bluuebunny/crossref_metadata_2025 huggingface dataset:
Laboratory Study of Polymer Solutions Used for Mobility Control During In Situ NAPL Recovery
Authors: Martel K. E. , Martel R. , Lefebvre R. , Gélinas P. J.
Published: February 2007

The use of surfactant solutions for the in situ recovery of residual NAPL in aquifers is increasingly considered as a viable remediation technique. The injection of a few pore volumes of high concentration surfactant solutions can mobilize most of the residual NAPL contacted by the solutions. However, the washing solutions’physico‐chemical properties (low density and high viscosity), combined with the natural porous media heterogeneity, can prevent a good sweep of the entire contaminated volume. From the petroleum industry, it is well‐known that polymer solutions can be injected following a surfactant solution slug to act as a mobility buffer and increase the overall sweep efficiency. The objective of our laboratory study is first to select and characterize polymers that would be suitable for aquifer restoration. Our experiments showed that among several polymers, xanthan gum solution rheology was made in order to predict shear rates, xanthan gum concentrations, salinity, and temperature effects on solution viscosity. The second set of experiments were made with a sand box which was designed to reproduce a simple heterogeneous media consisting of layers of sand with different permeability. These tests illustrate the xanthan gum solution's ability to increase surfactant solution's sweep efficiency and limit viscous fingering. The tests established that: (1) the injection of xanthan solution behind a surfactant solution slug decreases fluid velocity in high permeability layers and increases it in low‐permeability ones, thus increasing the sweep efficiency (2) xanthan solutions eliminate viscous fingering at the polymer/surfactant solution front; (3) a xanthan solution preflush is desirable to limit surfactant solution mobility and prevent surfactant adsorption on solids; and (4) depending on site heterogeneity injection strategies should be applied to limit overriding by low‐density surfactant solution.
Comparison of Fiberglass and Other Polymeric Well Casings, Part III. Sorption and Leaching of Trace‐Level Metals
Authors: Ranney Thomas A. , Parker Louise V.
Published: February 2007

This series of experiments was initiated to determine the overall suitability of three alternative polymeric well casing materials (fluorinated ethylene propylene [FEP], fiberglass‐reinforced epoxy [FRE], and fiberglass‐reinforced plastic [FRP]) for use in ground water monitoring wells and to compare these materials with polyvinyl chloride (PVC) and polytetrafluoroethylene (PTFE) well casings. This paper focuses on sorption and leaching of metals.

Generally, the fiberglass materials leached more metal contaminants than PVC, FEP, and PTFE. However, with one exception (Pb leaching from FRP), leached concentrations were below maximum allowable limits set by the U.S. Environmental Protection Agency (EPA) for drinking water. With respect to sorption, none of the polymers sorbed the anions tested, but all of them sorbed one or more of the cations tested. FEP and PTFE were much less sorptive than the other materials.
A Field and Laboratory Investigation of Air Fingering During Air Sparging
Authors: Clayton Wilson S.
Published: February 2007

Since the rejection of the bubble flow conceptual model for in situ air sparging, most practitioners have adopted the conceptual model of air channeling, which generally implies the development of widely spaced, discreet air channels that bypass large regions of the subsurface. While air channeling clearly develops in response to stratigraphic heterogeneity, the universality of widely spaced air channels in homogeneous media is not supported by available evidence. Air channeling results in low bulk air saturation due to bypassing, and field and laboratory measurements of air saturations and previously published studies were used to evaluate if air channeling is realistic. The results indicated that homogeneous coarse sands are prone to the development of air channeling, and that homogeneous fine sands show higher air saturations and are not prone to air channeling. Breakthrough air saturations, which represent the minimum air saturations, that will conduct air flow, of approximately 0.02 to 0.04 were observed in coarse sands. In contrast, breakthrough air saturations of 0.10 to 0.13 were observed in fine sands and medium sands. The transition between these behaviors falls at about 15 to 20 cm water air entry pressure. These result indicate that, at both the field and laboratory scale, coarse sands are more prone to air channeling and bypassing than fine sands. Additionally, the larger air gradients and capillary pressures in fine sands result in a less buoyancy‐dominated flow pattern, with a larger lateral extent of air flow.
Beyond BTEX
Authors: Barcelona Michael J.
Published: February 2007

“It's definitely not a time to become complacent with our current understanding of contaminant fate and transport processes.”

“In the coming year, we are going to solicit short one‐ to two‐page field Innovation Notes in GWMR.”
Monitoring of Unregulated Contaminants in Public Water Systems
Authors: Job Charles
Published: February 2007

“This revised program would have significant monitoring burden reduction for ground water supplied systems as compared to the existing program.”

