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USGS2009

Groundwater-Quality Assessment, Pike County, Pennsylvania, 2007

Pike County, a 545 square-mile area in northeastern Pennsylvania, has experienced the largest relative population growth of any county in the state from 1990 to 2000 and its population is projected to grow substantially through 2025. This growing population may result in added dependence and stresses on water resources, including the potential to reduce the quantity and degrade the quality of groundwater and associated stream base flow with changing land use. Groundwater is the main source of drinking water in the county and is derived primarily from fractured-rock aquifers (shales, siltstones, and sandstones) and some unconsolidated glacial deposits that are recharged locally from precipitation. The principal land uses in the county as of 2005 were public, residential, agricultural, hunt club/private recreational, roads, and commercial. The public lands cover a third of the county and include national park, state park, and other state lands, much of which are forested. Individual on-site wells and wastewater disposal are common in many residential areas. In 2007, the U.S. Geological Survey, in cooperation with the Pike County Conservation District, began a study to provide current information on groundwater quality throughout the county that will be helpful for water-resource planning. The countywide reconnaissance assessment of groundwater quality documents current conditions with existing land uses and may serve as a baseline of groundwater quality for future comparison. Twenty wells were sampled in 2007 throughout Pike County to represent groundwater quality in the principal land uses (commercial, high-density and moderate-density residential with on-site wastewater disposal, residential in a sewered area, pre-development, and undeveloped) and geologic units (five fractured-rock aquifers and one glacial unconsolidated aquifer). Analyses selected for the groundwater samples were intended to identify naturally occurring constituents from the aquifer or constituents introduced by human activities that pose a health risk or otherwise were of concern in groundwater in the county. The analyses included major ions, nutrients, selected trace metals, volatile organic compounds (VOCs), selected organic wastewater compounds, gross alpha-particle and gross beta-particle activity, uranium, and radon-222. Analyses of the 20 samples were primarily for dissolved constituents, but six samples were analyzed for both dissolved and total metals. Results of the 2007 sampling indicated few water-quality problems, although concentrations of some constituents indicated influence of human activities on groundwater. No constituent analyzed exceeded any primary drinking-water standard or maximum contaminant level (MCL) established by the U.S. Environmental Protection Agency. Radon-222 levels were greater than, or equal to, the proposed MCL of 300 picocuries per liter (pCi/L) in water from 15 (75 percent) of the 20 wells. Radon-222 levels did not exceed the alternative MCL of 4,000 pCi/L in any groundwater sample. Radon-222 is naturally occurring, and the greatest concentrations (up to 2,650 pCi/L) were in water samples from wells in members of the Catskill Formation, a fractured-rock aquifer. The dissolved arsenic concentration of 3.9 micrograms per liter (ug/L) in one sample was greater than the health-advisory (HA) level of 2 ug/L but less than the MCL of 10 ug/L. Recommended or secondary maximum contaminant levels (SMCLs) were exceeded for pH, dissolved iron, and dissolved manganese. In six samples analyzed for dissolved and total concentrations of selected metals, total concentrations commonly were much greater than dissolved concentrations of iron, and to a lesser degree, for arsenic, lead, copper, and manganese. Concentrations of iron above the SMCL of 300 ug/L may be more widespread in the county for particulate iron than for dissolved iron. The total arsenic concentration in one of the six samples was greater than the HA level of

Scientific Investigations Report↗

USGS2009

Characterization of Groundwater Quality Based on Regional Geologic Setting in the Piedmont and Blue Ridge Physiographic Provinces, North Carolina

A compilation of groundwater-quality data collected as part of two U.S. Geological Survey studies provides a basis for understanding the ambient geochemistry related to geologic setting in the Piedmont and Blue Ridge Physiographic Provinces (hereafter referred to as Piedmont and Mountains Provinces) of North Carolina. Although the geology is complex, a grouping of the sampled wells into assemblages of geologic units described as 'geozones' provides a basis for comparison across the region. Analyses of these two data sets provide a description of water-quality conditions in bedrock aquifers of the Piedmont and Mountains Provinces of North Carolina. Analyzed data were collected between 1997 and 2008 from a network of 79 wells representing 8 regional geozones distributed throughout the Piedmont and Mountains Provinces. This area has experienced high rates of population growth and an increased demand for water resources. Groundwater was used by about 34 percent of the population in the 65 counties of this region in 2005. An improved understanding of the quality and quantity of available groundwater resources is needed to plan effectively for future growth and development. The use of regional geologic setting to characterize groundwater-quality conditions in the Piedmont and Mountains Provinces is the focus of this investigation. Data evaluation included an examination of selected properties and the ionic composition of groundwater in the geozones. No major differences in overall ionic chemistry of groundwater among the geozones were evident with the data examined. Variability in the cationic and anionic composition of groundwater within a particular geozone appeared to reflect local differences in lithologic setting, hydrologic and geochemical conditions, and(or) land-use effects. The most common exceedances of the drinking-water criteria (in accordance with Federal and State water-quality standards) occurred for radon, pH, manganese, iron, and zinc. Radon had the most exceedances, with groundwater from 61 of the 69 sampled wells having activities higher than the U.S. Environmental Protection Agency's proposed maximum contaminant level of 300 picocuries per liter. Overall, the Milton and the Raleigh and Charlotte geozones had the greatest number, eight each, of water-quality properties or constituents that exceeded applicable drinking-water criteria in at least one well. The Eastern Blue Ridge and Felsic intrusive geozones each had seven properties or constituents that exceeded criteria, and the Carolina slate geozone had six. Based on limited data, initial results of statistical comparison tests identified statistically significant differences in concentrations of some groundwater constituents among the geozones. Statistically significant differences in median values of specific conductance and median concentrations of calcium, potassium, sodium, bicarbonate, chloride, silica, ammonia, aluminum, antimony, cadmium, and uranium were identified between one or more geozone pairs. Overall, the groundwater constituents appear to be influenced most significantly by the Inner Piedmont, Carolina slate, and Felsic intrusive geozones. The study data indicate that grouping and evaluating analytical data on the basis of regional geozone setting can be useful for characterizing water-quality conditions in bedrock aquifers of the Piedmont and Blue Ridge Provinces of North Carolina.

North Carolina↗

USGS2010

Hydrologic conditions, stream-water quality, and selected groundwater studies conducted in the Lawrenceville area, Georgia, 2003-2008

Hydrologic studies conducted during 2003-2008 as part of the U.S. Geological Survey Cooperative Water Program with the City of Lawrenceville, Georgia, provide important data for the management of water resources. The Cooperative Water Program includes (1) hydrologic monitoring (precipitation, streamflow, and groundwater levels) to quantify baseline conditions in anticipation of expanded groundwater development, (2) surface-water-quality monitoring to provide an understanding of how stream quality is affected by natural (such as precipitation) and anthropogenic factors (such as impervious area), and (3) geologic studies to better understand groundwater flow and hydrologic processes in a crystalline rock setting. The hydrologic monitoring network includes each of the two watersheds projected for groundwater development?the Redland-Pew Creek and upper Alcovy River watersheds?and the upper Apalachee River watershed, which serves as a background or control watershed because of its similar hydrologic and geologic characteristics to the other two watersheds. In each watershed, precipitation was generally greater during 2003-2005 than during 2006-2008, and correspondingly streamflow and groundwater levels decreased. In the upper Alcovy River and Redland-Pew Creek watersheds, groundwater level declines during 2003-2008 were mostly between 2 and 7 feet, with maximum observed declines of as much as 28.5 feet in the upper Alcovy River watershed, and 49.1 feet in the Redland-Pew Creek watershed. Synoptic base-flow measurements were used to locate and quantify gains or losses to streamflow resulting from groundwater interaction (groundwater seepage). In September 2006, seepage gains were measured at five of nine reaches evaluated in the upper Alcovy River watershed, with losses in the other four. The four losing reaches were near the confluence of the Alcovy River and Cedar Creek where the stream gradient is low and bedrock is at or near the land surface. In the Redland-Pew Creek watershed, groundwater seepage gains were observed at each of the 10 reaches measured during September 2008. Continuous specific conductance, temperature, and turbidity data were collected at gage sites located on Pew and Shoal Creeks, which drain about 32 percent of the city area, and at a background site on the Apalachee River located outside the city boundary. Continuous surface-water monitoring data indicate that reduced precipitation during 2006-2008 resulted in lower turbidity and higher stream temperature and specific conductance than in 2003-2005. In comparison to the other two stream sites, water at the Apalachee River site had the lowest mean and median values for specific conductance, and the greatest mean and median values for turbidity during October 2005-December 2008. In addition to continuous water-quality monitoring, samples were collected periodically to determine fecal-coliform bacteria concentrations. None of the individual samples at the three sites exceeded the Georgia Environmental Protection Division (GaEPD) limit of 4,000 most probable number of colonies per 100 milliliters (MPN col/100 mL) for November through April. In the Redland-Pew Creek and Shoal Creek watersheds, the GaEPD 30-day geometric mean standard of 200 MPN col/100 mL for May-October was exceeded twice during two sampling periods in May-October 2007 and twice during two sampling periods in May-October 2008. Groundwater studies conducted during 2003-2007 include the collection of borehole geophysical logs from four test wells drilled in the upper Alcovy River watershed to provide insight into subsurface geologic characteristics. A flowmeter survey was conducted in a well south of Rhodes Jordan Park to help assess the interconnection of the well with surface water and the effectiveness of a liner-packer assembly installed to eliminate that interconnection. At that same well, hydraulic packer tests were conducted in the open-hole section of the well, and water samp

