drinking water supply.

California↗

USGS2015

Results of mineral, chemical, and sulfate isotopic analyses of water, soil, rocks, and soil extracts from the Pariette Draw Watershed, Uinta Basin, Utah

In 2010, Utah Department of Environmental Quality (DEQ) Division of Water Quality (UDWQ, 2010) determined that water quality in Pariette Draw was in violation of Federal and State water quality criteria for total dissolved solids (TDS), selenium (Se), and boron (B). The measure of total dissolved solids is the sum of all the major ion concentrations in solution and in this case, the dominant ions are sodium (Na) and sulfate (SO4), which can form salts like thenardite (Na2SO4) and mirabilite (Na2SO4⋅H2O). The Utah Department of Environmental Quality (2010) classified the contamination as natural background and from nonpoint sources related to regional lithology and irrigation practices. Although the daily loads of the constituents of concern and water chemistry have been characterized for parts of the watershed, little is known about the controls that bedrock and soil mineralogy have on salt, Se, and B storage and the water-rock interactions that influence the mobility of these components in ground and surface waters. Studies in the Uncompahgre River watershed in Colorado by Tuttle and others (2014a, 2014b) show that salt derived from weathering of shale in a semiarid climate is stored in a variety of minerals that contribute solutes to runoff and surface waters based on a complex set of conditions such as water availability, geomorphic position (for example, topography controls the depth of salt accumulation in soils), water-table fluctuations, redox conditions, mineral dissolution kinetics, ion-exchange reactions, and secondary mineral formation. Elements like Se and B commonly reside in soluble salt phases, so knowledge of the behavior of salt minerals also sheds light on the behavior of associated contaminants. The goal of this study was to establish a process-based understanding of salt, Se, and B behavior to address whether these contaminants can be better managed, or if uncontrollable natural processes will overwhelm any attempts to bring Pariette Draw into compliance with respect to recently established total maximum daily limits (TMDLs). We collected data to refine our knowledge about the role of rock weathering and soil formation in the transport and storage of salt in the watershed and to show how salt is cycled under irrigated and natural conditions. Our approach was to sample rock, soils, and sediment on irrigated and natural terrain for mineralogical analysis to determine the residence of salt and associated Se and B, classify minerals as primary (related to rock formation) or secondary weathering products, and characterize mineral dissolution kinetics. Mineral and chemical analyses and selective extractions of rocks and soils provide useful information in understanding solute movement and mineral dissolution/ formation. The resulting data are critical in determining residence of salt, Se, and B in weathered rock and soil and understanding the mobility during water-rock-soil interactions. This report summarizes our methods for sample and data collection and tabulates the mineral, chemical, and isotopic data collected.

Utah↗

USGS2014

Mercury speciation in the Mt. Amiata mining district (Italy): interplay between urban activities and mercury contamination

A fundamental step to evaluate the biogeochemical and eco-toxicological significance of Hg dispersion in the environment is to determine speciation of Hg in solid matrices. In this study, several analytical techniques such as scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), sequential chemical extractions (SCEs), and X-ray absorption spectroscopy (XANES) were used to identify Hg compounds and Hg speciation in samples collected from the Mt. Amiata Hg mining district, southern Tuscany, Italy. Different geological materials, such as mine waste calcine (retorted ore), soil, stream sediment, and stream water suspended particulate matter were analyzed. Results show that the samples were generally composed of highly insoluble Hg compounds such as sulphides (HgS, cinnabar and metacinnabar), and more soluble Hg halides such as those associated with the mosesite group. Other moderately soluble Hg compounds, HgCl 2 , HgO and Hg 0 , were also identified in stream sediments draining the mining area. The presence of these minerals suggests active and continuous runoff of soluble Hg compounds from calcines, where such Hg compounds form during retorting, or later in secondary processes. Specifically, we suggest that, due to the proximity of Hg mines to the urban center of Abbadia San Salvatore, the influence of other anthropogenic activities was a key factor for Hg speciation, resulting in the formation of unusual Hg-minerals such as mosesite.

Tuscany↗

USGS1991

Role of exposure mode in the bioavailability of triphenyl phosphate to aquatic organisms

A laboratory study was conducted to investigate the role of the route of triphenyl phosphate (TPP) entry on its aquatic bioavailability and acute biological effects. Three TPP treatments were used for exposures of fish and invertebrates. These consisted of TPP dosed directly into water with and without clean sediment and TPP spiked onto sediment prior to aqueous exposures. Results of static acute toxicity tests (no sediment) were 0.78 mg/L (96-h LC50) for bluegill, 0.36 mg/L (48-h EC50) for midge, and 0.25 mg/L (96-h EC50) for scud. At 24 h, the sediment (1.1% organic carbon)/water partition coefficient (Kp) for TPP was 112. Use of this partition coefficient model to predict the sediment-mediated reduction of TPP concentration in water during toxicity tests resulted in a value that was only 10% less than the nominal value. However, the required nominal concentration of TPP to cause acute toxicity responses in test organisms was significantly higher than the predicted value by the model for both clay and soil-derived sediment. Direct spiking of TPP to soil minimized TPP bioavailability. Data from parallel experiments designed to track TPP residues in water through time suggest that sorption kinetics control residue bioavailability in the initial 24 h of exposure and may account for observed differences in LC50 and EC50 values from the sediment treatments.

