Geology topics

Bryan D. Schaap

Publications and source records attributed to Bryan D. Schaap.

15 recordsLinked to original sources

USGS2006

Occurrence of trihalomethanes in the nation's ground water and drinking-water supply wells, 1985-2002

This report describes the occurrence of trihalomethanes (THMs) in the Nation's ground water and drinking-water supply wells based on analysis of 5,642 samples of untreated ground water and source water collected or compiled during 1985-2002 by the U.S. Geological Survey National Water-Quality Assessment (NAWQA) Program. THMs are a group of volatile organic compounds (VOCs) with natural and anthropogenic sources that are of interest because they are associated with acute and chronic health problems in humans. THMs occur in water primarily from chlorination and are classified as disinfection by-products. In this report, the four THMs are discussed in the order of chloroform, bromodichloromethane, dibromochloromethane, and then bromoform; this sequence corresponds to largest to smallest chlorine content and smallest to largest bromine content. Four trihalomethanes were detected in less than 20 percent of samples from studies of (1) aquifers, (2) shallow ground water in agricultural areas, (3) shallow ground water in urban areas, (4) domestic wells, and (5) public wells. Detection frequencies for individual THMs in the five studies ranged from zero for shallow ground water in agricultural areas to 19.5 percent for shallow ground water in urban areas. None of the samples from aquifer studies, domestic wells, or public wells had total THM concentrations (the sum of the concentrations of chloroform, bromodichloromethane, dibromochloromethane, and bromoform) greater than or equal to the U.S. Environmental Protection Agency Maximum Contaminant Level of 80 micrograms per liter (?g/L). Comparisons of results among studies of aquifers, shallow ground water in agricultural areas, and shallow ground water in urban areas were used to describe the occurrence of the four THMs in ground water for three different land-use settings-mixed, agricultural, and urban, respectively. At the 0.2-?g/L assessment level, one or more of the four THMs were detected in 7.9 percent of the samples from aquifer studies, 2.2 percent of the samples from shallow ground water in agricultural areas, and 19.5 percent of the samples from shallow ground water in urban areas. In general, detection frequencies and concentrations of the four THMs were greater in shallow ground water in urban areas compared to aquifer studies and to shallow ground water in agricultural areas. For all three of these studies, the most common two-THM mixture at the 0.2-?g/L assessment level was chloroform-bromodichloromethane, and this was the only two-THM mixture found in samples of shallow ground water in agricultural areas. Comparisons of results between studies of domestic wells and public wells were used to describe the occurrence of the four THMs in two different supplies of ground water used for drinking water. At the 0.2-?g/L assessment level, one or more of the four THMs were detected in 5.2 percent of the domestic well samples and in 14.7 percent of the public well samples. In general, detection frequencies and THM concentrations were greater in samples from public wells than from domestic wells. At the 0.2-?g/L assessment level, the six possible two-THM mixtures occurred about six times more frequently in samples from public wells than from domestic wells. One of the most common two-THM mixtures in samples from domestic and public wells was bromodichloromethane-dibromochloromethane. Detection frequency is associated with the chlorine content of the THM compound. In general, for each of the five studies, as the chlorine content of the THM compound decreased, the detection frequency at the 0.2-?g/L assessment level also decreased. The exception was the study of public wells in which the detection frequency of the THMs decreased in the following order: chloroform, bromoform, dibromochloromethane, and bromodichloromethane. At the 0.2-?g/L assessment level, the median concentration for one or more of the four THMs ranged from 0.3 ?g/L (shallow ground water in agricultural a

Scientific Investigations Report↗

USGS2006

Reconnaissance-level assessment of water and bottom-sediment quality, including pesticides and mercury, in Yankton Sioux Tribe wetlands, Charles Mix County, South Dakota, June-July 2005

