Geology topics

Martha L. Jagucki

Publications and source records attributed to Martha L. Jagucki.

13 recordsLinked to original sources

USGS2018

Baseline water quality of an area undergoing shale-gas development in the Muskingum River watershed, Ohio, 2015–16

In 2015–16, the U.S. Geological Survey, in cooperation with the Muskingum Watershed Conservancy District, led a study to assess baseline (2015–16) surface-water quality in six lake drainage basins within the Muskingum River watershed that are in the early years of shale-gas development. In 2015, 9 of the 10 most active counties in Ohio for oil and gas development were wholly or partially within the Muskingum River watershed. In addition to shale gas development, the area has a history of conventional oil and gas development and coal mining. In all, 30 surface-water sites were sampled: 20 in tributaries flowing to the lakes, 4 in lakes themselves, and 6 downstream of the lakes. At each of the 30 sites, 6 samples were collected to characterize surface-water chemistry throughout a range of hydrologic conditions. The sampling generally occurred during low flows (periods of greater groundwater contribution) rather than during runoff events (periods of high stream stage). Trilinear diagrams of major ion chemistry revealed three main types of water in the study area―sulfate-dominated waters, bicarbonate-dominated waters, and waters with mixed bicarbonate and chloride anions. Most sites produced samples of bicarbonate-dominated water, and 11 sites produced samples with sulfate-type waters. Mixed bicarbonate and chloride waters were found in samples from two of the six lake drainage basins studied. The baseline (2015–16) assessment of surface-water quality in the study area indicated that few water-chemistry constituents and properties occurred at concentrations or levels that would adversely affect aquatic organisms. Chemical-specific, aquatic life use criteria were not met in only three instances: two were for total dissolved solids at sites likely impacted by coal mining in their drainage basins (hereafter referred to as “mine-impacted sites”), and one was for dissolved oxygen. Mine drainage from historical coal mining in the region likely affected the quality of about one-third of the streams sampled. To simplify interpretation of water-chemistry results, 11 sites with sulfate-type water were identified as mine-impacted sites based on water-quality criteria established by Ohio Department of Natural Resources, Division of Mineral Resources Management, and separated out for subsequent statistical analysis. Concentrations or levels of bicarbonate, boron, calcium, carbonate, total dissolved solids, fluoride, magnesium, lithium, pH, potassium, sodium, specific conductance, strontium, sulfate, and suspended sediment in water were higher (significance level of 0.05) at mine-impacted stream sites than at non-mine-impacted stream sites. An accidental release of oil- and gas-related brines could increase salinity (sodium and chloride), the concentration of total dissolved solids in shallow groundwater and streams, and specific conductance. For this study, chloride concentrations in the study area ranged from 2.12 to 76.1 milligrams per liter. Sources of chloride in water samples were evaluated using binary mixing curves and ratios of chloride to bromide. These ratios indicated that 13 samples from 3 sites in the drainage basin that contained the highest density of conventional oil and gas wells in the study, as well as 4 samples collected from other drainage basins, likely contained a component of brine. Concentrations or levels of barium, bromide, chloride, iron, lithium, manganese, and sodium were significantly higher (alpha = 0.05) in samples with a component of brine than in samples without a component of brine. Benzene, toluene, ethylbenzene and xylene (BTEX), compounds that occur naturally in crude oil, made up 24 of the 45 detections (53 percent) of volatile organic compounds in the study area. The BTEX detections were not associated with sites containing a component of brine. The only volatile organic compound detected in any of the 17 samples that contained a component of brine was acetone, detected in 3 (18 percent) of these samples and in 11 percent of samples not containing a component of brine. Considering that BTEX are gasoline hydrocarbons and that most of the detections occurred during warmer months in and around the lakes, the BTEX detections likely are associated with increases in outdoor activities such as automobile and boating traffic. Radium-226 and radium-228 were included in the list of analytes for this study because production water from shale-gas drilling can contain these naturally occurring radioactive materials. Concentrations of radium-226 exceeded background levels in only two surface-water samples. Concentrations of radium-228 exceeded background levels in one surface-water sample. A brine signature potentially indicative of oil and gas contamination was detected in samples collected at two sites that contained active or plugged waste injection wells, or both. Results from the study indicated significant differences in the median concentrations of bromide, chloride, lithium, manganese, sodium, and total dissolved nitrogen between sites with and without injection wells in their drainage areas. Median concentrations of bromide, chloride, lithium, and sodium, which are common oil- and gas-related contaminants, were higher at sites with injection wells in their drainage areas compared to sites without injection wells. Historical (1960s, 1970s, and 1980s) chloride concentrations and streamflow data at or near five of the six sampling sites downstream from each lake dam were compared to current (2015–16) values. An analysis of covariance was done to test the effects of streamflow, time (decade), and the combined effects (cross product) of streamflow and time on chloride concentrations. Those analyses indicated that streamflow was not significant in explaining the variation in chloride concentration, likely because streamflow in those locations is controlled by dam operations; therefore, association between runoff-generating events and streamflow is less direct than in unregulated streams. From the 1980s to the study period (2015–16), data for three of the five lakes indicated an increase in chloride concentrations. The comparison of historical and current (2015–16) study data from samples collected at another lake indicated that chloride concentrations increased from the 1960s to the 1970s, but concentrations in the 1970s and 2015–16 were similar even though 13 samples from this lake drainage basin were classified as having a component of brine. Median chloride concentrations for the fifth lake, however, seemed to decrease from the 1980s to 2015–16.

