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USGS2012

Status and understanding of groundwater quality in the two southern San Joaquin Valley study units, 2005-2006 - California GAMA Priority Basin Project

Groundwater quality in the southern San Joaquin Valley was investigated from October 2005 through March 2006 as part of the Priority Basin Project of the Groundwater Ambient Monitoring and Assessment (GAMA) Program. The GAMA Priority Basin Project is conducted by the U.S. Geological Survey (USGS) in collaboration with the California State Water Resources Control Board and the Lawrence Livermore National Laboratory. There are two study units located in the southern San Joaquin Valley: the Southeast San Joaquin Valley (SESJ) study unit and the Kern County Subbasin (KERN) study unit. The GAMA Priority Basin Project in the SESJ and KERN study units was designed to provide a statistically unbiased, spatially distributed assessment of untreated groundwater quality within the primary aquifers. The status assessment is based on water-quality and ancillary data collected in 2005 and 2006 by the USGS from 130 wells on a spatially distributed grid, and water-quality data from the California Department of Public Health (CDPH) database. Data was collected from an additional 19 wells for the understanding assessment. The aquifer systems (hereinafter referred to as primary aquifers) were defined as that part of the aquifer corresponding to the perforation interval of wells listed in the CDPH database for the SESJ and KERN study units. The status assessment of groundwater quality used data from samples analyzed for anthropogenic constituents such as volatile organic compounds (VOCs) and pesticides, as well as naturally occurring inorganic constituents such as major ions and trace elements. The status assessment is intended to characterize the quality of untreated groundwater resources within the primary aquifers in the SESJ and KERN study units, not the quality of drinking water delivered to consumers. Although the status assessment applies to untreated groundwater, Federal and California regulatory and non-regulatory water-quality benchmarks that apply to drinking water are used to provide context for the results. Relative-concentrations (sample concentration divided by benchmark concentration) were used for evaluating groundwater. A relative-concentration greater than 1.0 indicates a concentration greater than the benchmark and is classified as high. The relative-concentration threshold for classifying inorganic constituents as moderate or low was 0.5; for organic constituents the threshold between moderate and low was 0.1. Aquifer-scale proportion was used as the primary metric for assessing the quality of untreated groundwater for the study units. High aquifer-scale proportion is defined as the areal percentage of the primary aquifers with a high relative-concentration for a particular constituent or class of constituents. Moderate and low aquifer-scale proportions were defined as the areal percentage of the primary aquifers with moderate and low relative-concentrations, respectively. Two statistical approaches—grid-based and spatially weighted—were used to evaluate aquifer-scale proportions for individual constituents and classes of constituents. Grid-based and spatially weighted estimates were comparable for the two study units in the southern San Joaquin Valley (within 90 percent confidence intervals). The status assessment showed that inorganic constituents were more prevalent than organic constituents and that relative-concentrations were higher for inorganic constituents than for organic constituents. For inorganic constituents with human-health benchmarks, the relative-concentration of at least one constituent in the SESJ study unit was high in 30 percent of the primary aquifers. In the KERN study unit, the relative-concentration of at least one constituent was high in 23 percent of the primary aquifers. In the SESJ and KERN study units, the inorganic constituents with human-health benchmarks detected at high relative-concentrations in more than 2 percent of the primary aquifers were arsenic, boron, vanadium, nitrate, uranium, and gross alpha radioactivity. Additional constituents with human-health benchmarks—antimony, radium, and fluoride—were detected at high relative-concentrations in the KERN study unit. For inorganic constituents with aesthetic benchmarks (secondary maximum contaminant levels, SMCLs), the relative-concentration of at least one constituent in the SESJ study unit was high in 6.6 percent of the primary aquifers. In the KERN study unit, the relative-concentration of at least one constituent was high in 22 percent of the primary aquifers. Inorganic constituents with aesthetic benchmarks detected at high relative-concentrations in the primary aquifers in the SESJ and KERN study units were iron and manganese. Additional constituents with aesthetic benchmarks—total dissolved solids (TDS), sulfate, and chloride—were detected at high relative-concentrations in the KERN study unit. In contrast, the status assessment for organic constituents with human-health benchmarks showed that relative-concentrations were high in 4.8 percent and 2.1 percent of the primary aquifers in the SESJ and KERN study units, respectively. The special-interest constituent, perchlorate, was detected at high relative-concentrations in 1.2 percent of the primary aquifers in the SESJ study unit. Twenty-eight of the 78 VOCs (not including fumigants) analyzed were detected. Of these 28 VOCs, benzene had high relative-concentrations in the SESJ study unit, and relative-concentrations for the other 27 VOCs were moderate and low. Five of the 10 fumigants were detected; 1,2-dibromo-3-chloropropane (DBCP) was the only fumigant with high relative-concentrations in the SESJ and KERN study units. Of the 136 pesticides and pesticide degradates analyzed, 33 were detected. Human-health benchmarks were established for eighteen of the detected pesticides. Dieldrin was detected at moderate relative-concentrations in the SESJ and KERN study units. All other pesticides detected with human-health benchmarks were present at low relative-concentrations. The detection frequencies for two of these pesticides—simazine and atrazine—were greater than or equal to 10 percent in the SESJ and KERN study units. The understanding assessment of groundwater quality included an analysis of correlations of selected water-quality constituents or classes of constituents with potential explanatory factors. The understanding assessment indicated that the concentrations of many trace elements and major ions were correlated to well depth, groundwater age, and/or geochemical conditions. Many trace elements were positively correlated with depth. Arsenic, boron, vanadium, fluoride, manganese, and iron concentrations increased with well depth or depth to top-of-perforations. The concentrations for these trace elements also were higher in older (pre-modern) groundwater. In contrast, uranium concentrations decreased with increasing depth and groundwater age. Most trace elements were correlated to geochemical conditions. Arsenic, antimony, boron, fluoride, manganese, and iron concentrations generally were higher wherever the pH of the groundwater was greater than 7.6. Concentrations for these constituents generally were higher at low concentrations of dissolved oxygen (DO). Uranium was the exception; uranium concentrations generally were lower at high pH and at high concentrations of DO. Nitrate concentrations generally were lower in deeper wells. Nitrate concentrations also were higher in groundwater with higher DO. Total dissolved solids, sulfate, and chloride concentrations were higher in the KERN study unit than in the SESJ study unit. Total dissolved solids were negatively correlated with pH in the KERN study unit. Total dissolved solids and sulfate were higher in areas with more agricultural land use. Chloride concentrations increased with depth to top-of-perforations in the KERN study unit. Organic constituents and constituents of special interest, like many inorganic constituents, were correlated with well depth, groundwater age, and DO. Unlike most trace elements, however, solvent and pesticide detections, and total trihalomethanes (THM), DBCP, and perchlorate concentrations decreased with increasing well depth. Volatile organic compound, solvent, and pesticide detections, and THM concentrations also were lower in older (pre-modern) groundwater than in modern-age groundwater. Solvent detections and total THM, DBCP, and perchlorate concentrations increased with increasing DO concentrations.