During June and July 2005, water and bottom-sediment samples were collected from selected Yankton Sioux Tribe wetlands within the historic Reservation area of eastern Charles Mix County as part of a reconnaissance-level assessment by the U.S. Geological Survey and Yankton Sioux Tribe. The water samples were analyzed for pesticides and mercury species. In addition, the water samples were analyzed for physical properties and chemical constituents that might help further characterize the water quality of the wetlands. The bottom-sediment samples were analyzed for mercury species. During June 2005, water samples were collected from 19 wetlands and were analyzed for 61 widely used pesticide compounds. Many pesticides were not detected in any of the water samples and many others were detected only at low concentrations in a few of the samples. Thirteen pesticides were detected in water samples from at least one of the wetlands. Atrazine and de-ethyl atrazine were detected at each of the 19 wetlands. The minimum, maximum, and median dissolved atrazine concentrations were 0.056, 0.567, and 0.151 microgram per liter (?g/L), respectively. Four pesticides (alachlor, carbaryl, chlorpyrifos, and dicamba) were detected in only one wetland each. The number of pesticides detected in any of the 19 wetlands ranged from 3 to 8, with a median of 6. In addition to the results for this study, recent previous studies have frequently found atrazine in Lake Andes and the Missouri River, but none of the atrazine concentrations have been greater than 3 ?g/L, the U.S. Environmental Protection Agency's Maximum Contaminant Level for atrazine in drinking water. During June and July 2005, water and bottom-sediment samples were collected from 10 wetlands. Water samples from each of the wetlands were analyzed for major ions, organic carbon, and mercury species, and bottom-sediment samples were analyzed for mercury species. For the whole-water samples, the total mercury concentrations ranged from 1.11 to 29.65 nanograms per liter (ng/L), with a median of 10.56 ng/L. The methylmercury concentrations ranged from 0.45 to 14.03 ng/L, with a median of 2.28 ng/L. For the bottom-sediment samples, the total mercury concentration ranged from 21.3 to 74.6 nanograms per gram (ng/g), with a median of 54.2 ng/g. The methylmercury concentrations ranged from <0.11 to 2.04 ng/g, with a median of 0.78 ng/g. The total mercury concentrations in the water samples were all much less than 2 ?g/L (2,000 ng/L), the U.S. Environmental Protection Agency's Maximum Contaminant Level for mercury in drinking water. However, water samples from four of the wetlands had concentrations larger than 0.012 ?g/L (12 ng/L), the State of South Dakota's chronic standard for surface waters, including wetlands. Maximum methylmercury concentrations for this study are larger than reported concentrations for wetlands in North Dakota and concentrations reported for the Cheyenne River Indian Reservation in South Dakota.

South Dakota↗

USGS2004

Digital data to support development of a pesticide management plan for the Standing Rock Indian Reservation, Sioux County, North Dakota, and Corson County, South Dakota

As part of a program to support development of pesticide management plans for Indian Reservations, the U.S. Geological Survey has been working in cooperation with the U.S. Environmental Protection Agency to make selected information available to the Tribes or in a format easier for the Tribes to use. As a result of this program, four digital data sets related to the geology or hydrology of the Standing Rock Indian Reservation were produced as part of this report. The digital data sets are based on maps published in 1982 at the 1:250,000 scale in "Geohydrology of the Standing Rock Indian Reservation, North and South Dakota," U.S. Geological Survey Hydrologic Investigations Atlas HA-644 by L.W. Howells. The digital data sets were created by 1) scanning the appropriate map to create an image file, 2) registering the image file to real-world coordinates, 3) creating a new image file rectified to real-world coordinates, and 4) digitizing of the features of interest using the rectified image as a guide. As digital data sets, the information can be used in a geographic information system in combination with other information to help develop a pesticide management plan.

Data Series↗

USGS2004

Compilation of Data to Support Development of a Pesticide Management Plan by the Yankton Sioux Tribe, Charles Mix County, South Dakota

