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At least 1,711 records · Page 95Linked to original sources
USGS2000

Methodology for applying monitored natural attenuation to petroleum hydrocarbon-contaminated ground-water systems with examples from South Carolina

Natural attenuation processes such as dispersion, advection, and biogradation serve to decrease concentrations of disssolved contaminants as they are transported in all ground-water systems. However, the efficiency of these natural attenuation processes and the degree to which they help attain remediation goals, varies considerably from site to site. This report provides a methodology for quantifying various natural attenuation mechanisms. This methodology incorporates information on (1) concentrations of contaminants in space and/or time; (2) ambient reduction/oxidation (redox) conditions; (3) rates and directions of ground-water flow; (4) rates of contaminant biodegradation; and (5) demographic considerations, such as the presence of nearby receptor exposure points or property boundaries. This document outlines the hydrologic, geochemical, and biologic data needed to assess the efficiency of natural attenuation, provides a screening tool for making preliminary assessments, and provides examples of how to determine when natural attenuation can be a useful component of site remediation at leaking underground storage tank sites. At a site in the Piedmont Physiographic Province (Laurens, South Carolina), hydrologic and water-chemistry data indicate that the natural attenuation capacity for benzene is approximately 5 percent per foot of flowpath. As a result, benzene concentrations would decrease from about 28,000 micrograms per liter in ground water at the source area to less than 5 micrograms per liter 200 feet downgradient and prior to discharging to a stream. Because of this rapid attenuation, contaminants do not presently impact the stream downgradient of the site. In contrast, at a site in the coastal Plain Physiographic Province (Charleston, South Carolina), hydrologic and water-chemistry data indicate that, even thought the site has a substantial natural attenuation capacity, it may not be sufficient to fully protect a nearby point of ground-water discharge. These two sites illustrate how the efficiency of natural attenuation processes acting on petroleum hydrocarbons can be systematically evaluated using hydrologic, geochemical, and microbiologic methods. These methods, in turn, can be used to assess the role that the natural attenuation of petroleum hydrocarbons can play in achieving overall site remediation.

South Carolina↗
USGS2000

Probability of detecting atrazine/desethyl-atrazine and elevated concentrations of nitrate plus nitrate as nitrogen in ground water in the Idaho part of the western Snake River Plain

As ground water continues to provide an ever-growing proportion of Idaho?s drinking water, concerns about the quality of that resource are increasing. Pesticides (most commonly, atrazine/desethyl-atrazine, hereafter referred to as atrazine) and nitrite plus nitrate as nitrogen (hereafter referred to as nitrate) have been detected in many aquifers in the State. To provide a sound hydrogeologic basis for atrazine and nitrate management in southern Idaho—the largest region of land and water use in the State—the U.S. Geological Survey produced maps showing the probability of detecting these contaminants in ground water in the upper Snake River Basin (published in a 1998 report) and the western Snake River Plain (published in this report). The atrazine probability map for the western Snake River Plain was constructed by overlaying ground-water quality data with hydrogeologic and anthropogenic data in a geographic information system (GIS). A data set was produced in which each well had corresponding information on land use, geology, precipitation, soil characteristics, regional depth to ground water, well depth, water level, and atrazine use. These data were analyzed by logistic regression using a statistical software package. Several preliminary multivariate models were developed and those that best predicted the detection of atrazine were selected. The multivariate models then were entered into a GIS and the probability maps were produced. Land use, precipitation, soil hydrologic group, and well depth were significantly correlated with atrazine detections in the western Snake River Plain. These variables also were important in the 1998 probability study of the upper Snake River Basin. The effectiveness of the probability models for atrazine might be improved if more detailed data were available for atrazine application. A preliminary atrazine probability map for the entire Snake River Plain in Idaho, based on a data set representing that region, also was produced. In areas where this map overlaps the 1998 map of the upper Snake River Basin, the two maps show broadly similar probabilities of detecting atrazine. Logistic regression also was used to develop a preliminary statistical model that predicts the probability of detecting elevated nitrate in the western Snake River Plain. A nitrate probability map was produced from this model. Results showed that elevated nitrate concentrations were correlated with land use, soil organic content, well depth, and water level. Detailed information on nitrate input, specifically fertilizer application, might have improved the effectiveness of this model.