“Note that the systems being monitored may total up to 3600, less than one‐eighth the number under the existing program.”
A Rapid Drawdown Event Related to Quarry Operations in a Dolomite Aquifer
Authors: Onsen John J , Fassbender Wayne P. , Jurcek Patrick , Barreto Laura L. , Boyer Larry F.
Published: February 2007

Two active quarries are mining stone from the Silurian dolomite aquifer in Waukesha County in southeastern Wisconsin. The village in which the quarries are located uses local zoning to control the depth of mining and to institute a long‐term water level monitoring program and well guarantee/one with the quarry owners. Water levels dropped as much as 40 feet in at least 24 residential wells surrounding the quarries over a period of a few hours to days. The rapid decline in head was caused by a single boring drilled lo a depth of 75 feel he low the floor of one quarry. The borehole penetrated a localized fracture zone under confined artesian head. Water levels recovered to previous static levels within nine days after grouting the borehole. The rapid drawdown event demonstrates the potential impact of mining in fractured aquifers. The apparent complete recovery of the aquifer demonstrates that quick response can sometimes restore an aquifer. However, the potential for blasting into a similar zone illustrates the need for a well‐thought‐out aquifer monitoring program and emergency response plan. The experience of the village is a good example of managing conflicting uses of a finite resource and collecting baseline data needed to make informed decisions.
Design Screening Tools for Passive Funnel and Gate Systems
Authors: Sedivy Robert A. , Shafer John M. , Bilbrey Lacrecia C.
Published: February 2007

The funnel and gate remediation concept (Star and Cherry 1993) represents a promising, yet relatively under‐developed, technology for the passive control and in situ remediation of contaminated ground water. Effective design and implementation of such a system may, however, prove difficult under conditions of large or unpredictable variations in contaminant migration or ground water flow.

Numerical modeling of two‐dimensional ground water flow has been used to predict the hydraulic performance of passive, straight, or winged funnel and gate configurations over a range of hydrogeologic and ambient ground water flow conditions. The results of these analyses were used to construct generic correlation diagrams relating upstream capture zone or gale through put to the barrier, gale, and aquifer characteristics. These diagrams serve as useful screening tools to (1) quantitatively estimate the capture zone of pre‐determined funnel and gale configurations, or (2) develop preliminary funnel and gale designs that will yield a desired capture zone, independent of aquifer characteristics.
Evidence for MTBE in Heating Oil
Authors: Robbins Gary A. , Henebry Brent J. , Schmitt Barbara M. , Bartolomeo Frank B. , Green Aaron , Zack Peter
Published: February 2007

“Contamination of heating oil with MTBE could result in increasing the environmental impact of subsurface heating oil releases.”
Compatibility of Bentonite and DNAPLs
Authors: McCaulou Douglas R. , Huling Scott G.
Published: February 2007

The compatibility of dense nonaqueous phase liquids (DNAPLs). triehloroelhylene (TCE), methylene chloride (MC), and creosote with commercially available sodium bentonite pellets was evaluated using stainless steel, double ring, falling head permeameters. The hydraulic conductivity (K) of the bentonite clay was measured under three experimental conditions: (1) water soluble constituents of the DNAPLs were used to hydrate and permeate the bentonite: (2) bentonite pellets were submersed in DNAPL prior to hydration and permeation with water: and (3) DNAPLs were pooled on water‐hydrated bentonite. Further, the effect of hydraulic head (2.5. 145, and 710 cm) on water‐hydrated bentonite permeated with TCE and the effects of TCE exposure time to mixtures of bentonite grout and sand were measured. Solubility concentrations of DNAPL constituents did not effect the hydraulic conductivity of the bentonite pellets relative to baseline (water only) measurements; a competent hydraulic barrier was formed (K < 5 × 10−9 cm/s). Bentonite pellets submersed in DNAPLs retained their rigid shape, did not swell, and did not perform as a hydraulic barrier. However, when the DNAPL was removed and replaced with water, the DNAPL‐wetted pellets imbibed water to swell and form an adequate hydraulic barrier (K < 6 × 10−9 cm/s). Competent hydraulic barriers constructed with bentonite pellets and hydrated with water were subsequently permeated with TCE, MC, or creosote DNAPLs developing desiccation cracks up to 5 mm wide. The intrinsic permeability of water‐hydrated bentonite was 46 to 2640 limes greater to DNAPLs relative to water, indicating that the desiccation cracks predominantly facilitated preferential DNAPL transport. The propagation rate of cracks was positively correlated to the hydraulic gradient, bin the formation of cracks is chemically dependent on the contact lime of DNAPL. Silica sand is expansively inert, yet 95, 90, 83, 75, and 50% (wt sand/wt bentonite) mixtures with bentonite grout were insufficient to prevent desiccation cracks and hydraulic failure. The incompatibility between DNAPLs and bentonite observed in this study is important due id the numerous exploratory borings in DNAPL/ones, the increasing dependency on hydraulic containment as a remedial alternative, and the fact that such remedial systems are often designed to be functional for many years.
Naturally Occurring Arsenic in Sandstone Aquifer Water Supply Wells of Northeastern Wisconsin
Authors: Burkel Rebecca S. , Stoll Richard C.
Published: February 2007

The U.S. Environmental Protection Agency (EPA) maximum contaminant level (MCL) of 50 μg/L for arsenic was exceeded in 86 of 2125 water supply wells sampled over a broad geographic range in pails of Drown. Outagamie and Winnebago Counties, Wisconsin. The hydrologic and geochemical properties of the area were examined and the source of arsenic was determined to be natural, Ground water collected from two geologic formations, the St. Peter Sandstone and the overlying Platteville/Galena Dolomite, was found to be the principal source of the elevated arsenic concentrations. These two Formations supply a large portion of eastern Wisconsin private wells with their drinking water.

