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At least 145 records · Page 8Linked to original sources
USGS1994

Methods of analysis and quality-assurance practices of the U.S. Geological Survey organic laboratory, Sacramento, California: Determination of pesticides in water by solid-phase extraction and capillary-column gas chromatography/mass spectrometry

Analytical method and quality-assurance practices were developed for a study of the fate and transport of pesticides in the Sacramento-San Joaquin Delta and the Sacramento and San Joaquin River. Water samples were filtered to remove suspended parti- culate matter and pumped through C-8 solid-phase extraction cartridges to extract the pesticides. The cartridges were dried with carbon dioxide, and the pesticides were eluted with three 2-milliliter aliquots of hexane:diethyl ether (1:1). The eluants were analyzed using capillary-column gas chromatography/mass spectrometry in full-scan mode. Method detection limits for analytes determined per 1,500-milliliter samples ranged from 0.006 to 0.047 microgram per liter. Recoveries ranged from 47 to 89 percent for 12 pesticides in organic-free, Sacramento River and San Joaquin River water samples fortified at 0.05 and 0.26 microgram per liter. The method was modified to improve the pesticide recovery by reducing the sample volume to 1,000 milliliters. Internal standards were added to improve quantitative precision and accuracy. The analysis also was expanded to include a total of 21 pesticides. The method detection limits for 1,000-milliliter samples ranged from 0.022 to 0.129 microgram per liter. Recoveries ranged from 38 to 128 percent for 21 pesticides in organic-free, Sacramento River and San Joaquin River water samples fortified at 0.10 and 0.75 microgram per liter.

California↗
USGS2024

Survey effort and targeted landbird community metrics at Indiana lowland forest restoration sites

Many sampling and analytical methods can estimate the abundance, distributions, and diversity of birds and other wildlife. However, challenges with sample size and analytical capacity can make these methods difficult to implement for resource-limited monitoring programs. To apprise efficient and attainable sampling designs for landbird monitoring programs with limited observational data, we used breeding season bird point survey data collected in 2016 at four forest restoration sites in Indiana, USA. We evaluated three subsets of observed species richness, total possibly breeding landbirds, Partners in Flight Regional Conservation Concern (PIF RCC) landbirds, and interior forest specialists (IFSs). Simulated surveys based on field data were used to conduct Bayesian Michaelis–Menten curve analyses estimating observed species as a function of sampling effort. On comparing simulated survey sets with multiple habitat types versus those with one habitat, we found that those with multiple habitat types had estimated 39%–83% greater observed PIF RCC species richness and required 41%–55% fewer visits per point to observe an equivalent proportion of PIF RCC species. Even with multiple habitats in a survey set, the number of visits per point required to detect 50% of observable species was 30% higher for PIF RCC species than for total breeding landbird species. Low detection rates of IFS species at two field sites made precise estimation of required effort to observe these species difficult. However, qualitatively, we found that only sites containing mature forest fragments had detections of several bird species designated as high-confidence IFS species. Our results suggest that deriving specialized species diversity metrics from point survey data can add value when interpreting those data. Additionally, designing studies to collect these metrics may require explicitly planning to visit multiple habitat types at a monitoring site and increasing the number of visits per survey point.

Indiana↗
USGS1993

Methods of analysis by the U.S. Geological Survey National Water Quality Laboratory-Determination of chromium in water by graphite furnace atomic absorption spectrophotometry

Graphite furnace atomic absorption spectrophotometry is a sensitive, precise, and accurate method for the determination of chromium in natural water samples. The detection limit for this analytical method is 0.4 microg/L with a working linear limit of 25.0 microg/L. The precision at the detection limit ranges from 20 to 57 percent relative standard deviation (RSD) with an improvement to 4.6 percent RSD for concentrations more than 3 microg/L. Accuracy of this method was determined for a variety of reference standards that was representative of the analytical range. The results were within the established standard deviations. Samples were spiked with known concentrations of chromium with recoveries ranging from 84 to 122 percent. In addition, a comparison of data between graphite furnace atomic absorption spectrophotometry and direct-current plasma atomic emission spectrometry resulted in suitable agreement between the two methods, with an average deviation of +/- 2.0 microg/L throughout the analytical range.