Ohio↗

USGS2015

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

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

Geauga County↗

USGS2013

The quality of our Nation's waters: factors affecting public-supply-well vulnerability to contamination: understanding observed water quality and anticipating future water quality

As part of the U.S. Geological Survey National Water-Quality Assessment (NAWQA) Program, a study was conducted from 2001 to 2011 to shed light on factors that affect the vulnerability of water from public-supply wells to contamination (referred to hereafter as “public-supply-well vulnerability”). The study was designed as a follow-up to earlier NAWQA studies that found mixtures of contaminants at low concentrations in groundwater near the water table in urban areas across the Nation and, less frequently, in deeper groundwater typically used for public supply. Beside the factors affecting public-supply-well vulnerability to contamination, this circular describes measures that can be used to determine which factor (or factors) plays a dominant role at an individual public-supply well. Case-study examples are used throughout to show how such information can be used to improve water quality. In general, the vulnerability of the water from public-supply wells to contamination is a function of contaminant input within the area that contributes water to a well, the mobility and persistence of a contaminant once released to the groundwater, and the ease of groundwater and contaminant movement from the point of recharge to the open interval of a well. The following measures described in this circular are particularly useful for indicating which contaminants in an aquifer might reach an individual public-supply well and when, how, and at what concentration they might arrive: * Sources of recharge—Information on the sources of recharge for a well provides insight into contaminants that might enter the aquifer with the recharge water and potentially reach the well. * Geochemical conditions—Information on the geochemical conditions encountered by groundwater traveling to a well provides insight into contaminants that might persist in the water all the way to the well. * Groundwater-age mixtures—Information on the ages of the different waters that mix in a well provides insight into the time lag between contaminant input at the water table and contaminant arrival at the well. It also provides insight into the potential for in-well dilution of contaminated water by unaffected groundwater of a different age that simultaneously enters the well. Preferential flow pathways—pathways that provide little resistance to flow—can influence how all other factors affect public-supply-well vulnerability to contamination. For example, preferential flow pathways can influence whether a contaminant source is physically linked to a well, whether contaminant concentrations are substantially altered before contaminated groundwater reaches a well, and whether contaminated groundwater can arrive at a well within a timeframe of concern to the well owner. Methods for recognizing the influence of preferential flow pathways on the quality of water from a public-supply well are presented in this circular and can provide opportunities to prevent or mitigate the deterioration of a water supply. Knowing what water-quality variables to measure, what spatial and temporal scales on which to measure them, and how to interpret the resulting data makes it possible for samples from public-supply wells to provide a broad window into a well’s past and present water quality—and possibly future water quality. Such insight can enable resource managers to prioritize actions for sustaining a high-quality groundwater source of drinking water.