Idaho↗
USGS2000

Documentation of a computer program to simulate lake-aquifer interaction using the MODFLOW ground water flow model and the MOC3D solute-transport model

Heads and flow patterns in surficial aquifers can be strongly influenced by the presence of stationary surface-water bodies (lakes) that are in direct contact, vertically and laterally, with the aquifer. Conversely, lake stages can be significantly affected by the volume of water that seeps through the lakebed that separates the lake from the aquifer. For these reasons, a set of computer subroutines called the Lake Package (LAK3) was developed to represent lake/aquifer interaction in numerical simulations using the U.S. Geological Survey three-dimensional, finite-difference, modular ground-water flow model MODFLOW and the U.S. Geological Survey three-dimensional method-of-characteristics solute-transport model MOC3D. In the Lake Package described in this report, a lake is represented as a volume of space within the model grid which consists of inactive cells extending downward from the upper surface of the grid. Active model grid cells bordering this space, representing the adjacent aquifer, exchange water with the lake at a rate determined by the relative heads and by conductances that are based on grid cell dimensions, hydraulic conductivities of the aquifer material, and user-specified leakance distributions that represent the resistance to flow through the material of the lakebed. Parts of the lake may become "dry" as upper layers of the model are dewatered, with a concomitant reduction in lake surface area, and may subsequently rewet when aquifer heads rise. An empirical approximation has been encoded to simulate the rewetting of a lake that becomes completely dry. The variations of lake stages are determined by independent water budgets computed for each lake in the model grid. This lake budget process makes the package a simulator of the response of lake stage to hydraulic stresses applied to the aquifer. Implementation of a lake water budget requires input of parameters including those representing the rate of lake atmospheric recharge and evaporation, overland runoff, and the rate of any direct withdrawal from, or augmentation of, the lake volume. The lake/aquifer interaction may be simulated in both transient and steady-state flow conditions, and the user may specify that lake stages be computed explicitly, semi-implicitly, or fully-implicitly in transient simulations. The lakes, and all sources of water entering the lakes, may have solute concentrations associated with them for use in solute-transport simulations using MOC3D. The Stream Package of MODFLOW-2000 and MOC3D represents stream connections to lakes, either as inflows or outflows. Because lakes with irregular bathymetry can exist as separate pools of water at lower stages, that coalesce to become a single body of water at higher stages, logic was added to the Lake Package to allow the representation of this process as a user option. If this option is selected, a system of linked pools (sublakes) is identified in each time step and stages are equalized based on current relative sublake surface areas.

Water-Resources Investigations Report↗
USGS2000

Water budget estimates for the 14 hydrographic areas in the middle Humboldt River basin, north-central Nevada

Water budgets were developed for the 14 hydrographic areas in the middle Humboldt River Basin of north-central Nevada. The water budgets include estimates of average annual precipitation, runoff, water yield, ground-water recharge and subsurface flow, and evapotranspiration (ET) determined from recently developed or revised methods. Ground-water pumping is not included in the budget estimates. The estimated budgets represent average annual volumes over a 30-year reference period ( 1961-90) and are compared to water budgets developed more than 30 years ago. Annual inflow to the middle Humboldt River basin is about 5 million acre-feet. An estimated 4.6 million is from precipitation in the 14 hydrographic areas and about 350,000 acre-feet is inflow from the Humboldt River. Annual outflow is about 5.1 million acre-feet, of which ET accounts for 4.8 million acre-feet, and outflow of the Humboldt River is about 300,000 acre-feet. Average annual precipitation in the hydrographic areas for 1961-90 ranged from 105 to 128 percent of that for the 1912-63 period. The annual volume ofET in the 14 areas was 102 to almost 134 percent of that previously estimated, although the percentage of annual precipitation lost to ET is similar. About 15 percent of the annual precipitation in mountain-block areas becomes water yield (either ground water or runoff) as compared to previous estimates of 11 percent. On the basis of mass-balance calculations, ground-water recharge on average is about 145 percent of previous estimates.

