Search USGS⌕ Search

SEARCH · Search USGS

Results for “Scientific Investigations Report”

Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,405 records · Page 78Linked to original sources
USGS2005

Hydrogeology and trichloroethene contamination in the sea-level aquifer beneath the Logistics Center, Fort Lewis, Washington

The U.S. Army disposed of waste trichloroethene (TCE) and other materials in the East Gate Disposal Yard near the Logistics Center on Fort Lewis, Washington, from the 1940s to the early 1970s. As a result, ground water contaminated with primarily TCE extends more than 3 miles downgradient from the East Gate Disposal Yard. The site is underlain by a complex and heterogeneous sequence of glacial and non-glacial deposits that have been broadly categorized into an upper and a lower aquifer (the latter referred to as the sea-level aquifer). TCE contamination was detected in both aquifers. This report describes an investigation by the U.S. Geological Survey (USGS) of the source, migration, and attenuation of TCE in the sea-level aquifer. A refined conceptual model for ground-water flow and contaminant migration into and through the sea-level aquifer was developed in large part from interpretation of environmental tracer data. The tracers used included stable isotopes of oxygen (18O), hydrogen (2H), and carbon (13C); the radioactive hydrogen isotope tritium (3H); common ions and redox-related analytes; chlorofluorocarbons; and sulfur hexafluoride. Tracer and TCE concentrations were determined for samples collected by the USGS from 37 wells and two surface-water sites in American Lake during 1999-2000. Ground-water levels were measured by the USGS in more than 40 wells during 2000-01, and were combined with measurements by the U.S. Army and others to create potentiometric-surface maps. Localized ground-water flow features were identified that are of particular relevance to the migration of TCE in the study area. A ridge of ground water beneath American Lake diverts the flow of TCE-contaminated ground water in the sea-level aquifer to the west around the southern end of the lake. Tracer data provided clear evidence that American Lake is a significant source of recharge to the sea-level aquifer that has created that ridge of ground water. High ground-water altitudes at locations north and northeast of the Logistics Center combined with the ridge beneath American Lake prevent TCE contaminated water beneath the Logistics Center from migrating toward municipal water-supply wells northeast of the site. The 1999-2000 TCE concentrations measured by the USGS at older wells screened in the sea-level aquifer were similar to those measured since 1995, but the known downgradient extent of the TCE contamination expanded nearly 2 miles after the Army installed and sampled new wells during 2003-04. Concentrations of TCE in the sea-level aquifer were consistently highest in the upper part of the aquifer throughout the plume, although TCE has spread throughout much of the thickness of the aquifer in the downgradient portions of the plume. Environmental tracer data indicated that the primary pathway for contaminant migration into the sea-level aquifer is through the previously identified confining unit window, an area where the predominately fine-grained confining unit is relatively coarse grained and more permeable. Other less substantial pathways for contaminant migration also were identified near the East Gate Disposal Yard and the I-5 pump-and-treat facilities. Those areas are near active pumping wells and ground-water reintroduction facilities, but there is no evidence that the contaminant migration was caused or enhanced by those activities. Within the sea-level aquifer, TCE concentrations continue to migrate westward in the flow field strongly influenced by ground-water recharge from American Lake. Historical data are not available to definitively determine if the 5-?g/L leading edge of the current TCE plume is stable or if it is still moving downgradient. However, an evaluation of the available data combined with TCE traveltime estimates indicates that the peak TCE concentrations in the sea-level aquifer may have not yet reached the wells near the currently defined leading edge of the plume. Hypothetically, the 5-?g/L leading edge

Scientific Investigations Report↗
USGS2021

Substrate particle-size distribution, dissolved-oxygen concentrations, sediment temperatures, and groundwater/surface-water exchange in shoreline spawning habitat of sockeye salmon (Oncorhynchus nerka) of Lake Ozette, Western Washington

Sockeye salmon ( Oncorhynchus nerka ) spawn at beaches along Lake Ozette’s shoreline and within its tributary streams including Umbrella Creek and Big River in western Washington. The tributary-spawning aggregate of the Lake Ozette sockeye salmon population has been increasing from very low abundance through hatchery supplementation, but the beach-spawning aggregate has decreased from the early 20th century resulting in an Endangered Species Act listing of the Lake Ozette sockeye salmon population as “Threatened” in 1999. Among several factors inhibiting the recovery of beach spawning sockeye salmon, the quality of spawning habitat in beaches and low dissolved-oxygen concentrations in beach gravels during incubation were identified as important limitations on the recovery of this population. Proliferation of primarily native near-shore vegetation during the 20th century, as a result of alterations in the lake hydroperiod, accompanied by fine-grained sediment deposition was hypothesized as a potential cause of low rates of water circulation and dissolved-oxygen concentrations in beach spawning gravels. The potential for shoreline vegetation removal to restore spawning habitat function, including dissolved-oxygen concentrations, was evaluated in this report by measuring continuous dissolved-oxygen concentrations with data-logging dissolved-oxygen sensors, by measuring particle-size distribution of beach sediment, and by estimating groundwater/surface-water exchange using vertical sediment temperature profiles at three shoreline sampling areas. These sampling areas included an area of current spawning devoid of shoreline vegetation, an adjacent vegetated area, and an adjacent treatment area where a 3-meter-wide swath of existing above-ground vegetation was removed in 2018 prior to the study. Substrate particle-size distributions, dissolved-oxygen concentrations, sediment temperatures, and groundwater/surface-water exchange were compared among the three shoreline sampling areas. Median grain size (D 50 ) of sediment varied at sampling stations from medium sand fine to coarse gravel. The coarsest sediment generally occurred in the current spawning area that was devoid of vegetation; whereas the vegetated shoreline and the shoreline where above-ground vegetation was removed were characterized by finer sediment. Removal of above-ground vegetation resulted in increased D 50 at the most shoreward station at the treatment sampling area from 8.2 millimeters in 2018 to 21.6 millimeters in 2019 but other changes in substrate particle-size distribution in the treatment area were negligible. Increased grain size from 2018 to 2019 at this site suggests that while higher wave energy was allowed to mobilize sediment in the backshore area of the treatment area and winnow fine sediment during the winter, residual root structure in the treatment area may have limited the ability of wave energy to mobilize sediment after removal. During the November 2018 to March 2019 incubation period for sockeye salmon, dissolved-oxygen concentrations at the depth of sockeye salmon egg pockets (15–25 centimeters) within all three shoreline sampling areas were less than 1 milligram per liter throughout the deployment time (October 2018—May 2019) and below the threshold to sustain sockeye salmon embryo development (3 milligrams per liter). In addition, the similarity of dissolved-oxygen concentrations among all three shoreline sampling areas indicates that above-ground vegetation removal did not increase subsurface dissolved-oxygen concentrations. Groundwater/surface-water exchange measured from sediment temperature profiles were variable both within and across shoreline sampling areas. At the most lakeward stations, groundwater discharge to the lake ranged from 0.25 to 0.007 meter per day and was highest at the control station and lowest at the vegetated station. However, in general, the differences in groundwater/surface-water exchange across the three shoreline sampling areas were negligible. Collectively, these results suggest the process of removing above-ground vegetation had little effect on subsurface dissolved-oxygen concentrations and groundwater/surface-water exchange during the study period, but limitations of the study design, including retention of below-surface root cohesion after above-ground vegetation removal, too narrow of a band of vegetation removal, and a limited duration of the monitoring period, may have pre vented wave energy from winnowing fine-grained sediment along the shoreline and altering subsurface dissolved-oxygen concentrations during the study period. Response of the substrate particle-size distribution, groundwater/surface-water exchange, and subsurface dissolved-oxygen concentrations to shoreline vegetation removal that includes root-zone removal over a larger extent and longer periods than the 7-month study period from October 2018 to May 2019, however, remain unknown and warrant further investigation.