Open-File Report↗
USGS2003

Concentrations and co-occurrence correlations of 88 volatile organic compounds (VOCs) in the ambient air of 13 semi-rural to urban locations in the United States

The ambient air concentrations of 88 volatile organic compounds were determined in samples taken at 13 semi-rural to urban locations in Maine, Massachusetts, New Jersey, Pennsylvania, Ohio, Illinois, Louisiana, and California. The sampling periods ranged from 7 to 29 months, yielding a large data set with a total of 23,191 individual air concentration values, some of which were designated "ND" (not detected). For each compound at each sampling site, the air concentrations (ca, ppbV) are reported in terms of means, medians, and means of the detected values. The analytical method utilized adsorption/thermal desorption with air-sampling cartridges. The analytes included numerous halogenated alkanes, halogenated alkenes, ethers, alcohols, nitriles, esters, ketones, aromatics, a disulfide, and a furan. At some sites, the air concentrations of the gasoline-related aromatic compounds and the gasoline additive methyl tert-butyl ether were seasonally dependent, with concentrations that maximized in the winter. For each site studied here, the concentrations of some compounds were highly correlated one with another (e.g., the BTEX group (benzene, toluene, ethylbenzene, and the xylenes). Other aromatic compounds were also all generally correlated with one another, while the concentrations of other compound pairs were not correlated (e.g., benzene was not correlated with CFC-12). The concentrations found for the BTEX group were generally lower than the values that have been previously reported for urbanized and industrialized areas of other nations. ?? 2003 Elsevier Ltd. All rights reserved.

Atmospheric Environment↗
USGS1985

Interlaboratory comparability, bias, and precision for four laboratories measuring constituents in precipitation, November 1982-August 1983

Four laboratories were evaluated in their analysis of identical natural and simulated precipitation water samples. Interlaboratory comparability was evaluated using analysis of variance coupled with Duncan 's multiple range test, and linear-regression models describing the relations between individual laboratory analytical results for natural precipitation samples. Results of the statistical analyses indicate that certain pairs of laboratories produce different results when analyzing identical samples. Analyte bias for each laboratory was examined using analysis of variance coupled with Duncan 's multiple range test on data produced by the laboratories from the analysis of identical simulated precipitation samples. Bias for a given analyte produced by a single laboratory has been indicated when the laboratory mean for that analyte is shown to be significantly different from the mean for the most-probable analyte concentrations in the simulated precipitation samples. Ion-chromatographic methods for the determination of chloride, nitrate, and sulfate have been compared with the colorimetric methods that were also in use during the study period. Comparisons were made using analysis of variance coupled with Duncan 's multiple range test for means produced by the two methods. Analyte precision for each laboratory has been estimated by calculating a pooled variance for each analyte. Analyte estimated precisions have been compared using F-tests and differences in analyte precisions for laboratory pairs have been reported. (USGS)

Water-Resources Investigations Report↗
USGS2020

Ungulate migrations of the western United States, Volume 1

Across the western United States, many ungulate herds must migrate seasonally to access resources and avoid harsh winter conditions. Because these migration paths cover vast landscapes (in other words migration distances up to 150 miles [241 kilometers]), they are increasingly threatened by roads, fencing, subdivisions, and other development. Over the last decade, many new tracking studies have been conducted on migratory herds, and analytical methods have been developed that allow for population-level corridors and stopovers to be mapped and prioritized. In 2018, the U.S. Geological Survey assembled a Corridor Mapping Team to provide technical assistance to western states working to map bison, elk, moose, mule deer, and pronghorn migrations using existing Global Positioning System data. Led by the Wyoming Cooperative Fish and Wildlife Research Unit, the team consists of federal scientists, university researchers, and biologists and analysts from participating state agencies. In its first year, the team has worked to develop standardized analytical and computational methods and a workflow applicable to datasets typically collected by state agencies. In 2019, the team completed analyses necessary to map corridors, stopovers, routes and winter ranges in Arizona, Idaho, Nevada, Utah, and Wyoming. A total of 26 corridors, 16 migration routes, 25 stopovers, and 9 winter ranges were mapped across these states and are included in this report. This report and associated data release provide the means for the habitats required for migration to be taken into account by state and federal transportation officials, land and wildlife managers, planners, and other conservationists working to maintain big-game migration in the western states.

