bluuebunny/crossref_metadata_2025_split huggingface dataset:
Stable Isotopes (δ18O, δ2H) of Pore Waters in Clay‐Rich Aquitards: A Comparison and Evaluation of Measurement Techniques
Authors: Kelln Chris J. , Wassenaar Leonard I. , Hendry M. Jim 
Published: February 2007

AbstractPore water collected from piezometers installed in a thick clay‐rich till were used to compare and evaluate four techniques for obtaining δD and δ18O values in these media. The techniques included mechanical squeezing, centrifugation, azeotropic distillation, and a direct soil‐water equilibration technique. Direct CO2‐core equilibration yielded sufficiently accurate and reproducible δ18O results of pore water in clay‐rich tills. In addition, this method eliminated the need for labor‐intensive complete extraction of water from the geologic media. Mechanical squeezing and centrifugation produced results similar to direct equilibration. However, both of these methods exhibited a greater degree of variability and were laborious and more time consuming. Small differences in δ18O values between piezometer water and equilibrated, squeezed, and centhfuged samples suggested that each method collected different fractions of the clay‐water reservoir. Although these subtle differences were not conclusive, they did suggest the presence of weakly bound water and highlighted the difference between these three techniques for determining the stable isotopic composition of pore water in clay‐rich aquitards. Azeotropic distillation produced a high level of discrepancy in δD andδ18O results compared to the other methods. Incomplete extraction was considered the most probable cause of this error. The results of this study suggested that direct equilibration is the best method for determining detailed δD and δ18O values of pore water in clay‐rich aquitards.
Analysis of Water Saturation, NAPL Content, Degradation Half‐Life, and Lower Boundary Conditions on VOC Transport Modeling: Implications for Closure of Soil Venting Systems
Authors: DiGiulio Dominic C. , Varadhan Ravi 
Published: February 2007

AbstractSimulations using a one‐dimensional, analytical, vadose zone, solute‐transport screening code (VFLUX) were conducted to assess the effect of water saturation, NAPL saturation, degradation half‐life, and boundary conditions at the vadose zone/ground water interface on model output. At high initial soil concentrations, model output was significantly affected by input parameters and lower boundary conditions yet still resulted in consistent decision‐making to initiate or continue venting application. At lower soil concentrations, however, typical of what is observed after prolonged venting application, differences in model input and selection of lower boundary conditions resulted in inconsistent decision‐making. Specifically, under conditions of low water saturation, use of a first‐type, time‐dependent lower boundary condition indicated that the primary direction of mass flux was from ground water to the vadose zone, suggesting little benefit from continued venting application. Use of a finite, zero‐gradient lower boundary condition, though, indicated continued mass flux from the vadose zone to ground water, suggesting a continued need for venting application. In this situation, sensitivity analysis of input parameters, selection of boundary conditions, and consideration of overall objectives in vadose zone modeling become critical in regulatory decision‐making.
Vitamin B12 and Reduced Titanium for Remediation of Residual Chlorinated Solvents: Field Experiment
Authors: Sorel Dominique , Lesage Suzanne , Brown Susan , Millar Kelly 
Published: February 2007

AbstractA first pilot‐scale field experiment using vitamin B12 and reduced titanium was conducted in an in situ vertical circulation column at CFB Borden. The objective of the experiment was to test the applicability of the technology for restoring aquifer source zones contaminated by chlorinated solvents—tetrachloroethene (PCE) and 1,1,1‐trichloroethane (1,1,1‐TCA)—in a mixture of dense nonaqueous phase liquids (DNAPLs). Vitamin B12 promotes the reductive dechlorination of chlorinated organics. A highly reducing and slightly alkaline environment must be maintained (Eh < ‐ 480 mV and 7 < pH < 9) to maximize the rate of degradation. In this field test, PCE and 1,1,1‐TCA degraded to a limited extent under experimental conditions, with 1,1,1‐TCA degrading more readily. Indigenous bacteria were found to metabolize citrate, which caused titanium to precipitate, limiting degradation. The addition of glucose at the end of a second field season effectively limited citrate degradation and helped recover the optimal redox potential by keeping reduced titanium in solution. A laboratory column was used to confirm field results. The column also produced a significant biomass, which provided an additional source of organic carbon onto which the solvents sorbed.
Refractive Flow and Treatment Systems: Conceptual, Analytical, and Numerical Modeling
Authors: Edwards David A. , Dick Vincent B. , Little James W. , Boyle Susan L. 
Published: February 2007