California↗
USGS2012

Water-quality characteristics and trend analyses for the Tongue, Powder, Cheyenne, and Belle Fourche River drainage basins, Wyoming and Montana, for selected periods, water years 1991 through 2010

The Powder River structural basin in northeastern Wyoming and southeastern Montana is an area of ongoing coalbed natural gas (CBNG) development. Waters produced during CBNG development are managed with a variety of techniques, including surface impoundments and discharges into stream drainages. The interaction of CBNG-produced waters with the atmosphere and the semiarid soils of the Powder River structural basin can affect water chemistry in several ways. Specific conductance and sodium adsorption ratios (SAR) of CBNG-produced waters that are discharged to streams have been of particular concern because they have the potential to affect the use of the water for irrigation. Water-quality monitoring has been conducted since 2001 at main-stem and tributary sites in the Tongue, Powder, Cheyenne, and Belle Fourche River drainage basins in response to concerns about CBNG effects. A study was conducted to summarize characteristics of stream-water quality for water years 2001–10 (October 1, 2000, to September 30, 2010) and examine trends in specific conductance, SAR, and primary constituents that contribute to specific conductance and SAR for changes through time (water years 1991–2010) that may have occurred as a result of CBNG development. Specific conductance and SAR are the focus characteristics of this report. Dissolved calcium, magnesium, and sodium, which are primary contributors to specific conductance and SAR, as well as dissolved alkalinity, chloride, and sulfate, which are other primary contributors to specific conductance, also are described. Stream-water quality in the Tongue, Powder, Cheyenne, and Belle Fourche River drainage basins was variable during water years 2001–10, in part because of variations in streamflow. In general, annual runoff was less than average during water years 2001–06 and near or above average during water years 2007–10. Stream water of the Tongue River had the smallest specific conductance values, sodium adsorption ratios, and major ion concentrations of the main-stem streams. Sites in the Tongue River drainage basin typically had the smallest range of specific conductance and SAR values. The water chemistry of sites in the Powder River drainage basin generally was the most variable as a result of diverse characteristics of that basin. Plains tributaries in the Powder River drainage basin had the largest range of specific conductance and SAR values, in part due to the many tributaries that receive CBNG-produced waters. Trends were analyzed using the seasonal Kendall test with flow-adjusted concentrations to determine changes to water quality through time at sites in the Tongue, Powder, Cheyenne, and Belle Fourche River drainage basins. Trends were evaluated for water years 2001–10 for 17 sites, which generally were on the main-stem streams and primary tributaries. Trends were evaluated for water years 2005–10 for 26 sites to increase the spatial coverage of sites. Trends were evaluated for water years 1991–2010 for eight sites to include water-quality data collected prior to widespread CBNG development and expand the temporal context of trends. Consistent patterns were not observed in trend results for water years 2001–10 for flow-adjusted specific conductance and SAR values in the Tongue, Powder, and Belle Fourche River drainage basins. Significant (p-values less than 0.05) upward trends in flow-adjusted specific conductance values were determined for 3 sites, a downward trend was determined for 1 site, and no significant (p-value greater than 0.05) trends were determined for 13 sites. One of the sites with a significant upward trend was the Tongue River at the Wyoming-Montana State line. No trend in flow-adjusted specific conductance values was determined for the Powder River at Moorhead, Mont. Significant upward trends in flow-adjusted SAR values were determined for 2 sites and no significant trends were determined for 15 sites. No trends in flow-adjusted SAR values were determined for the Tongue River at the Wyoming-Montana State line or for the Powder River at Moorhead, Mont. One of the sites with a significant upward trend in flow-adjusted SAR values was the Powder River at Arvada, Wyo. For water years 2005–10, significant upward trends in flow-adjusted specific conductance values were determined no significant trends were determined for 13 sites. A significant upward trend was determined for flow-adjusted specific conductance values for the Tongue River at the Wyoming-Montana State line. No trend in flow-adjusted specific conductance values was determined for the Powder River at Moorhead, Mont. Significant upward trends in flow-adjusted SAR values were determined for 4 sites, downward trends were determined for 5 sites, and no significant trend was determined for 17 sites. No trends in flow-adjusted SAR values were determined for the Tongue River at the Wyoming-Montana State line or for the Powder River at Moorhead, Mont. Results of the seasonal Kendall test applied to flow-adjusted specific conductance values for water years 1991–2010 indicated no significant trend for eight sites in the Tongue, Powder, and Belle Fourche River drainage basins. No significant trend in flow-adjusted specific conductance was determined for the Tongue River at the Wyoming-Montana State line or the Powder River at Moorhead, Mont. Results of the seasonal Kendall test applied to flow-adjusted SAR values for water years 1991–2010 indicated an upward trend for one site and no significant trend for four sites in the Powder and Belle Fourche River drainage basins. The significant upward trend in flow-adjusted SAR values was determined for the Powder River at Arvada, Wyo., for water years 1991–2010. Results indicate that CBNG development in the Powder River structural basin may have contributed to some trends, such as the upward trend in flow-adjusted SAR for the Powder River at Arvada, Wyo., for water years 1991–2010. An upward trend in flow-adjusted alkalinity concentrations for water years 2001–10 also was determined for the Powder River at Arvada, Wyo. Trend results are consistent with changes that can occur from the addition of sodium and bicarbonate associated with CBNG-produced waters to the Powder River. Upward trends in constituents at other sites, including the Belle Fourche River, may be the result of declining CBNG development, indicating that CBNG-produced waters may have had a dilution effect on some streams. The factors affecting other trends could not be determined because multiple factors could have been affecting the stream-water quality or because trends were observed at sites upstream from CBNG development that may have affected water-quality trends at sites downstream.

Wyoming;Montana↗
USGS2013

The effects of artificial recharge on groundwater levels and water quality in the west hydrogeologic unit of the Warren subbasin, San Bernardino County, California

