bluuebunny/crossref_metadata_2025 huggingface dataset:
Ground‐Water Quality and Flow in a Shallow Glaciofluvial Aquifer Impacted by Agricultural Contamination
Authors: Kehew Alan E. , Straw W. Thomas , Steinman William K. , Barrese Patrick G. , Passarella Giuseppe , Peng Wei‐Shyuan
Published: August 2005

The Prairie Ronde fan, a discrete glaciofluvial deposit in southwestern Michigan, contains a productive but highly vulnerable unconfined aquifer used for irrigation, municipal, and domestic supply. A comprehensive hydrogeological study of the aquifer delineated shallow, local flow systems that interact with ponds and wetlands on the fan surface, overlying a deeper intermediate/regional flow system extending to the base of the glacial drift. Ground water within the shallow flow systems contains tritium concentrations indicative of a post‐bomb age and is heavily impacted by nonpoint source contamination. Nitrate commonly exceeds drinking water standards in the shallow flow system. Although no continuous physical barrier separates the two flow systems, the deeper flow system is generally lacking in tritium as well as nonpoint source contaminants derived from surface land uses. High capacity pumping from the deeper flow system, however, will likely draw contaminants downward from the shallow flow system.

Background‐water quality in the aquifer is controlled by equilibrium with calcite and slight undersaturation with respect to dolomite. No spatial trends in major ions were observed, suggesting that carbonate mineral equilibrium is achieved rapidly in the vadose zone and further chemical evolution along ground‐water flow paths is minimal. Iron concentrations are highly variable in the aquifer and not correlated with depth. Recharge from lakes and wetlands is a significant cause of elevated iron concentrations in the shallow flow systems.
A Kernel Estimator for Stochastic Subsurface Characterization
Authors: All A. I. , Lall U.
Published: August 2005

A nonparametric statistical methodology based on kernel function estimation is developed for assessing the probability that a particular location in the aquifer has high or low conductivity using borehole information. The approach presented is an alternative to Indicator Kriging. Soils are classified through a binary indicator function defined as 0 for low and as 1 for a high conductivity soil. Estimates of the probability of occurrence of a high or low conductivity soil are made on a three‐dimensional grid. Each such estimate is formed as a local weighted average of the indicator function values that lie within an averaging interval or bandwidth of the point of estimate. A different vertical bandwidth is chosen at each borehole log. Horizontal bandwidths are selected independently at each horizontal level. These bandwidths are chosen by cross validation. Observations closer to the point of estimate are weighted higher using a kernel or weight function. Unlike Kriging, the underlying stochastic process is not assumed to be stationary. An application using data from Lake Bonneville deposits in Davis County, Utah is presented.
A Numerical Method for Solving the Water Flow Equation in Unsaturated Porous Media
Authors: Amokrane H. , Villeneuve J. P.
Published: August 2005

A numerical procedure based on the MacCormack method was used for the simulation of one‐dimensional isothermal transient movement of liquid phase water in an unsaturated soil including precipitation, evaporation, and moisture removal from soil by the roots of transpiring plants. The numerical model utilized finite‐difference explicit predictor‐corrector equations and it was applied to a few flow problems. Comparison between the numerical results and laboratory or field experimental values was very promising. Our predicted values also agreed reasonably well with previously published numerical solutions. The proposed procedure was found to be easily adapted for solving the nonlinear soil‐water flow equation. However, it required only a knowledge of soil hydraulic conductivity and its water potential or diffusivity as functions of moisture content.
Multiple Tracers of Shallow Ground‐Water Flow and Recharge in Hilly Loess
Authors: O'Brien R. , Keller C. K. , Smith J. L.
Published: August 2005

Vertical profiles of tritium and nitrate pore‐water concentrations were determined to ∼8 m depth across two loess hillslopes. Mean recharge fluxes, estimated from chloride mass balance, are 5–10 times larger at the mid‐ and toe‐slope positions than at the top‐slope; the magnitudes of the values compare reasonably with results from other methods. The tritium and nitrate profiles exhibit multiple peaks which indicate that piston flow is not the sole flow process in this system. Results of a simple 1‐D mixing model suggest that infiltration‐exfiltration cycles in zones of plant root activity explain the shallow tritium peaks. Deeper peaks result from preferential vertical and/or lateral flow. The importance of these dispersive processes is underlined by great dilution of observed tritium concentrations, relative to expected concentrations assuming piston flow. In this setting, chloride is useful as a recharge estimator while tritium and nitrate serve as tracers of landscape‐scale water movement.
Enhanced Organic Contaminant Sorption on Soil Treated with Cationic Surfactants
Authors: Brown Michael J. , Burris David R.
Published: August 2005

Batch sorption and column transport laboratory experiments were performed to investigate the use of cationic surfactants to enhance sorption of dissolved organic contaminants in aquifer material with low organic carbon content. The experiments used sand from the Borden aquifer in Ontario, Canada, treated with hexadecyltrimethylammonium (HDTMA+) surfactant. Test results indicate that organic cations are strongly adsorbed by cation exchange reactions on the solid surface. Further adsorption occurs in admicelles, which form by hydrophobic interactions between adsorbed and mobile HDTMA+ monomers. The nonlinear adsorption isotherm may be described by Langmuir adsorption theory. The retardation factor for HDTMA+ on Borden aquifer material is approximately 460 when aqueous surfactant concentrations are less than 100 mg/l, while HDTMA+ is relatively mobile at higher concentrations. Column experiments suggest that the adsorption reaction is very rapid, and thus independent of ground‐water flow velocity. A column treated with HDTMA+ equivalent to 33% of CEC and flushed with 325 pore volumes of surfactant‐free water showed that although the HDTMA+ modified zone was smeared downgradient, all HDTMA+ mass remained adsorbed within the column. The results indicate that an essentially stationary surfactant‐modified zone can be created.

