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Hydraulic and mechanical properties affecting ground-water flow and aquifer-system compaction, San Joaquin Valley, California

This report summarizes hydraulic and mechanical properties affecting ground-water flow and aquifer-system compaction in the San Joaquin Valley, a broad alluviated intermontane structural trough that constitutes the southern two-thirds of the Central Valley of California. These values will be used to constrain a coupled ground-water flow and aquifer-system compaction model of the western San Joaquin Valley called WESTSIM. A main objective of the WESTSIM model is to evaluate potential future land subsidence that might occur under conditions in which deliveries of imported surface water for agricultural use are reduced and ground-water pumping is increased. Storage values generally are components of the total aquifer-system storage and include inelastic and elastic skeletal storage values of the aquifers and the aquitards that primarily govern the potential amount of land subsidence. Vertical hydraulic conductivity values generally are for discrete thicknesses of sediments, usually aquitards, that primarily govern the rate of land subsidence. The data were compiled from published sources and include results of aquifer tests, stress-strain analyses of borehole extensometer observations, laboratory consolidation tests, and calibrated models of aquifer-system compaction.

Open-File Report↗

Ground-water areas and well logs, central Sevier Valley, Utah

Between September 1959 and June 1960 the United States Geological Survey and the Utah State Engineer, with financial assistance from Garfield, Millard, Piute, Sanpete, and Sevier Counties and from local water-users’ associations, cooperated in an investigation to determine the structural framework of the central Sevier Valley and to evaluate the valley’s ground-water potential. An important aspect of the study was the drilling of 22 test holes under private contract. These data and other data collected during the course of the larger ground-water investigation of which the test drilling was a part will be evaluated in a report on the geology and ground-water resources of the central Sevier Valley. The present report has been prepared to make available the logs of test holes and to describe in general terms the availability of ground water in the different areas of the valley.

Utah↗

Ground-water data for Michigan, 1980

The purpose of this report is to make available the 1980 records of water levels and related data for the principal aquifers of the State. This report is written for municipalities, industries, institutions, consultants, drillers, hydrologists and other people interested in the ground-water resources.

Michigan↗

Ground-water conditions in the Dutch Flats area, Scotts Bluff and Sioux Counties, Nebraska, with a section on chemical quality of the ground water

The U.S. Department of the Interior (DOI) studied contamination induced by irrigation drainage in 26 areas of the Western United States during 1986-95. Comprehensive compilation, synthesis, and evaluation of the data resulting from these studies were initiated by DOI in 1992. Soils and ground water in irrigated areas of the West can contain high concentrations of selenium because of (1) residual selenium from the soil's parent rock beneath irrigated land; (2) selenium derived from rocks in mountains upland from irrigated land by erosion and transport along local drainages, and (3) selenium brought into the area in surface water imported for irrigation. Application of irrigation water to seleniferous soils can dissolve and mobilize selenium and create hydraulic gradients that cause the discharge of seleniferous ground water into irrigation drains. Given a source of selenium, the magnitude of selenium contamination in drainage-affected aquatic ecosystems is strongly related to the aridity of the area and the presence of terminal lakes and ponds. Marine sedimentary rocks and deposits of Late Cretaceous or Tertiary age are generally seleniferous in the Western United States. Depending on their origin and history, some Tertiary continental sedimentary deposits also are seleniferous. Irrigation of areas associated with these rocks and deposits can result in concentrations of selenium in water that exceed criteria for the protection of freshwater aquatic life. Geologic and climatic data for the Western United States were evaluated and incorporated into a geographic information system (GIS) to produce a map identifying areas susceptible to irrigation-induced selenium contamination. Land is considered susceptible where a geologic source of selenium is in or near the area and where the evaporation rate is more than 2.5 times the precipitation rate. In the Western United States, about 160,000 square miles of land, which includes about 4,100 square miles (2.6 million acres) of land irrigated for agriculture, has been identified as being susceptible. Biological data were used to evaluate the reliability of the map. In 12 of DOI's 26 study areas, concentrations of selenium measured in bird eggs were elevated sufficiently to significantly reduce hatchability of the eggs. The GIS map identifies 9 of those 12 areas. Deformed bird embryos having classic symptoms of selenium toxicosis were found in four of the study areas, and the map identifies all four as susceptible to irrigation-induced selenium contamination. The report describes the geography, geology, and ground-water resources of the Dutch Flats area in Scotts Bluff and Sioux Counties, Nebr. The area comprises about 60 square miles and consists predominantly of relatively flat-lying terraces. Farming is the principal occupation in the area. The farm lands are irrigated largely from surface water; ground water is used only as a supplementary supply during drought periods. The climate in the area is semiarid, and the mean annual precipitation is about 16 inches. The rocks exposed in the Dutch Flats area are of Tertiary sad Quaternary age. A map showing the areas of outcrop of the rock formations is included in the report. Sufficient unconfined ground water for irrigation supplies is contained in the deposits of the .third terrace, and wells that yield 1,000 to 2,000 gallons a minute probably could be developed. The depth to water in the area ranges from a few feet to about 80 feet sad averages about 30 feet. The depth to water varies throughout the year; it is least in the late summer when the recharge from irrigation is greatest, sad it is greatest in the early spring before irrigation is begun. A map showing the depth to water in September 1949 is included in the report. The ground-water reservoir is recharged by seepage from irrigation canals and laterals, by seepage from irrigation water applied to the farms, and, to a much lesser extent, by precipitation. In the area b

