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USGS2000

Availability of Ground-Water Data for California, Water Year 1999

The Water Resources Division of the U.S. Geological Survey, in cooperation with Federal, State, and local water agencies, obtains a large amount of data pertaining to the ground-water resources of California each water year. These data constitute a valuable data base for developing an improved understanding of the water resources of the State. Beginning with the 1985 water year and continuing through 1993, these data were published in a report series entitled ?Water Resources Data for California, Volume 5. Ground-Water Data.? Prior to the introduction of this series, historical ground-water information was published in U.S. Geological Survey Water-Supply Papers. In 1994, the Volume 5 Ground-Water Data report was discontinued, but data continue to be available in our data bases. This Fact Sheet serves as an index to ground-water data for 1999. The 2-page report contains a map of California showing the number of wells (by county) with available water-level and water-quality data for the current water year (fig. 2) and instructions for obtaining this and other ground-water information contained in the data bases of the Water Resources Division, California District.

Fact Sheet↗

USGS1999

Availability of Ground-Water Data For California, Water Year 1998

The Water Resources Division of the U.S. Geological Survey, in cooperation with Federal, State, and local water agencies, obtains a large amount of data pertaining to the ground-water resources of California each water year. These data constitute a valuable data base for developing an improved understanding of the water resources of the State. Beginning with the 1985 water year and continuing through 1993, these data were published in a report series entitled ?Water Resources Data for California, Volume 5. Ground-Water Data.? Prior to the introduction of this series, historical ground-water information was published in U.S. Geological Survey Water-Supply Papers. In 1994, the Volume 5 Ground-Water Data report was discontinued, but data continue to be available in our data bases. This Fact Sheet serves as an index to ground-water data for 1998. The 2-page report contains a map of California showing the number of wells (by county) with available water-level and water-quality data for the current water year (fig. 2) and instructions for obtaining this and other ground-water information contained in the data bases of the Water Resources Division, California District.

Fact Sheet↗

USGS1983

Numerical simulation of ground-water flow in lower Satus Creek Basin, Yakima Indian Reservation, Washington

A multilayer numerical model of steady-state ground-water flow in lower Satus Creek basin was constructed, calibrated using time-averaged data, and used to estimate the long-term effects of proposed irrigation-water management plans on ground-water levels in the area. Model computations showed that irrigation of new lands in the Satus uplands would raise ground-water levels in lower Satus Creek basin and thereby increase the size of the waterlogged areas. The model also demonstrated that pumping water from wells, reducing the amount of irrigation water used in the lowlands, and stopping leakage from Satus No. 2 and 3 Pump Canals were all effective methods to alleviate present waterlogging in some parts of the basin and to counteract some of the anticipated ground-water-level rises that would be caused by irrigating the uplands. The proposed changes in water use affected model-computed ground-water levels most in the eastern part of the basin between Satus No. 2 and No. 3 Pump Canals. The effects on ground-water levels in the western part of the basin between Satus Creek and Satus No. 2 Pump Canal were smaller. (USGS)

Water-Resources Investigations Report↗

USGS2001

Availability Of Ground-Water Data For California, Water Year 2000

The Water Resources Division of the U.S. Geological Survey, in cooperation with Federal, State, and local water agencies, obtains a large amount of data pertaining to the ground-water resources of California each water year. These data constitute a valuable database for developing an improved understanding of the water resources of the State. Beginning with the 1985 water year and continuing through 1993, these data were published in a report series entitled ?Water Resources Data for California, Volume 5. Ground-Water Data.? Prior to the introduction of this series, historical ground-water information was published in U.S. Geological Survey Water-Supply Papers. In 1994, the Volume 5 Ground-Water Data report was discontinued, but data continue to be available in our databases. This Fact Sheet serves as an index to ground-water data for water year 2000. The 2-page report contains a map of California showing the number of wells (by county) with available water-level and water-quality data for water year 2000 (fig. 2) and instructions for obtaining this and other ground-water information contained in the databases of the Water Resources Division, California District.