Between the late 1940s and 1994, groundwater levels in the Warren subbasin, California, declined by as much as 300 feet because pumping exceeded sparse natural recharge. In response, the local water district, Hi-Desert Water District, implemented an artificial-recharge program in early 1995 using imported water from the California State Water Project. Subsequently, the water table rose by as much as 250 feet; however, a study done by the U.S. Geological Survey found that the rising water table entrained high-nitrate septic effluent, which caused nitrate (as nitrogen) concentrations in some wells to increase to more than the U.S. Environmental Protection Agency maximum contaminant level of 10 milligrams per liter.. A new artificial-recharge site (site 3) was constructed in 2006 and this study, which started in 2004, was done to address concerns about the possible migration of nitrates in the unsaturated zone. The objectives of this study were to: (1) characterize the hydraulic, chemical, and microbiological properties of the unsaturated zone; (2) monitor changes in water levels and water quality in response to the artificial-recharge program at site 3; (3) determine if nitrates from septic effluent infiltrated through the unsaturated zone to the water table; (4) determine the potential for nitrates within the unsaturated zone to mobilize and contaminate the groundwater as the water table rises in response to artificial recharge; and (5) determine the presence and amount of dissolved organic carbon because of its potential to react with disinfection byproducts during the treatment of water for public use. Two monitoring sites were installed and instrumented with heat-dissipation probes, advanced tensiometers, suction-cup lysimeters, and wells so that the arrival and effects of recharging water from the State Water Project through the 250 to 425 foot-thick unsaturated zone and groundwater system could be closely observed. Monitoring site YVUZ-1 was located between two recharge ponds in the middle of site 3, and YVUZ-2 was located approximately 1,200 feet down-gradient and to the southeast in an area where septic systems have been in use since about 1960. Site YVUZ-3 only went to a depth of 42 feet and was used to sample the upper part of the unsaturated zone near a golf course. Prior to the start of artificial recharge at site 3, nitrate concentrations reported as nitrogen from the soil leachate below YVUZ-1 did not exceed 1.58 milligrams per kilogram. Nitrate-reducing bacteria concentrations of 4,300 most probable number were found at about 220 feet below land surface and at the top of the water table at YVUZ-1. Nitrate concentrations at YVUZ-2 reached a maximum concentration of about 25 milligrams per kilogram between about 100 and 121 feet below land surface; concentrations of nitrate-reducing or denitrifying bacteria were as high as 21,000 most probable number at 36 feet below land surface but did not exceed 40 most probable number below about 150 feet below land surface. Between June 2006 and September 2009, more than 9,800 acre feet of water from the State Water Project was released to site 3 ponds. The infiltration of the recharge water was predominantly vertical with limited lateral spreading to a depth of about 200 feet below land surface at YVUZ-1. Lateral spreading of the recharge water with depth was caused by geologic heterogeneities within the unsaturated zone, and resulted in varied arrival times of the recharge water to the instruments and slower rates of vertical movement with depth. No abrupt changes in soil moisture were observed at YVUZ-2, indicating that the recharge water had not reached that site by September 2009. Water levels from the monitoring wells at both sites and from five production wells nearby showed that the water table rose at a mean rate of about 0.08 feet per day between June 2006 and January 2009. The arrival of the water from the State Water Project caused relatively rapid changes in the stable-isotopic ratios from the lysimeters at YVUZ-1. The estimated average rate of infiltration of the recharge water through the unsaturated zone ranged from 3.7 to 25 feet per day. The recharge water arrived at the monitoring well below the recharge ponds between August 2007 and March 2008; the rate of vertical movement to the monitoring well was between 0.6 and 0.9 feet per day. By September 2008, a production well located 375 feet west of site 3 was producing almost 100 percent infiltrated recharge water. By contrast, the stable-isotope data from the lysimeters at YVUZ-2 showed that the recharge water had not reached this site by September 2009, but that septic effluent in the unsaturated zone likely had mixed with the native pore water to at least 154 feet below land surface. Assuming vertical infiltration, the minimum rate of infiltration of septic effluent since 1960 was about 3 feet per year. The isotopic data from the lysimeters at YVUZ-3 indicated two different sources of water to the upper 43 feet–irrigation-return flow and precipitation. Nitrate concentrations of the water from the State Water Project did not exceed 1 milligram per liter. Prior to artificial recharge, nitrate concentrations of the pore water at YVUZ-1 ranged between 6 to 18.2 milligrams per liter. After the arrival of the recharge water, the nitrate concentrations from the lysimeters and well at YVUZ-1 decreased to less than 1 milligram per liter, with the exception of samples collected at 205.5 feet, which did not exceed 4.12 milligrams per liter. The decrease in nitrate concentrations after artificial recharge indicated that the rising water table did not result in an increase of nitrates below YVUZ-1. At YVUZ-2, nitrate concentrations ranged between 12 to 479 milligrams per liter. The highest nitrate concentrations were at 92 feet below land surface and were almost seven times that of samples collected from a nearby septic tank. Nitrate concentrations from the lysimeter at 273 feet below land surface increased from 6 to almost 58 milligrams per liter after it was saturated by the rising water table in December 2007. These increases could be the result of the mobilization of high-nitrate water from regional sources of septic effluent after saturation, or the result of high-nitrate water present at the top of the water table that may be diluted deeper in the aquifer. Nitrate concentrations in groundwater from five nearby production wells and from both monitoring wells were less than 5 milligrams per liter before artificial recharge started. Nitrate concentrations decreased to less than 3 milligrams per liter in three of the production wells and the monitoring well below the recharge ponds after artificial recharge. Dissolved organic carbon concentrations were measured in the recharge water and groundwater because of the potential for dissolved organic carbon to react with chlorine to form trihalomethanes during the water-treatment process. The dissolved organic carbon concentrations of the recharge water were 3.1 milligrams per liter or less, and dissolved organic carbon concentrations of the groundwater were less than 1 milligram per liter. Even though recharge water was present in some of the wells by September 2008, the concentrations of both dissolved organic carbon and trihalomethane formation potential in the groundwater did not increase. Interpretation of these data suggests that the dissolved organic carbon from the recharge water is altered or metabolized in the unsaturated zone, either by absorption to the grain particles in the soil or by microbiological processes.

California↗
USGS2013

Groundwater and surface-water interactions near White Bear Lake, Minnesota, through 2011

