bluuebunny/crossref_metadata_2025 huggingface dataset:
Ammonium Ion, Humic Materials, and Trihalomethane Potential in Northeastern Kansas Ground Waters
Authors: Denne Jane E. , Hathaway Lawrence R. , McCool S. Patrick
Published: March 2006

Glacial buried‐valley aquifers serve as primary sources of potable ground water in northeastern Kansas. A long known problem, however, is that a large percentage of well waters in this region exceed the U.S. Environmental Protection Agency (EPA) limits for nitrate (NO−3). A detailed study of the hydrogeology and water quality of the buried valleys has confirmed the nitrate problem and led to a recognition that some well waters with low ( 5 mg/l) NO−3 concentrations have anomalous ( 0.5 mg/l) ammonium ion (NH+4) levels, with an NH+4 range from <0.1 to 4.8 mg/l. The extractable NH+4 concentrations in related glacial sediments range up to approximately 75 mg/kg, and the amounts generally increase from an average of 2 mg/kg in the topsoil downward to bedrock. Migration of brines from subjacent Permian or Pennsylvanian bedrock into the unconsolidated sediments locally may cause desorption of NH+4 and an increase in its levels in the associated ground waters. Numerous test holes drilled in the study area showed a black scum on the fluid and cuttings, which may be from buried humic materials. Recently measured total organic carbon (TOC) contents of the ground waters confirm a significant level in some areas, with a range from 0.1 to 2.4 mg/l as C. Chlorination of water with dissolved organics may lead to production of halogenated compounds. Two public‐water‐supply well waters contained total trihalomethane (TTHM) levels close to the maximum contaminant level (MCL) of 100 /μg/l in chlorinated samples quenched after one week. The presence of NH+4 inhibits the formation of THMs, but it also can give rise to odor and taste problems in the finished water. The inhibition of THM formation by NH+4 is achieved by reactions which compete with the organics for combination with chlorine. These reactions make maintaining appropriate chlorine residuals difficult and also may lead to production of undesirable side products. Present efforts to evaluate the regional water‐quality problems are focused in Nemaha County, Kansas.
A Comparative Study of Specific Yield Determinations for a Shallow Sand Aquifer
Authors: Nwankwor G. I. , Cherry J. A. , Gillham R. W.
Published: March 2006

Using the type‐curve methods of Boulton (1963) and Neuman (1972), and comparisons, at various times, of the cumulative volume of water pumped to the volume of the water‐table drawdown cone (volume‐balance method), values of specific yield were obtained from pumping test data from numerous piezometers in an unconfined sand aquifer. The long‐term value of specific yield for the aquifer was determined from measurements of the laboratory drainage curve of the aquifer material.

The volume‐balance method gave specific yield values of 0.02, 0.05, 0.12, 0.20, 0.23, and 0.25 at times of 0.25, 0.66, 10, 26, 45, and 65 hours, respectively, indicating a gradual increase in specific yield and an asymptotic approach to the long‐term value of 0.30 determined from the laboratory method. The type‐curve methods provided values of 0.07 and 0.08, which correspond to the volume‐balance values at early times, but which are less than one‐third of the value obtained from the laboratory method and from the volume‐balance method applied at the end of the pumping test (2.7 days). The type‐curve procedures therefore provide unrealistically low values of specific yield for application to problems concerning the long‐term yield characteristics of the aquifer.

The observed trend towards increasing values of specific yield with increasing duration of pumping, and the vertical hydraulic head profiles that were measured during the pumping test indicate that both delayed drainage from above the water table and downward hydraulic gradients in the saturated zone can be important hydraulic effects contributing to the delayed‐drawdown segment that is characteristic of time‐drawdown graphs for unconfined aquifers.
Gravity Delineation of a Buried Valley in Quartzite
Authors: Hansen Donald S.
Published: March 2006

A gravity survey was conducted in a 94‐square‐mile area of northeastern Hanson County, South Dakota. The 340 measured gravity values, together with test‐hole data, were used to approximately delineate a buried valley eroded into the Sioux Quartzite of Precambrian age. This valley contains, in places, an aquifer composed of quartzose sand of pre‐Cretaceous age derived from the Sioux Quartzite. The bottom of the valley is approximately 450–600 ft below land surface. Simple Bouguer values were determined from measured gravity data, referenced to a local base station, and interpolated to a 0.5‐ by 0.5‐mile grid. The interpolated simple Bouguer values of residual gravity were determined using a five‐ring, inverse‐weighted filtering method. The second derivative of the interpolated gravity values, as well as their downward continuation, did not delineate the buried valley as well. Subsequent drilling of nine test holes showed that the gravity method can be used for approximately delineating subsurface features
TOC Determinations in Ground Water
Authors: Barcelona Michael J.
Published: March 2006

