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USGS2020

One-Water Hydrologic Flow Model: A MODFLOW based conjunctive-use simulation software

The U.S. Geological Survey’s (USGS) Modular Ground-Water Flow Model (MODFLOW-2005) is a computer program that simulates groundwater flow by using finite differences. The MODFLOW-2005 framework uses a modular design that allows for the easy development and incorporation of new features called processes and packages that work with or modify inputs to the groundwater-flow equation. A process solves a flow equation or set of equations. For example, the central part of MODFLOW is the groundwater-flow process that solves the groundwater-flow equation; the surface-water routing process is an additional process that solves the surface-water flow equation. Packages are code related to the groundwater-flow process. For example, the subsidence package modifies the groundwater-flow process by including aquifer compaction effects on flow. With the development of new packages and processes, the MODFLOW-2005 base framework diverged into multiple independent versions designed for specific simulation needs. This divergence limited each independent MODFLOW release to its specific purpose, so that there was no longer a single, comprehensive, general-purpose hydraulic-simulation framework. The MODFLOW One-Water Hydrologic Flow Model (MF-OWHM, also informally known as OneWater) is an integrated hydrologic flow model that combines multiple MODFLOW-2005 variants in one cohesive simulation software; changes were made to enable multiple capabilities in one code. This fusion of the MODFLOW-2005 versions resulted in a simulation software that can be used to address and analyze a wide class of conjunctive-use, water-management, water-food-security, and climate-crop-water scenarios. As a second core version of MODFLOW-2005, MF-OWHM maintains backward compatibility with existing MODFLOW-2005 versions, with features that include the following: Process-based simulation. Saturated groundwater flow (three-dimensional). Surface-water flow (one- and two-dimensional). Stream and river flow. Lake and reservoir storage. Landscape simulation and irrigated agriculture. Land-use and crop simulation. Root uptake of groundwater. Actual evapotranspiration. Estimated irrigation demand. Reservoir operations. Aquifer compaction and subsidence by vertical model-grid deformation. Seawater intrusion by a sharp-interface assumption. Karst-aquifer and fractured-bedrock flow. Turbulent and laminar-pipe network flow. Unsaturated groundwater flow (one-dimensional). Internal linkages among the processes that couple hydraulic head, flow, and deformation. Redesigned code for faster simulation, increased user-input options, easier model updates, and more robust error reporting than in previous models. MF-OWHM is a MODFLOW-2005 based integrated hydrologic model that can simulate and analyze varying environmental conditions to allow for the evaluation of management options from many components of human and natural water movement through a physically based, supply and demand framework. The term “integrated,” in the context of this report, refers to the tight coupling of groundwater flow, surface-water flow, landscape processes, aquifer compaction and subsidence, reservoir operations, and conduit (karst) flow. Another benefit of this integrated hydrologic model is that models developed to run by MODFLOW-2005, MODFLOW-NWT, MODFLOW-CFP, or MODFLOW-FMP can also be simulated with MF-OWHM. At the time of this report’s publication, MF-OWHM version 2 (MF-OWHM2) does not include a direct internal simulation of snowmelt, advanced mountainous watershed rainfall-runoff simulation, detailed shallow soil-moisture accounting, or atmospheric moisture content. Atmospheric moisture may be accounted for indirectly by, optionally, specifying a pan-evaporation rate, reference evapotranspiration, and precipitation. These features are not included to ensure that simulation runtime remains short enough to enable the use of automated methods of calibrating model parameters to field observations, which typically require many simulation model runs. The MF-OWHM approach is to include as much detail as possible to simulate hydrological processes, providing the simulation runtimes remain reasonable enough to allow for robust parameter estimation and model calibration. To represent both natural and human-influenced flow, MF-OWHM integrates physically based flow processes derived from MODFLOW-2005 in a supply and demand framework. From this integration, the physically based movement of groundwater, surface water, imported water, and precipitation serve as supply to meet consumptive demands associated with irrigated and non-irrigated agriculture, natural vegetation, and urban water uses. Water consumption is determined by balancing the available water supply with water demand, leading to the concept of a demand-driven, supply-constrained simulation. The MF-OWHM Supply-and-Demand Framework is especially useful for the analysis of agricultural water use, where there are often few data available to describe changes in land-use through time, such as crop type and distribution, and the associated changes in groundwater pumpage. This framework attempts to satisfy each land-use water demand with available water supplies—that is, groundwater uptake, precipitation, and irrigation. An option provided in MF-OWHM2 is to automatically increase groundwater pumping for irrigation, which often is unknown, by the calculated residual between demand and the other available sources of supply. From large- to small-scale applications, the physically based supply and demand framework provides key capabilities for simulating and analyzing historical, current, and future conjunctive-use of surface water and groundwater. To achieve the physically based supply and demand framework, the MODFLOW-2005 standard of no inter-package and -process communication was relaxed for MF-OWHM2. Traditional MODFLOW simulation models required that all packages and processes interact through the groundwater-flow equation or by removing the water flow from the simulation domain. For example, the MODFLOW-2005 representation of a groundwater well extracts water from the groundwater-flow equation (by subtraction) and removes it from the simulation domain. This feature is available in the MF-OWHM framework, but options have been added to allow the specification of a use or destination of pumped groundwater within the model domain, for example, it can be used for irrigation, managed aquifer recharge, or return-flow to streams.