Circular↗

USGS2012

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

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

New Mexico↗

USGS2011

Assessing the vulnerability of public-supply wells to contamination—Edwards aquifer near San Antonio, Texas

This fact sheet highlights findings from the vulnerability study of a public-supply well field in San Antonio, Texas. The well field consists of six production wells that tap the Edwards aquifer. Typically, one or two wells are pumped at a time, yielding an average total of 20-21 million gallons per day. Water samples were collected from public-supply wells in the well field and from monitoring wells installed along general directions of flow to the well field. Samples from the well field contained some constituents of concern for drinking-water quality, including nitrate; the pesticide compounds atrazine, deethylatrazine, and simazine; and the volatile organic compounds tetrachloroethene (also called perchloroethene, or PCE), chloroform, bromoform, and dibromochloromethane. These constituents were detected in untreated water at concentrations much less than established drinking-water standards, where such standards exist. Overall, the study findings point to four primary factors that affect the movement and fate of contaminants and the vulnerability of the public-supply well field in San Antonio, Texas: (1) groundwater age (how long ago water entered, or recharged, the aquifer), (2) fast pathways for flow of groundwater through features formed or enlarged by dissolution of bedrock, (3) recharge characteristics of the aquifer, and (4) natural geochemical processes within the aquifer. A computer-model simulation of groundwater flow and transport was used to estimate the traveltime (or age) of water particles entering public-supply well W4 in the well field. Modeled findings show that almost half of the water reaching the public-supply well is less than 2 years old. Such a large percentage of very young water indicates that (1) contaminants entering the aquifer may be transported rapidly to the well, (2) there is limited time for chemical reactions to occur in the aquifer that may attenuate contaminants, and (3) should recharge water become contaminated with pathogenic microorganisms (which have limited survival times in aquifers), the microorganisms may be able to persist to the well. Features formed or enlarged by dissolution of bedrock allow most of the water reaching the well field to travel rapidly from the recharge zone to the supply wells along fast pathways rather than through the aquifer matrix. Supporting evidence includes (1) geophysical logging and flowmeter measurements in public-supply well W4 and in nearby monitoring wells showing that most of the flow volume into and out of the wells occurs in three horizontal zones, thought to be dissolution-enlarged bedding planes; and (2) fluctuations in groundwater chemistry that can be correlated to individual precipitation events. Analysis of water samples collected from shallow, intermediate, and deep zones of the Edwards aquifer at public-supply well W4 and from nearby monitoring wells reveal that water in the vicinity of the selected well field is notably well mixed throughout the sampled thickness of the Edwards aquifer, showing little of the chemical variation with depth that is commonly seen in other aquifers. Contaminants were found at all depths, and they did not enter the well through a specific horizon. The well-mixed nature of the Edwards aquifer is caused by the recharge characteristics of the area combined with fast flow paths through karst features. Constituents of concern in the Edwards aquifer for the long-term sustainability of the groundwater resource include the nutrient nitrate and anthropogenic contaminants such as atrazine, PCE, and chloroform. A scenario of hypothetical contaminant loading in the aquifer recharge zone was evaluated by using results from groundwater-flow-model particle tracking to assess the response of the aquifer to potential contamination. Results indicate that the concentrations at public-supply well W4 would begin to respond to contaminant loading in the recharge zone within 1 year because of short traveltimes through fast flow paths. Within 10 years, contaminant concentrations in the public-supply well would be equal to 90 percent of the input concentration for a contaminant (such as nitrate) that does not degrade in the oxic conditions of the Edwards aquifer.

Texas↗

USGS2010

Assessing the vulnerability of public-supply wells to contamination: Glacial aquifer system in Woodbury, Connecticut