Nevada↗
USGS2001

Occurrence, distribution, and loads of selected pesticides in streams in the Lake Erie-Lake St. Clair basin, 1996–98

Thirty pesticides or their degradates were detected in 315 samples collected from 10 streams in the Lake Erie-Lake St. Clair Basin between March 1996 and February 1998 as part of the U.S. Geological Survey’s National Water-Quality Assessment (NAWQA) Program. Atrazine was detected in every sample, and deethylatrazine, metolachlor, and simazine were detected in more than 90 percent of all samples. Atrazine and metolachlor, the most heavily applied pesticides in the Basin, had the highest detected concentrations (85 and 78 micrograms per liter, respectively). No annual average concentrations exceeded the U.S. Environmental Protection Agency Maximum Contaminant Level or health advisory level at any of the surface-water-sampling sites. Seasonally elevated pesticide concentrations, however, have economic consequences on water-treatment facilities required to remove pesticides in water to meet drinking-water standards. From May through July, when most pesticides are transported by runoff into streams, time-weighted average concentrations of atrazine exceeded the Maximum Contaminant Level at five row-crop sites, and time-weighted average concentrations of atrazine and cyanazine frequently exceeded lifetime adult health advisories at these same sites. For some heavily used herbicides such as atrazine, metolachlor, cyanazine, and acetochlor, elevated concentrations persisted 4 to 6 weeks after the initial maximum concentration in the row-crop streams was measured. Land use and physical processes can affect the occurrence and distribution of pesticides. Pesticides were detected at greater frequency and at higher concentrations in samples from streams in basins dominated by row-crop agriculture than in samples from streams in urban or pasture/forest areas. Maximum measured concentrations were higher in 1997 than in 1996 and probably were related to greater precipitation in 1997. Generally, the number of pesticides detected in a basin increased with basin size. Pesticide concentrations showed strong seasonal trends related to the timing and amount of pesticide application. Row-crop herbicides applied in the spring, such as atrazine, had maximum measured concentrations in the spring; pesticides typically applied in late summer and early fall, such as diazinon, had maximum measured concentrations then. The increased number of detections and maximum measured concentrations of acetochlor and the corresponding decrease in the number of detections and concentrations of alachlor reflected changes in the amount of pesticides applied during the sampling period. The percentage of the applied atrazine that was detected in streams, in general, increased when the percentage of impermeable soils within each basin increased. Loads and yields of selected pesticides were calculated. The highest loads calculated were those for atrazine and metolachlor in the Maumee River at Waterville, Ohio, with 47,000 and 44,000 pounds per year, respectively. Of the row-crop basins, either the St. Joseph River near Newville, Ind., or the Auglaize River near Fort Jennings, Ohio, had the highest yields for the herbicides acetochlor, alachlor, atrazine, cyanazine, metolachlor, and simazine. The Cuyahoga River at Cleveland, Ohio, had the highest yields for diazinon and prometon—pesticides that typically are applied heavily in urban areas. The percentage of the applied atrazine that was calculated in the stream was determined for each basin in 1997. The export of atrazine ranged from 0.10 percent at the River Raisin near Manchester, Mich., to 10.6 percent at the St. Joseph River near Newville, Ind.

