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USGS2000

Methodology, data collection, and data analysis for determination of water-mixing patterns induced by aerators and mixers

The U.S. Geological Survey collected and analyzed data to describe mixing patterns induced by aerators and mixers to aid in the calibration and verification of a three-dimensional hydrodynamic model. During September 1995, three-dimensional water-velocity profiles were collected during the operation of fine-bubble and coarse-bubble aerators in a test tank at the U.S. Army Corps of Engineers Waterways Experiment Station. Three-dimensional water velocity, water-temperature, pH, dissolved oxygen concentration, and specific conductivity profiles were collected during operation of a coarse-bubble aerator in a reservoir in Schaumburg, Illinois, during summer 1996 and summer 1997, during strongly stratified and weakly stratified conditions. The effects of a submersible mixer alone and in combination with coarse-bubble aerators and a surface mixer alone also were investigated during summer 1997. The mixing patterns induced by the operation of aerators, submersible mixers, and surface mixers were described and compared with mixing patterns predicted by model simulations. Bubble-plume characteristics during tests in strongly stratified and weakly stratified conditions in the reservoir were documented and compared with characteristics simulated by different models. Lemckert and Imberger?s model simulates an entrainment rate similar to the rate measured during a test in the reservoir under strongly stratified conditions, whereas Schladow?s one-dimensional model appears to underestimate the total entrainment rate by about 50 percent. Schladow?s model was accurate during weak stratification but underestimated the radius of the plume during strong stratification. For 5 days during daylight hours, water temperature profiles were collected continuously during the operation of four aerators. Water temperatures in the reservoir were significantly affected by the operation of the aeration system. These changes were compared to simulations from a one-dimensional Dynamic Lake Model (DLM) simulation. DLM accurately simulated changes as a result of aeration, including daily changes. On the basis of temporal and spatial dissolved oxygen measurements, the volumetric quantity of oxygen in the reservoir was quantified before and after operation of a submersible mixer. A net loss of oxygen was calculated. This net loss may have resulted from a net warming of water throughout the reservoir or submerged supersaturated water releasing oxygen when the water came in contact with the atmosphere.

Water-Resources Investigations Report↗
USGS2000

Sensitivity of ground water to contamination in Lawrence County, South Dakota

Ground-water supplies in Lawrence County, South Dakota, can be contaminated by agricultural, urban, suburban, commercial, and industrial land uses. To address this issue, the U.S. Geological Survey in cooperation with Lawrence County and the City of Spearfish mapped the sensitivity of ground water to contamination in Lawrence County. Sensitivity of ground water to contamination was determined by delineating hydrogeologic settings with common hydrogeologic characteristics as described in the DRASTIC method, developed by the U.S. Environmental Protection Agency and the National Water Well Association. Within the framework of 11 hydrogeologic settings, sensitivity to contamination was ranked for six intrinsic hydrogeologic characteristics: (1) aquifer media, (2) unsaturated media (3) hydraulic conductivity, (4) recharge rate, (5) depth to water, and (6) land-surface slope. The rating conventions of DRASTIC were modified to provide a relative ranking of hydrogeologic characteristics without assignment of a combined numerical score. Soil characteristics were not included as a map layer because detailed digital data were not available; however, the general distribution of two soil characteristics were shown. A total of 956 polygons were delineated and assigned a sensitivity-unit code that represented unique groups of sensitivity rank for the six intrinsic hydrogeologic characteristics. The polygons were created by overlaying and intersecting maps that describe the geology, precipitation, land-surface elevation, and depth to water using a geographic information system. Thirty drainage areas upstream from potential streamflow-loss zones were delineated to describe an additional mechanism of transport of potential contamination. The sensitivity of ground water to contamination was presented on a 1:100,000-scale map with code and label explanations. Limitations of the sensitivity map are described to facilitate appropriate use of the map as a screening tool to compare sensitivity to contamination.

Water-Resources Investigations Report↗
USGS2000

Quality-assurance design applied to an assessment of agricultural pesticides in ground water from carbonate bedrock aquifers in the Great Valley of eastern Pennsylvania

