bluuebunny/crossref_metadata_2025 huggingface dataset:
Fluoride in Nebraska's Ground Water
Authors: Gosselin David C. , Headrick Jacqueline , Harvey F. Edwin , Tremblay Rod , McFarland Kimberly
Published: February 2007

Fluoride concentrations in ground water are generally low but play an important role in dental health. This study evaluates the vertical and spatial distribution of fluoride in Nebraska's ground water and examines the geological and geochemical processes that control its concentration. Data from 1794 domestic wells sampled by the Nebraska Department of Health and Human Services. Regulation, and Licensure (NDOH) had a range of fluoride concentrations from <0.1 to 2.6 mg/L. and a median concentration of 0.3 mg/L. The median fluoride concentrations for Nebraska's 13 ground water regions varied from 0.2 to 0.7 mg/L. In each of these regions, individual wells may have either insufficient or overabundant F concentrations; we recommend that individual private water systems be tested for fluoride. Based on these data, system‐specific recommendations can be made regarding the necessity for fluoridation.

Geochemical data indicated that the majority of fluoride occurs as F. Dissolution of F‐bearing minerals controls fluoride occurrence. Apatite plus minor amounts of fluorite along with significant ground water residence times are the primary factors controlling F in the water from the Dakota Formation in Knox County, as well as in other parts of northeastern Nebraska. In western and southwestern Nebraska, dissolution of volcanic glass is the most probable source of F Long residence times plus fluorite also may contribute to the F concentrations in the Chadron Formation.
Construction and Testing of a Durable Platinum Wire Eh Electrode for In Situ Redox Measurements in the Subsurface
Authors: Swerhone G. D. W. , Lawrence J. R. , Richards J. G. , Hendry M. J.
Published: February 2007

We have developed a rugged, durable platinum wire Eh electrode for application in subsurface environments. The electrode design is described in detail and its performance under aerobic and anaerobic steady‐state and transient conditions is assessed. The electrode consists of a 0.5‐mm‐diameter platinum wire (99.99% purity) cast in a glass fiber‐reinforced epoxy jacket. The construction allowed installation through direct insertion into sandy media to depths up to several meters. Data collection was through connection to a datalogger with high impedance input; data points were collected every 10 seconds and averaged and stored once an hour. The electrodes functioned in situ for periods of more than three years and gave reliable readings during oxic, anoxic, and transitional conditions. Performance testing and examination of electrodes recovered after three years in situ indicated that they were not impacted by corrosion, dissolution, or poisoning.
Comment on “Caution Against Interpreting Gasoline Release Dates Based on BTEX Ratios in Ground Water,” by Pedro J.J. Alvarez, Richard C. Heathcote, and Susan E. Powers, Fall 1998 Ground Water Monitoring & Remediation, v. 18, no. 4: 69‐76.
Authors: Kaplan Isaac (Ian) R. , Galperin Yakov
Published: February 2007

“Our experience shows that BTEX ratios, when used cautiously, often provide valuable information on the age of gasoline fuel release.”
Investigation and Remediation of a 1,2–Dichloroethane Spill Part I: Short and Long‐Term Remediation Strategies
Authors: Sehayek Lily , Vandell Terry D. , Sleep Brent E. , Lee Michael D. , Chien Calvin
Published: February 2007

Release of an estimated 150,000 gallons (568,000 L).of 1.2–dichloroethane (EDC) from a buried pipeline into a ditch and surrounding soil resulted in shallow subsurface contamination of a Gulf Coast site. Short‐term remediation included removal of EDC DNAPI. (dense nonaqueous phase liquid) by dredging and vacuuming the ditch, and by dredging the river where the ditch discharged. EDC saturation in shallow impacted sediments located beneath the ditch was at or below residual saturation and these sediments were therefore left in place. The ditch was lined, backfilled, and capped. Long‐term remediation includes EDC DNAPL recovery and hydraulic containment from the shallow zone with long‐term monitoring of the shallow, intermediate, and deep (200 foot) aquifers. Ground water, DNAPL., and dissolved phase models were used to guide field investigations and the selection of an effective remedial action strategy. The DNAPL. modeling was conducted for a two‐dimensional vertical cross section of the site, and included the three aquifers separated by two aquitards with microfractures. These aquitards were modeled using a dual porosity approach. Matrix and fracture properties of the aquitards used for DNAPL modeling were determined from small‐scale laboratory properties. These properties were consistent with effective hydraulic conductivity determined from ground water flow modeling. A sensitivity analysis demonstrated that the vertical migration of EDC was attenuated by dissolution of EDC into the matrix of the upper aquitard. When the organic/water entry pressure of the aquitard matrix, or the solubility of EDC were decreased to unrealislically low values. EDC DNAPL. accumulated in the aquifer below the upper aquitard.