Archives of Environmental Contamination and Toxico↗

USGS2018

Lead and strontium isotopes as monitors of anthropogenic contaminants in the surficial environment

Book chapter↗

USGS2016

Pb-Sr isotopic and geochemical constraints on sources and processes of lead contamination in well waters and soil from former fruit orchards, Pennsylvania, USA: A legacy of anthropogenic activities

Isotopic discrimination can be an effective tool in establishing a direct link between sources of Pb contamination and the presence of anomalously high concentrations of Pb in waters, soils, and organisms. Residential wells supplying water containing up to 1600 ppb Pb to houses built on the former Mohr orchards commercial site, near Allentown, PA, were evaluated to discern anthropogenic from geogenic sources. Pb (n = 144) and Sr (n = 40) isotopic data and REE (n = 29) data were determined for waters from residential wells, test wells (drilled for this study), and surface waters from pond and creeks. Local soils, sediments, bedrock, Zn-Pb mineralization and coal were also analyzed (n = 94), together with locally used Pb-As pesticide (n = 5). Waters from residential and test wells show overlapping values of 206 Pb/ 207 Pb, 208 Pb/ 207 Pb and 87 Sr/ 86 Sr. Larger negative Ce anomalies (Ce/Ce*) distinguish residential wells from test wells. Results show that residential and test well waters, sediments from residential water filters in water tanks, and surface waters display broad linear trends in Pb isotope plots. Pb isotope data for soils, bedrock, and pesticides have contrasting ranges and overlapping trends. Contributions of Pb from soils to residential well waters are limited and implicated primarily in wells having shallow water-bearing zones and carrying high sediment contents. Pb isotope data for residential wells, test wells, and surface waters show substantial overlap with Pb data reflecting anthropogenic actions (e.g., burning fossil fuels, industrial and urban processing activities). Limited contributions of Pb from bedrock, soils, and pesticides are evident. High Pb concentrations in the residential waters are likely related to sediment build up in residential water tanks. Redox reactions, triggered by influx of groundwater via wells into the residential water systems and leading to subtle changes in pH, are implicated in precipitation of Fe oxyhydroxides, oxidative scavenging of Ce(IV), and desorption and release of Pb into the residential water systems. The Pb isotope features in the residences and the region are best interpreted as reflecting a legacy of industrial Pb present in underlying aquifers that currently supply the drinking water wells.

Pennsylvania↗

USGS2016

Occurrence, distribution, and volume of metals-contaminated sediment of selected streams draining the Tri-State Mining District, Missouri, Oklahoma, and Kansas, 2011–12

Lead and zinc were mined in the Tri-State Mining District (TSMD) of southwest Missouri, northeast Oklahoma, and southeast Kansas for more than 100 years. The effects of mining on the landscape are still evident, nearly 50 years after the last mine ceased operation. The legacies of mining are the mine waste and discharge of groundwater from underground mines. The mine-waste piles and underground mines are continuous sources of trace metals (primarily lead, zinc, and cadmium) to the streams that drain the TSMD. Many previous studies characterized the horizontal extent of mine-waste contamination in streams but little information exists on the depth of mine-waste contamination in these streams. Characterizing the vertical extent of contamination is difficult because of the large amount of coarse-grained material, ranging from coarse gravel to boulders, within channel sediment. The U.S. Geological Survey, in cooperation with U.S. Fish and Wildlife service, collected channel-sediment samples at depth for subsequent analyses that would allow attainment of the following goals: (1) determination of the relation between concentration and depth for lead, zinc and cadmium in channel sediments and flood-plain sediments, and (2) determination of the volume of gravel-bar sediment from the surface to the maximum depth with concentrations of these metals that exceeded sediment-quality guidelines. For the purpose of this report, volume of gravel-bar sediment is considered to be distributed in two forms, gravel bars and the wetted channel, and this study focused on gravel bars. Concentrations of lead, zinc, and cadmium in samples were compared to the consensus probable effects concentration (CPEC) and Tri-State Mining District specific probable effects concentration (TPEC) sediment-quality guidelines. During the study, more than 700 sediment samples were collected from borings at multiple sites, including gravel bars and flood plains, along Center Creek, Turkey Creek, Shoal Creek, Tar Creek, and Spring River in order to characterize the vertical extent of mine waste in select streams in the TSMD. The largest concentrations of lead, zinc, and cadmium in gravel bar-sediment samples generally were detected in Turkey Creek and Tar Creek and the smallest concentrations were detected in Shoal Creek followed by the Spring River. Gravel bar-sediment samples from Turkey Creek exceeded the CPEC for cadmium (minimum of 70 percent of samples), lead (94 percent), and zinc (99 percent) at a slightly higher frequency than similar samples from Tar Creek (69 percent, 88 percent, and 96 percent, respectively). Gravel bar-sediment samples from Turkey Creek also contained the largest concentrations of cadmium (174 milligrams per kilogram [mg/kg]) and lead (7,520 mg/kg) detected; however, the largest zinc concentration (46,600 mg/kg) was detected in a gravel bar-sediment sample from Tar Creek. In contrast, none of the 65 gravel bar-sediment samples from Shoal Creek contained cadmium above the x-ray fluorescence reporting level of 12 mg/kg, and lead and zinc exceeded the CPEC in only 12 percent and 74 percent of samples, respectively. In most cases, concentrations of lead and zinc above the CPEC or TPEC were present at the maximum depth of boring, which indicated that nearly the entire thickness of sediment in the stream has been contaminated by mine wastes. Approximately 284,000 cubic yards of channel sediment from land surface to the maximum depth that exceeded the CPEC and approximately 236,000 cubic yards of channel sediment from land surface to the maximum depth that exceeded the TPEC were estimated along 37.6 of the 55.1 miles of Center Creek, Turkey Creek, Shoal Creek, and Tar Creek examined in this study. Mine-waste contamination reported along additional reaches of these streams is beyond the scope of this study. Flood-plain cores collected in the TSMD generally only had exceedances of the CPEC and TPEC for lead and zinc in the top 1 or 2 feet of soil with a few exceptions, such as cores in low areas near the stream or cores in areas disturbed by past mining.

