bluuebunny/crossref_metadata_2025 huggingface dataset:
Feasibility Study of In‐Well Vapor Stripping Using Airlift Pumping
Authors: Gvirtzman Haim , Gonen Ori
Published: February 2007

This study tests the feasibility of an aquifer remediation concept proposed by Gvirtzman and Gorelick (1992) that involves the removal of volatile organic compounds (VOCs) dissolved in ground water. The principal is 10 inject air into a well, creating airlift pumping, which is used as a means of in‐well vapor stripping. The partially treated water is diverted away from the well and infiltrates back to the water table, thus allowing remediation of a larger aquifer volume.

A remediation well prototype, constructed in a laboratory aquifer model, was used to demonstrate the processes involved. The removal rates of trichloroethylene, toluene, and chloroform were monitored using eight triple‐level observation wells. The continuous decrease of VOC concentrations during the short‐term experiment has yielded macroscopic evidence that the process offers some promise. It was found that the flow field in the saturated zone. involving the continuous water circulation between the pumping well and the recharging area, caused temporal and spatial variation in remediation efficiency.
Estimating the Horizontal Gradient in Heterogeneous, Unconfined Aquifers: Comparison of Three‐Point Schemes
Authors: Cole Bryce E. , Silliman Stephen E.
Published: February 2007

At least two approaches may be used to estimate the horizontal components of the hydraulic gradient based on measured heads from three observation points. First, the gradient may be estimated by passing a plane through the measured heads (h‐method). Second, if the elevation of the base of the aquifer is known to be spatially constant, an estimate of the gradient may be obtained using the squares of the measured heads (h2‐ method). In the present study, these methods are examined in application to a heterogeneous system. Using Monte Carlo analysis, we demonstrate that the magnitude of the gradient estimated via the h‐method involved significant bias, which increased when the distance separating the wells increased. In contrast, bias in the estimated magnitude of the gradient based on the h2‐method decreased with increasing separation among the wells. Estimation variances for both the magnitude and orientation of the gradient also decreased with separation distance. The variance in the orientation was observed to remain relatively high, however, even at relatively large separations among the wells (e.g., 10 integral scales). These results are Interpreted as implying that the best estimate of the gradient for steady flow in an unconfined aquifer is derived from the h2‐ method with the wells separated by significant distances. These results also demonstrate the uncertainty inherent in estimating the gradient based on limited field data.
Using Vertical Circulation Wells for Partitioning Tracer Tests and Remediation of DNAPLs
Authors: Chen L. , Knox R. C.
Published: February 2007

Two different vertical circulation well (VCW) systems (Type A and Type B) were used to detect and subsequently remove tetrachloro‐ethylene (PCE) spilled in a three‐dimensional sand tank. The Type A system has one injection interval and one extraction interval. The Type B system has two injection intervals separated by an intermediate extraction interval. PCE was detected through partitioning tracer tests using ethanol and 2,2‐dimethyl‐3‐pentanol as the non‐partitioning and partitioning tracers, respectively. The concentration breakthrough curves for the tracers exhibited significant chromatographic separation due to partitioning of the 2,2‐dimethyl‐3‐pentanol into the PCE. Because of the unique streamline distribution generated by the VCW systems, injected solutions did not sweep through the entire contaminated pore volume, which resulted in less than 100 percent detection of the spilled PCE. However, multiple tests along the borehole of the well were used to delineate the vertical profile of PCE residual saturation. Three food‐ grade surfactants were used to remediate the spilled PCE. For surfactant‐enhanced solubilization, the PCE effluent concentrations for the VCW systems were approximately eight (Type A) and 13 (Type B) times higher than that of a pump‐and‐treat system using water alone. The VCW effluent concentrations are actually diluted because the extraction rate exceeds the injection rate. Removing the effects of dilution occurring in the borehole, the concentrations leaving the treatment zones around the VCW are found to be 32 (Type A) and 52 (Type B) times higher than using water alone. During surfactant‐enhanced mobilization, the Type A VCW system was unable to capture all of the PCE‐surfactant microemulsion as it migrated downward. The uncaptured PCE could have negative impacts on ground water quality due to its increased solubility. The Type B system was found to be hydraulically more efficient than the Type A system both in terms of overall PCE removal and capturing mobilized microemulsions.
Diffusion Samplers as an Inexpensive Approach to Monitoring VOCs in Ground Water
Authors: Vroblesky Don A. , Hyde W. Thomas
Published: February 2007