Scientific Investigations Report↗
USGS1998

Nonlethal evaluation of the physiological health of unionid mussels: Method for biopsy and glycogen analysis

In long-lived unionid mussels, many short-term measures of growth are of limited value. Changes in physiological condition may be an early indication of stress, because the increased energy demand associated with stress often results in a depletion of glycogen reserves, the principal storage form of carbohydrates in unionid mussels. Our goal was to nonlethally extract tissue from freshwater mussels and then to develop a rapid and dependable method for the analysis of glycogen in the tissue extracts. A biopsy technique was developed to remove between 5 and 10 mg of foot tissue in Amblema plicata plicata. The survival rate did not differ between biopsied and non-biopsied mussels during a 581-d observation period, demonstrating that the biopsy technique will allow nonlethal evaluation of the physiological condition of individual mussels through measurement of changes in contaminant, genetic, and biochemical indicators in tissue. We also modified the standard alkaline digestion and phenol-sulfuric acid analysis of glycogen for use on the small samples of biopsied tissue and to reduce analysis time and cost. We present quality control data, including method detection limits and estimates of precision and bias. The modified analytical method is rapid and accurate and has a method detection limit of 0.014 mg glycogen. Glycogen content in the biopsied samples was well above the method detection limit; it ranged from 0.09 to 0.36 mg, indicating that the method should be applicable to native mussels.

Journal of the North American Benthological Societ↗
USGS2001

Determination of drugs in surface water and wastewater samples by liquid chromatography-mass spectrometry: Methods and preliminary results including toxicity studies with Vibrio fischeri

In the present work a combined analytical method involving toxicity and liquid chromatography-electrospray ionization-mass spectrometry (LC-ESI-MS) was developed for the determination of pharmaceutical compounds in water samples. The drugs investigated were the analgesics: ibuprofen, ketoprofen, naproxen, and diclofenac, the decomposition product of the acetyl salicylic acid: salicylic acid and one lipid lowering agent, gemfibrozil. The selected compounds are acidic substances, very polar and all of them are analgesic compounds that can be purchased without medical prescription. The developed protocol consisted, first of all, on the use Microtox?? and ToxAlert??100 toxicity tests with Vibrio fischeri for the different pharmaceutical drugs. The 50% effective concentration (EC50) values and the toxicity units (TU) were determined for every compound using both systems. Sample enrichment of water samples was achieved by solid-phase extraction procedure (SPE), using the Merck LiChrolut?? EN cartridges followed by LC-ESI-MS. Average recoveries loading 1 l of samples with pH=2 varied from 69 to 91% and the detection limits in the range of 15-56 ng/l. The developed method was applied to real samples from wastewater and surface-river waters of Catalonia (north-east of Spain). One batch of samples was analyzed in parallel also by High Resolution Gas Chromatography coupled with Mass Spectrometry (HRGC-MS) and the results have been compared with the LC-ESI-MS method developed in this work. ?? 2001 Elsevier Science B.V. All rights reserved.

Conference Paper↗
USGS2012

Analytical resource assessment method for continuous (unconventional) oil and gas accumulations - The "ACCESS" Method

The U.S. Geological Survey (USGS) periodically assesses petroleum resources of areas within the United States and the world. The purpose of this report is to explain the development of an analytic probabilistic method and spreadsheet software system called Analytic Cell-Based Continuous Energy Spreadsheet System (ACCESS). The ACCESS method is based upon mathematical equations derived from probability theory. The ACCESS spreadsheet can be used to calculate estimates of the undeveloped oil, gas, and NGL (natural gas liquids) resources in a continuous-type assessment unit. An assessment unit is a mappable volume of rock in a total petroleum system. In this report, the geologic assessment model is defined first, the analytic probabilistic method is described second, and the spreadsheet ACCESS is described third. In this revised version of Open-File Report 00-044 , the text has been updated to reflect modifications that were made to the ACCESS program. Two versions of the program are added as appendixes.

