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At least 361 records · Page 20Linked to original sources
USGS2006

Groundwater-transported dissolved organic nitrogen exports from coastal watersheds

We analyzed groundwater-transported nitrogen (N) exports from 41 watershed segments that comprised 10 Cape Cod, Massachusetts watersheds to test the hypotheses that chemical form of N exports is related to land use and to length of flow paths through watersheds. In the absence of human habitation, these glacial outwash-plain watersheds exported largely dissolved organic N (DON) but at relatively low annual rate. Addition of people to watersheds increased rates of both total dissolved N (TDN) and DON export through groundwater. Percent of TDN as DON in groundwater was negatively related to path length of groundwater through aquifers, but %DON was not significantly related to population density on the watersheds. DON was often the dominant form of N exported from the watersheds, even at high population densities. Our results suggest that natural sources are not entirely responsible for organic N exports from watersheds, but, instead, a substantial portion of anthropogenic N introduced to watersheds is exported as DON. This finding is in disagreement with previous results, which suggest that anthropogenic N is exported from watersheds largely as NO 3- and that DON exported from watersheds is from natural sources.

Massachusetts↗
USGS2021

Cloud water interception in Hawai‘i: Developing capacity to characterize the spatial patterns and effects on water and ecological processes responses in Hawai‘i

Cloud-water interception (CWI) is the process by which fog or cloud water droplets are captured and accumulate on the leaves and branches of plants, some of which drips to the ground. Prior studies in Hawai'i indicate that CWI is highly variable and can contribute substantially to total precipitation. In this study, we monitored CWI and other processes at five mountain field sites on the Islands of Oʻahu, Maui, and Hawaiʻi to explore how CWI (1) varies with different climate and vegetation characteristics, (2) affects plant water use and growth, and (3) contributes to water resources. Results show that annual CWI varied from 158 to 910 mm, accounting for 3-34% of total water input at individual sites. This large variation was caused by differences in the quantity of cloud water, wind speed, and vegetation structure between sites. We developed a model to predict CWI using both climatic and forest canopy characteristics. On average, the model underestimated annual CWI by 18%, but reproduced the site differences relatively well. Plant water use decreased during periods of fog events mainly because of associated higher humidity. This new CWI model can be used to assess impacts of climate and land cover change on CWI and provide valuable information for resource management in Hawai‘i, which was not previously possible. At one field site, we explored the impacts of fog water on hydrological and ecological processes. Fog effects on native plant growth were indirect, primarily buffering effects of solar radiation. Removal of grass allowed natural regeneration of seedlings but did not alter soil moisture values. A soil data-collection program was initiated to help evaluate the role CWI has in providing moisture for plants, reducing wildfire risk within the fog zone, and contributing to groundwater recharge to aquifers that supply drinking water and groundwater discharge to streams.

Hawaii↗
USGS2021

Natural and anthropogenic geochemical tracers to investigate residence times and groundwater–surface-water interactions in an urban alluvial aquifer

A multi-component geochemical dataset was collected from groundwater and surface-water bodies associated with the urban Fountain Creek alluvial aquifer, Colorado, USA, to facilitate analysis of recharge sources, geochemical interactions, and groundwater-residence times. Results indicate that groundwater can be separated into three distinct geochemical zones based on location within the flow system and proximity to surface water, and these zones can be used to infer sources of recharge and groundwater movement through the aquifer. Rare-earth-element concentrations and detections of wastewater-indicator compounds indicate the presence of effluent from wastewater-treatment plants in both groundwater and surface water. Effluent presence in groundwater indicates that streams in the area lose to groundwater in some seasons and are a source of focused groundwater recharge. Distributions of pharmaceuticals and wastewater-indicator compounds also inform an understanding of groundwater–surface-water interactions. Noble-gas isotopes corroborate rare-earth-element data in indicating geochemical evolution within the aquifer from recharge area to discharge area and qualitatively indicate variable groundwater-residence times and mixing with pre-modern groundwater. Quantitative groundwater-residence times calculated from 3 H/ 3 He, SF 6 , and lumped-parameter modeling generally are less than 20 years, but the presence of mixing with older groundwater of an unknown age is also indicated at selected locations. Future investigations would benefit by including groundwater-age tracers suited to quantification of mixing for both young (years to decades) and old (centuries and millennia) groundwater. This multi-faceted analysis facilitated development of a conceptual model for the investigated groundwater-flow system and illustrates the application of an encompassing suite of analytes in exploring hydrologic and geochemical interactions in complex systems.

Colorado↗
USGS2016

The source of groundwater and solutes to Many Devils Wash at a former uranium mill site in Shiprock, New Mexico