Kansas, Missouri, Oklahoma↗

USGS1998

Detailed study of selenium and selected constituents in water, bottom sediment, soil, and biota associated with irrigation drainage in the San Juan River area, New Mexico, 1991-95

In response to increasing concern about the quality of irrigation drainage and its potential effects on fish, wildlife, and human health, the U.S. Department of the Interior began the National Irrigation Water Quality Program (NIWQP) to investigate these concerns at irrigation projects sponsored by the Department. The San Juan River area in northwestern New Mexico was one of the areas designated for study. Study teams composed of scientists from the U.S. Geological Survey, the U.S. Fish and Wildlife Service, the Bureau of Reclamation, and the Bureau of Indian Affairs collected water, bottom-sediment, soil, and biological samples at 61 sites in the San Juan River area during 1993-94. Supplemental data collection conducted during 1991-95 by the Bureau of Indian Affairs and its contractor extended the time period and sampling sites available for analysis. Analytical chemistry performed on samples indicated that most potentially toxic elements other than selenium generally were not high enough to be of concern to fish, wildlife, and human health. Element concentrations in some water, bottom-sediment, soil, and biological samples exceeded applicable standards and criteria suggested by researchers in current literature. Selenium concentrations in water samples from 28 sites in the study area exceeded the 2-microgramper-liter (lg/L) wildlife-habitat standard. Vanadium concentrations in water exceeded the 100-Kg/L standard for livestock-drinking water at one site. In biota, selenium and aluminum concentrations regularly equaled or exceeded avian dietary threshold concentrations. In bottom sediment and soil, element concentrations above the upper limit of the baseline range for western soils were: selenium, 24 exceedances; lead, 2 exceedances; molybdenum, 2 exceedances;strontium, 4 exceedances; and zinc, 4 exceedances. Concentrations of total selenium in bottom-sediment and soil samples were significantly greater for Cretaceous than for non-Cretaceous soil types in the study area and were generally similar for habitats within and outside irrigation-affected areas. Mean and median total-selenium concentrations in samples from areas with Cretaceous soil types were 4.6 and 2.2 micrograms per gram (ps/g), respectively. Mean and median total-selenium concentrations in samples from areas with non-Cretaceous soil types were 0.6 and 0.15 pg/g, respectively. Samples from the study area had low concentrations of organic constituents. Organochlorine pesticides and polychlorinated biphenyls were detected in a few biological samples at low concentrations. Polycyclic aromatic hydrocarbon (PAH) compounds were not detected in whole-water samples collected using conventional water-sampling techniques. In tests involving the use of semipermeable-membrane devices to supplement conventional water assays for PAH's, low concentrations of PAH's were found at several locations in the Hammond Irrigation Supply Canal, but were not detected in the Hammond ponds at the downstream reach of the Hammond irrigation service area. PAH compounds do not appear to reach the San Juan River through the Hammond Canal. Data indicate that water samples from irrigation-drainage-affected habitats had increased mean selenium concentrations compared with samples from irrigation-delivery habitat. The mean selenium concentration in water was greatest at seeps and tributaries draining irrigated land (17 μg/L); less in irrigation drains and in ponds on irrigated land (61.tg/L); and least in backwater, the San Juan River, and irrigation-supply water (0.5 - 0.6 μg/L). Statistical tests imply that irrigation significantly increases selenium concentrations in water samples when a Department of the Interior irrigation project is developed on selenium-rich sediments. Water samples from sites with Cretaceous soils had significantly greater selenium concentrations than water samples from sites with non-Cretaceous soils. Water samples from Department of the Interior project irrigation-drainage sites developed on Cretaceous soils contained a mean selenium concentration about 10 times greater than those in samples from Department of the Interior project sites developed on non-Cretaceous soils. Selenium was much less concentrated in water than in bottom sediment, soil, or biota in the study area. The range in concentrations of dissolved selenium in water was less than 1 ptg/L to 37 1.1g/L (less than 1 to 37 parts per billion). The range in concentrations of total selenium in bottom sediment and soil was less than 0.1 to 23lig/g (less than 100 to 23,000 parts per billion). The range in concentration of selenium in biota was less than 0.1 to 24.0 fig/g (less than 100 to 24,000 parts per billion). Data indicated that bioaccumulation and leaching from soil were the important processes at the study area that lead to elevated levels of selenium. Other processes examined included: (1) evapoconcentration of selenium; (2) atmospheric deposition of aerosols containing selenium; and (3) contamination of surface water by point-source or non-point-source discharges. Selenium concentrations in biological samples were evaluated by a number of variables including: (1) media sampled (emergent and submergent plants, nektonic and benthic invertebrates, omnivore/herbivore and carnivore fish, and terrestrial and aquatic amphibians); (2) habitat (San Juan River main-stem reaches, backwaters, tributary reaches, irrigation delivery or drainage canals, and ponds); (3) irrigation project area and reference sites; and (4) soil type (non-Cretaceous or Cretaceous soils). Graphical techniques and nonparametric statistical tests were applied to determine the influence of selected physiographic variables on selenium concentrations in biological samples collected in the San Juan River area. Species of sucker and of smaller fish contained significantly higher selenium concentrations in the upstream portion of the river where a productive community of plants and animals is found that is associated with warming, nutrient-rich waters discharged from an upstream reservoir. Selenium concentrations in algae, odonates, and mosquitofish collected from both irrigation-drain and pond habitats underlain by Cretaceous soils were significantly greater than in those collected from similar habitats underlain by non-Cretaceous soils. Investigators conclude that the major factor affecting the variability of selenium accumulation in biota at aquatic habitats was the presence of underlying Cretaceous soils. Median selenium concentrations were less than 2 lAg/g for plant samples, less than 7 μg/g for invertebrate samples, and less than 6 lAg/g for whole-fish samples collected from aquatic habitats underlain by non-Cretaceous soils. Similar samples collected from aquatic habitats underlain by Cretaceous soils contained median selenium concentrations two to five times greater. Leaching of selenium from Cretaceous soils in the San Juan River area increases the accumulation of selenium concentrations in the biota and thereby increases the exposure and potential health risks associated with selenium to migratory birds, fish, and other wildlife that use these aquatic habitats extensively. Aquatic habitats presenting the greatest average exposure to excess selenium concentrations in the diets of resident wildlife are from consumption of plants, invertebrates, and fish at irrigation-drain habitats underlain by Cretaceous soils. Of the irrigation projects evaluated in the San Juan River area, the highest median selenium concentrations in algae, cattail leaves, odonate nymphs, mosquitofish, and leopard frog samples from the study area were collected from the east hogback irrigation drain.