Determinations of total organic carbon (TOC) can provide valuable diagnostic evidence of the extent of ground‐water contamination by organic compounds. The usefulness of conventional TOC results in monitoring efforts is limited by the bias introduced during the purging of inorganic carbon prior to analysis. A modified TOC procedure has been evaluated to permit the quantitation of the volatile organic carbon (VOC) fraction in water samples. The methodology consists of trapping the VOC in a manner analogous to commercial purge and trap instruments which are used for specific organic compound separations. The method has been found to be sensitive, accurate and reasonably precise for TOC determinations of standard solutions as well as on ground‐water samples. Volatile organic carbon levels can range from 9–50% of the TOC in both uncontaminated and contaminated ground waters. The reporting of the volatile and nonvolatile fractions of the TOC will enhance both monitoring and research efforts, since it permits more complete characterization of the organic carbon content of ground‐water samples.
A Routing Technique for Estimating Ground–Water Recharge
Authors: Senarath D.C.H. , Rushton K. R.
Published: March 2006

A technique is presented for the estimation of ground–water recharge in a region where the formations overlying an aquifer cannot transmit all of the available water to the aquifer. The method is based on a routing model which is derived from the physical nature of formations overlying the aquifer. The model takes into account precipitation, evapotranspiration, soil moisture balance and the passage of water through strata such as boulder clay. The validity of the model is tested by calculated and field stream flow hydrographs.
Observed Drawdown Pattern Around a Well Partially Penetrating a Vertically Extensive Water‐Table Aquifer
Authors: Sayed Shabbir A. S.
Published: March 2006

In order to understand the flow pattern around a pumping well partially penetrating a vertically extensive aquifer, a specially designed pumping test was carried out in Pakistan. In this paper salient features of the test have been described. The spatial distributions of drawdown have been shown graphically. Some of the preliminary conclusions made from the drawdown pattern include:

The distance beyond which the flow is likely to be horizontal increases with decrease in the degree of aquifer penetration.

In equidistant observation wells open at different depths, (1) the drawdowns tend to merge at larger times, provided the observation point is located within the screened section of the aquifer; (2) the less the depth of penetration is, the earlier the drawdowns start merging; and (3) the initial rate of drawdown near the aquifer top is slow but catches up with time to exceed those at deeper points.
A Study on Confined Flow of Ground Water Through a Tunnel
Authors: Chisyaki Takeshi
Published: March 2006

Confined flow of ground water through a tunnel, which might be encountered in tunneling under the bottom of a sea or river, is numerically analyzed by a reductive finite element method formulated in our research. That is, the rate and potential distribution of the confined flow of ground water through an opening are obtained in connection with the permeability of rock masses, the thickness of covered ground, the location of impermeable bedrock, and other variables.

In addition, flow through an opening in the ground with highly permeable masses and discharge of ground water through a tunnel in grouted masses are illustrated, and some useful results for the practical application of tunneling work are obtained.
A Model of Regional Ground‐Water Flow in Secondary‐Permeability Terrane
Authors: Gerhart James M.
Published: March 2006

The ground‐water flow system in the Lower Susquehanna River Basin in Pennsylvania and Maryland can be considered as one complex unconfined aquifer in which secondary porosity and permeability are the dominant influences on the occurrence and flow of ground water. The degree of development of secondary porosity and permeability in the various lithologies of the lower basin determines the aquifer characteristics of each lithology. Based on qualitative evidence, the use of a porous‐media model was assumed to be appropriate on a regional scale and a finite‐difference ground‐water flow model was constructed for the lower basin.

The conceptual model of ground‐water flow in the lower basin incorporates the major features of the flow system. Through the use of two layers, 21 hydrogeologic units, and five topographic settings, the conceptual model was systematically reduced to arrive at a simplified conceptual model. Further reduction produced a numerical model representation of the conceptual model, in which the essential features of the lower‐basin flow system were quantified for input into the numerical model.

The model was calibrated under both steady‐state and transient conditions, and was used to evaluate the water‐supply potential of the 21 hydrogeologic units. The carbonate units have the greatest potential for ground‐water development and the Triassic sedimentary and crystalline units have the least potential. A total ground‐water yield potential of about 900 million gallons per day could be obtained from the lower basin with a consequent 50‐percent reduction of base flow in streams.
Contamination of an Unconfined Sand Aquifer by Waste Pulp Liquor: A Case Study
Authors: Robertson W. D. , Barker J. F. , LeBeau Y. , Marcoux S.
Published: March 2006

A zone of contaminated ground water has been identified in an unconfined sand aquifer adjacent to a pit into which spent pulp liquor was intermittently discharged from 1970 to 1979. A network of multilevel sampling, bundle‐type piezometers was installed. Up to seven depthspecific sampling points were incorporated into each piezometer providing a cost‐effective means for three‐dimensional mapping of hydraulic head and water quality in the unconfined sand aquifer. Ground‐water samples retrieved from this network showed an area of contamination 900 m long, 400 m wide, and more than 25 m deep. This plume is dispersed about the ground‐water flow lines passing beneath the waste disposal pit, and it terminates at a vigorous ground‐water discharge area located 800 m from the pit.