Assessments to determine whether agricultural pesticides are present in ground water are performed by the Commonwealth of Pennsylvania under the aquifer monitoring provisions of the State Pesticides and Ground Water Strategy. Pennsylvania's Department of Agriculture conducts the monitoring and collects samples; the Department of Environmental Protection (PaDEP) Laboratory analyzes the samples to measure pesticide concentration. To evaluate the quality of the measurements of pesticide concentration for a groundwater assessment, a quality-assurance design was developed and applied to a selected assessment area in Pennsylvania. This report describes the quality-assurance design, describes how and where the design was applied, describes procedures used to collect and analyze samples and to evaluate the results, and summarizes the quality assurance results along with the assessment results. The design was applied in an agricultural area of the Delaware River Basin in Berks, Lebanon, Lehigh, and Northampton Counties to evaluate the bias and variability in laboratory results for pesticides. The design—with random spatial and temporal components—included four data-quality objectives for bias and variability. The spatial design was primary and represented an area comprising 30 sampling cells. A quality-assurance sampling frequency of 20 percent of cells was selected to ensure a sample number of five or more for analysis. Quality-control samples included blanks, spikes, and replicates of laboratory water and spikes, replicates, and 2-lab splits of groundwater. Two analytical laboratories, the PaDEP Laboratory and a U.S. Geological Survey Laboratory, were part of the design. Bias and variability were evaluated by use of data collected from October 1997 through January 1998 for alachlor, atrazine, cyanazine, metolachlor, simazine, pendimethalin, metribuzin, and chlorpyrifos. Results of analyses of field blanks indicate that collection, processing, transport, and laboratory analysis procedures did not contaminate the samples; there were no false-positive results. Pesticides were detected in water when pesticides were spiked into (added to) samples. There were no false negatives for the eight pesticides in all spiked samples. Negative bias was characteristic of analytical results for the eight pesticides, and bias was generally in excess of 10 percent from the ‘true’ or expected concentration (34 of 39 analyses, or 87 percent of the ground-water results) for pesticide concentrations ranging from 0.31 to 0.51 mg/L (micrograms per liter). The magnitude of the negative bias for the eight pesticides, with the exception of cyanazine, would result in reported concentrations commonly 75-80 percent of the expected concentration in the water sample. The bias for cyanazine was negative and within 10 percent of the expected concentration. A comparison of spiked pesticide-concentration recoveries in laboratory water and ground water indicated no effect of the ground-water matrix, and matrix interference was not a source of the negative bias. Results for the laboratory-water spikes submitted in triplicate showed large variability for recoveries of atrazine, cyanazine, and pendimethalin. The relative standard deviation (RSD) was used as a measure of method variability over the course of the study for laboratory waters at a concentration of 0.4 mg/L. An RSD of about 11 percent (or about ?0.05 mg/L)characterizes the method results for alachlor, chlorpyrifos, metolachlor, metribuzin, and simazine. Atrazine and pendimethalin have RSD values of about 17 and 23 percent, respectively. Cyanazine showed the largest RSD at nearly 51 percent. The pesticides with low variability in laboratory-water spikes also had low variability in ground water. The assessment results showed that atrazinewas the most commonly detected pesticide in ground water in the assessment area. Atrazine was detected in water from 22 of the 28 wells sampled, and recovery results for atrazine were some of the worst (largest negative bias). Concentrations of the eight pesticides in ground water from wells were generally less than 0.3 µg/L. Only six individual measurements of the concentrations in water from six of the wells were at or above 0.3 µg/L, five for atrazine and one for metolachlor. There were eight additional detections of metolachlor and simazine at concentrations less than 0.1 µg/L. No well water contained more than one pesticide at concentra-tions at or above 0.3 µg/L. Evidence exists, how-ever, for a pattern of co-occurrence of metolachlor and simazine at low concentrations with higher concentrations of atrazine. Large variability in replicate samples and negative bias for pesticide recovery from spiked samples indicate the need to use data for pesticide recovery in the interpretation of measured pesti-cide concentrations in ground water. Data from samples spiked with known amounts of pesticides were a critical component of a quality-assurance design for the monitoring component of the Pesti-cides and Ground Water Strategy. Trigger concentrations, the concentrations that require action under the Pesticides and Ground Water Strategy, should be considered maximums for action. This consideration is needed because of the magnitude of negative bias.

Water-Resources Investigations Report↗
USGS2001

Documentation and verification of VST2D; a model for simulating transient, Variably Saturated, coupled water-heat-solute Transport in heterogeneous, anisotropic 2-Dimensional, ground-water systems with variable fluid density

This report describes a model for simulating transient, Variably Saturated, coupled water-heatsolute Transport in heterogeneous, anisotropic, 2-Dimensional, ground-water systems with variable fluid density (VST2D). VST2D was developed to help understand the effects of natural and anthropogenic factors on quantity and quality of variably saturated ground-water systems. The model solves simultaneously for one or more dependent variables (pressure, temperature, and concentration) at nodes in a horizontal or vertical mesh using a quasi-linearized general minimum residual method. This approach enhances computational speed beyond the speed of a sequential approach. Heterogeneous and anisotropic conditions are implemented locally using individual element property descriptions. This implementation allows local principal directions to differ among elements and from the global solution domain coordinates. Boundary conditions can include time-varying pressure head (or moisture content), heat, and/or concentration; fluxes distributed along domain boundaries and/or at internal node points; and/or convective moisture, heat, and solute fluxes along the domain boundaries; and/or unit hydraulic gradient along domain boundaries. Other model features include temperature and concentration dependent density (liquid and vapor) and viscosity, sorption and/or decay of a solute, and capability to determine moisture content beyond residual to zero. These features are described in the documentation together with development of the governing equations, application of the finite-element formulation (using the Galerkin approach), solution procedure, mass and energy balance considerations, input requirements, and output options. The VST2D model was verified, and results included solutions for problems of water transport under isohaline and isothermal conditions, heat transport under isobaric and isohaline conditions, solute transport under isobaric and isothermal conditions, and coupled water-heat-solute transport. The first three problems considered in model verification were compared to either analytical or numerical solutions, whereas the coupled problem was compared to measured laboratory results for which no known analytic solutions or numerical models are available. The test results indicate the model is accurate and applicable for a wide range of conditions, including when water (liquid and vapor), heat (sensible and latent), and solute are coupled in ground-water systems. The cumulative residual errors for the coupled problem tested was less than 10–8 cubic centimeter per cubic centimeter, 10-5 moles per kilogram, and 102 calories per cubic meter for liquid water content, solute concentration and heat content, respectively. This model should be useful to hydrologists, engineers, and researchers interested in studying coupled processes associated with variably saturated transport in ground-water systems.