Techniques and Methods↗

USGS2021

Hydrogeology and simulation of groundwater flow in Columbia County, Wisconsin

This report describes the regional hydrogeology and groundwater resources of Columbia County, Wisconsin, and documents a regional groundwater flow model developed for the county. Regional hydrostratigraphic units include the unlithified aquifer, the upper bedrock aquifer, and the Elk Mound aquifer. The unlithified aquifer consists of deposits that range in composition from sand and gravel outwash and stream deposits to silty, sandy till. This aquifer is less than 25 ft thick in much of eastern Columbia County, but consists of permeable sand and gravel extending to over 250 ft in depth in the Wisconsin River valley bottom. The upper bedrock aquifer consists of Ordovician and upper Cambrian sedimentary formations, including sandstone, siltstone and dolomitic strata. The upper bedrock aquifer underlies the unlithified aquifer in eastern portions of the County, but is absent to the west, where these formations are largely eroded. The contact between the Tunnel City Group and Wonewoc Formation (Top of Elk Mound Group) forms the base of the upper bedrock aquifer. Bedding plane fractures are common to this aquifer, although only a portion of the observed fractures appear to be hydraulically active. The upper bedrock aquifer is a significant source of groundwater at a regional scale. Measurements of hydraulic head showed a difference of several feet across the bottom of this aquifer to the underlying Wonewoc sandstone, indicating that the basal facies of the Tunnel City Group functions as an aquitard separating the upper bedrock aquifer from the Elk Mound aquifer. Conditions vary considerably within this aquifer, depending on the local lithostratigraphy. For example, where present, the St. Lawrence Fm. and fine-grained intervals of the Tunnel City Group may be locally-extensive aquitards. The Elk Mound aquifer consists of Cambrian sandstone of the Wonewoc, Eau Claire, and Mount Simon Formations. It is thin to absent in several locations but ranges up to 600 ft in thickness over much of southern Columbia County. The variation in thickness is due in large part to the irregular topography of the underlying Precambrian crystalline rock, which generally serves as the base of the groundwater system. In neighboring counties, a fine-grained facies within the Eau Claire Fm. acts as a regionally extensive aquitard, referred to as the Eau Claire aquitard. Much of the data collected and compiled for this study suggest that shale or dolomite within the Eau Claire Fm., which is the equivalent of the Eau Claire aquitard, occurs only within southwestern Columbia County. There is little to no evidence of the Eau Claire aquitard over most of the county. Where the dolomite and shale are absent, the Elk Mound aquifer is relatively homogenous and does not include a mappable aquitard. A three-dimensional steady-state flow model presented here represents long-term, average conditions in the regional groundwater system since about 1970. The model was constructed with the U.S. Geological Survey’s MODFLOW-NWT code; it has six layers with a uniform grid of 300 ft x 300 ft cells. Layers 1 and 2 simulate the unlithified aquifer and layer 3 represents the upper bedrock aquifer. The Elk Mound aquifer is simulated by layers 4, 5 and 6, representing the Wonewoc, Eau Claire, and Mount Simon Formations, respectively. The model extends beyond the boundaries of Columbia County to ensure that hydrologic conditions simulated within the County are consistent with regional conditions. Recharge to the groundwater flow model is based on results from a GIS-based soil-water-balance model. Recharge was simulated with the unsaturated zone flow (UZF) package in MODFLOW. This approach is particularly useful for quantifying groundwater discharge to riparian wetlands because UZF tracks recharge that would lead to the simulated water table exceeding the land surface (represented by the top of model layer 1) and reroutes it to nearby stream segments. The model includes pumping from 256 wells, and 178 of these are located within Columbia County. Pumping totaled about 28 million gallons per day (mgd) on average since 1970, with 7.2 mgd of the withdrawal from within the County. Model calibration was performed with the PEST parameter estimation code. Calibration targets included approximately 3,900 head measurements and 91 stream flow measurements. Four vertical-head differences across hydrogeologic units, calculated from data collected during packer testing in wells in Columbia County, were also used in model calibration. Results from the calibrated model provide a groundwater balance for the region. About 83 percent of groundwater originates as recharge to the water table, 12 percent comes from leakage from streams, and about 5 percent of the groundwater flows into the model domain from surrounding areas. About 95 percent of the simulated groundwater discharges to steams and other surface water features, about 3 percent flows across model boundaries to surrounding areas of the groundwater system, and pumping accounts for 2 percent of discharge. Simulated flow paths are relatively local, from recharge in upland areas to discharge in nearby streams and wetlands. The model has many potential applications, including simulation of the effects of existing or proposed high-capacity wells, estimating the zone of contribution for these wells, and understanding relationships between surface water and groundwater. Future refinements to the model, such as incorporating new information about the extent and hydraulic characteristics of the Tunnel City Group, will improve its utility in understanding advective flow between the upper bedrock and Elk Mound aquifers. If seasonal or annual variations in the groundwater system are of interest, this steady-state model could be brought into a transient mode.

Wisconsin↗

USGS2009

Quality of Shallow Groundwater and Drinking Water in the Mississippi Embayment-Texas Coastal Uplands Aquifer System and the Mississippi River Valley Alluvial Aquifer, South-Central United States, 1994-2004

The Mississippi embayment-Texas coastal uplands aquifer system is an important source of drinking water, providing about 724 million gallons per day to about 8.9 million people in Texas, Louisiana, Mississippi, Arkansas, Missouri, Tennessee, Kentucky, Illinois, and Alabama. The Mississippi River Valley alluvial aquifer ranks third in the Nation for total withdrawals of which more than 98 percent is used for irrigation. From 1994 through 2004, water-quality samples were collected from 169 domestic, monitoring, irrigation, and public-supply wells in the Mississippi embayment-Texas coastal uplands aquifer system and the Mississippi River Valley alluvial aquifer in various land-use settings and of varying well capacities as part of the U.S. Geological Survey's National Water-Quality Assessment Program. Groundwater samples were analyzed for physical properties and about 200 water-quality constituents, including total dissolved solids, major inorganic ions, trace elements, radon, nutrients, dissolved organic carbon, pesticides, pesticide degradates, and volatile organic compounds. The occurrence of nutrients and pesticides differed among four groups of the 114 shallow wells (less than or equal to 200 feet deep) in the study area. Tritium concentrations in samples from the Holocene alluvium, Pleistocene valley trains, and shallow Tertiary wells indicated a smaller component of recent groundwater than samples from the Pleistocene terrace deposits. Although the amount of agricultural land overlying the Mississippi River Valley alluvial aquifer was considerably greater than areas overlying parts of the shallow Tertiary and Pleistocene terrace deposits wells, nitrate was rarely detected and the number of pesticides detected was lower than other shallow wells. Nearly all samples from the Holocene alluvium and Pleistocene valley trains were anoxic, and the reducing conditions in these aquifers likely result in denitrification of nitrate. In contrast, most samples from the Pleistocene terrace deposits in Memphis, Tennessee, were oxic, and the maximum nitrate concentration measured was 6.2 milligrams per liter. Additionally, soils overlying the Holocene alluvium and Pleistocene valley trains, generally in areas near the wells, had lower infiltration rates and higher percentages of clay than soils overlying the shallow Tertiary and Pleistocene terrace deposits wells. Differences in these soil properties were associated with differences in the occurrence of pesticides. Pesticides were most commonly detected in samples from wells in the Pleistocene terrace deposits, which generally had the highest infiltration rates and lowest clay content. Median dissolved phosphorus concentrations were 0.07, 0.11, and 0.65 milligram per liter in samples from the shallow Tertiary, Pleistocene valley trains, and Holocene alluvium, respectively. The widespread occurrence of dissolved phosphorus at concentrations greater than 0.02 milligram per liter suggests either a natural source in the soils or aquifer sediments, or nonpoint sources such as fertilizer and animal waste or a combination of natural and human sources. Although phosphorus concentrations in samples from the Holocene alluvium were weakly correlated to concentrations of several inorganic constituents, elevated concentrations of phosphorus could not be attributed to a specific source. Phosphorus concentrations generally were highest where samples indicated anoxic and reducing conditions in the aquifers. Elevated dissolved phosphorus concentrations in base-flow samples from two streams in the study area suggest that transport of phosphorus with groundwater is a potential source contributing to high yields of phosphorus in the lower Mississippi River basin. Water from 55 deep wells (greater than 200 feet deep) completed in regional aquifers of Tertiary age represent a sample of the principal aquifers used for drinking-water supply in the study area. The wells were screened in both confined and

Scientific Investigations Report↗

USGS2011

Characterization of the Cretaceous aquifer structure of the Meskala region of the Essaouira Basin, Morocco

The aquifer of early Cretaceous age in the Meskala region of the Essaouira Basin is defined by interpretation of geological drilling data of oil and hydrogeological wells, field measurement and analysis of in situ fracture orientations, and the application of a morphostructural method to identify lineaments. These analyzes are used to develop a stratigraphic–structural model of the aquifer delimited by fault zones of two principal orientations: NNE and WNW. These fault zones define fault blocks that range in area from 4 to 150 km 2 . These blocks correspond either to elevated zones (horsts) or depressed zones (grabens). This structural setting with faults blocks of Meskala region is in accordance with the structure of the whole Essaouira Basin. Fault zones disrupt the continuity of the aquifer throughout the study area, create recharge and discharge zones, and create dip to the units from approximately 10° to near vertical in various orientations. Fracture measurements and morphometric-lineament analyzes help to identify unmapped faults, and represent features important to groundwater hydraulics and water quality within fault blocks. The above geologic features will enable a better understanding of the behaviour and hydro-geo-chemical and hydrodynamics of groundwater in the Meskala aquifer.