Fact Sheet↗

USGS2003

Effects of recharge, Upper Floridan aquifer heads, and time scale on simulated ground-water exchange with Lake Starr, a seepage lake in central Florida

Lake Starr and other lakes in the mantled karst terrain of Florida's Central Lake District are surrounded by a conductive surficial aquifer system that receives highly variable recharge from rainfall. In addition, downward leakage from these lakes varies as heads in the underlying Upper Floridan aquifer change seasonally and with pumpage. A saturated three-dimensional finite-difference ground-water flow model was used to simulate the effects of recharge, Upper Floridan aquifer heads, and model time scale on ground-water exchange with Lake Starr. The lake was simulated as an active part of the model using high hydraulic conductivity cells. Simulated ground-water flow was compared to net ground-water flow estimated from a rigorously derived water budget for the 2-year period August 1996-July 1998. Calibrating saturated ground-water flow models with monthly stress periods to a monthly lake water budget will result in underpredicting gross inflow to, and leakage from, ridge lakes in Florida. Underprediction of ground-water inflow occurs because recharge stresses and ground-water flow responses during rainy periods are averaged over too long a time period using monthly stress periods. When inflow is underestimated during calibration, leakage also is underestimated because inflow and leakage are correlated if lake stage is maintained over the long term. Underpredicted leakage reduces the implied effect of ground-water withdrawals from the Upper Floridan aquifer on the lake. Calibrating the weekly simulation required accounting for transient responses in the water table near the lake that generated the greater range of net ground-water flow values seen in the weekly water budget. Calibrating to the weekly lake water budget also required increasing the value of annual recharge in the nearshore region well above the initial estimate of 35 percent of the rainfall, and increasing the hydraulic conductivity of the deposits around and beneath the lake. To simulate the total ground-water inflow to lakes, saturated-flow models of lake basins need to account for the potential effects of rapid and efficient recharge in the surficial aquifer system closest to the lake. In this part of the basin, the ability to accurately estimate recharge is crucial because the water table is shallowest and the response time between rainfall and recharge is shortest. Use of the one-dimensional LEACHM model to simulate the effects of the unsaturated zone on the timing and magnitude of recharge in the nearshore improved the simulation of peak values of ground-water inflow to Lake Starr. Results of weekly simulations suggest that weekly recharge can approach the majority of weekly rainfall on the nearshore part of the lake basin. However, even though a weekly simulation with higher recharge in the nearshore was able to reproduce the extremes of ground-water exchange with the lake more accurately, it was not consistently better at predicting net ground-water flow within the water budget error than a simulation with lower recharge. The more subtle effects of rainfall and recharge on ground-water inflow to the lake were more difficult to simulate. The use of variably saturated flow modeling, with time scales that are shorter than weekly and finer spatial discretization, is probably necessary to understand these processes. The basin-wide model of Lake Starr had difficulty simulating the full spectrum of ground-water inflows observed in the water budget because of insufficient information about recharge to ground water, and because of practical limits on spatial and temporal discretization in a model at this scale. In contrast, the saturated flow model appeared to successfully simulate the effects of heads in the Upper Floridan aquifer on water levels and ground-water exchange with the lake at both weekly and monthly stress periods. Most of the variability in lake leakage can be explained by the average vertical head difference between the lake and a re

Water-Resources Investigations Report↗

USGS1980

Effects of the proposed Prosperity Reservoir on ground water and water quality in lower Center Creek basin, Missouri

Effects of the proposed Prosperity Reservoir on ground water and water quality in lower Center Creek basin depend partly on the effectiveness of Grove Creek as a hydrologic boundary between the reservoir site and the Oronogo-Duenweg mining belt. Results of two dye traces indicate that Grove Creek probably is not an effective boundary. Therefore, higher water levels near the reservoir may cause more ground water to move into the mining belt and cause a greater discharge of zinc-laden mine water into Center Creek. Ground-water-level measurements and seepage runs on Center Creek indicate a relationship between ground-water levels, mine-water discharge and seepage, and base flow in Center Creek. From March to October 1979, ground-water levels generally decreased from 5 to 20 feet at higher elevations (recharge areas) and from 1 to 3 feet near Center Creek (discharge area); total mine water discharged to the surface before entering Center Creek decreased from 5.4 to 2.2 cubic feet per second; mine-water seepage directly to Center Creek decreased from an estimated 1.9 to 1.1 cubic feet per second; and the discharge of Center Creek near Carterville decreased from 184 to 42 cubic feet per second. Fertilizer industry wastes discharged into Grove Creek resulted in significant increases of nitrogen and phosphorus in lower Center Creek.