Indiana, Michigan, New York, Ohio, Pennsylania↗
USGS2000

Arsenic concentration and selected geochemical characteristics for ground water and aquifer materials in southeastern Michigan

Fifty-six private wells, 20 public wells and 38 monitoring wells in ten counties in southeastern Michigan were sampled to determine the concentration of naturally-occurring arsenic and specific geochemical parameters. The majority of ground water samples were analyzed for pH, dissolved oxygen, oxidation/reduction potential, specific conductance, major ions, dissolved and suspended organic carbon, and arsenic. Selected samples were analyzed for minor elements, nutrients, the isotope ratio of carbon and the concentration of tritium. The Mississippian Marshall Sandstone comprises a major aquifer in southeastern Michigan. To compare the lithology of the Marshall Aquifer to water chemistry, two new wells were drilled through the Marshall Sandstone to the underlying Coldwater Shale. Depth-specific bedrock and water samples were collected from these wells. For public and private drinking-water wells, the lowest concentration detected by USGS analysis was <1 microgram per liter and the highest was 220 micrograms per liter. Arsenic concentrations near or exceeding the current USEPA standard of 50 micrograms per liter occurred in ground water from each of the major aquifers in the study area. In the two newly-drilled wells, the lowest concentration detected by the USGS was <1 microgram per liter at about 350 ft below land surface and the highest concentration of 140 micrograms per liter was detected at around 50 ft below land surface. The data from this study may be used to indicate well characteristics and water chemistry factors that are related to arsenic in ground water in southeastern Michigan.

Michigan↗
USGS2000

Simulation of the recharge area for Frederick Springs, Dane County, Wisconsin

The Pheasant Branch watershed in Dane County is expected to undergo development. There are concerns that this development will adversely affect water resources, including Frederick Springs, a large spring complex in the watershed. The spring's recharge area was delineated using a telescopic mesh refinement (TMR) model constructed from an existing regional-scale ground-water flow model, and further refined by adding nearby surface-water features, a refined recharge array based on a surface-water model, and increasing the vertical leakage between the deep aquifers. This TMR model was formally optimized using the parameter estimation code UCODE. The results of optimization demonstrated that the best fit to measured heads and fluxes was obtained by using a horizontal hydraulic conductivity two times that of the original regional model for layer 2 and 80 percent smaller for layer 3. This range of parameter values was formally considered using a stochastic Monte Carlo approach. Two-hundred model runs used uniformly distributed, randomly sampled, horizontal hydraulic conductivity values within the range given by the TMR optimized values and the previously constructed regional model. A probability distribution of particles captured by the spring, or a probabilistic capture zone' was calculated from the realistic Monte Carlo results (136 runs of 200). In addition to portions of the local surface watershed, the capture zone encompassed distant areas in the North Fork of the Pheasant Branch watershed and areas entirely outside of the Pheasant Branch - demonstrating that the ground-watershed and surface watershed do not coincide. Analysis of samples from the springs and a nearby municipal well identified large contrasts in chemistry, even for springs within 50 feet of one another. The differences were stable over time, were present in both ion and isotope analyses, and showed a distinct gradation from high nitrate, high calcium, Ordovician-carbonate dominated water in western spring vents to low nitrate, lower calcium, Cambrian-sandstone influenced water in eastern spring vents. The difference in chemistry was attributed to distinctive bedrock geology as demonstrated by overlaying the 50 percent probability capture zone over a bedrock geology map for the area. This finding gives additional confidence to the capture zone calculated by the ground-water flow model.

Wisconsin↗
USGS2000

Climatology, hydrology, and simulation of an emergency outlet, Devils Lake basin, North Dakota

Devils Lake is a natural lake in northeastern North Dakota that is the terminus of a nearly 4,000-square-mile subbasin in the Red River of the North Basin. The lake has not reached its natural spill elevation to the Sheyenne River (a tributary of the Red River of the North) in recorded history. However, geologic evidence indicates a spill occurred sometime within the last 1,800 years. From 1993 to 1999, Devils Lake rose 24.5 feet and, at the present (August 2000), is about 13 feet below the natural spill elevation. The recent lake-level rise has caused flood damages exceeding $300 million and triggered development of future flood-control options to prevent further infrastructure damage and reduce the risk of a potentially catastrophic uncontrolled spill. Construction of an emergency outlet from the west end of Devils Lake to the Sheyenne River is one flood-control option being considered. This report describes the climatologic and hydrologic causes of the recent lake level rise, provides information on the potential for continued lake-level rises during the next 15 years, and describes the potential effectiveness of an emergency outlet in reducing future lake levels and in reducing the risk of an uncontrolled spill. The potential effects of an outlet on downstream water quantity and quality in the upper Sheyenne River also are described.