Essaouira Basin↗

USGS1986

Planning report for the Edwards-Trinity Regional Aquifer-System analysis in central Texas, southeast Oklahoma, and southwest Arkansas

The Edwards-Trinity regional aquifer system supplies more than 0.78 million acre-feet per year (700 million gallons per day) of water for central Texas and small adjacent parts of southeast Oklahoma and southwest Arkansas. The system consists of three major aquifers and at least three minor aquifers in predominantly Cretaceous rocks, which together have an areal extent of about 80,000 square miles. The major aquifers are the Edwards-Trinity (Plateau) in west-central Texas, the Edwards (Balcones Fault Zone) in south-central Texas, and the Trinity in north-central Texas, southeast Oklahoma, and southwest Arkansas. Current (1986) and future concerns about the aquifer system involve the ever-increasing demand for water, most of which is associated with rapid population increase. Decreases in or elimination of spring discharges and encroachment of water from downdip salinewater zones into updip freshwater zones are of primary concern in the area underlain by ttie Edwards (Balcones Fault Zone) aquifer. Water-level declines of several hundred feet in the Trinity aquifer are a serious concern in some metropolitan areas. The Edwards-Trinity regional aquifer-system analysis project, begun in October 1985 and scheduled to be completed by October 1991, is one of a series of similar projects being conducted nationwide. The project is intended to define the hydrogeologic framework, and to describe the geochemistry and groundwater flow of the aquifer system in order to provide a better understanding of the system's long-term water-yielding potential. A multidisciplinary approach will be used in which computer-based digital simulation of flow in the system will be the principal method of hydrogeologic investigation.

Arkansas, Oklahoma, Texas↗

USGS2022

Characterization of the Sevier/Toroweap Fault Zone in Kane County, Utah, using controlled-source audio-frequency magnetotelluric (CSAMT) surveys

The Sevier/Toroweap Fault Zone is a major north-south-striking fault located in northern Arizona and southwestern Utah. In partnership with the National Park Service, the U.S. Geological Survey conducted two geophysical controlled-source audio-frequency magnetotelluric (CSAMT) surveys that transected the Sevier/Toroweap Fault Zone at Clay Flat, Utah, a potential pull-apart basin, west of a site of proposed groundwater pumping to evaluate the subsurface hydrogeology. The goal of the surveys was to enhance understanding of the interconnectedness of the Navajo aquifer, the region’s primary groundwater source, across two groundwater basins to the east and west of the fault zone, Water Rights Area (WRA) 81 and WRA 85. In the Kane County, Utah, area, the Sevier/Toroweap Fault Zone consists of the Sevier section (to the north) and the northern Toroweap section (to the south). Two survey lines totaling 7 kilometers of CSAMT survey data were collected. The CSAMT survey line SV1 transected both the Sevier section and the northern Toroweap section of the fault zone; survey line SV2 transected only the Sevier section. Although offset of the Navajo Sandstone, the main component of the Navajo aquifer, by the Sevier/Toroweap Fault Zone is generally accepted as the geologic reason that the Navajo aquifer is disconnected in the study area, results of the CSAMT surveys suggest that vertical offset of the Navajo Sandstone of the Glen Canyon Group across the Sevier/Toroweap Fault Zone is insufficient to completely disconnect the aquifer in the study area. The effects of faulting on groundwater north and south of the study area, where offset of water-bearing layers may be greater, requires further study. A clearer understanding of groundwater movement across the Sevier /Toroweap Fault Zone will aid water-resource managers in making informed decisions concerning groundwater rights.

Utah↗

USGS2018

Radium mobility and the age of groundwater in public-drinking-water supplies from the Cambrian-Ordovician aquifer system, north-central USA

High radium (Ra) concentrations in potable portions of the Cambrian-Ordovician (C-O) aquifer system were investigated using water-quality data and environmental tracers ( 3 H, 3 He trit , SF 6 , 14 C and 4 He rad ) of groundwater age from 80 public-supply wells (PSWs). Groundwater ages were estimated by calibration of tracers to lumped parameter models and ranged from modern (<50 yr) in upgradient, regionally unconfined areas to ancient (>1 Myr) in the most downgradient, confined portions of the potable system. More than 80 and 40 percent of mean groundwater ages were older than 1000 and 50,000 yr, respectively. Anoxic, Fe-reducing conditions and increased mineralization develop with time in the aquifer system and mobilize Ra into solution resulting in the frequent occurrence of combined Ra (Ra c = 226 Ra + 228 Ra) at concentrations exceeding the USEPA MCL of 185 mBq/L (5 pCi/L). The distribution of the three Ra isotopes comprising total Ra (Ra t = 224 Ra + 226 Ra + 228 Ra) differed across the aquifer system. The concentrations of 224 Ra and 228 Ra were strongly correlated and comprised a larger proportion of the Ra t concentration in samples from the regionally unconfined area, where arkosic sandstones provide an enhanced source for progeny from the 232 Th decay series. 226 Ra comprised a larger proportion of the Ra t concentration in samples from downgradient confined regions. Concentrations of Ra t were significantly greater in samples from the regionally confined area of the aquifer system because of the increase in 226 Ra concentrations there as compared to the regionally unconfined area. 226 Ra distribution coefficients decreased substantially with anoxic conditions and increasing ionic strength of groundwater (mineralization), indicating that Ra is mobilized to solution from solid phases of the aquifer as adsorption capacity is diminished. The amount of 226 Ra released from solid phases by alpha-recoil mechanisms and retained in solution increases relative to the amount of Ra sequestered by adsorption processes or co-precipitation with barite as adsorption capacity and the concentration of Ba decreases. Although 226 Ra occurred at concentrations greater than 224 Ra or 228 Ra, the ingestion exposure risk was greater for 228 Ra owing to its greater toxicity. In addition, 224 Ra added substantial alpha-particle radioactivity to potable samples from the C-O aquifer system. Thus, monitoring for Ra isotopes and gross-alpha-activity (GAA) is important in upgradient, regionally unconfined areas as downgradient, and GAA measurements made within 72 h of sample collection would best capture alpha-particle radiation from the short-lived 224 Ra.