Nebraska↗

An appraisal of the ground-water resources of the Juniata River Basin, Pennsylvania

This report describes the availability, quantity, quality, variability, and cost of development of the ground-water resources in the Juniata River basin, one of the larger sub-basins of the Susquehanna River basin. The report has been prepared for and under specifications established by the Corps of Engineers, U. S. Army, and the Public Health Service, Department of Health, Education, and Welfare. A comprehensive study of the water and related land resources of the Susquehanna River basin was authorized by the Congress of the United States in October 1961, and the task of preparing a report and of coordinating the work being done by others in support of the study was assigned to the Corps of Engineers. The comprehensive study is being conducted by several Federal departments and independent agencies in cooperation with the States of New York, Pennsylvania, and Maryland. The Public Health Service under its authority in the Federal Water Pollution Control Act (P. L. 660) initiated a comprehensive water quality control program for the Chesapeake drainage basin, which includes the Susquehanna River basin.

Pennsylvania↗

Hydrogeology and hydrogeologic terranes of the Blue Ridge and Piedmont Physiographic Provinces in the eastern United States

Severe and prolonged droughts between 1961 and 1988, combined with increased demands for freshwater supplies in the United States, have resulted in a critical need to assess the potential for development of ground- and surface-water supplies. Rapid industrial growth and urban expansion have caused existing freshwater supplies to be used at or near maximum capacity. Begun in 1978, the Regional Aquifer-System Analysis (RASA) Program of the U.S. Geological Survey (USGS) is a systematic effort to study a number of the Nation's most important aquifer systems, which, in aggregate, underlie much of the country and represent an important component of the Nation's total water supply. The broad objective for each of the 28 studies in the program is to assemble geologic, hydrologic, and geochemical information, to analyze and develop an understanding of the system, and to develop predictive capabilities that will contribute to the effective management of the system. In 1988, as part of the RASA Program, the USGS began a 6-year study of the ground-water resources of parts of 11 States in the Eastern United States (Swain and others, 1991). The study was designated the Appalachian Valley and Piedmont Regional Aquifer-System Analysis (APRASA). The APRASA team investigated ground-water resources primarily in the unglaciated part of the Valley and Ridge, the Blue Ridge, the New England, and the Piedmont Physiographic Provinces (fig. 1). For the purposes of this report, the small area in the New England Physiographic Province that is within the study area in New Jersey and Pennsylvania was considered part of the Piedmont Physiographic Province. The results of the APRASA are contained in about 50 reports and abstracts, including reports on simulation of ground-water flow in three type areas, this atlas, and chapters in Professional Paper 1422. These chapters include the summary (Chapter A), descriptions of recharge rates and surface- and ground-water relations (Chapter B), hydrogeologic terranes in the Valley and Ridge Physiographic Province (Chapter C), and ground-water geochemistry (Chapter D). The purposes of this atlas are to summarize the hydrogeology, to describe an analysis of maps and well records, and to present a classification and map of the hydrogeologic terranes of the Blue Ridge and Piedmont Physiographic Provinces within the APRASA study area. Hydrogeologic terranes are defined for this atlas as regionally mappable areas characterized by similar water-yielding properties of a grouping of selected rock types. The hydrogeologic terranes represent areas of distinct hydrologic character. The terranes are intended to help water users locate and develop adequate water supplies and to help hydrologists interpret the regional hydrogeology. Previous investigations provide maps and descriptions of the geologic units, describe the local quantity and quality of ground water within these units, and establish the statistical methods for comparing the water-yielding properties of these units. State geologic maps show the distribution of geologic units at a scale of 1:500,000 for Alabama (Osborne and others, 1989), Georgia (Lawton and others, 1976), North Carolina (Brown and Parker, 1985), and Virginia (Calver and Hobbs, 1963). State maps show geologic units at a scale of 1:250,000 for Maryland (Cleaves and others, 1968), New Jersey (Lewis and Kummel, 1912), Pennsylvania (Berg and others, 1980), South Carolina (Overstreet and Bell, 1965), Tennessee (Hardeman, 1966), and West Virginia (Cardwell and others, 1968). Quadrangle geologic maps show geologic units at a scale of 1:24,000 for parts of Delaware within the APRASA area (Woodruff and Thompson, 1972, 1975). Many reports have been published describing the groundwater resources of a county, parts of a county, multi-county areas, or river basins. The statistical methods used in this atlas are based largely on those used by Helsel and Hirsch (1992) and by Knopman (1990, p. 7-9). In her analysis of well records in the USGS Ground-Water Site Inventory (GWSI) data base, Knopman (1990) ranked factors that must be taken into account when assessing the water-yielding potential of the rocks in the Valley and Ridge, the Blue Ridge, and the Piedmont Physiographic Provinces in Pennsylvania. Readers are referred to Helsel and Hirsch (1992) and Knopman (1990) for details regarding statistical methods.