This fact sheet highlights findings from the vulnerability study of a public-supply well in Woodbury, Connecticut. The well typically produces water at the rate of 72 gallons per minute from the glacial aquifer system in the Pomperaug River Basin. Water samples were collected at the public-supply well and at monitoring wells installed in or near the simulated zone of contribution to the supply well. Samples of untreated water from the public-supply wellhead contained several types of undesirable constituents, including 11 volatile organic compounds (VOCs), nitrate, pesticides, uranium, and radon. Most of these constituents were detected at concentrations below drinking-water standards, where such standards exist. Only concentrations of the VOC trichlorethylene exceeded the Maximum Contaminant Level (MCL) of 5 micrograms per liter (ug/L) established by U.S. Environmental Protection Agency for drinking water. Radon concentrations exceeded a proposed-but not finalized-MCL of 300 picocuries per liter (pCi/L). Overall, the study findings point to four main factors that affect the movement and fate of contaminants and the vulnerability of the public-supply well in Woodbury: (1) groundwater age (how long ago water entered, or recharged, the aquifer); (2) the percentage of recharge received through urban areas; (3) the percentage of recharge received through dry wells and their proximity to the public-supply well; and (4) natural geochemical processes occurring within the aquifer system; that is, processes that affect the amounts and distribution of chemical substances in aquifer sediments and groundwater. A computer-model simulation of groundwater flow to the public-supply well was used to estimate the age of water particles entering the well along the length of the well screen. About 90 percent of the simulated flow to the well consists of water that entered the aquifer 9 or fewer years ago. Such young water is vulnerable to contaminants resulting from human activities, as indicated by the solvents, fuel components, road salt, and septic-system leachate that were detected in the glacial aquifer system during the current study. Age-dating combined with chemical modeling suggests that less than 2 percent of water produced by the public-supply well is water from the deep bedrock that is "old" (water that recharged, or entered, the aquifer before 1952). Such a small percentage of old groundwater entering the public-supply well offers little potential for dilution of young waters containing contaminants from human activities. Shallow groundwater that originated as recharge through urban areas generally had higher median concentrations and more detections of volatile organic compounds (VOCs) than did groundwater from the deep glacial deposits or fractured bedrock that originated mainly as recharge through agricultural and undeveloped land. Shallow groundwater was also found to be affected by road salt and septic-system leachate. A chemical mixing model indicates that up to 15 percent of nitrate in water from the supply well is likely from septic-system leachate. The Connecticut Department of Public Health has identified several potential sources of contamination in the commercial area of Woodbury (several light industrial or commercial properties where hazardous materials and petroleum products are used and stored). To reduce stormwater runoff in the commercial area, water from the parking lots and pavement is channeled into dry wells-drains that shunt water directly into the aquifer system, bypassing the soil and unsaturated zones. A computer-model simulation of groundwater flow indicates that approximately 16 percent of the water produced by the public-supply well is derived from runoff captured by these drains. Traveltime for water from the dry wells to the public-supply well ranges from about 1.5 to less than 4 years. Dry wells have the potential to enhance contaminant movement to the supply well, suggesting that stormwater-control methods cannot be considered separately from groundwater quality—they are linked. Water-quality protection in this setting depends on the entire community. If residents and businesses take steps to reduce input of manmade contaminants to groundwater, a positive effect on quality of the supply-well water might begin to be seen in less than 10 years, owing to the short residence time of water in the aquifer.

Connecticut↗

USGS2009

Assessing the Vulnerability of Public-Supply Wells to Contamination: Central Valley Aquifer System near Modesto, California

This fact sheet highlights findings from the vulnerability study of a public-supply well in Modesto, California. The well selected for study pumps on average about 1,600 gallons per minute from the Central Valley aquifer system during peak summer demand. Water samples were collected at the public-supply well and at monitoring wells installed in the Modesto vicinity. Samples from the public-supply wellhead contained the undesirable constituents uranium, nitrate, arsenic, volatile organic compounds (VOCs), and pesticides, although none were present at concentrations exceeding drinking-water standards. Of these contaminants, uranium and nitrate pose the most significant water-quality risk to the public-supply well because human activities have caused concentrations in groundwater to increase over time. Overall, study findings point to four primary factors that affect the movement and (or) fate of contaminants and the vulnerability of the public-supply well in Modesto: (1) groundwater age (how long ago water entered, or recharged, the aquifer); (2) irrigation and agricultural and municipal pumping that drives contaminants downward into the primary production zone of the aquifer; (3) short-circuiting of contaminated water down the public-supply well during the low-pumping season; and (4) natural geochemical conditions of the aquifer. A local-scale computer model of groundwater flow and transport to the public-supply well was constructed to simulate long-term nitrate and uranium concentrations reaching the well. With regard to nitrate, two conflicting processes influence concentrations in the area contributing recharge to the well: (1) Beneath land that is being farmed or has recently been farmed (within the last 10 to 20 years), downward-moving irrigation waters contain elevated nitrate concentrations; yet (2) the proportion of agricultural land has decreased and the proportion of urban land has increased since 1960. Urban land use is associated with low nitrate concentrations in recharge (3.1 milligrams per liter). Results of the simulation indicate that nitrate concentrations in the public-supply well peaked in the late 1990s and will decrease slightly from the current level of 5.5 milligrams per liter during the next 100 years. A lag time of 20 to 30 years between peak nitrate concentrations in recharge and peak concentrations in the well is the result of the wide range of ages of water reaching the public-supply well combined with changing nitrogen input concentrations over time. As for uranium, simulation results show that concentrations in the public-supply well will likely approach the Maximum Contaminant Level of 30 micrograms per liter over time; however, it will take more than 100 years because of the contribution of old water at depth in the public-supply well that dilutes uranium concentrations in shallower water entering the well. This allows time to evaluate management strategies and to alter well-construction or pumping strategies to prevent uranium concentrations from exceeding the drinking-water standard.