Applied Geochemistry↗

USGS2018

Water-quality observations of the San Antonio segment of the Edwards aquifer, Texas, with an emphasis on processes influencing nutrient and pesticide geochemistry and factors affecting aquifer vulnerability, 2010–16

As questions regarding the influence of increasing urbanization on water quality in the Edwards aquifer are raised, a better understanding of the sources, fate, and transport of compounds of concern in the aquifer—in particular, nutrients and pesticides—is needed to improve water management decision-making capabilities. The U.S. Geological Survey, in cooperation with the San Antonio Water System, performed a study from 2010 to 2016 to better understand how water quality changes under a range of hydrologic conditions and in contrasting land-cover settings (rural and urban) in the Edwards aquifer. The study design included continuous hydrologic monitoring, continuous water-quality monitoring, and discrete sample collection for a detailed characterization of water quality at a network of sites throughout the aquifer system. The sites were selected to encompass a “source-to-sink” (that is, from aquifer recharge to aquifer discharge) approach. Network sites were selected to characterize rainfall, recharging surface water, and groundwater; groundwater sites included wells in the unconfined part of the aquifer (unconfined wells) and in the confined part of the aquifer (confined wells) and a major discharging spring. Storm-related samples—including rainfall samples, stormwater-runoff (surface-water) samples, and groundwater samples—were collected to characterize the aquifer response to recharge. Elevated nitrate concentrations relative to national background values and the widespread detection of pesticides indicate that the Edwards aquifer is vulnerable to contamination and that vulnerability is affected by factors such as land cover, aquifer hydrogeology, and changes in hydrologic conditions. Greater vulnerability of groundwater in urban areas relative to rural areas was evident from results for urban groundwater sites, which generally had higher nitrate concentrations, elevated δ 15 N-nitrate values, a greater diversity of pesticides, and higher pesticide concentrations. The continuum of water quality from unconfined rural groundwater sites (least affected by anthropogenic contamination) to unconfined urban groundwater sites (most affected by anthropogenic contamination) demonstrates enhanced vulnerability of urban versus rural land cover. Differences in contaminant occurrences and concentration among unconfined urban wells indicate that the urban parts of the aquifer are not uniformly vulnerable, but rather are affected by spatial differences in the sources of nutrients and pesticides. In urban areas, the shallow, unconfined groundwater sites showed greater temporal variability in both nutrient and pesticide concentrations, as well as a greater degree of contamination, than did deeper, confined groundwater sites. In comparison to that of the shallow, unconfined groundwater sites, the water quality of the deeper, confined groundwater sites was relatively invariant during this multiyear study. Although aquifer hydrogeology is an important factor related to aquifer vulnerability, land cover likely has a greater influence on pesticide contamination of groundwater. Temporal variability in hydrologic conditions for the Edwards aquifer is apparent in data for surface water as a source of groundwater recharge, water-level altitude in wells, spring discharge, and groundwater quality. This temporal variability affects recharge sources, recharge amounts, groundwater traveltimes, flow routing, water-rock interaction processes, dilution, mixing, and, in turn, water quality. Relations of land cover, aquifer hydrogeology, and changing hydrologic conditions to water quality are complex but provide insight into the vulnerability of Edwards aquifer groundwater—a vital drinking-water resource.

Texas↗

USGS2015

Groundwater quality in Geauga County, Ohio: status, including detection frequency of methane in water wells, 2009, and changes during 1978-2009

Domestic wells that are not safeguarded by regular water-quality testing provide drinking water for 79 percent of the residents of Geauga County, in northeastern Ohio. Since 1978, the U.S. Geological Survey (USGS) has worked cooperatively with the Board of Commissioners and Geauga County Planning Commission to monitor the quality of groundwater in four commonly used aquifers in county—the glacial deposits, the Pottsville Formation, the Cuyahoga Group, and the Berea Sandstone. A 33-percent growth in population from 1980 to 2009 increased the potential for humans to influence groundwater resources by withdrawing more groundwater, disposing of more human waste near the land surface, treating an expanded network of township roads with deicing salt, and likely using more solvents, pesticides, and other chemicals on the land surface than were used in preceding decades. To describe the status of groundwater quality in 2009 and its suitability for drinking, USGS personnel collected samples of water prior to treatment from 16 wells (mostly domestic) during June 9–19. The samples were analyzed for 92 properties and constituents, 41 of which had human-health benchmarks to which analytical results could be compared to evaluate suitability for drinking. Four of these benchmarks were exceeded at the following frequencies: arsenic (2 of 16 wells, 12.5 percent), total coliform bacteria (2 of 16 wells, 12.5 percent), fecal coliform bacteria (1 of 14 wells, 7 percent), and sodium (6 of 16 wells, 38 percent). No domestic wells sampled in 2009 exceeded the health-based benchmark of 300 micrograms per liter (µg/L) for manganese, although 5 of 65 wells (8 percent) sampled since 1978 have. Analyses from domestic wells were augmented with water-quality data from seven public-supply well fields that were obtained from the Ohio Environmental Protection Agency. These public-supply data were typically collected between 2000 and 2010 and represent water samples that were collected prior to treatment or that were treated by a method that does not effectively remove the constituents of interest. Similar to the domestic-well data, these data indicated that some samples from public-supply wells have also exceeded health-based benchmarks for arsenic and sodium, along with occasional exceedances of health-based benchmarks for cadmium and lead. Concentrations of nitrate, pesticides, and volatile organic compounds in ground-water samples from domestic and (or) public-supply wells were either considerably less than the human-health benchmarks for these constituents or were not detected. Water-quality data collected in 2009 were also compared to aesthetically based benchmarks developed by the U.S. Environmental Protection Agency, called Secondary Maximum Contaminant Levels (SMCLs). Iron and manganese most frequently exceeded SMCLs (in samples from 10 of 16 domestic wells and in untreated water from 3 of 4 public-supply well fields). To evaluate the frequency of methane detection in water wells in the county, the USGS sampled 16 wells across the county and screened the samples for combustible gas within the headspace (the air above the water in a closed container). Water from three (19 percent) of the wells contained detectable combustible gas (0.10 to 0.40 percent by volume). All three detections were from wells tapping the Cuyahoga Group or the Berea Sandstone, and all detections were less than the lower explosive limit of 5 percent by volume—the concentration at which methane in air can be flammable if an ignition source is present. Analyses of dissolved gas composition in water from these three wells showed methane concentrations ranging from 0.007 to 1.8 milligrams per liter (mg/L). The primary effect of human activities on groundwater quality found during this study is the input of salinity, or chloride, near land surface. On the basis of ratios of chloride to bromide, the main sources of chloride are road salt and septic leachate rather than oil-field brines (either spilled at land surface or sprayed on roads for dust control). The correlation of chloride concentration to distance of well from road for 31 wells in the county sampled by the U.S. Geological Survey in 1999 suggests that road salt is the dominant source of chloride. The majority of constituents exceeding health-based and aesthetically based benchmarks in groundwater were those that are naturally present in aquifer rocks and sediments rather than constituents introduced by human activities. Concentrations of such natural contaminants are controlled by geochemical processes in the subsurface, particularly by oxidation-reduction (redox) reactions. The categorization of redox conditions based on the water quality of 116 samples collected from 65 wells in Geauga County during 1978 through 2009 indicates that most groundwater samples were strongly reducing (60 percent) or oxic (18 percent). Oxic waters were found only in the Pottsville Formation and Berea Sandstone and were generally associated with nitrate at concentrations of 0.38 to 6.0 mg/L. Strongly reducing waters occurred in all four commonly used aquifers and were associated with the following naturally occurring contaminants: (1) arsenic and manganese at concentrations exceeding the health-based benchmarks (10 µg/L and 300 µg/L, respectively) in some samples, (2) iron and manganese at concentrations exceeding the aesthetically based standards (300 µg/L and 50 µg/L, respectively) in most samples, and (3) total sulfides (consisting of hydrogen sulfide gas with its characteristic rotten-egg odor and [or] iron sulfide minerals that appear as finely disseminated particulates in water). Because of the association of redox conditions with specific contaminants, attempts were made to further document spatially where oxic and strongly reducing conditions occur so that contaminant occurrence can be better anticipated by planners and well owners. Within the Pottsville Formation, wells tapping strongly reducing groundwater tended to have a greater thickness of overlying low-permeability (recharge-inhibiting) material such as clay and shale than other wells tapping oxic or nitrate-reducing groundwater. In the Berea Sandstone, oxic conditions were found at well locations where either depth to groundwater was shallow (less than 45 feet [ft] below land surface) or the measured water level was within the open interval (uncased portion) of the well, whereas strongly reducing groundwater was found at well locations where depths to water were greater than 60 ft below land surface and measured water levels were 15 ft or more above the open interval of the well. To evaluate whether constituent concentrations consistently increased or decreased over time, the strength of the association between sampling year (time) and constituent concentration was statistically evaluated for 116 water-quality samples collected by the USGS in 1978, 1980, 1986, 1999, and 2009 from a total of 65 wells across the county (generally domestic wells or wells serving small businesses or churches). Results indicate that many of the constituents that have been analyzed for decades exhibited no consistent temporal trends at a statistically significant level (p-value less than 0.05); fluctuations in concentrations of these constituents represent natural variation in groundwater quality. Dissolved oxygen, calcium, and sulfate concentrations and chloride:bromide ratios increased over time in one or more aquifers, while pH and concentrations of bromide and dissolved organic carbon decreased over time. Detections of total coliform bacteria and nitrate did not become more frequent from 1986 to 2009, even though potential sources of these constituents, such as number of septic systems (linked to population) and percent developed land in the county, increased during this period.