The Shiprock Disposal Site is the location of the former Navajo Mill (Mill), a uranium ore-processing facility, located on a terrace overlooking the San Juan River in the town of Shiprock, New Mexico. Following the closure of the Mill, all tailings and associated materials were encapsulated in a disposal cell built on top of the former Mill and tailings piles. The milling operations, conducted at the site from 1954 to 1968, created radioactive tailings and process-related wastes that are now found in the groundwater. Elevated concentrations of constituents of concern—ammonium, manganese, nitrate, selenium, strontium, sulfate, and uranium—have also been measured in groundwater seeps in the nearby Many Devils Wash arroyo, leading to the inference that these constituents originated from the Mill. These constituents have also been reported in groundwater that is associated with Mancos Shale, the bedrock that underlies the site. The objective of this report is to increase understanding of the source of water and solutes to the groundwater beneath Many Devils Wash and to establish the background concentrations for groundwater that is in contact with the Mancos Shale at the site. This report presents evidence on three working hypotheses: (1) the water and solutes in Many Devils Wash originated from the operations at the former Mill, (2) groundwater in deep aquifers is upwelling under artesian pressure to recharge the shallow groundwater beneath Many Devils Wash, and (3) the groundwater beneath Many Devils Wash originates as precipitation that infiltrates into the shallow aquifer system and discharges to Many Devils Wash in a series of springs on the east side of the wash. The solute concentrations in the shallow groundwater of Many Devils Wash would result from the interaction of the water and the Mancos Shale if the source of water was upwelling from deep aquifers or precipitation. In order to compare the groundwater from various wells to groundwater that has been affected by Mill activities, a classification system was developed to determine which wells were most likely to have been affected. Affects to groundwater by the Mill were determined by using the reported uranium alpha activity ratios measured in groundwater samples, along with the concentration of the uranium and the location of the wells relative to the Mill. Activity ratios of 1.2 or less were determined to be the most reliable indicator of Mill-affected groundwater. Wells with samples that had a reported activity ratio of 1.2 or less were classified as Mill affected. To compare groundwater with background water-quality, data from groundwater seeps and springs in the Upper Eagle Nest Arroyo and Salt Creek Wash, located north of the San Juan River, are also presented and analyzed. Based on groundwater elevations and tritium concentrations measured in wells located between the disposal cell and Many Devils Wash, Mill water is not likely to reach Many Devils Wash. The tritium concentrations also indicate that groundwater from the Mill has not substantially affected Many Devils Wash in the past. Upwelling from deep aquifers was also determined to be an unlikely source, primarily by comparing the composition of the stable isotopes of water in the shallow groundwater with those reported in groundwater samples from the deeper aquifers. The stable-isotope compositions of the shallow groundwater around the site are enriched relative to the San Juan River and local meteoric lines, which suggests that most of the shallow groundwater has been influenced by evaporation and therefore was recharged at the surface. Several observations indicate that focused recharge is the likely source of groundwater in the area of Many Devils Wash. The visible erosional features in Many Devils Wash provide evidence of piping and groundwater sapping, and the distribution and type of vegetation in Many Devils Wash suggest that the focused recharge of precipitation is occurring. The estimated recharge from precipitation was calculated to be 0.0008 inches per year (in/yr) by using the mass-balance approach from reported seep discharge and 0.0011 in/yr using the chloride mass-balance approach. A conceptual model of groundwater quality beneath Many Devils Wash is presented to explain the source of solutes in the groundwater beneath Many Devils Wash. The major-ion concentrations and geochemical evolution in the groundwater beneath Many Devils Wash and across the study area support the conceptual model that the underlying Mancos Shale is the source of solutes. Differences in the major-ion composition between groundwater samples collected around the site, result from the degree of weathering to the Mancos Shale. The cation distribution appears to be an indicator of effects from the Mill, with samples from the Mill-affected wells largely having a calcium/magnesium-sulfate composition that resembles the reported compositions of more weathered shale; however, that composition could change if the Mill-processed water flowed into areas where the Mancos Shale was less weathered. On the basis of the widespread presence of uranium in the Mancos Shale and the distribution of aqueous uranium in the analog sites and other sites in the region, it appears likely that uranium in the groundwater of Many Devils Wash is naturally sourced from the Mancos Shale.

New Mexico↗
USGS2013

Estimating nitrate concentrations in groundwater at selected wells and springs in the surficial aquifer system and Upper Floridan aquifer, Dougherty Plain and Marianna Lowlands, Georgia, Florida, and Alabama, 2002-50

Groundwater from the surficial aquifer system and Upper Floridan aquifer in the Dougherty Plain and Marianna Lowlands in southwestern Georgia, northwestern Florida, and southeastern Alabama is affected by elevated nitrate concentrations as a result of the vulnerability of the aquifer, irrigation water-supply development, and intensive agricultural land use. The region relies primarily on groundwater from the Upper Floridan aquifer for drinking-water and irrigation supply. Elevated nitrate concentrations in drinking water are a concern because infants under 6 months of age who drink water containing nitrate concentrations above the U.S. Environmental Protection Agency maximum contaminant level of 10 milligrams per liter as nitrogen can become seriously ill with blue baby syndrome. In response to concerns about water quality in domestic wells and in springs in the lower Apalachicola–Chattahoochee–Flint River Basin, the Florida Department of Environmental Protection funded a study in cooperation with the U.S. Geological Survey to examine water quality in groundwater and springs that provide base flow to the Chipola River. A three-dimensional, steady-state, regional-scale groundwater-flow model and two local-scale models were used in conjunction with particle tracking to identify travel times and areas contributing recharge to six groundwater sites—three long-term monitor wells (CP-18A, CP-21A, and RF-41) and three springs (Jackson Blue Spring, Baltzell Springs Group, and Sandbag Spring) in the lower Apalachicola–Chattahoochee–Flint River Basin. Estimated nitrate input to groundwater at land surface, based on previous studies of nitrogen fertilizer sales and atmospheric nitrate deposition data, were used in the advective transport models for the period 2002 to 2050. Nitrate concentrations in groundwater samples collected from the six sites during 1993 to 2007 and groundwater age tracer data were used to calibrate the transport aspect of the simulations. Measured nitrate concentrations (as nitrogen) in wells and springs sampled during the study ranged from 0.37 to 12.73 milligrams per liter. Average apparent ages of groundwater calculated from measurements of chlorofluorocarbon, sulfur hexafluoride, and tritium from wells CP-18A, CP-21A,and RF-41 were about 23, 29, and 32 years, respectively. Average apparent ages of groundwater from Baltzell Springs Group, Sandbag Spring, and Jackson Blue Spring were about 16, 18, and 19 years, respectively. Simulated travel times of particles from the six selected sites ranged from less than 1 day to 511 years; both the minimum and maximum particle travel times were estimated for water from Jackson Blue Spring. Median simulated travel times of particles were about 30, 38, and 62 years for Jackson Blue Spring, Sandbag Spring, and Baltzell Springs Group, respectively. Study results indicated that travel times for approximately 50 percent of the particles from all spring sites were less than 50 years. The median simulated travel times of particles arriving at receptor wells CP-18A, CP-21A, and RF-41 were about 50, 35, and 36 years, respectively. All particle travel times were within the same order of magnitude as the tracer-derived average apparent ages for water, although slightly older than the measured ages. Travel time estimates were substantially greater than the measured age for groundwater reaching well CP-18A, as confirmed by the average apparent age of water determined from tracers. Local-scale particle-tracking models were used to predict nitrate concentrations in the three monitor wells and three springs from 2002 to 2050 for three nitrogen management scenarios: (1) fixed input of nitrate at the 2001 level, (2) reduction of nitrate inputs of 4 percent per year (from the previous year) from 2002 to 2050, and (3) elimination of nitrate input after 2001. Simulated nitrate concentrations in well CP-21A peaked at 7.82 milligrams per liter in 2030, and concentrations in background well RF-41 peaked at 1.10 milligrams per liter in 2020. The simulated particle travel times were longer than indicated by age dating analysis for groundwater in well CP-18A; to account for the poor calibration fit at this well, nitrate concentrations were shifted 21 years. With the shift, simulated nitrate concentrations in groundwater at CP-18A peaked at 13.76 milligrams per liter in 2026. For groundwater in Baltzell Springs Group, Jackson Blue Spring, and Sandbag Spring, simulated nitrate concentrations peaked at 3.77 milligrams per liter in 2006, 3.51 milligrams per liter in 2011, and 0.81 milligram per liter in 2018, respectively, under the three management scenarios. In management scenario 3 (elimination of nitrate input after 2001), simulated nitrate concentrations in Baltzell Springs Group decreased to less than background concentrations (0.10 milligram per liter) by 2033, and in Sandbag Spring concentrations decreased to less than background by 2041. Simulations using nitrate management scenarios 1 (fixed input of nitrate at 2001 levels) and 2 (reduction of 4.0 percent per year) indicate that nitrate concentrations in groundwater may remain above background concentrations through 2050 at all sites.