The contaminated ground water is characterized by elevated concentrations of sodium (3,000 mg/1), chloride (590 mg/1), alkalinity (2,700 mg/1), total organic carbon (2,000 mg/1), chemical oxygen demand (10,800 mg/1), biological oxygen demand (2,000 mg/1), tannin and lignin (780 mg/1), and lower sulphate (1 mg/1) compared to background ground waters in the area. The apparent rate of sodium migration is more than 50 m/yr and is close to the average linear ground‐water velocity. Removal of some organic matter by biological transformation has produced the increased alkalinity in the contaminated ground water and somewhat reduced pH. Tannin and lignin are relatively inert compared to other organic compounds found in the waste liquor. Extremely low sulphate levels occurring in the highly contaminated ground waters indicate the existence of conditions favorable for microbially‐mediated sulphate reduction.
Evolution of Regional Hydrogeologic Setup of a Hard Rock Aquifer Through R‐C Analog Model
Authors: Gupta C. P. , Thangarajan M. , Rao V.V.S. Gurunadha
Published: March 2006

Conceptualization of regional hydrogeologic setup in a hard rock granitic terrain by employing sparse data obtained through conventional methods is usually not possible. In such situations, aquifer simulation could be employed as a useful tool. An attempt was made to evolve the regional pattern of hydrogeologic parameters in a granitic basin. During the process of model calibration, the field estimates of hydrogeological parameters as well as those of recharge and ground‐water extraction were appropriately modified. A first‐order estimate of the effluent outflow from the aquifer to ephemeral streams was made only from the flow model. The calibrated model satisfactorily reproduced the historical response of the aquifer and could be used for prognosis.
Automatic Generation of Flow Nets with Conventional Ground‐Water Modeling Algorithmsa
Authors: Fogg Graham E. , Senger R. K.
Published: March 2006

Though flow nets offer one of the best means of visualizing ground‐water flow fields, accurate construction of flow nets can be very difficult in heterogeneous, anisotropic media or in regional cross sections where vertical exaggeration of scale is great. A method was developed for automatically generating the streamlines of a flow net using conventional ground‐water flow modeling algorithms. The method can be implemented using most any of the existing computer programs for flow modeling, and no modification of the programs is necessary. One need only replace the hydraulic head and conductivity terms in the steady‐state ground‐water flow equation with the stream function and an inverse form of hydraulic conductivity, respectively. Possible boundary conditions include prescribed stream function (Dirichlet type) and prescribed stream function gradient (Neumann type). The former can be determined from prior knowledge of recharge or discharge rates or from boundary fluxes computed in previous simulations of hydraulic head distribution. The latter can be determined from data on hydraulic head along the boundaries, raising the possibility of solving for the streamlines directly without first solving for the head distribution. The method is generally not appropriate when sources or sinks occur inside the flow region, and it will not handle transient conditions. Accuracy of the method is demonstrated in three hypothetical test problems and a vertical‐plane model through the Palo Duro Basin of Texas and New Mexico.
THE POWER OF THE ELECTRONIC WORKSHEET: MODELING WITHOUT SPECIAL PROGRAMS
Authors: Olsthoorn T. N.
Published: March 2006

Abstract. So‐called spreadsheet programs are forerunners of new general software from which the ground‐water engineer is likely to benefit–no more special programs each capable of fulfilling just that single task it was explicitly designed for, but programs suitable to do almost any job, where only the fantasy of the user limits the possibilities. Moreover, this new software shows us what user friendliness looks like and proves that it is completely superfluous to be a computer specialist to use it.

With a spreadsheet you can build a simple finite‐difference model from scratch within one or two minutes. With some extra time a wide versatility of problems can be solved as the multiaquifer, three‐dimensional, phreatic and transient ground‐water flow examples prove. This way any hydrologist should be able to solve diverging ground‐water models himself without depending on special numerical models. All he needs beyond a microcomputer and a spreadsheet program is a good knowledge of the water balance.
Gradient Controlled Caves, Trapper‐Medicine Lodge Area, Bighorn Basin, Wyoming
Authors: Huntoon Peter W.
Published: March 2006

Extensive caves have developed under canyons in the Trapper‐Medicine Lodge recharge area where ground‐water flow rates became maximized within the Madison carbonates during Cenozoic time. The large flow rates resulted directly from the superposition of steep local gradients on the ground‐water circulation system as a consequence of the erosion of confining units in the region. The cave forming process in this area is gradient controlled, a conclusion that has possible applicability elsewhere.
An Interpretation of Dug Well Performance Using a Digital Model
Authors: Lawrence A. R.
Published: March 2006

Dug wells in the Deccan basalts of India can provide a means of determining the permeability of the unconfined aquifer within the weathered layer. The layered nature of this aquifer, together with its low permeability, produces a complicated ground‐water flow pattern around large‐diameter dug wells when they are pumped. A digital model, which successfully simulated the head distribution in and around a large‐diameter pumping well demonstrated that recovery, rather than drawdown, data from such tests are more suitable for analysis.
Some Computational Experiences Using Embedding Technique for Ground‐Water Management
Authors: Tung Yeou‐Koung , Koltermann Christine E.
Published: March 2006

A distributed parameter ground‐water management model was developed using finite‐difference approximations of the governing partial differential equation for ground‐water flow in a confined aquifer. The resulting system of simultaneous equations was embedded in an optimization model, which used hydraulic heads and pumpages as unknown state variables and decision variables, respectively. The model was applied to several hypothetical examples of varying size and complexity and to one real‐world example, the Las Vegas Valley aquifer. The grid spacing, time increment, bounds placed on pumpage, and the number of constraints were found to affect not only the execution time, but also whether the model would execute at all.