Water-Resources Investigations Report↗
USGS2000

Ground-water quality in alluvial aquifers in the eastern Iowa basins, Iowa and Minnesota

The quality of shallow alluvial ground water that is used for domestic supplies in the Wapsipinicon, Cedar, Iowa, and Skunk River Basins (Eastern Iowa Basins) is described. Water samples from 32 domestic-supply wells were collected from June through July 1998. This study of ground-water quality in alluvial aquifers in the Eastern Iowa Basins is part of the U.S. Geological Survey's National Water-Quality Assessment Program. Calcium and bicarbonate were the dominant ions in solution, likely derived from the dissolution of carbonate minerals in the alluvial aquifer material. Concentrations of iron exceeded the U.S. Environmental Protection Agency Secondary Maximum Contaminant Level (300 micrograms per liter) for drinking water in 53 percent of the samples, and 50 percent of the samples exceeded the Secondary Maximum Contaminant Level for manganese (50 micrograms per liter). pH and alkalinity increased and sulfate concentrations decreased with increasing well depth. Nitrite plus nitrate nitrogen was detected in 53 percent of the samples and exceeded the U.S. Environmental Protection Agency Maximum Contaminant Level of 10 milligrams per liter for drinking water in 13 percent of the samples. Nitrite plus nitrate nitrogen concentrations were negatively correlated with well depth and positively correlated with percentage of oxygen saturation. Ammonia plus organic nitrogen concentrations were positively correlated with well depth, and ratios of nitrite plus nitrate to ammonia were positively correlated with percentage of oxygen saturation. The majority of samples, 72 percent, contained water recharged since the early 1950's. The recharge date of water was earlier in deeper wells. Nitrite plus nitrate and total pesticide concentrations were greater in more recently recharged water. Eight pesticides and eight pesticide metabolites were detected in ground-water samples. Atrazine was the most commonly detected pesticide, and metolachlor ethanesulfonic acid was the most commonly detected metabolite. No pesticide detections exceeded U.S. Environmental Protection Agency drinking-water Maximum Contaminant Levels. The effects of land use on ground-water quality also were examined. There was a positive correlation between percentage of land used for soybean production and concentrations of metolachlor, metolachlor ethanesulfonic acid, and metolachlor oxanilic acid in ground-water samples. Data from this study and from previous studies in the Eastern Iowa Basins were compared statistically by well type (domestic, municipal, and monitoring wells). Well depths were significantly greater in domestic and municipal wells than in monitoring wells. pH, calcium, sulfate, chloride, and atrazine concentrations were significantly higher in municipal-well samples than in domestic-well samples. pH and sulfate concentrations were significantly higher in municipal-well samples than in monitoring-well samples. Ammonia was significantly higher in domestic-well samples than in monitoring-well samples, chloride was significantly higher in monitoring-well samples than in domestic-well samples, and fluoride was significantly higher in domestic-well samples than in municipal-well samples.

Iowa, Minnesota↗
USGS2000

Field tests of polyethylene-membrane diffusion samplers for characterizing volatile organic compounds in stream-bottom sediments, Nyanza Chemical Waste Dump Superfund site, Ashland, Massachusetts

A plume of volatile organic compounds (VOCs) in ground water extends from the Nyanza Chemical Waste Dump Superfund site in Ashland, Massachusetts, northward toward a mill pond on the Sudbury River and eastward toward the Sudbury River and former mill raceway downstream from the mill pond. Polyethylene-membrane water-to-vapor (vapor) and water-to-water (water) diffusion samplers were installed January 1999 in bottom sediments along the Sudbury River and former mill raceway in a pilot study to determine if vapor samplers would be useful in this setting for delineating a plume of contaminants in ground water near the river and raceway, to evaluate equilibration time for vapor-diffusion samplers, and to determine if diffusion samplers might be an alternative to seepage meters (inverted steel drums) and sediment sampling for evaluating concentrations of VOCs in bottom sediments. Of five tested compounds (benzene, trichloroethene, toluene, tetrachloroethene, and chlorobenzene), chlorobenzene and trichloroethene were most frequently detected in vapor from vapor-diffusion samplers. The distribution of VOCs was generally consistent with a previously mapped plume of contaminants in ground water. The field evaluation of equilibration times for vapor-diffusion samplers was inconclusive because of changing hydrologic conditions that may have affected concentrations of VOCs, possible variations in concentrations ofVOCs over short distances, and imprecise sampling and analytical methods. The limited data, however, indicated that equilibration may require 3 weeks or more in some settings. VOCs detected in samples from water-diffusion samplers and their concentrations were comparable to results from seepage meters, and VOCs detected in vapor-diffusion samplers correlated with VOCs detected in water-diffusion samplers. These results indicate that either vapor-or water-diffusion samplers would serve as an economical alternative to seepage meters for sampling of VOCs in pore water from stream-bottom sediments. Results from diffusion samplers correlated poorly with results from sediment samples, partly because of high quantitation limits for chemical analyses of sediments. In general, results from the diffusion samplers better represented the distribution of VOCs than the results from the sediment samples. This pilot study indicates that diffusion samplers are an economical means of identifying 'hotspots' for contaminants in bottom sediments and can provide insights on transport pathways for contaminants near surface-water bodies. After establishing equilibration times for a particular site, diffusion samplers also may be useful for studying variations in concentrations of VOCs over short distances, variations with time and changing hydrologic conditions, and processes such as chemical transformations by biodegradation and exchanges between surface water and ground water in the hyporheic zone.