Alabama, Florida, Georgia↗
USGS2011

Groundwater availability of the Denver Basin aquifer system, Colorado

The Denver Basin aquifer system is a critical water resource for growing municipal, industrial, and domestic uses along the semiarid Front Range urban corridor of Colorado. The confined bedrock aquifer system is located along the eastern edge of the Rocky Mountain Front Range where the mountains meet the Great Plains physiographic province. Continued population growth and the resulting need for additional water supplies in the Denver Basin and throughout the western United States emphasize the need to continually monitor and reassess the availability of groundwater resources. In 2004, the U.S. Geological Survey initiated large-scale regional studies to provide updated groundwater-availability assessments of important principal aquifers across the United States, including the Denver Basin. This study of the Denver Basin aquifer system evaluates the hydrologic effects of continued pumping and documents an updated groundwater flow model useful for appraisal of hydrologic conditions.

Colorado↗
USGS2019

Groundwater-Level Elevations in the Denver Basin Bedrock Aquifers of Elbert County, Colorado, 2015–18

Public and domestic water supplies in Elbert County, Colorado, rely on groundwater withdrawals from five bedrock aquifers in the Denver Basin aquifer system (lower Dawson, upper Dawson, Denver, Arapahoe, and Laramie-Fox Hills) to meet water demands. Increased pumping in response to regional population growth and development has led to declining groundwater levels in neighboring Douglas County. The U.S. Geological Survey, in cooperation with the Elbert County Board of County Commissioners, began a study in 2015 to monitor groundwater levels within Elbert County. The purpose of this study is to report on groundwater levels measured between April 2015 and June 2018, and analyze trends and changes in groundwater-level elevations throughout the county. Discrete groundwater levels were measured at 42 wells within Elbert County. Six of those wells contained equipment to make and record continuous groundwater-level measurements at hourly intervals. All five aquifers had wells with a rise in groundwater-level elevation and wells with a decline in groundwater-level elevation, based on a relative change in groundwater-level elevation between the April 2015 and April 2018 measurements. All aquifers except the upper Dawson had more wells with significant negative trends in discrete groundwater-level elevations than significant positive trends; however, at least one well within the upper Dawson, lower Dawson, Arapahoe, and Laramie-Fox Hills aquifers had a significant positive trend. Wells screened in the lower Dawson aquifer consistently had the most significant negative trends, with an average trend of −1.96 feet per year (ft/year). The upper Dawson, Denver, Arapahoe, and Laramie-Fox Hills aquifers had average trends of 0.03 ft/year, −1.04 ft/year, −0.46 ft/year, and −0.65 ft/year, respectively. Trends in continuous groundwater-level elevations were in agreement with significant trends in discrete groundwater-level elevations. Potentiometric-surface maps of the upper and lower Dawson aquifers for April 2015 and April 2018 show that differences in hydraulic head from the two measurement periods were greatest along the western part of Elbert County. Results of this study could guide future groundwater monitoring in the county and aid in long-term planning of water resources.

Colorado↗
USGS2011

Effects of natural and human factors on groundwater quality of basin-fill aquifers in the southwestern United States: Conceptual models for selected contaminants

As part of the U.S. Geological Survey National Water-Quality Assessment (NAWQA) Program, the Southwest Principal Aquifers (SWPA) study is building a better understanding of the factors that affect water quality in basin-fill aquifers in the Southwestern United States. The SWPA study area includes four principal aquifers of the United States: the Basin and Range basin-fill aquifers in California, Nevada, Utah, and Arizona; the Rio Grande aquifer system in New Mexico and Colorado; and the California Coastal Basin and Central Valley aquifer systems in California. Similarities in the hydrogeology, land- and water-use practices, and water-quality issues for alluvial basins within the study area allow for regional analysis through synthesis of the baseline knowledge of groundwater-quality conditions in basins previously studied by the NAWQA Program. Resulting improvements in the understanding of the sources, movement, and fate of contaminants are assisting in the development of tools used to assess aquifer susceptibility and vulnerability. This report synthesizes previously published information about the groundwater systems and water quality of 15 information-rich basin-fill aquifers (SWPA case-study basins) into conceptual models of the primary natural and human factors commonly affecting groundwater quality with respect to selected contaminants, thereby helping to build a regional understanding of the susceptibility and vulnerability of basin-fill aquifers to those contaminants. Four relatively common contaminants (dissolved solids, nitrate, arsenic, and uranium) and two contaminant classes (volatile organic compounds (VOCs) and pesticide compounds) were investigated for sources and controls affecting their occurrence and distribution above specified levels of concern in groundwater of the case-study basins. Conceptual models of factors that are important to aquifer vulnerability with respect to those contaminants and contaminant classes were subsequently formed. The conceptual models are intended in part to provide a foundation for subsequent development of regional-scale statistical models that relate specific constituent concentrations or occurrence in groundwater to natural and human factors.