Washington↗
USGS2013

Prioritization of constituents for national- and regional-scale ambient monitoring of water and sediment in the United States

A total of 2,541 constituents were evaluated and prioritized for national- and regional-scale ambient monitoring of water and sediment in the United States. This prioritization was done by the U.S. Geological Survey (USGS) in preparation for the upcoming third decade (Cycle 3; 2013–23) of the National Water-Quality Assessment (NAWQA) Program. This report provides the methods used to prioritize the constituents and the results of that prioritization. Constituents were prioritized by the NAWQA National Target Analyte Strategy (NTAS) work group on the basis of available information on physical and chemical properties, observed or predicted environmental occurrence and fate, and observed or anticipated adverse effects on human health or aquatic life. Constituents were evaluated within constituent groups that were determined on the basis of physical or chemical properties or on uses or sources. Some constituents were evaluated within more than one constituent group. Although comparable objectives were used in the prioritization of constituents within the different constituent groups, differences in the availability of information accessed for each constituent group led to the development of separate prioritization approaches adapted to each constituent group to make best use of available resources. Constituents were assigned to one of three prioritization tiers: Tier 1, those having the highest priority for inclusion in ambient monitoring of water or sediment on a national or regional scale (including NAWQA Cycle 3 monitoring) on the basis of their likelihood of environmental occurrence in ambient water or sediment, or likelihood of effects on human health or aquatic life; Tier 2, those having intermediate priority for monitoring on the basis of their lower likelihood of environmental occurrence or lower likelihood of effects on human health or aquatic life; and Tier 3, those having low or no priority for monitoring on the basis of evidence of nonoccurrence or lack of effects on human health or aquatic life, or of having insufficient evidence of potential occurrence or effects to justify placement into Tier 2. Of the 1,081 constituents determined to be of highest priority for ambient monitoring (Tier 1), 602 were identified for water and 686 were identified for sediment (note that some constituents were evaluated for both water and sediment). These constituents included various types of organic compounds, trace elements and other inorganic constituents, and radionuclides. Some of these constituents are difficult to analyze, whereas others are mixtures, isomers, congeners, salts, and acids of other constituents; therefore, modifications to the list of high-priority constituents for ambient monitoring could be made on the basis of the availability of suitable methods for preparation, extraction, or analysis. An additional 1,460 constituents were placed into Tiers 2 or 3 for water or sediment, including some constituents that had been placed into Tier 1 for a different matrix; 436 constituents were placed into Tier 2 for water and 246 constituents into Tier 2 for sediment; 979 constituents were placed into Tier 3 for water and 779 constituents into Tier 3 for sediment.

Scientific Investigations Report↗
USGS2024

Wildland fire effects on sediment, salinity, and selenium yields in a basin underlain by Cretaceous marine shales near Rangely, Colorado

Understanding and quantifying soil erosion from rangelands is a high priority for land managers, especially in areas underlain by Cretaceous Mancos Shale, which is a natural source of sediment, salinity, and selenium to surface waters in many areas of western Colorado and eastern Utah. The purpose of this report is to present the results of a U.S. Geological Survey study that assessed sediment, salinity, and selenium yields after the Dead Dog wildfire (fire began June 11, 2017) in northwestern Colorado. Two methodologies were used to quantify erosion, with different data requirements and analytical complexity. The first approach was the use of a process-based erosion model, the Watershed Erosion Prediction Project, which uses inputs of climate, topography, vegetation, and soils data from existing datasets to predict erosion, making this approach easily extensible to other areas. The second approach required more complex data collection and was used to measure erosion and deposition by differencing digital elevation models created from uncrewed aerial vehicle imagery collected in 2016 (pre-fire) and 2021 (post-fire). Sediment, salinity, and selenium yields were calculated from the volumetric estimates of erosion from both methods, and a discussion of factors that may have contributed to overall findings, including vegetation, fire effects, and soil characteristics, is included. The two approaches yielded different outputs. Results from the Watershed Erosion Prediction Project model indicated that almost no erosion occurred after the Dead Dog fire. However, morphological changes in the study basin after the Dead Dog fire were visible in the pre- and post-fire imagery and measured in the digital elevation model differencing technique, with net erosion occurring in channel and landscape extents, though calculated erosion rates and salinity and selenium yields were relatively small. Visible and measured morphological changes consisted primarily of incision and deposition within stream channels and rill incision and expansion on steeper slopes. Widespread sheet erosion was not evident. Much of the new erosion originated within, and immediately below, previously vegetated areas that were then burned by the wildfire. Greater erosion rates and salinity and selenium yields were measured in the channel extent relative to the landscape extent. Calculated erosion rates ranged from 0.24 to 0.45 megagrams per hectare per year. These results indicate that the Dead Dog fire resulted in increased erosion in the study basin, yet these effects were relatively small based on the overall magnitude of modeled and measured erosion from the Watershed Erosion Prediction Project and the digital elevation model differencing technique. Minimal erosion in the basin is likely due to local site characteristics typical of soils derived from Mancos Shale, including the presence of robust physical crusts and biological soil crusts, and limitations of the methods based on data availability. Focusing uncrewed aerial vehicle flights on key areas (individual steep slopes, high-intensity burn areas, specific stream reaches) could likely increase understanding of erosional process with less effort and error than doing landscape-level flights.