Water-Resources Investigations Report↗
USGS2000

Effect of Georgetown Lake on the water quality of Clear Creek, Georgetown, Colorado, 1997-98

Georgetown Lake is a recreational reservoir located in the upper Clear Creek Basin, a designated Superfund site because of extensive metal mining in the past. Metals concentrations in Clear Creek increase as the stream receives runoff from mining-affected areas. In 1997, the U.S. Geological Survey, in cooperation with the U.S. Environmental Protection Agency, began a study to determine the effect of the reservoir on the transport of metals in Clear Creek. A bathymetric survey determined the capacity of the reservoir to be about 440 acre-feet of water, which remained constant during the study. Average water residence time in the reservoir is about 1-3 days during high flow. During low flow (10 cubic feet per second), average residence is about 22 days without ice cover and about 15 days with a 3-foot-thick ice cover. Sediment samples collected from the bottom of Georgetown Lake contained substantial concentrations of iron (average 25,500 milligrams per kilogram), aluminum (average 12,300 milligrams per kilogram), zinc (2,830 milligrams per kilogram), lead (618 milligrams per kilogram), manganese (548 milligrams per kilogram), and sulfide minerals (average 602 milligrams per kilogram as S). Sediment also contained abundant sulfate-reducing bacteria, indicating anoxic conditions. Algae and diatoms common to cold-water lakes were identified in sediment samples; one genus of algae is known to adapt to low-light conditions such as exist beneath ice cover. Vertical profiles of temperature, specific conductance, pH, and dissolved-oxygen concentrations were measured in the reservoir on July 28, 1997, when inflow to the reservoir was about 170 cubic feet per second and average residence time of water was about 1.3 days, and on February 13, 1998, when the reservoir was covered with about 3 feet of ice, inflow was about 15 cubic feet per second, and average residence time was about 12 days. The measurements on July 28, 1997, showed that the reservoir water was well mixed, although pH and dissolved-oxygen concentrations were increased by photosynthesis near the bottom of the reservoir. Measurements on February 13, 1998, indicated thermal and chemical stratification with warmer water (about 4 degrees Celsius) beneath colder water and increases in pH and dissolved-oxygen concentrations generally occurring near the top of the warmer layer. Concentrations of dissolved oxygen were saturated to over-saturated throughout the water column on both dates, although the concentrations were greater on February 13, 1998, because of colder temperature and photosynthesis. Median pH was about 0.5 unit higher on February 13, 1998, than on July 28, 1997, largely because the longer residence time on February 13, 1998, allowed greater cumulative effects of photosynthesis. Samples of inflow and outflow water were collected from August 1997 to August 1998. Dissolved cadmium and dissolved lead in inflow and outflow samples exceeded acute and chronic water-quality standards during some of the sampling period, whereas dissolved zinc exceeded both standards in inflow and outflow samples during the entire sampling period. Chromium, nickel, and silver were detected in a few samples at small concentrations. Arsenic, selenium, and thallium were not reported in any water samples. Georgetown Lake removes some metals from inflow water and releases others to outflow water. From August 1997 to August 1998, Georgetown Lake estimated outflow loads were about 21 percent less than the inflow load of cadmium and about 11 percent less than the inflow load of zinc. Estimated inflow loads were about 18 percent less than the outflow load of copper, about 13 percent less than the outflow load of iron, and about 27 percent less than the outflow load of manganese. Inflow and outflow loads of lead were essentially balanced. The outflow load of nitrite plus nitrate was about 14 percent less than the inflow load, probably because of plant uptake.