Georgia↗

USGS2010

Hydrogeology and groundwater quality of Highlands County, Florida

Groundwater is the main source of water supply in Highlands County, Florida. As the demand for water in the county increases, additional information about local groundwater resources is needed to manage and develop the water supply effectively. To address the need for additional data, a study was conducted to evaluate the hydrogeology and groundwater quality of Highlands County. Total groundwater use in Highlands County has increased steadily since 1965. Total groundwater withdrawals increased from about 37 million gallons per day in 1965 to about 107 million gallons per day in 2005. Much of this increase in water use is related to agricultural activities, especially citrus cultivation, which increased more than 300 percent from 1965 to 2005. Highlands County is underlain by three principal hydrogeologic units. The uppermost water-bearing unit is the surficial aquifer, which is underlain by the intermediate aquifer system/intermediate confining unit. The lowermost hydrogeologic unit is the Floridan aquifer system, which consists of the Upper Floridan aquifer, as many as three middle confining units, and the Lower Floridan aquifer. The surficial aquifer consists primarily of fine-to-medium grained quartz sand with varying amounts of clay and silt. The aquifer system is unconfined and underlies the entire county. The thickness of the surficial aquifer is highly variable, ranging from less than 50 to more than 300 feet. Groundwater in the surficial aquifer is recharged primarily by precipitation, but also by septic tanks, irrigation from wells, seepage from lakes and streams, and the lateral groundwater inflow from adjacent areas. The intermediate aquifer system/intermediate confining unit acts as a confining layer (except where breached by sinkholes) that restricts the vertical movement of water between the surficial aquifer and the underlying Upper Floridan aquifer. The sediments have varying degrees of permeability and consist of permeable limestone, dolostone, or sand, or relatively impermeable layers of clay, clayey sand, or clayey carbonates. The thickness of the intermediate aquifer system/ intermediate confining unit ranges from about 200 feet in northwestern Highlands County to more than 600 feet in the southwestern part. Although the intermediate aquifer system is present in the county, it is unclear where the aquifer system grades into a confining unit in the eastern part of the county. Up to two water-bearing units are present in the intermediate aquifer system within the county. The lateral continuity and water-bearing potential of the various aquifers within the intermediate aquifer system are highly variable. The Floridan aquifer system is composed of a thick sequence of limestone and dolostone of Upper Paleocene to Oligocene age. The top of the aquifer system ranges from less than 200 feet below NGVD 29 in extreme northwestern Highlands County to more than 600 feet below NGVD 29 in the southwestern part. The principal source of groundwater supply in the county is the Upper Floridan aquifer. As of 2005, about 89 percent of the groundwater withdrawn from the county was obtained from this aquifer, mostly for agricultural irrigation and public supply. Over most of Highlands County, the Upper Floridan aquifer generally contains freshwater, and the Lower Floridan aquifer contains more mineralized water. The potentiometric surface of the Upper Floridan aquifer is constantly fluctuating, mainly in response to seasonal variations in rainfall and groundwater withdrawals. The potentiometric surface of the Upper Floridan aquifer in May 2007, which represents the hydrologic conditions near the end of the dry season when water levels generally are near their lowest, ranged from about 79 feet above NGVD 29 in northwestern Highlands County to about 40 feet above NGVD 29 in the southeastern part of the county. The potentiometric surface of the Upper Floridan aquifer in September 2007 was about 3 to 10 feet high

Scientific Investigations Report↗

USGS2012

Preliminary assessment of water chemistry related to groundwater flooding in Wawarsing, New York, 2009-11

Water-quality samples collected in an area prone to groundwater flooding in Wawarsing, New York, were analyzed and assessed to better understand the hydrologic system and to aid in the assessment of contributing water sources. Above average rainfall over the past decade, and the presence of a pressurized water tunnel that passes about 700 feet beneath Wawarsing, could both contribute to groundwater flooding. Water samples were collected from surface-water bodies, springs, and wells and analyzed for major and trace inorganic constituents, dissolved gases, age tracers, and stable isotopes. Distinct differences in chemistry exist between tunnel water and groundwater in unconsolidated deposits and in bedrock, and among groundwater samples collected from some bedrock wells during high head pressure and low head pressure of the Rondout-West Branch Tunnel. Samples from bedrock wells generally had relatively higher concentrations of sulfate (SO 4 2- ), strontium (Sr), barium (Ba), and lower concentrations of calcium (Ca) and bicarbonate (HCO 3 - ), as compared to unconsolidated wells. Differences in stable-isotope ratios among oxygen-18 to oxygen-16 (δ 18 O), hydrogen-2 to hydrogen-1 (δ 2 H), sulfur-34 to sulfur-32(δ 34 S) of SO 4 2- , Sr-87 to Sr-86 ( 87 Sr/ 86 Sr), and C-13 to C-12 (δ 13 C) of dissolved inorganic carbon (DIC) indicate a potential for distinguishing water in the Delaware-West Branch Tunnel from native groundwater. For example, 87 Sr/ 86 Sr ratios were more depleted in groundwater samples from most bedrock wells, as compared to samples from surface-water sources, springs, and wells screened in unconsolidated deposits in the study area. Age-tracer data provided useful information on pathways of the groundwater-flow system, but were limited by inherent problems with dissolved gases in bedrock wells. The sulfur hexafluoride (SF 6 ) and (or) chlorofluorocarbons (CFCs) apparent recharge years of most water samples from wells screened in unconsolidated deposits and springs ranged from 2003 to 2010 (current) and indicate short flow paths from the point of groundwater recharge. All but three of the samples from bedrock wells had interference problems with dissolved gases, mainly caused by excess air from degassing of hydrogen sulfide and methane. The SF 6 and (or) CFC apparent recharge years of samples from three of the bedrock wells ranged from the 1940s to the early 2000s; the sample with the early 2000s recharge year was from a flowing artesian well that was chemically similar to water samples collected at the influent to the tunnel at Rondout Reservoir and the most hydraulically responsive to water tunnel pressure compared to other bedrock wells. Data described in this report can be used, together with hydrogeologic data, to improve the understanding of source waters and groundwater-flow patterns and pathways, and to help assess the mixing of different source waters in water samples. Differences in stable isotope ratios, major and trace constituent concentrations, saturation indexes, tritium concentrations, and apparent groundwater ages will be used to estimate the proportion of water that originates from Rondout-West Branch Tunnel leakage.