Diffusion samplers installed in observation wells were found to be capable of yielding polyethylene to transmit other volatile compounds, such as benzene and toluene, indicates that the samplers can be used for a variety of volatile organic compounds. In wells at the study area, the volatile organic compound concentrations in water samples obtained using the samplers without prior purging were similar to concentrations in water samples obtained from the respective wells using traditional purging and sampling approaches. The low cost associated with this approach makes it a viable option for monitoring large observation‐well networks for volatile organic compounds.
Caution Against Interpreting Gasoline Release Dates Based on BTEX Ratios in Ground Water
Authors: Alvarez Pedro J. J. , Heathcote Richard C. , Powers Susan E.
Published: February 2007

“Traces of MTBE in ground water (>10 ppb) do not necessarily indicate recent gasoline contamination.”
Design for a Packer/Vacuum Slug Test System for Estimating Hydraulic Conductivity in Wells with LNAPLs, Casing Leaks, or Water Tables Intersecting the Screens
Authors: Strobel Michael L. , Strobel Carissa J. , Delin Geoffrey N.
Published: February 2007

“Results indicate that the packer/vacuum system is an adequate method for obtaining values of hydraulic conductivity.”
Analysis of Nitrate‐Nitrogen Movement Near High‐Capacity Irrigation Wells
Authors: Chen Xunhong , Ayers Jerry F. , Gosselin David C.
Published: February 2007

AGalerkin finite‐element model coupled with a particle tracking routine was developed to analyze the flow and transport dynamics near a high‐capacity irrigation well. The model was used to compute the head distribution around the pumping well, to determine the area of influence, and to define ground water flowlines during short‐term pumping periods typical of those used to collect water quality samples from high‐capacity wells. In addition to hypothetical example results, the model was used to qualitatively analyze data obtained from pump‐and‐sample experiments conducted in an unconfined alluvial aquifer within the Platte River valley of south‐central Nebraska where nitrate‐nitrogen (NO3‐N) contamination is prevalent.

Simulation results of both the hypothetical and field cases suggest that short‐term pumping events, impact a limited volume of aquifer. The area of influence and flowlines are affected by aquifer anisotropy, pumping rate, and well construction characteristics). Ground water above or below the screened intervals does not enter a partially penetrating well in anisotropic aquifers. In aquifers where NO3‐N concentration varies vertically and horizontally, waler quality samples from an irrigation, or other high‐capacity, well provide only limited information about ground water contamination. A numerical model is thus recommended for calculating the area of influence and determining flowlines around high‐capacity wells so that information derived from water quality samples collected at the wellhead can be better interpreted.
Field Observations of Tidal and Seasonal Variations in Ground Water Discharge to Tidal Estuarine Surface Water
Authors: Robinson Michael , Gallagher Dan , Reay William
Published: February 2007

A field study of the tidal and seasonal variations in upland, shoreline, and nearshore hydrological processes associated with ground water discharge from the unconfined Columbia Aquifer was conducted. The study, performed along a tidal subestuary of the Chesapeake Bay, involved measurement of water table elevation, ground water discharge, potentiometric had differentials across the sediment‐water interface, and ground water salinity. Fresh ground water discharge rates calculated from the measured water table gradient using the Dupuit assumptions varied from 6.1 X 10‐3 to 3.8 X 10‐2 m3/day per m of shoreline during the study period, May 1994 to September 1995. Variation in discharge rates were associated with seasonal recharge patterns.

Integrated total discharge rates based on seepage meter measurements decreased with distance offshore from a maximum of 3.3 L/m2 hr at the shoreline to 0.5 L/m2hr at 30 m offshore Maximum instantaneous discharge rates calculated from potentiometric head differentials were much higher than integrated discharge rates and ranged from 19.2 L/m2hr at 4.8 m offshore to 0.8 L/m2hr at 19.8 m offshore. Instantaneous discharge rates were inversely correlated to tidal elevation and fluctuated rapidly decreasing from 19.2 L/m2hr to 2.5 L/m2 hr during a several‐hour period.