The U.S. Environmental Protection Agency is working with the Yankton Sioux Tribe to develop a pesticide management plan to reduce potential for contamination of ground water that may result from the use of registered pesticides. The purpose of this study was to compile technical information to support development of a pesticide management plan by the Yankton Sioux Tribe for the area within the Yankton Sioux Reservation, Charles Mix County, South Dakota. Five pesticides (alachlor, atrazine, cyanazine, metolachlor, and simazine) were selected by the U.S. Environmental Protection Agency for the management plan approach because they had been identified as probable or possible human carcinogens and they often had been associated with ground-water contamination in many areas and at high concentrations. This report provides a compilation of data to support development of a pesticide management plan. Available data sets are summarized in the text of this report, and actual data sets are provided in one Compact Disk?Read-Only Memory that is included with the report. The compact disk contains data sets pertinent to the development of a pesticide management plan. Pesticide use for the study area is described using information from state and national databases. Within South Dakota, pesticides commonly are applied to corn and soybean crops, which are the primary row crops grown in the study area. Water-quality analyses for pesticides are summarized for several surface-water sites. Pesticide concentrations in most samples were found to be below minimum reporting levels. Topographic data are presented in the form of 30-meter digital elevation model grids and delineation of drainage basins. Geohydrologic data are provided for the surficial deposits and the bedrock units. A high-resolution (30-by-30 meters) land-cover and land-use database is provided and summarized in a tabular format. More than 91 percent of the study area is used for row crops, pasture, or hay, and almost 6 percent of the study area is covered by water or wetlands. Average monthly and yearly precipitation data are summarized in a tabular format. Irrigation information associated with permitted and licensed diversion points is provided. A composite of aerial photographs of Charles Mix County is provided. This report also describes and summarizes the data sets and files, and how the data are relevant to development of a pesticide management plan.

Open-File Report↗

USGS2003

Simulation of ground-water flow in the Cedar River alluvium, northwest Black Hawk County and southwest Bremer County, Iowa

Flooding and high ground-water levels after large or frequent rainstorms have occurred in an area of about 30 square miles along the eastern bank of the Cedar River from Cedar Falls in northwest Black Hawk County to Janesville in southwest Bremer County, Iowa. The U.S. Geological Survey, in cooperation with Black Hawk County, conducted a hydrologic study of the Cedar River alluvium in the northwest Black Hawk and southwest Bremer Counties, to improve understanding of the ground-water flow system and evaluate the effects of hypothetical variations in recharge and discharge conditions. A steady-state ground-water flow model was constructed for the area using November 2001 hydrologic conditions. The model was discretized into an 83-row by 47-column grid of cells measuring approximately 500 feet by 500 feet. Two model layers, one for the alluvium and one for the underlying bedrock units, were used to represent flow in the area. Precipitation during 2001 was similar to historical normals. Precipitation during 1999, especially during the summer when flooding occurred, was well above the historical normals. Borings in the unconsolidated deposits in the study area confirmed the presence of a bedrock valley dipping to the south in the central part of the study area. Water-level measurements in 2001 indicate that ground-water flow in much of the alluvial aquifer parallels the direction of flow in the Cedar River toward the south rather than following shorter flow paths to the west toward the Cedar River. Under steady-state conditions and 2001 pumpage, primary sources of inflow to the ground-water flow system are the Cedar River (65.5 percent), recharge through infiltration of precipitation and upland runoff (31.4 percent), and subsurface flow across the lateral boundaries (3.1 percent). The primary components of outflow from the ground-water flow system are intermittent streams (56.0 percent) and the Cedar River (43.7 percent). Two hypothetical scenarios were used to assess the potential effects of higher river levels and increased recharge compared to the steadystate conditions. For one scenario, river levels were set to bankfull conditions, and a recharge of 1.2 times the steady-state rate was applied. This simulation was used to evaluate the effects of wet conditions. This scenario led to increased water levels, in general, and large areas of shallow (0 to 10 feet) depths to water along the eastern part of the model area near Highway 218. For the second scenario, conditions were the same as for the first scenario, but streambed conductance of intermittent streams modeled as drains was increased to 10 times the steady-state value to simulate increased flow of water from the shallow groundwater flow system. The area with depth to water of 0 to 10 feet along the eastern part of the model area was substantially smaller than that of the first scenario. In general, once high ground-water levels occur, either because of high Cedar River water Abstract levels or above normal local precipitation or both, ground-water in the central part of the study area along Highway 218 flows toward the south rather than following shorter flow paths to the Cedar River. Intermittent streams in the study area discharge substantial amounts of water from the ground-water flow system.