Adsorbed HDTMA+ mass increased foc from 0.02 wt% on natural Borden aquifer material to 0.18 wt% on the treated sediments. Organic matter derived from the adsorbed HDTMA+ is an effective partitioning medium for dissolved HOC, and results indicate that it may sorb HOC more efficiently than natural foc on a unit weight basis. Batch sorption tests showed that sorption coefficients (Kd) for trichloroethylene (TCE), perchloroethylene (PCE), and 1,2,4‐trichlorobenzene (TCB) were 13 times higher on HDTMA+ treated Borden aquifer material compared to the natural sediments. Retardation factors estimated from column transport tests confirmed these results, and suggested that sorption of moderately hydrophobic organic contaminants on the HDTMA+ modified sediments was a rapid and reversible process. Data from these laboratory‐scale experiments indicate that it may be feasible to develop an enhanced sorption zone in situ in a low foc aquifer as part of a ground‐water remediation scheme for dissolved organic pollutants.
A Program for Analyzing Transient and Steady‐State Soil Gas Pump Tests
Authors: Falta Ronald W.
Published: August 2005

Soil gas pump tests are commonly performed to identify important unsaturated zone parameters such as the effective gas permeability tensor and the influence of tight or leaky confining units. An interactive FORTRAN computer program called GASSOLVE has been developed for analyzing these tests under both transient and steady‐state conditions. The code uses one of two general analytical solutions for radially symmetric gas flow to a well: the solution for transient compressible gas flow to a partially penetrating well in which the ground surface is open to the atmosphere; and the solution for transient compressible gas flow to a partially penetrating well bounded above by a leaky confining layer. Pump tests involving steady‐state conditions, fully penetrating wells, or tight confining layers are considered as special cases of these solutions. The field gas pressure data from multiple observation wells are inverted using a multidimensional nonlinear optimization routine to provide a best fit of the data with the selected analytical solution.
Physicochemical Controls on Nonconservative Anion Migration in Coarse‐Textured Alluvial Sediments
Authors: Seaman J.C. , Bertsch P.M. , Korom S.F. , Miller W.P.
Published: August 2005

Three sandy subsurface materials and a sandy surface soil (Orangeburg Series) from the Upper Coastal Plain, were used to assess the influence of mineralogy and surface chemistry on the determination of physical transport parameters using ionic tracers. The clay mineralogy of the surface soil consisted primarily of kaolinite, hydroxy‐interlayered vermiculite, and gibbsite, while the dominant clay mineralogy of the subsurface materials consisted of kaolinite, goethite, and mica (illite). Repacked columns of the four differing strata were leached with tritiated (∼ 200 pCi mL–1) Bromide solutions, either MgBr2 or KBr, of varying ionic strengths (0.1–0.001 N). Pore‐water velocities estimated by bulk density and mass flux were consistent with those estimated from tritium breakthrough. In contrast, Br– breakthrough differed drastically within the four materials and was altered by experimental conditions (sample drying, carrier cation, etc.). The retardation for 0.001 N KBr varied from 0.94 for the surface soil to 2.15 for the subsurface materials and increased with increasing Fe oxide content. For the subsurface samples, Br– was retarded to a greater degree in the presence of Mg2+ compared to K+. In contrast, oven drying the sample reduced the degree of Br– retardation observed for the subsurface materials. These results indicate that retardation can vary dramatically within materials of similar texture, mineralogy, and origin. The apparent conservative behavior of an ionic species under a given set of conditions (mineralogy, pH, ionic strength, scale size, predominant counter ion) does not automatically ensure that transport will remain conservative as those conditions are altered by changes in experimental design or unforeseen circumstances encountered at the field scale.
Biotransformation at 10° C of Di‐n‐Butyl Phthalate in Subsurface Microcosms
Authors: Chauret Christian , Inniss William E. , Mayfield Colin I.
Published: August 2005

