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USGS2006

Comprehensive water quality of the Boulder Creek Watershed, Colorado, during high-flow and low-flow conditions, 2000

Executive Summary The Boulder Creek Watershed, Colorado, is 1160 square kilometers in area and ranges in elevation from 1480 to 4120 meters above sea level. Streamflow originates primarily as snowmelt near the Continental Divide, and thus discharge varies seasonally and annually (Chapter 1). Most of the water in Boulder Creek is diverted for domestic, agricultural, and industrial use. Some diverted water is returned to the creek as wastewater effluent and by ditch returns, and additional water enters as groundwater and by transbasin diversions. These diversions and returns lead to complex temporal and spatial variations in discharge. The variations in discharge, along with natural factors such as geology and climate, and anthropogenic factors such as wastewater treatment, agriculture, mining, and urbanization, can affect water chemistry. As with many watersheds in the American West, dependable water quality and sufficient water supply are issues facing local water managers and users. Detailed water-quality and sediment sampling allows the identification of sources and sinks of chemical constituents and an understanding of the processes at work in a river system. This study, the most comprehensive water-quality analysis performed for Boulder Creek to date, was a cooperative effort of the U.S. Geological Survey (USGS) and the city of Boulder. Geographic information systems and modeling programs were used to delineate watershed boundaries, land cover, and geology (Chapter 2). During high-flow (June 2000) and low-flow (October 2000) conditions, researchers evaluated 226 water-quality variables, including basic water-quality indicators (Chapter 3), major ions and trace elements (Chapter 4), wastewater-derived organic compounds (Chapter 5), and pesticides (Chapter 6). Discharge (Chapter 1) and bed-sediment particle size and mineralogy (Chapter 7) were also evaluated. This cooperative study was facilitated by the Boulder Area Sustainability Information Network (BASIN), which provides public access to environmental information about the Boulder Creek Watershed on a website, www.basin.org. In addition to the USGS and city of Boulder data, researchers at the Institute of Arctic and Alpine Research at the University of Colorado provided water chemistry data for the headwaters of North Boulder Creek, upstream of the reach of the USGS/city of Boulder sampling sites (Chapter 8). Snowmelt produces high flows in Boulder Creek in late spring to early summer (Chapter 1). Because precipitation falling in the headwaters is very dilute (specific conductance about 5 microsiemens per centimeter), most chemical constituents are present in lower concentrations during high flows (Chapters 3, 4, 5, 6, and 8). However, concentrations of some constituents, such as total suspended solids (Chapter 3) and organic carbon (Chapter 5), increase during the spring snowmelt flush. The upper basin, which consists of alpine, subalpine, montane, and foothills regions west of the mouth of Boulder Canyon, is underlain by Precambrian igneous and metamorphic rocks (Chapter 1). Major dissolved inorganic constituents in headwater sites were found to be enriched by factors of 10 to 20 relative to precipitation; this is consistent with minor weathering of the local crystalline bedrock (Chapter 4). Some anthropogenic input is observed in the headwaters; precipitation introduces nitrogen derived from fossil fuel combustion and agricultural activities (Chapter 8). The lower basin, which consists of the plains region east of the mouth of Boulder Canyon, is underlain by Mesozoic sedimentary rock and Quaternary alluvium, and has substantially more anthropogenic sources. Concentrations of most dissolved inorganic constituents increased in the lower basin. Differentiation between natural and anthropogenic sources of some dissolved constituents is difficult because both sources contribute to the water composition in this region. The increase of most major constituents (bicarbonate, calcium, chloride, magnesium, sodium, and sulfate) is consistent with weathering of the underlying sedimentary bedrock (Chapter 4). It is likely that anthropogenic loading of constituents in this reach occurs during storm events. Fecal coliform concentrations were variable and in some cases exceeded state standards, primarily during low-flow conditions (Chapter 3). Effluent from Boulder’s 75th Street Wastewater Treatment Plant (WWTP) has a substantial impact on the water chemistry of lower Boulder Creek. The WWTP increases the concentrations of nutrients such as nitrogen and phosphorus (Chapter 3), major ions and trace metals (Chapter 4), and organic carbon (Chapter 5) in Boulder Creek. The effluent contained a spike in gadolinium, a rare earth element that is ingested for magnetic resonance imaging as a contrasting agent and then excreted to the urban wastewater system. The effluent also contained trace organic compounds such as surfactants, pharmaceuticals, hormones (Chapter 5), and pesticides (Chapter 6), which also were detected at downstream Boulder Creek sites. Water chemistry of Boulder Creek downstream of the WWTP is largely controlled by the degree of dilution of the wastewater effluent, which varies depending on the baseflow of Boulder Creek, the volume of wastewater effluent, and depletion by agricultural diversions. Coal Creek, a tributary of Boulder Creek, contains wastewater effluent from four additional WWTPs, and increases the load of many constituents in Boulder Creek. In addition to the impact from wastewater effluent, lower Boulder Creek is affected by agricultural land use. Eleven of 84 analyzed pesticides were detected in Boulder Creek or its inflows, primarily in the eastern section of the watershed (Chapter 6). This collaborative study provides an in-depth evaluation of the hydrology, water chemistry, and sediment mineralogy of North Boulder Creek, Middle Boulder Creek, Boulder Creek, and major inflows. The detailed sampling and analysis in this report provide a baseline for future reference, as well as information on the effect of land use and geology on water chemistry.