New York↗

USGS2012

Numerical model simulations of nitrate concentrations in groundwater using various nitrogen input scenarios, mid-Snake region, south-central Idaho

As part of the U.S. Geological Survey’s National Water Quality Assessment (NAWQA) program nitrate transport in groundwater was modeled in the mid-Snake River region in south-central Idaho to project future concentrations of nitrate. Model simulation results indicated that nitrate concentrations would continue to increase over time, eventually exceeding the U.S. Environmental Protection Agency maximum contaminant level for drinking water of 10 milligrams per liter in some areas. A subregional groundwater model simulated the change of nitrate concentrations in groundwater over time in response to three nitrogen input scenarios: (1) nitrogen input fixed at 2008 levels; (2) nitrogen input increased from 2008 to 2028 using the same rate of increase as the average rate of increase during the previous 10 years (1998 through 2008); after 2028, nitrogen input is fixed at 2028 levels; and (3) nitrogen input related to agriculture completely halted, with only nitrogen input from precipitation remaining. Scenarios 1 and 2 project that nitrate concentrations in groundwater continue to increase from 10 to 50 years beyond the year nitrogen input is fixed, depending on the location in the model area. Projected nitrate concentrations in groundwater increase by as much as 2–4 milligrams per liter in many areas, with nitrate concentrations in some areas reaching 10 milligrams per liter. Scenario 3, although unrealistic, estimates how long (20–50 years) it would take nitrate in groundwater to return to background concentrations—the “flushing time” of the system. The amount of nitrate concentration increase cannot be explained solely by differences in nitrogen input; in fact, some areas with the highest amount of nitrogen input have the lowest increase in nitrate concentration. The geometry of the aquifer and the pattern of regional groundwater flow through the aquifer greatly influence nitrate concentrations. The aquifer thins toward discharge areas along the Snake River which forces upward convergence of good-quality regional groundwater that mixes with the nitrate-laden groundwater in the uppermost parts of the aquifer, which results in lowered nitrate concentrations. A new method of inputting nitrogen to the subregional groundwater model was used that prorates nitrogen input by the probability of detecting nitrate concentrations greater than 2 mg/L. The probability map is based on correlations with physical factors, and prorates an existing nitrogen input dataset providing an estimate of nitrogen flux to the water table that accounts for new factors such as soil properties. The effectiveness of this updated nitrogen input method was evaluated using the software UCODE_2005.

Idaho↗

USGS2013

Simulations of groundwater flow, transport, and age in Albuquerque, New Mexico, for a study of transport of anthropogenic and natural contaminants (TANC) to public-supply wells

Vulnerability to contamination from manmade and natural sources can be characterized by the groundwater-age distribution measured in a supply well and the associated implications for the source depths of the withdrawn water. Coupled groundwater flow and transport models were developed to simulate the transport of the geochemical age-tracers carbon-14, tritium, and three chlorofluorocarbon species to public-supply wells in Albuquerque, New Mexico. A separate, regional-scale simulation of transport of carbon-14 that used the flow-field computed by a previously documented regional groundwater flow model was calibrated and used to specify the initial concentrations of carbon-14 in the local-scale transport model. Observations of the concentrations of each of the five chemical species, in addition to water-level observations and measurements of intra-borehole flow within a public-supply well, were used to calibrate parameters of the local-scale groundwater flow and transport models. The calibrated groundwater flow model simulates the mixing of “young” groundwater, which entered the groundwater flow system after 1950 as recharge at the water table, with older resident groundwater that is more likely associated with natural contaminants. Complexity of the aquifer system in the zone of transport between the water table and public-supply well screens was simulated with a geostatistically generated stratigraphic realization based upon observed lithologic transitions at borehole control locations. Because effective porosity was simulated as spatially uniform, the simulated age tracers are more efficiently transported through the portions of the simulated aquifer with relatively higher simulated hydraulic conductivity. Non-pumping groundwater wells with long screens that connect aquifer intervals having different hydraulic heads can provide alternate pathways for contaminant transport that are faster than the advective transport through the aquifer material. Simulation of flow and transport through these wells requires time discretization that adequately represents periods of pumping and non-pumping. The effects of intra-borehole flow are not fully represented in the simulation because it employs seasonal stress periods, which are longer than periods of pumping and non-pumping. Further simulations utilizing daily pumpage data and model stress periods may help quantify the relative effects of intra-borehole versus advective aquifer flow on the transport of contaminants near the public-supply wells. The fraction of young water withdrawn from the studied supply well varies with simulated pumping rates due to changes in the relative contributions to flow from different aquifer intervals. The advective transport of dissolved solutes from a known contaminant source to the public-supply wells was simulated by using particle-tracking. Because of the transient groundwater flow field, scenarios with alternative contaminant release times result in different simulated-particle fates, most of which are withdrawn from the aquifer at wells that are between the source and the studied supply well. The relatively small effective porosity required to simulate advective transport from the simulated contaminant source to the studied supply well is representative of a preferential pathway and not the predominant aquifer effective porosity that was estimated by the calibration of the model to observed chemical-tracer concentrations.

New Mexico↗

USGS2014

Evaluation of groundwater and surface-water interactions in the Caddo Nation Tribal Jurisdictional Area, Caddo County, Oklahoma, 2010-13

Streamflows, springs, and wetlands are important natural and cultural resources to the Caddo Nation. Consequently, the Caddo Nation is concerned about the vulnerability of the Rush Springs aquifer to overdrafting and whether the aquifer will continue to be a viable source of water to tribal members and other local residents in the future. Interest in the long-term viability of local water resources has resulted in ongoing development of a comprehensive water plan by the Caddo Nation. As part of a multiyear project with the Caddo Nation to provide information and tools to better manage and protect water resources, the U.S. Geological Survey studied the hydraulic connection between the Rush Springs aquifer and springs and streams overlying the aquifer. The Caddo Nation Tribal Jurisdictional Area is located in southwestern Oklahoma, primarily in Caddo County. Underlying the Caddo Nation Tribal Jurisdictional Area is the Permian-age Rush Springs aquifer. Water from the Rush Springs aquifer is used for irrigation, public, livestock and aquaculture, and other supply purposes. Groundwater from the Rush Springs aquifer also is withdrawn by domestic (self-supplied) wells, although domestic use was not included in the water-use summary in this report. Perennial streamflow in many streams and creeks overlying the Rush Springs aquifer, such as Cobb Creek, Lake Creek, and Willow Creek, originates from springs and seeps discharging from the aquifer. This report provides information on the evaluation of groundwater and surface-water resources in the Caddo Nation Jurisdictional Area, and in particular, information that describes the hydraulic connection between the Rush Springs aquifer and springs and streams overlying the aquifer. This report also includes data and analyses of base flow, evidence for groundwater and surface-water interactions, locations of springs and wetland areas, groundwater flows interpreted from potentiometric-surface maps, and hydrographs of water levels monitored in the Caddo Nation Tribal Jurisdictional Area from 2010 to 2013. Flow in streams overlying the Rush Springs aquifer, on average, were composed of 50 percent base flow in most years. Monthly mean base flow appeared to maintain streamflows throughout each year, but periods of zero flow were documented in daily hydrographs at each measured site, typically in the summer months. A pneumatic slug-test technique was used at 15 sites to determine the horizontal hydraulic conductivity of streambed sediments in streams overlying the Rush Springs aquifer. Converting horizontal hydraulic conductivities (Kh) from the slug-test analyses to vertical hydraulic conductivities (Kv) by using a ratio of Kv/Kh = 0.1 resulted in estimates of vertical streambed hydraulic conductivity ranging from 0.1 to 8.6 feet per day. Data obtained from a hydraulic potentiomanometer in streambed sediments and streams in August 2012 indicate that water flow was from the streambed sediments to the stream (gaining) at 6 of 15 sites, and that water flow was from the stream to the streambed sediments (losing) at 9 of 15 sites. The groundwater and surface-water interaction data collected at the Cobb Creek near Eakly, Okla., streamflow gaging station (07325800), indicate that the bedrock groundwater, alluvial groundwater, and surface-water resources are closely connected. Because of this hydrologic connection, large perennial streams in the study area may change from gaining to losing streams in the summer. The timing and severity of this change from a gaining to a losing condition probably is affected by the local or regional withdrawal of groundwater for irrigation in the summer growing season. Wells placed closer to streams have a greater and more immediate effect on alluvial groundwater levels and stream stages than wells placed farther from streams. Large-capacity irrigation wells, even those completed hundreds of feet below land surface in the bedrock aquifer, can induce surface-water flow from nearby streams by lowering alluvial groundwater levels below the stream altitude. Twenty-five new springs visible from public roads and paths were documented during a survey of springs in 2011. Most of the springs are in upland draws on the flanks of topographic ridges. Wetlands primarily were identified by using a combination of data sources including the National Wetlands Inventory, Soil Survey Geographic database frequently flooded soils maps, and aerial photographs. Regional flow directions were determined by analysis of water levels measured in 29 wells completed in the Rush 2 Springs aquifer in Caddo County and the Caddo Nation Tribal Jurisdictional Area. Water levels were monitored every 30 minutes in five wells by using a vented pressure transducer and a data-collection platform with real-time transmitting equipment in each well. Those five wells ranged in depth from 210 to 350 feet. Water levels in these five wells indicate that there was a decrease in water storage in the Rush Springs aquifer from October 2010 to June 2013.