Di‐n‐butyl phthalate (DBP) was found to be transformed by microorganisms under aerobic and anaerobic conditions at 10° C in microcosms simulating the Canadian Forces Base (CFB) Borden subsurface environment. Biotransformation of DBP was observed under aerobic, nitrate‐reducing, Fe(III)‐reducing, and sulfate‐reducing conditions. The biotransformation of DBP in the microcosms was significantly decreased as the redox potential was lowered, especially under sulfate‐reducing conditions. However, other factors such as nutrient depletion and buildup of toxic intermediates could have affected the biotransformation rates. The highest DBP biotransformation rate (0.57 μg DBP.g sediment−1.day−1) was observed under aerobic conditions whereas the lowest rate (0.05 μg DBP.g sediment−1.day−1) was under sulfate‐reducing conditions. Biotransformation of DBP at 10° C was significantly enhanced by the addition of 10 mM NaNO3 suggesting that both the addition of nitrate and high redox conditions favor its biotransformation in subsurface environments.
Biogeochemical Evolution of Domestic Waste Water in Septic Systems: 2. Application of Conceptual Model in Sandy Aquifers
Authors: Wilhelm Sheryl R. , Schiff Sherry L. , Robertson William D.
Published: August 2005

Aqueous geochemical data from unconfined sand aquifers beneath two operating domestic septic systems are used to illustrate and evaluate a conceptual model of septic‐system geochemistry. This model emphasizes the changing redox and alkalinity conditions in the septic system and the subsurface. The septic‐tank effluents flow as distinct plumes downward through the unsaturated zones and then primarily laterally in the ground‐water zones. The composition of the effluent was measured at several points in each system. At each site, the septic‐tank effluent underwent aerobic oxidation in the unsaturated zone, which caused conversion of NH4+ to NO3−, organic C to CO2 and organic S to SCh42‐. At the first site, calcium carbonate dissolution in the unsaturated zone buffered the acidity released by the redox reactions. In contrast, the second system was poorly buffered and the pH dropped from 6.7 to 4.9 as aerobic oxidation occurred. Below the water table a small amount of aerobic oxidation occurred at each site. Nitrate‐N concentrations in the cores of both plumes were above 25 mg/1 as the plumes traveled from the septic systems. At the second site, the ground‐water plume discharges to a river at the edge of the property. As the effluent flowed through the organic C‐rich sediments of the river bed, NO3− disappeared and alkalinity increased, presumably due to denitrification. Differences in sediment composition at the two sites also led to different behaviors of Fe, Al, and possibly PO43‐. The conceptual model offers an organized approach to interpreting the major geochemical trends observed in the two systems, which are determined mostly by the well‐aerated unsaturated zones below the drain fields and the amount of buffering material present in the sediments.
Uranium Contamination in the Great Miami Aquifer at the Fernald Environmental Management Project, Fernald, Ohio
Authors: Sidle W. C. , Lee P. Y.
Published: August 2005

Ground‐water investigations at a former U.S. Department of Energy nuclear weapons complex near Fernald, in southwestern Ohio, included the delineation of uranium contamination above the USEPA proposed drinking water standard of 20 μg/l. Contamination occurs in a buried valley and has migrated > 1.5 km south‐southeast of the facility boundary. Flooring of the plume(s) appears to be > 32 m below the water table of the Great Miami Aquifer. U6+ predominates in the modeled U‐O2‐CO2‐H2O system and U retardation decreases at depth. U234/U238 disequilibria analyses complement hydrogeologic studies which suggest that U leakage through the clayey till cap is less significant than the predominant transport pathway of infiltration via drainage channels incised into the aquifer.
A Generalized Approach for the Interpretation of Geophysical Well Logs in Ground‐Water Studies—Theory and Application
Authors: Paillet F. L. , Crowder R. E.
Published: August 2005

Quantitative analysis of geophysical logs in ground‐water studies often involves at least as broad a range of applications and variation in lithology as is typically encountered in petroleum exploration, making such logs difficult to calibrate and complicating inversion problem formulation. At the same time, data inversion and analysis depend on inversion model formulation and refinement, so that log interpretation cannot be deferred to a geophysical log specialist unless active involvement with interpretation can be maintained by such an expert over the lifetime of the project. We propose a generalized log‐interpretation procedure designed to guide hydrogeologists in the interpretation of geophysical logs, and in the integration of log data into ground‐water models that may be systematically refined and improved in an iterative way. The procedure is designed to maximize the effective use of three primary contributions from geophysical logs: (1) The continuous depth scale of the measurements along the well bore; (2) The in situ measurement of lithologic properties and the correlation with hydraulic properties of the formations over a finite sample volume; and (3) Multiple independent measurements that can potentially be inverted for multiple physical or hydraulic properties of interest. The approach is formulated in the context of geophysical inversion theory, and is designed to be interfaced with surface geophysical soundings and conventional hydraulic testing. The step‐by‐step procedures given in our generalized interpretation and inversion technique are based on both qualitative analysis designed to assist formulation of the interpretation model, and quantitative analysis used to assign numerical values to model parameters. The approach bases a decision as to whether quantitative inversion is statistically warranted by formulating an over‐determined inversion. If no such inversion is consistent with the inversion model, quantitative inversion is judged not possible with the given data set. Additional statistical criteria such as the statistical significance of regressions are used to guide the subsequent calibration of geophysical data in terms of hydraulic variables in those situations where quantitative data inversion is considered appropriate.
Probabilistic Assessment of Ground‐Water Contamination: 1. Geostatistical Framework
Authors: Rautman Christopher A. , Istok Jonathan D.
Published: August 2005