Arizona, California, Colorado, Nevada, New Mexico,↗
USGS2011

Water-level changes in the High Plains aquifer, predevelopment to 2009, 2007-08, and 2008-09, and change in water in storage, predevelopment to 2009

The High Plains aquifer underlies 111.8 million acres (175,000 square miles) in parts of eight States - Colorado, Kansas, Nebraska, New Mexico, Oklahoma, South Dakota, Texas, and Wyoming. Water-level declines began in parts of the High Plains aquifer soon after the beginning of substantial irrigation with groundwater in the aquifer area. This report presents water-level changes in the High Plains aquifer from the time before substantial groundwater irrigation development had occurred (about 1950 and termed "predevelopment" in this report) to 2009, from 2007-08, and from 2008-09. The report also presents change in water in storage in the aquifer, from predevelopment to 2009. Ninety-nine percent of the water-level changes from predevelopment to 2009 ranged from a rise of 41 feet to a decline of 178 feet. The area-weighted, average water-level changes in the aquifer were a decline of 14.0 feet from predevelopment to 2009, a decline of 0.1 foot from 2007-08, and a decline of 0.3 foot from 2008-09. Total water in storage in the aquifer in 2009 was about 2.9 billion acre-feet, which was a decline of about 274 million acre-feet since predevelopment.

Colorado;Kansas;Nebraska;New Mexico;Oklahoma;South↗
USGS2013

Water-level and storage changes in the High Plains aquifer, predevelopment to 2011 and 2009-11

The High Plains aquifer underlies 111.8 million acres (175,000 square miles) in parts of eight States--Colorado, Kansas, Nebraska, New Mexico, Oklahoma, South Dakota, Texas, and Wyoming. Water-level declines began in parts of the High Plains aquifer soon after the beginning of substantial irrigation with groundwater in the aquifer area. This report presents water-level changes in the High Plains aquifer from the time before substantial groundwater irrigation development began (generally before 1950, and termed "predevelopment" in this report) to 2011 and from 2009-11. The report also presents total water in storage, 2011, and change in water in storage in the aquifer from predevelopment to 2011. The methods to calculate area-weighted, average water-level changes; change in water in storage; and total water in storage for this report used geospatial data layers organized as rasters with a cell size of about 62 acres. These methods were modified from methods used in previous reports in an attempt to improve estimates of water-level changes and change in water in storage.Water-level changes from predevelopment to 2011, by well, ranged from a rise of 85 feet to a decline of 242 feet. The area-weighted, average water-level changes in the aquifer were an overall decline of 14.2 feet from predevelopment to 2011, and a decline of 0.1 foot from 2009-11. Total water in storage in the aquifer in 2011 was about 2.96 billion acre-feet, which was a decline of about 246 million acre-feet since predevelopment.

Colorado, Kansas, Nebraska, New Mexico, Oklahoma, ↗
USGS2014

Water-chemistry data collected in and near Kaloko-Honokohau National Historical Park, Hawaii, 2012–2014

Kaloko-Honokōhau National Historical Park (KAHO) on western Hawaiʻi was established in 1978 to preserve, interpret, and perpetuate traditional Native Hawaiian culture and activities, including the preservation of a variety of culturally and ecologically significant water resources that are vital to this mission. KAHO water bodies provide habitat for 1 threatened, 11 endangered, and 3 candidate threatened or endangered species. These habitats are sustained by, and in the case of ʻAimakapā Fishpond and the anchialine pools, entirely dependent on, groundwater from the Keauhou aquifer system. Development of inland impounded groundwater in the Keauhou aquifer system may affect the coastal freshwater-lens system on which KAHO depends, if the inland impounded-groundwater and coastal freshwater-lens systems are hydrologically connected. This report documents water-chemistry results from a U.S. Geological Survey study that collected and analyzed water samples from 2012 to 2014 from 25 sites in and near KAHO to investigate potential geochemical indicators in water that might indicate the presence or absence of a hydrologic connection between the inland impounded-groundwater and coastal freshwater-lens systems in the area. Samples were collected under high-tide and low-tide conditions for KAHO sites, and in dry-season and wet-season conditions for all sites. Samples were collected from two ocean sites, two fishponds, three anchialine pools, and three monitoring wells within KAHO. Two additional nearshore wells were sampled on property adjacent to and north of KAHO. Additional samples from the freshwater-lens system were collected from six inland wells located upslope from KAHO, including three production wells. Seven production wells in the inland impounded-groundwater system also were sampled. Water samples were analyzed for major ions, selected trace elements, rare-earth elements, strontium-isotope ratio, and stable isotopes of water. Precipitation samples from five sites were collected roughly along a transect upslope from KAHO. All precipitation samples were analyzed for stable isotopes of water and some precipitation samples were analyzed for rare-earth and selected trace elements.

Hawai'i↗
USGS2012

Groundwater status and trends for the Columbia Plateau Regional Aquifer System, Washington, Oregon, and Idaho

Well information and groundwater-level measurements for the Columbia Plateau Regional Aquifer System in Washington, Oregon, and Idaho, were compiled from data provided by the U.S. Geological Survey and seven other organizations. From the full set of about 60,000 wells and 450,000 water-level measurements a subset of 761 wells within the aquifers of the Columbia River Basalt Group (CRBG) then was used to develop a simple linear groundwater-level trend map for 1968–2009. The mean of the trends was a decline of 1.9 feet per year (ft/yr), with 72 percent of the water levels in wells declining. Rates of declines greater than 1.0 ft/yr were measured in 50 percent of wells, declines greater than 2.0 ft/yr in 38 percent of wells, declines greater than 4.0 ft/yr in 29 percent of wells, and declines greater than 8.0 ft/yr in 4 percent of wells. Water-level data were used to identify groups of wells with similar hydraulic heads and temporal trends to delineate areas of overall similar groundwater conditions. Discontinuities in hydraulic head between well groups were used to help infer the presence of barriers to groundwater flow such as changes in lithology or the occurrence of folds and faults. In areas without flow barriers, dissimilarities in response of well groups over time resulted from the formation of groundwater mounds caused by recharge from irrigation or regions of decline caused by pumping. The areas of focus for this analysis included the Umatilla area, Oregon, and the Palouse Slope/eastern Yakima Fold Belt in the Columbia Basin Ground Water Management Area (GWMA) consisting of Adams, Franklin, Grant, and Lincoln Counties, Washington. In the Umatilla area, water levels from 286 wells were used to identify multiple areas of high hydraulic gradient that indicate vertical and horizontal barriers to groundwater flow. These barriers divide the groundwater-flow system into several compartments with varying degrees of interconnection. Horizontal flow barriers commonly correspond to mapped geologic structure and result in horizontal hydraulic gradients that progressively become steeper from north to south corresponding to an increase in structural complexity that may be impeding recharge from the uplands into the heavily developed areas. Most CRBG aquifers in the Umatilla area are declining and since 1970, cumulative declines range from about 100 to 300 feet. Significant vertical hydraulic gradients are documented for relatively small areas near Umatilla, and since the 1970s, downward vertical gradients in these areas have been increasing as hydraulic heads in the deeper units have declined. The absence of vertical gradients over much of the area may be a consequence of flow through commingling wells that results in the equilibration of the heads between aquifers. On the Palouse Slope in the central GWMA, large groundwater declines occurred during 1968–2009 along a north-south swath in the middle of the region. An analysis of 1,195 wells along major flow paths and through the area of persistent groundwater-level declines indicates that barriers to flow are not as evident in this area as in Umatilla. This is consistent with the geologic interpretation of the Palouse Slope as being a gently folded structure created by voluminous sheet flows of CRBG lavas. Groundwater discharge into the sediment-filled coulees, where the upper aquifers are intersected at land surface by incised canyons, is proposed as an alternative to explain local steepening of the hydraulic gradient along the Palouse Slope previously attributed to the presence of a groundwater dam. Comparison of generalized potentiometric surface maps developed for pre-development conditions and post-2000 conditions indicate that pre-development groundwater flow was from the uplands toward the Columbia and Snake River and that post-2000 flow patterns in the area are controlled by irrigation practices that have resulted in broad regions of elevated or depressed hydraulic head. In some cases, irrigation-related changes in head have reversed groundwater flow directions. Evidence of significant vertical hydraulic gradients exists, although much of the aquifer thickness is affected by commingling of wells. The effect of commingling and its relative contribution to problems related to groundwater-level declines remains unclear.