Oklahoma↗

USGS2014

Updated study reporting levels (SRLs) for trace-element data collected for the California Groundwater Ambient Monitoring and Assessment (GAMA) Priority Basin Project, October 2009-March 2013

Groundwater samples have been collected in California as part of statewide investigations of groundwater quality conducted by the U.S. Geological Survey for the Groundwater Ambient Monitoring and Assessment (GAMA) Priority Basin Project (PBP). The GAMA-PBP is being conducted in cooperation with the California State Water Resources Control Board to assess and monitor the quality of groundwater resources used for drinking-water supply and to improve public knowledge of groundwater quality in California. Quality-control samples (source-solution blanks, equipment blanks, and field blanks) were collected in order to ensure the quality of the groundwater sample results. Olsen and others (2010) previously determined study reporting levels (SRLs) for trace-element results based primarily on field blanks collected in California from May 2004 through January 2008. SRLs are raised reporting levels used to reduce the likelihood of reporting false detections attributable to contamination bias. The purpose of this report is to identify any changes in the frequency and concentrations of detections in field blanks since the last evaluation and update the SRLs for more recent data accordingly. Constituents analyzed were aluminum (Al), antimony (Sb), arsenic (As), barium (Ba), beryllium (Be), boron (B), cadmium (Cd), chromium (Cr), cobalt (Co), copper (Cu), iron (Fe), lead (Pb), lithium (Li), manganese (Mn), molybdenum (Mo), nickel (Ni), selenium (Se), silver (Ag), strontium (Sr), thallium (Tl), tungsten (W), uranium (U), vanadium (V), and zinc (Zn). Data from 179 field blanks and equipment blanks collected from March 2006 through March 2013 by the GAMA-PBP indicated that for trace elements that had a change in detection frequency and concentration since the previous review, the shift occurred near October 2009, in conjunction with a change in the capsule filters used by the study. Results for 89 field blanks and equipment blanks collected from October 2009 through March 2013 were evaluated for potential contamination bias by using the same approach developed by Olsen and others (2010). Some data collected by the National Water-Quality Assessment (NAWQA) Program for the Southern California Coastal Drainages study unit were included to supplement the GAMA-PBP data. The detection frequency and upper threshold of potential contamination bias (BD-90/90) were determined from field-blank and equipment-blank data for each trace element. The BD-90/90 is the 90th percentile concentration of potential extrinsic contamination calculated by using the binomial probability distribution for greater than 90 percent confidence. Additionally, data from laboratory blanks and blind blanks analyzed by the National Water Quality Laboratory (NWQL) during water years 2010 through 2013, and compiled by the USGS Branch of Quality Systems (BQS), were considered for each trace element. These results were compared to each constituent’s reporting level to determine whether an SRL was necessary to minimize the potential for detections in the groundwater samples, attributed principally to contamination bias. Results of the evaluation were used to set SRLs for trace-element data for about 1,135 samples of groundwater collected by the GAMA-PBP between October 2009 and March 2013. Ten trace elements analyzed (Sb, As, Be, B, Cd, Li, Se, Ag, Tl, and U) had blank results that did not necessitate establishing SRLs during this review or the review by Olsen and others (2010). Five trace elements analyzed (Al, Ba, Cr, Sr, and V) had blank results that necessitated establishing an SRL during the previous review but did not need an SRL starting October 2009. One trace element (Fe) had field and laboratory-blank results that necessitated keeping the previous SRL (6 micrograms per liter [μg/L]). Two trace elements (Ni and W) had quality-control results that warranted decreasing the previous SRL, and five trace elements (Cu, Pb, Mn, Mo, and Zn) had field, laboratory, or blind blank results that warranted establishing an SRL for the first time or increasing the previous SRL. SRLs for Cu (2.1 μg/L), Pb (0.82 μg/L), Mn (0.66 μg/L), Mo (0.023 μg/L), Ni (0.21 μg/L), W (0.023 μg/L), and Zn (6.2 μg/L) were changed to these levels starting October 2009, based on the BD-90/90 concentration for field blanks or the 99th percentile concentration for laboratory or blind blanks. The SRL for Fe was maintained at 6 μg/L, based on the minimum laboratory reporting level for iron. SRLs for these eight constituents were at least an order of magnitude below the regulatory benchmarks established for drinking water for health and aesthetic purposes; therefore, the practice of reporting concentrations below the SRLs as less than or equal to (≤) the measured value would not prevent the identification of values greater than the drinking-water benchmarks. Co was detected in 99 percent of field blanks, and with a BD-90/90 concentration of 0.38 μg/L, all groundwater results starting October 2009 were coded as “reviewed and rejected.” Co does not currently have a regulatory benchmark for drinking water. The primary sources of contamination for trace elements inferred from this review are the equipment or processes used in the field to collect the samples or in the laboratory. In particular, contamination in field blanks of Co and Mn was attributed to the high-capacity 0.45-micrometer pore-size capsule filters that were in regular use beginning in October 2009 by several USGS programs, including the GAMA-PBP and NAWQA Program, for filtering samples for analysis of trace elements. The SRLs determined in this report are intended to be used for GAMA groundwater-quality data for samples collected October 2009 through March 2013, or for as long as quality-control data indicate contamination similar to what was observed in this report; quality-control data should be continuously reviewed and SRLs re-assessed on at least a study-unit basis.

California↗

USGS2014

Status and understanding of groundwater quality in the Sierra Nevada Regional study unit, 2008: California GAMA Priority Basin Project