Characterizing the extent and severity of ground‐water contamination at waste sites is expensive and time‐consuming. A probabilistic approach, based on the acceptance of uncertainty and a finite probability of making classification errors (contaminated relative to a regulatory threshold vs. uncontaminated), is presented as an alternative to traditional site characterization methodology. The approach utilizes geostatistical techniques to identify and model the spatial continuity of contamination at a site (variography) and to develop alternate plausible simulations of contamination fields (conditional simulation). Probabilistic summaries of many simulations provide tools for (a) estimating the range of plausible contaminant concentrations at unsampled locations, (b) identifying the locations of boundaries between contaminated and uncontaminated portions of the site and the degree of certainty in those locations, and (c) estimating the range of plausible values for total contaminant mass. The first paper in the series presents the geostatistical framework and illustrates the approach using synthetic data for a hypothetical site. The second paper presents an application of the proposed methodology to the probabilistic assessment of ground‐water contamination at a site involving ground‐water contamination by nitrate and herbicide in a shallow, unconfined alluvial aquifer in an agricultural area in eastern Oregon.
Macroscopic Models for Predicting Changes in Saturated Porous Media Properties Caused by Microbial Growth
Authors: Clement T. P. , Hooker B. S. , Skeen R. S.
Published: August 2005

Analytical equations are developed to model changes in porosity, specific surface area, and permeability caused by biomass accumulation in porous media. The proposed equations do not assume any specific pattern for microbial growth but instead are based on macroscopic estimates of average biomass concentrations. For porous media with a pore‐size distribution index value (λ) equal to 3, the macroscopic model predictions of porosity, specific surface area, and permeability changes are in exact agreement with biofilm‐model predictions. At other values of λ between 2 and 5, simulated porosity profiles are identical and relative specific surface area and permeability profiles show minor deviations. In comparison to biofilm‐based models, the macroscopic models are relatively simple to implement and are computationally more efficient. Simulations of biologically reactive flow in a one‐dimensional column show that the macroscopic and biofilm approach based transport codes predict almost identical porosity and permeability profiles. The macroscopic models are simple and useful tools for estimating changes in various porous media properties during bioremediation of contaminated aquifers.
Estimation of Spatial and Temporal Variability of Recharge Fluxes to an Alluvial Aquifer in a Fore Land Area by Water Chemistry and Isotopes
Authors: Guglielmi Y. , Mudry J.
Published: August 2005

The Var Valley (Southern France) is a typical setting in which alluvial water is situated in a fore land area. The alluvial aquifer is recharged by seepage from the intake area of the river Var and by subsurface infiltration from its fore land area.

Chemical and isotopic tracing of both sources is well contrasted, in accordance with the very different geology and relief in the two places. 18O, silica, and sulphate contents were chosen to calculate percentages of recharge from the Var river and the embanking Pliocene pudding stones. Differences among recharge estimates, calculated from the three tracers are low, about 10%. Ground‐water areas where component contributions to recharge are maximum (over 70% for Var inflow and over 40% for pudding stone inflow) are considered feeding areas. Discharge of leakage from pudding stones was calculated by the use of the Hantush formula on the whole surface of these areas: 0.53 ± 0.2 m3/sec, which corresponds to 1/5 of the total water budget of the alluvial aquifer.

Chemical surveying of alluvial water, during a water year, displays the constancy of ground‐water inflows over time, ranging from those when inflow surface water is nonexistent in the river Var during low‐water periods to those when it is massive in spate.

Thus, during periods without influence from the river Var, the inflows from the embanking formation sustain discharge of alluvial water and influence its chemical makeup. Taking these results into account, the protection area of the lower river Var water resource must be enlarged to include a part of the intake area of the adjacent reservoirs.
Estimating Hydraulic Conductivities in an Alluvial Basin from Sediment Facies Models
Authors: McCloskey Thomas F. , Finnemore E. John
Published: August 2005

It is not uncommon that hydraulic conductivity data are sparse in an area, and that information about subsurface sediment distributions are even more sparse or of poor quality. It is therefore desirable to have rational ways to estimate conductivity distributions for ground‐water flow modeling. Interpretations of the geologic history of a fault‐bounded sedimentary basin in south Santa Clara County, California, were used to estimate variations in sediment distribution and resulting relative hydraulic conductivities. Spatial sediment distributions were interpreted from the dominant infilling processes, using standard sedimentary facies models for alluvial fans and fluvial deposition. These sedimentary facies were categorized into interpreted hydrogeologic facies, which were then compared with measured hydraulic conductivity data obtained from scattered aquifer pumping tests in the basin. The comparison suggests that sedimentary facies models can provide a good basis for estimating the distribution of relative hydraulic conductivity. Further, the comparison provides a procedure for estimating hydraulic conductivities in areas where no measured values are available. This procedure provides a better basis for estimating hydraulic conductivities than methods which do not consider sedimentary processes.
Evaluation of Hydraulic Conductivity of Carson County Well Field, Amarillo, Texas
Authors: Xiang Jiannan
Published: August 2005