Washington, Oregon, Idaho↗
USGS2023

Attenuation of barium, strontium, cobalt, and nickel plumes formed during microbial iron-reduction in a crude-oil-contaminated aquifer

We assessed the spatial distribution of 35 elements in aquifer sediments and groundwater of a crude-oil-contaminated aquifer and show evidence of the dissolution of barium (Ba), strontium (Sr), cobalt (Co), and nickel (Ni) during hydrocarbon oxidation coupled to historic microbial Fe(III)-reduction near the oil. Trace element plumes occur in the crude-oil-contaminated aquifer, where 50% Co, 47% Ni, 24% Ba, and 15% Sr have been mobilized from the sediment near the oil into groundwater, resulting in dissolved masses >33, 18, three, and two times greater than estimated dissolved masses prior to contamination, respectively. Ba 2+ and Ni 2+ concentrations exceeded the World Health Organization’s drinking-water guidelines of 700 and 20 μg/L, respectively. Sediments attenuate trace element plumes in two geochemically distinct zones, resulting in <0.01% total trace element masses dissolved in groundwater, despite the substantial mobilization near the oil body. Geochemical modeling of the modern Fe(III)-reducing zone suggests trace elements are likely attenuated via coprecipitation with/without sorption on iron carbonate precipitates. In the suboxic transition zone at the leading edge of the plume, Fe(III)-hydroxides sorb Ba 2+ , Sr 2+ , Co 2+ , and Ni 2+ . This study emphasizes that slow but persistent biogeochemical activity can substantially alter aquifer chemistry over decadal timeframes, a phenomenon we term biogeochemical gradualism.

Minnesota↗
USGS2013

Geohydrology, water quality, and simulation of groundwater flow in the stratified-drift aquifer system in Virgil Creek and Dryden Lake Valleys, Town of Dryden, Tompkins County, New York