Geauga County↗

USGS1987

Geochemical evolution of waters within the north coast limestone aquifers of Puerto Rico: A conceptualization based on a flow path in the Barceloneta area

Water samples along a groundwater flow path in the Barceloneta area, Puerto Rico, were collected from wells screened in the Montebello Limestone Member of the Cibao Formation (artesian aquifer) and in the overlying Aguada and Aymamon Limestones (water table aquifer). The groundwater chemistry changes as water migrates from recharge areas to downgradient zones in the aquifers. Dissolved magnesium, dissolved sulfate, pH, and carbon-13 isotope generally increase down-gradient. Total inorganic carbon and calcium decrease within the freshwater parts of the aquifer. Mass transfer calculations show that the likely reaction model is carbon dioxide incorporation as water infiltrates through the soil zone, followed by calcite dissolution as water recharges the aquifer. As water moves downgradient within the artesian aquifer, carbon dioxide may degas as a result of calcite precipitation while gypsum and dolomite are dissolved. Within the water table aquifer, continuous recharge of waters rich in carbonic acid maintains the dissolution of the carbonate minerals. Near the coast the mixing of fresh groundwater with saltwater is the primary process affecting water chemistry within the water table aquifer.

Puerto Rico↗

USGS2012

Assessing the vulnerability of public-supply wells to contamination: Rio Grande aquifer system in Albuquerque, New Mexico

This fact sheet highlights findings from the vulnerability study of a public-supply well in Albuquerque, New Mexico (hereafter referred to as “the study well”). The study well produces about 3,000 gallons of water per minute from the Rio Grande aquifer system. Water samples were collected at the study well, at two other nearby public-supply wells, and at monitoring wells installed in or near the simulated zone of contribution to the study well. Untreated water samples from the study well contained arsenic at concentrations exceeding the Maximum Contaminant Level (MCL) of 10 micrograms per liter (µg/L) established by the U.S. Environmental Protection Agency for drinking water. Volatile organic compounds (VOCs) and nitrate also were detected, although at concentrations at least an order of magnitude less than established drinking-water standards, where such standards exist. Overall, study findings point to four primary influences on the movement and (or) fate of contaminants and the vulnerability of the public-supply well in Albuquerque: (1) groundwater age (how long ago water entered, or recharged, the aquifer), (2) groundwater development (introduction of manmade recharge and discharge sources), (3) natural geochemical conditions of the aquifer, and (4) seasonal pumping stresses. Concentrations of the isotope carbon-14 indicate that groundwater from most sampled wells in the local study area is predominantly water that entered, or recharged, the aquifer more than 6,000 years ago. However, the additional presence of the age tracer tritium in several groundwater samples at concentrations above 0.3 tritium units indicates that young (post-1950) recharge is reaching the aquifer across broad areas beneath Albuquerque. This young recharge is mixing with the thousands-of-years-old water, is migrating to depths as great as 245 feet below the water table, and is traveling to some (but not all) of the public-supply wells sampled. Most groundwater samples containing a fraction of young water also contain manmade VOCs, including chloroform (a byproduct of drinking-water chlorination), which indicates that the source of young recharge is, at least in part, infiltration of chlorinated municipal-supply water from leaking waterlines and sewerlines or from turf watering. Other likely manmade, urban recharge sources are seepage from constructed ponds and unlined portions of a stormwater diversion channel. A regional-scale computer-model simulation of groundwater flow and transport to the public-supply well shows that manmade sources of recharge and discharge that were added after about 1930 have greatly altered directions of groundwater flow near Albuquerque and have caused water levels to decline by as much as 120 feet. Local-scale simulations show that seasonal changes in the pumping schedule of the study well affect the age and quality of water produced by the well. Increased pumping during the summer causes significant volumes of water to flow downward from the shallow to the intermediate zones of the aquifer, causing a higher fraction of young water to be produced by the well in the summer than in the winter months and a corresponding increase in VOC detections in the summer relative to the winter. During the winter when the study-well pump is idle for several hours each day, old, high-arsenic water from the deep zone of the aquifer travels up the wellbore and exits into the intermediate zone of the aquifer. When the pump is activated in the winter (for a relatively short time each day), some of the leaked, high-arsenic water is recaptured by the well. This results in a higher arsenic concentration (commonly more than 12 µg/L) in water produced in the winter than in the summer, and a smaller fraction of young water being produced by the well in the winter than in the summer (6 percent in the winter, compared to 11 percent in the summer). Knowledge of the vertical flow direction (both natural and pumping-enhanced) in the vicinity of a long-screened well, coupled with understanding of variations in contaminant concentrations with depth in the aquifer, can help water managers predict the positive or negative effect that wellbore flow will have on water quality and can lead to development of strategies to mitigate contamination (such as changes in pumping schedules or development of devices to inhibit wellbore flow when the pump is off).