Three wells were found within Outagamie County to have an unusually low pH. Results suggest that the cause of the low pH in these wells is of natural origin induced by the oxidation of iron sulfide minerals. In this reaction iron sulfide minerals are oxidized. forming sulfuric acid causing a low pH and a high concentration of various metals to leach from native rock formations into the water supply.

Based on the data gathered from this study, an arsenic advisory area was designated for both Outagamie and Winnebago Counties. Guidelines were developed for well drillers and owners constructing new wells within the advisory area to reduce the likelihood of arsenic presence in the water supply. Fifteen wells containing arsenic exceeding the MCL were successfully reconstructed or new wells were constructed based on the guidelines developed. These constructions substantially reduced arsenic levels in the well water supplies.
Europeans Test Pesticide Models
Authors: Cohen Stuart
Published: February 2007

This column focuses on recent work in Europe. The intent is to present to American readers relevant studies they would not normally see. Much of the following was presented at the 9th International Congress of Pesticide Chemistry last summer in London. The congress was jointly sponsored by the International Union of Pure & Applied Chemistry and the Royal Society of Chemistry.
Statistical Comparison of Leachate from Hazardous, Codisposal, and Municipal Solid Waste Landfills
Authors: Gibbons Robert D. , Dolan David G. , May Helen , O'Leary Kevin , O'Hara Richard
Published: February 2007

There has been considerable debate regarding the chemical characterization of landfill leachate in general and the comparison of various types of landfill leachate (e.g., hazardous, codisposal, and municipal) in particular. For example, the preamble to the U.S. EPA Subtitle D regulation (40 CFR Parts 257 and 258) suggests that there are no significant differences between the number and concentration of toxic constituents in hazardous versus municipal solid waste landfill leachate. The purpose of this paper is to statistically test this hypothesis in a large leachate database comprising 1490 leachate samples from 283 sample points (i.e., monitoring location such as a leachate sump) in 93 landfill waste cells (i.e., a section of a facility that took a specific waste slream or collection of similar waste streams) from 48 sites with municipal, codisposal, or hazardous waste site histories. Results of the analysis reveal clear differention between landfill leachate types, both in terms of constituents detected and their concentrations. The result of the analysis is a classification function that can estimate the probability that new leachate or ground water sample was produced by the disposal of municipal, codisposal, or hazardous waste. This type of computation is illustrated, and applications of the model to Superfund cost‐allocation problems are discussed.
Nitrogen Removal from Landfill Leachate Using an Infiltration Bed Coupled with a Denitrification Barrier
Authors: Robertson W.D. , Anderson M.R.
Published: February 2007

Treatment of nitrogen in landfill leachate has received considerable attention recently because of the relatively low levels at which some nitrogen species (i.e., NH3) can be toxic to aquatic life forms. This study reports on the results of a three‐year, pilot‐scale field trial demonstrating the use of infiltration bed and nitrate barrier technology to achieve nitrogen removal in landfill leachate. The infiltration bed comprises an unsaturated sand layer overlying a saturated layer of waste cellulose solids (sawdust), which acts as a carbon source for heterotrophic denitrification. When loaded at a rate of 1 to 3 cm/day, the infiltration bed was successful at lowering leachate inorganic nitrogen (NH4++ NO3‐) levels averaging 24.8 mg/L N by 89%, including 96% in the third year of operation. The surface water discharge criteria for un‐ionized ammonia (NH3) were met on all occasions in the treated leachate during the second and third years of operation. Nitrogen attenuation is presumed to occur by a two‐step process in which leachate NH4+ is first oxidized to NO3‐ in the unsaturated sand layer and then is converted to nitrogen gas (N2) by denitrification occurring in the underlying sawdust layer. Mass balance calculations suggest that the sawdust layer has sufficient carbon to allow denitrification to proceed for long periods (1.0 to 30 years) without replenishment. Because this technology is simple to construct and is relatively maintenance free, it should be attractive for use at smaller landfills where the installation of conventional treatment plants may not be feasible.
Decontaminating Materials Used in Ground Water Sampling Devices: Organic Contaminants
Authors: Parker Louise V. , Ranney Thomas A.
Published: February 2007

In these studies, the efficiency of various decontamination protocols was tested on small pieces of materials commonly used in ground water sampling devices. Three materials, which ranged in ability to sorb organic solutes, were tested: stainless steel (SS), rigid polyvinyl chloride (PVC), and polytetrafluoroethylene (PTFE). The test pieces were exposed to two aqueous test solutions: One contained three volatile organic compounds (VOCs) and one nitroaromatic compound, and the other contained four pesticides. Also, three types of polymeric tubing were exposed to pesticide solutions. Generally, the contact times were 10 minutes and 24 hours for sorption and desorption.