New Mexico↗

USGS1998

The discharge of nitrate-contaminated groundwater from developed shoreline to marsh-fringed estuary

As residential development, on-site wastewater disposal, and groundwater contamination increase in the coastal zone, assessment of nutrient removal by soil and sedimentary processes becomes increasingly important. Nitrogen removal efficiency depends largely on the specific flow paths taken by groundwater as it discharges into nitrogen-limited estuarine waters. Shoreline salinity surveys, hydraulic studies, and thermal infrared imagery indicated that groundwater discharge into the Nauset Marsh estuary (Eastham, Massachusetts) occurred in high-velocity seeps immediately seaward of the upland-fringing salt marsh. Discharge was highly variable spatially and occurred through permeable, sandy sediments during low tide. Seepage chamber monitoring showed that dissolved inorganic nitrogen (principally nitrate) traversed nearly conservatively from the aquifer through shallow estuarine sediments to coastal waters at flux rates of 1–3 mmol m −2 h −1 . A significant relationship between pore water NO 3 -N concentrations and NO 3 -N flux rates may provide a rapid method of estimating nitrogen loading from groundwater to the water column.

Massachusets↗

USGS2004

Environmental setting, water quality, and ecological indicators of surface-water quality in the Mermentau River Basin, southwestern Louisiana, 1998-2001

The U.S. Geological Survey collected data from 29 wells and 24 surface-water sites in the Mermentau River Basin, 1998-2001, to better understand ground-water and surface-water quality; aquatic invertebrate communities; and habitat conditions, in relation to land use. This study was apart of the National Water-Quality Assessment Program, which was designed to assess water quality as it relates to various land uses. Water-quality data were evaluated with criteria established for the protection of drinking water and aquatic life, and bed-sediment data were compared to aquatic life criteria. Water-quality and ecological data were analyzed statistically in relation to drainage area and agricultural land-use integrity. Concentrations of nutrients and major inorganic ions in ground water and surface water generally were highest in the southeastern part of the study area where soils contain thick loess deposits. Peak concentrations of nutrients in surface water occurred March-may at two sites with high agricultural intensity; the lowest concentrations occurred August-January. The greatest potential for eutrophic conditions in surface water, based on nutrient concentrations, existed March-May, at about the same time or shortly after ricefields were drained. Secondary Maximum Contaminant Levels established by the U.S. Environmental Protection Agency (USEPA) were exceeded for sulfate, chloride, iron, or manganese in samples from 20 wells, and for iron or manganese in samples from all surface-water sites. Fewer pesticides were detected in ground water than in surface water. In 11 of of the 29 wells sampled, at least one pesticide or pesticide degradation product was detected. The most frequently detected pesticides or pesticide degradation products in ground water were the herbicides benzaton and atrazine. Concentrations of 47 pesticides and degradation products were detected in surface water. At least 3 pesticides were detected in all surface-water samples. In 72 percent of the samples at least 5 hydrophilic pesticides were detected, and in more than 70 percent of the samples at least 3 hydrophobic pesticides were detected. Although atrazine concentrations in three samples collected in the spring exceeded 3 micrograms per liter, the USEPA Maximum Contaminant Level of 3 micrograms per liter was not exceeded because it is based on an annual average of quarterly samples. Concentrations larger than 3.0 micrograms per liter were not detected in samples collected during other times of the year. Tebuthiuron was detected at all surface-water sites; the largest concentration (6.33 micrograms per liter) was detected at a site on Bayou des Cannes, and was the only detection that exceeded the criterion (1.6 micrograms per liter) for the protection of aquatic life. Malathion was detected at 16 surface-water sites; the largest concentration (0.113 micrograms per liter) was detected at a site on Bayou Lacassine and was the only detection that exceeded the criterion (0.1 micrograms per liter) for the protection of aquatic life. Concentrations of fipronil exceeded numeric targets for acute total maximum daily loads (2.3 micrograms per liter) at 3 sites and chronic total maximum daily loads (4.6 micrograms per liter) at 14 sites. Maximum pesticide concentrations in surface water usually occurred in the spring at about the same time or shortly after ricefields were drained. Concentrations of DDE in bed sediment at two sites exceeded interim freshwater sediment quality guidelines for the protection of aquatic life. Fipronil sulfide and desulfinylpronil were detected at all 17 sites from which bed-sediment samples were collected, but there are no current (2002) guidelines with which to evaluate the environmental effects of fipronil and degradation products. Two methods were used to group the ecological data-collection sites: (1) Sites were grouped before data collection (according to the study design) using drainage area