Colorado↗

USGS2003

Assessment of selected inorganic constituents in streams in the Central Arizona Basins study area, Arizona and northern Mexico, through 1998

Stream properties and water-chemistry constituent concentrations from data collected by the National Water-Quality Assessment and other U.S. Geological Survey water-quality programs were analyzed to (1) assess water quality, (2) determine natural and human factors affecting water quality, and (3) compute stream loads for the surface-water resources in the Central Arizona Basins study area. Stream temperature, pH, dissolved-oxygen concentration and percent saturation, and dissolved-solids, suspended-sediment, and nutrient concentration data collected at 41 stream-water quality monitoring stations through water year 1998 were used in this assessment. Water-quality standards applicable to the stream properties and water-chemistry constituent concentration data for the stations investigated in this study generally were met, although there were some exceedences. In a few samples from the White River, the Black River, and the Salt River below Stewart Mountain Dam, the pH in reaches designated as a domestic drinking water source was higher than the State of Arizona standard. More than half of the samples from the Salt River below Stewart Mountain Dam and almost all of the samples from the stations on the Central Arizona Project Canal—two of the three most important surface-water sources used for drinking water in the Central Arizona Basins study area—exceeded the U.S. Environmental Protection Agency drinking water Secondary Maximum Contaminant Level for dissolved solids. Two reach-specific standards for nutrients established by the State of Arizona were exceeded many times: (1) the annual mean concentration of total phosphorus was exceeded during several years at stations on the main stems of the Salt and Verde Rivers, and (2) the annual mean concentration of total nitrogen was exceeded during several years at the Salt River near Roosevelt and at the Salt River below Stewart Mountain Dam. Stream properties and water-chemistry constituent concentrations were related to streamflow, season, water management, stream permanence, and land and water use. Dissolved-oxygen percent saturation, pH, and nutrient concentrations were dependent on stream regulation, stream permanence, and upstream disposal of wastewater. Seasonality and correlation with streamflow were dependant on stream regulation, stream permanence, and upstream disposal of wastewater. Temporal trends in streamflow, stream properties, and water-chemistry constituent concentrations were common in streams in the Central Arizona Basins study area. Temporal trends in the streamflow of unregulated perennial reaches in the Central Highlands tended to be higher from 1900 through the 1930s, lower from the 1940s through the 1970s, and high again after the 1970s. This is similar to the pattern observed for the mean annual precipitation for the Southwestern United States and indicates long-term trends in flow of streams draining the Central Highlands were driven by long-term trends in climate. Streamflow increased over the period of record at stations on effluent-dependent reaches as a result of the increase in the urban population and associated wastewater returns to the Salt and Gila Rivers in the Phoenix metropolitan area and the Santa Cruz River in the Tucson metropolitan area. Concentrations of dissolved solids decreased in the Salt River below Stewart Mountain Dam and in the Verde River below Bartlett Dam. This decrease represents an improvement in the water quality and resulted from a concurrent increase in the amount of runoff entering the reservoirs. Stream loads of water-chemistry constituents were compared at different locations along the streams with one another, and stream loads were compared to upstream inputs of the constituent from natural and anthropogenic sources to determine the relative importance of different sources and to determine the fate of the water-chemistry constituent. Of the dissolved solids transported into the Basin and Range Lowlands each year from the Central Arizona Project Canal and from streams draining the Central Highlands, about 1.2 billion kilograms accumulated in the soil, unsaturated zone, and aquifers in agricultural and urban areas as a result of irrigating crops and urban vegetation. Stream loads of phosphorus decreased from the 91st Avenue Wastewater-Treatment Plant downstream to the Gila River at Gillespie Dam, probably as a result of adsorption of phosphorus to the streambed sediments. In this same reach, stream loads of nitrogen increased, most likely because of inputs from fertilizers. The annual mass of nitrogen and phosphorus input to developed basins from quantifiable sources was much larger than the mass input to basins that had little or no municipal or agricul-tural development. These computed inputs exclude the mass of nitrogen and phosphorus from sources such as geologic formations and soils that could not be quantified. The quantifiable annual inputs of nitrogen and phosphorus for the upper Salt River Basin and the upper Verde River Basin were similar to those for the West Clear Creek Basin. This similarity suggests that the small amount of municipal and agricultural development in the upper Salt River and the upper Verde River Basins did not greatly change the basin input flux. For basins with minimal urban and agricultural development, the largest quantifiable source of nitrogen was precipitation, and the largest source of phosphorus was human bodily waste treated by sewer and septic systems. This was in contrast to developed basins, for which fertilizer was the largest quantifiable source of both nutrients. For most basins examined, quantifiable inputs of nitrogen and phosphorus from nonpoint sources were greater than inputs from point sources. This relation emphasizes the importance of land- and water-management policies that protect surface-water resources from nonpoint sources of nutrients as well as from point sources. The amount of nitrogen and phosphorus transpor-ted out of basins was a small fraction of the total for the quantifiable inputs. This result indicated that most of the nutrients input to basins were not transported out of the basins in surface water, but rather were transported to the subsurface (the soil, unsaturated zone, or aquifer), released to the atmosphere (such as volatilized ammonia), or incorporated into the biomass.