In order to accommodate long‐term management goals, a lumped transient model should be used which incorporates all time periods the model encompasses. Some objective functions, such as the maximization of the head, can be executed in a stepwise manner in which the final heads from the current period are used as the initial heads for the next period. The embedding technique proved useful for small management problems, but had numerical difficulties with the large real‐world problems of considerable heterogeneity. Unless the embedding technique can become computationally efficient and stable, it should be bypassed in favor of the response matrix approach.
A Model Study of Salt‐Water Intrusion to a River Using the Sharp Interface Approximation
Authors: McElwee C. D.
Published: March 2006

Between Salina and Enterprise, Kansas, the salinity of the Smoky Hill River increases sharply. As a result, the river downstream at various times exceeds the recommended drinking‐water‐quality standards for chloride. The Smoky Hill and Kansas Rivers are important sources of water for several population centers in eastern Kansas. Therefore, this problem has an impact on a significant part of the Kansas population. The source of the saline water is predominantly from ground‐water dissolution of the Hutchinson Salt Member of the Wellington Formation of Permian age. The dissolution of the salt has caused a north‐south trending collapsed zone called the Wellington aquifer to occur along the present eastern extent of the salt. A confining shale layer exists between the Smoky Hill alluvium and the Wellington aquifer in most areas. However, between New Cambria and Solomon, Kansas, the layer is thin and fractured, allowing the salt water to move up into the alluvium.

The steady‐state model presented in this study indicates that the salt‐water layer of the alluvium in the Smoky Hill River valley should be in an unstable condition near the river. This indicates that unstable interface upconing should be a dominant mechanism for supplying salt water to the river system. The time‐varying model shows that the response of the chloride discharge to a flood event can be qualitatively explained by the unstable interface upconing mechanism. As the river stage rises, the salt‐water intrusion declines. As the river stage declines, the salt‐water intrusion increases beyond its normal value and subsides to the normal value over the period of a few months if no new flood events occur. During rising river stage, the river is supplying the ground‐water system, and the salt‐water intrusion or unstable upconing is shut off. During falling river stage, bank storage and perhaps an elevated water table cause the fresh ground‐water discharge to be greater than normal, which in turn causes greater than normal salt‐water intrusion. In addition, the time‐varying model shows that several years would elapse before significant benefit would be seen in the river system from a proposed Wellington aquifer relief‐well scheme.
A New Method of Contaminant Plume Analysis
Authors: Domenico P. A. , Robbins G. A.
Published: March 2006

This paper develops an analytical expression for contaminant transport from a finite source in a continuous flow regime. The model requires some numerical integration and its degree of accuracy for near‐field problems depends on discretization procedures applied to the source boundary. A second model for a continuous source is developed by extending a well‐known pulse model. This second model is particularly useful in that it permits the determination of several potential unknowns directly from a concentration distribution. These include the source concentration, source dimensions, the position of the center of mass which is the product of the seepage velocity and the time since the contaminant first entered the ground water, and up to three dispersivities for a three‐dimensional problem. As a demonstration of its utility, this second model is applied with reasonable success to a well‐defined field condition. A comparison of the two models indicates that, except for minor differences in the very near field, the results from each are virtually identical.
Laboratory Investigation and Analysis of a Ground‐Water Flowmeter
Authors: Melville Joel G. , Molz Fred J. , Güven Oktay
Published: March 2006

The ground‐water flowmeter system, model 3OL, manufactured by K‐V Associates Inc., Falmouth, Massachusetts was tested under controlled laboratory conditions. The influence of slotted pipe schedule, slot orientation, backfill materials, endcap bags, isolated regions of high hydraulic conductivity, and channelization near the slotted pipe wall was measured. The physical concept of the flow‐meter in an ideal configuration was analyzed, and with the aid of an analytical model, the significance of the thermal and hydraulic characteristics of the aquifer and backfill materials is clarified. Results indicate that the basic instrument response is linear, consistent, and predictable qualitatively in a laboratory environment. Analysis and measurements show clearly that very small channelization around a slotted pipe casing or between the slotted pipe and the probe endcap can invalidate the instrument response. Additional potential complications arise due to unknown permeability contrasts between the aquifer matrix and the material used to backfill around the probe.
Movement of Volatile Organics Through a Fractured Rock Aquifer
Authors: E.Spayd Steven
Published: March 2006

In response to the detection of contaminants in several municipal water supply wells in a northern New Jersey community, the New Jersey Department of Environmental Protection (NJDEP) undertook a detailed assessment of the movement of volatile organics through the Brunswick fractured rock aquifer. Understanding the directional or anisotropic behavior of ground‐water flow within the aquifer proved to be a crucial factor for identification of the sources of contamination. Since the ground‐water flow occurs in a direction predominantly parallel to the strike of the aquifer, the resulting distribution of contaminants allowed the differentiation of two overlapping plumes, each over 4,000 feet in length and each emerging from discrete adjacent sources.