Missouri↗

USGS1969

Ground-water data as of 1967, Central Coastal Subregion, California

Most usable ground water in the predominantly mountainous Central Coastal Subregion occurs in alluvium-filled valleys and coastal plains and in deeper aquifers of Quaternary and Tertiary age. The intervening mountainous areas are underlain by consolidated sedimentary, igneous, and metamorphic rocks, mainly of Mesozoic age. These older rocks contain only small quantities of recoverable ground water and, therefore, are not considered a major source of ground water. In the Central Coastal Subregion, 24 basins have been identified as significant sources of ground water. The total area of the 24 basins is about 3,500 square miles. The water-bearing deposits range in thickness from about 200 to 4,000 feet. Depending on local conditions, recharge infiltrates at rates of less than 1½ feet per day to more than 10 feet per day in the upper part of alluvial fans and stream channels and at the outcrops of the deeper aquifers. The maximum measured depth to water in the water-bearing deposits is 568 ft. In several valleys there are flowing wells. Total storage capacity of 16 of the basins is more than 20,000,000 acre-feet . The usable storage capacity of 18 of the basins is more than 7,600,000 acre-feet; the limiting factors are sea-water intrusion and high pumping lift. Ground-water temperature ranges from about 55° to about 75°F . The dissolved-solids content of the water is generally less than 800 parts per million, but locally is more than 11,000 parts per million. The predominant water type is calcium bicarbonate, but sodium, magnesium, sulfate, and chloride are present locally in significant quantities. Properly constructed wells in some areas can yield 425 gallons per minute.

California↗

USGS1999

Ground-water quality in alluvial basins that have minimal urban development, south-central Arizona

Ground-water quality data (1917-96) from 772 wells in 16 alluvial basins that have minimal urban development were used to determine the effect of nonurban factors on ground-water quality in south- central Arizona. Characterization of the spatial variability of ground-water quality within and among alluvial basins that have minimal urban development will provide a baseline to which water- quality problems associated with urbanization can be compared. Four water-type categories--calcium carbonate, calcium mixed anion, sodium carbonate, and sodium chloride--were used to classify the 13 alluvial basins for which adequate data were available. Ground-water quality was compared to U.S. Environmental Protaection Agency maximum contaminant levels for drinking water, depth of well, and depth to top of perforated interval for five alluvial basins that represented the four water-type categories. Exceedances of maximum contaminant levels for fluoride and nitrate occurred in three and four basins, respectively, of the five selected basins. Specific-conductance values for ground water in the five selected basins tend to increase in a northwesterly direction toward the central part of Arizona as the extent of evaporite deposits increases. The results of this study, which are part of the U.S. Geological Survey's National Water-Quality Assessment Program, can be used to determine the effects of urban land-use activities on ground-water quality in similar hydrogeologic conditions and may be the best indicator available for nonurban ground-water quality in the region.

Water-Resources Investigations Report↗

USGS2007

Evaluation of ground-water and boron sources by use of boron stable-isotope ratios, tritium, and selected water-chemistry constituents near Beverly Shores, northwestern Indiana, 2004