Central Arizona Basins study area↗

USGS2018

Carbonate system parameters of an algal-dominated reef along west Maui

Constraining coral reef metabolism and carbon chemistry dynamics are fundamental for understanding and predicting reef vulnerability to rising coastal CO 2 concentrations and decreasing seawater pH. However, few studies exist along reefs occupying densely inhabited shorelines with known input from land-based sources of pollution. The shallow coral reefs off Kahekili, West Maui, are exposed to nutrient-enriched, low-pH submarine groundwater discharge (SGD) and are particularly vulnerable to the compounding stressors from land-based sources of pollution and lower seawater pH. To constrain the carbonate chemistry system, nutrients and carbonate chemistry were measured along the Kahekili reef flat every 4 h over a 6-d sampling period in March 2016. Abiotic process – primarily SGD fluxes – controlled the carbonate chemistry adjacent to the primary SGD vent site, with nutrient-laden freshwater decreasing pH levels and favoring undersaturated aragonite saturation (Ω arag ) conditions. In contrast, diurnal variability in the carbonate chemistry at other sites along the reef flat was driven by reef community metabolism. Superimposed on the diurnal signal was a transition during the second sampling period to a surplus of total alkalinity (TA) and dissolved inorganic carbon (DIC) compared to ocean end-member TA and DIC measurements. A shift from net community production and calcification to net respiration and carbonate dissolution was identified. This transition occurred during a period of increased SGD-driven nutrient loading, lower wave height, and reduced current speeds. This detailed study of carbon chemistry dynamics highlights the need to incorporate local effects of nearshore oceanographic processes into predictions of coral reef vulnerability and resilience.

Hawaii↗

USGS1995

Seasonal cycles of dissolved constituents in streamwater in two forested catchments in the mid-Atlantic region of the eastern U.S.A.

Streamwater discharge and chemistry of two small catchments on Catoctin Mountain in north-central Maryland have been monitored since 1982. Repetitive seasonal cycles in stream-water chemistry have been observed each year, along with seasonal cycles in the volume of stream discharge and in groundwater levels. The hypothesis that the observed streamwater chemical cycles are related to seasonal changes in the hydrological flow paths that contribute to streamflow is examined using a combination of data on groundwater levels, shallow and deep groundwater chemistry, streamwater discharge, streamwater chemistry, soil-water chemistry, and estimates of water residence times. The concentrations of constituents derived from rock weathering, particularly bicarbonate and silica, increase in streamwater during the summer when the water table is below the regolith-bedrock interface and stream discharge consists primarily of deep groundwater from the fractured-bedrock aquifer. Conversely, the concentrations in streamwater of atmospherically derived components, particularly sulfate, increase in winter when the water table is above the regolith-bedrock interface and stream discharge consists primarily of shallow groundwater from the regolith. Tritium and chlorofluorocarbon (CFC) measurements suggest that the groundwater in these systems is young, with a residence time of less than several years. The results of this study have implications for the design of large-scale water-quality monitoring programs.

Maryland↗

USGS2009

Regional variations in water quality and relationships to soil and bedrock weathering in the southern Sacramento Valley, California, USA

Regional patterns in ground- and surface-water chemistry of the southern Sacramento Valley in California were evaluated using publicly available geochemical data from the US Geological Survey's National Water Information System (NWIS). Within the boundaries of the study area, more than 2300 ground-water analyses and more than 20,000 surface-water analyses were available. Ground-waters from the west side of the Sacramento Valley contain greater concentrations of Na, Ca, Mg, B, Cl and SO 4 , while the east-side ground-waters contain greater concentrations of silica and K. These differences result from variations in surface-water chemistry as well as from chemical reactions between water and aquifer materials. Sediments that fill the Sacramento Valley were derived from highlands to the west (the Coast Ranges) and east (the Sierra Nevada Mountains), the former having an oceanic provenance and the latter continental. These geologic differences are at least in part responsible for the observed patterns in ground-water chemistry. Thermal springs that are common along the west side of the Sacramento Valley appear to have an effect on surface-water chemistry, which in turn may affect the ground-water chemistry.

Applied Geochemistry↗

USGS2005

An evaluation of effects of groundwater exchange on nearshore habitats and water quality of western Lake Erie

Historically, the high potentiometric surface of groundwater in the Silurian/Devonian carbonate aquifer in Monroe County, MI resulted in discharge of highly mineralized, SO 4 -rich groundwater to the Lake Erie shoreline near both Erie State Game Area (ESGA) and Pointe Mouillee State Game Area (PMSGA). Recently, regional groundwater levels near PMSGA have been drawn down as much as 45 m below lake level in apparent response to quarry dewatering. From August to November of 2003, we conducted preliminary studies of groundwater flow dynamics and chemistry, shallow lake water chemistry, and fish and invertebrate communities at both sites. Consistent with regional observations, groundwater flow direction in the nearshore at ESGA was upward, or toward Lake Erie, and shallow nearshore groundwater chemistry was influenced by regional groundwater chemistry. In contrast, at PMSGA, the groundwater flow potential was downward and lake water, influenced by quarry discharge seeping downward into nearshore sediments, produced a different lake and shallow groundwater chemistry than at ESGA. Although the invertebrate and young fish community was similar at the two sites, taxonomic groups tolerant of degraded water quality were more prevalent at PMSGA. Sensitive taxa were more prevalent at ESGA. We propose a conceptual model, based on well-described models of groundwater/seawater interaction along coastal margins, to describe the interconnection among geologic, hydrologic, chemical, and biological processes in the different nearshore habitats of Lake Erie, and we identify processes that warrant further detailed study in the Great Lakes.

Lake Erie↗

USGS2003

Identifying relationships between baseflow geochemistry and land use with synoptic sampling and R-mode factor analysis

The relationship between land use and stream chemistry is often explored through synoptic sampling of rivers at baseflow conditions. However, baseflow chemistry is likely to vary temporally and spatially with land use. The purpose of our study is to examine the usefulness of the synoptic sampling approach for identifying the relationship between complex land use configurations and stream water quality. This study compares biogeochemical data from three synoptic sampling events representing the temporal variability of baseflow chemistry and land use using R - mode factor analysis . Separate R - mode factor analyses of the data from individual sampling events yielded only two consistent factors. Agricultural activity was associated with elevated levels of Ca 2+ , Mg 2+ , alkalinity, and frequently K + , SO 2- 4 , and NO - 3 . Urban areas were associated with higher concentrations of Na + , K + , and Cl - . Other retained factors were not consistent among sampling events, and some factors were difficult to interpret in the context of biogeochemical sources and processes. When all data were combined, further associations were revealed such as an inverse relationship between the proportion of wetlands and stream nitrate concentrations. We also found that barren lands were associated with elevated sulfate levels. This research suggests that an individual sampling event is unlikely to characterize adequately the complex processes controlling interactions between land use and stream chemistry. Combining data collected over two years during three synoptic sampling events appears to enhance our ability to understand processes linking stream chemistry and land use.