Colorado↗
USGS2000

Estimating the probability of elevated nitrate (NO2+NO3-N) concentrations in ground water in the Columbia Basin Ground Water Management Area, Washington

Logistic regression was used to relate anthropogenic (man-made) and natural factors to the occurrence of elevated concentrations of nitrite plus nitrate as nitrogen in ground water in the Columbia Basin Ground Water Management Area, eastern Washington. Variables that were analyzed included well depth, depth of well casing, ground-water recharge rates, presence of canals, fertilizer application amounts, soils, surficial geology, and land-use types. The variables that best explain the occurrence of nitrate concentrations above 3 milligrams per liter in wells were the amount of fertilizer applied annually within a 2-kilometer radius of a well and the depth of the well casing; the variables that best explain the occurrence of nitrate above 10 milligrams per liter included the amount of fertilizer applied annually within a 3-kilometer radius of a well, the depth of the well casing, and the mean soil hydrologic group, which is a measure of soil infiltration rate. Based on the relations between these variables and elevated nitrate concentrations, models were developed using logistic regression that predict the probability that ground water will exceed a nitrate concentration of either 3 milligrams per liter or 10 milligrams per liter. Maps were produced that illustrate the predicted probability that ground-water nitrate concentrations will exceed 3 milligrams per liter or 10 milligrams per liter for wells cased to 78 feet below land surface (median casing depth) and the predicted depth to which wells would need to be cased in order to have an 80-percent probability of drawing water with a nitrate concentration below either 3 milligrams per liter or 10 milligrams per liter. Maps showing the predicted probability for the occurrence of elevated nitrate concentrations indicate that the irrigated agricultural regions are most at risk. The predicted depths to which wells need to be cased in order to have an 80-percent chance of obtaining low nitrate ground water exceed 600 feet in the irrigated agricultural regions, whereas wells in dryland agricultural areas generally need a casing in excess of 400 feet. The predicted depth to which wells need to be cased to have at least an 80-percent chance to draw water with a nitrate concentration less than 10 milligrams per liter generally did not exceed 800 feet, with a 200-foot casing depth typical of the majority of the area.

Washington↗
USGS2000

Estimated flow-duration curves for selected ungaged sites in the Cimarron and lower Arkansas River basins in Kansas

Flow-duration curves for 1968-98 were estimated for 16 ungaged sites in the Cimarron and lower Arkansas River Basins in south-central Kansas. The method of estimation used six unique factors of flow duration: (1) mean streamflow and percentage duration of mean streamflow, (2) ratio of 1-percent-duration streamflow to mean streamflow, (3) ratio of 0.1-percent-duration streamflow to 1-percent-duration streamflow, (4) ratio of 50-percent-duration streamflow to mean streamflow, (5) percentage duration of appreciable streamflow (0.10 cubic foot per second), and (6) average slope of the flow-duration curve. These factors were previously developed from a regionalized study of flow-duration curves using streamflow data for 1921-76. The method was tested on a currently measured, continuous-record streamflow-gaging station on the Little Arkansas River at Valley Center, Kansas, and was found to adequately estimate the computed flow-duration curve for the station. The low-flow parts of the estimated flow-duration curves were improved substantially using low- to medium-flow discharge measurements made concurrently with discharge measurements and flow-duration analyses performed at nearby, long-term, continuous-record, streamflow-gaging stations. The estimated flow-duration curves at the ungaged sites can be used for projecting future flow frequencies for assessment of total maximum daily loads (TMDL's) or other water-quality constituents and for water-availability studies.

Kansas↗
USGS2000

Suspended-sediment budget, flow distribution, and lake circulation for the Fox Chain of Lakes in Lake and McHenry Counties, Illinois, 1997-99

The Fox Chain of Lakes is a glacial lake system in McHenry and Lake Counties in northern Illinois and southern Wisconsin. Sedimentation and nutrient overloading have occurred in the lake system since the first dam was built (1907) in McHenry to raise water levels in the lake system. Using data collected from December 1, 1997, to June 1, 1999, suspended-sediment budgets were constructed for the most upstream lake in the system, Grass Lake, and for the lakes downstream from Grass Lake. A total of 64,900 tons of suspended sediment entered Grass Lake during the study, whereas a total of 70,600 tons of suspended sediment exited the lake, indicating a net scour of 5,700 tons of sediment. A total of 44,100 tons of suspended sediment was measured exiting the Fox Chain of Lakes at Johnsburg, whereas 85,600 tons entered the system downstream from Grass Lake. These suspended-sediment loads indicate a net deposition of 41,500 tons downstream from Grass Lake, which represents a trapping efficiency of 48.5 percent. A large amount of recreational boating takes place on the Fox Chain of Lakes during summer months, and suspended-sediment load was observed to rise from 110 tons per day to 339 tons per day during the 1999 Memorial Day weekend (May 26 ?31, 1999). Presumably, this rise was the result of the boating traffic because no other hydrologic event is known to have occurred that might have caused the rise. This study covers a relatively short period and may not represent the long-term processes of the Fox Chain of Lakes system, although the sediment transport was probably higher than an average year. The bed sediments found on the bottom of the lakes are composed of mainly fine particles in the silt-clay range. The Grass Lake sediments were characterized as black peat with an organic content of between 9 and 18 percent, and the median particle size ranged from 0.000811 to 0.0013976 inches. Other bed material samples were collected at streamflow-gaging stations on the tributaries to the Fox Chain of Lakes. With the exception of Grass Lake Outlet at Lotus Woods, most of the bed sediments are sand size or larger. The bed material at the streamflow-gaging station at Grass Lake Outlet at Lotus Woods contains 31.5 percent silt- and clay-sized particles. The bed material at Nippersink Creek near Spring Grove also has higher silt content (10.7 percent) than the bed material found in the Fox River at Wilmot (2.1 percent) and Johnsburg (1.3 percent). Additionally, water velocities at 80 cross sections in the Fox Chain of Lakes were collected to provide sample circulation patterns during two separate 1-week periods, and discharge was measured at 18 locations in the lakes. These data were collected to be available for use in hydrodynamic models.