The U.S. Geological Survey, in cooperation with the White Bear Lake Conservation District, the Minnesota Pollution Control Agency, the Minnesota Department of Natural Resources, and other State, county, municipal, and regional planning agencies, watershed organizations, and private organizations, conducted a study to characterize groundwater and surface-water interactions near White Bear Lake through 2011. During 2010 and 2011, White Bear Lake and other lakes in the northeastern part of the Twin Cities Metropolitan Area were at historically low levels. Previous periods of lower water levels in White Bear Lake correlate with periods of lower precipitation; however, recent urban expansion and increased pumping from the Prairie du Chien-Jordan aquifer have raised the question of whether a decline in precipitation is the primary cause for the recent water-level decline in White Bear Lake. Understanding and quantifying the amount of groundwater inflow to a lake and water discharge from a lake to aquifers is commonly difficult but is important in the management of lake levels. Three methods were used in the study to assess groundwater and surface-water interactions on White Bear Lake: (1) a historical assessment (1978-2011) of levels in White Bear Lake, local groundwater levels, and their relation to historical precipitation and groundwater withdrawals in the White Bear Lake area; (2) recent (2010-11) hydrologic and water-quality data collected from White Bear Lake, other lakes, and wells; and (3) water-balance assessments for White Bear Lake in March and August 2011. An analysis of covariance between average annual lake-level change and annual precipitation indicated the relation between the two variables was significantly different from 2003 through 2011 compared with 1978 through 2002, requiring an average of 4 more inches of precipitation per year to maintain the lake level. This shift in the linear relation between annual lake-level change and annual precipitation indicated the net effect of the non-precipitation terms on the water balance has changed relative to precipitation. The average amount of precipitation required each year to maintain the lake level has increased from 33 inches per year during 1978-2002 to 37 inches per year during 2003-11. The combination of lower precipitation and an increase in groundwater withdrawals can explain the change in the lake-level response to precipitation. Annual and summer groundwater withdrawals from the Prairie du Chien-Jordan aquifer have more than doubled from 1980 through 2010. Results from a regression model constructed with annual lake-level change, annual precipitation minus evaporation, and annual volume of groundwater withdrawn from the Prairie du Chien-Jordan aquifer indicated groundwater withdrawals had a greater effect than precipitation minus evaporation on water levels in the White Bear Lake area for all years since 2003. The recent (2003-11) decline in White Bear Lake reflects the declining water levels in the Prairie du Chien-Jordan aquifer; increases in groundwater withdrawals from this aquifer are a likely cause for declines in groundwater levels and lake levels. Synoptic, static groundwater-level and lake-level measurements in March/April and August 2011 indicated groundwater was potentially flowing into White Bear Lake from glacial aquifers to the northeast and south, and lake water was potentially discharging from White Bear Lake to the underlying glacial and Prairie du Chien-Jordan aquifers and glacial aquifers to the northwest. Groundwater levels in the Prairie du Chien-Jordan aquifer below White Bear Lake are approximately 0 to 19 feet lower than surface-water levels in the lake, indicating groundwater from the aquifer likely does not flow into White Bear Lake, but lake water may discharge into the aquifer. Groundwater levels from March/April to August 2011 declined more than 10 feet in the Prairie du Chien-Jordan aquifer south of White Bear Lake and to the north in Hugo, Minnesota. Water-quality analyses of pore water from nearshore lake-sediment and well-water samples, seepage-meter measurements, and hydraulic-head differences measured in White Bear Lake also indicated groundwater was potentially flowing into White Bear Lake from shallow glacial aquifers to the east and south. Negative temperature anomalies determined in shallow waters in the water-quality survey conducted in White Bear Lake indicated several shallow-water areas where groundwater may be flowing into the lake from glacial aquifers below the lake. Cool lake-sediment temperatures (less than 18 degrees Celsius) were measured in eight areas along the northeast, east, south, and southwest shores of White Bear Lake, indicating potential areas where groundwater may flow into the lake. Stable isotope analyses of well-water, precipitation, and lake-water samples indicated wells downgradient from White Bear Lake screened in the glacial buried aquifer or open to the Prairie du Chien-Jordan aquifer receive a mixture of surface water and groundwater; the largest surface-water contributions are in wells closer to White Bear Lake. A wide range in oxygen-18/oxygen-16 and deuterium/protium ratios was measured in well-water samples, indicating different sources of water are supplying water to the wells. Well water with oxygen-18/oxygen-16 and deuterium/protium ratios that plot close to the meteoric water line consisted mostly of groundwater because deuterium/protium ratios for most groundwater usually are similar to ratios for rainwater and snow, plotting close to meteoric water lines. Well water with oxygen-18/oxygen-16 and deuterium/protium ratios that plot between the meteoric water line and ratios for the surface-water samples from White Bear Lake consists of a mixture of surface water and groundwater; the percentage of each source varies relative to its ratios. White Bear Lake is the likely source of the surface water to the wells that have a mixture of surface water and groundwater because (1) it is the only large, deep lake near these wells; (2) these wells are near and downgradient from White Bear Lake; and (3) these wells obtain their water from relatively deep depths, and White Bear Lake is the deepest lake in that area. The percentages of surface-water contribution to the three wells screened in the glacial buried aquifer receiving surface water were 16, 48, and 83 percent. The percentages of surface-water contribution ranged from 5 to 79 percent for the five wells open to the Prairie du Chien-Jordan aquifer receiving surface water; wells closest to White Bear Lake had the largest percentages of surface-water contribution. Water-balance analysis of White Bear Lake in March and August 2011 indicated a potential discharge of 2.8 and 4.5 inches per month, respectively, over the area of the lake from the lake to local aquifers. Most of the sediments from a 12.4-foot lake core collected at the deepest part of White Bear Lake consisted of silts, sands, and gravels likely slumped from shallower waters, with a very low amount of low-permeability, organic material.

Minnesota↗
USGS2010

Hydrogeomorphic segments and hydraulic microhabitats of the Niobrara River, Nebraska— With special emphasis on the Niobrara National Scenic River