Open-File Report↗
USGS2001

Methods of analysis by the U.S. Geological Survey National Water Quality Laboratory-Determination of pesticides in water by graphitized carbon-based solid-phase extraction and high-performance liquid chromatography/mass spectrometry

In 1996, the U.S. Geological Survey National Water Quality Laboratory (NWQL) developed and implemented a graphitized carbon-based solid-phase extraction and high-performance liquid chromatographic analytical method to determine polar pesticide concentrations in surface- and ground-water samples. Subsequently, the NWQL developed a complementary analysis that uses high-performance liquid chromatography/mass spectrometry to detect, identify, and quantify polar pesticides and pesticide metabolites in filtered water at concentrations as low as 10 nanograms per liter. This new method was designed to improve sensitivity and selectivity over the prior method, and to reduce known interferences from natural organic matter. In this new method, pesticides are extracted from filtered water samples by useing a 0.5-gram graphitized carbon-based solid-phase extraction cartridge, eluted from the cartridge, and concentrations determined by using high-performance liquid chromatography with electrospray ionization-mass spectrometry. The upper concentration limit is 1.000 microgram per liter ( μ g /L) for most compounds. Single-operator method detection limits in organic-free water samples fortified with pesticides at a concentration of 0.025 μg/L ranged from 0.0019 to 0.022 μ g /L for all compounds in the method. The grand mean (mean of mean recoveries for individual compounds) recoveries in organic-free water samples ranged from 72 to 89 percent, fortified with pesticides at three concentrations between 0.025 and 0.5 μ g /L. Grand mean recoveries in ground- and surface-water samples ranged from 46 to 119 percent, also fortified with pesticides at three concentrations between 0.025 and 0.5 μ g /L. Long-term recoveries from reagent water spikes were used to demonstrate that 38 of 65 compounds can be reported without qualification of the quantitative result across the analytical range of the method. The remaining 27 are reported with qualified estimates of concentration because of greater variability of recovery.

Water-Resources Investigations Report↗
USGS1969

Establishment of gold-quartz standard GQS-1

A homogeneous gold-quartz standard, GQS-1, was prepared from a heterogeneous gold-bearing quartz by chemical treatment. The concentration of gold in GQS-1 was determined by both instrumental neutron activation analysis and radioisotope dilution analysis to be 2.61?0.10 parts per million. Analysis of 10 samples of the standard by both instrumental neutron activation analysis and radioisotope dilution analysis failed to reveal heterogeneity within the standard. The precision of the analytical methods, expressed as standard error, was approximately 0.1 part per million. The analytical data were also used to estimate the average size of gold particles. The chemical treatment apparently reduced the average diameter of the gold particles by at least an order of magnitude and increased the concentration of gold grains by a factor of at least 4,000.

Circular↗
USGS2020

Introduction to linked and dynamic decisions

Often, a decision maker is faced with a series of linked decisions, rather than an isolated one-off decision. In natural resource management, it is common to make a similar type of decision on a regular basis (e.g., annually). Such linked decisions have two important properties: they are dynamic, that is, the actions taken early on affect immediate outcomes as well as the effects of actions taken later; and they may be adaptive, that is, early actions might generate learning that can be applied to later actions. This situation has given rise to the development of methods for adaptive management. This chapter provides an overview of the decision analytical methods available to support framing and solving dynamic decisions, and briefly reviews the case studies that follow.

Book chapter↗
USGS2001

Methods of analysis by the U. S. Geological Survey National Water Quality Laboratory-Determination of organic plus inorganic mercury in filtered and unfiltered natural water with cold vapor; atomic fluorescence spectrometry

An analytical method using cold vapor-atomic fluorescence spectrometry was developed by the U.S. Geological Survey in 2001 for the determination of organic plus inorganic mercury in filtered and unfiltered natural water. This method was developed to eliminate the use of acid dichromate preservative and to provide capability to measure ambient mercury concentrations in natural water. Dissolved mercury includes all oxidizable mercury species present in natural water that has been filtered through a 0.45- micrometer pore size capsule filter. Wholewater recoverable mercury includes dissolved mercury species and mercury species adsorbed to particulate matter in unfiltered natural water. Mercury species can include elemental mercury, mercury (II), mercury (II) complexes, various alkyl- and phenylmercury compounds, and other forms of mercury. In this method, samples are collected and processed according to standard U.S. Geological Survey protocols. Samples are preserved onsite with 6N hydrochloric acid in a ratio of 1 to 100 in a borosilicateglass bottle with fluoropolymer-lined cap. Mercury species are oxidized to mercury (II) by using bromine monochloride; excess oxidation reagent is neutralized with hydroxylamine hydrochloride. Elemental mercury produced after adding stannous chloride is purged from the solution with ultrapure argon gas into a cell in which the mercury concentration is measured by atomic fluorescence emission at 253.7 nanometers. The analytical response is linear up to 125 nanograms per liter (ng/L) of mercury, and the short-term method detection limit is about 5 ng/L. The analytical variability at 50 ng/L is about 10 percent. This report describes the method and compares the use of hydrochloric acid to acid dichromate as a field preservative. Ambient mercury concentrations in hydrochloric acidpreserved samples stored in borosilicate-glass bottles with fluoropolymer-lined caps are shown to be stable for at least 30 days. Mercury concentrations are stable for at least 5 months after bromine monochloride is added to the sample bottles in the laboratory. The long-term average percent recoveries at 20, 45, and 75 ng/L in reagent water, filtered and unfiltered ground water, and filtered and unfiltered surface water range from 89 to 108, 96 to 103, and 94 to 98 percent, respectively.