In 2002, the U.S. Geological Survey, in cooperation with the Tompkins County Planning Department and the Town of Dryden, New York, began a study of the stratified-drift aquifer system in the Virgil Creek and Dryden Lake Valleys in the Town of Dryden, Tompkins County. The study provided geohydrologic data needed by the town and county to develop a strategy to manage and protect their water resources. In this study area, three extensive confined sand and gravel aquifers (the upper, middle, and lower confined aquifers) compose the stratified-drift aquifer system. The Dryden Lake Valley is a glaciated valley oriented parallel to the direction of ice movement. Erosion by ice extensively widened and deepened the valley, truncated bedrock hillsides, and formed a nearly straight, U-shaped bedrock trough. The maximum thickness of the valley fill in the central part of the valley is about 400 feet (ft). The Virgil Creek Valley in the east part of the study area underwent less severe erosion by ice than the Dryden Lake Valley, and hence, it has a bedrock floor that is several hundred feet higher in altitude than that in the Dryden Lake Valley. The sources and amounts of recharge were difficult to identify in most areas because the confined aquifers are overlain by confining units. However, in the vicinity of the Virgil Creek Dam, the upper confined aquifer crops out at land surface in the floodplain of a gorge eroded by Virgil Creek, and this is where the aquifer receives large amounts of recharge from precipitation that directly falls over the aquifer and from seepage losses from Virgil Creek. The results of streamflow measurements made in Virgil Creek where it flows through the gorge indicated that the stream lost 1.2 cubic feet per second (ft 3 /s) or 0.78 million gallons per day (Mgal/d) of water in the reach extending from 220 ft downstream from the dam to 1,200 ft upstream from the dam. In the southern part of the study area, large amounts of recharge also replenish the stratified-drift aquifers at the Valley Heads Moraine, which consists of heterogeneous sediments including coarse-grained outwash and kame sediments, as well as zones containing till with a fine-grained matrix. In the southern part of the study area, the confining units are thin and likely to be discontinuous in some places, resulting in windows of permeable sediment, which can more readily transmit recharge from precipitation and from tributaries that lose water as they flow over the valley floor. In contrast, in the northern part of the study area, the confining units are thick, continuous, and comprise homogeneous fine-grained sediments that more effectively confine the aquifers than in the southern part of the study area. Most groundwater in the northern part of the study area discharges to the Village of Dryden municipal production wells, to the outlet to Dryden Lake, to Virgil Creek, and as groundwater underflow that exits the northern boundary of the study area. Most northward-flowing groundwater in the southern part of the study area discharges to Dryden Lake, to the inlet to Dryden Lake, and to homeowner, nonmunicipal community (a mobile home community and several apartments), and commercial wells. Most of this pumped water is returned to the groundwater system via septic systems. Most southward-flowing groundwater in the southern part of the study area discharges to the headwaters of Owego Creek and to agricultural wells; some flow also exits the southern boundary of the study area as groundwater underflow. The largest user of groundwater in the study area is the Village of Dryden. Water use in the village has approximately tripled between the early 1970s when withdrawals ranged between 18 and 30 million gallons per year (Mgal/yr) and from 2000 through 2008 when withdrawals ranged between 75 and 85 Mgal/yr. The estimated groundwater use by homeowners, nonmunicipal communities, and small commercial facilities outside the area supplied by the Village of Dryden municipal wells is estimated to be about 18.4 Mgal/yr. Most of this pumped water is returned to the groundwater system via septic systems. For this investigation, an aquifer test was conducted at the Village of Dryden production well TM 981 (finished in the middle confined aquifer at a well depth of 72 ft) at the Jay Street pumping station during June 19&ndash;21, 2007. The aquifer test consisted of pumping production well TM 981 at 104 gallons per minute over a 24-hour period. The drawdown in well TM 981 at the end of 24 hours of pumping was 19.2 ft. Results of the aquifer-test analysis for a partially penetrating well in a confined aquifer indicated that the transmissivity was 1,560 feet squared per day, and the horizontal hydraulic conductivity was 87 feet per day, based on a saturated thickness of 18 ft. During 2003&ndash;5, 14 surface-water samples were collected at 8 sites, including Virgil Creek, Dryden Lake outlet, and several tributaries. During 2003 through 2009, eight groundwater samples were collected from eight wells, including three municipal production wells, two test wells, and three domestic wells. Calcium dominates the cation composition, and bicarbonate dominates the anion composition in most groundwater and surface-water samples. None of the common inorganic constituents collected exceeded any Federal or State water-quality standards. Results from a three-dimensional, finite-difference groundwater-flow model were used to compute a water budget and to estimate the areal extent of the zone of groundwater contribution to the Village of Dryden municipal production wells. The model-computed water budget indicated that the sources of recharge to the confined aquifer system are precipitation that falls directly on the valley-fill sediments (40 percent of total recharge), stream leakage (35.5 percent), seepage from wetlands and ponds (12 percent), unchanneled runoff and groundwater inflow from the uplands (8.5 percent), and groundwater underflow into the eastern end of the model area (4 percent). Most groundwater discharges to surface-water bodies, including Dryden Lake (33 percent), streams (33 percent), and wetlands and ponds (10 percent of the total). In addition, some groundwater discharges as underflow out of the southern and northern ends of the model area (15 percent), to simulated pumping wells (4.5 percent), and to drains that represent seepage from the bluffs exposed in the gorge in the vicinity of the Virgil Creek Dam (4.5 percent). The areal extents of the zones of groundwater contribution for Village of Dryden municipal production wells TM 202 (Lake Road pump station, finished in the upper confined aquifer) and TM 981 (Jay Street pump station, finished in the middle confined aquifer) are 0.5 square mile (mi 2 ) and 0.9 mi 2 , respectively. The areal extent of the zone of contribution to production well TM 202 extends 2.2 miles (mi) southeast into the Virgil Creek Valley, whereas production well TM 981 extends 3.8 mi south in the Dryden Lake Valley. The areal extent of the zone of contribution to production well TM1046 (South Street pump station) is 1.4 mi 2 and extends 2.4 mi into Dryden Lake Valley and 0.5 mi into Virgil Creek Valley.

New York↗
USGS2018

Preliminary evaluation of the hydrogeology and groundwater quality of the Mississippi River Valley alluvial aquifer and Memphis aquifer at the Tennessee Valley Authority Allen Power Plants, Memphis, Shelby County, Tennessee

The hydrogeology, groundwater quality, and potential for hydraulic connection between the Mississippi River Valley alluvial aquifer and the Memphis aquifer in the area of the Tennessee Valley Authority (TVA) Allen Combined Cycle and Allen Fossil Plants in southwestern Memphis, Tennessee, were evaluated from September through December 2017. The study was designed as a preliminary assessment of the potential for leakage of groundwater from the Mississippi River Valley alluvial aquifer through the underlying upper Claiborne confining unit into the underlying Memphis aquifer at the plants. A short-term aquifer test of four of the five Memphis aquifer production wells installed at the Allen Combined Cycle Plant induced drawdown in water levels in the Mississippi River Valley alluvial aquifer, locally. The largest drawdown occurred in the eastern and southeastern parts of the TVA plants area, and generally was coincident with locations where stratigraphic data show increased thickness of and depth to the base of the alluvium and decreased thickness and inferred offset in the base of the confining unit relative to nearby locations. In contrast, stratigraphic data for most other locations at the site indicate shallower depths to the base of the alluvium and more consistent thickness of and depth to the base of the confining unit, which corresponds with areas where less drawdown was observed during the test. Water-quality results for samples from the production wells and from monitoring wells screened in the Mississippi River Valley alluvial aquifer indicate that groundwater with higher dissolved-solids concentrations and tritium from this shallow aquifer has mixed with water in the upper part of the Memphis aquifer at one of the production wells. Results of the study collectively confirm that the Mississippi River Valley alluvial and Memphis aquifers are hydraulically connected near the TVA plants area.

Tennessee↗
USGS2012

Quality of water from crystalline rock aquifers in New England, New Jersey, and New York, 1995-2007