Fact Sheet↗

USGS2009

Assessing the vulnerability of public-supply wells to contamination: Floridan aquifer system near Tampa, Florida

This fact sheet highlights findings from the vulnerability study of a public-supply well in Temple Terrace, Florida, northeast of Tampa. The well selected for study typically produces water at the rate of 700 gallons per minute from the Upper Floridan aquifer. Water samples were collected at the public-supply well and at monitoring wells installed in or near the simulated zone of contribution to the supply well. Samples of untreated water from the public-supply wellhead contained the undesirable constituents nitrate, arsenic, uranium, radon-222, volatile organic compounds (VOCs), and pesticides, although all were detected at concentrations less than established drinking-water standards, where such standards exist. Overall, study findings point to four primary factors that affect the movement and fate of contaminants and the vulnerability of the public-supply well in Temple Terrace: (1) groundwater age (how long ago water entered, or recharged, the aquifer); (2) short-circuiting of contaminated water through sinkholes; (3) natural geochemical processes within the aquifer; and (4) pumping stress. Although the public-supply well is completed in the Upper Floridan aquifer, it produces water with concentrations of nitrate, VOCs, and the natural contaminant radon that are intermediate between the typical composition of water from the Upper Floridan aquifer and that of the overlying surficial aquifer system. Mixing calculations show that the water produced by the public-supply well could consist of upwards of 50 percent water from the surficial aquifer system mixed with water from the Upper Floridan aquifer. Anthropogenically affected water from the surficial aquifer system travels rapidly to depth through sinkholes that must be directly connected to the cavernous zone intersected by the public-supply well (and several other production wells in the region). Such solution features serve as fast pathways to the well and circumvent the natural attenuation of nitrate and radon that occurs when water from the surficial aquifer flows downward through the confining unit and then through the Upper Floridan aquifer matrix. Roughly 50 percent of the simulated flow to the public-supply well consists of water less than about 10 years old, thus making the well vulnerable to contamination from human activities. Sampling at various depths in the public-supply well during pumping and nonpumping conditions showed that water entering the well from the cavernous zone had much higher arsenic concentrations during pumping conditions (18.9 ug/L) than during nonpumping conditions (4.2 ug/L). This implies that movement of arsenic to the public-supply well from the cavernous zone is enhanced by pumping. One possible explanation is that pumping increases the movement of water with elevated dissolved oxygen content through the cavernous zone, which causes dissolution of arsenic associated with pyrite. All public-supply wells in the area may not have the same level of vulnerability as the well studied - many of the public-supply wells in the region have lower pumping rates and longer open intervals that may draw in a larger proportion of old water that predates anthropogenic influences. Determining the similarity of water produced by various public-supply wells in the region to that of the surficial aquifer system is one measure of well vulnerability that could be used to prioritize monitoring and land-use planning efforts to protect the most vulnerable wells.