The investigations and subsequent cleanup agreements between the NJDEP and the responsible parties allowed savings of several million dollars for the U.S. EPA's Super‐fund Program which otherwise would have been used for cleanup of the site. The privately funded cleanup program includes treatment of the affected municipal wells and on‐site remedial actions designed to fully restore the aquifer within 10 years.
Stable Carbon Isotopes of HCO3 in the Aquia Aquifer, Maryland: Evidence for an Isotopically Heavy Source of CO2
Authors: Chapelle Francis H. , Knobel LeRoy L.
Published: March 2006

Concentrations of HCO3 and δ13C values of dissolved inorganic carbon change along the hydrologic gradient of the Aquia aquifer. In the outcrop area, meteoric recharge rapidly dissolves carbonate shell material (δ13C ∼ 0.0 per mil) in the presence of soil‐gas CO2 (δ13C∼–26 per mil). HCO3 concentrations in this area range from 150‐200 mg/1 and δ13C values of dissolved HCO3 are approximately –13.0 per mil. Concentrations of HCO3 decrease gradually (to about 130 mg/1) and δ13C values become slightly heavier (to about –11.4 per mil) as water flows away from the outcrop area. These trends reflect progressive dissolution of metastable carbonate shell material and subsequent precipitation of secondary calcite cement. At about 40 miles downgradient in the flow system, HCO3 concentrations increase sharply (to about 400 mg/1), and δ13C values become significantly heavier (δ13C ∼–6.2 per mil). The observed 1:1 molar ratio of Na+ to HCO‐3 in this downgradient water shows that dissolution of isotopically heavy carbonate shell material cannot by itself explain the observed δ13C trend. Rather, the Na:HCO‐3 ratio demonstrates that shell material dissolution must take place in the presence of CO2. Because the aquifer in this area is closed to both soil‐gas and atmospheric CC>2, an aquifer‐generated source of isotopically heavy (δ13C ∼–5.3 per mil) CO2 is implied. Possible sources of aquifer‐generated CO2 include bacterially‐mediated fermentation of lignitic aquifer materials and bacterially‐mediated methanogenesis.
A Hydraulic Trap for Preventing Collector Well Contamination: A Case Study
Authors: Ophori Duke U. , Farvolden Robert N.
Published: March 2006

A hydraulic trap in the form of a purge well is proposed for the Forwell collector well K‐71. The trap, which will protect well K‐71 from contamination by contaminants migrating downgradient from the old Breslube waste disposal site, is based on a qualitative flow net obtained from a finite‐element model of the Forwell Aquifer. The trap constitutes pumping at the position of observation well OW 9‐80 at a continuous rate of at least 6.1 X 10‐3 m3/s. The uniqueness of the trap lies in its simplicity and relatively low cost.
Ground‐Water Model of Two‐Phase Immiscible Flow in Coarse Material
Authors: Hochmuth David P. , Sunada Daniel K.
Published: March 2006

A numerical model was developed to simulate the behavior of two‐phase immiscible fluids in ground‐water systems for specific application to hydrocarbon spills and leaks. The model is a two‐dimensional areal flow model using the finite‐element method. A verification of the numerical model was performed using both an approximate analytical solution and a laboratory investigation. The verification results show that the numerical model adequately describes the behavior of immiscible two‐phase flow within a coarse porous material.
Ground‐Water Flow in the Coastal Plain Aquifers of South Carolina
Authors: Aucott Walter R. , Speiran Gary K.
Published: March 2006

The characteristics of the Coastal Plain aquifers of South Carolina are being studied as a part of the Regional Aquifer System Analysis program of the United States Geological Survey. Potentiometric maps were constructed for the Middendorf aquifer of Cretaceous age and for the Floridan aquifer system and its sand facies equivalent, Tertiary sand aquifer, prior to development. Also constructed was a potentiometric decline map for the period prior to development to November 1982 for the Middendorf aquifer. These maps are used to describe the ground‐water flow system.

The Coastal Plain aquifers are recharged primarily by precipitation in their outcrop areas. Ground water flows from these areas of recharge, through the aquifers, and discharges to upper Coastal Plain rivers, overlying aquifers as upward leakage, and wells.

Ground‐water flow in the Floridan aquifer system and the Tertiary sand aquifer prior to development is generally perpendicular to the coast. Predevelopment flow in the Cretaceous aquifers, however, turns northeastward as it approaches the coast, almost paralleling the coast. The change in flow direction is caused by less effective intervening confining units, the aquifers being closer to the land surface, and the rivers at lower altitudes farther upstream in the vicinity of the North Carolina/South Carolina State line.