Iowa↗

USGS2002

Reconnaissance-level assessment of water quality near Flandreau, South Dakota

This report presents water-quality data that have been compiled and collected for a reconnaissance-level assessment of water quality near Flandreau, South Dakota. The investigation was initiated as a cooperative effort between the U.S. Geological Survey and the Flandreau Santee Sioux Tribe. Members of the Flandreau Santee Sioux Tribe have expressed concern that Tribal members residing in the city of Flandreau experience more health problems than the general population in the surrounding area. Prior to December 2000, water for the city of Flandreau was supplied by wells completed in the Big Sioux aquifer within the city of Flandreau. After December 2000, water for the city of Flandreau was supplied by the Big Sioux Community Water System from wells completed in the Big Sioux aquifer along the Big Sioux River near Egan, about 8 river miles downstream of Flandreau. There is some concern that the public and private water supplies provided by wells completed in the Big Sioux aquifer near the Big Sioux River may contain chemicals that contribute to the health problems. Data compiled from other investigations provide information about the water quality of the Big Sioux River and the Big Sioux aquifer in the Flandreau area from 1978 through 2001. The median, minimum, and maximum values are presented for fecal bacteria, nitrate, arsenic, and atrazine. Nitrate concentrations of water from Flandreau public-supply wells occasionally exceeded the Maximum Contaminant Level of 10 milligrams per liter for public drinking water. For this study, untreated-water samples were collected from the Big Sioux River in Flandreau and from five wells completed in the Big Sioux aquifer in and near Flandreau. Treated-water samples from the Big Sioux Community Water System were collected at a site about midway between the treatment facility near Egan and the city of Flandreau. The first round of sampling occurred during July 9-12, 2001, and the second round of sampling occurred during August 20-27, 2001. Samples were analyzed for a broad range of compounds, including major ions, nutrients, trace elements, pesticides, antibiotics, and organic wastewater compounds, some of which might cause adverse health effects after long-term exposure. Samples collected on August 27, 2001, from the Big Sioux River also were analyzed for human pharmaceutical compounds. The quality of the water in the Big Sioux River and the Big Sioux aquifer in the Flandreau area cannot be thoroughly characterized with the limited number of samples collected within a 2-month period, and for many analytes, neither drinking-water standards nor associations with adverse health effects have been established. Concentrations of some selected analytes were less than U.S. Environmental Protection Agency drinking-water standards at the time of the sampling, and concentrations of most organic compounds were less than the respective method reporting levels for most of the samples.

South Dakota↗

USGS2002

Sediment accumulation and distribution in Lake Kampeska, Watertown, South Dakota

Lake Kampeska is a natural lake of about 5,075 acres located within the city limits of Watertown, South Dakota. The lake is important as a water supply and recreational resource. Sediment accumulation has been a concern for many years, and several studies have been conducted to learn more about the sediment, including how fast it is accumulating. This study attempted to evaluate previously estimated sediment-accumulation rates and to describe the distribution of sediment in the lake. Analysis of cesium-137 concentrations in sediment cores and changes in lake-bottom elevation over time led to the conclusion that during about the last 50 years, the sediment has been accumulating at a rate on the order of 0.01 foot per year or less. Changes in lake-bottom elevation during this time period indicate that the only significant deposition occurred in the area near the connection of Lake Kampeska to the Big Sioux River. Direct physical measurements and marine seismic surveys indicate that the flat-bottom interior part of the lake has 10 feet or more of sediment over a relatively irregular subbottom.

Water-Resources Investigations Report↗

USGS2001

Effects of remedial grouting on the ground-water flow system at Red Rock Dam near Pella, Iowa