Crystalline bedrock aquifers in New England and parts of New Jersey and New York (NECR aquifers) are a major source of drinking water. Because the quality of water in these aquifers is highly variable, the U.S. Geological Survey (USGS) statistically analyzed chemical data on samples of untreated groundwater collected from 117 domestic bedrock wells in New England, New York, and New Jersey, and from 4,775 public-supply bedrock wells in New England to characterize the quality of the groundwater. The domestic-well data were from samples collected by the USGS National Water-Quality Assessment (NAWQA) Program from 1995 through 2007. The public-supply-well data were from samples collected for the U.S. Environmental Protection Agency (USEPA) Safe Drinking Water Act (SDWA) Program from 1997 through 2007. Chemical data compiled from the domestic wells include pH, specific conductance, dissolved oxygen, alkalinity, and turbidity; 6 nitrogen and phosphorus compounds, 14 major ions, 23 trace elements, 222 radon gas (radon), 48 pesticide compounds, and 82 volatile organic compounds (VOCs). Additional samples were collected from the domestic wells for the analysis of gross alpha- and gross beta-particle radioactivity, radium isotopes, chlorofluorocarbon isotopes, and the dissolved gases methane, carbon dioxide, nitrogen, and argon. Chemical data compiled from the public-supply wells include pH, specific conductance, nitrate, iron, manganese, sodium, chloride, fluoride, arsenic, uranium, radon, combined radium ( 226 radium plus 228 radium), gross alpha-particle radioactivity, and methyl tert -butyl ether (M t BE). Patterns in fluoride, arsenic, uranium, and radon distributions were discernable when the data were compared to lithology groupings of the bedrock, indicating that the type of bedrock has an effect on the quality of groundwater from NECR aquifers. Fluoride concentrations were significantly higher in groundwater samples from the alkali granite, peraluminous granite, and metaluminous granite lithology groups than from samples in the other lithology groups. Water samples from 1.4 percent of 2,167 studied wells had fluoride concentrations that were equal to or greater than the maximum contaminant level (MCL) of 4 milligrams per liter (mg/L) and 7.5 percent of the wells had fluoride concentrations that were equal to or greater than the secondary MCL of 2 mg/L. For arsenic, groundwater samples from the calcareous metasedimentary rocks in the New Hampshire-Maine geologic province, peraluminous granite, and pelitic rocks lithology groups had higher concentrations than did samples from the other lithology groups. Water samples from 13.3 percent of 2,054 studied wells had arsenic concentrations that were equal to or greater than the MCL of 10 micrograms per liter (μg/L), about double the national rate of occurrence in community-supply systems and in domestic wells of the United States. Uranium concentrations were significantly higher in groundwater samples from the peraluminous granite, alkali granite, and calcareous metasedimentary rocks in the New Hampshire-Maine geologic province lithology groups than from samples in the other lithology groups. Water samples from 14.2 percent of 556 studied wells had uranium concentrations equal to or greater than the MCL of 30 μg/L. Radon activities were equal to or greater than the proposed MCL of 300 picocuries per liter (pCi/L) in 95 percent of 943 studied wells, and 33 percent of the wells had radon activities were equal to or greater than the proposed alternative maximum contaminant level (AMCL) of 4,000 pCi/L. Radon activities exceeded the proposed AMCL in 20 percent or more of groundwater samples in each of the studied lithology groups with a minimum of 9 samples, but radon activities were significantly higher in groundwater samples from the alkali granite, peraluminous granite, and Narragansett basin metasedimentary rocks lithology groups. Water samples from 3.2 percent of 564 studied wells had combined radium activities equal to or greater than the MCL of 5 pCi/L; however, combined radium activities were not significantly different among the studied lithology groups. Land use and population density also were evaluated to explain patterns in water quality. Concentrations of nitrate, sodium, chloride, and MtBE from the studied wells were significantly greater in areas of high population density (≥50 persons per square kilometer) than in areas of low population density (<50 persons per square kilometer). Concentrations of sodium, chloride, and M t BE from the studied wells were significantly greater in areas classified as developed (urban lands) than in areas classified as undeveloped (forested), agricultural, or mixed (no dominant land use). Nitrate concentrations from the public-supply wells were not significantly different among the four land use categories, but nitrate concentrations from the domestic wells were significantly greater in areas classified as developed than in areas classified as undeveloped, agricultural, or mixed. Chloride to bromide mass ratios in the domestic well samples indicate that the groundwater was probably affected by at least three halogen sources: local precipitation and recharge waters, remnant seawater and connate waters evolved from seawater, and recharge waters affected by road salt. The groundwater in the NECR aquifers generally contained low concentrations of nitrate, VOCs, and pesticides. Less than 1 percent of water samples from 4,781 studied wells had concentrations of nitrate greater than the MCL of 10 mg/L. Less than 1 percent of water samples from 1,299 studied wells exceeded the USEPA advisory level of 20 to 40 μg/L for M t BE. None of the other studied VOCs exceeded a human health benchmark. M t BE (36 percent frequency detection) and chloroform (32.9 percent frequency detection) were the most frequently detected (>0.02 μg/L) VOCs in the domestic wells. M t BE was detected more often in water samples with apparent ages of less than 25 years than in water samples with apparent ages greater than 25 years. This finding is consistent with the time period of high M t BE use in areas in the United States where reformulated gasoline was mandated. The largest pesticide concentration was an estimated concentration of 0.06 μg/L for the herbicide metolachlor. Deethylatrazine, a degradate of atrazine, (18 percent frequency detection) and atrazine (8 percent frequency detection) were the only pesticide compounds detected (>0.001 μg/L) in more than 3 percent of the domestic wells. None of the detected pesticide compounds exceeded human health benchmarks. Concentrations of nitrate and gross alpha-particle activities were significantly greater in the water samples from the domestic wells than in samples from the public-supply wells. Concentrations of sodium, chloride, iron, manganese, and uranium were significantly greater in the water samples from the public-supply wells than in the samples from the domestic wells. One possible explanation may be related to differences in field processing (filtered samples from the domestic wells compared to unfiltered samples from the public-supply wells). The high frequency of detections for a wide variety of manmade and naturally occurring contaminants in both domestic and public-supply wells shows the vulnerability of NECR aquifers to contamination. The highly variable water quality and the association with highly variable lithology of crystalline bedrock underscores the importance of testing individual wells to determine if concentrations for the most commonly detected contaminants exceed human health benchmarks.

Connecticut, Maine, Massachusetts, New Hampshire, ↗
USGS2024

Status and understanding of groundwater quality in the Mojave Basin Domestic-Supply Aquifer study unit, 2018—California GAMA Priority Basin Project