Michigan↗

USGS1997

Variations in pore-water quality, mineralogy, and sedimentary texture of clay-silts in the lower Miocene Kirkwood Formation, Atlantic City, New Jersey

Properties of and pore-water solute chemistry in confining units in the New Jersey Coastal Plain were studied to determine whether leakage of solute-enriched pore water from confining units affects regional aquifer-water chemistry, which ultimately may result in aquifer waters with high sodium and bicarbonate concentrations. Pore-water samples collected from a continuously cored borehole in the lower Miocene Kirkwood Formation at Atlantic City, NJ, were analyzed: 15 samples were obtained from clay-silt confining-unit sediments, and four samples were from silt interbeds in the sand of the major confined aquifer in the region, the Atlantic City 800-ft sand. The samples were analyzed to assess interrelations among mineralogy, texture, fluidretention properties, sediment chemistry, and pore-water chemistry, and to document the scale of variation in these properties. Linear regressions were developed to describe the relations of constituents dissolved in 14 pore-water samples collected from the lower confining unit overlying the Atlantic City 800-ft sand and from the silt interbeds in the upper sand unit of the Atlantic City 800-ft sand. The regressions were for concentrations of magnesium and calcium (m = 0.27, R2 = 0.99); concentrations of sodium and the sum of calcium and magnesium (m = 0.17, R 2 = 0.92); concentrations of sulfate and the sum of calcium and magnesium (m = 1.14, R 2 = 0.99); and concentrations of sodium and sulfate (m = 0.14, R 2 = 0.89). The percentage of fine sand was greatest in the shallowest sampled interval, where pore-water concentrations of calcium, magnesium, and sulfate were greatest. The pore-water samples were of three distinct water-quality types (hydrogeochemical facies): a calcium-sulfate type, a mixed calcium-sodium-sulfate-chloride-bicarbonate type, and a sodium-sulfate-bicarbonate-chloride type. The first two types were found only in the lower confining unit; the third type was found only in the composite confining unit underlying the Atlantic City 800-ft sand. Each of these hydrogeochemical facies generally is found within distinct intervals over a range of tens of feet in the core. Krige estimates of pore-water–constituent variations with depth were made by using only the analytical results for the 14 samples from the lower confining unit overlying the Atlantic City 800-ft sand and the silt interbeds in the upper sand unit of the Atlantic City 800-ft sand. Geostatistical analysis of the pore-water–quality data generally resulted in two types of semivariograms. One semivariogram type best fits concentration trends with depth for calcium, magnesium, strontium, sodium, sulfate, and specific conductance; lithium and chloride may also fit this semivariogram type. The other semivariogram type best fits concentration trends with depth for silica, cation exchange capacity, and dissolved inorganic carbon. The scale of variation of the concentrations and properties is indicated by the maximum lag autocorrelation distance of the theoretical semivariograms (the range) and ranged from 44 to 110 ft (13.4–33.5 m). The scale of variation of pore-water major-ion concentrations of sulfate, chloride, calcium, and magnesium alone is on the order of 65–70 ft (19.8–21.3 m). The semivariograms for all pore-water constituents except silica have significant variance at the smallest lag distance, indicating that the constituent concentration varied over a larger scale than the sampling interval. The dominant exchangeable cation in the sediment is calcium. Cation exchange reactions do not appear to be the dominant process in the sediments of the lower confining unit above the Atlantic City 800-ft sand, because a linear correlation exists between the concentration of sodium and the sum of calcium and magnesium concentrations in the pore water; concentrations of all these constituents increase in the upward flow direction, and the ratio of sodium to chloride in the pore water is about 1.0. Two significant principal components explained 82.5% of the total variation in pore-water solute chemistry. Principal component 1 represents about 53% of the variation in pore-water quality and includes calcium, magnesium, sulfate, strontium, and lithium. Coupled chemical processes in the confining units, such as incongruent dissolution of carbonate and other mineral phases or redox transformations of sulfur, likely explain the covariance of these constituents. Principal component 2 represents about 30% of the variation and includes sodium, dissolved inorganic carbon, and chloride. Covariance of sodium and chloride probably is caused by the presence of residual seawater.

New Jersey↗

USGS2011

Loch Vale watershed long-term ecological research and monitoring program quality assurance report, 2003-09

The Loch Vale watershed project is a long-term research and monitoring program located in Rocky Mountain National Park that addresses watershed-scale ecosystem processes, particularly as they respond to atmospheric deposition and climate variability. Measurements of precipitation depth, precipitation chemistry, discharge, and surface-water quality are made within the watershed and elsewhere in Rocky Mountain National Park. As data collected for the program are used by resource managers, scientists, policy makers, and students, it is important that all data collected in Loch Vale watershed meet high standards of quality. In this report, data quality was evaluated for precipitation, discharge, and surface-water chemistry measurements collected during 2003-09. Equipment upgrades were made at the Loch Vale National Atmospheric Deposition Program monitoring site to improve precipitation measurements and evaluate variability in precipitation depth and chemistry. Additional solar panels and batteries have been installed to improve the power supply, and data completeness, at the NADP site. As a result of equipment malfunction, discharge data for the Loch Outlet were estimated from October 18, 2005, to August 17, 2006. Quality-assurance results indicate that more than 98 percent of all surface-water chemistry measurements were accurate and precise. Records that did not meet quality criteria were removed from the database. Measurements of precipitation depth, precipitation chemistry, discharge, and surface-water quality were all sufficiently complete and consistent to support project data needs.