Concentrations of boron greater than the U.S. Environmental Protection Agency (USEPA) 900 μg/L removal action level (RAL) standard were detected in water sampled by the USEPA in 2004 from three domestic wells near Beverly Shores, Indiana. The RAL regulates only human-affected concentrations of a constituent. A lack of well logs and screened depth information precluded identification of whether water from sampled wells, and their boron sources, were from human-affected or natural sources in the surficial aquifer, or associated with a previously defined natural, confined aquifer source of boron from the subtill or basal sand aquifers. A geochemically-based classification of the source of boron in ground water could potentially determine the similarity of boron to known sources or mixtures between known sources, or classify whether the relative age of the ground water predated the potential sources of contamination. The U.S. Geological Survey (USGS), in cooperation with the USEPA, investigated the use of a geochemical method that applied boron stable isotopes, and concentrations of boron, tritium, and other constituents to distinguish between natural and human-affected sources of boron in ground water and thereby determine if the RAL was applicable to the situation. Boron stable-isotope ratios and concentrations of boron in 17 ground-water samples and tritium concentrations in 9 ground-water samples collected in 2004 were used to identify geochemical differences between potential sources of boron in ground water near Beverly Shores, Indiana. Boron and δ 11 B analyses for this investigation were made on unacidified samples to assure consistency of the result with unacidified analyses of δ 11 B values from other investigations. Potential sources of boron included surficial-aquifer water affected by coal-combustion products (CCP) or domestic-wastewater, upward discharge of ground water from confined aquifers, and unaffected water from the surficial aquifer that was distant from human-affected boron sources. Boron concentrations in potential ground-water sources of boron were largest (15,700 to 24,400 μg/L) in samples of CCP-affected surficial aquifer water from four wells at a CCP landfill and smallest (27 to 63 μg/L) in three wells in the surficial aquifer that were distant from human-affected boron sources. Boron concentrations in water from the basal sand aquifer ranged from 656 μg/L to 1,800 μg/L. Boron concentrations in water from three domestic-wastewater-affected surficial aquifer wells ranged from 84 to 387 μg/L. Among the representative ground-water samples, boron concentrations from all four samples of CCP-affected surficial aquifer water and four of five samples of water from the basal sand aquifer had concentrations greater than the RAL. A comparison of boron concentrations in acid-preserved and unacidified samples indicated that boron concentrations reported for this investigation may be from about 11 to 16 percent less than would be reported in a standard analysis of an acidified sample. The stable isotope boron-11 was most enriched in comparison to boron-10 in ground water from a confined aquifer, the basal sand aquifer (δ 11 B, 24.6 to 34.0 per mil, five samples); it was most depleted in CCP-affected water from the surficial aquifer (δ 11 B, 0.1 to 6.6 per mil, four samples). Domestic-wastewater-affected water from the surficial aquifer (δ 11 B, 8.7 to 11.7 per mil, four samples) was enriched in boron-11, in comparison to individual samples of a borax detergent additive and a detergent with perborate bleach; it was intermediate in composition between basal sand aquifer water and CCP-affected water from the surficial aquifer. The similarity between a ground-water sample from the surficial aquifer and a hypothetical mixture of unaffected surficial aquifer and basal sand aquifer waters indicates the potential for long-term upward discharge of ground water into the surficial aquifer from one or more confined aquifers. Estimated δ 11 B values for acidified samples were depleted by 1.9 to 2.8 per mil in comparison to unacidified samples from the four wells sampled; those differences were small in comparison to the differences between δ 11 B values of representative sources of boron in ground water. Tritium concentrations ranged from 7.0 to 10.3 tritium units in six samples from the surficial aquifer and were less than 0.8 tritium units in three samples from the basal sand aquifer. Water from wells in the surficial aquifer represents predominantly modern, post-1972 recharge and sources of boron and other constituents. Water from the basal sand aquifer is associated with pre-1952 recharge from sources not affected by local boron inputs. Ground water from six wells (five domestic wells and one public-supply well) where the ground-water source was unknown had boron concentrations, boron isotope ratios, and tritium concentrations similar to water from the basal sand aquifer. Boron concentrations greater than the RAL were found in water from four of these six wells. The boron isotope and tritium data from these four wells indicate a natural source of boron in ground water; therefore, the RAL does not apply to boron concentrations in water from these wells. Water samples from two domestic wells where the ground-water source was unknown had boron concentrations less than the RAL and boron isotope ratios and tritium concentrations that were similar to domestic-wastewater-affected water from the surficial aquifer. The boron isotope ratio for a sample from one domestic well was similar to that of CCP-affected water from the surficial aquifer and detergent compositions; the boron concentration of that sample was less than the RAL. The classifications of differences among representative sources of boron in ground water and water samples from wells where the ground-water source was unknown generally agreed with distinctions based on strontium-87/strontium-86 ratios and concentrations of strontium, chloride, nitrate, and ammonia. This application of boron concentrations, boron isotope ratios, and tritium concentrations to classify differences in relation to potential sources of boron in ground water was able to distinguish between boron from natural sources and from human-affected sources that are subject to regulation.