Water-Resources Investigations Report↗
USGS2000

Hydrogeology, water quality, and stormwater-sediment chemistry of the Grande Wash area, Fort McDowell Indian Reservation, Maricopa County, Arizona

Grande Wash is a tributary of the Verde River and drains an area of 13 square miles within the McDowell Mountains and the Town of Fountain Hills in Central Arizona. The wash enters the Fort McDowell Indian Reservation at the eastern boundary of Fountain Hills and is incised in coarse-grained alluvium that is contiguous with the alluvial aquifer along the Verde River. The aquifer is used by the Fort McDowell Indian Community and the City of Phoenix for municipal water supplies. Episodic flows in Grande Wash, in response to storms, carry potentially hazardous runoff from Fountain Hills onto the reservation. Additional potential hazards to ground water include contamination from a wastewater-treatment plant located less than 1 mile upstream from the reservation boundary, and from a landfill and a cement-processing plant immediately adjacent to the main channel of the wash. Coarse-grained deposits in Grande Wash also include recent stream-channel deposits, soil backfill, landfill material, and the upper coarse-grained layer of basin-fill sediments. Surface-geophysical surveys and drilling indicated that the coarse-grained deposits are less than 60-feet thick along the wash and in adjacent areas within the reservation, and are underlain by a thick clay and silt unit, the base of which is below the bottom of the deepest monitor well (317 feet below land surface). The coarse-grained deposits form the alluvial aquifer beneath Grande Wash. Ground water in the alluvial aquifer beneath the wash is shallow and mounded above a less permeable clay and silt unit. Depth to water in the aquifer ranges from 1 to 22 feet below land surface. Saturation of the coarse-grained deposits does not extend laterally for more than about 1,000 feet from the main channel of Grande Wash; the extent varies in response to recharge amounts. Flux of ground water through the alluvial aquifer beneath the wash is toward the Verde River and is estimated to be about 8,000 cubic feet per day (about 0.2 acre-feet per day). The flow rate is four orders of magnitude less than the flow rate in the Verde River. Vertical flux of ground water through the underlying clay and silt unit is estimated to be 7,000 cubic feet per day (0.17 acre-feet per day). The volume of ground water in storage in the alluvial aquifer beneath Grande Wash is estimated to be about 5.6 million cubic feet (129 acre-feet). Concentrations of dissolved inorganic constituents in ground water and surface water are high relative to concentrations found in the regional aquifer in surrounding areas and are indicative of salts that can be expected to be mobilized by runoff in the drainage area. Concentrations of nitrate, chloride, and sulfate are near U.S. Environmental Protection Agency Primary or Secondary Drinking-Water Regulations. Concentrations of arsenic, antimony, and strontium are below drinking-water standards but can be attributed to geologic deposits in and near the study area. Low concentrations of anthropogenic compounds, including chloroform and dichlorobromomethane, were detected. These compounds are disinfection by-products of chlorinated water. Eight pesticide compounds were detected in the surface water, and two pesticide compounds were detected in the ground water. Pesticide concentrations were below U.S. Environmental Protection Agency Maximum Contaminant Levels. Several other organic anthropogenic compounds that probably originated from commercial activities in the area were detected but at concentrations below laboratory calibration standards. Concentrations of trace metals in the stormwater sediment collected from the sediment retention basin in the lowest part of the wash were low and several were below the laboratory’s detection limits. Concentrations of most organic compounds in the stormwater sediment were below detection limits. Organic compounds present at concentrations above detection limits were p-cresol and two phthalate esters—bis (2-ethylhexyl) phthalate and dibutyl phthalate. P-cresol is used in pesticides or in disinfectants and deodorizers, and phthalate esters are commonly used in plastics, hydraulic fluid, and electric capacitors.