EDC DNALM, did not reach the regional (deepest) aquifer in any of the cases modeled. The limited extent of vertical EDC migration predicted is supported by ground water monitoring conducted over the four years since the spill.
Design of Dry Barriers for Containment of Contaminants in Unsaturated Soils
Authors: Morris Carl E. , Thomson Bruce M. , Stormont John C.
Published: February 2007

A dry barrier consists of a laterally continuous soil layer that is dried by air flow. Dry atmospheric air is passed through a soil layer (preferably of a coarse texture). accumulates water vapor, then emerges from the formation as moist air. Removal of soil moisture limits or prevent downward water movement. Drying a soil layer with air is possible when atmospheric air contains less water vapor than soil pore gas. The design of an effective dry barrier is highly site dependent and requires knowledge of the site geology, of the extent of the contaminant plume, and climatic conditions. Climatic conditions at the site are important in two ways: (1) the efficiency of atmospheric air in drying: soil depends on its absolute humidity: and (2) the amount of infiltration from precipitation influences how much water has to be removed from the soil to maintain a dry barrier. The size of the barrier, combined with the climatic conditions, determines the air flow required to maintain the system. while the hydraulic characteristics of the soils determine the location and design of air injection and extraction wells. The electric power rate structure must be known to calculate operating costs. The principal factors which determine the feasibility of a dry barrier include: (1) the climate at the site and, most importantly, low‐absolute atmospheric humidity during much of the year; (2) a substantial unsaturated zone; and (3) the ability to circulate air through the unsaturated zone. The amount of initial soil moisture in the layer through which air is circulated may be an important factor in the feasibility of a dry barrier. A design study is presented that illustrates the trade‐offs between high capital costs of constructing a large number of air circulation wells vs. the high operating costs required to pump large volume of air over long distances through fewer wells. This study found that, under conditions similar to those in many arid regions, a dry barrier may be a technically and economically viable method of providing temporary waste containment.
Robowell: An Automated Process for Monitoring Ground Water Quality Using Established Sampling Protocols
Authors: Granato Gregory E. , Smith Kirk P.
Published: February 2007

Robowell is an automated process for monitoring selected ground water quality properties and constituents by pumping a well or multilevel sampler. Robowell was developed and tested to provide a cost‐effective monitoring system that meets protocols expected for manual sampling. The process uses commercially available electronics, instrumentation, and hardware, so it can be configured to monitor ground water quality using the equipment, purge protocol, and monitoring well design most appropriate for the monitoring site and the contaminants of interest. A Robowell prototype was installed on a sewage‐treatment plant infiltration bed that overlies a well‐studied u neon fined sand and gravel aquifer at the Massachusetts Military Reservation, Cape Cod, Massachusetts, during a time when two distinct plumes of constituents were released. The prototype was operated from May 10 to November 13, 1996, and quality‐assurance/quality‐control measurements demonstrated that the data obtained by the automated method was equivalent to data obtained by manual sampling methods using the same sampling protocols. Water level, specific conductance, pH, water temperature, dissolved oxygen, and dissolved ammonium were monitored by the prototype as the wells were purged according to U.S. Geological Survey (LJSGS) ground water sampling protocols. Remote access to the data record, via phone modem communications, indicated the arrival of each plume over a few days and the subsequent geochemical reactions over the following weeks. Real‐time availability of the monitoring record provided the information needed to initiate manual sampling efforts in response to changes in measured ground water quality, which proved the method and characterized the screened portion of the plume in detail through time. The methods and the case study described are presented to document the process for future use.
Chlorinated Decreasing Solvents: Physical‐Chemical Properties Affecting Aquifer Contamination and Remediation
Authors: Jackson Richard E. , Dwarakanath Varadarajan
Published: February 2007