Water‐level declines in the Cretaceous aquifers have occurred throughout much of the eastern part of the Coastal Plain of South Carolina due to pumpage in the Myrtle Beach and Florence areas. Large areally extensive water‐level declines have also occurred in the Floridan aquifer system in South Carolina due to pumpage in the Savannah, Georgia area.
A Tube and Cartridge Method for Down‐Hole Sampling for Trace Organic Compounds in Ground Water
Authors: Pankow James F. , Isabella Lome M. , Hewetson Janet P. , Cherry John A.
Published: March 2006

A small ground‐water sampling device has been developed which extends the down‐hole use of the adsorption/thermal desorption (ATD) analysis method for nonpolar organic compounds to very narrow piezometers (I.D. > 0.64 cm). The sampler consists of a sorbent cartridge, a flow restrictor, and a tube leading to the ground surface. The device is lowered down a piezometer, and water‐column pressure forces the sample through the cartridge. In the laboratory, the water is removed from the cartridge and the sorbed compounds are thermally desorbed to a gas chromatography (GC) column for analysis. Since the analytes are sorbed on the cartridge down‐hole, volatilization losses are avoided. Samples can be obtained without being influenced by the water column above the sampler or by tubing or pumps; many uncertainties associated with well purging and contamination from well casings and samplers can be minimized. The method was tested by sampling at a landfill. The coefficients of variation were in the 10‐18% range at the low μg/1 level. The limits of detection for several compounds were all under 0.1 μg/1, some being less than 1 ng/1. Sorption efficiencies of >93% were found for a variety of compounds. The method will be attractive when sensitivity and freedom from volatilization losses and sampler‐related contamination are required.
AUTOMATED DERIVATION OF PARAMETERS IN A NONLEAKY CONFINED AQUIFER WITH TRANSIENT FLOWa
Authors: Mukhopadhyay Amitabha
Published: March 2006

.Values of transmissivity and storage commonly are derived for a nonleaky confined aquifer by manual curve matching of pumping‐test data. Automatic matching of pumping‐test data with the Theis type curve is possible using the method of least squares, provided the Cooper‐Jacob approximation of the well function W(u) is considered. A FORTRAN program was developed to carry out this automated matching. Results derived from published data show that the method gives parameters close to the ones derived by the standard method of manual curve matching.
Migration and Attenuation of Selected Organics in a Sandy Aquifer – A Natural Gradient Experiment
Authors: Sutton P. A. , Barker J. F.
Published: March 2006

A natural gradient tracer test was conducted in an unconfined sandy aquifer at Borden, Ontario. N‐butyric acid, phenol, p‐chlorophenol, and dimethyl phthalate (DMP) were used as organic tracers at concentrations ranging from 70 to 100 ppm and chloride was used as a nonreactive tracer at a concentration of 243 ppm. Approximately 2,100 1 were injected below the water table and were monitored with a three‐dimensional network of bundle‐type, multilevel piezometers over a period of 60 days and once again after 204 days.

The plume gradually split into two zones due to local heterogeneity. The centers of mass for the organic compounds migrated at essentially the same rate as chloride, but attenuated at different rates. Butyric acid and phenol attenuated the most rapidly. Chlorophenol attenuated only slightly faster than chloride and DMP attenuated at roughly the same rate as chloride. Sorption does not appear to be important in the system studied. Dispersion and biodegradation probably produced the observed attenuation of organics.
Determination of Microbial Cell Numbers in Subsurface Samples
Authors: Webster JoAnn J. , Hampton Ginger J. , Wilson John T. , Ghiorse William C. , Leach Franklin R.
Published: March 2006

Ground‐water pollution by organic compounds has become a major environmental concern. Because the transport and fate of the organic pollutants may be influenced by microorganisms present in subsurface material, reliable measurements of the number of organisms in subsurface samples and their metabolic activity are needed. A special drilling rig and aseptic procedures have been developed by the Robert S. Kerr Environmental Research Laboratory of the United States Environmental Protection Agency to yield uncontaminated subsurface samples. The number of bacteria in subsurface samples has been determined by microscopic counting after acridine orange staining; the proportion of cells capable of respiration was determined by INT reduction. An independent measure of metabolic activity was obtained by measuring ATP extracted from the samples. A procedure and extradant for the extraction of ATP from subsurface material have been developed. The extractant contains reagents to reduce the loss of the extracted ATP. Subsurface samples from Oklahoma and Texas contain 106‐107 cells per g of subsurface material (depths of 2–9 m). Both methods show that usually between 1 and 10% of the cells were metabolically active. Thus, significant numbers of metabolically active bacteria exist in subsurface material with the potential to modify pollutants.
Nitrogen‐Isotope Ratios of Nitrate in Ground Water Under Fertilized Fields, Long Island, New York
Authors: Flipse William J. , Bonner Francis T.
Published: March 2006

Ground‐water samples from two heavily fertilized sites in Suffolk County, New York, were collected through the 1978 growing season and analyzed for nitrate‐N concentrations and nitrogen‐isotope ratios. Six wells were at a potato farm; six were on a golf course. The purpose of this study was to determine whether the 15N/14N ratios (δ15N values) of fertilizer are increased during transit from land surface to ground water to an extent which would preclude use of this ratio to distinguish agricultural from animal sources of nitrate in ground water.