Previous studies have shown direct evidence of under-seepage at Red Rock Dam on the Des Moines River near Pella, Iowa. Underseepage is thought to occur primarily on the northeast side of the dam in the lower bedrock of the St. Louis Limestone, which consists of discontinuous basal evaporite beds and an overlying cavity zone. Because of concerns about the integrity of the dam, the U.S. Army Corps of Engineers initiated a remedial grouting program in September 1991. To assess the effectiveness of the remedial grouting program and to evaluate methods for future assessments, a study was conducted by the U.S. Geological Survey in cooperation with the U.S. Army Corps of Engineers. Potentiometric surface maps of the overburden and bedrock indicate that the direction of ground-water flow on the northeast side of the dam has changed little from pre-grout to post-grout periods. A comparison of water levels, between a pre-grout date and a post-grout date, shows that water levels decreased but that the decrease may be more attributable to changes in dam operations than to remedial grouting. Waterlevel data for the same two dates indicate that a more gradual potentiometric surface exists on the northeast side of the dam than on the southwest side of the dam, which suggests that the hydraulic connection between Lake Red Rock and downgradient bedrock wells still is greater on the northeast side of the dam than on the southwest side. Hydrographs for some wells on the northeast side of the dam indicated a departure from pre-grout trends at approximately the same time grouting was initiated. To varying degrees, hydrographs for the same wells then appear to return to a trend similar to pre-grout years, possibly as a result of new flow paths developing over time after remedial grouting. Spearman correlation coefficients computed for water levels in wells, pool, and tailwater indicate that some areas on the northeast side of the dam appear to be less under the influence of changing pool elevations after grouting than before grouting. This suggests that the hydraulic connection between the Red Rock pool and some downgradient areas has decreased. Analysis of water samples collected from selected wells on the northeast side of the dam shows significant increases in sulfate concentrations beginning about the same time remedial grouting was done upgradient from the wells, possibly indicating that flow paths were cut off to these wells, thereby reducing the amount of mixing with fresh reservoir water. Observable changes in chloride concentrations or trends as a result of remedial grouting were not apparent. Analysis results for hydrogen and oxygen stable isotope samples collected since 1995 indicate large seasonal fluctuations of isotope ratios in the tailwater (assumed representative of the reservoir). Similar but more subdued fluctuations were observed at some wells, but other wells appeared to have little seasonal change. Stable sulfur isotope results indicate the presence of distinct water types between Lake Red Rock and in ground water from downgradient bedrock wells. Sulfur isotope values from samples from a bedrock well located upgradient from the grout curtain indicate a mixture of pool and ground water, whereas samples from downgradient overburden wells have values similar to the pool. Samples from the bedrock wells downgradient from the grout curtain have sulfur isotope values similar to a value obtained from analysis of a gypsum and anhydrite core sample. Hydrographs, statistical analysis of waterlevel data, and water-chemistry data suggest that underseepage on the northeast side of the dam has been reduced but not completely eliminated. Some areas appear to have been affected to a greater degree and for a longer period of time than other areas. Future monitoring of water levels, water chemistry, and stable isotopes can aid in the evaluation of the long-term effectiveness of remedial grouting.

Iowa↗

USGS2001

Hydrologic setting and geochemical characterization of free-phase hydrocarbons in the alluvial aquifer at Mandan, North Dakota, November 2000