Water-Resources Investigations Report↗

USGS2001

A spatially referenced regression model (SPARROW) for suspended sediment in streams of the Conterminous U.S.

Suspended sediment has long been recognized as an important contaminant affecting water resources. Besides its direct role in determining water clarity, bridge scour and reservoir storage, sediment serves as a vehicle for the transport of many binding contaminants, including nutrients, trace metals, semi-volatile organic compounds, a nd numerous pesticides (U.S. Environmental Protection Agency, 2000a). Recent efforts to addr ess water-quality concerns through the Total Maximum Daily Load (TMDL) process have iden tified sediment as the single most prevalent cause of impairment in the Nation’s streams a nd rivers (U.S. Environmental Protection Agency, 2000b). Moreover, sediment has been identified as a medium for the tran sport and sequestration of organic carbon, playing a potentia lly important role in understa nding sources and sinks in the global carbon budget (Stallard, 1998). A comprehensive understanding of sediment fate a nd transport is considered essential to the design and implementation of effective plans for sediment management (Osterkamp and others, 1998, U.S. General Accounting Office, 1990). An exte nsive literature addr essing the problem of quantifying sediment transport has produced a nu mber of methods for estimating its flux (see Cohn, 1995, and Robertson and Roerish, 1999, for us eful surveys). The accuracy of these methods is compromised by uncertainty in the concentration measurements and by the highly episodic nature of sediment movement, particul arly when the methods are applied to smaller basins. However, for annual or decadal flux es timates, the methods are generally reliable if calibrated with extended periods of data (Robertson and Roerish, 1999). A substantial literature also supports the Universal Soil Loss Equation (U SLE) (Soil Conservation Service, 1983), an engineering method for estimating sheet and rill erosion, although the empirical credentials of the USLE have recently been questioned (Tri mble and Crosson, 2000). Conversely, relatively little direct evidence is available concerning the fate of sediment. The common practice of quantifying sediment fate with a sediment deliv ery ratio, estimated from a simple empirical relation with upstream basin area, does not artic ulate the relative importance of individual storage sites within a basin (Wolman, 1977). Rates of sediment deposition in reservoirs and flood plains can be determined from empirical measurement s , but only a limited number of sites have been monitored, and net rates of deposition or loss from other potential sinks and sources is largely unknown (Stallard, 1998). In particular, little is known about how much sediment loss from fields ultimately makes its way to stream channels, and how much sediment is subsequently stored in or lost from th e streambed (Meade and Parker, 1985, Trimble and Crosson, 2000). This paper reports on recent progress made to a ddress empirically the question of sediment fate and transport on a national scale. The model pres ented here is based on the SPAtially Referenced Regression On Watershed attr ibutes (SPARROW) methodology, fi rst used to estimate the distribution of nutrients in str eams and rivers of the United Stat es, and subsequently shown to describe land and stream processes affecting the delivery of nutrients (Smith and others, 1997, Alexander and others, 2000, Preston and Brakeb ill, 1999). The model makes use of numerous spatial datasets, available at the national level, to explain long-term sediment water-quality conditions in major streams and rivers throughou t the United States. Sediment sources are identified using sediment erosion rates from the National Resources I nventory (NRI) (Natural Resources Conservation Service, 2000) and apportioned over the landscape according to 30- meter resolution land-use information from th e National Land Cover Data set (NLCD) (U.S. Geological Survey, 2000a). More than 76,000 reservoirs from the National Inventory of Dams (NID) (U.S. Army Corps of Engin eers, 1996) are identified as pot ential sediment sinks. Other, non-anthropogenic sources and sinks are identified using soil in formation from the State Soil Survey Geographic (STATSGO) data base (Schwarz and Alexander, 1995) and spatial coverages representing surficial rock t ype and vegetative cover. The SPA RROW model empirically relates these diverse spatial datasets to estimates of long-term, mean annual sediment flux computed from concentration and flow measurements co llected over the period 1985 -95 from more than 400 monitoring stations maintained by the Na tional Stream Quality Accounting Network (Alexander and others, 1998), the National Wa ter Quality Assessment Program, and U.S. Geological Survey District offices (Turcios and Gray, in press). Th e calibrated model is used to estimate sediment flux for over 60,000 stream segments included in the River Reach File 1 (RF1) stream network (Alexander and others, 1999). SPARROW uses statis tical methods to calibrate a simple, structural model of riverine water quality, one that imposes mass ba lance in accounting for changes in contaminant flux. As applied here, the mass-balance approach facilitates the interpretation of model results in terms of physical processes affecting sediment transport, and makes possible the estimation of various rates of sediment generation and loss associated with stream channels and features of the landscape. The statistical approach provides a basi s for assessing the error of these inferred rates and of the error in extrapolated estimates of sediment flux made for streams in the RF1 network. An important implication of the holistic modeling approach adopted in this analysis is that estimates of sediment production and loss ar e based on, and therefore consistent with, measurements of in-stream flux. Other ancillary information, such as direct measurements of long-term sediment storage and release from rese rvoirs (Steffen, 1996), is incorporated into the analysis by specifying additional equations expl aining these ancillary variables. The imposition of cross-equation constraints affords this info rmation a statistically consistent weight in explaining in-stream sediment flux. Thus, the me thodology described here represents a general framework for synthesizing a wide spectrum of available information relevant to the understanding of sediment fate and transport.