Indiana↗

USGS1983

Ground-water-use trends in the Twin Cities metropolitan area, Minnesota, 1880-1980

Detailed ground-water-use information from 1880 to 1980 has been collected and analyzed for the Twin Cities metropolitan area. Interpretation of historic water-use data was required to help water-resource planners and managers assess future trends in water use. Data were also needed for three computer-simulation models of ground-water flow being developed in the Twin Cities area. Methods were developed to collect, evaluate, store, and retrieve information from all local, State, and Federal agencies1 records and publications. A computerized water-use data base was constructed to facilitate generation of statistics on water-use trends and to store and retrieve data for the flow models. Ground-water use was analyzed by use category and aquifer and several trends were observed. Eighty percent of ground water currently withdrawn is from wells in the Prairie du Chien-Jordan aquifer. Ground-water use increased from 1880 until the early 1970's, and then declined slightly in the late 1970's. Industrial use in particular declined during the 1970's as a result of conservation that was prompted by increased sewagetreatment and energy costs. The intensity of pumping has decreased within the St. Paul and Minneapolis city limits and increased outside the city limits. The seasonal variability of ground-water use became more pronounced as the percentage of water used for irrigation and air conditioning increased.

Minneosta↗

USGS1984

Ground-water resources of the Mattapoisett River Valley, Plymouth County, Massachusetts

Ground-water withdrawals by municipal wells in the Mettapoisett River valley, Massachusetts, are expected to triple in the next two decades. State and local concern about the long-term impacts of these withdrawals on ground-water levels and streamflow made it necessary to assess the ground-water resources of the valley and to develop a digital ground-water-flow model for management purposes. Ten pumping scenarios, which represent the present and proposed withdrawals from the aquifer, were simulated using reduced recharge conditions. Under conditions simulating 1965 average annual recharge, predicted water levels in the aquifer are as much as 9 feet lower than average annual levels. At the highest withdrawal rates, the predicted drawdown in four wells exceeds the estimated available drawdown. Under conditions representative of the 7-day 10-year low flow of the river, predicted water levels decline as much as 19 feet. Simulated withdrawals in six scenarios use all of the available ground-water discharge. If this drought condition should occur and streamflow is not supplemented by surface water, the model results indicate that the river in the southern half of the valley will stop flowing under most pumping plans. (USGS)

Water-Resources Investigations Report↗

USGS2003

Heat as a tool for studying the movement of ground water near streams

Stream temperature has long been recognized as an important water quality parameter. Temperature plays a key role in the health of a stream’s aquatic life, both in the water column and in the benthic habitat of streambed sediments. Many fish are sensitive to temperature. For example, anadromous salmon require specific temperature ranges to successfully develop, migrate, and spawn [see Halupka and others, 2000]. Metabolic rates, oxygen requirements and availability, predation patterns, and susceptibility of organisms to contaminants are but a few of the many environmental responses regulated by temperature. Hydrologists traditionally treated streams and ground water as distinct, independent resources to be utilized and managed separately. With increasing demands on water supplies, however, hydrologists realized that streams and ground water are parts of a single, interconnected resource [see Winter and others, 1998]. Attempts to distinguish these resources for analytical or regulatory purposes are fraught with difficulty because each domain can supply (or drain) the other, with attendant possibilities for contamination exchange. Sustained depletion of one resource usually results in depletion of the other, propagating adverse effects within the watershed. An understanding of the interconnections between surface water and ground water is therefore essential. This understanding is still incomplete, but receiving growing attention from the research community. Exchanges between streams and shallow ground-water systems play a key role in controlling temperatures not only in streams, but also in their underlying sediments. As a result, analyses of subsurface temperature patterns provide information about surface-water/ground-water interactions. Chemical tracers are commonly used for tracing flow between streams and ground water. Introduction of chemical tracers in near-stream environments is, however, limited by real and perceived issues regarding introduced contamination and practical constraints. As an alternative, naturally occurring variations in temperature can be used to track (or trace) the heat carried by flowing water. The hydraulic transport of heat enables its use as a tracer. Differences between temperatures in the stream and surrounding sediments are now being analyzed to trace the movement of ground water to and from streams. As shown in the subsequent chapters of this circular, tracing the transport of heat leads to a better understanding of the magnitudes and mechanisms of stream/ground-water exchanges, and helps quantify the resulting effects on stream and streambed temperatures. Chapter 1 describes the general principals and procedures by which the natural transport of heat can be utilized to infer the movement of subsurface water near streams. This information sets the foundation for understanding the advanced applications in chapters 2 through 8. Each of these chapters provides a case study, using heat tracing as a tool, of interactions between surface water and ground water for a different location in the western United States. Technical details of the use of heat as an environmental tracer appear in appendices.