Free-phase hydrocarbons are present in the alluvial aquifer at Mandan, North Dakota. A large contaminant body of the hydrocarbons [light nonaqueous phase liquid (LNAPL)] floats on the water table about 20 feet below land surface. The main LNAPL body is about 6 feet thick, and the areal extent is about 657,000 square feet. A study was conducted to describe the hydrologic setting and characterize the geochemical composition of the free-phase hydrocarbons in the alluvial aquifer. Most of the study area is underlain by alluvium of the Heart River Valley that ranges in thickness from about 25 to 109 feet. The alluvium can be divided into three stratigraphic units silty clay, silty sand, and sand and is underlain by shales and sandstones. Monitoring wells were installed prior to this study, to an average depth of about 29 feet. Regional ground-water flow in the Heart River aquifer generally may be from west-northwest to eastsoutheast and is influenced by hydraulic connections to the river. Hydraulic connections also are probable between the aquifer and the Missouri River. Ground-water flow across the north boundary of the aquifer is minimal because of adjacent shales and sandstones of relatively low permeability. Recharge occurs from infiltration of precipitation and is spatially variable depending on the thickness of overlying clays and silts. Although the general water-table gradient may be from west-northwest to east-southeast, the flow directions can vary depending on the river stage and recharge events. Any movement of the LNAPL is influenced by the gradients created by changes in water-level altitudes. LNAPL samples were collected from monitoring wells using dedicated bailers. The samples were transferred to glass containers, stored in the dark, and refrigerated before shipment for analysis by a variety of analytical techniques. For comparison purposes, reference-fuel samples provided by the refinery in Mandan also were analyzed. These reference-fuel samples included a current diesel fuel, a closely related but slightly broader refinery-cut fuel, a crude-oil composite, unleaded regular gasoline, and additives. Four principal analytical techniques were used for geochemical characterization: Purge-and-trap gas chromatography/mass spectrometry (volatile components); capillary gas chromatography/mass spectrometry (semivolatile components); isotope ratio mass spectrometry (carbon isotopes; whole oils); and liquid chromatography/mass spectrometry with electrospray ionization (additives and other organic components). Volatile analytes included solvents, disinfection byproducts, halogenated hydrocarbons, and alkylbenzenes, including benzene, toluene, ethylbenzene, and meta-, para-, and orf/zo-xylenes. Semivolatile analytes included rt-alkanes, isoprenoid alkanes, cycloalkanes, and polycyclic aromatic hydrocarbons and related compounds (naphthalenes, phenanthrenes, and dibenzothiophenes and their alkylated derivatives). Of the additives, only the diesel-fuel additive with the red dye marker was amenable to electrospray ionization. Results indicate the LNAPL consists of closely correlatable diesel fuel at various stages of degradation. All LNAPL samples contained the red dye marker for diesel fuel. None of the samples contained chlorinated solvents associated with industries such as drycleaning or automotive maintenance. Solvents such as acetone, dimethyl ether, and methylene chloride and the gasoline additives methyl-t-butyl ether (MTBE), ethyl-t-butyl ether (ETBE), and t-amyl-methyl ether (TAME) were not found. With one possible exception, no evidence of a different diesel or other hydrocarbon fuel contribution was identified. At one site near the north edge of the main LNAPL body, evidence exists for traces of possible gasoline components in addition to the diesel fuel. The geochemical analysis of the LNAPL and correlations with other fuel products and additives strongly suggest episodic releases of a single, local-source, diesel fuel into the aquifer over an extended period of time.

North Dakota↗

USGS2000

Aquifer test to determine hydraulic properties of the Elm aquifer near Aberdeen, South Dakota

The Elm aquifer, which consists of sandy and gravelly glacial-outwash deposits, is present in several counties in northeastern South Dakota. An aquifer test was conducted northeast of Aberdeen during the fall of 1999 to determine the hydraulic properties of the Elm aquifer in that area. An improved understanding of the properties of the aquifer will be useful in the possible development of the aquifer as a water resource. Historical water-level data indicate that the saturated thickness of the Elm aquifer can change considerably over time. From September 1977 through November 1985, water levels at three wells completed in the Elm aquifer near the aquifer test site varied by 5.1 ft, 9.50 ft, and 11.1 ft. From June 1982 through October 1999, water levels at five wells completed in the Elm aquifer near the aquifer test site varied by 8.7 ft, 11.4 ft, 13.2 ft, 13.8 ft, and 19.7 ft. The water levels during the fall of 1999 were among the highest on record, so the aquifer test was affected by portions of the aquifer being saturated that might not be saturated during drier times. The aquifer test was conducted using five existing wells that had been installed prior to this study. Well A, the pumped well, has an operating irrigation pump and is centrally located among the wells. Wells B, C, D, and E are about 70 ft, 1,390 ft, 2,200 ft, and 3,100 ft, respectively, in different directions from Well A. Using vented pressure transducers and programmable data loggers, water-level data were collected at the five wells prior to, during, and after the pumping, which started on November 19, 1999, and continued a little over 72 hours. Based on available drilling logs, the Elm aquifer near the test area was assumed to be unconfined. The Neuman (1974) method theoretical response curves that most closely match the observed water-level changes at Wells A and B were calculated using software (AQTESOLV for Windows Version 2.13-Professional) developed by Glenn M. Duffield of HydroSOLVE, Inc. These best fit theoretical response curves are based on a transmissivity of 24,000 ft2/d or a hydraulic conductivity of about 600 ft/d, a storage coefficient of 0.05, a specific yield of 0.42, and vertical hydraulic conductivity equal to horizontal hydraulic conductivity. The theoretical type curves match the observed data fairly closely at Wells A and B until about 2,500 minutes and 1,000 minutes, respectively, after pumping began. The increasing rate of drawdown after these breaks is an indication that a no-flow boundary (an area with much lower hydraulic conductivity) likely was encountered and that Wells A and B may be completed in a part of the Elm aquifer with limited hydraulic connection to the rest of the aquifer. Additional analysis indicates that if different assumptions regarding the screened interval for Well B and aquifer anisotropy are used, type curves can be calculated that fit the observed data using a lower specific yield that is within the commonly accepted range. When the screened interval for Well B was reduced to 5 ft near the top of the aquifer and horizontal hydraulic conductivity was set to 20 times vertical hydraulic conductivity, the type curves calculated using a specific yield of 0.1 and a transmissivity of 30,200 ft2/d also matched the observed data from Wells A and B fairly well. A version of the Theim equilibrium equation was used to calculate the theoretical drawdown in an idealized unconfined aquifer when a perfectly efficient well is being pumped at a constant rate. These calculations were performed for a range of pumping rates, drawdowns at the wells, and distances between wells that might be found in a production well field in the Elm aquifer. Although the aquifer test indicates that hydraulic conductivity near the well may be adequate to support a production well, the comparison of drawdown and recovery curves indicates the possibility that heterogeneities may limit the productive capacity of specific loca