Groundwater quality in the Sierra Nevada Regional (SNR) study unit was investigated as part of the California State Water Resources Control Board’s Groundwater Ambient Monitoring and Assessment Program Priority Basin Project. The study was designed to provide statistically unbiased assessments of the quality of untreated groundwater within the primary aquifer system of the Sierra Nevada. The primary aquifer system for the SNR study unit was delineated by the depth intervals over which wells in the State of California’s database of public drinking-water supply wells are open or screened. Two types of assessments were made: (1) a status assessment that described the current quality of the groundwater resource, and (2) an evaluation of relations between groundwater quality and potential explanatory factors that represent characteristics of the primary aquifer system. The assessments characterize untreated groundwater quality, rather than the quality of treated drinking water delivered to consumers by water distributors. The status assessment was based on water-quality data collected by the U.S. Geological Survey from 83 wells in the SNR study unit in 2008 and from 117 wells in 3 small study units within the SNR study unit in 2006–07 and on water-quality data compiled in the State’s database for 1,066 wells sampled in 2006–08. To provide some context for the results, water-quality data were converted to relative-concentrations (RCs), which are the sample concentrations divided by the concentrations of Federal or California regulatory and non-regulatory benchmarks for drinking-water quality. RCs for inorganic constituents (major ions, trace elements, nutrients, and radioactive constituents) were classified as “high” (RC > 1.0, indicating that concentration is above the benchmark), “moderate” (1.0 ≥ RC > 0.5), or “low” (RC ≤ 0.5). For organic constituents (volatile organic compounds and pesticides) and special-interest constituents (perchlorate and N -nitrosodimethylamine [NDMA]), the boundary between moderate and low RCs was set at 0.1. All benchmarks used for organic constituents were health-based, whereas health-based and aesthetic-based benchmarks were used for inorganic constituents. The primary metric used for quantifying regional-scale groundwater quality was “aquifer-scale proportion.” Aquifer-scale proportions were calculated as the areal percentages of the primary aquifer system having high, moderate, and low RCs for a given constituent or class of constituents. The SNR study unit area was classified into four aquifer lithologic types—granitic rocks, metamorphic rocks, sedimentary deposits, and volcanic rocks—and aquifer-scale proportions were calculated on an area-weighted basis for each of the four aquifer lithologies and for the study unit as a whole (aggregated system). The results of the status assessment indicated that inorganic constituents were present at high and moderate RCs in greater proportions in the SNR study unit aggregated primary aquifer system than were organic constituents and that there were significant differences (p < 0.05) between the four aquifer lithologies. One or more inorganic constituents with health-based benchmarks were present at high RCs in 16 percent of the aggregated primary aquifer system and at moderate RCs in 21 percent. Arsenic (9.7 percent), uranium (2.9 percent), boron (2.0 percent), fluoride (1.8 percent), and nitrate (1.4 percent) were the constituents most commonly present at high RCs. For inorganic constituents with aesthetic-based benchmarks, 18 percent of the aggregated primary aquifer system had high RCs of one or more constituent, and 6.8 percent had moderate RCs. Iron (15.8 percent), manganese (15.1 percent), and total dissolved solids (1.3 percent) were the constituents most commonly present at high RCs. Organic constituents were not detected in 72 percent of the primary aquifer system. One or more organic constituents had high RCs in 0.1 percent of the primary aquifer system, moderate RCs in 3.0 percent, and low RCs in 25 percent. Proportions of the four lithologic primary aquifer systems with high or moderate concentrations of organic constituents were not significantly different. Three organic constituents had area-weighted detection frequencies greater than 10 percent in the primary aquifer system as a whole or at least one of the four lithologic primary aquifer systems: the gasoline oxygenate methyl tert -butyl ether, the trihalomethane chloroform, and the herbicide simazine. The special-interest constituent perchlorate was detected at high RCs in 0.01 percent of the primary aquifer system and at moderate RCs in 1.0 percent, and detection frequencies could be accounted for by the distribution of perchlorate under natural conditions. Statistical tests were used to evaluate relations between constituent concentrations and potential explanatory factors descriptive of land use, geography, depth, geochemical conditions, and groundwater age. Higher concentrations of trace elements, radioactive constituents, and constituents with aesthetic-based benchmarks generally were associated with anoxic conditions, higher pH, and location within a particular compositional band in the Sierra Nevada batholith corresponding to the southwestern part of the study unit. High concentrations of organic constituents generally were associated with greater proportions of urban land use. No significant relations were observed between the concentrations of organic constituents and measures of well depth or groundwater age, perhaps because of the high proportions of springs and modern groundwater in the dataset.

California↗

USGS2014

Stream-water and groundwater quality in and near the Citizen Potawatomi Nation Tribal Jurisdictional Area, Pottawatomie County, Oklahoma, 2012-13

The Citizen Potawatomi Nation needs to characterize their existing surface-water and groundwater resources in and near their tribal jurisdictional area to complete a water-resource management plan. Water resources in this area include surface water from the North Canadian and Little Rivers and groundwater from the terrace and alluvial aquifers and underlying bedrock aquifers. To assist in this effort, the U.S. Geological Survey (USGS), in cooperation with the Citizen Potawatomi Nation, collected water-quality samples at 4 sites on 3 streams and from 30 wells during 2012 and 2013 in and near the Citizen Potawatomi Nation Tribal Jurisdictional Area in central Oklahoma. Stream samples were collected eight times on the North Canadian River at the upstream USGS streamflow-gaging station North Canadian River near Harrah, Okla. (07241550); at the downstream USGS streamflow-gaging station North Canadian River at Shawnee, Okla. (07241800); and on the Little River at the USGS streamflow-gaging station Little River near Tecumseh, Okla., (07230500). Stream samples also were collected three times at an ungaged site, Deer Creek near McLoud, Okla. (07241590). Water properties were measured, and water samples were analyzed for concentrations of major ions, nutrients, trace elements, counts of fecal-indicator bacteria, and 69 organic compounds. The highest concentrations of dissolved solids and chlorides were measured in stream-water samples collected at the Little River near Tecumseh station. The Secondary Maximum Contaminant Level (SMCL) for dissolved solids in drinking water of 500 milligrams per liter (mg/L) was exceeded in 7 of 8 stream-water samples, with a median concentration of 844 mg/L at that station. The 250-mg/L SMCL for chloride was exceeded in 5 of the 8 stream-water samples collected at that station. Median concentrations of total dissolved nitrogen were about an order of magnitude higher in stream-water samples collected at the two stations on the North Canadian River than concentrations in stream-water samples collected at the Little River near Tecumseh station and the Deer Creek site. Median concentrations of total dissolved nitrogen were 4.36 and 2.89 mg/L in stream-water samples collected at the two North Canadian River stations, 0.35 mg/L in stream-water samples collected at the Little River near Tecumseh station, and 0.76 mg/L in stream-water samples collected at the Deer Creek site. Similar to nitrogen, median concentrations of total dissolved phosphorus were higher by about two orders of magnitude in stream-water samples collected at the two stations on the North Canadian River than concentrations in stream-water samples collected at the Little River near Tecumseh station and the Deer Creek site. Median concentrations of total dissolved phosphorus were 1.05 and 0.805 mg/L in stream-water samples collected at the two North Canadian River stations, 0.007 mg/L in stream-water samples collected at the Little River near Tecumseh station, and 0.032 mg/L from the Deer Creek site. Dissolved concentrations of total nitrogen, nitrate-nitrogen, orthophosphorus, and total phosphorus were highest in stream-water samples collected at the two North Canadian River stations at low streamflows, indicating that wastewater effluent may have been a notable source of these nutrients. Concentrations of most trace elements increased with increasing streamflow in stream-water samples collected at the two North Canadian River stations, indicating that most trace elements are washed into the river by runoff from the land surface or resuspended from streambed sediments. In general, most trace-element concentrations were below respective Maximum Contaminant Levels (MCLs) for public drinking-water supplies, except for one stream-water sample with an arsenic concentration of 10.1 micrograms per liter (µg/L) collected from the North Canadian River and one stream-water sample with a barium concentration of 2,690 µg/L collected from the Little River. At least one stream-water sample from each of the four stream sites sampled in this study contained a lead concentration exceeding the SMCL of 15 µg/L. All of these samples were collected during high streamflows. A greater number of organic compounds were detected in stream-water samples collected at the two stations on the North Canadian River than in stream-water samples collected at the Tecumseh station and Deer Creek site. In the 8 stream-water samples collected at the upstream Harrah station, 213 detections of organic compounds were measured, whereas in 8 samples collected at the downstream Shawnee station, 203 detections of organic compounds were measured. In contrast, 59 detections of organic compounds were measured in the 8 stream-water samples collected at the Tecumseh station, and 25 detections of organic compounds were measured in the 3 stream-water samples collected at the Deer Creek site; however, the 8 detections of 7 organic compounds in the 2 equipment-blank samples is problematic for evaluating these data, especially for the Deer Creek and Little River samples because of the comparatively low detection frequency and should be taken into consideration when evaluating these results. Groundwater samples also were collected once from 30 wells producing water from the Garber-Wellington aquifer; Admire, Chase, and Council Grove Groups; the Vanoss Formation; and the terrace and alluvial aquifers along the North Canadian River. Water properties were measured, and samples were analyzed for concentrations of major ions, nutrients, trace elements, and selected radionuclides in groundwater. Of 30 wells sampled for this study, 26 were completed in bedrock aquifers, and 4 were completed in terrace and alluvial aquifers. In general, groundwater in the study area is very hard, with a median concentration of 180 mg/L as calcium carbonate in water samples collected from the 30 wells. Concentrations of sulfate exceeded the 250-mg/L SMCL in two groundwater samples, and dissolved solids concentrations exceeded the 500-mg/L SMCL in nine groundwater samples. Trace-element concentrations did not exceed respective MCLs in the 30 groundwater samples collected for this study. Concentrations of the radionuclide uranium ranged from 0.03 to 79.5 µg/L, with a median concentration of 1.9 µg/L in the 30 groundwater samples collected. Two of the groundwater samples collected for this study had uranium concentrations exceeding the MCL of 30 µg/L, with concentrations of 79.5 and 31.1 µg/L. Generally, uranium concentrations were highest in water samples collected from wells completed in the Wellington Formation and the Chase, Council Grove, and Admire Groups in the southern and eastern parts of the study area.