Colorado↗
USGS2005

Simulation of flow and sediment mobility using a multidimensional flow model for the White Sturgeon critical-habitat reach, Kootenai River near Bonners Ferry, Idaho

In 1994, the Kootenai River white sturgeon (Acipenser transmontanus) was listed as an Endangered Species as a direct result of two related observations. First, biologists observed that the white sturgeon population in the Kootenai River was declining. Second, they observed a decline in recruitment of juvenile sturgeon beginning in the 1950s with an almost total absence of recruitment since 1974, following the closure of Libby Dam in 1972. This second observation was attributed to changes in spawning and (or) rearing habitat resulting from alterations in the physical habitat, including flow regime, sediment-transport regime, and bed morphology of the river. The Kootenai River White Sturgeon Recovery Team was established to find and implement ways to improve spawning and rearing habitat used by white sturgeon. They identified the need to develop and apply a multidimensional flow model to certain reaches of the river to quantify physical habitat in a spatially distributed manner. The U.S. Geological Survey has addressed these needs by developing, calibrating, and validating a multidimensional flow model used to simulate streamflow and sediment mobility in the white sturgeon critical-habitat reach of the Kootenai River. This report describes the model and limitations, presents the results of a few simple simulations, and demonstrates how the model can be used to link physical characteristics of streamflow to biological or other habitat data. This study was conducted in cooperation with the Kootenai Tribe of Idaho along a 23-kilometer reach of the Kootenai River, including the white sturgeon spawning reach near Bonners Ferry, Idaho that is about 108 to 131 kilometers below Libby Dam. U.S. Geological Survey's MultiDimensional Surface-Water Modeling System was used to construct a flow model for the critical-habitat reach of the Kootenai River white sturgeon, between river kilometers 228.4 and 245.9. Given streamflow, bed roughness, and downstream water-surface elevation, the model computes the velocity field, water-surface elevations, and boundary shear stress throughout the modeled reach. The 17.5 kilometer model reach was subdivided into two segments on the basis of predominant grain size: a straight reach with a sand, gravel, and cobble substrate located between the upstream model boundary at river kilometer 245.9 and the upstream end of Ambush Rock at river kilometer 244.6, and a meandering reach with a predominately sand substrate located between upstream end of Ambush Rock and the downstream model boundary at river kilometer 228.4. Model cell size in the x and y (horizontal) dimensions is 5 meters by 5 meters along the computational grid centerline with 15 nodes in the z (vertical) dimension. The model was calibrated to historical streamflows evenly distributed between 141.6 and 2,548.9 cubic meters per second. The model was validated by comparing simulated velocities with velocities measured at 15 cross sections during steady streamflow. These 15 cross sections were each measured multiple (7-13) times to obtain velocities suitable for comparison to the model results. Comparison of modeled and measured velocities suggests that the model does a good job of reproducing flow patterns in the river, although some discrepancies were noted. The model was used to simulate water-surface elevation, depth, velocity, bed shear stress, and sediment mobility for Kootenai River streamflows of 170, 566, 1,130, 1,700, and 2,270 cubic meters per second (6,000, 20,000, 40,000, 60,000, and 80,000 cubic feet per second). The three lowest streamflow simulations represent a range of typical river conditions before and since the construction of Libby Dam, and the highest streamflow simulation (2,270 cubic meters per second) is approximately equal to the annual median peak streamflow prior to emplacement of Libby Dam in 1972. Streamflow greater than 566 cubic meters per second were incrementally increased by 570 cubic meters per second. For each

Scientific Investigations Report↗
USGS2014

Steady-state numerical groundwater flow model of the Great Basin carbonate and alluvial aquifer system

This report describes the construction, calibration, evaluation, and results of a steady-state numerical groundwater flow model of the Great Basin carbonate and alluvial aquifer system that was developed as part of the U.S. Geological Survey National Water Census Initiative to evaluate the nation’s groundwater availability. The study area spans 110,000 square miles across five states. The numerical model uses MODFLOW-2005, and incorporates and tests complex hydrogeologic and hydrologic elements of a conceptual understanding of an interconnected groundwater system throughout the region, including mountains, basins, consolidated rocks, and basin fill. The level of discretization in this model has not been previously available throughout the study area. Observations used to calibrate the model are those of water levels and discharge to evapotranspiration, springs, rivers, and lakes. Composite scaled sensitivities indicate the simulated values of discharge to springs, rivers, and lakes provide as much information about model parameters as do simulated water-level values. The model has 176 parameters and little parameter correlation. The simulated equivalents to observations provide enough information to constrain most parameters to smaller ranges than the conceptual constraints, and most parameter values are within reasonable ranges. Model fit to observations, comparison of simulated to conceptual water-level contours, and comparison of simulated to conceptual water budgets indicate this model provides a reasonable representation of the regional groundwater system. Eighty-six percent of the simulated values of water levels in wells are within 119 feet (one standard deviation of the error) of the observed values. Ninety percent of the simulated discharges are within 30 percent of the observed values. Total simulated recharge in the study area is within 10 percent of the conceptual amount; total simulated discharge is the same as conceptual discharge. Comparison of simulated hydraulic heads with the conceptual potentiometric surface indicates that the model accurately depicts major features of the hydraulic-head distribution. The incorporation of new recharge estimates and of mountain springs and streams as model observations creates higher simulated recharge mounds under many mountain ranges and highlights that in many cases, the regional flow paths go around, not through (or under) mountain ranges. Results from the model show that much of the flow in the groundwater system occurs in deeper layers, even though about 86 percent of the discharge occurs in layer 1. Over 95 percent of the recharge moves down from layer 1, and about 25 percent moves down to layer 8. The model was used to delineate six simulated groundwater flow regions that connect recharge areas to discharge areas. The eastern Great Salt Lake and Great Salt Lake Desert model regions contain 75 percent of the groundwater budget, but only 42 percent of the study area. In contrast, the more southern Death Valley and Colorado model regions contain only 12 percent of the groundwater budget, but 37 percent of the study area. Examples of potential use of the model to investigate the groundwater system include (1) the effects of different recharge, (2) different interpretations of the extent or offset of long faults or fault zones, and (3) different conceptual models of the spatial variation of hydraulic properties. The model can also be used to examine the ultimate effects of groundwater withdrawals on a regional scale, to provide boundary conditions for local-scale models, and to guide data collection.