Groundwater quality in the western part of the Mojave Desert in San Bernardino County, California, was investigated in 2018 as part of the California State Water Resources Control Board Groundwater Ambient Monitoring and Assessment Program Priority Basin Project. The Mojave Basin Domestic-Supply Aquifer study unit (MOBS) region was divided into two study areas—floodplain and regional—to assess differences between the two major aquifers used for drinking water supply in the area. This assessment characterized the quality of ambient groundwater and not the quality of treated drinking water. The study included three components: (1) a status assessment, which characterized the quality of groundwater resources used for domestic drinking-water supply in the floodplain and regional study areas; (2) a brief understanding assessment, which evaluated factors that could potentially affect the quality of groundwater used by domestic wells in the region; and (3) a comparative assessment between the groundwater resources used by domestic wells and public-supply wells in the two study areas. The domestic-well assessment was based on data collected by the U.S. Geological Survey from 48 domestic wells in January–May 2018. The public-supply assessment was based on data for samples from 322 public-supply wells in 2008–18, either collected by the U.S. Geological Survey or compiled from the California State Water Resources Control Boards Division of Drinking Water publicly available database. Concentrations of water-quality constituents in ambient groundwater were compared to regulatory and non-regulatory benchmarks typically used by the State of California and Federal agencies as health-based or aesthetic standards for public drinking water. Relative concentrations, defined as the measured concentration divided by the benchmark concentration, were classified as high (greater than 1.0), moderate (greater than 0.5 for inorganic constituents or 0.1 for organic and special-interest constituents, and not high), or low (concentrations lower than moderate). The floodplain and regional study areas were divided into 15 and 35 grid cells, respectively, and grid-based methods were used to compute the areal proportions of the two study areas with high, moderate, or low relative concentrations of individual constituents and classes of constituents. For the domestic-supply assessment, one or more inorganic constituents with health-based benchmarks were detected at high relative concentrations in 58 percent of the regional study area and 13 percent of the floodplain study area. The inorganic constituents with health-based benchmarks detected at high relative concentrations in the regional study area were arsenic, chromium and hexavalent chromium, fluoride, adjusted gross alpha particle activity, uranium, molybdenum, strontium, and nitrate; only arsenic was detected at high relative concentrations in the floodplain study area. One or more inorganic constituents with secondary maximum contaminant level benchmarks were detected at high concentrations in 15 and 6.7 percent of the regional and floodplain study areas, respectively. The constituents detected at high relative concentrations in the regional study area were total dissolved solids, chloride, sulfate, and iron; only total dissolved solids and sulfate were detected at high relative concentrations in the floodplain study area. Organic constituents were not detected at moderate or high relative concentrations in either the regional or floodplain study areas. Volatile organic compounds were detected at low relative concentrations in 21 and 27 percent of the regional and floodplain study areas, respectively, and pesticides were detected at low relative concentrations in 9.1 and 20 percent of the regional and floodplain study areas, respectively. The only individual organic constituent detected in more than 10 percent of either study area was the trihalomethane trichloromethane. Total coliform bacteria were detected in 15 and 27 percent of the grid wells in the regional and floodplain study areas, respectively. The greater prevalence of high relative concentrations of many inorganic constituents in the regional study area compared to the floodplain area likely indicates the greater diversity of geologic material at depth in aquifer material and generally finer-grained alluvium compared to the floodplain study area combined with generally older groundwater that has had more contact time with aquifer materials. In general, trace element concentrations (1) increased with increasing groundwater age, (2) increased with distance from recharge sources in the mountains, and (3) increased with closer proximity to some types of geological units. In general, groundwater from domestic wells in the floodplain study area is young, with most samples containing a component of modern groundwater based on tritium and unadjusted carbon-14 activities, whereas groundwater from domestic wells in the regional study area generally is old, with most samples having unadjusted carbon-14 ages of 5,000–40,000 years. Public-supply wells in MOBS generally were deeper than domestic wells and presumably are in contact with older, more weathered alluvium that may have more mobile trace elements, such as arsenic or uranium. However, only 26 percent of the public-supply regional study area had high relative concentrations of inorganic constituents, compared to 58 percent for the domestic regional study area. The percentages of the public-supply and domestic floodplain study areas with high relative concentrations of inorganic constituents were 11 and 13 percent, respectively. The ages of groundwater used by public-supply and domestic wells in each study area were similar, which was not expected given the greater depth of the public-supply wells. Three potential factors may contribute to these results: (1) greater spatial footprint of domestic well network, which may result in domestic wells pumping groundwater from fractured bedrock or mineralized areas not used by public-supply wells; (2) greater pumping rates in public-supply wells, resulting in more water being withdrawn from coarse-grained, heterogeneous alluvium than finer-grained layers, which may have higher concentrations of (or more mobile) inorganic constituents; and (3) a greater degree of well management with public-supply wells, which may include pausing use of or decommissioning wells if treating or blending water is not feasible to lower constituent concentrations.

California↗
USGS2010

Fate and transport of petroleum hydrocarbons in the subsurface near Cass Lake, Minnesota

The U.S. Geological Survey (USGS) investigated the natural attenuation of subsurface petroleum hydrocarbons leaked over an unknown number of years from an oil pipeline under the Enbridge Energy Limited Partnership South Cass Lake Pumping Station, in Cass Lake, Minnesota. Three weeks of field work conducted between May 2007 and July 2008 delineated a dissolved plume of aromatic hydrocarbons and characterized the biodegradation processes of the petroleum. Field activities included installing monitoring wells, collecting sediment cores, sampling water from wells, and measuring water-table elevations. Geochemical measurements included concentrations of constituents in both spilled and pipeline oil, dissolved alkylbenzenes and redox constituents, sediment bioavailable iron, and aquifer microbial populations. Groundwater in this area flows east-southeast at approximately 26 meters per year. Results from the oil analyses indicate a high degree of biodegradation, characterized by nearly complete absence of n-alkanes. Cass Lake oil samples were more degraded than two oil samples collected in 2008 from the similarly contaminated USGS Bemidji, Minnesota, research site 40 kilometers away. Based on 19 ratios developed for comparing oil sources, the conclusion is that the oils at the two sites appear to be from the same hydrocarbon source. In the Cass Lake groundwater plume, benzene concentrations decrease by three orders of magnitude within 150 meters (m) downgradient from the oil body floating on the water table (between well MW-10 and USGS-4 well nest). The depths of the highest benzene concentrations increase with distance downgradient from the oil, a condition typical of plumes in shallow, unconfined aquifers. Background groundwater, which is nearly saturated with oxygen, becomes almost entirely anaerobic in the plume. As at the Bemidji site, the most important biodegradation processes are anaerobic and dominated by iron reduction. The similarity between the Cass Lake and Bemidji benzene degradation rates, redox conditions, and aquifer material all support a hypothesis that the Cass Lake plume, like the Bemidji plume, is decades old. As concentrations of alkylbenzenes in the oil decrease over time, the benzene concentrations in the groundwater plume will also decrease and the plume is expected to shrink. The Fox Creek wetland, about 250 m south of the Cass Lake site, is the nearest receptor to the south.

Scientific Investigations Report↗