Colorado↗

USGS2006

Flow paths in the Edwards aquifer, northern Medina and northeastern Uvalde Counties, Texas, based on hydrologic identification and geochemical characterization and simulation

The U.S. Geological Survey, in cooperation with the San Antonio Water System, conducted a 4-year study during 2001– 04 to identify major ground-water flow paths in the Edwards aquifer in northern Medina and northeastern Uvalde Counties, Texas. The study involved use of geologic structure, surfacewater and ground-water data, and geochemistry to identify ground-water flow paths. Relay ramps and associated faulting in northern Medina County appear to channel ground-water flow along four distinct flow paths that move water toward the southwest. The northwestern Medina flow path is bounded on the north by the Woodard Cave fault and on the south by the Parkers Creek fault. Water moves downdip toward the southwest until the flow encounters a cross fault along Seco Creek. This barrier to flow might force part or most of the flow to the south. Departure hydrographs for two wells and discharge departure for a streamflow-gaging station provide evidence for flow in the northwestern Medina flow path. The north-central Medina flow path (northern part) is bounded by the Parkers Creek fault on the north and the Medina Lake fault on the south. The adjacent north-central Medina flow path (southern part) is bounded on the north by the Medina Lake fault and on the south by the Diversion Lake fault. The north-central Medina flow path is separated into a northern and southern part because of water-level differences. Ground water in both parts of the northcentral Medina flow path moves downgradient (and down relay ramp) from eastern Medina County toward the southwest. The north-central Medina flow path is hypothesized to turn south in the vicinity of Seco Creek as it begins to be influenced by structural features. Departure hydrographs for four wells and Medina Lake and discharge departure for a streamflow-gaging station provide evidence for flow in the north-central Medina flow path. The south-central Medina flow path is bounded on the north by the Seco Creek and Diversion Lake faults and on the south by the Haby Crossing fault. Because of bounding faults oriented northeast-southwest and adjacent flow paths directed south by other geologic structures, the south-central Medina flow path follows the configuration of the adjacent flow paths—oriented initially southwest and then south. Immediately after turning south, the south-central Medina flow path turns sharply east. Departure hydrographs for four wells and discharge departure for a streamflow-gaging station provide evidence for flow in the south-central Medina flow path. Statistical correlations between water-level departures for 11 continuously monitored wells provide additional evidence for the hypothesized flow paths. Of the 55 combinations of departure dataset pairs, the stronger correlations (those greater than .6) are all among wells in the same flow path, with one exception. Simulations of compositional differences in water chemistry along a hypothesized flow path in the Edwards aquifer and between ground-water and surface-water systems near Medina Lake were developed using the geochemical model PHREEQC. Ground-water chemistry for samples from five wells in the Edwards aquifer in the northwestern Medina flow path were used to evaluate the evolution of ground-water chemistry in the northwestern Medina flow path. Seven simulations were done for samples from pairs of these wells collected during 2001–03; three of the seven yielded plausible models. Ground-water samples from 13 wells were used to evaluate the evolution of ground-water chemistry in the north-central Medina flow path (northern and southern parts). Five of the wells in the most upgradient part of the flow path were completed in the Trinity aquifer; the remaining eight were completed in the Edwards aquifer. Nineteen simulations were done for samples from well pairs collected during 1995–2003; eight of the 19 yielded plausible models. Ground-water samples from seven wells were used to evaluate the evolution of ground-water chemistry in the south-central Medina flow path. One well was the Trinity aquifer end-member well upgradient from all flow paths, and another was a Trinity aquifer well in the most upgradient part of the flow path; all other wells were completed in the Edwards aquifer. Nine simulations were done for samples from well pairs collected during 1996–2003; seven of the nine yielded plausible models. The plausible models demonstrate that the four hypothesized flow paths can be partially supported geochemically.

Texas↗

USGS2010

Quality of groundwater at and near an aquifer storage and recovery site, Bexar, Atascosa, and Wilson Counties, Texas, June 2004-August 2008