Great Basin↗
USGS2022

Seasonal and long-term clarity trend assessment of Lake Tahoe, California–Nevada

The clarity of Lake Tahoe, observed using a Secchi disk on a regular basis since the late 1960s, continues to be a sentinel metric of lake health. Water clarity is influenced by physical and biological processes and has declined in the five decades of monitoring, revealing differences between summer (June–September) and winter (December–March). This document summarizes key findings of a study of Lake Tahoe water clarity, including long-term variability and the relative importance of several influencing variables and processes. This study, prepared in cooperation with the Nevada Division of Environmental Protection, focused on (1) an apparent divergence in clarity trends between summer and winter periods, (2) observed changes in in-lake physical and ecological variables that may influence or control seasonal and annual clarity trends, and (3) five research hypotheses regarding lake clarity that were developed by Lake Tahoe management agencies. Previously collected data were used to complete this study. Trend analysis confirmed that winter clarity stabilized (that is, there is no longer a statistically significant trend up or down) during the last 20 years. Evaluation of clarity for selected months in the 50-year Secchi disk clarity dataset showed that only two summer months, July and August, had statistically significant decreases in clarity from 2000–19. Different subsets of available data were analyzed to reveal the presence or absences of trends for each season, decade, and month. Five hypotheses related to lake clarity were part of the study described by this report. Hypothesis 1 stated that clarity is controlled predominantly by the distribution and volumetric density of fine particles in suspension. This hypothesis was studied using available data describing in-lake fine (0–20 micrometers) particles from 2008–19. Water clarity was negatively correlated with in-lake particle abundance, with particles in the 1.0-4.6 μm range having the greatest effect, consistent with light-scattering theory. Estimated abundances of diatoms of the genus Cyclotella also were found to be negatively correlated with clarity. Data limitations precluded a complete investigation of hypothesis 2, which stated that the observed improvements in winter water clarity are a response to decreasing fine suspended-sediment concentrations in the lake resulting from load reductions from upland sources in and near urbanized areas. Data describing fine-sediment loading from urban areas to the lake were only available since 2014, and only once or twice per month. A slight, statistically significant, negative correlation was identified between urban fine-particle loading and monthly lake clarity with a 4-month lag. Particle abundance in monitored streams is highly correlated with simultaneous particle abundance in the lake. Hypothesis 3 stated that changing hydrodynamic conditions in the lake are increasing thermal stability and resistance to mixing. Trend analyses performed on stability index and buoyancy frequency time series computed from long-term observations of lake temperatures support the hypothesis that hydrodynamic conditions have evolved since 1969 to increase the lake’s resistance to mixing. The date of maximum mixing in winter has become progressively earlier in the year. Lake density stratification, defined using the stability index, is commencing earlier in the year and extending a month longer than in the early years of the monitoring program. Hypothesis 4 stated that the trend of decreasing summer clarity is a result of earlier, prolonged, and more intense stratification. Statistically significant correlations were found between summer clarity and (1) date of onset of stratification, (2) duration of stratification, and (3) buoyancy frequency. Hypothesis 5 stated that ecological (food web) interactions are causing changes in the trends of seasonal or annual clarity; data supporting hypothesis 5 were limited to examples from other systems and to intermittent monitoring of Lake Tahoe and Emerald Bay. The resulting narrative assessment was motivated by a 6-year study of Mysis shrimp disappearance and return in Emerald Bay. The available data and a large body of published literature are consistent with the inference that Mysis shrimp-induced food web changes are causing changes in the trends of seasonal or annual clarity. This food-web study focused on the relations between introduced Mysis shrimp, the native cladocerans ( Daphnia and Bosmina ) that were largely eliminated following Mysis introduction, and the effect on fine particles within the lake. The records of Mysis and other zooplankton data for Lake Tahoe are episodic and have large gaps. Consequently, statistical analyses could not be conducted to compare zooplankton data with other variables. The long-term record, however, indicates that the key effect was a change to the phytoplankton assemblage, where larger diatoms disappeared, likely due to Mysis grazing, only to be replaced by Cyclotella that are an order-of-magnitude smaller and have increased the abundance and volumetric density of total fine particles in suspension (biotic and abiotic).

California↗
USGS2014

An overview comparing results from two decades of monitoring for pesticides in the Nation’s streams and rivers, 1992-2001 and 2002-2011

This report provides an overview of the U.S. Geological Survey National Water-Quality Assessment program and National Stream Quality Accounting Network findings for pesticide occurrence in U.S. streams and rivers during 2002–11 and compares them to findings for the previous decade (1992–2001). In addition, pesticide stream concentrations were compared to Human Health Benchmarks (HHBs) and chronic Aquatic Life Benchmarks (ALBs). The comparisons between the decades were intended to be simple and descriptive. Trends over time are being evaluated separately in a series of studies involving rigorous trend analysis. During both decades, one or more pesticides or pesticide degradates were detected more than 90 percent of the time in streams across all types of land uses. For individual pesticides during 2002–11, atrazine (and degradate, deethylatrazine), carbaryl, fipronil (and degradates), metolachlor, prometon, and simazine were detected in streams more than 50 percent of the time. In contrast, alachlor, chlorpyrifos, cyanazine, diazinon, EPTC, Dacthal, and tebuthiuron were detected less frequently in streams during the second decade than during the first decade. During 2002–11, only one stream had an annual mean pesticide concentration that exceeded an HHB. In contrast, 17 percent of agriculture land-use streams and one mixed land-use stream had annual mean pesticide concentrations that exceeded HHBs during 1992–2001. The difference between the first and second decades in terms of percent of streams exceeding HHBs was attributed to regulatory changes. During 2002–11, nearly two-thirds of agriculture land-use streams and nearly one-half of mixed land-use streams exceeded chronic ALBs. For urban land use, 90 percent of the streams exceeded a chronic ALB. Fipronil, metolachlor, malathion, cis-permethrin, and dichlorvos exceeded chronic ALBs for more than 10 percent of the streams. For agriculture and mixed land-use streams, the overall percent of streams that exceeded a chronic ALB was very similar between the decades. For urban land-use streams, the percent of streams exceeding a chronic ALB during 2002–11 nearly doubled that seen during 1992–2001. The reason for this difference was the inclusion of fipronil monitoring during the second decade. Across all land-use streams, the percent of streams exceeding a chronic ALB for fipronil during 2002–11 was greater than all other insecticides during both decades. The percent of streams exceeding a chronic ALB for metolachlor, chlorpyrifos, diazinon, malathion, and carbaryl decreased from the first decade to the second decade. The results of the 2002–11 summary and comparison to 1992–2001 are consistent with the results from more rigorous trend analysis of pesticide stream concentrations for individual streams in various regions of the U.S.

Scientific Investigations Report↗
USGS2021

Groundwater conditions and trends, 2009–19, Saipan, Commonwealth of the Northern Mariana Islands