Chlorinated degreasing solvents are multicomponent liquids containing not only the chlorinated hydrocarbons with which their name is associated (e.g., trichloroethylene or |TCE]. perchloroethylene or [PCE], 1,1,1‐trichlorocihane [TCA]) but also a number of organic additives included as corrosion inhibitors and antioxidants. The additives, such as 1,4‐dioxane, are likely to be of significant public‐health importance as ground water contaminants due to their toxicity, solubility, and mobility. Following their use in vapor degreasing systems by industry, chlorinated degreasing solvents will also contain about 25% solubilized oil and grease.

A number of physical‐chemical properties become especially important in the light of the multicomponent nature of these solvents. First, the higher aqueous solubility and lower sorption of the additives makes it is reasonable to expect that faster moving plumes of these solvent additives will precede plumes of the chlorinated hydrocarbons. Second, due to high losses of chlorinated hydrocarbons by volatilization from vapor degreasers during years in the middle of the century, it is probable that background concentrations of these hydrocarbons are present in ground water flow systems due to their downwind washout. Finally, the solubilized oil and grease may cause profound changes to the wettability of aquifer materials contacted by the solvents during their subsurface migration. It is argued, therefore, that the wettability of aquifer materials contaminated by chlorinated degreasing solvents needs to be experimentally determined before remediation of DNAPL at each site, rather than being simply assumed as water wet.
Instrumentation Design and Installation for Monitoring Air Injection Ground Water Remediation Technologies
Authors: Hall B.L. , Baldwin C.K. , Lachmar T.E. , Dupont R.R.
Published: February 2007

An in situ instrumentation bundle was designed for inclusion in monitoring wells that were installed at the Wasatch Trailer Sales site in Layton, Utah, to evaluate in situ air sparging (IAS) and in‐well aeration (IWA). Sensors for the bundle were selected based on laboratory evaluation of accuracy and precision, as well as consideration of size and cost. SenSym pressure transducers, Campbell Scientific Inc. (CSI) T‐type thermocouples, and dissolved oxygen (DO) probes manufactured by Technalithics Inc. (Waco, Texas), were selected for each of the 27 saturated zone bundles. Each saturated zone bundle also included a stirring blade to mix water near the DO probe. A Figaro oxygen sensor was included in the vadose zone bundle. The monitoring wells were installed by direct push technique to minimize soil disruption and to ensure intimate contact between the 18 inch (46 cm) long screens and the soil. A data acquisition system, comprised of a CSI 21X data logger and four CSI AM416 multiplexers, was used to control the stirring blades and record signals from more than 70 in situ sensors. The instrumentation performed well during evaluation of IAS and IWA at the site. However, the SenSym pressure transducers were not adequately temperature compensated and will need to be replaced.
Evaluation of Hydrogeo‐chemical Conditions for Development of Nuclear Criticality in Low‐Level Waste Disposal Facilities
Authors: Toran Laura , Cohen‐Bradley Virginia
Published: February 2007

The under ground disposal of fissile isotope‐bearing wastes poses some unique issues. Specifically, radionuclides such as 235U disposed in low‐level waste facilities, if present in the correct concentration and geometry, can create a nuclear criticality event that releases radioactivity to ground water. This paper reports the results of a study of the potential for 235U to be transported by ground water within low‐level waste facilities and to concentrate to form a critical mass. Coupled hydrologic and geochemical modeling was used to investigate two possible mechanisms for concentrating mobile uranium: sorption on high capacity sites and precipitation in a reducing zone. The hydrogeochemical modeling showed that (1) it is difficult to mobilize uranium from sorption sites then re‐deposit it; (2) if uranium is already in solution it can accumulate in zones of high sorption, and (3) reducing zones can accumulate sufficient uranium in the presence of oxygenated ground water. Site‐specific disposal practices, such as the commingling of large quantities of depleted (nonfissile) uranium and the difficulty of bringing sufficient mass together in the correct geometry, limit the potential for criticality safety concerns. In order to determine appropriate disposal practices, hydrogeochemical modeling can be used to study the future mobility and accumulation of the waste.
Denitrification and Phosphate Removal in Experiments Using Al Stearate
Authors: Stoessell R.K. , Easley D.H. , Yamazaki G.P.
Published: February 2007