AbstractRefractive flow and treatment (RFT) systems are designed for passive or low‐maintenance in situ ground water remediation for rock or soil of low to moderate permeability. An RFT system captures and refracts contaminated ground water and conveys it to an in situ permeable treatment zone without the need for pumping. Flow to the treatment zone is through one or more high‐permeability collection cells, and flow from the treatment zone back into the adjacent native media is through one or more high‐permeability dispersal cells.Conceptual, analytical, and numerical modeling demonstrates the potential for RFT systems to be successful. Analytical modeling shows that the most important factor for this success is that RFT system components be engineered to have comparatively high hydraulic conductivities. A numerical model, capable of representing site‐specific conditions, is required for actual RFT system design.
Monitored Natural Attenuation of Contaminants in the Subsurface: Applications
Authors: Azadpour‐Keeley Ann , Keeley Jack W. , Russell Hugh H. , Sewell Guy W. 
Published: February 2007

AbstractIn recent years there has been increasing interest in the application of passive technologies to reduce or remove contaminants from the subsurface environment including soil and ground water. In most cases, the impetus for this interest lies in a perceived savings compared with more traditional remedial alternatives. In a few cases, the infrastructure at contaminated sites, such as buildings, paved areas, and utilities, makes the use of conventional remedial measures difficult and expensive.To demonstrate that natural processes are effective in reaching established goals, it is necessary to determine that transformation processes are taking place at a rate that is protective of human health and the environment and that these processes will continue for an acceptable period of time. The basic conditions that must be present to confirm natural attenuation processes arc taking place are discussed along with the behavior of contaminated plumes, monitoring requirements, data analysis, rates of degradation, and mathematical modeling.
Funnel‐and‐Gate Performance in a Moderately Heterogeneous Flow Domain
Authors: Bilbrey Lacrecia C. , Shafer John M. 
Published: February 2007

AbstractThe funnel‐and‐gate ground water remediation technology (Starr and Cherry 1994) has received increased attention and application as an in situ alternative to the typical pump‐and‐treat system. Understanding the effects of heterogeneity on system performance can mean the difference between a successful remediation project and one that fails to meet its cleanup goals.In an attempt to characterize and quantify the effects of heterogeneity on funnel‐and‐gate system performance, a numerical modeling study of 15 simulated heterogeneous flow domains was conducted. Each realization was tested to determine if the predicted capture width met the capture width expected for a homogeneous flow domain with the same hulk properties. This study revealed that the capture width of the funnel‐and‐gate system varied significantly with the level of heterogeneity of the aquifer.Two possible remedies were investigated for bringing systems with less than acceptable capture widths to acceptable levels of performance. First, it was determined that enlarging the funnel and gate via a factor of safety applied to the design capture width could compensate for the capture width variation in the heterogeneous flow domains. In addition, it was shown that the use of a pumping well downstream of the funnel and gate could compensate for the effects of aquifer heterogeneity on the funnel‐and‐gate capture width. However, if a pumping well is placed downstream of the funnel and gate to control the hydraulic gradient through the gate, consideration should be given to the gate residence time in relation to the geochemistry of the contaminant removal or destruction process in the gate.
Comparison of Temporal Trends in VOCs as Measured with PDB Samplers and Low‐Flow Sampling Methods
Authors: Harte Philip T. 
Published: February 2007