Alabama, Delaware, Georgia, Maryland, New Jersey, ↗

Ground-water quality data for Oklahoma; 1982-84

The U.S. Geological Survey has collected data on Oklahoma's ground-water resources since 1934. Most of these data were collected as part of specific ground-water studies conducted in cooperation with various federal, state, and local agencies. Ground-water quality data, as well as data on construction, yield, water levels, and other physical well parameters collected prior to 1982 are available from the U.S. Geological Survey, Oklahoma District Office. Although water-quality data for wells, test holes, and springs have been published, they are scattered through a variety of reports and are not readily available on a statewide basis. The purpose of this report is to make available all of the ground-water quality data collected by the U.S. Geological Survey in the Sate of Oklahoma. This report contains 412 ground-water quality analyses since 1982 from 341 sites in 25 counties.

Open-File Report↗

Hypothetical modeling of redox conditions within a complex ground-water flow field in a glacial setting

This report describes a modeling approach for studying how redox conditions evolve under the influence of a complex ground-water flow field. The distribution of redox conditions within a flow system is of interest because of the intrinsic susceptibility of an aquifer to redox-sensitive, naturally occurring contaminants - such as arsenic - as well as anthropogenic contaminants - such as chlorinated solvents. The MODFLOW-MT3D-RT3D suite of code was applied to a glacial valley-fill aquifer to demonstrate a method for testing the interaction of flow patterns, sources of reactive organic carbon, and availability of electron acceptors in controlling redox conditions. Modeling results show how three hypothetical distributions of organic carbon influence the development of redox conditions in a water-supply aquifer. The distribution of strongly reduced water depends on the balance between the rate of redox reactions and the capability of different parts of the flow system to transmit oxygenated water. The method can take account of changes in the flow system induced by pumping that result in a new distribution of reduced water.

Scientific Investigations Report↗

Maps showing distribution of dissolved solids and dominant chemical type in ground water, Basin and Range Province, Southern California

This map report is one of a series of geologic and hydrologic maps of States in the Basin and Range Province. These map reports contain information on ground-water hydrology, ground-water quality, surface distribution of selected rock types, data on tectonic conditions, areal geophysical data, Pleistocene lakes and marshes and natural resources. This information is the basis for a summary report that characterizes the Basin and Range Province. The geologic and hydrologic characterization will be used to evaluate the Province for prospective regions for further study relative to isolation of high-level radioactive waste. (Bedinger, Sargent and Reed, 1984).