The contaminants were removed from the nonpermeable SS and the less‐sorptive rigid PVC test pieces simply by washing with a hot detergent solution and rinsing with hot water. Additional treatment was required for the PTFE test pieces exposed to the VOCs and for the low‐density polyethylene (LDPE) tubing exposed to the pesticide test solution. Solvent rinsing did not improve removal of the three VOCs from the PTFE and only marginally improved removal of the residual pesticides from the LDPE. However, a hot water and detergent wash and rinse followed by oven drying at approximately 105°C was effective for removing the VOCs from the PTFE and substantially reduced pesticide contamination from the LDPE.
Ground Water Sampling Bias Observed in Shallow, Conventional Wells
Authors: Hutchins Stephen R. , Acree Steven D.
Published: February 2007

A previous field demonstration project on nitrate‐based bioremediation of a fuel‐contaminated aquifer used short‐screened clustered well points in addition to shallow (10 foot), conventional monitoring wells to monitor the progress of remediation during surface application of recharge. These well systems were placed in the center and at one edge of each of two treatment cells. One cell received recharge amended with nitrate (nitrate cell), and the other received unamended recharge (control cell). Data from the clustered well points were averaged to provide a mean estimate for comparison with the associated conventional monitoring well.

Conservative tracer profiles were similar for each of the four systems, with better fits obtained for well systems located at the edge of the treatment cells. However, aromatic hydrocarbon and electron acceptor profiles varied greatly for the two center well systems, with the conventional monitoring well data suggesting that remediation was proceeding at a much more rapid rate than indicated by the cluster well points. Later tests with an electromagnetic borehole flowmeter demonstrated a significant vertical flow through the well‐bore of the conventional monitoring well under simulated operating conditions. This created an artifact during sampling, thought to arise from preferential flow of recharge water from the water table to deeper portions of the contaminated zone resulting in several effects, including an actual decreased residence time of water sampled by the conventional well. These data provide additional evidence that conventional monitoring wells may be inadequate for monitoring remediation in the presence of significant vertical hydraulic gradients, even for fairly shallow homogeneous aquifers.
Cyclodextrin‐Enhanced Solubilization of Organic Contaminants with Implications for Aquifer Remediation
Authors: McCray John E. , Boving Thomas B. , Brusseau Mark L.
Published: February 2007

Reagents that enhance the aqueous solubility of non‐aqueous phase organic liquid (NAPL) contaminants are under investigation for use in enhanced subsurface remediation technologies. Cyclodextrin, a glucose‐based molecule, is such a reagent. In this paper, laboratory experiments and numerical model simulations are used to evaluate and understand the potential remediation performance of cyclodextrin. Physical properties of cyclodextrin solutions such as density, viscosity, and NAPL‐aqueous inter‐facial tension are measured. Our analysis indicates that no serious obstacles exist related to fluid properties that would prevent the use of cyclodextrin solutions for subsurface NAPL remediation. Cyclodextrin‐enhanced solubilization for a large suite of typical ground water contaminants is measured in the laboratory, and the results are related to the physicochemical properties of the organic compounds. The most‐hydrophobic contaminants experience a larger relative solubility enhancement than the less‐hydrophobic contaminants but have lower aqueous‐phase apparent solubilities. Numerical model simulations of enhanced‐solubilization flushing of NAPL‐contaminated soil demonstrate that the more‐hydrophilic compounds exhibit the greatest mass‐removal rates due to their greater apparent solubilities, and thus are initially more effectively removed from soil by enhanced‐solubilization‐flushing reagents. However, the relatively more hydrophobic contaminants exhibit a greater improvement in contaminant mass‐removal (compared with water flushing) than that exhibited for the relatively hydrophilic contaminants.
Remedial Options for Creosote‐ Contaminated Sites
Authors: Wu Wei‐Jr , Delshad Mojdeh , Oolman Timothy , Pope Gary A.
Published: February 2007

Free‐phase DNAPL recovery operations are becoming increasingly prevalent at creosote‐contaminated aquifer sites. This paper illustrates the potential of both classical and innovative recovery methods. The UTCHEM multiphase flow and transport numerical simulator was used to predict the migration of creosote DNAPL during a hypothetical spill event, during a long‐term redistribution after the spill, and for a variety of subsequent free‐phase DNAPL recovery operations. The physical parameters used for the DNAPL and the aquifer in the model are estimates for a specific creosote DNAPL site. Other simulations were also conducted using physical parameters that are typical of a trichloroethene (TCE) DNAPL. Dramatic differences in DNAPL migration were observed between these simulations.
Using the Stabilization Plateau to Estimate Optimum Well Purge Volume
Authors: Hurt Burhara F. , Tomlinson Rodger B. , Chaseling Janet
Published: February 2007