AbstractThe effectiveness of passive diffusion bag (pdb) samplers in the measurement of selected volatile organic compounds (VOCs) is dependent on a number of factors. At some sites and wells, pdb sampling methods provide an attractive alternative to other sampling methods. In this discussion, I provide two examples of comparisons of temporal trends in tetrachloroethylene (PCE) concentrations from passive and low‐flow sampling methods. At the example field site, large changes in PCE concentrations occurred over the deployment period(s) of the pdb samplers, yet the concentrations from the pdb samples are similar to the low‐flow samples and the overall trends are the same.
Extraction Rate Problems Lead to Increased Costs at Pump‐and‐Treat Facilities: A Call to Improve Reporting of Rates
Authors: Boice Richard 
Published: February 2007

AbstractExperiences at five pump‐and‐treatment (P&T) facilities provide three important lessons:1. To reduce future costs, it is important to use the best hydraulic information possible for designing P&T systems, and to incorporate flexibility to compensate for uncertainties in hydraulic conditions. A phased approach to P&T system construction and hydraulic testing has been successful.2. In practice, downtimes and maintenance problems result in significant reductions in the average ground water extraction rates. This indicates that operation and maintenance were more difficult than expected and warrant more attention. Furthermore, P&T systems are generally designed to attain the model optimized extraction rates only when the system is in full operation. Designers must recognize that P&T systems have downtimes, and, therefore, the uptime pumping must be sufficient to maintain capture. Generally, P&T systems should achieve model‐optimized extraction rates on an average basis rather than only when the system is in full operation.3. During operation of P&T systems, the average extraction rates should be routinely correlated to capture zone evaluations and included in monitoring reports. The average extraction rates should be compared to the model‐derived extraction rates to assess whether the design objectives are being met and should be included in routine monitoring reports to confirm maintenance of pumping rates under which capture has been demonstrated.
Assessment of Water Quality After 10 Years of Reclaimed Water Injection: The Nardò Fractured Aquifer (Southern Italy)
Authors: Masciopinto Costantino , Carrieri Carmelo 
Published: February 2007

AbstractExperimental studies have been carried out in a fractured coastal aquifer of the Salento region (Nardò, Italy), which has been subjected to 12,000 m3/day of treated municipal waste water injected into a natural sinkhole since 1991. The analytical parameters of ground water sampled in 30 monitoring wells in the area down gradient from the sinkhole, taking into account the direction of ground water flow, have been compared before and after injection. The water table mound (1.5 m), the reduction of sea water extent (2 km), and the spreading of injected pollutants were evaluated by means of a mathematical model. The predicted values in the monitoring wells were adjusted to inorganic nitrogen biodegradation using transformation rates developed in laboratory tests. After 10 years, the injection has increased the volume of the available resource for agricultural and drinking water use, without any notable decrease in the preexisting ground water quality. Moreover, to preserve water resources from pollution, the mathematical model allowed the maximum constituent concentrations (standards) in waste water reclamation for recharge to be identified. A precautionary area around the sinkhole was also defined so that withdrawal prohibition could be implemented to avoid risks to human health.
Keeping Up with All That Literature: The IronRefs Database Turns 500
Authors: Tratnyek Paul G. 
Published: February 2007

AbstractThe IronRefs database covers published research on remediation applications of zero‐valent metals and is accessible at http://www.cgr.ese.ogi.edu/ironrefs/. The rapid growth of ground water remediation applications of zero‐valent metals is reflected in the rapid growth of this database, which exceeded 500 records in December 2001. This is much more complete coverage of this topic than can be obtained from any of the major commercial databases of the scientific literature. Specialized databases such as IronRefs, prepared by experts in a particular field, are becoming increasingly common on the Web and offer distinctive benefits over traditional options for keeping up with the literature in rapidly growing fields of science and engineering.
Geophysical Study of Annular Well Seals
Authors: Christman Martin C. , Benson Craig H. , Edil Tuncer B. 
Published: February 2007