Oklahoma↗

USGS2014

Estimates of groundwater recharge rates and sources in the East Mountain area, Eastern Bernalillo County, New Mexico, 2005-12

The U.S. Geological Survey, in cooperation with the Bernalillo County Public Works Division, has conducted a monitoring program in the East Mountain area of eastern Bernalillo County, New Mexico, since 2000 to better define the hydrogeologic characteristics of the East Mountain area and to provide scientific information that will assist in the sustainable management of water resources. This report presents estimates of groundwater recharge to the aquifers that supply water to a network of springs that discharged within the East Mountain area of eastern Bernalillo County during 2005–12. Chloride concentration, the mass ratio of chloride to bromide, and the stable isotope ratios of hydrogen and oxygen were used to estimate annual groundwater recharge rates and to identify the sources and timing of recharge to the aquifers in the East Mountain area. Groundwater recharge rates were estimated by using a chloride mass-balance (CMB) method applied to data from selected springs located in the study area. Eleven springs and four downgradient monitoring wells were sampled for this study. On the basis of chloride concentrations and the mass ratio of chloride to bromide, eight of the eleven sampled springs are considered representative of dilute groundwater recharged by meteoric water in the Sandia Mountains. Eight of the eleven springs sampled as part of this investigation are considered representative of dilute groundwater not influenced by nonmeteoric chloride sources on the basis of analysis of chloride concentrations and the mass ratio of chloride to bromide. Chloride concentrations at three of the sampled springs were likely affected by nonmeteoric chloride sources. Results of CMB calculations for the eight springs with Cl:Br ratios and chloride concentrations within the range of dilute groundwater (not influenced by nonmeteoric chloride sources) indicated that between about 5.5 and 23 percent of annual precipitation recharges the groundwater system. The variation in estimated recharge rates indicated that the mechanisms for recharge and groundwater movement in the East Mountain area are complex and that factors such as climate variability, the extent and interconnection of structural features such as faults and fractures, and potential solution enhancement of the aquifers all play important roles in the rates and timing of recharge. Stable isotope data from springs and snowpacks sampled in the East Mountain area were compared with local, regional, and global meteoric water lines and were analyzed along with values representing the stable isotope composition of winter precipitation and summer monsoonal rains. Results of the stable isotope analysis from springs in this study suggested that winter precipitation is the primary source of groundwater recharge to the aquifers supplying the springs, but there is a component of more isotopically enriched precipitation being recharged as well, likely from summer monsoonal rains. Specific conductance, groundwater-level hydrographs, snowpack chemistry, and snow-water equivalent data were used to inform the analyses and corroborate the findings of the CMB and stable isotope results.

New Mexico↗

USGS2014

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

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

Great Basin↗

USGS2016

Hydrologic data and groundwater-flow simulations in the Brown Ditch Watershed, Indiana Dunes National Lakeshore, near Beverly Shores and Town of Pines, Indiana

The U.S. Geological Survey (USGS) collected data and simulated groundwater flow to increase understanding of the hydrology and the effects of drainage alterations on the water table in the vicinity of Great Marsh, near Beverly Shores and Town of Pines, Indiana. Prior land-management practices have modified drainage and caused changes in the distribution of open water, streams and ditches, and groundwater abundance and flow paths. Collected hydrologic data indicate that the majority of water entering Great Marsh flows from the southern dune ridge beneath Town of Pines, Indiana. Groundwater flow is intercepted by Brown Ditch in the eastern portion of the study area and Derby Ditch in the western portion of the study area. A smaller amount of groundwater from the northern dune ridge beneath Beverly Shores also contributed water to Great Marsh. Continuous groundwater-level data collected indicate that the predominant north-south groundwater-flow gradients vary during the course of the year due to increased levels of precipitation or during periods of drainage obstructions. Continuous surface-water discharge and surface-water elevation were measured at three USGS streamgages, one each on Brown, Kintzele and Derby Ditches. The monthly mean discharge statistics indicate that during the period of record— June 2012 to September 2013—streamflow in Kintzele Ditch was lowest during July 2012 and highest during April 2013. In Derby Ditch, streamflow also was lowest during July 2012 and highest during April 2013. Periods of relatively high and low groundwater levels during August 1982, March 2013, and April 2014 were examined and simulated by using MODFLOW and companion software. Results from the simulation of conditions during March 2013 include that nearly 100 percent of all water entering the area simulating Town of Pines is from recharge. Of all the water simulated to enter the eastern and western portions of Great Marsh, nearly 20 and 18 percent, respectively, flows from Town of Pines to the western and eastern portions of Great Marsh. The dune ridges beneath Town of Pines and to a lesser extent beneath Beverly Shores are a major source of recharge to the surficial aquifer and Great Marsh. Results from the simulation of the conditions of April 2014 include that, despite increases in the amount of water entering Great Marsh due to a beaver-dam-modified hydrologic condition, there is still virtually zero simulated groundwater flow from Great Marsh to Town of Pines. The volume of water simulated to be entering the zone representing Beverly Shores decreased by 0.43 cubic foot per second from the results of the March 2013 simulation. This simulated difference in water budgets can be attributed to increased simulated recharge in Great Marsh and Town of Pines. Effects of the inclusion of the beaver dam included the increase of the simulated water table and simulated inundated area upstream of the beaver dam due to the effects of ponding surface water. Results from the simulation scenario that includes six proposed pool-riffle control structures in Brown Ditch under the hydrologic conditions of March 2013 indicate areas inundated by water are larger, including areas just to the north of the entrance of Brown Ditch into Great Marsh, and areas north of the confluence of Brown and Kintzele Ditches. Results from the scenario simulating the increase of the Lake Michigan water level to the historical high of May 31, 1998, showed inundated areas of Great Marsh south of Beverly Shores enlarged on both sides of Lakeshore County Road with the greatest enlargement simulated to be southeast of the intersection of Lakeshore County Road and Beverly Drive. For the scenario simulating the decrease of the Lake Michigan water level to the historical low of December 23, 2007, results show little change from the original March 2013 inundated area. The results of this study can be used by water-resource managers to understand how surrounding ditches affect water levels in Great Marsh and other inland wetlands and residential areas. The groundwater model developed can be applied to answer questions about how alterations to the drainage system in the area affects water levels in the public and residential areas surrounding Great Marsh. The modeling methods developed in this study provide a template for other studies of groundwater flow and groundwater/surface-water interactions within the shallow surficial aquifer in northern Indiana, and in similar hydrologic settings that include surficial sand aquifers in coastal areas.