The U.S. Geological Survey, in cooperation with the San Antonio Water System, did a study during 2004–08 to characterize the quality of native groundwater from the Edwards aquifer and pre- and post-injection water from the Carrizo aquifer at and near an aquifer storage and recovery (ASR) site in Bexar, Atascosa, and Wilson Counties, Texas. Groundwater samples were collected and analyzed for selected physical properties and constituents to characterize the quality of native groundwater from the Edwards aquifer and pre- and post-injection water from the Carrizo aquifer at and near the ASR site. Geochemical and isotope data indicated no substantial changes in major-ion, trace-element, and isotope chemistry occurred as the water from the Edwards aquifer was transferred through a 38-mile pipeline to the aquifer storage and recovery site. The samples collected from the four ASR recovery wells were similar in major-ion and stable isotope chemistry compared to the samples collected from the Edwards aquifer source wells and the ASR injection well. The similarity could indicate that as Edwards aquifer water was injected, it displaced native Carrizo aquifer water, or, alternatively, if mixing of Edwards and Carrizo aquifer waters was occurring, the major-ion and stable isotope signatures for the Carrizo aquifer water might have been obscured by the signatures of the injected Edwards aquifer water. Differences in the dissolved iron and dissolved manganese concentrations indicate that either minor amounts of mixing occurred between the waters from the two aquifers, or as Edwards aquifer water displaced Carrizo aquifer water it dissolved the iron and manganese directly from the Carrizo Sand. Concentrations of radium-226 in the samples collected at the ASR recovery wells were smaller than the concentrations in samples collected from the Edwards aquifer source wells and from the ASR injection well. The smaller radium-226 concentrations in the samples collected from the ASR recovery wells likely indicate some degree of mixing of the two waters occurred rather than continued decay of radium-226 in the injected water. Geochemical and isotope data measured in samples collected in May 2005 from two Carrizo aquifer monitoring wells and in July 2008 from the three ASR production-only wells in the northern section of the ASR site indicate that injected Edwards aquifer water had not migrated to these five sites. Geochemical and isotope data measured in samples collected from Carrizo aquifer wells in 2004, 2005, and 2008 were graphically analyzed to determine if changes in chemistry could be detected. Major-ion, trace element, and isotope chemistry varied spatially in the samples collected from the Carrizo aquifer. With the exception of a few samples, major-ion concentrations measured in samples collected in Carrizo aquifer wells in 2004, 2005, and 2008 were similar. A slightly larger sulfate concentration and a slightly smaller bicarbonate concentration were measured in samples collected in 2005 and 2008 from well NC1 compared to samples collected at well NC1 in 2004. Larger sodium concentrations and smaller calcium, magnesium, bicarbonate, and sulfate concentrations were measured in samples collected in 2008 from well WC1 than in samples collected at this well in 2004 and 2005. Larger calcium and magnesium concentrations and a smaller sodium concentration were measured in the samples collected in 2008 at well EC2 compared to samples collected at this well in 2004 and 2005. While in some cases the computed percent differences (compared to concentrations from June 2004) in dissolved iron and dissolved manganese concentrations in 11 wells sampled in the Carrizo aquifer in 2005 and 2008 were quite large, no trends that might have been caused by migration of injected Edwards aquifer water were observed. Because of the natural variation in geochemical data in the Carrizo aquifer and the small data set collected for this study, differences in major-ion and trace element data among the samples collected in 2004, 2005 and 2008 cannot be directly attributed to the ASR site operations. When the data were analyzed graphically, no appreciable differences in isotope concentrations were observed between samples collected in 2004 and 2008 from Carrizo aquifer wells, indicating that the Edwards aquifer source water might not have affected the isotope chemistry of the native Carrizo aquifer water near the sampled Carrizo wells by July 2008.

Texas↗

USGS2022

Hydrogeology and groundwater quality in the San Agustin Basin, New Mexico, 1975–2019

This report describes the findings of a U.S. Geological Survey study, completed in cooperation with the Bureau of Land Management, focused on better understanding the present-day (1975–2019) hydrogeology and groundwater quality of the San Agustin Basin in west-central New Mexico to support sustainable groundwater resource management. The basin hosts a relatively undeveloped basin-fill and alluvium aquifer system and is topographically divided into east and west subbasins by the McClure Hills. Groundwater chemistry and groundwater elevation data were compiled, collected, and interpreted in the context of groundwater flow and quality. The analyses presented in this report consider groundwater chemistry data collected within the last decade (2010–19) and groundwater elevation data collected from 1975 through 2019 to provide insight into present-day conditions. Groundwater elevations show that groundwater typically moves from the highlands to the lowlands, with a prominent east to west regional trend. Groundwater elevations were lowest in the southwestern portion of the west subbasin, where estimated flow directions suggest underflow through the local highlands into the northern East Fork Gila River watershed, which is further supported by historical groundwater elevation data from the northern East Fork Gila River watershed. Gradual groundwater elevation gradients (about 2 feet per mile) near the east and west subbasin divide suggest that groundwater slowly flows from the east subbasin to the west subbasin. Quantitative analyses of groundwater chemistry data show that groundwater in both subbasins has similar chemical characteristics. A systematic east to west groundwater evolution in water chemistry was not observed despite evidenced subbasin connectivity. The absence of this pattern suggests that groundwater mixing is regionally prevalent, sediment reactivity is low and variable, and (or) recharge conditions are comparable in both subbasins. Groundwater chemistry was generally independent of aquifer type, suggesting that the aquifers are hydrologically well connected. Corrected carbon-14 groundwater age estimates in the basin ranged from 232 to 13,916 years before present with a median of 5,409 years. A wide range of groundwater ages is therefore present in the basin, with waters commonly being thousands of years old, thereby supporting generally slow regional groundwater movement. A component of relatively young groundwater, for which estimated ages could not be accurately computed, is also present in the basin, and it may commonly mix with older waters. The spatial distribution of categorical and quantitative groundwater ages indicates that most recharge likely occurs in the highlands through mountain-block recharge and as focused recharge within arroyos, although evidence of modern (1953 and after) groundwater was minimal at sampled sites. Median annual gradients (groundwater elevation change over time) indicate that most groundwater elevations in the lowlands changed little (−0.2 to 0.2 foot per year) from 1975 through 2019. Groundwater elevations in the highlands varied more annually, which is likely due to recharge from precipitation events. These more variable groundwater elevations in the highlands compared with the lowlands, along with groundwater ages, provide further evidence that most groundwater recharge takes place in the highlands, with minimal recharge in the lowlands. Median groundwater elevation change for all sites was −0.05 foot per year. Temporal consistency of lowland groundwater elevations suggests that regional groundwater dynamics have been more or less stable through time under current climate and development conditions, although median annual gradients indicate that groundwater elevations may have slightly declined on average between 1975 and 2019.