California↗

Maps showing distribution of dissolved solids and dominant chemical type in ground water, Basin and Range Province, New Mexico

This map report is one of a series of geologic and hydrologic maps of States in the Basin and Range Province. These map reports contain information on ground-water hydrology, ground-water quality, surface distribution of selected rock types, data on tectonic conditions, areal geophysical data, Pleistocene lakes and marshes and natural resources. This information is the basis for a summary report that characterizes the Basin and Range Province. The geologic and hydrologic characterization will be used to evaluate the Province for prospective regions for further study relative to isolation of high-level radioactive waste. (Bedinger, Sargent and Reed, 1984).

New Mexico↗

Maps showing distribution of dissolved solids and dominant chemical type in ground water, Basin and Range Province, Nevada

This map report is one of a series of geologic and hydrologic maps of States in the Basin and Range Province. These map reports contain information on ground-water hydrology, ground-water quality, surface distribution of selected rock types, data on tectonic conditions, areal geophysical data, Pleistocene lakes and marshes and natural resources. This information is the basis for a summary report that characterizes the Basin and Range Province. The geologic and hydrologic characterization will be used to evaluate the Province for prospective regions for further study relative to isolation of high-level radioactive waste. (Bedinger, Sargent and Reed, 1984).

Nevada↗

Maps showing distribution of dissolved solids and dominant chemical type in ground water, Basin and Range Province, Oregon

This map report is one of a series of geologic and hydrologic maps of States in the Basin and Range Province. These map reports contain information on ground-water hydrology, ground-water quality, surface distribution of selected rock types, data on tectonic conditions, areal geophysical data, Pleistocene lakes and marshes and natural resources. This information is the basis for a summary report that characterizes the Basin and Range Province. The geologic and hydrologic characterization will be used to evaluate the Province for prospective regions for further study relative to isolation of high-level radioactive waste. (Bedinger, Sargent and Reed, 1984).

Oregon↗

Maps showing distribution of dissolved solids and dominant chemical type in ground water, Basin and Range Province, Texas

This map report is one of a series of geologic and hydrologic maps of States in the Basin and Range Province. These map reports contain information on ground-water hydrology, ground-water quality, surface distribution of selected rock types, data on tectonic conditions, areal geophysical data, Pleistocene lakes and marshes and natural resources. This information is the basis for a summary report that characterizes the Basin and Range Province. The geologic and hydrologic characterization will be used to evaluate the Province for prospective regions for further study relative to isolation of high-level radioactive waste. (Bedinger, Sargent and Reed, 1984).

Texas↗

Maps showing distribution of dissolved solids and dominant chemical type in ground water, Basin and Range province, Utah

This map report is one of a series of geologic and hydrologic maps of States in the Basin and Range Province. These map reports contain information on ground-water hydrology, ground-water quality, surface distribution of selected rock types, data on tectonic conditions, areal geophysical data, Pleistocene lakes and marshes and natural resources. This information is the basis for a summary report that characterizes the Basin and Range Province. The geologic and hydrologic characterization will be used to evaluate the Province for prospective regions for further study relative to isolation of high-level radioactive waste. (Bedinger, Sargent and Reed, 1984).

Utah↗

Mapped minerals at Questa, New Mexico, using airborne visible-infrared imaging spectrometer (AVIRIS) data – Preliminary report for: First quarterly report of the U.S. Geological Survey investigation of baseline and pre-mining ground-water quality in the Red River Valley Basin, New Mexico, November 13, 2001

This preliminary study for the First Quarterly Report has spectrally mapped hydrothermally altered minerals useful in assisting in assessment of water quality of the Red River. Airborne Visible-Infrared Imaging Spectrometer (AVIRIS) data was analyzed to characterize mined and unmined ground at Questa, New Mexico. AVIRIS data covers the Red River drainage north of the river, from between the town of Questa on the west, to east of the town of Red River. The data was calibrated and analyzed using U.S. Geological Survey custom software and spectral mineral library. AVIRIS data was tested for spectral features that matched similar features in the spectral mineral library. Goodness-of-fit and band-depth were calculated for each comparison of spectral features and used to identify surface mineralogy. Mineral distribution, mineral associations, and AVIRIS pixel spectra were examined. Mineral maps show the distribution of iron hydroxides, iron sulfates, clays, micas, carbonates, and other minerals. Initial results show a system of alteration suites that overprint each other. Quartz-sericite-pyrite (QSP) alteration grading out to propylitic alteration (epidote and calcite) was identified at the Questa Mine (molybdenum porphyry) and a similar alteration pattern was mapped at the landslide ("scar") areas. Supergene weathering overprints the altered rock, as shown by jarosite, kaolinite, and gypsum. In the spectral analysis, hydrothermally altered ground appears to be more extensive at the unmined Goat Hill Gulch and the mined ground, than the ?scars? to the east. Though the "scars" have similar overall altered mineral suites, there are differences between the "scars" in sericite, kaolinite, jarosite, gypsum, and calcite abundance. Fieldwork has verified the results at the central unmined "scar" areas.