Arizona↗
USGS2000

Ground-water quality in the upper Santa Cruz Basin, Arizona, 1998

Fifty-eight ground-water samples were collected and analyzed in 1998 by the U.S. Geological Survey and the Arizona Department of Environmental Quality to assess ground-water quality and to identify factors affecting ground-water quality in the Upper Santa Cruz Basin. In addition, pre-existing groundwater quality data for six wells were analyzed to determine changes in the ground-water quality of the basin over time. Twenty-nine percent of the ground-water samples collected had concentrations of at least one constituent that exceeded a Federal or State water-quality standard. The Maximum Contaminant Levels of the U.S. Environmental Protection Agency and the aquifer water-quality standards of the State of Arizona were exceeded for arsenic, fluoride, and nitrite plus nitrate. The Secondary Maximum Contaminant Levels of the U.S. Environmental Protection Agency were exceeded for fluoride, iron, manganese, pH, sulfate, and dissolved solids. Ground-water quality in the basin is affected by natural factors and human activities. The natural factors that have the most effect on ground-water quality in the basin are depth in the aquifer and distance from major faults. Ground-water temperatures and pH significantly increased with well depth (p≤0.05). Concentrations of dissolved solids, alkalinity, calcium, potassium, chloride, and sulfate were significantly higher in samples collected from wells less than 2 kilometers from major faults than in samples from wells greater than 2 kilometers from major faults (p≤0.05). Previous studies have attributed this relation to the upward migration through faults of ground water from gypsiferous mudstones. Ground-water quality was not significantly different among the various basin-fill units; between parts of the basin fill that differ in thickness, lateral extent, and composition north and south of an inferred fault; or among areas that differ in distance from stream alluvium (p>0.05). Human activities have a substantial effect on ground-water quality in the basin. Ground water that contained recent (post-1953) recharge from urban areas had significantly higher concentrations of nitrite plus nitrate than ground water that did not contain recent recharge from the land surface (p≤0.05). Ground water that contained recent recharge from present agricultural areas had significantly higher concentrations of nitrite plus nitrate, calcium, and potassium than ground water that did not contain recent recharge from the land surface (p≤0.05). Ground water that contained recent recharge from present agricultural areas also had significantly higher concentrations of calcium, potassium, alkalinity, and dissolved solids than ground water that contained recent recharge from urban areas (p≤0.05). Pre-existing ground-water quality data for six wells indicated that from the 1980s to 1998, concentrations of nitrite plus nitrate and dissolved solids significantly increased at a well in an agricultural area, concentrations of nitrite plus nitrate significantly increased at a well where the land use had changed from rangeland to urban, and concentrations of nitrite plus nitrate and dissolved solids significantly decreased at a well in an urban area (p≤0.10). Constituents did not significantly increase or decrease from the 1980s to 1998 at an additional well in an agricultural area, at an additional well where the land use had changed from rangeland to urban, and at a well where the land use had changed from agricultural to urban (p≤0.10).

Arizona↗
USGS2000

Pesticides and their metabolites in selected surface-water public supplies in New York State, 1999

Sixteen different pesticides or their metabolites (degradations products) where detected in water samples collected in 1999 from three networks of lakes and reservoirs in upstate New York that are sources of public water supply. The networks sampled included the New York City network (10 reservoirs); the Finger Lakes-Great Lakes network (three Finger Lakes and two Great Lakes that supply large and small cities) and the western New York reservoir network (three reservoirs that supply small cities or towns). The concentrations of the compounds detected in the samples generally were low. Only a few of the compounds detected had a concentration exceeding 1 mg/L (microgram per liter), and no compounds detected in the New York City reservoirs network had concentrations exceeding 0.05 mg/L. None of the compounds detected exceeded any Federal or State water-quality standard. Compounds that were most frequently detected, and whose concentrations were highest, were the three herbicides atrazine, metolachlor, and simazine, and two herbicide metabolites (the atrazine metabolite deethylatrazine, and the metolachlor metabolite metolachlor ESA). Most of these compounds, or their parent compounds, are used on corn or other row crops. Median total pesticide and metabolite concentration for each network ranged from less than 0.02 mg/L for the New York City reservoirs network to more than 2 mg/L for the western New York reservoir network; the median for the Finger Lakes.Great Lakes network was about 0.1 mg/L. These differences reflect the amount of agricultural land use within each of the three networks, although other factors can affect pesticide and metabolite concentrations. The watersheds of the New York City reservoirs have the lowest percentage of agricultural land, and those of the western New York reservoirs have the highest. The highest herbicide or herbicide-metabolite concentrations among the New York City reservoirs were in the Cannonsville reservoir, whose watershed has a high percentage of agricultural land. The highest pesticide concentrations of the Lake sites were in Cayuga Lake, and the highest pesticide concentrations of the western New York reservoir sites were at the LeRoy reservoir. The drought conditions in 1999 resulted in a general decrease in median total concentrations, and in the median number of detected compounds, in all networks, from January through September. Pesticide concentrations at the western New York reservoir sites were lower in 1999 than in 1998, as a result of the late-spring and early-summer drought conditions in 1999. Concentrations of pesticides in surface-water supplies are likely to be higher during years with normal or high streamflows than in years of drought, and the small reservoirs are likely to show a greater change in pesticide concentrations from drought year to nondrought years than the larger water bodies.