Circular↗

USGS2002

Ground-Water Resources of Big Elk Creek Basin, Pennsylvania and Maryland

Many rural areas in southeastern Pennsylvania, including the Big Elk Creek Basin, are undergoing a rapid population increase. New development and an expanding population increase consumptive water use, increase surface runoff, and have the potential to reduce ground-water recharge. The Big Elk Creek Basin is between the Delaware and Susquehanna River Basins and drains directly to the Chesapeake Bay. Both the Delaware and Susquehanna River Basins have basin commissions that regulate and oversee surface-water and ground-water withdrawals. The Big Elk Creek Basin does not have a regulatory agency to oversee withdrawal of water. Ground-water quantity and quality were evaluated for the 79.4-mi2 (square mile) study area that extends from the headwaters of Big Elk Creek in Chester County, Pa., downstream to the U.S. Geological Survey (USGS) streamflowmeasurement station 01495000, Big Elk Creek at Elk Mills, Md., and to inactive USGS streamflowmeasurement station 01495500, Little Elk Creek at Childs, Md. (fig. 1). The study was done by the USGS in cooperation with the Chester County Water Resources Authority and the Chester County Health Department. The full results of the study are published in a technical report by Sloto (2002). This fact sheet summarizes the key findings presented in the technical report.

Pennsylvania↗

USGS1995

Reversal of declining ground-water levels in the Chicago area

Abundant water resources have been an important part of the economic development of the Chicago area for more than a century. The city of Chicago, Ill., and other lakefront towns have used Lake Michigan as a water supply. Where water from Lake Michigan was not available or a need for supplemental water supplies was present, deep wells (generally greater than 700 feet) provided a clean, reliable, and abundant water supply from the Cambrian-Ordovician aquifer. Public water suppliers withdraw the most ground water in the eight-county Chicago area (Cook, Du Page, Grundy, Kane, Kendall, Lake, McHenry, and Will Counties). This report describes a reversal in the trend of declining ground-water levels in the Cambrian-Ordovician aquifer in the Chicago area as public water suppliers have converted from the withdrawal of ground water from wells to the withdrawal of surface water from Lake Michigan.

Illinois↗

USGS1993

National Water Quality Assessment Program; preliminary assessment of nitrate distribution in ground water in the Georgia-Florida Coastal Plain study unit, 1972-90

The U.S. Geological Survey has implemented the National Water Quality Assessment program to describe the quality of the surface- and ground- water resources in 60 large areas or study units in the Nation. The Georgia-Florida Coastal Plain study unit was one of the first 20 selected for study when the full-scale program was implemented in 1991. The study unit has an area of about 54,000 square miles and is located on the south- eastern coast of the United States. The primary source of water supply in this study unit is ground-water from the Upper Floridan aquifer of the Floridan aquifer system. The Upper Floridan aquifer is unconfined or semiconfined in some parts of the study unit, but in other parts is confined by the overlying surficial aquifer system and other confining units. The surficial aquifer system is also used for water supply in some parts of the study unit. Three land-resource areas have been delineated in the study unit on the basis of generalized soil classifications: the Central Florida Ridge, Coastal Flatwoods, and Southern Coastal Plain. Predominant land use and land cover as classified in the 1970's, are forest, agriculture, wetlands, and urban. Nitrate data for water from the Upper Floridan aquifer and the surficial aquifer system were obtained from the National Water Information System data base of the U.S. Geological Survey for the years 1972- 90. In the Upper Floridan aquifer, the highest median nitrate (as nitrogen) concentrations (0.43 and 0.26 milligrams per liter) were in water samples from wells in agricultural and urban areas where the aquifer was unconfined or semiconfined. The maximum contaminant level for nitrate (as nitrogen) in drinking water of 10 milligrams per liter was exceeded in 25 of the 726 water samples from this aquifer. These 25 samples were from wells in urban areas. In water samples from the surficial aquifer system, the highest median nitrate concentration, 8.7 milligrams per liter, was for water samples from agricultural areas in the Central Florida Ridge area. Nitrate (as nitrogen) concentrations exceeded 10 milligrams per liter in 50 of the 421 water samples from wells completed in the surficial aquifer system. Most of these 50 water samples were from wells in agricultural and urban areas (sewage spraying areas) in the Central Florida Ridge.