Florida↗

USGS2008

Assessing the vulnerability of public-supply wells to contamination—High Plains Aquifer near York, Nebraska

The U.S. Geological Survey's National Water-Quality Assessment (NAWQA) Program found, in studies from 1991 to 2001, low levels of mixtures of contaminants in ground water near the water table in urban areas across the Nation. Although contaminants were detected less frequently in deeper ground water typically developed for public supply the proximity of contaminant mixtures to underlying public-water-supply sources prompted the NAWQA Program to begin, in 2001, an intensive study to assess the vulnerability of public-supply wells to contamination. As part of this study, the pathways and processes by which contaminants reach public-supply wells in nine aquifer systems across the country are being investigated. In addition to studying the processes that occur below land surface—whereby contaminants are mobilized or attenuated—scientists are also investigating how human activities can affect the vulnerability of public-supply wells to contamination. This fact sheet highlights findings from two reports on the vulnerability study of a single, representative public-supply well in York, Nebraska. The selected high-capacity well typically produces more than 720,000 gallons per day from the upper confined aquifer of the High Plains aquifer. A possible source of contamination to the well is intensive, irrigated agriculture, which can sometimes result in elevated concentrations of nitrate and pesticides in ground water. In addition, a sampling of the selected public-supply well by the USGS in 2002 found low concentrations of the solvents trichloroethylene (TCE), tetrachloroethylene (PCE), and their degradation products, which may be linked to historical chemical use in urban and residential areas of York. Uranium and arsenic (which occur naturally in the sediments that make up the aquifers in the area) also were detected in 2002 at concentrations less than drinking-water standards but still of concern. Overall, the current NAWQA study found that three primary factors affect the movement and fate of contaminants and the vulnerability of the public-supply well in York: (1) timing of water entry (recharge) to the aquifer, (2) short-circuiting of natural flow paths through inactive wells, and (3) natural geochemical conditions of the aquifer. Study findings are intended to help water managers, drinking-water suppliers, policymakers, and scientists to better understand how and why contamination of public-supply wells occurs and whether water quality may improve or degrade. Additionally, study findings may be used to evaluate various pumping, resource-development, and land-management scenarios.

Fact Sheet↗

USGS2006

Simulation of Streamflow and Water Quality to Determine Fecal Coliform and Nitrate Concentrations and Loads in the Mad River Basin, Ohio

The Hydrological Simulation Program Fortran (HSPF) was used to simulate the concentrations and loads of fecal coliform and nitrate for streams in the Mad River Basin in west-central Ohio during the period 1999 through 2003. The Mad River Basin was divided into subbasins that were defined either by the 14-digit Hydrologic Unit (HU) boundaries or by streamflow-gaging-station locations used in the model. Model calibration and simulation processes required the formation of nine meteorologic zones to input meteorologic time-series data and water-quality data. Sources of fecal coliform and nitrate from wastewater-treatment discharges and combined sewer overflow discharges (CSOs) within the City of Springfield were point sources simulated in the model. Failing septic systems and cattle with direct access to streams were nonpoint sources included in the study but treated in the model as point sources. Other nonpoint sources were addressed by adjusting interflow and ground-water concentrations in the subsurface and maximum storage capacities and accumulation rates of the simulated constituents on the land surface for each meteorologic zone. Simulation results from the calibrated model show that several HUs exceeded the water-quality standard of 1,000 colony-forming units per 100 mL for fecal coliform based on the maximum 30-day geometric mean. Most HUs with high fecal coliform counts were within or downstream from the City of Springfield. No water-quality standard has been set for instream nitrate concentrations; however, the Ohio Environmental Protection Agency (Ohio EPA) considered a concentration of 5 mg/L or greater to be of concern. Simulation results indicate that several HUs in the agricultural areas of the basin exceeded this level. The calibrated model was modified to create scenarios that simulated loads of fecal coliform and nitrate that were either reduced or eliminated from selected sources. The revised models included the elimination of failing septic systems, elimination of direct access of cattle to streams, decrease in fecal coliform loads from the CSOs and selected wastewater-treatment facilities, and decrease in nitrate loads from land surfaces. The fecal coliform source-reduction model decreased the fecal coliform concentrations below a target concentration of 1,000 colonies per 100 milliliters for all HU outlets and decreased the load at the mouth of the Mad River by 73 percent. The nitrate source-reduction model decreased some HU mean concentrations to 5 milligrams per liter or less and decreased the load at the mouth of the Mad River by 52 percent. Other reduction scenarios may be run by Ohio EPA with the intent of identifying a management strategy that will attain a target concentration for the Mad River Basin.