AbstractGeophysical logging was conducted in 35 in‐service water and monitoring wells installed in unconsolidated sediments using a downhole ultrasonic probe to assess how sealant type, construction method, and site geology affect annular seals. Collapsed sand and gravel was frequently detected in the annulus of wells constructed with mud‐rotary methods, precluding the placement of sealant and, in some wells, potentially providing a preferential pathway for contamination. High‐solids bentonite grout appeared to create high‐quality seals when formation materials did not collapse into the annulus. Seals composed of bentonite chips and pellets remained intact when hydrated upon placement; those not hydrated during placement remained dry and porous, posing a risk of surface water infiltration. Seals made with cement‐bentonite grout were generally unsaturated and possibly cracked. Analysis of the data suggests that well designers should specify a construction method that minimizes collapse of the formation to ensure that the sealant is placed where intended. When collapse is avoided, high‐solids bentonite grout and hydrated bentonite chips and pellets appear to yield intact seals. However, bentonite chips and pellets may not hydrate adequately in the annulus unless hydration water is added during installation. When cement‐bentonite grouts are used, the well designer should ensure that the grout will remain intact and plastic after installation.
Direct Push Methods for Locating and Collecting Cores of Aquifer Sediment and Zero‐Valent Iron from a Permeable Reactive Barrier
Authors: Beck Frank P. , Clark Patrick J. , Puls Robert W. 
Published: February 2007

AbstractIt is often necessary to collect core samples that are not accommodated by standard sampling protocols, This paper describes innovative techniques using existing technology that enables researchers to collect samples at upgradient and downgradient interfaces from a zero‐valent iron wall so that the most active zone of chromium remediation and biologic activity can be studied. It describes the methodology used and how the direct‐push technology was adapted so that the desired samples could be collected. It also explains why new methods were needed and demonstrates the results of these efforts.
Soil Gas Screening for Chlorinated Solvents at Three Contaminated Karst Sites in Tennessee
Authors: Wolfe William J. , Williams Shannon D. 
Published: February 2007

AbstractSoil gas was sampled using active sampling techniques and passive collectors at three sites in Tennessee to evaluate the effectiveness of these techniques for locating chlorinated solvent sources and flowpaths in karst aquifers. Actively collected soil gas samples were analyzed in the field with a portable gas chromatograph, and the passive soil gas collectors were analyzed in the lab with gas chromatography/mass spectrometry. Results of the sampling indicate that the effectiveness of both techniques is highly dependent on the distribution of the contaminants in the subsurface, the geomorphic and hydrogeologic characteristics of the site, and, in one case, on seasonal conditions. Both active and passive techniques identified areas of elevated subsurface chlorinated solvent concentrations at a landfill site where contamination remains concentrated in the regolith. Neither technique detected chlorinated solvents known to be moving in the bedrock at a manufacturing site characterized by thick regolith and an absence of surficial karst features. Passive soil gas sampling had varied success detecting flowpaths for chloroform in the bedrock at a train derailment site characterized by shallow regolith and abundant surficial karst features. At the train derailment site, delineation of the contaminant flowpath through passive soil gas sampling was stronger and more detailed under winter conditions than summer.
A Geostatistically Based Ground Water Monitoring Study of Nonpoint Source No3‐‐N Concentrations
Authors: Carlson Rick A. , Osiensky James L. 
Published: February 2007

AbstractGeostatistical interpretations of ground water monitoring data are presented to define the spatial distributions of NO3‐‐N in the ground water at two demonstration test sites in the Idaho Snake River Plain. Sequential Gaussian simulation was used to delineate monthly ground water NO3‐‐N changes during and after implementation of a prescribed crop rotation at test site 1. Trend surface analyses were used to illustrate monthly ground water NO3‐‐N changes during and after a prescribed irrigation practice was implemented at test site 2. These evaluations suggest that geostatistically based ground water monitoring can be effective in the delineation of changes in ground water quality in shallow, unconfined aquifers in agricultural areas such as those in southern Idaho. Geostatistical methods showed spatial and temporal changes in ground water NO3‐‐N inferred to be a result of the agricultural practices implemented.
Associations Between Rural Land Uses and Ground Water Quality in the Ogallala Aquifer, Northwest Texas
Authors: Hudak Paul F. 
Published: February 2007