Florida, Georgia↗

USGS1984

Assessment of ground-water contamination by coal-tar derivatives, St. Louis Park area, Minnesota

Operation of a coal-tar distillation and wood-preserving facility in St. Louis Park, Minnesota, during 1918-72 contaminated ground water with coal-tar derivatives and inorganic chemicals. Coal-tar derivatives entered the groundwater system through three major paths: (1) Spills and drippings that percolated to the water table, (2) surface runoff and plant process water that was discharged to wetlands south of the former plant site, and (3) movement of coal tar directly into bedrock aquifers through a multiaquifer well on the site. In the drift, Platteville, and St. Peter aquifers, ground water flows laterally from west to east and vertically downward. Near the former plant site, creosote-like organic fluids have migrated vertically downward through the drift and are being partially dissolved by ground water. Ground water has preferentially mobilized low-molecular-weight compounds such as phenolic compounds, alkyl-benzenes, and naphthalene, although polynuclear aromatic hydrocarbons as heavy as benzo(a)pyrene have been mobilized at low concentrations. Sorption of high-molecular-weight compounds has retarded their migration down the hydraulic gradient compared to low-molecular-weight compounds in the plume. Some simple phenolic compounds are being degraded to methane and carbon dioxide by bacteria under anaerobic conditions in the drift-PlattevilleSt. Peter aquifer system. Other low-molecular-weight aromatic compounds are apparently being degraded by aerobic bacteria at the periphery of the plume where oxygen is available. Intermediate degradation products such as volatile fatty acids are likely present, but complete conversion of the organic contaminants to innocuous inorganic substances has not been demonstrated. Near and south of 36th and Wooddale Avenues, contaminants enter the St. Peter aquifer where the Glenwood confining unit has been eroded in a buried bedrock valley. Contaminants previously entered the Prairie du Chien-Jordan aquifer through at least one multiaquif er well (W38). Other sources of contaminants and the low concentrations of contaminants hamper delineation of the maximum areal extent of contaminants that are resistant to biologic degradation. These biorefractory compounds will probably continue to migrate down the hydraulic gradients in the drift and Platteville and St. Peter aquifers. Of particular concern with respect to the health risk to humans are the polynuclear aromatic hydrocarbons, which are a major constituent of coal tar and are found in municipal wells near the site that are completed in the Prairie du Chien-Jordan aquifer. The Prairie du Chien-Jordan aquifer lies 250 to 500 feet below land surface and is relatively well protected from nearsurface sources of contamination by overlying rocks. However, the aquifer has been contaminated since at least 1932 because coal-tar derivatives have entered the aquifer through multiaquifer wells. The most significant single source of contamination in the aquifer is a well drilled on the site in 1917 (well W23) that has contained liquid coal-tar since at least 1958. The introduction, dissolution, and movement of this coal-tar in ground water has contaminated nearby municipal wells. The composition of the tar in well W23, and the ratio of concentrations of individual compounds in water from well W23 to those in municipal well SLP15, are consistent with known hydrologic, chemical, and biologic processes, and the conclusion that contaminants in well SLP15 are due primarily to contaminants introduced at well W23. Most of the major polynuclear aromatic hydrocarbons in the tar, although slightly soluble in water and strongly sorbed by aquifer materials, have moved greater distances at higher concentrations than have the lower-molecular-weight, more soluble compounds such as phenolic compounds and naphthalene. The latter are apparently being degraded by bacteria. The direction and rate of contaminant movement within the Prairie du Chien-Jordan aquifer changes with time because the ground-water-flow system continually adjusts to hydraulic stresses caused by ground-water withdrawals and flow through multiaquifer wells. Contaminants can move rapidly through the Prairie du Chien-Jordan because the upper part of the aquifer is a carbonate rock having fracture and solution-channel permeability, low effective porosity, and relatively small surface area for sorption. Consequently, the concentration and composition of contaminants in water pumped from individual industrial and municipal wells completed in the aquifer fluctuate with time. Although contaminants have been in the aquifer for at least 50 years and their spatial distribution is complex, concentrations remain highest near their points of introduction through multiaquifer wells near and on the site of the former plant. Contaminants reached the Ironton-Galesville aquifer through at least two deep multiaquifer wells (W23 and W38), but the extent of contamination in this aquifer, and in the underlying Mount Simon-Hinckley aquifer, is not known.