Environmental assessment, ground‐water management, and aquifer remediation designs rely on comprehension of the hydraulic parameters of aquifers. Because of the heterogeneity of most aquifers, a number of pumping tests are commonly required to provide a reasonable hydraulic parameter distribution. Data for 11 pumping tests, conducted at the Carson County well field, Amarillo, Texas in the 1950s to 1970s were analyzed by the Theis solution and the Cooper and Jacob solution to provide information for optimal ground‐water management. The unconfined aquifer at the well field consists of sands, sandstone, gravels, and clay. A delayed gravity response was observed in the drawdown curves from pumping tests conducted in the unconfined aquifer. Because the Theis solution and the Cooper and Jacob solution do not take this delayed response, or other unsaturated effect into account, these two solutions may overestimate hydraulic conductivity of an unconfined aquifer. Therefore, the Neuman solution which considers the delayed gravity response was used to estimate the hydraulic parameters using the software AQTESOLV (by Geraghty & Miller, Inc., 1990). This paper presents the results of a study of the unconfined aquifer at Carson County well field, Amarillo, Texas. The analysis shows that the results obtained by the Neuman method are more reasonable than those obtained by the Theis solution and the Cooper and Jacob solution. According to results from the Neuman solution, the hydraulic conductivity of the unconfined aquifer of Carson County well field varies from 2.55 to 5.97 × 10−5 m/s (weighted average hydraulic conductivity is 4.13 × 10−5 m/s). The small difference of the estimated hydraulic conductivity between wells shows that the unconfined aquifer under Carson County well field is relatively uniform. The effects of infinitesimal borehole assumption, accuracy of individual parameters, skin effects, and spatial distribution of hydraulic conductivity are discussed as well. It is also shown that benefits from obtaining accurate results should be weighted against budget requirements.
Hydrology and Geochemistry of Thermal Waters in the Upper Napa Valley, California
Authors: Murray Kent S.
Published: August 2005

Shallow low‐to‐moderate temperature geothermal waters are found in the upper part of the Napa Valley near the town of Calistoga, California. The geology of the upper Napa Valley is dominated by Jurassic to Cretaceous eugosynclinal Franciscan assemblage and the late Tertiary (Pliocene) Sonoma Volcanic rocks. Minor post‐Pliocene normal faulting is evident in the volcanic rocks north and southeast of the study area. The thermal waters which have a sodium chloride chemistry with elevated concentrations of chloride, boron, and fluoride, are attributed to fault‐controlled hydrothermal circulation. The cold waters are characterized as mixed‐cation bicarbonate type with high concentrations of calcium, magnesium, and iron. The geothermal aquifer is believed to be recharged by the upwelling of thermal water along a linear fault zone aligned with the topographic axis of the Napa Valley. Data from 140 domestic water wells were used to evaluate the chemical character of the geothermal resource and to construct maps of chloride and boron concentrations. These maps were subsequently used to locate the source of the deep thermal water and zones of cold and hot water mixing, and to develop a conceptual model of the geothermal system.
Indicator Geostatistical Analysis of Sand Interconnections Within a Till
Authors: Sminchak Joel R. , Dominic David F. , Ritzi Robert W.
Published: August 2005

At the Fernald Environmental Management Project (FEMP) site in southwestern Ohio, sand and gravel lenses within till provide potential pathways for the flow of contamination into the underlying aquifer. These high‐permeability lenses account for 22% of the volume of the till, have a complex arrangement, and are smaller in scale than the site. Even the relatively dense subsurface sampling program at the FEMP site is not adequate to determine facies interconnections with certainty. To delineate probable facies boundaries, a binary indicator random variable was used to represent the presence of high or low‐permeability sediment. The 800 available lithologic logs that penetrate the till were coded with the binary system at 2 ft (0.6 m) intervals yielding 15,829 observations. These data were used to compute the declustered mean of indicator values in horizontal intervals, giving an estimate of the proportion of high‐permeability sediment in each vertical zone. The areal correlation in specific zones was examined through indicator variograms, which had pronounced anisotropy. Three‐dimensional indicator point kriging was used to produce maps of the probability of existence of high‐permeability sediment. These maps were used in a preliminary analysis of sand body interconnectedness. Results indicate that portions of sand bodies are interconnected through the entire interval studied and that the areal extent of vertical interconnection is up to 1000 ft.
Origin of Subsurface Brines in the Sichuan Basin
Authors: Xun Zhou , Cijun Li , Xiumin Ju , Qiang Du , Lihong Tong
Published: August 2005

Subsurface brines in the Sichuan Basin occur within sedimentary rocks ranging in age from Sinian to Cretaceous, especially within rocks of Triassic age. The chemical and isotopic compositions of the brines and general geological considerations suggest that the Sichuan Basin brines are derived from waters of different origin. Water in brines from Upper Cretaceous clastic reservoirs in Anren, and from basin margin aquifers of Lower Jurassic, Triassic, and Cambrian age are modern meteoric in origin. Salinity in these brines is from dissolution of salt‐bearing formations. Lower Jurassic and Upper Triassic clastic aquifers contain a mixture of meteoric water and brines from older rocks based on isotopic data. Brines in Middle and Lower Triassic carbonate aquifers originated from sea water and are residual brines left after evaporite precipitation. Brines from the Upper Sinian carbonate aquifer in Weiyuan originated from sea water mixed with magmatic waters.
Organic Carbon Dominated Trichloroethene Sorption in a Clay‐Rich Glacial Deposit
Authors: Allen‐King Richelle M. , McKay Larry D. , Trudell Mark R.
Published: August 2005