Seasonal variations in salinity patterns within the transition zone of the Columbia Aquifer were observed and indicated a dependence on fresh ground water discharge and surface water salinity/density gradient was observed within the transition zone. The gradient was created, in part, by the infiltration of surface water into tidally exposed sediments. Seasonal periods of low fresh ground water discharge and high surface water salinity were associate with intrusion of the surficial mixing zone landward while seasonal periods of high fresh ground water discharge and low surface water salinity were associated with a seaward movement of the mixing zone.
In Situ Vertical Circulation Column: Containment System for Small‐Scale DNAPL Field Experiments
Authors: Sorel Dominique , Cherry John A. , Lesage Suzanne
Published: February 2007

The in situ vertical circulation column (ISVCC) is a cylindrical containment system consisting of an instrumented steel cylinder used for experimental ground water studies in sandy aquifers. Vertical flow is imposed inside the ISVCC. Although vertical wells are an option, the ISVCC installed in the Borden Aquifer is instrumented with horizontal wells and monitoring ports to avoid creating vertical preferential flow paths. The cylinder was driven downward into the aquifer using a small backhoe equipped with a vibrating plate. The ISVCC penetrates the 2.3‐m‐thic sand aquifer and is keyed 20 cm into the underlying clay aquitard. The cylinder was installed inside a 2 m X 2 m steel sheet pile enclosure so that the enclosed segment of aquifer could be conveniently dewatered and then excavated to allow installation of the horizontal wells. The dispersivity of the column was comparable to literature values for long sand‐packed laboratory columns.

Pure phase DNAPL (tetrachloroethene and 1,1,1‐trichloroethane) was slowly pumped into two ports in the center of the column. Following this DNAPL injection, an aqueous solution of vitamin B12 and reduced titanium was circulated through the column to promote degradation of the solvents. Processes observed in the ISVCC included DNAPL distribution, dissolution, and degradation, and geochemical evolution of the aquifer.

The ISVCC provides a convenient means for testing in situ technologies in the experimental stage or for selection of proven technologies to find the most effective at a specific site. It is inexpensive, easy to install, and maximizes control over flow distribution in a heterogeneous aquifer. Its application will be restricted where low hydraulic conductivity beds are present in the aquifer.
Estimation of Biodegradation Rates Using Respiration Tests During In Situ Bioremediation of Weathered Diesel NAPL
Authors: Davis G.B. , Johnston C.D. , Patterson B.M. , Barber C. , Bennett M.
Published: February 2007

Respiration tests were carried out during a seven month bioremediation field trial to monitor biodegradation rates of weathered diesel non‐aqueous phase liquid (NAPL) contaminating a shallow sand aquifer. Multiple depth monitoring of oxygen concentrations and air‐filled porosity were carried out in nutrient amended and nonamended locations to assess the variability of degradation rate estimates calculated from respiration tests.

The field trial consisted of periodic addition of nutrients (nitrogen and phosphorus) and aeration of a 100 m2 trial plot. During the bioremediation trial, aeration was stopped periodically, and decreases in gaseous oxygen concentrations were logged semi‐continuously using data loggers attached to recently developed in situ oxygen probes placed at multiple depths above and within a thin NAPL‐contaminated zone. Oxygen usage rate coefficients were determined by fitting zero‐and first‐order rate equations to the oxygen concentration reduction curves, although only zero‐order rates were used to calculate biodegradation rates. Air‐filled porosity estimates were found to vary by up to a factor of two between sites and at different times.