Hydrophobic Al monostearate was tested as a low‐solubility denitrification substrate for anaerobic bacteria and a source of aluminum for phosphate precipitation. Flow‐through laboratory columns at 25 ± 2°C were used with O2‐saturated solutions containing 1x, 2x, 8x, and 16x concentrations of 2.26 mg/L NO3‐N and 3.26 mg/L PO4‐P. Denitrification was exponential, approximating first‐order reaction kinetics with the rate constant being a function of the initial nitrate concentration. The half life in minutes can be approximated by 5.29 (mg/L NO3‐ N°)1/2 where NO3‐N° was the initial input nitrate concentration. The reaction times were significantly shorter than those required using Ca distearate as a carbon source and much shorter than those using cellulose (white pine shavings) as a carbon source. Al stearate has potential for use in a flow‐through container for denitrification of oxidized effluent from home sewage systems.

Aqueous phosphate removal with Al stearate depended upon dissolution of the Al stearate followed by precipitation of Al phosphate. Only 5% to 10% of the phosphate was removed from the solution. The amounts removed were similar to those obtained using bauxite grains as an aluminum source, following saturation of sorption sites with phosphate on bauxite. Aqueous phosphate removal with Ca stearate was insignificant, as the released calcium was apparently precipitated as calcite rather than as hydroxyapatite.
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

Pore 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

Simulations 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

A 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

Refractive 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

In 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

The 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

The 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

Experiences 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

Experimental 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

The 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

Geophysical 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

It 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

Soil 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

Geostatistical 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

Recent 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

Remediation 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

Advanced 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.
Direct‐Push Electrical Conductivity Logging for High‐Resolution Hydrostratigraphic Characterization
Authors: Schulmeister M.K. , Butler J.J. , Healey J.M. , Zheng L. , Wysocki D.A. , McCall G.W.
Published: February 2007

Fine‐scale hydrostratigraphic features often play a critical role in controlling ground water flow and contaminant transport. Unfortunately, many conventional drilling‐ and geophysics‐based approaches are rarely capable of describing these features at the level of detail needed for contaminant predictions and remediation designs. Previous work has shown that direct‐push electrical conductivity (EC) logging can provide information about site hydrostratigraphy at a scale of relevance for contaminant transport investigations in many unconsolidated settings. In this study, we evaluate the resolution and quality of that information at a well‐studied research site that is underlain by highly stratified alluvial sediments. Geologic and hydrologic data, conventional geophysical logs, and particle‐size analyses are used to demonstrate the capability of direct‐push EC logging for the delineation of fine‐scale hydrostratigraphic features in saturated unconsolidated formations. When variations in pore‐fluid chemistry are small, the electrical conductivity of saturated media is primarily a function of clay content, and hydrostratigraphic features can be described at a level of detail (<2.5 cm in thickness) that has not previously been possible in the absence of continuous cores. Series of direct‐push EC logs can be used to map the lateral continuity of layers with non‐negligible clay content and to develop important new insights into flow and transport at a site. However, in sand and gravel intervals with negligible clay, EC logging provides little information about hydrostratigraphic features. As with all electrical logging methods, some site‐specific information about the relative importance of fluid and sediment contributions to electrical conductivity is needed. Ongoing research is directed at developing direct‐push methods that allow EC logging, water sampling, and hydraulic testing to be done concurrently.
Attenuation of a Mixed Chromium and Chlorinated Etjeme Ground Wate Plume in Estuarine Influenced Glaciated Sediments
Authors: Hellerich Lucas A. , Poneiera Matthew A. , Nikolaidis Nikolaos P. , Smets Barth F. , Dobbs Gregory M.
Published: February 2007