Ground water at both sites contained a greater proportion of 15N than the fertilizers being applied. At the potato farm, the average δ15N value of the fertilizers was 0.2%0; the average δ15N value of the ground‐water nitrate was 6.2 %0. At the golf course, the average δ15N value of the fertilizers was ‐5.9%0, and that of ground‐water nitrate was 6.5%0. The higher δ15N values of ground‐water nitrate are probably caused by isotopic fractionation during the volatile loss of ammonia from nitrogen applied in reduced forms (NH+4 and organic‐N).

The δ15N values of most ground‐water samples from both areas were less than 10%0, the upper limit of the range characteristic of agricultural sources of nitrate; these sources include both fertilizer nitrate and nitrate derived from increased mineralization of soil nitrogen through cultivation. Previous studies have shown that the S15N values of nitrate derived from human or animal waste generally exceed 10%0. The nitrogen‐isotope ratios of fertilizer‐derived nitrate were not altered to an extent that would make them indistinguishable from animal‐waste‐derived nitrates in ground water.
Comparison of Methods for Estimating Ground‐Water Pumpage for Irrigation
Authors: Frenzel Steven A.
Published: March 2006

Ground‐water pumpage for irrigation was measured at 32 sites on the eastern Snake River Plain in southern Idaho during 1983. Pumpage at these sites also was estimated by three commonly used methods, and pumpage estimates were compared to measured values to determine the accuracy of each estimate.

Statistical comparisons of estimated and metered pumpage using an F‐test showed that only estimates made using the instantaneous discharge method were not significantly different (α. = 0.01) from metered values.

Pumpage estimates made using the power consumption method reflect variability in pumping efficiency among sites. Pumpage estimates made using the crop‐consumptive use method reflect variability in water‐management practices. Pumpage estimates made using the instantaneous discharge method reflect variability in discharges at each site during the irrigation season.
A GENERAL PURPOSE MICROCOMPUTER AQUIFER TEST EVALUATION TECHNIQUE
Authors: Hemker C. J.
Published: March 2006

Abstract. Although determination of aquifer characteristics from pumping test data is generally carried out using type curves or other graphical techniques, a number of computer methods have been developed recently for this purpose. Based on the principle of least squares, these methods of nonlinear regression analysis can be applied to any flow system for which analytical expressions of the drawdown distribution are known. In view of the growing general interest in the application of microcomputers in ground‐water hydrology, a BASIC routine has been developed for estimating any number of aquifer parameters. The least squares solution is calculated by Marquardt's algorithm, using the singular‐value decomposition of the Jacobian matrix. The robust computing method obtained can be applied to all kinds of pumping tests. Aquifer characteristics as well as their standard deviations are computed with optimal speed and accuracy. The technique is demonstrated by a simple application to steady flow in a leaky aquifer and an example is provided. Other applications are easily implemented and programs for unsteady‐state aquifer tests, recovery tests and multiple aquifer tests are available.
Predictive Accuracy of a Ground–Water Model — Lessons from a Postaudit
Authors: Konikow Leonard F.
Published: March 2006

Hydrogeologic studies commonly include the development, calibration, and application of a deterministic simulation model. To help assess the value of using such models to make predictions, a postaudit was conducted on a previously studied area in the Salt River and lower Santa Cruz River basins in central Arizona. A deterministic, distributed‐parameter model of the ground‐water system in these alluvial basins was calibrated by Anderson (1968) using about 40 years of data (1923–64). The calibrated model was then used to predict future water‐level changes during the next 10 years (1965–74). Examination of actual water‐level changes in 77 wells from 1965–74 indicates a poor correlation between observed and predicted water‐level changes. The differences have a mean of 73 ft that is, predicted declines consistently exceeded those observed and a standard deviation of 47 ft. The bias in the predicted water‐level change can be accounted for by the large error in the assumed total pumpage during the prediction period. However, the spatial distribution of errors in predicted water‐level change does not correlate with the spatial distribution of errors in pumpage. Consequently, the lack of precision probably is not related only to errors in assumed pumpage, but may indicate the presence of other sources of error in the model, such as the two‐dimensional representation of a three‐dimensional problem or the lack of consideration of land‐subsidence processes. This type of postaudit is a valuable method of verifying a model, and an evaluation of predictive errors can provide an increased understanding of the system and aid in assessing the value of undertaking development of a revised model.
Comparative Study of Ground‐Water Mapping Techniques
Authors: Rouhani Shahrokh
Published: March 2006

Mapping of ground‐water spatial data is an important part of any geohydrologic investigation. There are three main classes of interpolators used for such mappings. The first group include simple estimators which are commonly used in practice. The second group are least‐squares estimators which are basically fitting processes. The last category are Gauss‐Markov estimators, such as kriging, which beside being exact interpolators, produce measures for the accuracy of the estimated field. These estimators are compared theoretically and numerically. These studies show that kriging yields relatively robust estimates. However, its suggested statistical inference method may not always produce robust estimates of the covariance function parameters. Simple estimators produce unstable results, while least‐squares methods ignore local variations by fitting a single polynomial function over the whole field. For this study, water‐table data from northwest Kansas are used.
Chromium Migration Through Sludge‐Treated Soils
Authors: Dreiss Shirley J.
Published: March 2006