New Mexico↗

USGS2017

Baseline assessment of groundwater quality in Pike County, Pennsylvania, 2015

The Devonian-age Marcellus Shale and the Ordovician-age Utica Shale, which have the potential for natural gas development, underlie Pike County and neighboring counties in northeastern Pennsylvania. In 2015, the U.S. Geological Survey, in cooperation with the Pike County Conservation District, conducted a study that expanded on a previous more limited 2012 study to assess baseline shallow groundwater quality in bedrock aquifers in Pike County prior to possible extensive shale-gas development. Seventy-nine water wells ranging in depths from 80 to 610 feet were sampled during June through September 2015 to provide data on the presence of methane and other aspects of existing groundwater quality in the various bedrock geologic units throughout the county, including concentrations of inorganic constituents commonly present at low values in shallow, fresh groundwater but elevated in brines associated with fluids extracted from geologic formations during shale-gas development. All groundwater samples collected in 2015 were analyzed for bacteria, dissolved and total major ions, nutrients, selected dissolved and total inorganic trace constituents (including metals and other elements), radon-222, gross alpha- and gross beta-particle activity, dissolved gases (methane, ethane, and propane), and, if sufficient methane was present, the isotopic composition of methane. Additionally, samples from 20 wells distributed throughout the county were analyzed for selected man-made volatile organic compounds, and samples from 13 wells where waters had detectable gross alpha activity were analyzed for radium-226 on the basis of relatively elevated gross alpha-particle activity. Results of the 2015 study show that groundwater quality generally met most drinking-water standards for constituents and properties included in analyses, but groundwater samples from some wells had one or more constituents or properties, including arsenic, iron, manganese, pH, bacteria, sodium, chloride, sulfate, total dissolved solids, and radon-222, that did not meet (commonly termed failed or exceeded) primary or secondary maximum contaminant levels (MCLs) or Health Advisories (HA) for drinking water. Except for iron, dissolved and total concentrations of major ions and most trace constituents generally were similar. Only 1 of 79 well-water samples had any constituent that exceeded a MCL, with an arsenic concentration of about 30 micrograms per liter (µg/L) that was higher than the MCL of 10 µg/L. However, total arsenic concentrations were higher than the HA of 2 µg/L in samples from another 12 of 79 wells (about 15 percent). Secondary maximum contaminant levels (SMCLs) were exceeded most frequently by pH and concentrations of iron and manganese. The pH was outside of the SMCL range of 6.5–8.5 in samples from 24 of 79 wells (30 percent), ranging from 5.5 to 9.2; more samples had pH values less than 6.5 than had pH values greater than 8.5. Total iron concentrations typically were much greater than dissolved iron concentrations, indicating substantial presence of iron in particulate phase, and exceeded the SMCL of 300 µg/L more often [35 of 79 samples (44 percent)] than dissolved iron concentrations [samples from 8 of 79 wells (10 percent)]. Total manganese concentrations exceeded the SMCL of 50 µg/L in samples from 31 of 79 wells (39 percent) and the HA of 300 µg/L in samples from 13 of 79 wells (about 16 percent). A few (1–2) samples had concentrations of sodium, chloride, sulfate, or TDS higher than the SMCLs of 60, 250, 250, and 500 mg/L, respectively. However, dissolved sodium concentrations were higher than the HA of 20 mg/L in samples from 15 of 79 wells (nearly 20 percent). Total coliform bacteria were detected in samples from 25 of 79 wells (32 percent) but Escherichia coli were not detected in any sample. Radon-222 activities ranged from 11 to 5,100 picocuries per liter (pCi/L), with a median of 1,440 pCi/L, and exceeded the proposed and the alternate proposed drinking-water standards of 300 and 4,000 pCi/L, respectively, in samples from 60 of 79 wells (75 percent) and in samples from 2 of 79 wells (3 percent), respectively. Groundwater samples from all wells were analyzed for dissolved methane by one contract laboratory that determined water from 19 of the 79 wells (24 percent) had concentrations of methane greater than the reporting level of 0.010 milligrams per liter (mg/L) with a maximum methane concentration of 2.5 mg/L. Methane concentrations in 18 replicate samples submitted to a second laboratory for dissolved gas and isotopic analysis generally were higher by as much as a factor of 2.7 from those determined by the first laboratory, indicating potential bias related to combined sampling and analytical methods, and therefore, caution needs to be used when comparing methane results determined by different methods. The isotopic composition of methane in 9 of 10 samples with sufficient dissolved methane (about 0.3 mg/L) for isotopic analysis is consistent with values reported for methane of microbial origin produced through carbon dioxide reduction; an isotopic shift in 1 or 2 samples may indicate subsequent methane oxidation. The low concentrations of ethane relative to methane in these samples further indicate that the methane may be of microbial origin. Groundwater samples with relatively elevated methane concentrations (near or greater than 0.3 mg/L) also had chemical compositions that differed in some respects from groundwater with relatively low methane concentrations (less than 0.3 mg/L) by having higher pH (greater than 8) and higher concentrations of sodium, lithium, boron, fluoride, arsenic, and bromide and chloride/bromide ratios indicative of mixing with a small amount of brine of probable natural occurrence. The spatial distribution of groundwater compositions differs by topographic setting and lithology and generally shows that (1) relatively dilute, slightly acidic, oxygenated, calcium-carbonate type waters tend to occur in the uplands underlain by the undivided Poplar Gap and Packerton members of the Catskill Formation in southwestern Pike County; (2) waters of near neutral pH with the highest amounts of hardness (calcium and magnesium) generally occur in areas of intermediate altitudes underlain by other members of the Catskill Formation; and (3) waters with pH values greater than 8, low oxygen concentrations, and the highest arsenic, sodium, lithium, bromide, and methane concentrations can be present in deep wells in uplands but most frequently occur in stream valleys, especially at low altitudes (less than about 1,200 feet above North American Vertical Datum of 1988) where groundwater may be discharging regionally, such as to the Delaware River in northern and eastern Pike County. Thus, the baseline assessment of groundwater quality in Pike County prior to gas-well development shows that shallow (less than about 1,000 feet deep) groundwater generally meets primary drinking-water standards for inorganic constituents but varies spatially, with methane and some constituents present in high concentrations in brine (and connate waters from gas and oil reservoirs) present at low to moderate concentrations in some parts of Pike County.