New Mexico↗

USGS2003

Geochemistry of the Birch Creek Drainage Basin, Idaho

The U.S. Survey and Idaho State University, in cooperation with the U.S. Department of Energy, are conducting studies to describe the chemical character of ground water that moves as underflow from drainage basins into the eastern Snake River Plain aquifer (ESRPA) system at and near the Idaho National Engineering and Environmental Laboratory (INEEL) and the effects of these recharge waters on the geochemistry of the ESRPA system. Each of these recharge waters has a hydrochemical character related to geochemical processes, especially water-rock interactions, that occur during migration to the ESRPA. Results of these studies will benefit ongoing and planned geochemical modeling of the ESRPA at the INEEL by providing model input on the hydrochemical character of water from each drainage basin. During 2000, water samples were collected from five wells and one surface-water site in the Birch Creek drainage basin and analyzed for selected inorganic constituents, nutrients, dissolved organic carbon, tritium, measurements of gross alpha and beta radioactivity, and stable isotopes. Four duplicate samples also were collected for quality assurance. Results, which include analyses of samples previously collected from four other sites, in the basin, show that most water from the Birch Creek drainage basin has a calcium-magnesium bicarbonate character. The Birch Creek Valley can be divided roughly into three hydrologic areas. In the northern part, ground water is forced to the surface by a basalt barrier and the sampling sites were either surface water or shallow wells. Water chemistry in this area was characterized by simple evaporation models, simple calcite-carbon dioxide models, or complex models involving carbonate and silicate minerals. The central part of the valley is filled by sedimentary material and the sampling sites were wells that are deeper than those in the northern part. Water chemistry in this area was characterized by simple calcite-dolomite-carbon dioxide models. In the southern part, ground water enters the ESRPA. In this area, the sampling sites were wells with depths and water levels much deeper than those in the northern and central parts of the valley. The calcium and carbon water chemistry in this area was characterized by a simple calcite-carbon dioxide model, but complex calcite-silicate models more accurately accounted for mass transfer in these areas. Throughout the geochemical system, calcite precipitated if it was an active phase in the models. Carbon dioxide either precipitated (outgassed) or dissolved depending on the partial pressure of carbon dioxide in water from the modeled sites. Dolomite was an active phase only in models from the central part of the system. Generally the entire geochemical system could be modeled with either evaporative models, carbonate models, or carbonate-silicate models. In both of the latter types of models, a significant amount of calcite precipitated relative to the mass transfer to and from the other active phases. The amount of calcite precipitated in the more complex models was consistent with the amount of calcite precipitated in the simpler models. This consistency suggests that, although the simpler models can predict calcium and carbon concentrations in Birch Creek Valley ground and surface water, silicate-mineral-based models are required to account for the other constituents. The amount of mass transfer to and from the silicate mineral phases was generally small compared with that in the carbonate phases. It appears that the water chemistry of well USGS 126B represents the chemistry of water recharging the ESRPA by means of underflow from the Birch Creek Valley.

Idaho↗

USGS2019

Isotopes matter

Two years ago, the King’s Centre for Visualization in Science (KCVS) at The King’s University, Edmonton released a new digital interactive version of the IUPAC Periodic Table of the Elements and Isotopes with accompanying educational resources at an International Conference on Chemistry Education. It can be found at www.isotopesmatter.com. The effort was part of an IUPAC project . The science behind this new table was developed by Inorganic Chemistry Division scientists working for over a decade on an earlier IUPAC project . These projects were joint efforts between the IUPAC Committee on Chemistry Education (CCE) and the Inorganic Chemistry Division.

Chemistry International↗

USGS1999

Effect of subalpine canopy removal on snowpack, soil solution, and nutrient export, Fraser Experimental Forest, CO

Research on the effects of vegetation manipulation on snowpack, soil water, and streamwater chemistry and flux has been underway at the Fraser Experimental Forest (FEF), CO, since 1982. Greater than 95% of FEF snowmelt passes through watersheds as subsurface flow where soil processes significantly alter meltwater chemistry. To better understand the mechanisms accounting for annual variation in watershed streamwater ion concentration and flux with snowmelt, we studied subsurface water flow, its ion concentration, and flux in conterminous forested and clear cut plots. Repetitive patterns in subsurface flow and chemistry were apparent. Control plot subsurface flow chemistry had the highest ion concentrations in late winter and fall. When shallow subsurface flow occurred, its Ca 2+ , SO 4 2− , and HCO 3 − concentrations were lower and K + higher than deep flow. The percentage of Ca 2+ , NO 3 − , SO 4 2− , and HCO 3 − flux in shallow depths was less and K + slightly greater than the percentage of total flow. Canopy removal increased precipitation reaching the forest floor by about 40%, increased peak snowpack water equivalent (SWE)>35%, increased the average snowpack Ca 2+ , NO 3 − , and NH 4 + content, reduced the snowpack K + content, and increased the runoff four-fold. Clear cutting doubled the percentage of subsurface flow at shallow depths, and increased K + concentration in shallow subsurface flow and NO 3 − concentrations in both shallow and deep flow. The percentage change in total Ca 2+ , SO 4 2− , and HCO 3 − flux in shallow depths was less than the change in water flux, while that of K + and NO 3 − flux was greater. Relative to the control, in the clear cut the percentage of total Ca 2+ flux at shallow depths increased from 5 to 12%, SO 4 2− 5·4 to 12%, HCO 3 − from 5·6 to 8·7%, K + from 6 to 35%, and NO 3 − from 2·7 to 17%. The increases in Ca 2+ and SO 4 2− flux were proportional to the increase in water flux, the flux of HCO 3 − increased proportionally less than water flux, and NO 3 − and K + were proportionally greater than water flux. Increased subsurface flow accounted for most of the increase in non-limiting nutrient loss. For limiting nutrients, loss of plant uptake and increased shallow subsurface flow accounted for the greater loss. Seasonal ion concentration patterns in streamwater and subsurface flow were similar .