This study concerns the problem of pump position in landfill monitoring wells and the correct time to stop purging and start sampling. Literature purge volume determination methods fail to use sufficient analyte values for comprehensive study of the stabilization plateau. From field studies it is recommended that prior to commencement of a sampling program a purge study be undertaken to determine pump position and optimum purge volume by conducting (1) a preliminary vertical electrical conductivity (EC) profile: (2) vertical profiling of formation water EC values by low‐flow pumping at 0.5 m vertical intervals‐while also noting EC vertical profile values to assure minimal effect on the water column water quality; and (3) a low‐flow, purge EC stabilization test with the pump positioned at highest formation water EC values. Sufficient EC values are needed to fulfill Conover's (1980) nonparametric tolerance interval sample size criteria, and to graphically delineate the stabilization plateau. This information will allow you to choose an optimum purge volume that allows a margin for error.
A Method for Predicting Chloride Concentrations in Leachate at Natural Attenuation Landfills in the Precambrian Shield Regions of Ontario, Canada
Authors: Gehrels Jim , Puumala Mark
Published: February 2007

Natural attenuation landfill sites continue to be the preferred method of domestic waste disposal in the Precambrian Shield regions of Ontario due to economic factors. The main challenge in siting these landfills is ensuring that there will be no adverse impact on off‐site water resources. Impact risk assessments are generally based on estimated volumes and strengths of chloride in the leachate. While volumes can be estimated using simple water balances, peak chloride concentration predictions are based on judgment and are quite variable. Since design chloride strengths dictate the size of the required attenuation zone, overestimating concentrations will typically make it impossible to find a suitable site, while underestimating concentrations increases the potential for adverse off‐site impacts occurring.

Hydrogeological data from active and closed landfills in the Precambrian Shield region were collected to help develop a reliable method of predicting peak chloride concentrations in leachate. This study focused on 21 sites located on relatively permeable sandy soils since landfills underlain by low permeability clayey soils retain leachate similar to lined facilities.

Linear regression analyses were conducted to determine if source chloride concentrations at the “sand” sites are significantly influenced by waste thickness, fill area, waste volume, waste deposition rate, hydraulic conductivity, upgradient flow length, depth to the water table, and moisture surplus.

A strong relationship (R = 0.957) was found to exist between source chloride concentrations and waste volume. This empirical volume versus chloride regression equation can be used as the basis for establishing design chloride concentrations at new natural attenuation landfills developed over sandy soils in the Precambrian Shield regions of Ontario. An alternative risk assessment approach is required for sites developed over clay soils.
Internet Listservices as a Valuable Resource for Environmental Professionals in Soil and Ground Water Remediation
Authors: Guerin Turlough F. , Schaffner I. Richard
Published: February 2007

In 1957, four computers across the United States were linked to form the first version of what we now know as the Internet. The Internet has grown beyond what anyone working in the U.S. Department of Defense Advanced Research Projects Agency (DARPA) more than 40 years ago could have imagined. Yet despite the phenomenal growth of Internet users, and access to information in all fields of endeavor, finding genuinely useful and helpful resources is still a challenge. This article distils information on the most useful Internet listservers for environmental professionals working the site remediation.
A Novel View of Wellbore Flow and Partial Mixing: Digital Image Analyses
Authors: Martin‐Hayden James M. , Wolfe Natalie
Published: February 2007

Although theories of thoroughly mixed and unmixed wellbore flow have been developed, recent studies suggest that ground water data variability and bias can result from various types of partial mixing. In this study, digital images of dye distributions within a vertical cross‐sectional model of a screened monitoring well allowed mixing processes to be recorded and characterized. Given the conditions represented by this study, two scales of well water mixing are evident: small‐scale mixing adjacent to the well screen and larger‐scale mixing with the water from the casing above the screen section. Evidence suggested that the small‐scale mixing initially caused concentrations at the pump to change more rapidly than the aforementioned theories predicted and to stabilize at biased concentrations. Larger‐scale mixing of casing water and screen section water resulted from either turbulent/viscous entrainment or, more likely, a slightly elevated casing water density. If this mixing occurs due to wellhead cooling where the casing water is significantly chemically altered, bias would result. These results suggest that concentration variability and bias before and during pumping are, in part, controlled by the characteristics and prevalence of small and large scale partial mixing throughout the wellbore in the presence of wellbore‐concentration heterogeneities. The bias and variability could be on the order of those concentration heterogeneities where concentration heterogeneities and partial mixing are present. Bias and variability of the type observed under these experimental conditions call for investigations into conditions that lead to partial mixing in the field and into the possible magnitude of the influences of these processes.
Can Contaminant Transport Models Predict Breakthrough?
Authors: Peng Wei‐Shyuan “Stone” , Hampton Duane R. , Konikow Leonard F. , Kambham Kiran , Benegar Jeffrey J.
Published: February 2007

A solute breakthrough curve measured during a two‐well tracer test was successfully predicted in 1986 using specialized contaminant transport models. Water was injected into a confined, unconsolidated sand aquifer and pumped out 125 feet (38.3 m) away at the same steady rate. The injected water was spiked with bromide for over three days; the outflow concentration was monitored for a month. Based on previous tests, the horizontal hydraulic conductivity of the thick aquifer varied by a factor of seven among 12 layers. Assuming stratified flow with small dispersivities, two research groups accurately predicted breakthrough with three‐dimensional (12‐layer) models using curvilinear elements following the arc‐shaped flowlines in this test.