The Environmental Protection Agency and the Tanner's Council of America jointly initiated a five‐year project in September 1980 to investigate the feasibility of using land treatment to dispose of chromium tanning sludges. These sludges contain high concentrations of Cr, in the range of 21,000 to 55,000 ppm on a dry weight basis. Chromium could migrate in soil waters at a land treatment site as either a soluble Cr (VI) species, HCrO4 or CrO42, or as Cr (III) or Cr (VI) in soluble complexes with organic or inorganic substances. Field measurements of Cr fluxes at an experimental test site near Santa Cruz, California indicate that Cr in tannery sludges exhibits a very low mobility. Less than 0.1% of the total Cr applied to a test plot was transported through the upper soil zone during a three‐month period. However, the sludge applications introduced high concentrations of nitrates and major cations. Estimates of contaminant fluxes based on measured concentrations in soil water collected with porous cup samplers contain large uncertainties. In addition to potential errors in moisture flux computations, chemical reactions in the cups can significantly alter the composition of soil‐water samples.
Contaminant Movement Under Pumpage‐Recharge Condition in Steady Ground‐Water Flow System
Authors: Gupta A. Das , Shrestha P. R. Onta
Published: March 2006

The transient movement of contaminant under pumpage and recharge conditions in steady ground‐water flow in a vertical cross section of a confined aquifer is simulated using a finite‐element numerical model based on Galerkin technique. Various factors like time step, space increment, and boundary condition affecting the accuracy of the numerical solution are considered in validating results of the numerical model with results of an analytical solution. The solution with the application problem illustrates the effectiveness of subsequent operation of pumpage on the movement of contaminant downstream of the point of injection.
Saturated Thickness for Drought and Litigation Protection
Authors: Peralta Richard C. , Dutram Paul W. , Peralta Ann W. , Yazdanian Amin
Published: March 2006

The legal doctrines of reasonable use and correlative rights are the recognized standards for resolving legal conflicts between interfering agricultural ground‐water users in Arkansas. Assuring that an adequate saturated thickness exists for all interfering users throughout the ground‐water withdrawal season provides water users with a degree of protection from both a successful litigious charge of “unreasonable use” and a mandated curtailment of ground‐water withdrawal in a droughty season.

The feasibility of maintaining a “target” saturated thickness and water‐table elevation by implementing a district‐wide sustained ground‐water withdrawal strategy has been previously demonstrated. Several models have been reported which create the spatially distributed sustained‐yield withdrawal strategies that will maintain those target levels. The development of satisfactory strategies requires knowledge of the minimum acceptable springtime saturated thickness for critical parts of the management district. This information can be gained through the iterative use of a dynamic ground‐water simulation model. In the iterative procedure, initial (springtime) saturated thickness is assumed. The change in saturated thickness resulting from withdrawals during the irrigation season is compared with an acceptability criterion. The assumed springtime saturated thickness is varied until the criterion is satisfied. The result is the minimum springtime saturated thickness needed for ground‐water users in a particular cell to achieve: (1) a measure of year‐round protection from successful litigation charging unreasonable use, and (2) some assurance that they will not need to curtail or limit ground‐water withdrawals during a droughty season.

This procedure was applied to a 3‐mile by 3‐mile (5‐km by 5‐km) cell in the Arkansas Grand Prairie, an important rice‐ and soybean‐producing area. The results indicate that a minimum of 13 feet (4 m) of saturated thickness are desirable for the center of the cell to provide for a droughty season.
Microbial Biomass, Activity, and Community Structure in Subsurface Soils
Authors: Federle Thomas W. , Dobbins Durell C. , Thornton‐Manning Janice R. , Jones Daniel D.
Published: March 2006

Microbial biomass, community structure and activity were determined in the subsurface horizons of four contrasting soil types common to Alabama. Biomass and community structure were determined by analyzing the fatty acids of the extractable phospholipids. Activity was estimated by measuring the rate of enzymatic hydrolysis of fluorescein diacetate (FDA). In all four soils, biomass and activity declined with increasing depth; however, the magnitude and pattern of this decline varied as a function of soil type. Biomass concentrations in the lower Ap horizon ranged from 8.2 to 18.0 nmoles phospholipid/g dry wt soil. In the deepest subsoil horizons, the range was 0.0085 to 0.059 nmoles phospholipid/g dry wt soil. The rate of FDA hydrolysis was highly correlated with biomass (r=0.90). Polyenoic fatty acids, which are present only in cukaryotic microorganisms, were found in all horizons; however, their relative abundance differed as a function of soil type. Stepwise regression analysis revealed that soil characteristics could explain 89 and 82% of the variation in biomass and activity, respectively. The results indicated that the vertical distribution of microorganisms in a soil profile differs greatly as a function of soil type. Hence, soil type may be an important determinant as to whether potential ground‐water pollutants are biodegraded as they pass through the unsaturated zone of a soil profile.