The Niobrara River is an ecologically and economically important resource in Nebraska. The Nebraska Department of Natural Resources’ recent designation of the hydraulically connected surface- and groundwater resources of the Niobrara River Basin as “fully appropriated” has emphasized the importance of understanding linkages between the physical and ecological dynamics of the Niobrara River so it can be sustainably managed. In cooperation with the Nebraska Game and Parks Commission, the U.S. Geological Survey investigated the hydrogeomorphic and hydraulic attributes of the Niobrara River in northern Nebraska. This report presents the results of an analysis of hydrogeomorphic segments and hydraulic microhabitats of the Niobrara River and its valley for the approximately 330-mile reach from Dunlap Diversion Dam to its confluence with the Missouri River. Two spatial scales were used to examine and quantify the hydrogeomorphic segments and hydraulic microhabitats of the Niobrara River: a basin scale and a reach scale. At the basin scale, digital spatial data and hydrologic data were analyzed to (1) test for differences between 36 previously determined longitudinal hydrogeomorphic segments; (2) quantitatively describe the hydrogeomorphic characteristics of the river and its valley; and (3) evaluate differences in hydraulic microhabitat over a range of flow regimes among three fluvial geomorphic provinces. The statistical analysis of hydrogeomorphic segments resulted in reclassification rates of 3 to 28 percent of the segments for the four descriptive geomorphic elements. The reassignment of classes by discriminant analysis resulted in a reduction from 36 to 25 total hydrogeomorphic segments because several adjoining segments shared the same ultimate class assignments. Virtually all of the segment mergers were in the Canyons and Restricted Bottoms (CRB) fluvial geomorphic province. The most frequent classes among hydrogeomorphic segments, and the dominant classes per unit length of river, are: a width-restricted valley confinement condition, sinuous-planview pattern, irregular channel width, and an alternate bar configuration. The Niobrara River in the study area flows through a diversity of fluvial geomorphic settings in its traverse across northern Nebraska. In the Meandering Bottoms (MB) fluvial geomorphic province, river discharge magnitudes are low, and the valley exerts little control on the channel-planview pattern. Within the CRB province, the river flows over a diversity of geologic formations, and the valley and river narrow and expand in approximate synchronicity. In the Braided Bottoms (BB) fluvial geomorphic province, the river primarily flows over Cretaceous Pierre Shale, the valley and channel are persistently wide, and the channel slope is generally uniform. The existence of vegetated islands and consequent multithread channel environments, indicated by a higher braided index, mostly coincided with reaches having gentler slopes and less unit stream power. Longitudinal hydrology curves indicate that the flow of the Niobrara River likely is dominated by groundwater as far downstream as Norden. Unit stream power values in the study area vary between 0 and almost 2 pounds per foot per second. Within the MB province, unit stream power steadily increases as the Niobrara gains discharge from groundwater inflow, and the channel slope steepens. The combination of steep slopes, a constrained channel width, and persistent flow within the CRB province results in unit stream power values that are between three and five times greater than those in less confined segments with comparable or greater discharges. With the exception of hydrogeomorphic segment 3, which is affected by Spencer Dam, unit stream power values in the BB province are generally uniform. Channel sinuosity values in the study area varied generally between 1 and 2.5, but with locally higher values measured in the MB province and at the entrenched bedrock meanders of hydrogeomorphic segment 18 in the CRB province. The differences in channel morphology and hydraulic geometries between fluvial geomorphic provinces are evident in the types, relative abundance, and response of hydraulic microhabitats to changing discharges. The four gaging stations chosen for hydraulic microhabitat analysis are distributed among three different fluvial geomorphic provinces. In the MB province, the smaller channel and lower discharges resulted in the dominance of shallow and intermediate-depth hydraulic environments with the vast majority of hydraulic microhabitat restricted to shallow categories even during upper-decile discharges. In the CRB province, intermediate depth hydraulic conditions, particularly intermediate-swift, dominate over all ranges of discharge. Hydraulic microhabitat conditions were most diverse in the BB province, with most hydraulic microhabitat categories present over the entire range of discharges analyzed. The calculated differences in hydraulic microhabitat distributions, abundance, and adjustments between streamflow-gaging stations were the result of differences in physical structure of the channel and subsequent channel hydraulic geometry. At the reach scale, field measurements made in water years 2008 and 2009 in four study reaches within the Scenic Reach were used to (1) characterize the elevation and geomorphic processes associated with fluvial landforms, (2) build hydraulic geometry relations, (3) examine flow hydraulics over a range of discharges, and (4) examine the types and responses of hydraulic microhabitats to a range of flow magnitudes. Four landform groups were identified and named in order of increasing elevation: low flood plains, intermediate flood plains, low terraces, and high terraces. The terraces were poorly characterized because the surveys did not extend across the full width of the alluvial valley bottom. The two lowest fluvial landforms are likely active in the modern hydroclimatic regime. Sediment samples obtained in the study reaches indicate that the primary bed material in the active channel ranged in size from coarse silt to coarse sand. Grain-size distributions from samples also indicate that the bed of the Niobrara River among the study reaches coarsens and has increasing grainsize variability in the downstream direction. Values of at-a-station hydraulic geometry exponents indicate that the Niobrara River in the study reaches adjusts its geometry to changing discharges primarily through increases in flow depth and velocity. Relations at one cross section indicated that, at least locally, changes in width were also an important channel adjustment mechanism. Hydraulic behavior over the range of flows measured was not consistent among all study reaches, but two general modes of hydraulic behavior were observed in the reaches with substantial coverage of the bed by fine sediment. At the Sunny Brook and Muleshoe study reaches, average boundary-shear stress remained approximately constant, and hydraulic resistance decreased, for discharges below 900 cubic feet per second (ft 3 /s). Above 900 ft 3 /s, average boundary shear stress and hydraulic resistance both increased. The Rock Barn study reach did not exhibit the same two-mode hydraulic behavior observed at the Sunny Brook and Muleshoe reaches. The coincident increase in boundary shear stress above 900 ft 3 /s observed at the Sunny Brook and Muleshoe study reaches represents a potential hydraulic threshold above which bedload transport rates were likely to increase markedly. No consistent bed-adjustment pattern (scour or fill) was identified in the study reaches over the range of flows or over the measurement season. Analysis of hydraulic microhabitats over the range of discharges measured at the study reaches indicates that some percentage of most habitat niche categories was available for at least one discharge condition, but the majority of hydraulic habitat available was within the intermediate-swift and deepswift habitat niche categories. Deep-swift conditions dominated nearly all study reaches under all measured discharge conditions. Slight differences in habitat distributions were observed between the study reaches with substantial coverage of the bed by fine sediment—Sunny Brook, Muleshoe, and Rock Barn—and the bedrock-dominated reach, Crooked Creek. Although the four study reaches occupy three different hydrogeomorphic segments, the types, relative abundance, and response of hydraulic microhabitat niche distributions to changing discharge conditions generally were similar among all reaches.