Water-Resources Investigations Report↗
USGS2018

Data analysis considerations for pesticides determined by National Water Quality Laboratory schedule 2437

In 2013, the U.S. Geological Survey National Water Quality Laboratory (NWQL) made a new method available for the analysis of pesticides in filtered water samples: laboratory schedule 2437. Schedule 2437 is an improvement on previous analytical methods because it determines the concentrations of 225 fungicides, herbicides, insecticides, and associated degradates in one method at similar or lower concentrations than previously available methods. Additionally, the pesticides included in schedule 2437 were strategically identified in a prioritization analysis that assessed likelihood of occurrence, prevalence of use, and potential toxicity. When the NWQL reports pesticide concentrations for analytes in schedule 2437, the laboratory also provides supplemental information useful to data users for assessing method performance and understanding data quality. That supplemental information is discussed in this report, along with an initial analysis of analytical recovery of pesticides in water-quality samples analyzed by schedule 2437 during 2013–2015. A total of 523 field matrix spike samples and their paired environmental samples and 277 laboratory reagent spike samples were analyzed for this report (1,323 samples total). These samples were collected in the field as part of the U.S. Geological Survey National Water-Quality Assessment groundwater and surface-water studies and as part of the NWQL quality-control program. This report reviews how pesticide samples are processed by the NWQL, addresses how to obtain all the data necessary to interpret pesticide concentrations, explains the circumstances that result in a reporting level change or the occurrence of a raised reporting level, and describes the calculation and assessment of recovery. This report also discusses reasons why a data user might choose to exclude data in an interpretive analysis and outlines the approach used to identify the potential for decreased data quality in the assessment of method recovery. The information provided in this report is essential to understanding pesticide data determined by schedule 2437 and should be reviewed before interpretation of these data.

Scientific Investigations Report↗
USGS1985

A method for the determination of vanadium and iron oxidation states in naturally occurring oxides and silicates

A valence-specific analytical method for determining V 3+ in ore minerals has been developed that involves two steps: dissolution of a mineral sample without disturbing the V 3+ /V tot ratio, followed by determination of V 3+ in the presence of V 4+ . The samples are dissolved in a mixture of hydrofluoric and sulphuric acids at 100° in Teflon-lined reaction vessels. Tervalent vanadium is then determined colorimetrically by formation of a V 3+ -thiocyanate complex in aqueous-acetone medium. Fe 3+ is measured semi-quantitatively in the same solution. The method has been tested with two naturally occurring samples containing vanadium and iron. The results obtained were supported by those obtained by other methods, including electron spin resonance spectroscopy, thermogravimetric analysis, and Mössbauer spectroscopy.

Talanta↗
USGS1956

Selected annotated bibliography of the geology of uraniferous and radioactive native bituminous substances, exclusive of coals, in the United States