South Dakota↗
USGS2000

Estimation and comparison of potential runoff-contributing areas in Kansas using topographic, soil, and land-use information

Digital topographic, soil, and land-use information was used to estimate potential runoff-contributing areas in Kansas. The results were used to compare 91 selected subbasins representing slope, soil, land-use, and runoff variability across the State. Potential runoff-contributing areas were estimated collectively for the processes of infiltration-excess and saturation-excess overland flow using a set of environmental conditions that represented, in relative terms, very high, high, moderate, low, very low, and extremely low potential for runoff. Various rainfall-intensity and soil-permeability values were used to represent the threshold conditions at which infiltration-excess overland flow may occur. Antecedent soil-moisture conditions and a topographic wetness index (TWI) were used to represent the threshold conditions at which saturation-excess overland flow may occur. Land-use patterns were superimposed over the potential runoff-contributing areas for each set of environmental conditions. Results indicated that the very low potential-runoff conditions (soil permeability less than or equal to 1.14 inches per hour and TWI greater than or equal to 14.4) provided the best statewide ability to quantitatively distinguish subbasins as having relatively high, moderate, or low potential for runoff on the basis of the percentage of potential runoff-contributing areas within each subbasin. The very low and (or) extremely low potential-runoff conditions (soil permeability less than or equal to 0.57 inch per hour and TWI greater than or equal to 16.3) provided the best ability to qualitatively compare potential for runoff among areas within individual subbasins. The majority of subbasins with relatively high potential for runoff are located in the eastern half of the State where soil permeability is generally less and precipitation is typically greater. The ability to distinguish subbasins as having relatively high, moderate, or low potential for runoff was possible mostly due to the variability of soil permeability across the State. The spatial distribution of potential contributing areas, in combination with the superimposed land-use patterns, may be used to help identify and prioritize subbasin areas for the implementation of best-management practices to manage runoff and meet Federally mandated total maximum daily load requirements.

Water-Resources Investigations Report↗
USGS2000

Distribution and potential for adverse biological effects of inorganic elements and organic compounds in bottom sediment, lower Charles River, Massachusetts

Surficial-sediment samples and cores collected from the lower Charles River Basin are generally enriched in inorganic elements and organic compounds, including polychlorinated byphenyls, total organochlorine pesticides, and polyaromatic hydrocarbons. Median concentrations of selected inorganic elements and organic compounds measured in surficial-sediment samples collected from the lower Charles River ranged from 1. 3 to 3 5 times higher than median concentrations of these constituents measured in samples collected from urban rivers across the conterminous United States by the U.S. Geological Survey's National Water Quality Assessment Program (NAWQA). The distribution of the inorganic elements in surficial sediment throughout the basin appears to be controlled primarily by in-stream processes associated with sediment transport and the presence of an anoxic zone within a non-tidal salt wedge in the basin. In contrast, the distribution of organic compounds appears to reflect local point and non-point sources. Inorganic elements and organic compounds are present at sufficiently high concentrations at many surficial-sediment sampling sites to cause potentially severe biological effects to benthic organisms living in and on the bottom sediment. Ratios of acid volatile sulfide to simultaneously extracted metals, however, suggest that some inorganic elements would be toxic in fewer than 25 percent of the surficial-sediment samples. Many individual polyaromatic hydrocarbons, total petroleum hydrocarbons, and lead measured in cores exceeded exposure-based soil-concentration standards for direct contact and incident ingestion at areas where restoration of public wading and swimming beaches is being considered.