Nebraska↗
USGS2017

Groundwater quality in the Western San Joaquin Valley study unit, 2010: California GAMA Priority Basin Project

Water quality in groundwater resources used for public drinking-water supply in the Western San Joaquin Valley (WSJV) was investigated by the USGS in cooperation with the California State Water Resources Control Board (SWRCB) as part of its Groundwater Ambient Monitoring and Assessment (GAMA) Program Priority Basin Project. The WSJV includes two study areas: the Delta–Mendota and Westside subbasins of the San Joaquin Valley groundwater basin. Study objectives for the WSJV study unit included two assessment types: (1) a status assessment yielding quantitative estimates of the current (2010) status of groundwater quality in the groundwater resources used for public drinking water, and (2) an evaluation of natural and anthropogenic factors that could be affecting the groundwater quality. The assessments characterized the quality of untreated groundwater, not the quality of treated drinking water delivered to consumers by water distributors. The status assessment was based on data collected from 43 wells sampled by the U.S. Geological Survey for the GAMA Priority Basin Project (USGS-GAMA) in 2010 and data compiled in the SWRCB Division of Drinking Water (SWRCB-DDW) database for 74 additional public-supply wells sampled for regulatory compliance purposes between 2007 and 2010. To provide context, concentrations of constituents measured in groundwater were compared to U.S. Environmental Protection Agency (EPA) and SWRCB-DDW regulatory and non-regulatory benchmarks for drinking-water quality. The status assessment used a spatially weighted, grid-based method to estimate the proportion of the groundwater resources used for public drinking water that has concentrations for particular constituents or class of constituents approaching or above benchmark concentrations. This method provides statistically unbiased results at the study-area scale within the WSJV study unit, and permits comparison of the two study areas to other areas assessed by the GAMA Priority Basin Project statewide. Groundwater resources used for public drinking water in the WSJV study unit are among the most saline and most affected by high concentrations of inorganic constituents of all groundwater resources used for public drinking water that have been assessed by the GAMA Priority Basin Project statewide. Among the 82 GAMA Priority Basin Project study areas statewide, the Delta–Mendota study area ranked above the 90th percentile for aquifer-scale proportions of groundwater resources having concentrations of total dissolved solids (TDS), sulfate, chloride, manganese, boron, chromium(VI), selenium, and strontium above benchmarks, and the Westside study area ranked above the 90th percentile for TDS, sulfate, manganese, and boron. In the WSJV study unit as a whole, one or more inorganic constituents with regulatory or non-regulatory, health-based benchmarks were present at concentrations above benchmarks in about 53 percent of the groundwater resources used for public drinking water, and one or more organic constituents with regulatory health-based benchmarks were detected at concentrations above benchmarks in about 3 percent of the resource. Individual constituents present at concentrations greater than health-based benchmarks in greater than 2 percent of groundwater resources used for public drinking water included: boron (51 percent, SWRCB-DDW notification level), chromium(VI) (25 percent, SWRCB-DDW maximum contaminant level (MCL)), arsenic (10 percent, EPA MCL), strontium (5.1 percent, EPA Lifetime health advisory level (HAL)), nitrate (3.9 percent, EPA MCL), molybdenum (3.8 percent, EPA HAL), selenium (2.6 percent, EPA MCL), and benzene (2.6 percent, SWRCB-DDW MCL). In addition, 50 percent of the resource had TDS concentrations greater than non-regulatory, aesthetic-based SWRCB-DDW upper secondary maximum contaminant level (SMCL), and 44 percent had manganese concentrations greater than the SWRCB-DDW SMCL. Natural and anthropogenic factors that could affect the groundwater quality were evaluated by using results from statistical testing of associations between constituent concentrations and values of potential explanatory factors, inferences from geochemical and age-dating tracer results, and by considering the water-quality results in the context of the hydrogeologic setting of the WSJV study unit. Natural factors, particularly the lithologies of the source areas for groundwater recharge and of the aquifers, were the dominant factors affecting groundwater quality in most of the WSJV study unit. However, where groundwater resources used for public supply included groundwater recharged in the modern era, mobilization of constituents by recharge of water used for irrigation also affected groundwater quality. Public-supply wells in the Westside study area had a median depth of 305 m and primarily tapped groundwater recharged hundreds to thousands of years ago, whereas public-supply wells in the Delta–Mendota study area had a median depth of 85 m and primarily tapped either groundwater recharged within the last 60 years or groundwater consisting of mixtures of this modern recharge and older recharge. Public-supply wells in the WSJV study unit are screened in the Tulare Formation and zones above and below the Corcoran Clay Member are used. The Tulare Formation primarily consists of alluvial sediments derived from the Coast Ranges to the west, except along the valley trough at the eastern margin of the WSJV study unit where the Tulare Formation consists of fluvial sands derived from the Sierra Nevada to the east. Groundwater from wells screened in the Sierra Nevada sands had manganese-reducing or manganese- and iron-reducing oxidation-reduction (redox) conditions. These redox conditions commonly were associated with elevated arsenic or molybdenum concentrations, and the dominance of arsenic(III) in the dissolved arsenic supports reductive dissolution of iron and manganese oxyhydroxides as the mechanism. In addition, groundwater from many wells screened in Sierra Nevada sands contained low concentrations of nitrite or ammonium, indicating reduction of nitrate by denitrification or dissimilatory processes, respectively. Geology of the Coast Ranges westward of the study unit strongly affects groundwater quality in the WSJV. Elevated concentrations of TDS, sulfate, boron, selenium and strontium in groundwater were primarily associated with aquifer sediments and recharge derived from areas of the Coast Ranges dominated by Cretaceous-to-Miocene age, organic-rich, reduced marine shales, known as the source of selenium in WSJV soils, surface water, and groundwater. Low sulfur-isotopic values (δ34S) of dissolved sulfate indicate that the sulfate was largely derived from oxidation of biogenic pyrite from the shales, and correlations with trace element concentrations, geologic setting, and groundwater geochemical modeling indicated that distributions of sulfate, strontium, and selenium in groundwater were controlled by dissolution of secondary sulfate minerals in soils and sediments. Elevated concentrations of chromium(VI) were primarily associated with aquifer sediments and recharge derived from areas of the Coast Ranges dominated by the Franciscan Complex and ultramafic rocks. The Franciscan Complex also has boron-rich, sodium-chloride dominated hydrothermal fluids that contribute to elevated concentrations of boron and TDS. Groundwater from wells screened in Coast Ranges alluvium was primarily oxic and relatively alkaline (median pH value of 7.55) in the Delta–Mendota study area, and primarily nitrate-reducing or suboxic and alkaline (median pH value of 8.4) in the Westside study area. Many groundwater samples from those wells have elevated concentrations of arsenic(V), molybdenum, selenium, or chromium(VI), consistent with desorption of metal oxyanions from mineral surfaces under those geochemical conditions. High concentrations of benzene were associated with deep wells located in the vicinity of petroleum deposits at the southern end of the Westside study area. Groundwater from these wells had premodern age and anoxic geochemical conditions, and the ratios among concentrations of hydrocarbon constituents were different from ratios found in fuels and combustion products, which is consistent with a geogenic source for the benzene rather than contamination from anthropogenic sources. Water stable-isotope compositions, groundwater recharge temperatures, and groundwater ages were used to infer four types of groundwater: (1) groundwater derived from natural recharge of water from major rivers draining the Sierra Nevada; (2) groundwater primarily derived from natural recharge of water from Coast Ranges runoff; (3) groundwater derived from recharge of pumped groundwater applied to the land surface for irrigation; and (4) groundwater derived from recharge during a period of much cooler paleoclimate. Water previously used for irrigation was found both above and below the Corcoran Clay, supporting earlier inferences that this clay member is no longer a robust confining unit. Recharge of water used for irrigation has direct and indirect effects on groundwater quality. Elevated nitrate concentrations and detections of herbicides and fumigants in the Delta–Mendota study area generally were associated with greater agricultural land use near the well and with water recharged during the last 60 years. However, the extent of the groundwater resource affected by agricultural sources of nitrate was limited by groundwater redox conditions sufficient to reduce nitrate. The detection frequency of perchlorate in Delta–Mendota groundwater was greater than expected for natural conditions. Perchlorate, nitrate, selenium, and strontium concentrations were correlated with one another and were greater in groundwater inferred to be recharge of previously pumped groundwater used for irrigation. The source of the perchlorate, selenium, and strontium appears to be salts deposited in the soils and sediments of the arid WSJV that are dissolved and flushed into groundwater by the increased amount of recharge caused by irrigation. In the Delta–Mendota study area, the groundwater with elevated concentrations of selenium was found deeper in the aquifer system than it was reported by a previous study 25 years earlier, suggesting that this transient front of groundwater with elevated concentrations of constituents derived from dissolution of soil salts by irrigation recharge is moving down through the aquifer system and is now reaching the depth zone used for public drinking water supply.