AbstractRecent nitrate, chloride, and bromide concentrations were studied in the Ogallala Aquifer of northwest Texas. The study included 361 wells with a median depth of 92 m in a rural area dominated by agricultural activity and oil and gas production. Only five observations surpassed the 44.3 mg/L standard for nitrate (10 mg/L NO3‐N). Four other observations, and one from the preceding set, exceeded the secondary standard of 250 mg/L for chloride. Maximum concentrations were 91.2 mg/L, 1530 mg/L, and 0.70 mg/L for nitrate, chloride, and bromide, respectively. Chloride/bromide ratios covered a broad range, from 30.4 to 10930, but medians were < 160 for each of two years analyzed. There were statistically significant correlations between nitrate and chloride, and chloride and well depth. Results of this study suggest that agricultural activity has locally impacted ground water in north‐west Texas. Regionally, low aquifer recharge rates have curtailed ground water contamination from potentially adverse land uses.
Polymer‐Enhanced DNAPL Flushing from Low‐Permeability Media: An Experimental Study
Authors: Darwish Mohamed I.M. , McCray John E. , Currie Peter K. , Zitha Pacelli L.J. 
Published: February 2007

AbstractRemediation of dense nonaqueous phase liquids (DNAPLs) is recognized as one of the most difficult problems associated with ground water pollution. The pump‐and‐treat technique, usually consisting of a continuous operation of extraction‐injection wells, is widely used for ground water remediation. In a stratified or otherwise heterogeneous aquifer, however, this technique suffers from tailing and rebound problems, which limit its cleanup efficiency and result in higher operation costs. The tailing and rebound is usually due to slow diffusion of contaminants out of lower‐ permeability heterogeneities into the flow regime of the higher‐permeability zone. In this study, we conduct bench‐scale experiments to investigate a novel polymer system and injection method to improve the pump‐and‐treat technique for DNAPL trapped in a layer of porous media that has a relatively low permeability compared to the surrounding media. This technique might be useful, for example, to remove DNAPL from these low‐permeability zones after removal of DNAPL from the higher‐permeability zones by a more traditional remediation method. The polymer system consists of a mixture of anionic and cationic polyacrylamides in solution and the injection method is based on flow‐induced polymer adsorption, called bridging adsorption. The study includes single and parallel‐column experiments. The measured polymer penetration depths were compared with values predicted from a numerical simulation, which was developed previously by the authors of this paper. The experiments and simulations show that the polymer injection leads to a modification of the permeability contrast that favors a more efficient pump‐and‐treat process. These results suggest that additional research to upscale the technology to pilot scales is warranted.
Delineation of Ground Water Flow in Fractured Rock in the Southwestern Part of Manhattan, New York, Through Use of Advanced Borehole Geophysical Methods
Authors: Stumm Frederick , Chowdhury Shafiul 
Published: February 2007

AbstractAdvanced borehole‐geophysical methods were used to assess the geohydrology of fractured crystalline bedrock at five test boreholes in southwestern Manhattan Island, New York, in preparation for construction of a third water tunnel for New York City. The boreholes penetrated gneiss and other crystalline bedrock that has an overall southwest to northwest dipping foliation with a 60° dip. Most of the fractures encountered are either nearly horizontal or have moderate northwest dip azimuths. Fracture indexes range from 0.25 to 0.44 fracture per foot (0.3 m) of borehole.Electromagnetic (EM) and heat‐pulse flowmeter logs obtained under ambient and pumping conditions, together with other geophysical logs, indicate transmissive fracture zones in each borehole. Pumping tests of each borehole indicated transmissivity ranges from <2 to 360 ft2/day (0.2 to 33 m2/day). Ground water appears to flow within an interconnected fracture network toward the south and west within the study area. No correlation was indicated between the fracture index and the total borehole transmissivity.