Conterminous United States↗

USGS2008

The persistence of lead from past gasoline emissions and mining drainage in a large riparian system: Evidence from lead isotopes in the Sacramento River, California

Lead concentrations and isotope ratios measured in river water colloids and streambed sediment samples along 426 km of the Sacramento River, California reveal that the influence of lead from the historical mining of massive sulfide deposits in the West Shasta Cu-mining district (at the headwaters of the Sacramento River) is confined to a 60 km stretch of river immediately downstream of that mining region, whereas inputs from past leaded gasoline emissions and historical hydraulic Au-mining in the Sierra Nevadan foothills are the dominant lead sources in the remaining 370 km of the river. Binary mixing calculations suggest that more than 50% of the lead in the Sacramento River outside of the region of influence of the West Shasta Cu-mining district is derived from past depositions of leaded gasoline emissions. This predominance is the first direct documentation of the geographic extent of gasoline lead persistence throughout a large riparian system (>160,000 km 2 ) and corroborates previous observations based on samples taken at the mouth of the Sacramento River. In addition, new analyses of sediment samples from the hydraulic gold mines of the Sierra Nevada foothills confirm the present-day fluxes into the Sacramento River of contaminant metals derived from historical hydraulic Au-mining that occurred during the latter half of the 19th and early part of the 20th centuries. These fluxes occur predominantly during periods of elevated river discharge associated with heavy winter precipitation in northern California. In the broadest context, the study demonstrates the potential for altered precipitation patterns resulting from climate change to affect the mobility and transport of soil-bound contaminants in the surface environment.

Geochimica et Cosmochimica Acta↗

USGS2024

Status of water quality in groundwater resources used for drinking-water supply in the southeastern San Joaquin Valley, 2013–15—California GAMA Priority Basin Project

The California Groundwater Ambient Monitoring and Assessment Program Priority Basin Project (GAMA-PBP) investigated water quality of groundwater resources used for drinking-water supplies in the Madera-Chowchilla, Kings, Kaweah, Tule, and Tulare Lake groundwater subbasins of the southeastern San Joaquin Valley during 2013–15. The study focused primarily on groundwater resources used for domestic-supply wells in the southeastern San Joaquin Valley (SESJV-D), which correspond mostly to shallower parts of aquifer systems, compared to the groundwater resources used for public-supply wells in the southeastern San Joaquin Valley (SESJV-P). The investigation had three components: (1) characterization of the status of water quality in the SESJV-D, (2) comparison between water quality in the SESJV-D and SESJV-P, and (3) identification of natural and anthropogenic factors that potentially could affect water quality in these resources. The characterization of water quality in the SESJV-D was based on data collected from 198 domestic wells sampled during 2013–15 by the U.S. Geological Survey (USGS); characterization of water quality in the SESJV-P was based on data collected from 124 wells sampled by the USGS during 2005–18 and an additional 1,577 wells with publicly available data reported to the California State Water Resources Control Board Division of Drinking Water (SWRCB-DDW). Measured concentrations were compared to regulatory and non-regulatory drinking-water quality benchmarks. A grid-based method was used to estimate the areal proportions of each study area and the whole southeastern San Joaquin Valley with high (greater than benchmark concentration), moderate (greater than half of the benchmark for inorganic and one-tenth of the benchmark for organic), and low concentrations relative to those benchmarks. Natural and anthropogenic factors that could affect groundwater quality for the SESJV-D were identified in the context of the hydrogeologic setting of the southeastern San Joaquin Valley. The considered factors represented hydrologic conditions and position in the groundwater flow system (well depth, lateral position, presence of hydric soils, percentage of coarse-grained sediment, and aridity index), land-use characteristics (percentages of agricultural, urban, and natural land use, percentage of orchard or vineyard land use, and densities of septic tanks and underground storage tanks near the wells), and geochemical conditions (groundwater age class, oxidation-reduction class, pH, and dissolved oxygen and bicarbonate concentrations). Factors are compared between SESJV-D and SESJV-P at the scale of the five study areas. One or more inorganic constituents with U.S. Environmental Protection Agency (EPA) or California maximum contaminant levels (MCLs) were detected at high concentrations in 47 percent of the SESJV-D and in 32 percent of the SESJV-P. The inorganic constituents most commonly present at high concentrations in the SESJV-D were nitrate, uranium, and arsenic. Within the SESJV-D, the proportion of the study area with high concentrations of inorganic constituents ranged from 19 percent in Madera-Chowchilla to 60 percent in Kings and Tulare Lake. One or more inorganic constituents with California State Water Resources Control Board Division of Drinking Water secondary maximum contaminant levels (SMCL-CAs) were detected at high concentrations in 14 percent of the SESJV-D and in 19 percent of the SESJV-P. The constituents most commonly present at high concentrations were manganese, iron, and total dissolved solids (TDS). Although the proportion of SESJV-D and SESJV-P with high concentrations of TDS greater than the upper SMCL were similar at 4 percent, the proportion of the SESJV-D with moderate concentrations (between the recommended and upper SMCL-CA), 30 percent, was greater than the proportion of the SESJV-P with moderate concentrations, 12 percent. One or more organic constituents with MCLs were present at high concentrations in 19 percent of the SESJV-D and in 12 percent of the SESJV-P. All the constituents detected at high concentrations in the SESJV-D were fumigants, primarily 1,2,3-trichloropropane (1,2,3-TCP) and 1,2-dibromo-3-chloropropane (DBCP). Fumigants also were the constituents most commonly detected at high concentrations in the SESJV-P, although high concentrations of solvents also were detected. The SESJV-D dataset included analysis of many organic constituents without MCL benchmarks and with detection levels far below drinking water benchmark concentrations; detections at these low concentrations can be used as tracers of anthropogenic influence on groundwater. Pesticides and degradates of pesticides were detected in 60 percent of the SESJV-D; the most frequently detected pesticides were the herbicides simazine, didealkylatrazine (CAAT, a degradate of simazine and atrazine), diuron, and bromacil.