Groundwater is the primary source of municipal water for Saipan. Nearly all groundwater for the municipal water supply is withdrawn from a freshwater-lens system with a limited amount of freshwater that is susceptible to saltwater intrusion. The status of Saipan’s groundwater resources has not been thoroughly assessed since 2003. The U.S. Geological Survey—in cooperation with the Office of Grants Management, Commonwealth of the Northern Mariana Islands, and in collaboration with the Commonwealth Utilities Corporation—assessed the status and characteristics of Saipan’s groundwater resources by (1) evaluating groundwater withdrawals from municipal production wells during 2014–19, (2) evaluating chloride concentrations of municipal groundwater withdrawals during 2009–19, and (3) collecting salinity profiles at selected groundwater-monitoring wells during 2018–19. At the time of preparation of this report (2019), the periods of groundwater-withdrawal and chloride-concentration data represent the only periods of data available since 2003. During 2014–19, groundwater for the municipal water supply was withdrawn from about 143 production wells. Most of the wells are drilled into limestone formations in the southern plateau and the Kagman Peninsula and generally have withdrawal rates of about 40–60 gallons per minute. Records of monthly groundwater withdrawals from municipal production wells were available for May 2014–March 2019; during that period, monthly withdrawals ranged from 5.7 to 12.8 million gallons per day (Mgal/d) and averaged 9.3 Mgal/d, although records were unavailable for 9 months (May 2015–January 2016). Private wells, mainly located on the western coastal plain, currently are permitted to withdraw a total of about 7 Mgal/d of groundwater. Actual groundwater withdrawals from private wells, however, are uncertain because withdrawal records for private wells are not available. The Commonwealth Utilities Corporation measured the chloride concentration of groundwater pumped from each of its production wells about twice a year from 2009–19; during this period, 146 production wells were active and sampled. Only 32 of the 146 (22 percent) municipal production wells had median chloride concentrations less than or equal to 250 milligrams per liter (mg/L), the secondary drinking water standard set by the U.S. Environmental Protection Agency. Eighty-one wells (55 percent) pumped water with median chloride concentrations above 500 mg/L. The Mann-Kendall test was used to determine if chloride concentrations of groundwater withdrawals at 146 municipal production wells had statistically significant trends during December 2009–February 2019. Trends were considered statistically significant for probability values (p-values) less than or equal to 0.05. Test results indicate an upward trend at 9 wells, a downward trend at 52 wells, and no trend at 85 wells. Salinity profiles were measured in 12 selected monitor wells during July–August 2018 and were measured in six of the twelve selected monitor wells during March 2019. The salinity profiles were used to estimate the thickness of the freshwater lens at 10 monitor wells; freshwater-lens thickness was greatest (46 ft) in a monitor well in the Dan Dan well field near the northern part of the southern plateau. Freshwater-lens-thickness estimates elsewhere were (1) between 0 and 28 ft for the remaining monitor wells on the southern plateau, (2) between 19 and 21 ft for monitor wells on the Kagman Peninsula, (3) 2 ft for a monitor well in the Sablan Quarry well field on west-central Saipan, and (4) 8 ft for a monitor well in the Marpi Quarry well field on northern Saipan.

Commonwealth of the Norhtern Marianas Islands, Sai↗
USGS2011

Numerical simulation of groundwater flow for the Yakima River basin aquifer system, Washington

A regional, three-dimensional, transient numerical model of groundwater flow was constructed for the Yakima River basin aquifer system to better understand the groundwater-flow system and its relation to surface-water resources. The model described in this report can be used as a tool by water-management agencies and other stakeholders to quantitatively evaluate proposed alternative management strategies that consider the interrelation between groundwater availability and surface-water resources. The model was constructed using the U.S. Geological Survey finite-difference model MODFLOW. The model uses 1,000-foot grid cells that subdivide the model domain by 600 rows and 600 columns. Forty-eight hydrogeologic units in the model are included in 24 model layers. The Yakima River, all major tributaries, and major agricultural drains are included in the model as either drain cells or streamflow-routing cells. Recharge was estimated from previous work using physical process models. Groundwater pumpage specified in the model is derived from monthly pumpage values previously estimated from another component of this study. The pumpage values include estimates for wells with standby/reserve rights that are used in drought years. The model was calibrated to the transient conditions for October 1959 to September 2001. Calibration was completed by using traditional trial-and-error methods and automated parameter-estimation techniques. The model simulates the shape and slope of the water table that generally is consistent with mapped water levels. At well observation points, the average difference between simulated and measured hydraulic heads is -49 feet with a root-mean-square error divided by the total difference in water levels of 4 percent. Simulated river streamflow was compared to measured streamflow at seven sites. Annual differences between measured and simulated streamflow for the sites ranged from 1 to 9 percent. Calibrated model output includes a 42-year estimate of a monthly water budget for the aquifer system. Five applications (scenarios) of the model were completed to obtain a better understanding of the relation between pumpage and surface-water resources and groundwater levels. For the first three scenarios, the calibrated transient model was used to simulate conditions without: (1) pumpage from all hydrogeologic units, (2) pumpage from basalt hydrogeologic units, and (3) exempt-well pumpage. The simulation results indicated potential streamflow capture by the existing pumpage from 1960 through 2001. The quantity of streamflow capture generally was inversely related to the total quantity of pumpage eliminated in the model scenarios. For the fourth scenario, the model simulated 1994 through 2001 under existing conditions with additional pumpage estimated for pending groundwater applications. The differences between the calibrated model streamflow and this scenario indicated additional decreases in streamflow of 91 cubic feet per second in the model domain. Existing conditions representing 1994 through 2001 were projected through 2025 for the fifth scenario and indicated additional streamflow decreases of 38 cubic feet per second and groundwater-level declines.

Scientific Investigations Report↗
USGS2019

Tritium as an indicator of modern, mixed, and premodern groundwater age

Categorical classification of groundwater age is often used for the assessment and understanding of groundwater resources. This report presents a tritium-based age classification system for the conterminous United States based on tritium ( 3 H) thresholds that vary in space and time: modern (recharged in 1953 or later), if the measured value is larger than an upper threshold; premodern (recharged prior to 1953) if the measured value is smaller than a lower threshold; or mixed if the measured value is between the two thresholds. Inclusion of spatially varying thresholds, rather than a single threshold, accounts for the observed systematic variation in 3 H deposition across the United States. Inclusion of time-varying thresholds, rather than a single threshold, accounts for the date of sampling given the radioactive decay of 3 H. The efficacy of the tritium-based age classification system was evaluated at national and regional scales. The system was evaluated at a national scale by classifying samples from 1,788 public-supply wells distributed across 19 principal aquifers and comparing those results with expectations based on hydrogeologic principles. The regional-scale data are from five paired networks of shallow and deep wells (287 wells). As expected, modern groundwater is more prevalent in shallow wells than in deeper wells, in fractured-rock and carbonate aquifers as compared to clastic aquifers, in unconfined areas as compared to confined areas, and in humid climates as compared to arid climates. The results from a tritium-based age classification system compared favorably with the results of 14 previous studies of groundwater ages that used different age tracers and analytical methods. The wells and samples from the Cambrian-Ordovician aquifer that had been analyzed using a more complex multi-tracer analysis were also analyzed using the tritium-based age classification system, and there was a close match between the two methods. The results from these various studies suggest that the tritium-based age classification system may be informative as a screening tool prior to selecting more expensive and complex age-dating tracers and methods, or to provide an explanatory variable for other water-quality data where more complex methods or tracers are not available. This work improves on previous groundwater age classification using 3 H by developing methods that (1) determine 3 H thresholds for groundwater recharged in 1953 or later that minimize the misclassification of modern samples as mixed; (2) determine a pre-1953 threshold to estimate premodern background concentrations; and (3) add a mixed category to classify samples that are clearly neither entirely modern nor entirely premodern. As with any tritium-based approach, it can fail when the 3 H record in precipitation does not accurately reflect the record of 3 H in recharge