Can contaminant transport models commonly used in industry, that use rectangular blocks, also reproduce this breakthrough curve? The two‐well test was simulated with four MODFLOW‐based models, MT3D (FD and HMOC options), MODFLOWT, MOC3D, and MODFLOW‐SURFACT.

Using the same 12 layers and small dispersivity used in the successful 1986 simulations, these models fit almost as accurately as the models using curvilinear blocks. Subtle variations in the curves illustrate differences among the codes. Sensitivities of the results to number and size of grid blocks, number of layers, boundary conditions, and values of dispersivity and porosity are briefly presented. The fit between calculated and measured breakthrough curves degenerated as the number of layers and/or grid blocks decreased, reflecting a loss of model predictive power as the level of characterization lessened. Therefore, the breakthrough curve for most field sites can be predicted only qualitatively due to limited characterization of the hydrogeology and contaminant source strength.
Cyclodextrin‐Enhanced Vertical Flushing of a Trichloroethene Contaminated Aquifer
Authors: Blanford W.J. , Barackrnan M.L. , Boing T.B. , Klingel E.J. , Johnson G.R. , Brusseau M.L.
Published: February 2007

Pilot‐scale testing of an innovative ground water remediation technology was conducted in a source zone of a trichloroethene‐contaminated Superfund site in Tucson, Arizona. The technology is designed to enhance the removal of low‐solubility organic contaminants from heterogeneous sedimentary aquifers by using a dual‐screened vertical circulation well to inject and extract solutions containing a complexing sugar (hydroxypropyl‐beta‐cyclodextrin (HPCD]). Prior to initiating the pilot test, tracer tests were conducted to determine hydraulic characteristics of the vertical flow field and to evaluate trichloroethene‐elution behavior during water flushing. The pilot test involved injecting approximately 4 m3 of a 20% HPCD solution into the upper screened interval of the well and extracting from the lower screened interval. The results of the pilot test indicate that the cyclodextrin solution increased the rate of trichloroethene removal from the aquifer. The concentrations of trichloroethene in the ground water extracted from the lower screened interval of the well increased by a factor of three (∼750 μg/L) in the presence of the cyclodextrin pulse, compared to concentrations obtained during previous water flushing (∼250 μg/L). Furthermore, the concentration of trichloroethene in water collected from the circulation well under static conditions was reduced to 6% of the levels measured prior to the test.
DNAPL to LNAPL Transitions During Horizontal Cosolvent Flooding
Authors: Roeder Eberhard , Falta Ronald W. , Lee Cindy M. , Coates John T.
Published: February 2007

Cosolvent flooding is a technology with the potential to remove nonaqueous phase liquid (NAPL) sources from the subsurface. It can be used to initiate separate phase mobilization, which allows removal of NAPL within very few pore volumes. Mobilization may result in a sinking DNAPL bank during horizontal flooding of NAPLs denser than water. Reversal of phase density difference between aqueous and DNAPL phases could potentially avoid this downward migration of mobilized DNAPLs. We achieved phase density difference reversal and made DNAPLs float using two components in the cosolvent flooding solution. A low‐density cosolvent partitions preferentially into the DNAPL and swells it, which causes a reduction in density of the DNAPL and reversal of the density difference between the NAPL and aqueous phases. A highdensity additive that remains in the aqueous phase allows the cosolvent flooding solution overall to have a density greater than that of water and permits control of the flooding instability. This study focused on tert‐butanol as the swelling cosolvent and tetrachloroethylene as the contaminant. In batch tests with sucrose and glycerol as dense additives, phase density difference reversal occurred. To investigate the applicability of phase density difference reversal as a remediation technology, horizontal column and sandbox experiments were performed. These experiments demonstrated the occurrence of phase density difference reversal and effective remediation in horizontal cosolvent floods.
The Effect of Air Bubbles and Headspace on the Aqueous Concentrations of Volatile Organic Compounds in Sampling Vials
Authors: Nadim Farhad , Liu Shili , Hoag George E.
Published: February 2007

The presence of headspace and air bubbles in volatile organic analysis sampling vials lowers the actual aqueous concentration of these compounds due to the partitioning of solutes into the gaseous phase. This could make the sample invalid for analysis.

In this work, the effects of air bubbles and headspace on the aqueous concentration of 60 volatile organic compounds listed in U.S.Environmental Protection Agency (U.S. EPA) Method 8260 were evaluated experimentally and theoretically. The results showed that for air to water ratios of 1 to 20 and less, there was no significant effect on the aqueous concentrations of target organic solutes in the sampling vials. When the air to water ratio was increased to 1 to 10, the recovery rates of four organic compounds were lower than the control. Laboratory experiments on sampling vials showed that the presence of air bubbles or headspace with the volumetric air to water ratios of 1 to 20 and less do not produce any significant effect on the original concentrations for most targeted volatile organic compounds.