California↗
USGS2014

U.S. Geological Survey Karst Interest Group Proceedings, Carlsbad, New Mexico, April 29-May 2, 2014

Karst aquifer systems are present throughout parts of the United States and some of its territories, and have developed in carbonate rocks (primarily limestone and dolomite) that span an interval of time encompassing more than 550 million years. The depositional environments, diagenetic processes, post-depositional tectonic events, and geochemical weathering processes that form karst aquifers are varied and complex, and involve biological, chemical, and physical changes. These factors, combined with the diverse climatic regimes under which karst development in these rocks has taken place, result in the unique dual- or triple-porosity nature of karst aquifers. These complex hydrogeologic systems typically represent challenging and unique conditions to scientists attempting to study groundwater flow and contaminant transport in these terrains. The dissolution of carbonate rocks and the subsequent development of distinct and beautiful landscapes, caverns, and springs has resulted in the most exceptional karst areas of the United States being designated as national or state parks; commercial caverns and known privately owned caves number in the tens of thousands. Both public and private properties provide access for scientists to study the flow of groundwater in situ. Likewise, the range and complexity of landforms and groundwater flow systems associated with karst terrains are enormous, perhaps more than for any other aquifer type. Karst aquifers and landscapes that form in tropical areas, such as the cockpit karst along the north coast of Puerto Rico, differ greatly from karst landforms in more arid climates, such as the Edwards Plateau in west-central Texas or the Guadalupe Mountains near Carlsbad, New Mexico, where hypogenic processes have played a major role in speleogenesis. Many of these public and private lands also contain unique flora and fauna associated with these karst hydrogeologic systems. As a result, numerous federal, state, and local agencies have a strong interest in the study of karst terrains. Many of the major springs and aquifers in the United States have developed in carbonate rocks, such as the Floridan aquifer system in Florida and parts of Alabama, Georgia, and South Carolina; the Ozark Plateaus aquifer system in parts of Arkansas, Kansas, Missouri, and Oklahoma; and the Edwards-Trinity aquifer system in west-central Texas. These aquifers, and the springs that discharge from them, serve as major water-supply sources and as unique ecological habitats. Competition for the water resources of karst aquifers is common, and urban development and the lack of attenuation of contaminants in karst areas can impact the ecosystem and water quality of these aquifers. The concept for developing a platform for interaction among scientists within the U.S. Geological Survey (USGS) working on karst-related studies evolved from the November 1999 National Ground-Water Meeting of the USGS. As a result, the Karst Interest Group (KIG) was formed in 2000. The KIG is a loose-knit, grass-roots organization of USGS and non-USGS scientists and researchers devoted to fostering better communication among scientists working on, or interested in, karst science. The primary mission of the KIG is to encourage and support interdisciplinary collaboration and technology transfer among scientists working in karst areas. Additionally, the KIG encourages collaborative studies between the different mission areas of the USGS as well as other federal and state agencies, and with researchers from academia and institutes. The KIG also encourages younger scientists by participation of students in the poster and oral sessions. To accomplish its mission, the KIG has organized a series of workshops that are held near nationally important karst areas. To date (2014) six KIG workshops, including the workshop documented in this report, have been held. The workshops typically include oral and poster sessions on selected karst-related topics and research, as well as field trips to local karst features. Proceedings of the workshops are published by the USGS and are available online at http://water.usgs.gov/ogw/karst/kig . The first KIG workshop was held in St. Petersburg, Florida, February 13–16, 2001, in the vicinity of the large springs and other karst features of the Floridan aquifer system. The second KIG workshop was held August 20–22, 2002, in Shepherdstown, West Virginia, in proximity to the carbonate aquifers of the northern Shenandoah Valley and highlighted an invited presentation on karst literature by the late Barry F. Beck of P.E. LaMoreaux and Associates. The third KIG workshop was held September 12–15, 2005, in Rapid City, South Dakota, nearby to karst features in evaporites and limestones of the Madison Group in the Black Hills of South Dakota, including Wind Cave National Park and Jewel Cave National Monument. The workshop also included a featured presentation by Thomas Casadevall, Central Region Director, USGS, on the status of earth science at the USGS and evening trips to Jewel Cave led by Mike Wiles, National Park Service (NPS) and Wind Cave led by Rod Horrocks, NPS. The fourth KIG workshop was held May 27–29, 2008, and hosted by the Hoffman Environmental Research Institute and Center for Cave and Karst Studies at Western Kentucky University in Bowling Green, Kentucky, near Mammoth Cave National Park and karst features of the Chester Upland and Pennyroyal Plateau. The workshop featured a late-night field trip into Mammoth Cave with Rickard Toomey and Rick Olsen, NPS. The fifth workshop was held April 26–29, 2011, and was a joint meeting of the USGS KIG and University of Arkansas HydroDays, hosted by the Department of Geosciences at the University of Arkansas in Fayetteville. The workshop featured an outstanding field trip to the unique karst terrain along the Buffalo National River of the southern Ozarks and a keynote presentation on paleokarst in the United States by Art and Peggy Palmer. This sixth and current 2014 KIG workshop is hosted by the National Cave and Karst Research Institute (NCKRI) in Carlsbad, New Mexico, with Director of NCKRI, George Veni, serving as co-chair of the workshop with Eve Kuniansky, USGS. The session planning committee for this sixth workshop includes Van Brahana, USGS retired and University of Arkansas Professor Emeritus; Tom Byl, USGS and Tennessee State University; Zelda Bailey, former Director of NCKRI and retired Director, National Institute of Standards and Technology, Boulder Laboratory, Colorado; Patrick Tucci, USGS retired; and Mike Bradley, Allan Clark, Geoff Delin, Daniel Doctor, James Kaufmann, Eve Kuniansky, Randy Orndorff, Larry Spangler, and Dave Weary of the USGS. The karst hydrology field trip on Thursday will be led by Lewis Land (NCKRI karst hydrologist) and the optional Friday field trip on the geology of Carlsbad Caverns National Park will be led by George Veni. The keynote speaker is Dr. Penelope Boston, Director of Cave and Karst Studies at New Mexico Tech, Socorro, and Academic Director at NCKRI, who will address the future of karst research. Additionally, there is a featured presentation “Irish karst and its management,” by Caoimhe Hickey, The Geological Survey of Ireland, preceding a panel discussion on “Collaboration During Times of Limited Resources.” The extended abstracts of USGS authors were peer reviewed and approved for publication by the U.S. Geological Survey. Articles submitted by university researchers and other federal and state agencies did not go through the formal USGS peer review and approval process, and therefore may not adhere to our editorial standards or stratigraphic nomenclature and is not research conducted or data collected by the USGS. However, all articles had at a minimum of two peer reviews, and all articles were edited for consistency of appearance in the published Proceedings. The use of trade, firm or product names in any article is for descriptive purposes only and does not imply endorsement by the U.S. Government. The USGS, Office of Groundwater, provides technical support for the Karst Interest Group website and public availability of the Proceedings from these workshops, and the USGS Groundwater Resources Program funds the publication costs. Finally, the cover illustration is the work of Ann Tihansky, USGS, used since the first KIG workshop in 2000.