Conterminous United States↗
USGS2006

Factors affecting occurrence and distribution of selected contaminants in ground water from selected areas in the Piedmont Aquifer System, Eastern United States, 1993-2003

Results of ground-water sampling from 255 wells and 19 springs in 11 studies done by the U.S. Geological Survey National Water-Quality Assessment (NAWQA) Program within the Piedmont Aquifer System (PAS) were analyzed to determine the factors affecting occurrence and distribution of selected contaminants. The contaminants, which were selected on the basis of potential human-health effects, included nitrate, pesticides, volatile organic compounds (VOCs), and radon. The PAS was subdivided on the basis of the general rock type of the aquifers into three areas for the study—crystalline, carbonate, and siliciclastic. The 11 studies were designed to areally represent an individual aquifer rock type and overall are representative of the PAS in their distribution; 7 studies are in the crystalline-rock aquifers, 3 studies are in the siliciclasticrock aquifers, and 1 study is in the carbonate-rock aquifers. Four of the studies were focused on land use, 1 in an agricultural area and 3 in urban areas. The remaining studies had wells representing a range of land-use types. Analysis of results of nitrate sampling indicated that in 8 of the 10 areas where nitrate concentrations were measured, median concentrations of nitrate were below 3 mg/L (milligrams per liter); 2 of the 10 areas had statistically significant higher median concentrations when compared to the other 8 areas. The agricultural land-use study in the carbonate-rock aquifer in the Lower Susquehanna River Basin had the highest median nitrate concentration (11 mg/L), and 60 percent of the wells sampled exceeded the U.S. Environmental Protection Agency (USEPA) Maximum Contaminant Level (MCL) of 10 mg/L. The major aquifer study in the crystalline-rock aquifer of the Lower Susquehanna River Basin Study Unit had the second-highest median nitrate concentration. Nitrate concentrations were positively correlated to the percentage of agricultural land use around the well, the total input of nitrogen from all sources, dissolved oxygen concentration, lithology, depth to water, and soil-matrix characteristics. A linear regression model was used to determine that increases in the percentage of agricultural land use, the input of nitrogen from all sources, and dissolved oxygen were the most significant variables affecting increased concentration of nitrate. A logistic regression model was used to determine that those same factors were the most significant variables affecting whether or not the nitrate concentration would exceed 4 mg/L. Of the analysis of samples from 253 wells and 19 springs for 47 pesticides, no sample had a pesticide concentration that exceeded any USEPA MCL. The most frequently detected pesticide was desethyl atrazine, a degradation product of atrazine; the detection frequency was 47 percent. Other frequently detected pesticides included atrazine, metolachlor, simazine, alachlor, prometon, and dieldrin. Detection frequency was affected by the analytical reporting limits; the frequency of detection was somewhat lower when all pesticides were censored to the highest common detection limit. Source factors such as agricultural land use (for agricultural herbicides), urban land use (for insecticides), and the application rate were found to have positive statistical correlations with pesticide concentration. Transport factors such as depth to water and percentage of well-drained soils, sand, or silt typically were positively correlated with higher pesticide concentrations. Sampling for VOCs was conducted in 187 wells and 19 springs that were sampled for 59 VOCs. There were 137 detections of VOCs above the common censoring limit of 0.2 µg/L. The most frequently detected VOCs were chloroform, a trihalomethane, and methyl-tert butyl ether (MTBE), a fuel oxygenate. Seventy-nine wells had at least one VOC detected. The detections were related to land use and well depth. Kendall’s tau correlations indicated a significant positive correlation between chloroform concentration and urban land use, leaking underground storage tanks, population density, and well depth. MTBE concentrations also were positively correlated to urban land use, leaking underground storage tanks, population density, and well depth. Radon was sampled at 205 sites. The subdivisions used for analysis of other contaminants were not adequate for analysis of radon because radon varies on the basis of variations in mineralogy that are not reflected by the general lithologic categories used for the rest of the studies. Concentrations of radon were highest in areas where the crystalline-rock aquifers had felsic mineralogy, and the lowest concentrations of radon were in areas where the crystalline-rocks aquifer had mafic mineralogy. Water from wells in siliciclastic-rock aquifers had concentrations of radon lower than that in the felsic crystalline-rock aquifers. More than 90 percent of the wells sampled for radon exceeded the proposed MCL of 300 pCi/L (picoCuries per liter); however, only 13 percent of those wells had concentrations in water that exceeded the alternative maximum contaminant level (AMCL), a higher level that can be used by municipalities addressing other sources of radon exposure. Overall, concentrations of constituents were related to land-use factors for nitrate, pesticides, VOCs, and to aquifer lithology for radon. None of the 47 pesticides or 59 VOCs analyzed exceeded the MCLs where those constituents were sampled. Concentrations exceeded the MCL for nitrate in 11 percent of the wells sampled. Nearly 91 percent of the wells sampled exceeded the proposed MCL for radon. Additional sampling in selected areas would improve overall understanding of the PAS and increase the possibility of creating predictive models of ground-water quality in this area.

Alabama, Delaware, Georgia, Maryland, New Jersey, ↗
USGS2007

Description and User Manual for a Web-Based Interface to a Transit-Loss Accounting Program for Monument and Fountain Creeks, El Paso and Pueblo Counties, Colorado

The U.S. Geological Survey, in cooperation with Colorado Springs Utilities, the Colorado Water Conservation Board, and the El Paso County Water Authority, began a study in 2004 with the following objectives: (1) Apply a stream-aquifer model to Monument Creek, (2) use the results of the modeling to develop a transit-loss accounting program for Monument Creek, (3) revise an existing accounting program for Fountain Creek to easily incorporate ongoing and future changes in management of return flows of reusable water, and (4) integrate the two accounting programs into a single program and develop a Web-based interface to the integrated program that incorporates simple and reliable data entry that is automated to the fullest extent possible. This report describes the results of completing objectives (2), (3), and (4) of that study. The accounting program for Monument Creek was developed first by (1) using the existing accounting program for Fountain Creek as a prototype, (2) incorporating the transit-loss results from a stream-aquifer modeling analysis of Monument Creek, and (3) developing new output reports. The capabilities of the existing accounting program for Fountain Creek then were incorporated into the program for Monument Creek and the output reports were expanded to include Fountain Creek. A Web-based interface to the new transit-loss accounting program then was developed that provided automated data entry. An integrated system of 34 nodes and 33 subreaches was integrated by combining the independent node and subreach systems used in the previously completed stream-aquifer modeling studies for the Monument and Fountain Creek reaches. Important operational criteria that were implemented in the new transit-loss accounting program for Monument and Fountain Creeks included the following: (1) Retain all the reusable water-management capabilities incorporated into the existing accounting program for Fountain Creek; (2) enable daily accounting and transit-loss computations for a variable number of reusable return flows discharged into Monument Creek at selected locations; (3) enable diversion of all or a part of a reusable return flow at any selected node for purposes of storage in off-stream reservoirs or other similar types of reusable water management; (4) and provide flexibility in the accounting program to change the number of return-flow entities, the locations at which the return flows discharge into Monument or Fountain Creeks, or the locations to which the return flows are delivered. The primary component of the Web-based interface is a data-entry form that displays data stored in the accounting program input file; the data-entry form allows for entry and modification of new data, which then is rewritten to the input file. When the data-entry form is displayed, up-to-date discharge data for each station are automatically computed and entered on the data-entry form. Data for native return flows, reusable return flows, reusable return flow diversions, and native diversions also are entered automatically or manually, if needed. In computing the estimated quantities of reusable return flow and the associated transit losses, the accounting program uses two sets of computations. The first set of computations is made between any two adjacent streamflow-gaging stations (termed 'stream-segment loop'); the primary purpose of the stream-segment loop is to estimate the loss or gain in native discharge between the two adjacent streamflow-gaging stations. The second set of computations is made between any two adjacent nodes (termed 'subreach loop'); the actual transit-loss computations are made in the subreach loop, using the result from the stream-segment loop. The stream-segment loop is completed for a stream segment, and then the subreach loop is completed for each subreach within the segment. When the subreach loop is completed for all subreaches within a stream segment, the stream-segment loop is initiated for the ne