Minnesota↗

USGS2003

Probability of detecting elevated concentrations of nitrate in ground water in a six-county area of south-central Idaho

A probability map constructed for this study identified several areas in a six-county region of south-central Idaho with high probabilities of detecting elevated concentrations (greater than 2 milligrams per liter) of nitrate. An increasing proportion of Idaho’s ground water being used for drinking water and large increases in the inputs of nitrogen to ground water in Cassia, Gooding, Jerome, Lincoln, Minidoka, and Twin Falls Counties have prompted concerns about the quality of the resource. The probability map was constructed to assist regulatory and resource agencies in managing land use and protecting water resources. To construct the probability map, hydrogeologic and anthropogenic data were integrated with ground-water quality data in a geographic information system. The resulting data set contained land use, geology, precipitation, soil characteristics, depth to ground water, nitrogen input, and ground-water velocity information for each of the 1,365 samples collected from 1991 to 2001. Logistic regression analysis was used to determine the most statistically significant variables related to the detection of elevated nitrate concentrations. The resulting multivariate probability model showed that ground-water velocity, nitrogen input, precipitation, soil drainage, land use, and depth to ground water were significantly correlated with elevated nitrate concentrations. A subset of the water-quality data set was used to verify these results. Linear regression of the percentage of predicted probabilities of elevated nitrate concentrations and the actual percentage of elevated nitrate concentrations with the model data set and the verification data set both showed good correlations: r-squared values were 0.96 and 0.97, respectively. Statistical comparisons of both data sets showed that ground-water samples containing elevated nitrate concentrations had significantly higher probabilities of detection (p < 0.001) than samples without elevated nitrate concentrations. On the basis of these results, a map identifying the probability of detecting elevated nitrate concentrations was constructed. High-probability areas on the map coincided with regions of agricultural land use and high nitrogen input, except in southern Gooding County and western Jerome County. In these areas, high ground-water velocities representing a predominance of regional ground water resulted in a low probability of detecting elevated nitrate concentrations. Areas of poor prediction tended to be congregated along the transition zone between high and low ground-water velocities in Jerome and Gooding Counties, indicating a mix of regional and recently recharged ground water.

Idaho↗

USGS1995

A hydrogeologic approach to identify land uses that overlie ground-water flow paths, Broward County, Florida

A hydrogeologic approach that integrates the use of hydrogeologic and spatial tools aids in the identification of land uses that overlie ground- water flow paths and permits a better understanding of ground-water flow systems. A mathematical model was used to simulate the ground-water flow system in Broward County, particle-tracking software was used to determine flow paths leading to the monitor wells in Broward County, and a Geographic Information System was used to identify which land uses overlie the flow paths. A procedure using a geographic information system to evaluate the output from a ground-water flow model has been documented. The ground-water flow model was used to represent steady-state conditions during selected wet- and dry-season months, and an advective flow particle- tracking program was used to simulate the direction of ground-water flow in the aquifer system. Digital spatial data layers were created from the particle pathlines that lead to the vicinity of the open interval of selected wells in the Broward County ground-water quality monitoring network. Buffer zone data layers were created, surrounding the particle pathlines to represent the area of contribution to the water sampled from the monitor wells. Spatial data layers, combined with a land-use data layer, were used to identify the land uses that overlie the ground-water flow paths leading to the monitor wells. The simulation analysis was performed on five Broward County wells with different hydraulic parameters to determine the source of ground-water stress, determine selected particle pathlines, and identify land use in buffer zones in the vicinity of the wells. The flow paths that lead to the grid cells containing wells G-2355, G-2373, and G-2373A did not vary between the wet- and dry-season conditions. Changes in the area of contribution for wells G-2345X and G-2369 were attributed to variations in rainfall patterns, well-field pumpage, and surface-water management practices. Additionally, using a different open interval at a site, such as for wells G-2373 and G-2373A, can result in a very different area that overlies the flow path leading to the monitor well.

Water-Resources Investigations Report↗