Scientific Investigations Report↗
USGS2020

Groundwater quality and geochemistry of West Virginia’s southern coal fields

Coal mining has been the dominant industry and land use in West Virginia’s southern coal fields since the mid-1800s. Mortality rates for a variety of serious chronic conditions, such as diabetes, heart disease, and some forms of cancer in Appalachian coal mining regions, are higher than in areas lacking substantial coal mining activity within the Appalachian Region or elsewhere in the United States. Causes of the increased mortality and morbidity are not clear, but poor diet, high rates of smoking, socioeconomic factors, and the quality of groundwater used by area residents are all possible contributing factors. This study was conducted by the U.S. Geological Survey in cooperation with the West Virginia Department of Health and Human Resources and the West Virginia Department of Environmental Protection, with grant support from the Centers for Disease Control and Prevention (CDC) to assess the quality of groundwater in southern West Virginia. The data from this assessment of groundwater quality may be used by the CDC and other agencies to potentially investigate the role or lack thereof of groundwater quality with respect to mortality and morbidity rates in the region. The study was conducted in a region where a high density of current or past coal mining combined with a lack of advanced sewage treatment could affect concentrations of commonly occurring constituents plus contaminants, including nitrate, trace metals, major ions, indicator bacteria, radon, hydrogen sulfide, and dissolved hydrocarbons. Because rural residential wells and mine outfalls are considered private sources of water in the region, and are therefore unregulated and unmonitored, water-quality data are sparse. To fill the data gap and assess the groundwater quality in the region, water-quality samples were collected from 60 sites in a 10-county area. The 60 sites sampled included 46 rural residential homeowner wells and 14 mine outfall discharges used for residential supply. For this study, all samples were collected prior to any filtration or other treatments, typically at the pressure tank, and are indicative of total and dissolved constituents in the untreated water. Generally, data for the 60 sites indicate that most waters sampled do not exceed thresholds for most U.S. Environmental Protection Agency (EPA) drinking-water standards and U.S. Geological Survey (USGS) drinking-water screening criteria. However, there were several notable exceptions. Turbidity exceeded the 5-Nephelometric Turbidity Unit (NTU) EPA treatment technique (TT) drinking-water standard in 14 of 60 (23 percent) sites sampled and exceeded the 1-NTU TT standard in 51 of 60 (85 percent) sites sampled. Turbidity is common in many wells in southern West Virginia and may be attributed to iron oxyhydroxide precipitates, sediment carried into the aquifers from the shallow soil zone due to improperly constructed or cased wells or transported to the aquifer in shallow stress-relief fracture zones or through permeable bedding-plane partings. For the sites sampled, 31 of 60 (52 percent) had pH values at, above, or below the upper and lower range of the EPA Secondary Maximum Contaminant Level (SMCL, 6.5–8.5 standard units). Of those 31 sites, 28 (90 percent) were indicative of acidic corrosive water and 3 (10 percent) were indicative of alkaline water. The Langelier Saturation Index (LSI), which is a measure of the corrosivity of the water, was computed for all sites sampled for the study. Eighty-two percent of the sites sampled had waters that were classified as corrosive, based on a LSI less than −0.5. Corrosive water has the potential to leach lead, copper, and other metals from lead, copper, galvanized, or lead-tin soldered connections in water lines. The chloride to sulfate mass ratio also was assessed with the alkalinity to indicate the potential to promote galvanic corrosion (PPGC) of water lines and plumbing fixtures. Only one of the sites (1.7 percent) classified as a corrosive water site, had a PPGC considered high; the remaining sites were classified as having either a moderate (53.3 percent) or low (45 percent) PPGC. Therefore, the type of plumbing systems sampled for this study may be affected by corrosive water, but the potential for leaching trace metals and other constituents from residential plumbing systems containing older galvanized pipes or lead-tin soldered copper pipes is moderate to low. The indicator bacteria total coliform and Escherichia coli ( E. coli ) also were detected in groundwater samples to varying degrees. Total coliforms, which are a broad class of indicator bacteria, are common in groundwater in southern West Virginia and were detected in 39 of the 60 sites (65 percent) sampled. The presence of total coliform bacteria is a potential indicator of surface contamination, due to improperly constructed or cased wells, or infiltration of soil or other surface contaminants into the aquifer or well bore. E. coli bacteria, however, are much more indicative of fecal contamination of groundwater from either human or animal sources, and 14 of the 60 (23 percent) sites sampled had detections of E. coli . Although only a few strains of E. coli are known pathogens, their presence in groundwater may be an indicator of other related pathogens such as viruses and should be regarded as a serious potential issue. Water treatment such as chlorination, ozonation, or ultraviolet light may be appropriate to kill potential pathogenic bacteria or viruses in the source water. Manganese and iron were prevalent contaminants in the groundwater samples collected for this study, with 30 of 60 (50 percent) sites analyzed for manganese and 25 of 60 (42 percent) sites analyzed for iron exceeding the proposed 50- and 300-micrograms per liter (µg/L) SMCL drinking-water standards, respectively, for aesthetic criteria such as taste, odor, or staining of plumbing fixtures. Fourteen of the 60 sites sampled (23 percent) had concentrations of manganese that exceeded the 300-µg/L USGS health-based screening level, and 1 site exceeded the 1,600-µg/L EPA drinking-water equivalent level, which is based on a lifetime exposure level. Sodium is another common constituent in groundwater within the study area. Sodium has an EPA health-based value (HBV) of 20 milligrams per liter (mg/L) for individuals who are on a sodium-restricted diet for blood pressure or other health reasons. Sodium concentrations exceeded the 20-mg/L EPA HBV in 27 of 60 (45 percent) samples. Radon, a naturally occurring carcinogenic radioactive gas known to cause lung cancer, was detected at concentrations at or exceeding the proposed 300-picocuries per liter (pCi/L) EPA Maximum Contaminant Level (MCL) in 12 of the 60 (20 percent) sites sampled. Sites with radon gas concentrations exceeding the 300-pCi/L proposed MCL have the potential for airborne concentrations of radon to exceed the 4-pCi/L indoor air standard. Inhalation of radon can cause lung cancer, and the 4-pCi/L indoor air standard is based on an inhalation standard. Therefore, homeowners whose wells have radon gas concentrations exceeding 300 pCi/L may be advised to have their indoor air tested to determine if indoor air concentrations exceed the 4-pCi/L indoor air standard established by the EPA. Various factors were analyzed statistically and graphically to determine whether they have an influence on groundwater quality within the study area, including topographic setting, well depth, type of mining (surface or underground), type of site (well or mine outfall), and geologic formation. Only geologic formation and the type of site sampled had strong statistical correlations with one or more of the constituents of concern for this study. The overall chemistry of outfalls (mine outfalls) and wells was significantly different, with a much higher dissolved oxygen content in outfalls than in wells. The dissolved oxygen content is the primary component driving the oxidation and reduction of minerals, and the precipitation of minerals that are saturated or super saturated with respect to various cations and anions. Median dissolved oxygen concentrations for the outfalls sampled was 8.75 mg/L, and only 0.4 mg/L for the wells sampled. Median concentrations of sulfate and selenium were much higher in waters from the outfalls sampled, with median concentrations of 73.75 mg/L and 2.35 µg/L, respectively, compared to the wells sampled, which had median concentrations of 18.3 mg/L and less than (<) the 0.05-µg/L method detection limit, respectively. The maximum selenium concentration was for a well, with a concentration of 16.6 µg/L. The geochemical processes that control sulfate and selenium concentrations in groundwater are similar and are the result of the oxidation of sulfide minerals such as pyrite and ferroselite. Iron and manganese concentrations were elevated in most of the wells sampled, with median concentrations of 269.5 and 124.5 µg/L, respectively, but were rarely detected in the outfalls sampled, with median concentrations of < 4.0 and < 0.4 µg/L, respectively. The difference in iron and manganese between wells and outfalls is indicative of the role of dissolved oxygen on processes controlling groundwater chemistry in the region. Three principal geologic formations were assessed for the study, and the overall chemistry for the Pocahontas, New River, and Kanawha Formations varied substantially with respect to several constituents. Concentrations of calcium, magnesium, and total dissolved solids were highest for sites sampled in the Pocahontas Formation, with median concentrations of 41.9, 18.6, and 312 mg/L, respectively. For constituents that are commonly associated with mining activity, the highest concentrations were for sites sampled in the New River Formation, with median concentrations of iron and manganese of 2,450 µg/L and 482 µg/L, respectively, and a median pH of 6.35 standard units. Concentrations of barium also were elevated in samples collected from sites in the New River Formation, with a median barium concentration of 184 µg/L. The source of the barium is not fully known but may be associated with commingling of shallow groundwater with deeper brines or dissolution of the mineral barite. The highest median sulfate concentrations were from sites sampled in the Pocahontas Formation, with a median concentration of 64.0 mg/L. Of the 12 sites at or exceeding the 300-pCi/L proposed drinking-water standard for radon, 8 (67 percent of MCL exceedances) were for sites deriving water from the Kanawha Formation, 3 (25 percent of MCL exceedances) were for sites deriving water from the New River Formation, and only 1 site was for water from the Pocahontas Formation (8 percent of proposed MCL exceedances). Dissolved hydrocarbons, including methane, ethane, propane, propene, n - and i -butane, 1-butene, n - and i -pentane, pentane, 2- and 3-ethyl pentane, hexane, and benzene were analyzed in samples collected from 59 of the 60 sites to assess the potential occurrence and sources of these trace gases in groundwater within the study area. Results of the analysis indicate that most of the gas is of shallow biogenic origin, possibly associated with coal-bed methane, but a subset of samples has a gas signature and a chloride to bromide ratio indicative of potential mixing with deeper thermogenic gases. Only 2 of the 59 (3.3 percent) sites sampled had concentrations of methane gas, which is a highly combustible and explosive gas, exceeding the 10 milligrams per kilogram level of concern established by the U.S. Office of Surface Mining Reclamation and Enforcement. Principal components analysis was used to assess the primary geochemical processes occurring in the aquifers sampled. The first principal component had significant positive loadings for bromide, chloride, silica, ammonia, barium, iron, manganese, and arsenic, and significant negative loadings for dissolved oxygen, potassium, nitrate, and uranium, and reflects reduction and oxidation (redox) processes occurring in deeper anoxic groundwater or shallow oxic groundwater. The strong positive loadings for iron, manganese, barium, and arsenic are correlated with reducing conditions often found deeper in the aquifer. More oxic water is correlated with oxidation of nitrogen species to nitrate and environmental mobilization of uranium and sulfate in shallow wells and mine outfalls.

West Virginia↗