California↗

USGS2025

Quality of groundwater used for domestic supply in the Gilroy-Hollister basin and surrounding areas, California, 2022

More than 2 million Californians rely on groundwater from domestic wells for drinking-water supply. This report summarizes a 2022 California Groundwater Ambient Monitoring and Assessment Priority Basin Project (GAMA-PBP) water-quality survey of 33 domestic and small-system drinking-water supply wells in the Gilroy-Hollister Valley groundwater basin and the surrounding areas, where more than 20,000 residents are estimated to utilize privately owned domestic wells. The study area includes the Llagas subbasin in the north, the North San Benito subbasin in the south, and the surrounding uplands. The study was focused on groundwater resources used for domestic drinking-water supply, which are mostly drawn from shallower parts of aquifer systems rather than those of groundwater resources used for public drinking-water supply in the same area. This assessment characterized the quality of ambient groundwater in the aquifer before filtration or treatment, rather than the quality of drinking water delivered to the tap. To provide context, the measured concentrations of constituents in groundwater were compared to Federal and California State regulatory and non-regulatory benchmarks for drinking-water quality. A grid-based method was used to estimate the areal proportions of groundwater resources used for domestic drinking wells that have water-quality constituents present at high concentrations (above the benchmark), moderate concentrations (between one-half of the benchmark and the benchmark for inorganic constituents, or between one-tenth of the benchmark and the benchmark for organic constituents), and low concentrations (less than one-half or one-tenth the benchmark for inorganic and organic constituents, respectively). This method provides statistically representative results at the study-area scale and permits comparisons to other GAMA-PBP study areas. In the study area, inorganic constituents in groundwater were greater than regulatory benchmarks (U.S. Environmental Protection Agency [EPA] or State of California maximum contaminant levels [MCLs]) for public drinking-water quality in 24 percent of domestic groundwater resources. The inorganic constituents present at concentrations greater than MCLs for drinking water were nitrate (as nitrogen), barium, chromium, and selenium. Total dissolved solids (TDS) or manganese were present at concentrations greater than the secondary maximum contaminant levels (SMCLs) that the State of California uses as aesthetic-based benchmarks in 48 percent of domestic groundwater resources. No volatile organic compounds or pesticide constituents were present at concentrations greater than regulatory benchmarks. Total coliform bacteria and enterococci were detected in 4 percent of domestic groundwater resources. Per- and polyfluoroalkyl substances (PFAS) were detected in 19 percent of domestic groundwater resources, and 10 percent had concentrations greater than recently enacted (April 2024) EPA MCLs. Physical and chemical factors from natural and anthropogenic sources that could affect the groundwater quality were evaluated using results from statistical testing of associations between constituent concentrations and potential explanatory variables. In this study, relevant physical factors include well construction characteristics, groundwater age, site proximity to groundwater recharge or discharge zones, and potential sources of contamination. Relevant chemical factors include the initial chemistry of the recharge water, the mineralogy of the aquifer sediments, and the subsequent shifts in chemistry as biologic and geologic reactions alter groundwater in the subsurface. Nitrate concentrations were correlated to agricultural land use, distance from the boundary of the Gilroy-Hollister Valley groundwater basin, and the proportion of modern (post-1950s) water captured by the well. Denitrification under anoxic redox conditions can mitigate some nitrate derived from fertilizer application. Total dissolved solids primarily were derived from water-rock interactions with soils and aquifer materials in the study area, but there were high concentrations where agricultural practices contributed additional TDS. Mineralogy of aquifer sediments and rocks also affect barium, selenium, boron, and chromium concentrations in the Gilroy-Hollister Valley groundwater basin. PFAS were positively correlated with urban land use and the proportion of modern water captured by the well.