Water-Resources Investigations Report↗

USGS1999

Concentrations and possible sources of nitrate in water from the Silurian-Devonian aquifer, Cedar Falls, Iowa

Carbonate rocks of the Silurian-Devonian aquifer are the primary source of water for Cedar Falls, Iowa. A trend of increasing nitrate concentrations has been detected in samples from Cedar Falls water-supply wells 9 and 10, and 1998 nitrate concentrations were close to the U.S. Environmental Protection Agency's Maximum Contaminant Level of 10 milligrams per liter as nitrogen in drinking water. These wells are located in an area where the Silurian-Devonian aquifer is covered by 90 feet of alluvial and glacial deposits. A study to evaluate the concentrations and sources of nitrate in Cedar Falls water-supply wells 9 and 10 was conducted by the U.S. Geological Survey in cooperation with Cedar Falls Utilities. Water-level measurements from a network of Silurian-Devonian observation wells in the Cedar Falls area were used to determine that ground-water flow in the Silurian-Devonian aquifer is generally from northwest to southeast and down the Cedar River Valley. Water samples were collected from Cedar Falls water-supply wells 5, 9, and 10 and a domestic well in 1998. Chlorofluorocarbon analytical results indicate that time of recharge was the mid-1970’s for water from Cedar Falls water-supply well 9. Tritium analytical results indicate that the time of recharge was after 1953 for water from all four sampled wells. Nitrogen isotope rations in water from all four wells indicate that the primary source of nitrate in these wells is probably inorganic nitrogen fertilizer. High nitrate concentrations in samples from Cedar Falls water-supply wells 9 and 10 are probably the result of nitrogen fertilizer applications in the area contributing recharge to the wells. Locally, the nitrate concentrations increase with depth, and the estimated time of recharge for the shallower well is later than the estimated time of recharge for the deeper wells. This suggests that the nitrate and water sampled in the Cedar Falls water-supply wells 9 and 10 are moving along predominantly horizontal ground-water flow paths through the Silurian-Devonian aquifer. Land-use data from 1941 through 1994 indicate that increased nitrate concentrations observed in water from wells 9 and 10 are not the results of increased agricultural land use near the wells. Within 1 mile of the water tower between wells 9 and 10, the proportion of agricultural land has remained fairly stable since 1941. Nitrogen fertilizer sales in Iowa have been higher in recent years than during the mid- 1970’s. This suggests that nitrate concentrations in water from well 9 may persist at present levels or could increase in future years if fertilizer use increases and if higher nitrate concentrations are directly related to higher nitrogen fertilizer use.