Scientific Investigations Report↗
USGS2009

Summary of surface-water quality data from the Illinois River Basin in Northeast Oklahoma, 1970-2007

The quality of streams in the Illinois River Basin of northeastern Oklahoma is potentially threatened by increased quantities of wastes discharged from increasing human populations, grazing of about 160,000 cattle, and confined animal feeding operations raising about 20 million chickens. Increasing numbers of humans and livestock in the basin contribute nutrients and bacteria to surface water and groundwater, causing greater than the typical concentrations of those constituents for this region. Consequences of increasing contributions of these substances can include increased algal growth (eutrophication) in streams and lakes; impairment of habitat for native aquatic animals, including desirable game fish species; impairment of drinking-water quality by sediments, turbidity, taste-and-odor causing chemicals, toxic algal compounds, and bacteria; and reduction in the aesthetic quality of the streams. The U.S. Geological Survey, in cooperation with the Oklahoma Scenic Rivers Commission, prepared this report to summarize the surface-water-quality data collected by the U.S. Geological Survey at five long-term surface-water-quality monitoring sites. The data summarized include major ions, nutrients, sediment, and fecal-indicator bacteria from the Illinois River Basin in Oklahoma for 1970 through 2007. General water chemistry, concentrations of nitrogen and phosphorus compounds, chlorophyll-a (an indicator of algal biomass), fecal-indicator bacteria counts, and sediment concentrations were similar among the five long-term monitoring sites in the Illinois River Basin in northeast Oklahoma. Most water samples were phosphorus-limited, meaning that they contained a smaller proportion of phosphorus, relative to nitrogen, than typically occurs in algal tissues. Greater degrees of nitrogen limitation occurred at three of the five sites which were sampled back to the 1970s, probably due to use of detergents containing greater concentrations of phosphorus than in subsequent periods. Concentrations of nitrogen, phosphorus, and sediment, and counts of bacteria generally increased with streamflow at the five sites, probably due to runoff from the land surface and re-suspension of streambed sediments. Phosphorus concentrations typically exceeded the Oklahoma standard of 0.037 milligrams per liter for Scenic Rivers. Concentrations of chlorophyll-a in phytoplankton in water samples collected at the five sites were not well correlated with streamflow, nor to concentrations of the nutrients nitrogen and phosphorus, probably because much of the algae growing in these streams are periphyton attached to streambed cobbles and other debris, rather than phytoplankton in the water column. Sediment concentrations correlated with phosphorus concentrations in water samples collected at the sites, probably due to sorption of phosphorus to soil particles and streambed sediments and runoff of soils and animal wastes at the land surface and resuspension of streambed sediments and phosphorus during wet, high-flow periods. Fecal coliform bacteria counts at the five sites sometimes exceeded the Oklahoma Primary Body Contact Standard of 400 colonies per 100 milliliters when streamflows were greater than 1000 cubic feet per second. Ultimately, Lake Tenkiller, an important ecological and economic resource for the region, receives the compounds that runoff the land surface or seep to local streams from groundwater in the basin. Because of eutrophication from increased nutrient loading, Lake Tenkiller is listed for impairment by diminished dissolved oxygen concentrations, phosphorus, and chlorophyll-a by the State of Oklahoma in evaluation of surface-water quality required by section 303d of the Clean Water Act. Stored phosphorus in soils and streambed and lakebed sediments may continue to provide phosphorus to local streams and lakes for decades to come. Steps are being made to reduce local sources of phosphorus, including upgrades in capacity and effective

Arkansas, Oklahoma↗
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↗
USGS2024

Phytoplankton, taste-and-odor compounds, and cyanotoxin occurrence in four water-supply reservoirs in the Triangle area of North Carolina, April–October 2014

Prior to 2014, local utilities and State agencies monitored for cyanotoxins and taste-and-odor (T&O) compounds and reported occasional detections in three water-supply reservoirs in Wake County, North Carolina. Comparable data for cyanotoxins and T&O compounds were lacking for other water-supply reservoirs in the Triangle area of North Carolina. This report assesses whether cyanotoxins and T&O compounds occurred in four previously unmonitored North Carolina Triangle area water-supply reservoirs at levels that exceed existing North Carolina and U.S. Environmental Protection Agency recreational and drinking water health advisory, guidance, and criterion levels based on data collected during the peak phytoplankton growth period in 2014. Samples were collected from five sites across the study reservoirs (Cane Creek Reservoir, West Fork Eno River Reservoir, B. Everett Jordan Lake, and University Lake) between April and October 2014 and analyzed for physical characteristics, chemical constituents, phytoplankton communities, cyanotoxins, and T&O compounds. Lake stratification during the sampling period in 2014 could indicate that the deep zones of the water column, during stratified anoxic conditions, may serve as possible sources of nutrients and metals for algal growth and other biogeochemical processes. Differences in phytoplankton communities were attributed to variability in environmental conditions across the sites and sampling events. Differences generally were greater among sites than among sampling events for phytoplankton communities and environmental conditions. Phytoplankton community assemblages, within reservoirs, often were dominated by cyanobacteria that contained genera capable of producing T&O compounds and cyanotoxins during summer and fall months. The occurrence and associated biovolumes of potential producers of cyanotoxins and T&O compounds varied across the sites and sampling events. Of 20 samples collected during the study, the T&O compound geosmin and the cyanotoxin microcystin were present in 19 and 18 samples, respectively. While not harmful, the aesthetically displeasing geosmin concentrations periodically exceeded the human detection threshold of 15 nanograms per liter at most sites. The T&O compound 2-methylisoborneol (MIB) was detected in 11 of 20 samples, with concentrations below the human detection threshold of 15 nanograms per liter in all but one sample. The cyanotoxin anatoxin-a was detected in two of the samples. No other cyanotoxins were detected during the study. In general, results did not indicate the biovolume of any given phytoplankton genera in the study was correlated with increased concentrations of MIB, geosmin, or microcystin. Results from this study indicated that microcystin concentrations in the water-supply reservoirs in the Triangle area were below EPA-recommended recreational level of 8 micrograms per liter, but periodically exceeded the EPA finished-water 10-day health advisory level of 0.3 microgram per liter for bottle-fed infants and preschool-age children. This suggests longer term data collection may be necessary to better understand the magnitude and frequency of cyanotoxin concentrations in these four water-supply reservoirs, particularly those with an elevated risk of exceeding the EPA 10-day health advisory levels in the finished drinking water or those with a higher frequency of T&O compound occurrence.