The experimental results also indicated that in 40 mL sampling vials with headspace range of 2 to 8 mL, the recovery rates of most volatile organic compounds with high values of Henry's law constant (> 0.01 Atm m3/mol. at 25°C) were larger than the calculated rates.
Biodegradation of Creosote Compounds: Comparison of Experiments at Different Scales
Authors: Broholm Kim , Arvin Erik
Published: February 2007

This paper compares the results of biodegradation experiments with creosote compounds performed at different scales. The experiments include field observations, field experiments, large‐scale intact laboratory column experiments, model fracture experiments, and batch experiments. Most of the experiments were conducted with till or ground water from the field site at Ringe on the island of Funen. Although the experiments were conducted on different scales, they revealed that some phenomena—e.g., an extensive biodegradation potential of several of the creosote compounds, the inhibitory influence of the pyrroles on the biodegradation of benzene, and the biodegradation of benzothiophene occurs only in the presence of a primary substrate. The experiments show that some biodegradation processes of organic compounds may be common to different microorganisms.
Long‐Term Ground Water Quality Impacts from the Use of Hexazinone for the Commercial Production of Lowbush Blueberries
Authors: Keizer Jonathan P. , MacQuarrie Kerry T.B. , Milburn Paul H. , McCully Kevin V. , King Russ R. , Embleton E. Jean
Published: February 2007

Lowbush blueberries, native to eastern Canada and Maine, are an important economic crop in these areas. Herbicides containing the active ingredient hexazinone are commonly applied to blueberry fields, and there is a high frequency of detection of relatively low concentrations of hexazinone in domestic wells located close to areas of lowbush blueberry production. The objective of this study was to determine the long‐term impacts from hexazinone‐based herbicide use on ground water quality in the immediate growing areas.

Physical and chemical hydrogeologic data were collected for an outwash sand and gravel aquifer in southwestern New Brunswick, Canada. The majority of the land overlying the aquifer is devoted to lowbush blueberry production. Twenty‐one nested monitoring wells were sampled for hexazinone and hexazinone metabolites over a four‐year period. Hexazinone was consistently detected at values of 1 to 8 parts per billion (ppb) in all but two of these wells, one that is upgradient of herbicide applications, and one that is downgradient with anoxic conditions. Hexazinone metabolites B and A1 were also detected in all but two of the 21 wells at values ranging from 0.5 to 2.5 ppb. The hexazinone and metabolite data suggest both aerobic and anaerobic degradation of hexazinone. Complete degradation of hexazinone appears to occur only in the one downgradient well exhibiting anoxic ground water conditions. Concentrations of hexazinone and its metabolites in the ground water were essentially constant over the four‐year period.
Bacterial Production Stimulated Across the Zone of Influence of a Ground Water Circulation Well in a BTEX‐Contaminated Aquifer
Authors: Montgomery Michael T. , Spargo Barry J. , Mueller James G. , Coffin Richard B. , Smith David C. , Boyd Thomas J.
Published: February 2007

Benzene, toluene, ethylbenzene, and xylene (BTEX) hydrocarbons are typically the most abundant carbon source for bacteria in gasoline‐contaminated ground water. In situ bioremediation strategies often involve stimulating bacterial heterotrophic production in an attempt to increase carbon demand of the assemblage. This may, in turn, stimulate biodegradation of contaminant hydrocarbons. In this study, ground water circulation wells (GCWs) were used as an in situ treatment for a fuel‐contaminated aquifer to stimulate bacterial production, purportedly by increasing oxygen transfer to the subsurface, circulating limiting nutrients, enhancing bioavailability of hydrocarbons, or by removing metabolically inhibitory volatile organics. Bacterial production, as measured by rates of bacterial protein synthesis, was stimulated across the zone of influence (ZOI) of a series of GCWs. Productivity increased from ∼102 to >105 ng C/L hour across the ZOI, suggesting that treatment stimulated overall biodegradation of carbon sources present in the ground water. However, even if BTEX carbon met all bacterial carbon demand, biodegradation would account for <4.3% of the total estimated BTEX removed from the ground water. Although bacterial productivity measurements alone cannot prove the effectiveness of in situ bioremediation, they can estimate the maximum amount of contaminant that may be biodegraded by a treatment system.
Used Motor Oil as a Source of MTBE, TAME, and BTEX to Ground Water
Authors: Baker Ronald J. , Best Eric W. , Baehr Arthur L
Published: February 2007

Methyl tert‐butyl ether (MTBE), the widely used gasoline oxygenate, has been identified as a common ground water contaminant, and BTEX compounds (benzene, toluene, ethylbenzene, and xylenes) have long been associated with gasoline spills. Because not all instances of ground water contamination by MTBE and BTEX can be attributed to spills or leaking storage tanks, other potential sources need to be considered. In this study, used motor oil was investigated as a potential source of these contaminants. MTBE in oil was measured directly by methanol extraction and gas chromatography using a flame ionization detector (GC/FID). Water was equilibrated with oil samples and analyzed for MTBE, BTEX, and the oxygenate tert‐amyl methyl ether (TAME) by purge‐ and‐trap concentration followed by GC/FID analysis. Raoult's law was used to calculate oil‐phase concentrations of MTBE, BTEX, and TAME from aqueous‐phase concentrations. MTBE, TAME, and BTEX were not detected in any of five new motor oil samples, whereas these compounds were found at significant concentrations in all six samples of the used motor oil tested for MTBE and all four samples tested for TAME and BTEX. MTBE concentrations in used motor oil were on the order of 100 mg/L. TAME concentrations ranged from 2.2 to 87 mg/L. Concentrations of benzene were 29 to 66 mg/L, but those of other BTEX compounds were higher, typically 500 to 2000 mg/L.
A Simple Model of Soil‐Gas Concentrations Sparged into an Unlined Unsaturated Zone
Authors: Ostendorf David W. , Hinlein Erich S. , Lutenegger Alan J. , Tehrany Pierre S.
Published: February 2007