Scientific Investigations Report↗

USGS2001

Ground-water quality in Geauga County, Ohio — Review of previous studies, status in 1999, and comparison of 1986 and 1999 data

Most residents in Geauga County, Ohio, rely on ground water as their primary source of drinking water. With population growing at a steady rate, the possibility that human activity will affect ground-water quality becomes considerable. This report presents the results of a study by the U.S. Geological Survey (USGS), in cooperation with the Geauga County Planning Commission and Board of County Commissioners, to provide a brief synopsis of work previously done within the county, to assess the present (1999) ground-water quality, and to determine any changes in groundwater quality between 1986 and 1999. Previous studies of ground-water quality in the county have consistently reported that manganese and iron concentrations in ground water in Geauga County often exceed the U.S. Environmental Protection Agency (USEPA) Secondary Maximum Contaminant Level (SMCL). Road salt and, less commonly, oil-field brines and volatile organic compounds (VOCs) have been found in ground water at isolated locations. Nitrate has not been detected above the USEPA Maximum Contaminant Level (MCL) of 10 milligrams per liter as N; however, nitrate has been found in some locations at levels that may indicate the effects of fertilizer application or effluent from septic systems. Between June 7 and July 1, 1999, USGS personnel collected a total of 31 water-quality samples from wells completed in glacial deposits, the Pottsville Formation, the Cuyahoga Group, and the Berea Sandstone. All samples were analyzed for VOCs, sulfide, dissolved organic carbon, major ions, trace elements, alkalinity, total coliforms, and Escherichia coli bacteria. Fourteen of the samples also were analyzed for tritium. Water-quality data were used to determine (1) suitability of water for drinking, (2) age of ground water, (3) stratigraphic variation in water quality, (4) controls on water quality, and (5) temporal variation in water quality. Water from 16 of the 31 samples exceeded the Geauga County General Health District’s standard of 0 colonies of total coliform bacteria per 100 milliliters of water. Esthetically based SMCLs were exceeded in the indicated number of wells for pH (8), sulfate (1), dissolved solids (3), iron (19), and manganese (18). Hydrogen sulfide was detected at or above the detection limit of 0.01 milligram per liter in 17 of the 31 water samples. A range of water types was found among and within the four principal stratigraphic units. The waters can be categorized in three groups based on predominant anion type: bicarbonatetype waters, chloride-type waters, and sulfatetype waters. Chloride-to-bromide ratio analyses indicate that water from 8 of the 31 wells is in some way affected by human activity. Five other samples were in a chloride-to-bromide ratio range that could indicate possible effects of human activity. Ground-water-quality data from the current study were compared to data collected in 1986. Statistical analyses of data from the 16 wells that were sampled in both years did not indicate any significant changes that could be attributed to human activity.

Ohio↗

USGS1995

Hydrogeology and water quality at the management systems evaluation area near Piketon, Ohio