New Mexico↗

A Graphical-User Interface for the U. S. Geological Survey's SUTRA Code using Argus ONE (for simulation of variable-density saturated-unsaturated ground-water flow with solute or energy transport)

This report describes a Graphical-User Interface (GUI) for SUTRA, the U.S. Geological Survey (USGS) model for saturated-unsaturated variable-fluid-density ground-water flow with solute or energy transport,which combines a USGS-developed code that interfaces SUTRA with Argus ONE, a commercial software product developed by Argus Interware. This product, known as Argus Open Numerical Environments (Argus ONE TM ), is a programmable system with geographic-information-system-like (GIS-like) functionality that includes automated gridding and meshing capabilities for linking geospatial information with finite-difference and finite-element numerical model discretizations. The GUI for SUTRA is based on a public-domain Plug-In Extension (PIE) to Argus ONE that automates the use of ArgusONE to: automatically create the appropriate geospatial information coverages (information layers) for SUTRA, provide menus and dialogs for inputting geospatial information and simulation control parameters for SUTRA, and allow visualization of SUTRA simulation results. Following simulation control data and geospatial data input bythe user through the GUI, ArgusONE creates text files in a format required for normal input to SUTRA,and SUTRA can be executed within the Argus ONE environment. Then, hydraulic head, pressure, solute concentration, temperature, saturation and velocity results from the SUTRA simulation may be visualized. Although the GUI for SUTRA discussed in this report provides all of the graphical pre- and post-processor functions required for running SUTRA, it is also possible for advanced users to apply programmable features within Argus ONE to modify the GUI to meet the unique demands of particular ground-water modeling projects.

Open-File Report↗

Hydrologic budget of the Beaverdam Creek basin, Maryland

A hydrologic budget is a statement accounting for the water gains and losses for selected periods in an area. Weekly measurements of precipitation streamflow, surface-water storage, ground-water stage, and soil resistivity were made during a 2year period, April 1, 1950, to March 28, 1952, in the Beaverdam Creek basin, Wicomico County, Md. The hydrologic measurements are summarized in two budgets, a total budget and a ground-water budget, and in supporting tables and graphs. The results of the investigation have some potentially significant applications because they describe a method for determining the annual replenishment of the water supply of a basin and the ways of water disposal under natural conditions. The information helps to determine the 'safe' yield of water in diversion from natural to artificial discharge. The drainage basin of Beaverdam Creek was selected because it appeared to have fewer hydrologic variables than are generally found. However, the methods may prove applicable in many places under a variety of conditions. The measurements are expressed in inches of water over the area of the basin. The equation of the hydrologic cycle is the budget balance: P= R+E+ASW+ delta SW + delta SM + delta GW where P is precipitation; R is runoff; ET is evapotranspiration; delta SW is change in surface-water storage; delta SM is change in soil moisture; and delta GW is change in ground-water storage. In this report 'change' is the final quantity minus the initial quantity and thus is synonymous with 'increase.' Further, ,delta GW= delta H .x Yg, in which delta H is the change in ground-water stage and Yg is the gravity yield, or the specific yield of the sediments as measured during the short periods of declining ground-water levels characteristic of the area. The complex sum of the revised equation P ? R - delta SW ? ET - delta SM, which is equal to delta H. x Yg, has been named the 'infiltration residual'; it is equivalent to ground-water recharge. Two unmeasured, but not entirely unknown, quantities, evapotranspiration, (ET) and gravity yield, (Yg), are included in the equation. They are derived statistically by a method of convergent approximations, one of the contributions of this investigation. On the basis of laboratory analysis, well-field tests, and general information on rates of drainage from saturated sediments, a gravity yield of 14 percent was assumed as a first approximation. The equation was then solved, by weeks, for evapotranspiration, ET. The evapotranspiration losses were plotted against the calendar week. Using the time of year as a control, a smooth curve was fitted to the evapotranspiration data, and modified values of ET were read from the curve. These were used to compute weekly values of the infiltration residual which were plotted against ground-water stage. The slope of the line of best fit gave a closer approximation of gravity yield, Yg. The process was repeated. The approximations converged, so that a fourth and final approximation resulted in a close grouping of all the points along a line whose slope indicated a Yg of 11.0 percent, and a slightly asymmetric bell-shaped curve of total evapotranspiration by weeks was obtained that is considered representative of this area. Check calculations of gravity yield were made during periods of low evapotranspiration and high infiltration, which substantiate the computed average of 11.0 percent. Refinements in the method of deriving the ground-water budget were introduced to supplement the techniques developed by Meinzer and Stearns in the study of the Pomperaug River basin in Connecticut in 1913 and 1916. The hydrologic equation for the ground-water cycle may be written Gr=D + delta H. x Yg + ETg, in which Gr is ground-water recharge (infiltration); D is ground-water drainage; delta H is the change in mean ground-water stage (final stage minus initial stage); Yg is gravity yield (taken as 11.0 percent in computations here); an