We derive an analytical model of soil‐gas contamination sparged into an imlined unsaturated zone. A nonaqueous phase liquid (NAPL) source lies in the capillary fringe, with an exponential sparge constant within the radius of influence and a constant ambient evaporation rate beyond. Advection, diffusion, and dispersion govern the conservative soil‐gas response, expressed as a quasi‐steady series solution with radial Bessel and hyperbolic vertical dependence. Simulations suggest that sparged contamination initially spreads beyond the radius of influence down a negative gradient. This gradient eventually reverses, leading to a subsequent influx of ambient contamination. Soil‐gas concentrations accordingly reflect slowly varying source conditions as well as slowly varying diffusive transport through the radius of influence. The two time scales are independent: One depends on NAPL, airflow, and capillary fringe characteristics, the other on soil moisture, gaseous diffusivity, and unsaturated zone thickness. The influx of ambient contamination generates an asymptotic soil‐gas concentration much less than the initial source concentration. The simple model is applied to a pilot‐scale sparging study at Plattsburgh Air Force Base in upstate New York, with physically plausible results.
An Environmentally Friendly Decontamination Protocol for Ground Water Sampling Devices
Authors: Parker Louise V. , Ranney Thomas A.
Published: February 2007

Several detergent‐washing/air‐drying decontamination protocols were tested to determine their ability to remove residual contamination from two types of ground water sampling devices. We tested a relatively simply constructed device, a bailer, and a much more complex, and theoretically more difficult to decontaminate, bladder pump. The devices were decontaminated after sampling ground water that was contaminated with organics that varied in their hydrophobic nature and propensity to be sorbed by the materials in the devices. These studies showed that a hot‐detergent wash, hot‐water rinse, and hot‐air drying protocol was effective.
Laboratory Comparison of Polyethylene and Dialysis Membrane Diffusion Samplers
Authors: Ehlke Theodore A. , Imbrigiotta Thomas E. , Dale Jeffrey M.
Published: February 2007

The ability of diffusion samplers constructed from regenerated cellulose dialysis membrane and low density, lay flat polyethylene tubing to collect volatile organic compounds and inorganic ions was compared in a laboratory study. Concentrations of vinyl chloride, cis‐1, 2‐dichloroethene, bromochloromethane, trichloroethene, bromodichloromethane, and tetrachloroethene collected by both types of diffusion samplers reached equilibrium with the concentrations of these compounds in test solution within three days. Concentrations of bromide and iron collected by the dialysis membrane diffusion samplers reached equilibrium with the concentrations of these compounds in a test solution within three to seven days. No detectable concentrations of bromide or iron were found in polyethylene diffusion samplers even after 21 days. No measurable concentrations of aluminum, arsenic, barium, cadmium, chromium, iron, mercury, manganese, nickel, and lead, or sulfide, were leached out of dialysis membrane samplers over seven days. Compared with using a gas‐tight syringe to sample the diffusion sampler, clipping the bag and pouring the water sample into a sample vial resulted in only a small 6.2% average loss of volatile organic compounds. Dialysis membrane diffusion samplers offer promise for use in sampling ground water for inorganic constituents as well as volatile organic compounds.
Ground Water Recharge and Chemical Contaminants: Challenges in Communicating the Connections and Collisions of Two Disparate Worlds
Authors: Daughton Christian G.
Published: February 2007

Our knowledge base regarding the presence and significance of chemicals foreign to the subsurface environment is large and growing — the papers in this volume serving as testament. However, complex questions with few answers surround the unknowns regarding the potential for environmental or human health effects from trace levels of xenobiotics in ground water, especially ground water augmented with treated waste water. Public acceptance for direct or indirect ground water recharge using treated municipal waste water (especially sewage) spans the spectrum from unquestioned embrace to outright rejection. In this paper, I detour around the issues most commonly discussed regarding ground water recharge and instead focus on some of the less‐recognized issues—those that emanate from the mysteries created at the many literal and virtual interfaces involved with the subsurface world. My major objective is to catalyze discussion that advances our understanding of the barriers to public acceptance of waste water reuse with its ultimate culmination in direct reuse for drinking. I pose what could be a key question as to whether much of the public's frustration or ambivalence in its decision‐making process for accepting, or rejecting, water reuse (for various purposes including personal use) emanates from fundamental inaccuracies, misrepresentation, or oversimplification of what water is and how it functions in the environment—just exactly what the water cycle is. These questions suggest it might behoove us to revisit some very elementary aspects of our science and how we are conveying them to the public.