The relative contributions of organic carbon and mineral matter to trichloroethene (TCE) sorption were determined for a natural, clay‐rich till from Sarnia, Ont. using laboratory batch tests. Linear TCE sorption coefficients of the two till samples (approximataely 12 to 15 m depth) were 64.2 l/kg and 151 l/kg and the organic carbon contents (foc) were 0.68% and 1.95%, respectively. To ascertain the importance of sorption to mineral matter versus organic carbon, till samples were treated by baking. The foc was reduced by 44 to 90% in treated samples compared to natural samples. TCE sorption coefficients were also reduced to 0.48 to 4.64 l/kg in treated samples. Surface area measurements suggested that treating the till samples appeared to have little effect on the mineral matter. The results indicated that TCE sorption is dominated by the naturally occurring organic carbon. The organic carbon normalized sorption coefficients (Koc) for the natural (untreated) samples were 16 to 500 times greater than those typically reported for sediment and soil samples, indicating the more lipophilic character of the organic matter in the till. Koc estimates which accounted for the oxidation state of the organic carbon in the till assuming the carbon is primarily from Devonian‐age shale fragments resulted in values close to (within a factor of 2 to 5) those observed. Thus, both the nature and amount of organic carbon in the till play major roles in controlling the magnitude of TCE sorption in this clay‐rich deposit.
On the Strategy of Estimating Regional‐Scale Transmissivity Fields
Authors: Christensen Steen
Published: August 2005

A case study of a leaky fluvioglacial aquifer concentrates on methods of estimating the zonated log10‐transmissivities of a regional‐scale ground‐water model covering 450 km2. Mainly three estimation methods are discussed: (a) kriging based on local measurements and predictions, (b) hydrologic inversion (i.e., nonlinear regression) based on head data, and (c) hydrologic inversion based on head data and on prior estimates from kriging. (a) Due to the shortage of data which is usual in heterogeneous aquifers, the present study questions the practical value of forming zonal kriging estimates from local data whenever estimates are to be used as an input to ground‐water models. In some parts of the homogeneous aquifers local data are sufficient to make such estimates, (b) In this study zonal hydrogeological parameters can be estimated by inversion based on head data. However, inaccuracies in head data may seriously damage the reliability of estimated parameters and, as a consequence, the ground‐water model, (c) Using zonal kriging estimates as prior information in the regression reduces the width of the confidence intervals of the parameters with prior information by up to 75%. The study indicates, however, that using prior information in the estimation of the hydrologic model parameters only minimally reduces the uncertainty of the predicted hydraulic heads.

For this specific case, the results suggest that in order to parameterize and identify the parameters of the ground‐water model one should concentrate on qualitative mapping of the hydrogeology, on sampling accurate head data and on subsequent estimation of the zonal parameters by inversion (or manual calibration).
Verifying the Integrity of Annular and Back‐Filled Seals for Vadose‐Zone Monitoring Wells
Authors: Dunnivant Frank M. , Porro Indrek , Bishop Carolyn , Hubbell Joel , Giles John R. , Newman Meredith E.
Published: August 2005

Monitoring the movement of contaminants throughout the vadose zone requires the use of wells and the credibility of a monitoring program depends on obtaining an adequate seal between the well casing and borehole wall. The credibility of monitoring well installation was evaluated during the Idaho National Engineering Laboratory's Large Scale Pumping and Infiltration Test. Wells were drilled in and around a 6.5 acre infiltration basin with an air rotary rig using a downhole hammer, cased with PVC or steel, and the annular space back‐filled with alternating layers of bentonite and sand. The purpose of completing the wells in this manner was to isolate fractured intervals (subvertical and subhorizontal interflow zones) in order to observe water movement during the infiltration test. Bentonite was used between sand intervals to prevent the borehole (or annular space) from serving as a conduit for vertical water flow or tracer migration. Neutron probes were used to confirm the presence and locations of each completion interval (sand or bentonite) by distinguishing differences in background‐water content of the back‐filling materials. Upon flooding of the infiltration basin with water containing radioactive tracers, water flow and tracer transport were monitored using neutron probes and an in situ, downhole gamma spectroscopy system, respectively. Results confirm that each well was installed correctly; water and tracers flowed through natural fractures in the subsurface and arrived at the monitoring sites located at sand completion zones. Significant water or tracer flow through the annular space between the well casing and borehole was not observed.
Distinguishing Natural Hydrocarbons from Anthropogenic Contamination in Ground Water
Authors: Lesage Suzanne , Xu Hao , Novakowski Kent S.
Published: August 2005