This report presents the results of a study by the U.S. Geological Survey, The Ohio State University, and the U.S. Department of Agriculture to describe the hydrology, water quality, and geochemical factors controlling water quality at the Ohio Management Systems Evaluation Area (MSEA). The Ohio MSEA is located on a 650-acre farm in the Scioto River Valley in Pike County, south-central Ohio. The farm is underlain by an incised bedrock valley filled with about 70 feet of sand and gravel outwash deposits that are covered by a veneer of silty clay alluvium and silty loam and sandy loam soils. Outwash sediment are composed predominantly of dolomite, quartz, and calcite, and have a median organic carbon concentration of 0.39 weight percent. Horizontal hydraulic conductivity of the sediment based on results of multiple-well aquifer tests ranges from 400 to 560 feet per day. Ground-water flow is from east to west-southwest at an average velocity of 1.5 to 2.5 feet per day. Ground water and surface water at the site are highly interconnected. Big Beaver Creek recharges the outwash aquifer along the eastern edge of the study area, and ground water discharges to the Scioto River at the western edge of the study area. High-stage events on the Scioto River cause frequent flow reversals in the aquifer that allow streamwater to travel a maximum observed distance of 190 feet inland. A zone of oxidizing waters (characterized by high dissolved oxygen concentration and Eh) is found in shallow ground water for several hundred feet adjacent to Big Beaver Creek and the Scioto River. This zone of oxidizing ground water is caused by the periodic inflow of surface waters to the aquifer. A ground-water budget for the study area indicates that the aquifer received 17.7 inches of recharge during water year 1992; of this amount, 72 percent originated as infiltrating precipitation, 28 percent as infiltration of surface water from Big Beaver Creek, and 0.2 percent as leakage from bedrock. Areal variation in water quality is caused by areal differences in the relative importance of these three recharge sources. The effects of bedrock leakage are evident only in the northeast corner of the study area. Here, deep outwash waters are transitional in composition between the calcium magnesium bicarbonate waters found elsewhere in the outwash aquifer and the calcium sodium chloride waters of the bedrock aquifer. Mixing calculations indicate that these deep outwash waters are composed of as much as 26 percent bedrock water. In the southern part of the MSEA, ground water is diluted by surface water from Big Beaver Creek as it recharges the aquifer through a sand and gravel streambed. At the northeast corner of the MSEA, however, Big Beaver Creek flows across a shale streambed through which no infiltration occurs. Redox reactions in the outwash aquifer control variations in aquifer chemistry with depth. From the water table to about 40 feet below land surface, oxidizing conditions are characterized by the presence of dissolved oxygen and nitrates in ground water, Eh greater than 200 millivolts, ferrihydrite coatings on sediment grains, and the absence of dissolved iron and manganese. From about 40 feet below land surface to the base of the aquifer, reducing conditions are characterized by dissolved oxygen concentrations less than 2 mg/L, Eh less than 200 millivolts, and the presence of dissolved iron and manganese. Denitrification in the reducing zone naturally remediates anthropogenic nitrate contamination of the aquifer while oxidizing pyrite in the aquifer sediment.

Ohio↗

USGS1995

Ground-water levels and directions of flow in Geauga County, Ohio, September 1994, and changes in ground-water levels, 1986-94

This report presents the results of a study by the U.S. Geological Survey, in cooperation with the Geauga County Planning Commission and Board of County Commissioners, to determine directions of ground-water flow and to assess differences from 1986 to 1994 in groundwater levels in the glacial deposits and Pottsville Formation, Cuyahoga Group, and the Berea Sandstone. Water levels were measured in 219 wells in Geauga County, Ohio, in September 1994. Water levels measured in January and February 1986 in 88 of the 219 wells were used for comparison. Water-level maps constructed from measurements made in September 1994 show that ground-water levels in the Pottsville Formation and the glacial deposits generally correspond to the land-surface configuration and that ground water flows from the uplands to adjacent streams and buried valleys. Ground-water flow in the Cuyahoga Group is generally downward from the Pottsville Formation to the Berea Sandstone. Directions of ground-water flow in the Berea Sandstone are toward outcrop areas at the north and east edges of Geauga County and toward subcrops beneath buried glacial valley deposits in Chardon, Chester, Munson, and Russell Townships and along the west edge of the county. A comparison of water level measurements in 1986 and 1994 indicates that water levels declined in 70 percent of the measured wells and increased in 30 percent. The change in water levels from 1986 to 1994 ranged from an increase of 13.58 feet to a decrease of 29.25 feet. Thirty percent of all water-level changes were less than 1 foot in magnitude. In nearly 80 percent of the wells, water-level changes were within the range of plus or minus 5 feet. Among the wells for which two or more historical measurements were available, the 1994 water levels in 54 percent were outside the range of water-levels observed in previous studies (only 24 percent were greater than 1 foot outside of the previously-observed range). Water-level declines of greater than 10 feet were primarily in the Cuyahoga Group and Berea Sandstone. Some factors considered in the analysis of the differences in water levels in 1986 and 1994 were changes in water use, population, and the amount of available recharge. Water level differences could not be correlated to population changes between the 1980 and 1990 censuses. A decrease in the available recharge from 1986 to 1994 may be part of the cause for the decrease in water levels observed in two-thirds of the wells in and adjacent to Geauga County. Effects of withdrawal rates due to population increase on water levels, if present, are overshadowed by the effects of annual variations in precipitation.

Ohio↗