Massachusetts↗
USGS2000

Equations for estimating Clark unit-hydrograph parameters for small rural watersheds in Illinois

Equations for estimating the time of concentration ( T C ) and storage coefficient ( R ) of the Clark unit-hydrograph method were developed for small rural watersheds [0.02–2.3 square miles (mi 2 )] in Illinois. The equations will provide State and local engineers and planners with more accurate methods to estimate the T C and R for use in simulating discharge hydrographs on small rural watersheds when designing stormwater-management facilities and other hydraulic structures, determining flood-plain boundaries, and assessing the safety of structures in rivers. The rainfall and runoff data from gaged small rural watersheds (0.02–2.3 mi 2 ) with insignificant amounts of impervious land cover in Illinois were used to develop the equations. Equations were developed on the basis of data for 121 storms that occurred in 39 watersheds. Data for 29 storms in 18 watersheds were used to verify the equations. T C and R were determined by calibrating available rainfall and runoff data, using the U.S. Army Corps of Engineers Flood Hydrograph Package HEC-1. The mathematical relations between watershed and storm characteristics, and T C and R were determined by multiple-linear regression of the logarithms of the values. Main-channel length and slope were identified as important watershed characteristics for estimating T C and R . The estimation equations had coefficients of determination of 0.73 and 0.64 for the logarithms of T C and R , respectively. When storm characteristics were added in the regression of hydrograph parameters utilizing length and slope, only minimal increases to the coefficient of determination resulted. Thus, storm characteristics were not considered further in development of the equations. Simulation of the measured discharge hydrographs for the verification storms utilizing T C and R obtained from the estimation equations yielded good results. The error in peak discharge for 21 of the 29 verification storms was less than 25 percent, and the error in time-to-peak discharge for 18 of the 29 verification storms also was less than 25 percent. Therefore, applying the estimation equations to determine T C and R for design-storm simulation may result in reliable design hydrographs, as long as the physical characteristics of the watersheds under consideration are within the range of those characteristics for the watersheds in this study [area: 0.02–2.3 mi 2 , main-channel length: 0.17–3.4 miles, main-channel slope: 10.5–229 feet per mile, and insignificant percentage of impervious cover].

Illinois↗
USGS2000

Hydrogeologic and geochemical characteristics of the Ogallala and White River aquifers, Cheyenne, Wyoming

The Ogallala aquifer and the underlying White River aquifer are important ground-water resources of public and private drinking water in the Cheyenne, Wyoming area. In 1997, as part of a cooperative project between the Cheyenne Board of Public Utilities and the U.S. Geological Survey, a well was installed to develop information for those two aquifers. Information provided for the Ogallala aquifer included core descriptions, geophysical logs, water levels, aquifer transmissivity, water quality, isotopic analysis, and geochemical modeling. Information for the White River aquifer was limited to core descriptions and geophysical logs.Evaluation of the core obtained from the drill hole showed the sediments to be primarily sands, silts, and clays. The thickness of the Ogallala Formation at the well site was estimated to be 246 feet. Water levels and precipitation from October 1, 1998 to September 30, 1999 indicated that water levels responded to precipitation. During that time, water levels ranged from 6,002.41 feet to 6,004.27 feet above mean sea level. The transmissivity was estimated to be 1.1 feet squared/day. The temperature differences between the municipal water and the Ogallala aquifer water were examined in relation to selected hydraulic conductivities and it was found that the warmer municipal water would slightly increase the hydraulic conductivity if the water were injected into the Ogallala aquifer.The water quality of a sample from the Ogallala 1 well indicated the predominant major ions were calcium, magnesium, and bicarbonate. Isotopic analyses of hydrogen-2, tritium, chlorine-36, carbon-14, and carbon-13 indicated the water was a mixture of pre- and post-1953 recharge. A simple geochemical mixing model indicated there was the potential for dissolution of anhydrite, calcite, gypsum, and dolomite and precipitation of goethite, hematite, pyrolusite, and amorphous ferric hydroxide if municipal and Ogallala aquifer waters were mixed.

Water-Resources Investigations Report↗