Differentiation between natural and anthropogenic sources of ground‐water contamination by petroleum hydrocarbons is necessary in areas where natural hydrocarbons may be present in the subsurface. Because of the similarity in composition between natural and refined petroleum, the use of statistical techniques to discern trends is required. In this study, both multivariate plotting techniques and principal component analysis were used to investigate the origin of hydrocarbons from a variety of study sites. Ground‐water and gas samples were collected from the Niagara Falls area and from three gasoline stations where leaking underground storage tanks had been found. Although soil gas surveys are used to indicate the presence of hydrocarbons, they were not useful in differentiating between natural and anthropogenic sources of contamination in ground water. Propane and pentene were found to be the most useful chemical parameters in discriminating between the natural and anthropogenic sources. These chemicals are not usually measured in investigations of ground‐water contamination, yet analysis can be conducted by most environmental laboratories using conventional methods.
Use of Solute Chemistry and Isotopes to Identify Sources of Ground‐Water Recharge in the Nile Aquifer System, Upper Egypt
Authors: Awad Mostafa A. , El Arabi Nahed E. , Hamza Mokhtar S.
Published: August 2005

Twelve ground‐water samples were collected in the Nag Hammadi area, from Quaternary and Plio‐Pleistocene age aquifers. The isotopic data indicate that the main recharge source of the Quaternary aquifer is the recent River Nile water, which is isotopically enriched from evaporation in Lake Nasser. Sources of recharge to the Plio‐Pleistocene aquifer are: (1) Old Nile water depleted in isotope composition, which was trapped in the geological formation, characterized by low permeability and clay lenses prior to the construction of the Aswan High Dam; and (2) The leakage of palaeo water from the deep aquifer system through main faults which bisect the study area. The variation in the chemistry of ground water is thought to be related to mixing between the different water sources and leaching of fertilizers in the newly reclaimed areas in the desert fringes.
Ground‐Water Solute Transport with Hydrogeochemical Reactions
Authors: García‐Delgado Rafael A. , Koussis Antonis D.
Published: August 2005

Chemical contamination of ground water is typically associated with multicomponent solutions of reactive substances, the mobility of which is affected by their reactivity. In predicting geochemical transport, it is therefore important that the liquid and solid phase reactions be modeled, along with the flow‐controlled processes. This demanding task is typically carried out on powerful computers. Frequently, however, field data are available for a limited number of species, or, a small number of species suffices to characterize ground‐water quality. In such cases it is desirable to be able to model the transport on a widely available class of inexpensive computers. We report on the development of a 2‐D model for the transport of reactive species that runs efficiently on PCs. The model follows a modified one‐step procedure that adopts total (aqueous and adsorbed) concentrations and aqueous concentrations of components, and accounts for aqueous complexation and for competitive sorption via isotherms or selectivity coefficients. The use of principal directions of transport coordinates, dimensional splitting, and a specialized algorithm for handling advection‐dominated transport render it compact and efficient. Mass conservation is satisfied with high accuracy.
Development and Testing of a Kinetic Model for Oxygen Transport in Porous Media in the Presence of Trapped Gas
Authors: Donaldson J. H. , Istok J. D. , Humphrey M. D. , O'Reilly K. T. , Hawelka C. A. , Mohr D. H.
Published: August 2005

The ability to predict the transport of dissolved gases in the presence of small amounts of trapped gas in an otherwise water‐saturated porous medium is needed for a variety of applications. However, an existing model based on equilibrium partitioning of dissolved gas between aqueous and trapped gas phases does not accurately predict the shape of experimentally observed breakthrough and elution curves in column experiments. The objective of this study was to develop and test a kinetic model for dissolved gas transport that combines the advection‐dispersion equation with diffusion controlled mass transfer of dissolved gas between the aqueous and trapped gas phases. The model assumes one‐dimensional, steady‐state ground‐water flow, a single dissolved gas component, and a stationary trapped gas phase with constant volume. The model contains three independent parameters: the Peclet number, P, retardation factor, R, and dimensionless mass transfer parameter, ω. The model accurately described the shape of breakthrough and elution curves for dissolved oxygen in column experiments performed with a poorly graded sand and varying amount and composition of trapped gas. Estimated values of P for the bromide tracer increased from 5.92 to 174, corresponding to a decrease in dispersivity from 5.02 to 0.17 cm, as the trapped gas volume increased from 0 to 30% of the pore space. It is speculated that this effect is due to a narrower pore size distribution (and hence more uniform pore scale velocity distribution) caused by trapped gas bubbles selectively occupying the largest pores. Estimated values of R increased from 1 to 13.6 as the trapped gas volume increased and confirmed earlier observations that even small amounts of trapped gas can significantly reduce rates of dissolved oxygen transport. Estimated values of ω ranged from 0.3 to 12.1. Although it was not possible to independently measure mass transfer coefficients or interfacial areas, values computed from flow rates and estimated w values are consistent with values computed by assuming (1) that interfacial area is proportional to trapped gas volume, (2) that trapped gas bubbles are spheres with diameters the same size as soil particles, and (3) that mass transfer is limited by diffusion of dissolved oxygen through water films surrounding trapped gas bubbles.
Site‐Specific Variability in BTEX Biodegradation Under Denitrifying Conditions
Authors: Kao Chih‐Ming , Borden Robert C.
Published: August 2005