California↗

USGS2004

Water quality in Big Cypress National Preserve and Everglades National Park — Trends and spatial characteristics of selected constituents

Seasonal changes in water levels and flows in Big Cypress National Preserve (BICY) and Everglades National Park (EVER) affect water quality. As water levels and flows decline during the dry season, physical, geochemical and biological processes increase the breakdown of organic materials and the build-up of organic waste, nutrients, and other constituents in the remaining surface water. For example, concentrations of total phosphorus in the marsh are less than 0.01 milligram per liter (mg/L) during much of the year. Concentrations can rise briefly above this value during the dry season and occasionally exceed 0.1 mg/L under drought conditions. Long-term changes in water levels, flows, water management, and upstream land use also affect water quality in BICY and EVER, based on analysis of available data (1959-2000). During the 1980's and early 1990's, specific conductance and concentrations of chloride increased in the Taylor Slough and Shark River Slough. Chloride concentrations more than doubled from 1960 to 1990, primarily due to greater canal transport of high dissolved solids into the sloughs. Some apparent long-term trends in sulfate and total phosphorus were likely attributable, at least in part, to high percentages of less-than and zero values and to changes in reporting levels over the period of record. High values in nutrient concentrations were evident during dry periods of the 1980's and were attributable either to increased canal inflows of nutrient-rich water, increased nutrient releases from breakdown of organic bottom sediment, or increased build-up of nutrient waste from concentrations of aquatic biota and wildlife in remaining ponds. Long-term changes in water quality over the period of record are less pronounced in the western Everglades and the Big Cypress Swamp; however, short-term seasonal and drought-related changes are evident. Water quality varies spatially across the region because of natural variations in geology, hydrology, and vegetation and because of differences in water management and land use. Nutrient concentrations are relatively low in BICY and EVER compared with concentrations in parts of the northern Everglades that are near agricultural and urban lands. Concentrations of total phosphorus generally are higher in BICY (median values, 1991-2000, were mostly greater than 0.015 mg/L) than in EVER (median values, 1991-2000, less than 0.01 mg/L), probably because of higher phosphorus in natural sources such as shallow soils, rocks, and ground water in the Big Cypress region than in the Everglades region. Conversely, concentrations of chloride and sulfate are higher in EVER (median values in Shark River Slough, 1991-2000, mostly greater than 2 mg/L sulfate and 50 mg/L chloride) than in BICY (median values, 1991-2000, less than 1 mg/L sulfate and at most sites less than 20 mg/L chloride), probably because of the canal transport system, which conveys more water from an agricultural source into EVER than into BICY. Trace elements and contaminants such as pesticides and other toxic organic compounds are in relatively low concentrations in BICY and EVER compared with concentrations in parts of the northern Everglades near agricultural and urban sources. Concentrations rarely exceeded aquatic life criteria in BICY and EVER. Atrazine was the only pesticide found in water that exceeded the criteria (in 2 out of 304 samples). The pesticides heptachlor expoxide, lindane, and p,p?-DDE exceeded criteria in canal bed sediments in 1, 2, and 16 percent of the samples, respectively.

Florida↗

USGS2009

Sources of land-derived runoff to a coral reef-fringed embayment identified using geochemical tracers in nearshore sediment traps

Geochemical tracers, including Ba, Co, Th, 7 Be, 137 Cs and 210 Pb, and magnetic properties were used to characterize terrestrial runoff collected in nearshore time-series sediment traps in Hanalei Bay, Kauai, during flood and dry conditions in summer 2006, and to fingerprint possible runoff sources in the lower watershed. In combination, the tracers indicate that runoff during a flood in August could have come from cultivated taro fields bordering the lower reach of the river. Land-based runoff associated with summer floods may have a greater impact on coral reef communities in Hanalei Bay than in winter because sediment persists for several months. During dry periods, sediment carried by the Hanalei River appears to have been mobilized primarily by undercutting of low 7 Be, low 137 Cs riverbanks composed of soil weathered from tholeiitic basalt with low Ba and Co concentrations. Following a moderate rainfall event in September, high 7 Be sediment carried by the Hanalei River was probably mobilized by overland flow in the upper watershed. Ba-desorption in low-salinity coastal water limited its use to a qualitative runoff tracer in nearshore sediment. 210 Pb had limited usefulness as a terrestrial tracer in the nearshore due to a large dissolved oceanic source and scavenging onto resuspended bottom sediment. 210 Pb-scavenging does, however, illustrate the role resuspension could play in the accumulation of particle-reactive contaminants in nearshore sediment. Co and 137 Cs were not affected by desorption or geochemical scavenging and showed the greatest potential as quantitative sediment provenance indicators in material collected in nearshore sediment traps.

Estuarine, Coastal and Shelf Science↗

USGS2000

Occurrence of organochlorine pesticides in streambed sediment and fish from selected streams on the island of Oahu, Hawaii, 1998

Organochlorine pesticides were heavily used from the mid-1940s to the mid-1980s. The persistence of organochlorine pesticides, their tendency to accumulate in soil, sediment, and biota, and their harmful effects on wildlife brought this class of compounds into disfavor and eventually resulted in restriction or cancellation of most of them in the United States (Nowell and others, 1999). Despite use restrictions, these compounds continue to be detected in sediment and fish tissue samples. This study was undertaken as part of the National Water-Quality Assessment (NAWQA) program of the U.S. Geological Survey (USGS). The NAWQA program assesses watersheds as integrated systems, focusing on chemical concentrations, physical conditions, and biological status in streams. One component of NAWQA is an occurrence survey of organic contaminants and trace elements in stream bed sediment and fish tissue. The goal of the Oahu stream bed sediment and fish tissue occurrence survey was to determine which organochlorine contaminants are present in streams around the island, and with which land uses they are associated. An understanding of relations between land use and organochlorine compounds will allow land management practices to be designed to reduce the loading of contaminants to streams and nearshore waters.

Hawaii↗