North Carolina↗
USGS2007

Occurrence of organic wastewater compounds in selected surface-water supplies, Triangle area of North Carolina, 2002-2005

Selected organic wastewater compounds, such as household, industrial, and agricultural-use compounds, sterols, pharmaceuticals, and antibiotics, were measured at eight sites classified as drinking-water supplies in the Triangle Area of North Carolina. From October 2002 through July 2005, seven of the sites were sampled twice, and one site was sampled 28 times, for a total of 42 sets of environmental samples. Samples were analyzed for as many as 126 compounds using three laboratory analytical methods. These methods were developed by the U.S. Geological Survey to detect low levels (generally less than or equal to 1.0 microgram per liter) of the target compounds in filtered water. Because analyses were conducted on filtered samples, the results presented in this report may not reflect the total concentration of organic wastewater compounds in the waters that were sampled. Various quality-control samples were used to quality assure the results in terms of method performance and possible laboratory or field contamination. Of the 108 organic wastewater compounds that met method performance criteria, 24 were detected in at least one sample during the study. These 24 compounds included 3 pharmaceutical compounds, 6 fire retardants and plasticizers, 3 antibiotics, 3 pesticides, 6 fragrances and flavorants, 1 disinfectant, and 2 miscellaneous-use compounds, all of which likely originated from a variety of domestic, industrial, and agricultural sources. The 10 most frequently detected compounds included acetyl-hexamethyl tetrahydronaphthalene and hexahydro-hexamethyl cyclopentabenzopyran (synthetic musks that are widely used in personal-care products and are known endocrine disruptors); tri(2-chloroethyl) phosphate, tri(dichloroisopropyl) phosphate, and tributyl phosphate (fire retardants); metolachlor (herbicide); caffeine (nonprescription stimulant); cotinine (metabolite of nicotine); acetaminophen (nonprescription analgesic); and sulfamethoxazole (prescription antibiotic). The occurrence and distribution of organic wastewater compounds varied considerably among sampling sites, but at least one compound was detected at every location. The most organic wastewater compounds (19) were detected at the Neuse River above U.S. 70 at Smithfield, where two-thirds of the total number of samples were collected. The fewest organic wastewater compounds (1) were detected at the Eno River at Hillsborough. The detection of multiple organic wastewater compounds was common, with a median of 3.5 and as many as 12 compounds observed in individual samples. Some compounds, including acetaminophen, cotinine, tri(2-chloroethyl) phosphate, and metolachlor, were detected at numerous sites and in numerous samples, indicating that they are widely distributed in the environment. Other organic wastewater compounds, including acetyl-hexamethyl tetrahydronaphthalene and hexahydro-hexamethyl cyclopentabenzopyran, were detected in numerous samples but at only one location, indicating that sources of these compounds are more site specific. Results indicate that municipal wastewater may be a source of antibiotics and synthetic musks; however, the three sites in this study that are located downstream from wastewater discharges also receive runoff from agricultural, urban, and rural residential lands. Source identification was not an objective of this study. Concentrations of individual compounds generally were less than 0.5 microgram per liter. No concentrations exceeded Federal drinking-water standards or health advisories, nor water-quality criteria established by the State of North Carolina; however, such criteria are available for only a few of the compounds that were studied. Compared with other surface waters that have been sampled across the United States, the Triangle Area water-supply sites had fewer detections of organic wastewater compounds; however, differences in study design and analytical methods used among studies must be considered when mak

North Carolina↗
USGS2010

Approach, passage, and survival of juvenile salmonids at Little Goose Dam, Washington: Post-construction evaluation of a temporary spillway weir, 2009

This report describes a study of dam passage and survival of radio-tagged juvenile salmonids after installation of a temporary spillway weir (TSW) at Little Goose Dam, Washington, in 2009. The purpose of the study was to document fish passage and survival when the dam was operated with the TSW in place. Spillway weirs are one of several methods used to improve downstream passage of juvenile salmonids. Each spillway weir design is based on the concept of providing an overflow weir with a depth more similar to the natural migration depth of juvenile salmonids than conventional spill bays. Little Goose Dam was the last of the four lower Snake River dams to have a spillway weir installed. This was the first year that some form of surface passage device was operating at all Snake River and Columbia River dams between Lewiston, Idaho, and the Columbia River estuary. The study design stipulated that a total of 30 percent of the river discharge would continuously be passed over the TSW and the conventional spill bays, and this percentage was achieved. The TSW also was to be operated at the ?low crest? elevation during the spring and the ?high crest? elevation during the summer, but the TSW was only operated at the low crest elevation during this study. Behavior, passage, and survival of spring and summer juvenile salmonid migrants passing through Little Goose Dam were examined using radio telemetry. Survival was estimated using the Route Specific Survival Model (RSSM) by releasing tagged fish near Central Ferry State Park 21 kilometers upstream of the dam and in the tailrace approximately 0.5 kilometer downstream of the dam. From April 18 to May 21, 2009, 1,520 yearling Chinook salmon (Oncorhynchus tshawytscha) and 1,517 juvenile steelhead (O. mykiss) were radio tagged and released. From June 6 to July 5, 2009, 4,251 subyearling Chinook salmon (O. tshawytscha) were radio tagged and released. Release dates of subyearling Chinook salmon were selected to avoid ?reservoir-type? fish that cease to migrate around July. Detection sites were installed in the forebay 2 kilometers upstream of the dam, on the dam, and at several sites downstream. Detection equipment was operated from April 18 to June 5, 2009, and from June 6 to July 6, 2009, hereinafter referred to as the study periods. We describe passage behaviors through the forebay, main passage routes, and tailrace, survival probabilities through the pool (release to the forebay) and forebay and passage and survival probabilities through the main passage routes (TSW, conventional spill bays, turbines, juvenile bypass), and survival passing the concrete (the dam itself) and the dam (concrete plus the forebay).

Scientific Investigations Report↗