Iowa↗

USGS1996

Delineation of flooding within the upper Mississippi River Basin—Flood of June 19-July 31, 1993, in Davenport, Iowa, and vicinity

The hydrologic investigations atlas shows areas in and near Davenport, Iowa, that were flooded by the Mississippi River in 1993. This atlas also depicts the Federal Emergency Management Agency 100-year flood boundary. The drainage basin upstream from Mississippi River Lock and Dam 15 at Davenport received between 100 and 250 percent of normal rainfall from January through July, 1993. The profile of the maximum water-surface elevations of the 1993 flood in the Davenport area is less than the Federal Emergency Management Agency 100-year flood profile. The Mississippi River Lock and Dam 15 tailwater elevation was above the flood elevation from June 19 to July 31, 1993, but did not exceed the 100-year flood elevation. For most of the time during October 1992 through September 1993, the daily mean discharge of the Mississippi River at Clinton, Iowa, greatly exceeded the monthly mean discharges from October 1874 through September 1993, but was less than the 100-year flood discharge. The daily mean discharge at Keokuk, Iowa, exceeded the 100-year flood discharge for nearly the entire month of July 1993.

Illinois, Iowa↗

USGS1996

Delineation of flooding within the upper Mississippi River Basin — Flood of June 18 through August 4, 1993, in Des Moines and vicinity, Iowa

This hydrologic investigations atlas shows the areas in and near Des Moines, Iowa, that were flooded by the Des Moines and the Raccoon Rivers and Walnut, Fourmile, and Beaver Creeks from June 18 through August 4, 1993. This map also depicts the Federal Emergency Management Agency 100-year flood boundaries. The area drained by the Des Moines River upstream from Des Moines received more than 100 percent of normal rainfall in May, June, and July, 1993. At Boone, which is located about 35 miles north-northeast of Des Moines, July rainfall was 424 percent of normal. The discharges at streamflow- gaging stations on the Des Moines River near Stratford, downstream from Saylorville Lake, and at Des Moines are shown. The cumulative discharge for inflow-gaging stations in the Des Moines area and discharge for the Des Moines River below the Raccoon River at Des Moines from July 8 through 21, 1993, are shown. The water-surface elevations of Saylorville Lake from June 18 through August 4, 1993, are shown. Profiles of the maximum water- surface elevations of the Des Moines and Raccoon Rivers during the 1993 flood in Des Moines and vicinity are higher than the respective Federal Emergency Management Agency 100- and 500-year flood profiles.

Iowa↗

USGS1995

Urban stormwater runoff study at Davenport, Iowa

Urban storm water runoff is being investigated as a nonpoint source of pollution across the country as urban areas with populations over 100,000 conduct studies designed to meet U.S. Environmental Protection Agency guidelines for National Pollutant Discharge Elimination System permits for their stormwater discharges. From 1991 through 1994, the City of Davenport, Iowa (fig. 1), and the U.S. Geological Survey cooperatively conducted a study designed to meet technical conditions of the permit application and to develop the criteria for ongoing monitoring during the term of the permit.

Iowa↗

USGS1995

Delineation of flooding within the upper Mississippi River Basin, 1993 — Flood of June 29-September 18, 1993, in Iowa City and vicinity, Iowa

The hydrologic investigations atlas shows the areas in and around Iowa City, Iowa, that were flooded by the Iowa River in 1993. This map also depicts the Federal Emergency Management Agency (FEMA) 100-year flood boundaries. The drainage basin of the Iowa River at Iowa City received well over 100 percent of normal rainfall in June, July, and August, 1993. At the Cedar Rapids airport, located about 20 miles north-northwest of Iowa City, July rainfall was 414 percent of normal. The discharges at U.S. Geological Survey streamflow-gaging stations on the Iowa River upstream of Coralville Reservoir, just downstream from Coralville Reservoir, and at Iowa City are shown. A profile of the maximum water-surface elevations of the 1993 flood in Iowa City and vicinity is higher than the FEMA 100-year flood profile. The water-surface elevation of Coralville Reservoir is shown from June 29-September 18, 1993.

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