Water Supply Paper↗

Private Domestic-Well Characteristics and the Distribution of Domestic Withdrawals among Aquifers in the Virginia Coastal Plain

A comprehensive analysis of private domestic wells and self-supplied domestic ground-water withdrawals in the Coastal Plain Physiographic Province of Virginia indicates that the magnitudes of these withdrawals and their effects on local and regional ground-water flow are larger and more important than previous reports have stated. Self-supplied ground-water withdrawals for domestic use in the Virginia Coastal Plain are estimated to be approximately 40 million gallons per day, or about 28 percent of all ground-water withdrawals in the area. Contrary to widely held assumptions, only 22 percent of domestic wells in the Virginia Coastal Plain are completed in the shallow, unconfined surficial aquifer to which the water is returned directly by home septic systems. Fifty-three percent of the wells are completed in six deeper confined aquifers, and the remaining 25 percent are completed in the Potomac aquifer and confining zone, the deepest units in the confined system. Assuming an equal rate of withdrawal per well, 78 percent of domestic ground-water withdrawal, or about 30 million gallons per day, is removed from the regional confined ground-water system. Domestic ground-water withdrawal from an estimated 200,000 private wells supplies more than 15 percent of the population of the area and provides almost the entire source of water in some rural counties. The geographic distribution of these withdrawals is dependent on the self-supplied population and is highly variable. Domestic-well characteristics vary spatially as well, primarily because of geographic differences in depths to particular aquifers, but also because of well-drilling practices that are influenced by geographic, regulatory, and socioeconomic factors. Domestic ground-water withdrawals in the Virginia Coastal Plain were characterized as part of a larger study to analyze the regional ground-water flow system. Characterizing the withdrawals required differentiation of the withdrawals among the aquifers in the area in addition to determination of the geographic distribution of the withdrawals. Because of a lack of comprehensive data on private-well construction and distribution, a sample of private domestic-well records was used to estimate well characteristics and approximate the proportion of wells and withdrawals associated with each aquifer. Construction data on 2,846 private domestic wells were collected from 29 counties and independent cities (localities) having appreciable self-supplied populations and representing private domestic withdrawals of about 31 million gallons per day. Within each locality, geographically stratified random sampling of well records by tax plat characterized details of well construction for the population of domestic wells. Because neither specific location data nor aquifer elevations were available for individual wells, the primary aquifer in which each well is completed was estimated by cross-referencing the screen elevation estimated from the well record with a generalized configuration of hydrogeologic units underlying the locality in which the well is located. For each locality, summarizing the results of this process allowed the determination of the proportion of wells and withdrawals associated with each aquifer. Additional evaluation of spatial data was used to apply the domestic withdrawal rates developed for each aquifer in each locality to a detailed ground-water study of the portion of the Virginia Coastal Plain east of the Chesapeake Bay, which is known as the Eastern Shore Peninsula. Because domestic withdrawal estimates are based on the self-supplied population, the geographic distribution of withdrawals within each of the Eastern Shore counties was estimated by using population data from the 2000 U.S. Census at the resolution of census block groups and further refining the distribution based on road density. The allocation of withdrawals among aquifers was then determined by cross-referencing the spatial distribut

Scientific Investigations Report↗