New York↗
USGS2000

Ground-water quality atlas of Oakland County, Michigan

The U.S. Geological Survey (USGS), in cooperation with Oakland County Health Division (OCHD), collected 140 water samples from 38 wells in Oakland County during 1998 to better understand ground-water quality. OCHD had observed temporal variations in concentrations of various constituents, so two additional sets of samples were collected to evaluate potential short-term variability related to sample collection procedures and long-term seasonal variability. Replicate samples from 28 wells were analyzed in the Michigan Department of Environmental Quality (MDEQ) Drinking Water Laboratory to compare MDEQ’s analytical results to those obtained from the USGS National Water Quality Laboratory. Several additional databases describing population, land use, water supply, soils, geology, and flows of ground water and surface water are presented in the first part of the report to assist in interpreting the water-quality data. Maps created from these databases are provided in the first portion of the report as an extension of the study-area description. The U.S. Environmental Protection Agency (USEPA) has established Maximum Contaminant Levels (MCL) and Secondary Maximum Contaminant Levels (SMCL) for which samples were analyzed in this study. Water from the 38 wells sampled by the USGS did not exceed the SMCL or MCL for sulfate, fluoride, or nitrite. However, water from 26 wells exceeded the SMCL for iron, water from 12 wells exceeded the SMCL for manganese, and water from 12 wells exceeded the SMCL for dissolved solids. Water from two wells exceeded the MCL for nitrate, although nitrate concentrations in water from most wells was below the detection limit. Water from seven wells exceeded the SMCL for chloride, and water from all wells contained detectable concentrations of chloride. Water from five wells exceeded the MCL for arsenic, and most of the wells sampled contained detectable concentrations of arsenic. These five wells were identified from previous MDEQ analyses to have elevated arsenic concentrations, and were sampled to obtain additional chemistry information. Replicate samples were collected from 26 of the 38 wells for analysis at the MDEQ Drinking-Water Laboratory to compare the results with the USGS National Water Quality Laboratory. The results of the replicate analyses indicate close agreement between the laboratories, with mean differences for nitrate, chloride, and arsenic of 0.10 milligrams per liter (mg/L) as nitrogen, 6.8 mg/L, and 0.0008 mg/L, respectively between the USGS and MDEQ analyses. Potential health effects associated with ingesting nitrate, chloride, and arsenic are provided with the water-quality data, along with references for further information.

Michigan↗
USGS2000

Hydrogeology of the regional aquifer near Flagstaff, Arizona, 1994-97

Sandstones, siltstones, and limestones that are Pennsylvanian to Permian in age underlie the southern part of the Colorado Plateau near Flagstaff, Arizona, and contain a complex regional aquifer that has become increasingly important as a source of water for domestic, municipal, and recreational uses. Ground-water flow in the regional aquifer is poorly understood in this area because (1) depth of the aquifer limits exploratory drilling and testing and (2) the geologic structure increases the complexity of the aquifer characteristics and the ground-water flow system. Four methods were used to improve the understanding of the hydrogeology of the regional aquifer near Flagstaff. • Remote-sensing techniques and geologic mapping provided data to identify many structural features that indicate a more complex structural environment and history than previously realized. • Data from surface-geophysical techniques that included ground-penetrating radar, seismic reflection and seismic refraction, and square-array resistivity, verified that some of the geologic structures expressed at land surface propagate deep into the subsurface and through the principal water-bearing zones of the regional aquifer at near-vertical angles. • A well and spring inventory, borehole-geophysical methods, and well and aquifer tests provided additional information relating aquifer and ground-water flow characteristics to geologic structure. • Water-chemistry data, which included major ion, nutrient, trace-element, and radioactive and stable-isotope analyses, provided an independent means of verifying the hydrogeologic characteristics of the aquifer and were used to determine recharge and discharge areas, groundwater movement, and ground-water age. Ground-water recharge occurs throughout the area but is greatest at higher altitudes where precipitation is greater and in areas where heavily fractured rock units of the aquifer are exposed. The estimated annual average recharge to the regional aquifer in the study area is about 290,000 acre-feet. Ground water flows laterally and vertically through pore spaces in the rock and along faults and other fractures from high-altitude areas in the southern part of the study area to regional drains north of the study area along the Little Colorado and Colorado Rivers, and to drains south of the study area along Oak Creek and the Verde Valley. Ground-water discharge in these areas—about 400,000 acre-feet per year—exceeds the annual recharge to the aquifer in the Flagstaff area, but ground water from areas outside the study area contributes to this discharge as well. The saturated thickness of the regional aquifer averages about 1,200 feet, and the amount of water in storage could be as much as 4,800,000 acrefeet, or about 10 percent of the total volume of the aquifer. The quality of water in the regional aquifer in terms of dissolved-solids concentrations is good for most uses throughout the area. Dissolvedsolids concentrations generally are less than 500 milligrams per liter. Water in the regional aquifer is primarily a calcium magnesium bicarbonate type. In some areas near the Rio de Flag, the water has significant nitrate and chloride components, which indicate direct recharge in these areas from the Rio de Flag. Oxygen and deuterium data indicate a common recharge source for water in the aquifer and that some sites receive recharge from surface waters where evaporation has occurred. Estimated carbon-14 ages and tritium activities indicate ground-water ages from less than 200 years in the Lake Mary area to more than 5,000 years in the Wupatki area. The regional aquifer is heterogeneous and anisotrophic and has a complex ground-water flow system. The most productive water-bearing material tends to be fine- to medium-grained sandstones, and ground-water flow and potential well yields are related to geologic structure. Fracturing associated with structural deformation increases recharge locally and also increases the potential for high well yields. Surface-geophysical techniques provided information on the orientation of high-angle, deep-seated structure in the saturated zone. Borehole-geophysical data identified horizontal to near-horizontal fractures as significant components of the fracture-flow system not apparent in the surface-geophysical data. Structural features that strike northwest appear to be areas that have the greatest potential for high well yields. A north-northeastward-striking structure may be just as promising, but additional data are needed to verify this relation.

Arizona↗