Laboratory microcosm experiments were conducted to evaluate the feasibility of benzene, toluene, ethylbenzene, m‐xylene, and o‐xylene (BTEX) biodegradation under denitrifying conditions. Nine different sources of inocula, including contaminated and uncont animated soil cores from four different sites and activated sludge, were used to establish microcosms. BTEX was not degraded under denitrifying conditions in microcosms inoculated with aquifer material from Rocky Point and Traverse City. However, rapid depletion of glucose under denitrifying conditions was observed in microcosms containing Rocky Point aquifer material. TEX degradation was observed in microcosms containing Rocky Point aquifer material. TEX degradation was observed in microcosms containing aquifer material from Fort Bragg and Sleeping Bear Dunes and sewage sludge. Benzene was recalcitrant in all microcosms tested. The degradation of o‐xylene ceased after toluene, ethylbenzene, and m‐xylene were depleted in the Fort Bragg and sludge microcosms, but o‐xylene continued to degrade in microcosms with contaminated Sleeping Bear Dunes soil. The most probable number (MPN) of denitrifiers in these nine different inocula were measured using a microtiter technique. There was no correlation between the MPN of denitrifiers and the TEX degradation rate under denitrifying conditions. Experimental results indicate that the degradation sequence and TEX degradation rate under denitrifying conditions may differ among sites. Results also indicate that denitrification alone may not be a suitable bioremediation technology for gasoline‐contaminated aquifers because of the inability of denitrifiers to degrade benzene.
Correcting for Diffusion in Carbon‐14 Dating of Ground Water
Authors: Sanford Ward E.
Published: August 2005

It has generally been recognized that molecular diffusion can be a significant process affecting the transport of carbon‐14 in the subsurface when occurring either from a permeable aquifer into a confining layer or from a fracture into a rock matrix. An analytical solution that is valid for steady‐state radionuclide transport through fractured rock is shown to be applicable to many multilayered aquifer systems. By plotting the ratio of the rate of diffusion to the rate of decay of carbon‐14 over the length scales representative of several common hydrogeologic settings, it is demonstrated that diffusion of carbon‐14 should often be not only a significant process, but a dominant one relative to decay. An age‐correction formula is developed and applied to the Bangkok Basin of Thailand, where a mean carbon‐14‐based age of 21,000 years was adjusted to 11,000 years to account for diffusion. This formula and its graphical representation should prove useful for many studies, for they can be used first to estimate the potential role of diffusion and then to make a simple first‐order age correction if necessary.
Design of a Ground‐Water Extraction/Reinjection System at a Superfund Site Using MODFLOW
Authors: Bumb Amar C. , Mitchell Judson T. , Gifford Seth K.
Published: August 2005

A sand and gravel quarry was simultaneously operated as a landfill. The underlying contaminated aquifer is unconfined at the landfill and becomes confined as it dips to the north. A ground‐water model based on the MODFLOW program was developed to evaluate remediation alternatives and provide a basis for modifying the Record of Decision for the site. Hydraulic conductivities were contoured and continuously varied across the modeled area instead of defining zones of constant hydraulic conductivities. The model was calibrated by matching monthly water levels and travel times for nonadsorbing contaminants to migrate from the landfill to the extent of the contaminant plume. Drawdown data from a 72‐hour pump test were used to confirm the model's ability to predict an accurate response to pumping stresses and to reduce the uncertainty of the model.

Modeling indicated that ground‐water recharge was required to prevent soil desaturation, minimize recontamination of ground water due to rebounding water levels, and to provide continuous flushing of the soils. The ground‐water extraction system designed for the site, consisting of eight extraction wells and one recharge trench, was predicted to reverse the natural ground‐water gradients observed at the edge of the contaminant plume, minimize travel distance for contaminants, and reduce contaminated ground‐water flow through clean aquifer soils. Recharged water was predicted to flow through the most heavily contaminated soils and be captured primarily by two extraction wells closest to the landfill. Model results were used to successfully modify the existing Record of Decision design.
Mobile NAPL Recovery: Conceptual, Field, and Mathematical Considerations
Authors: Sale Tom , Applegate David
Published: August 2005

Recovery of mobile Nonaqueous Phase Liquids (NAPLs), referred to as “oil recovery,” is one of the most common remedial technologies currently being implemented at sites where NAPLs have been released. The rationale for oil recovery typically includes resource recovery, mitigation of further NAPL migration, and compliance with regulatory mandates for source reduction. Efficient oil recovery can be achieved by optimizing conditions within the oil flow path. This concept is referred to as flow path management. Building on this concept, a waterflood oil recovery technique utilizing dual recovery and parallel delivery drain lines has been developed for recovery of creosote‐based wood‐treating oil, a Dense Nonaqueous Phase Liquid (DNAPL). Full‐scale application of this technique at a contaminated site has yielded 1.5 million gallons of DNAPL. Furthermore, an operational endpoint of 95 percent recovery of the mobile oil is being achieved. Building on the concept of flow path management and the observed performance of the waterflood oil recovery system, a first‐order analytical solution for DNAPL flow to a drain line has been derived and validated using field data. This solution leads to a set of useful design equations and further insight into the factors that control oil recovery.