Native bituminous substances are divided into two groups, 1) bitumens and, 2) pyrobitumens. Bitumens are composed principally of hydrocarbons substantially free from oxygenated bodies, are fusible, and are soluble in carbon disulfide. Native bitumens occur in liquid and solid forms. The native liquid bitumens include all petroleums or crude oils. Native solid bitumens include native waxes such as ozocerite, asphalts or petroleum tars, and asphaltites such as gilsonite and grahamite. Pyrobitumens are composed principally of hydrocarbons which may contain oxygenated bodies. They are infusible and are insoluble, or nearly insoluble, in carbon disulfide. Native pyrobitumens are divided into an oxygen-containing group including peats, lignites, and coals, and an essentially oxygen-free, asphaltic group including such substances as wurtzilite, albertite, impsonite, and ingramite. Thucholites, which are carbonaceous substances that may contain uranium, thorium, and rare earths, commonly are considered to be pyrobitumens. Their compositions are variable and may fall into either the oxygen-containing or oxygen-free group. All varieties of native bituminous substances may be associated with mineral matter. The nomenclature of bitumens and pyrobitumens is used very loosely in the literature. This circumstance arises from the difficulty in recognizing many of these substances by visual examination, and because many of them can be identified accurately only by chemical methods. Inasmuch as some of the chemical procedures are time-consuming and satisfactory analytical methods have not been devised for all these substances, geologists generally have not obtained precise identifications but rather have used names that appeared most appropriate to the circumstances. It is expected that future research will show many substances called "asphaltite," "thucholite," etc., to be incorrectly identified. The nomenclature used by the authors of the various references of this bibliography is followed without deviation or further discussion. The stratigraphic nomenclature also is that used by the authors. In this bibliography emphasis is placed on reports dealing with the uranium contents and radioactivity of native bituminous substances rather than on mineralogical and chemical studies of these substances. The distribution of the substances described in the references is shown on the accompanying map. The indicated presence of these substances does not infer that they contain sufficient radioactive elements to constitute ores.

Trace Elements Investigations↗
USGS2012

Resolving hyporheic and groundwater components of streambed water flux

Hyporheic and groundwater fluxes typically occur together in permeable sediments beneath flowing stream water. However, streambed water fluxes quantified using the thermal method are usually interpreted as representing either groundwater or hyporheic fluxes. Our purpose was to improve understanding of co-occurring groundwater and hyporheic fluxes using streambed temperature measurements and analysis of one-dimensional heat transport in shallow streambeds. First, we examined how changes in hyporheic and groundwater fluxes affect their relative magnitudes by reevaluating previously published simulations. These indicated that flux magnitudes are largely independent until a threshold is crossed, past which hyporheic fluxes are diminished by much larger (1000-fold) groundwater fluxes. We tested accurate quantification of co-occurring fluxes using one-dimensional approaches that are appropriate for analyzing streambed temperature data collected at field sites. The thermal analytical method, which uses an analytical solution to the one-dimensional heat transport equation, was used to analyze results from a numerical heat transport model, in which hyporheic flow was represented as increased thermal dispersion at shallow depths. We found that co-occurring groundwater and hyporheic fluxes can be quantified in streambeds, although not always accurately. For example, using a temperature time series collected in a sandy streambed, we found that hyporheic and groundwater flow could both be detected when thermal dispersion due to hyporheic flow was significant compared to thermal conduction. We provide guidance for when thermal data can be used to quantify both hyporheic and groundwater fluxes, and we show that neglecting thermal dispersion may affect accuracy and interpretation of estimated streambed water fluxes.

Water Resources Research↗
USGS2014

Numerical analysis of regional water levels to define aquifer hydrology

Two fundamental methods for studying aquifer hydrology are now in use. The first, applied many years ago, consists of detailed observation of aquifer inflow, outflow, and storage changes, and their variations in time. By analysis of these observations, estimates of the perennial recharge to the aquifer and other pertinent hydrologic data are obtained, all as gross characteristics of the aquifer. The need for greater detail gave rise to a second fundamental method: special field tests, such as pumping tests, by which the hydrologic coefficients could be measured in a comparatively short time. In order to evaluate properly the ability of an aquifer to serve as a source of perennial water supply, the geology and hydrology of the aquifer must be known in some detail over its entire area. The first method cannot supply the necessary detail in most cases, and the second method cannot ordinarily provide the needed areal coverage because of the lack of appropriate testing facilities. Thus an auxiliary third approach was sought which would combine the features of a simple data‐collection program with a final analysis yielding both adequate detail and areal coverage. A method designed to satisfy these requirements is described. Water‐level altitudes, usually observed in the course of more general ground‐water studies, are analyzed by numerical methods, using finite‐difference approximations of the basic differential equations which describe ground‐water flow. Analytical methods are given for nonsteady flow through homogeneous and nonhomogeneous aquifers. Both direct and statistical solutions are shown. The hydrologic factors are computed as functions of transmissibility, and for the nonhomogeneous aquifer the variations of transmissibility in space are computed also from the water‐level data. Knowledge of the absolute value of any one of the hydrologic factors at some location in the aquifer permits conversion of the computed functions to absolute terms for all the aquifer flow field studied.

Eos, Transactions, American Geophysical Union↗