Pennsylvania↗

USGS2015

Hexavalent and total chromium at low reporting concentrations in source-water aquifers and surface waters used for public supply in Illinois, 2013

On the basis of their recent review of the human health effects of hexavalent chromium [Cr(VI)] in public drinking water, the U.S. Environmental Protection Agency is considering the need for Federal regulation of Cr(VI). Presently, only total chromium is regulated, at a Maximum Contaminant Level (MCL) of 100 micrograms per liter (µg/L). The occurrence of Cr(VI) in groundwater and surface waters generally is attributed to industrial sources, but can be of natural origin. California’s recently established MCL for Cr(VI) of 10 µg/L illustrates the drinking-water concerns associated with Cr(VI). To improve understanding of the possible impact of a Cr(VI)-specific standard that approximates the California level on the management of Illinois’ public drinking water, the U.S. Geological Survey, in cooperation with the Illinois Environmental Protection Agency, assessed the occurrence and distribution of Cr(VI) in the State’s public-water supplies. During 2013, untreated water samples were collected to be analyzed for Cr(VI) and total chromium [Cr(T)] at 119 water-supply wells and 32 surface-water intakes; also, 32 treated surface-water samples were collected near the point of treatment and 32 near the furthest point of distribution. Public-supply sample sites were selected by a stratified random method. Samples typically were analyzed within 24 hours of collection at reporting limits of 0.02 µg/L for Cr(VI) and 0.1 µg/L for Cr(T). The occurrence of Cr(VI) was compared with selected geophysical, physical, and sampling factors that might more fully explain its distribution and magnitude of concentrations. The maximum concentration of Cr(VI) in groundwater was 2.1 µg/L. Maximum concentrations in untreated and treated surface water were 0.29 µg/L and 2.4 µg/L, respectively. All sample concentrations were below the California MCL; only 35 percent were below that State’s non-enforceable public health goal of 0.02 of µg/L. Cr(VI) was undetected in 43 percent of untreated groundwater samples, with a median of 0.06 µg/L when detected. All but two (94 percent) of untreated surface-water samples had detections. In untreated surface water, the median concentration was 0.09 µg/L, whereas in treated (tap and distributed) water the median was 0.20 µg/L. Surface waters treated with lime for softening typically had the greatest Cr(VI) concentrations (maximum, 2.4 µg/L; median, 1.2 µg/L). The maximum concentration of Cr(T) in groundwater was 1.8 µg/L. Maximum concentrations in untreated and treated surface water were 1.8 µg/L and 2.5 µg/L, respectively. All sample concentrations were below the Federal MCL. Total chromium was detected in 65 percent of untreated groundwater samples, with a median of 0.40 µg/L, when detected. All but one (97 percent) of untreated surface-water samples had detections. In untreated surface water, the median concentration was 0.40 µg/L, whereas in treated (tap and distributed) water the median was 0.30 µg/L. As with Cr(VI), surface waters treated with lime typically had the greatest Cr(T) concentrations. Examination of factors that might account for or be associated with the occurrence of Cr(VI) in public-supply source waters found few clearly evident factors. Associations in frequencies of occurrence and range of concentrations indicate that surface waters and groundwaters of shallow, unconsolidated, unconfined aquifers, particularly alluvial aquifers, are possibly most commonly affected by anthropogenic sources of Cr(VI). Groundwaters of deep (greater than 500 feet) bedrock aquifers, particularly the Cambrian-Ordovician aquifer system, are possibly most commonly affected by geologic sources of Cr(VI). Additional study, with supporting geologic and geochemical data that were not collected in this study, would be necessary to verify these associations. There was a weak positive relation (ρ = 0.23) between concentrations of Cr(VI) and Cr(T) in untreated water samples, with a much stronger positive relation (ρ = 0.86 and ρ = 0.90, respectively) in samples collected soon after treatment and near the endpoint of distribution. The stronger relation and greater similarity between Cr(VI) and Cr(T) concentrations in treated water samples indicate that Cr(VI) represents a greater proportion of the measured concentrations of Cr(T) in treated waters than in untreated waters. The analysis of spikes and other quality-assurance samples indicate uncertainties associated with obtaining or confirming consistently accurate analytical results for Cr(VI) at near the applied reporting limit of 0.02 µg/L.

Illinois↗

USGS2016

Volcanic aquifers of Hawai‘i—Hydrogeology, water budgets, and conceptual models

Hawai‘i’s aquifers have limited capacity to store fresh groundwater because each island is small and surrounded by saltwater. Saltwater also underlies much of the fresh groundwater. Fresh groundwater resources are, therefore, particularly vulnerable to human activity, short-term climate cycles, and long-term climate change. Availability of fresh groundwater for human use is constrained by the degree to which the impacts of withdrawal—such as lowering of the water table, saltwater intrusion, and reduction in the natural discharge to springs, streams, wetlands, and submarine seeps—are deemed acceptable. This report describes the hydrogeologic framework, groundwater budgets (inflows and outflows), conceptual models of groundwater occurrence and movement, and the factors limiting groundwater availability for the largest and most populated of the Hawaiian Islands—Kaua‘i, O‘ahu, Maui, and Hawai‘i Island. The bulk of each of Hawai‘i’s islands is built of many thin lava flows erupted from shield volcanoes; the great piles of lava flows form highly permeable aquifers. In some areas, low-permeability dikes cutting across the lava flows, or low-permeability ash and soil horizons interlayered with the lava flows, can substantially alter groundwater flow. On some islands, sedimentary rocks form thick semiconfining coastal-plain deposits, locally known as caprock, that impede natural groundwater discharge to the ocean. In some regions, thick lava flows that ponded in preexisting depressions form aquifers that are much less permeable than aquifers formed by thin lava flows. Fresh groundwater inflow to Hawai‘i’s aquifers comes from recharge. For predevelopment conditions (1870), estimates of groundwater recharge from this study are 871, 675, 1,279, and 5,291 million gallons per day (Mgal/d) for Kaua‘i, O‘ahu, Maui, and Hawai‘i Island, respectively. Estimates of recharge for recent conditions (2010 land cover and 1978–2007 rainfall for Kaua‘i, O‘ahu, and Maui; 2008 land cover and 1916–1983 rainfall for Hawai‘i Island) are 875, 660, 1,308, and 6,595 Mgal/d for Kaua‘i, O‘ahu, Maui, and Hawai‘i Island, respectively. Recent recharge values differ from predevelopment recharge values by only a few percent for all islands except Hawai‘i Island, where changes in forest cover affected recharge. Spatial distribution of recharge mimics the orographic rainfall pattern—recharge is high on windward slopes and mountain peaks below the top of the trade-wind inversion. Human activity such as irrigation also contributes to recharge in some areas. Outflows from Hawai‘i’s aquifers include withdrawals from wells and natural groundwater discharge to springs, streams, wetlands, and submarine seeps. Under predevelopment conditions, groundwater withdrawal is assumed to be negligible and natural groundwater discharge probably was equal, or close, to recharge. Under recent conditions (2000–2010), groundwater withdrawal averaged 19, 209, 104, and 103 Mgal/d on Kaua‘i, O‘ahu, Maui, and Hawai‘i Island, respectively. If recent withdrawal and recharge rates are maintained until steady state is achieved, natural groundwater discharge will be reduced by an amount equal to the withdrawal rate. Total recent withdrawal for the four islands is only about 5 percent of total recharge, but about half of the withdrawal comes from O‘ahu, whereas O‘ahu receives only 7 percent of the total recharge. Effects of high withdrawals on O‘ahu cannot be mitigated by the lower withdrawals on other islands because no freshwater flows between islands. Even within an island, high withdrawals from one area cannot be completely mitigated by recharge in another area. Water-level, saltwater/freshwater-transition-zone, spring, and stream base-flow data indicate an overall reduction in storage for most areas where groundwater has been developed. Groundwater occurrence and movement in Hawai‘i’s volcanic aquifers can be described in terms of four conceptual models: (1) fresh groundwater lenses in high-permeability lava-flow aquifers, (2) aquifers with groundwater impounded by dikes, (3) thickly saturated low-permeability aquifers, and (4) perched aquifers. In Hawai‘i, most fresh groundwater withdrawn for human use comes from freshwater lenses in the dike-free high-permeability lava-flow aquifers where the principal limiting factor to groundwater availability is saltwater intrusion, but impacts of reduced natural groundwater discharge may also limit availability. Dike-impounded groundwater is common near the center of Hawaiian shield volcanoes, where water moves and is stored in permeable lava flows between the dikes; groundwater availability in these aquifers is primarily limited by storage depletion and reduction of flow to adjacent aquifers and natural groundwater discharge. Thickly saturated low-permeability aquifers have been identified on Kaua‘i and Maui; groundwater availability is primarily limited by streamflow depletion and water-table decline. Perched groundwater is postulated to exist in some areas of Hawai‘i, but store much less water than other modes ofgroundwater occurrence. Limits on groundwater availability in perched aquifers include the potential of reducing inflow to other groundwater settings and reducing natural discharge and stream seepage. Some groundwater bodies in Hawai‘i are enigmatic; consequences of groundwater development in these bodies and their relation to groundwater availability are not completely understood.