Hydrological Processes↗

USGS2013

Use of soil-streamwater relationships to assess regional patterns of acidic deposition effects in the northeastern USA

Declines of acidic deposition levels by as much as 50% since 1990 have led to partial recovery of surface waters in the northeastern USA but continued depletion of soil calcium through this same period suggests a disconnection between soil and surface water chemistry. To investigate the role of soil-surface water interactions in recovery from acidification, the first regional survey to directly relate soil chemistry to stream chemistry during high flow was implemented in a 4144-km 2 area of the Catskill region of New York, where acidic deposition levels are among the highest in the East. More than 40% of 95 streams sampled in the southern Catskill Mountains were determined to be acidified and had inorganic monomeric aluminum concentrations that exceeded a threshold that is toxic to aquatic biota. More than 80% likely exceeded this threshold during the highest flows, but less than 10% of more than 100 streams sampled were acidified in the northwestern portion of the region. Median Oa horizon soil base saturation ranged from 50% to 80% at 200 sites across the region, but median base saturation in the upper 10 cm of the B horizon was less than 20% across the region and was only 2% in the southern area. Aluminum is likely to be interfering with root uptake of calcium in the mineral horizon in approximately half the sampled watersheds. Stream chemistry was highly variable over the Catskill region and, therefore, did not always reflect the calcium depletion of the B horizon that our sampling suggested was nearly ubiquitous throughout the region. Published 2013. This article is a U.S. Government work and is in the public domain in the USA.

New York↗

USGS2000

Microbial control of mineral–groundwater equilibria: Macroscale to microscale

Using field and laboratory experiments, the geomicrobiology of a petroleum-contaminated aquifer and the relationship between mineral alteration, groundwater chemistry, and microbial colonization were examined. Results indicate that indigenous microorganisms influence mineral weathering at two scales of interaction: macroscale processes that perturb general groundwater chemistry and therefore mineralwater equilibria; and microscale interactions, where attached organisms locally perturb mineral±water equilibria, potentially releasing limiting trace nutrients from the dissolving mineral. In the contaminated unconfined glacio-fluvial aquifer near Bemidji, Minnesota, USA, carbonate chemistry is influenced primarily at the macroscale. Under oxic conditions, respiration by native aerobic heterotrophs produces excess carbon dioxide that promotes calcite and dolomite dissolution. Aerobic microorganisms do not colonize dolomite surfaces and few occur on calcite. Within the anoxic groundwater, calcite overgrowths form on uncolonized calcite cleavage surfaces, possibly due to the consumption of acidity by dissimilatory iron-reducing bacteria. As molecular oxygen concentration increases downgradient of the oil pool, aerobes again dominate and residual hydrocarbons and ferrous iron are oxidized, resulting in macroscale carbonate-mineral dissolution and iron precipitation. Feldspars, in contrast, weather exclusively at the microscale near attached microorganisms, principally in the anoxic region of the plume. Native organisms preferentially colonize feldspars that contain trace phosphorus as apatite inclusions, apparently as a consequence of the low P concentration in the groundwater. These feldspars weather rapidly, whereas nearby feldspars without trace P are uncolonized and unweathered. Feldspar dissolution is accompanied by the precipitation of secondary minerals, sometimes on the bacterial cell wall itself. These observations suggest a tightly linked biogeochemical system whereby microbial processes control mineral diagenesis at many scales of interaction, and the mineralogy and mineral chemistry influence microbial ecology. Only the macroscale interaction, however, is easily observable by standard geochemical methods, and documentation of the microscale interactions requires microscopic examination of microorganisms on mineral surfaces and the locally intense diagenetic reactions that result.

Hydrogeology Journal↗

USGS2018

A novel high-frequency groundwater quality monitoring system

High-frequency, long-term monitoring of water quality has revolutionized the study of surface waters in recent years. However, application of these techniques to groundwater has been limited by the ability to remotely pump and analyze groundwater. This paper describes a novel autonomous groundwater quality monitoring system which samples multiple wells to evaluate temporal changes and identify trends in groundwater chemistry. The system, deployed near Fresno, California, USA, collects and transmits high-frequency data, including water temperature, specific conductance, pH, dissolved oxygen, and nitrate, from supply and monitoring wells, in real-time. The system consists of a water quality sonde and optical nitrate sensor, manifold, submersible three-phase pump, variable frequency drive, data collection platform, solar panels, and rechargeable battery bank. The manifold directs water from three wells to a single set of sensors, thereby reducing setup and operation costs associated with multi-sensor networks. Sampling multiple wells at high frequency for several years provided a means of monitoring the vertical distribution and transport of solutes in the aquifer. Initial results show short period variability of nitrate, specific conductivity, and dissolved oxygen in the shallow aquifer, while the deeper portion of the aquifer remains unchanged—observations that may be missed with traditional discrete sampling approaches. In this aquifer system, nitrate and specific conductance are increasing in the shallow aquifer, while invariant changes in deep groundwater chemistry likely reflect relatively slow groundwater flow. In contrast, systems with high groundwater velocity, such as karst aquifers, have been shown to exhibit higher-frequency groundwater chemistry changes. The stability of the deeper aquifer over the monitoring period was leveraged to develop estimates of measurement system uncertainty, which were typically lower than the manufacturer’s stated specifications, enabling the identification of subtle variability in water chemistry that may have otherwise been missed.

California↗