Indiana↗

USGS2016

Simulated effects of groundwater withdrawals from aquifers in Ocean County and vicinity, New Jersey

Rapid population growth since the 1930s in Ocean County and vicinity, New Jersey, has placed increasing demands upon the area’s freshwater resources. To examine effects of groundwater withdrawals, a three-dimensional groundwater-flow model was developed to simulate the groundwater-flow systems of five area aquifers: the unconfined Kirkwood-Cohansey aquifer system and Vincentown aquifer, and three confined aquifers— the Rio Grande water-bearing zone, the Atlantic City 800-foot sand, and the Piney Point aquifer. The influence of withdrawals is evaluated by using transient groundwater-flow model simulations that incorporate three withdrawal schemes. These are (1) no-withdrawal conditions; (2) 2000–03 withdrawal conditions, using reported monthly withdrawals at all production wells from January 2000 through December 2003; and (3) maximum-allocation withdrawal conditions using the maximum withdrawal allowed by New Jersey Department of Environmental Protection permits at each well. Particle tracking analysis, using results from model simulations, delineated particle flow paths from production wells to the point of recharge, and estimated particle travel times. Compared with no-withdrawal conditions, 2000–03 withdrawal conditions reduced the amount of groundwater flow out of the Kirkwood-Cohansey aquifer system into streams, increased the net flow of water into other layers, reduced net flow into or out of storage, and reduced flow from the Kirkwood-Cohansey aquifer system to constant head cells. Freshwater discharging to the Barnegat Bay-Little Egg Harbor estuary from streams and groundwater is essential to maintaining the ecology of the bay. Examination of selected stress periods indicates that simulated base flow in streams flowing into the Barnegat Bay-Little Egg Harbor estuary is reduced by as much as 49 cubic feet per second for 2000 to 2003 withdrawal conditions when compared with no-withdrawal conditions. In the three confined aquifers, water levels during periods of low recharge and high withdrawals, and high recharge and low withdrawals, were examined to determine seasonal effects on the confined flow systems. The simulated potentiometric surface of the Rio Grande water-bearing zone and the Atlantic City 800-foot sand during selected stress periods indicates substantial declines from no-withdrawal conditions to 2000–03 conditions as a result of groundwater withdrawals. Cones of depression in Toms River Township, Seaside Heights and Seaside Park Boroughs, and Barnegat Light Borough developed in the potentiometric surface of the Piney Point aquifer in response to withdrawals. Maximum-allocation withdrawals decreased flow out of the Kirkwood-Cohansey aquifer system to constant head cells, increased flow out of the aquifer system to adjacent and lower layers, and reduced groundwater discharge to streams when compared with 2000–03 withdrawal conditions. Increases in withdrawals from the Rio Grande water-bearing zone, the Atlantic City 800-foot sand, and the Piney Point aquifer result in an increase in simulated net groundwater flow into these aquifers. Base-flow reduction from 2000–03 conditions to maximum-allocation conditions of 25 to 29 cubic feet per second in all streams draining to the Barnegat Bay-Little Egg Harbor also is indicated. Potentiometric surfaces of the Rio Grande water-bearing zone, Atlantic City 800-foot sand, and the Piney Point aquifer during two stress periods of simulated maximum-allocation withdrawal conditions indicated the expansion of several cones of depression developed during 2000–03 withdrawals. Simulation of average 2000–03 withdrawal conditions indicated the extent to which the groundwater-flow system is susceptible to potential saltwater intrusion into near-shore wells. Travel time from recharge to discharge location ranged from 11 to approximately 50,700 years in near-shore Kirkwood-Cohansey aquifer system wells. Those in Seaside Heights Borough, in Island Beach State Park (Berkeley Township), and in Ship Bottom Borough have particle travel times from 140 to 12,000 years and flow paths that originated under Barnegat Bay or the Atlantic Ocean from the simulation of average maximum-allocation withdrawal conditions. Travel time along flow paths to wells screened in the Rio Grande water-bearing zone and the Atlantic City 800-foot sand from recharge to discharge point ranged from nearly 530 years to greater than 3.73 million years from the simulation of average 2000–03 withdrawal conditions. Particle tracking indicated that most wells screened in these aquifers derived a large part of their recharge from the Oswego River Basin, with a small portion of flow originating either beneath Barnegat Bay or to the east beneath the Atlantic Ocean. Travel time along flow paths that start beneath either Barnegat Bay or the Atlantic Ocean ranged from 2,300 to approximately 134,000 years from the simulation of average maximum-allocation withdrawal conditions."

New Jersey↗

USGS2017

Water quality and quantity and simulated surface-water and groundwater flow in the Laurel Hill Creek Basin, southwestern Pennsylvania, 1991–2007

Laurel Hill Creek is considered one of the most pristine waterways in southwestern Pennsylvania and has high recreational value as a high-quality cold-water fishery; however, the upper parts of the basin have documented water-quality impairments. Groundwater and surface water are withdrawn for public water supply and the basin has been identified as a Critical Water Planning Area (CWPA) under the State Water Plan. The U.S. Geological Survey, in cooperation with the Somerset County Conservation District, collected data and developed modeling tools to support the assessment of water-quality and water-quantity issues for a basin designated as a CWPA. Streams, springs, and groundwater wells were sampled for water quality in 2007. Streamflows were measured concurrent with water-quality sampling at main-stem sites on Laurel Hill Creek and tributaries in 2007. Stream temperatures were monitored continuously at five main-stem sites from 2007 to 2010. Water usage in the basin was summarized for 2003 and 2009 and a Water-Analysis Screening Tool (WAST) developed for the Pennsylvania State Water Plan was implemented to determine whether the water use in the basin exceeded the “safe yield” or “ the amount of water that can be withdrawn from a water resource over a period of time without impairing the long-term utility of a water resource .” A groundwater and surface-water flow (GSFLOW) model was developed for Laurel Hill Creek and calibrated to the measured daily streamflow from 1991 to 2007 for the streamflow-gaging station near the outlet of the basin at Ursina, Pa. The CWPA designation requires an assessment of current and future water use. The calibrated GSFLOW model can be used to assess the hydrologic effects of future changes in water use and land use in the basin. Analyses of samples collected for surface-water quality during base-flow conditions indicate that the highest nutrient concentrations in the main stem of Laurel Hill Creek were at sites in the northeastern part of the basin where agricultural activity is prominent. All of the total nitrogen (N) and a majority of the total phosphorus (P) concentrations in the main stem exceeded regional nutrient criteria levels of 0.31 and 0.01 milligrams per liter (mg/L), respectively. The highest total N and total P concentrations in the main stem were 1.42 and 0.06 mg/L, respectively. Tributary sites with the highest nutrient concentrations are in subbasins where treated wastewater is discharged, such as Kooser Run and Lost Creek. The highest total N and total P concentrations in subbasins were 3.45 and 0.11 mg/L, respectively. Dissolved chloride and sodium concentrations were highest in the upper part of the basin downstream from Interstate 76 because of road deicing salts. The mean base-flow concentrations of dissolved chloride and sodium were 117 and 77 mg/L, respectively, in samples from the main stem just below Interstate 76, and the mean concentrations in Clear Run were 210 and 118 mg/L, compared to concentrations less than 15 mg/L in tributaries that were not affected by highway runoff. Water quality in forested tributary subbasins underlain by the Allegheny and Pottsville Formations was influenced by acidic precipitation and, to a lesser extent, the underlying geology as indicated by pH values less than 5.0 and corresponding specific conductance ranging from 26 to 288 microsiemens per centimeter at 25 degrees Celsius for some samples; in contrast, pH values for main stem sites ranged from 6.6 to 8.5. Manganese (Mn) was the only dissolved constituent in the surface-water samples that exceeded the secondary maximum contaminant level (SMCL). More than one-half the samples from the main stem had Mn concentrations exceeding the SMCL level of 50 micrograms per liter (μg/L), whereas only 19 percent of samples from tributaries exceeded the SMCL for Mn. Stream temperatures along the main stem of Laurel Hill Creek became higher moving downstream. During the summer months of June through August, the daily mean temperatures at the five sites exceeded the limit of 18.9 degrees Celsius (°C) for a cold-water fishery. The maximum instantaneous values for each site ranged from 27.2 to 32.8 °C. Water-quality samples collected at groundwater sites (wells and springs) indicate that wells developed within the Mauch Chunk Formation had the best water quality, whereas wells developed within the Allegheny and Pottsville Formations yielded the poorest water quality. Waters from the Mauch Chunk Formation had the highest median pH (7.6) and alkalinity (80 mg/L calcium carbonate) values. The lowest pH and alkalinity median values were in waters from the Allegheny and Pottsville Formations. Groundwater samples collected from wells in the Allegheny and Pottsville Formations also had the highest concentrations of dissolved iron (Fe) and dissolved Mn. Seventy-eight percent of the groundwater samples collected from the Allegheny Formation exceeded the SMCL of 300 μg/L for Fe and 50 μg/L for Mn. Forty-three and 62 percent of the groundwater samples collected from the Pottsville Formation exceeded the SMCL for iron and Mn, respectively. The highest Fe and Mn concentrations for surface waters were measured for tributaries draining the Pottsville Formation. The highest median Fe concentration for tributaries was in samples from streams draining the Allegheny Formation. During base-flow conditions, the streamflow per unit area along the main stem of Laurel Hill Creek was lowest in the upper parts of the basin [farthest upstream site 0.07 cubic foot per second per square mile (ft 3 /s/mi 2 )] and highest (two sites averaging about 0.20 (ft 3 /s/mi 2 ) immediately downstream from Laurel Hill Lake in the center of the basin. Tributaries with the highest streamflow per unit area were those subbasins that drain the western ridge of the Laurel Hill Creek Basin. The mean streamflow per unit area for tributaries draining areas that extend into the western ridge and draining eastern or central sections was 0.24 and 0.05 ft 3 /s/mi 2 , respectively. In general, as the drainage area increased for tributary basins, the streamflow per unit area increased. Criteria established by the Pennsylvania Department of Environmental Protection indicate that the safe yield of water withdrawals from the Laurel Hill Creek Basin is 1.43 million gallons per day (Mgal/d). Water-use data for 2009 indicate that net (water withdrawals subtracted by water discharges) water withdrawals from groundwater and surface-water sources in the basin were approximately 1.93 Mgal/d. Water withdrawals were concentrated in the upper part of the basin with approximately 80 percent of the withdrawals occurring in the upper 36 mi 2 of the basin. Three subbasins—Allen Creek, Kooser Run, and Shafer Run— in the upper part were affected the most by water withdrawals such that safe yields were exceeded by more than 1,000 percent in the first two and more than 500 percent in the other. In the subbasin of Shafer Run, intermittent streamflow characterizes sections that historically have been perennial. The GSFLOW model of the Laurel Hill Creek Basin is a simple one-layer representation of the groundwater flow system. The GSFLOW model was primarily calibrated to reduce the error term associated with base-flow periods. The total amount of observed streamflow at the Laurel Hill Creek at Ursina, Pa. streamflow-gaging station and the simulated streamflow were within 0.1 percent over the entire modeled period; however, annual differences between simulated and observed streamflow showed a range of -27 to 24 percent from 1992 to 2007 with nine of the years having less than a 10-percent difference. The primary source of simulated streamflow in the GSFLOW model was the subsurface (interflow; 62 percent), followed by groundwater (25 percent) and surface runoff (13 percent). Most of the simulated subsurface flow that reached the stream was in the form of slow flow as opposed to preferential (fast) interflow.