The natural attenuation behavior of a ground water contaminant plume containing chromium and chlorinated ethenes in glaciated sediments was assessed using traditional and nontraditional methods. The mixed waste is transported through and attenuated within an estuarine influenced ground water aquifer of spatially varying redox character and organic carbon content. Contaminant fate and speciation were assessed as a function of geochemical conditions. Total, speciation‐based, and sequential chemical extraction analyses were performed to determine contaminant partitioning and the redox capacity of the aquifer. Chromium speciation and partitioning were correlated with the reductive capacity and redox conditions of the aquifer sediments spatially distributed within the aquifer. Reductive dechlorination and partitioning of chlorinated ethenes were correlated with the organic carbon content and redox conditions of the aquifer sediments. The data showed that sharp redox gradients existed within the aquifer. Active reduction and retardation of both chromium and chlorinated ethenes was exhibited. The aqueous hexavalent chromium concentrations decreased to near nondetect levels in the vicinity of the receptor, whereas degradation products of higher‐order chlorinated ethenes increased as a fraction of the total chlorinated ethene concentrations along the length of the plume. The potential for competition for reducing power under specific cases within the aquifer was suggested by the data, highlighting the need to include contaminant interactions in natural attenuation assessments.
The Technical Case for Eliminating the Use of the TPH Analysis in Assessing and Regulating Dissolved Petroleum Hydrocarbons in Ground Water
Authors: Zemo Dawn A. , Foote Gary R.
Published: February 2007

In many states, the total petroleum hydrocarbons (TPH) analysis based on gas chromatography‐flame ionization detection (GC‐FID) is still being used to assess and regulate ground water quality at petroleum release sites. The soluble fraction of fresh crude oil or fresh products that could potentially be dissolved into the ground water is limited to relatively few petroleum hydrocarbon constituents (primarily the C6 to C14 aromatics). Research by numerous investigators has shown that the reported TPH concentrations of ground water samples frequently do not represent dissolved petroleum hydrocarbons but rather represent nondissolved petroleum or polar nonhydrocarbon compounds. Nondissolved petroleum is frequently entrained within a sample when sampling ground water within affected soil, and polar nonhydrocarbons are present in ground water as a result of petroleum biodegradation or other factors. These constituents are being measured because the TPH analysis does not include steps to remove nondissolved petroleum or a silica gel cleanup to remove polars.

Many states have regulatory action levels for TPH in ground water that are in the 0.1 to 2 mg/L range. The technical basis for these action levels appears to be toxicity and/or organoleptic (taste and odor) properties of the dissolved petroleum hydrocarbons associated with fresh oil or fresh products. The presence of compounds measured as TPH that are not dissolved petroleum hydrocarbons has proven problematic for regulatory decision‐making because the comparison of concentration data to the regulatory criteria may not be correct. Because the TPH analysis does not reliably distinguish between dissolved petroleum hydrocarbons and other compounds, it should not be used to assess or regulate dissolved petroleum hydrocarbons, in ground water. We recommend that constituent‐specific analyses be used to assess and regulate ground water quality at petroleum hydrocarbon release sites. If TPH must be used due to regulatory requirements, samples should be cleaned up with silica gel to remove polars (and turbidity should be removed, if present) prior to analysis so that comparison to regulatory action levels that are based on properties of dissolved petroleum hydrocarbon constituents is technically appropriate.
Estimating Natural Attenuation Rate Constants Using a Fuzzy Framework
Authors: Uddameri Venkatesh
Published: February 2007

Fuzzy set theoretic approaches provide convenient tools to quantify subjective information and characterize the decision‐maker's preferences with minimal data. The estimation of natural attenuation and degradation rates, using the method of Buschek and Alcantar (1995), while pragmatic, is subject to significant imprecision due to mathematical simplifications and site complexities. In this paper, two fuzzy approaches, namely fuzzy arithmetic and fuzzy regression, are used to characterize the variability in the estimated degradation and attenuation rates. The variability in the input parameters can be characterized using membership functions that characterize the decision‐maker's perception of likely values. The choice of the membership function for critical inputs is seen to affect the variability in the estimated outputs. Similarly, the decision‐maker's belief related to the compatibility of the steady‐state model to represent the observed plume behavior at the site can also be quantified using a compatibility criterion. Sensitivity studies carried out using the fuzzy‐based estimation methodology are extremely useful to assess how differences in the decision‐makers’preferences will affect the estimated rate constants and associated variability. As such, the proposed methodology is of high value during negotiations related to monitored natural attenuation.