Hawai'i↗

USGS2012

Groundwater quality and occurrence and distribution of selected constituents in the Aquia and Upper Patapsco aquifers, Naval Air Station Patuxent River, St. Mary's County, Maryland, July 2008

The Naval Air Station Patuxent River in southern Maryland has continued to expand in the first decade of the 21st century, contributing to rapid population growth in the surrounding area. The increase in population has caused State and County water managers and others to be concerned about the impact of population growth on the quantity and quality of groundwater supplies. The U.S. Geological Survey has been investigating the groundwater resources of the air station since 1998. As part of that ongoing investigation, groundwater was sampled in 2008 in six wells in the Aquia aquifer and two wells in the Upper Patapsco aquifer in the vicinity of Naval Air Station Patuxent River and Webster Outlying Field. Groundwater samples were analyzed for basic chemistry (field parameters, major ions, and nutrients) as well as several water-quality issues of concern including the occurrence of arsenic and tungsten, and saltwater intrusion. The results of the 2008 groundwater-quality sampling indicate that the overall quality of groundwater in the Aquia aquifer has not changed since 1943; data are too limited to determine if groundwater quality has changed in the Upper Patapsco aquifer. At one well in the Aquia aquifer, the arsenic concentration exceeded the U.S. Environmental Protection Agency standard for drinking water. Arsenic was not detected in samples from the Upper Patapsco aquifer. Tungsten concentrations were detected at low concentrations near the laboratory reporting level in all eight samples. There was no evidence of saltwater intrusion in any of the wells.

Maryl↗

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↗

USGS2013

Geodatabase and characteristics of springs within and surrounding the Trinity aquifer outcrops in northern Bexar County, Texas, 2010--11

The U.S. Geological Survey, in cooperation with the Trinity Glen Rose Groundwater Conservation District, the Edwards Aquifer Authority, and the San Antonio River Authority, developed a geodatabase of springs within and surrounding the Trinity aquifer outcrops in a 331-square-mile study area in northern Bexar County, Texas. The data used to develop the geodatabase were compiled from existing reports and databases, along with spring data collected between October 2010 and September 2011. Characteristics including the location, discharge, and water-quality properties were collected for known springs and documented in the geodatabase. A total of 141 springs were located within the study area, and 46 springs were field verified. The discharge at springs with flow ranged from 0.003 to 1.46 cubic feet per second. The specific conductance of the water discharging from the springs ranged from 167 to 1,130 microsiemens per centimeter at 25 degrees Celsius with a majority of values in the range of 500 microsiemens per centimeter at 25 degrees Celsius.

Texas↗

USGS2012

Tabulated Transmissivity and Storage Properties of the Floridan Aquifer System in Florida and Parts of Georgia, South Carolina, and Alabama

A goal of the U.S. Geological Survey Groundwater Resources Program is to assess the availability of fresh water within each of the principal aquifers in the United States with the greatest groundwater withdrawals. The Floridan aquifer system (FAS), which covers an area of approximately 100,000 square miles in Florida and parts of Georgia, Alabama, Mississippi, and South Carolina, is one such principal aquifer, having the fifth largest groundwater withdrawals in the Nation, totaling 3.64 billion gallons per day in 2000. Compilation of FAS hydraulic properties is critical to the development and calibration of groundwater flow models that can be used to develop water budgets spatially and temporally, as well as to evaluate resource changes over time. Wells with aquifer test data were identified as Upper Floridan aquifer (UFA), Lower Floridan aquifer (LFA), Floridan aquifer system (FAS, Upper Floridan with some middle and/or Lower Floridan), or middle Floridan confining unit (MCU), based on the identification from the original database or report description, or comparison of the open interval of the well with previously published maps. This report consolidates aquifer hydraulic property data obtained from multiple databases and reports of the U.S. Geological Survey, various State agencies, and the Water Management Districts of Florida, that are compiled into tables to provide a single information source for transmissivity and storage properties of the FAS as of October 2011. Transmissivity calculated from aquifer pumping tests and specific-capacity data are included. Values for transmissivity and storage coefficients are intended for use in regional or sub regional groundwater flow models; thus, any tests (aquifer pumping tests and specific capacity data) that were conducted with packers or for open intervals less than 30 feet in length are excluded from the summary statistics and tables of this report, but are included in the database. The transmissivity distribution from the aquifer pumping tests is highly variable. The transmissivity based on aquifer pumping tests (from 1,045 values for the UFA and FAS) ranges from 8 to about 9,300,000 square feet per day (ft 2 /d) and values of storage coefficient (646 reported) range from 3x10 -9 to 0.41. The 64 transmissivity values for the LFA range from about 130 to 4,500,000 ft 2 /d, and the 17 storage coefficient values range from 7x10 -8 to 0.03. The 14 transmissivity values for the MCU range from 1 to about 600,000 ft 2 /d and the 10 storage coefficient values range from 8x10 -8 to 0.03. Transmissivity estimates for the UFA and FAS for 442 specific capacity tests range from approximately 200 to 1,000,000 ft 2 /d.

Alabama, Florida, Georgia, South Carolina↗