Pennsylvania↗

USGS2016

Simulation of climate change effects on streamflow, groundwater, and stream temperature using GSFLOW and SNTEMP in the Black Earth Creek Watershed, Wisconsin

A groundwater/surface-water model was constructed and calibrated for the Black Earth Creek watershed in south-central Wisconsin. The model was then run to simulate scenarios representing common societal concerns in the basin, focusing on maintaining a cold-water resource in an urbanizing fringe near its upper stream reaches and minimizing downstream flooding. Although groundwater and surface water are considered a single resource, many hydrologic models simplistically simulate feedback loops between the groundwater system and other hydrologic processes. These feedbacks include timing and rates of evapotranspiration, surface runoff, soil-zone flow, and interactions with the groundwater system; however, computer models can now routinely and iteratively couple the surface-water and groundwater systems—albeit with longer model run times. In this study, preliminary calibrations of uncoupled transient surface-water and steady-state groundwater models were used to form the starting point for final calibration of one transient computer simulation that iteratively couples groundwater and surface water. The computer code GSFLOW (Groundwater/Surface-water FLOW) was used to simulate the coupled hydrologic system; a surface-water model represented hydrologic processes in the atmosphere, at land surface, and within the soil zone, and a groundwater-flow model represented the unsaturated zone, saturated zone, and streams. The coupled GSFLOW model was run on a daily time step during water years 1985–2007. Early simulation times (1985–2000) were used for spin-up to make the simulation results less sensitive to initial conditions specified; the spin-up period was not included in the model calibration. Model calibration used observed heads, streamflows, solar radiation, and snowpack measurements from 2000 to 2007 for history matching. Calibration was performed by using the PEST parameter estimation software suite. Simulated streamflows from the calibrated GSFLOW model and other basin characteristics were used as input to the one-dimensional SNTEMP (Stream-Network TEMPerature) model. SNTEMP was used to simulate daily stream temperature in selected stream reaches in the watershed. The temperature model was calibrated to high-resolution stream temperature time-series data measured in 2005. The calibrated GSFLOW and SNTEMP models were then used to simulate effects of potential climate change for the years 2010 through 2100. An ensemble of climate models and emission scenarios was evaluated. Downscaled climate drivers for the simulation period showed increases in maximum and minimum air temperature. Scenarios of future precipitation, however, did not show a monotonic trend like temperature. Uncertainty in the climate drivers increased with time for both temperature and precipitation. Forecasts of potential climate change scenarios showed growing season length increasing by weeks, and both potential and actual evapotranspiration rates increasing appreciably, in response to increasing air temperature. Simulated actual evapotranspiration rates increased less than simulated potential evapotranspiration rates as a result of water limitation in the root zone during the summer high-evapotranspiration period. The hydrologic-system response to climate change was characterized by a reduction in the importance of the snowmelt pulse and an increase in the importance of fall and winter groundwater recharge. The less dynamic hydrologic regime is likely to result in drier soil conditions, with relatively less drying expected in groundwater-fed systems. Groundwater discharge in the current upper cold-water reaches of Black Earth Creek is expected to decrease; flooding in downstream reaches may appreciably increase. The magnitude of changes in forecasted flow and associated groundwater/surface-water interaction is dependent on the General Circulation Model and emission scenario chosen. Potential future changes in air temperature drivers were consistently upward regardless of General Circulation Model and emission scenario selected; thus, simulated stream temperatures are forecast to increase appreciably with future climate. However, the amount of temperature increase was variable. Such uncertainty is reflected in temperature model results, along with uncertainty in the groundwater/surface-water interaction itself. The estimated increase in annual average temperature ranged from approximately 3 to 6 degrees Celsius by 2100 in the upper reaches of Black Earth Creek and 2 to 4 degrees Celsius in reaches farther downstream. As with all forecasts that rely on projections of an unknowable future, the results are best considered to approximate potential outcomes of climate change given the underlying uncertainty.

Wisconsin↗

USGS2016

Potential corrosivity of untreated groundwater in the United States

Corrosive groundwater, if untreated, can dissolve lead and other metals from pipes and other components in water distribution systems. Two indicators of potential corrosivity—the Langelier Saturation Index (LSI) and the Potential to Promote Galvanic Corrosion (PPGC)—were used to identify which areas in the United States might be more susceptible to elevated concentrations of metals in household drinking water and which areas might be less susceptible. On the basis of the LSI, about one-third of the samples collected from about 21,000 groundwater sites are classified as potentially corrosive. On the basis of the PPGC, about two-thirds of the samples collected from about 27,000 groundwater sites are classified as moderate PPGC, and about one-tenth as high PPGC. Potentially corrosive groundwater occurs in all 50 states and the District of Columbia. National maps have been prepared to identify the occurrence of potentially corrosive groundwater in the 50 states and the District of Columbia. Eleven states and the District of Columbia were classified as having a very high prevalence of potentially corrosive groundwater, 14 states as having a high prevalence of potentially corrosive groundwater, 19 states as having a moderate prevalence of potentially corrosive groundwater, and 6 states as having a low prevalence of potentially corrosive groundwater. These findings have the greatest implication for people dependent on untreated groundwater for drinking water, such as the 44 million people that are self-supplied and depend on domestic wells or springs for their water supply.

Scientific Investigations Report↗