NAPL degradation rates calculated from measured air‐filled porosity and oxygen usage rate coefficients ranged up to 69 mg kg‐1 day‐1. These rates are comparable to and higher than rates quoted in other studies, despite the high concentrations and weathered state of the NAPL at this test site. For nutrient‐amended sites within the trial plot, estimates of NAPL degradation rates were two to three times higher than estimates from nonamended sites. Rates also increased with depth.
Investigation and Remediation of a 1,2‐Dichloroethane Spill Part II: Documentation of Natural Attenuation
Authors: Lee Michael D. , Sehayek Lily , Sleep Brent E. , Vandell Terry D.
Published: February 2007

A release of 1,2‐dichloroethane. also known as ethylene dichloride (EDC), resulted in shallow subsurface freephase contamination of a Gulf Coast site in the southern United States. The site stratigraphy consists primarily of a low permeability, surficial peat. silt, and clay zone underlain by fractured clay; a confined 12 in deep sand ground water flow zone; a confined 21 m deep fine sand zone of limited ground water flow, followed by a deep aquitard. The Gumbo clay and sandy clay aquitard below the release area overlies and protects the 61 m deep Upper Chicot Aquifer, which is a confined regional aquifer. An ongoing recovery and hydraulic containment program from the primary impacted and laterally and vertically restricted shallow 40‐foot sand zone has effectively recovered dense nonaqueous phase liquid (DNAPL) and contained dissolved phase EDC.

Natural attenuation of EDC was demonstrated through (1) a laboratory microcosm study substantiating the ability of the native microbial population in the deeper aquifer lo degrade EDC under anaerobic environmental conditions found at the site. (2) field investigations showing reductions in EDC concentrations over time in many of the wells on site, and (3) an evaluation of the ground water for EDC and its degradation products and oilier geo‐chemical parameters such as dissolved oxygen, redox potential, and pH. Degradation products of EDC found in the field investigations included 2‐chloroeihanol, ethanol. ethene, and ethane. Dissolved EDC concentrations in selected wells between the first recorded samples and the fourth quarter of 1997 ranged from greater than 4% to 99% reductions. First‐order exponential decay half‐lives ranged from 0.21 to 4.2 years for wells showing decreases in FDC concentrations over time. Elevated methane concentrations indicated carbon dioxide to be the major terminal electron acceptor.
The Relative Merits of Monitoring and Domestic Wells for Ground Water Quality Investigations
Authors: Jones Joseph L. , Roberts Lonna M.
Published: February 2007

The results of two studios of the effect of agricultural hind use on shallow ground water quality indicate that monitoring wells may be a better choice than domestic wells for studies of pesticide occurrence or transport, or for use as early‐warning indicators of potential drinking water contamination. Because domestic wells represent the used resource, and because domestic well water may be affected by historical rather than current pesticide and land‐use practices, domestic wells would be the best choice for an investigation of drinking water quality. The key difference between the domestic and monitoring wells appears to be that the monitoring wells in this study were installed exclusively to sample the shallowest possible ground water. For these studies. 48 shallow domestic wells and 41 monitoring wells were located randomly within two land‐use settings (row crops and orchards) in an irrigated agricultural region of eastern Washington and sampled for 145 pesticides (including nine pesticide degradates) and common water quality indicators. Constructing and sampling monitoring wells required approximately four times the resources (including manpower and materials) as locating and sampling domestic wells. Sample collection and quality assurance procedures and analytical techniques were identical except that a portable submersible pump was required for monitoring wells. In both land‐use sellings, no significant difference in nitrate concentration was found between well types; however, the average number of pesticides detected per well was significantly higher (p<0.05) in the monitoring wells. A greater variety of pesticides was detected in monitoring wells: many were detected only in monitoring wells. More than 60% of detections of pesticides that were found only in domestic wells were of compounds that are no longer in use. These differences in ground water quality found in this studs relate lo the depth of the well and are apparently related lo the age of ground water in the two types of wells and the greater effects of sorption, degradation, dilution, and dispersion that accompany longer ground water residence times. The decision to invest resources in monitoring wells should be made in light of the study objective and should consider these differences in results from the two types of wells as well as the relative costs.
Decision Analysis for Leachate Control at a Fractured Rock Landfill
Authors: Lepage Nicolas , Hamel Pascal , Lefebvre René , Therrien René , Blais Chantale
Published: February 2007

The municipal landfill at the Complexe Environnemental de Saint‐Michel (CESM) in Montreal, which is the third largest in North America, is located in a former quarry in fractured limestone. Impressive measures are taken to monitor and control biogas and leachate generated at the site. Leachate containment is presently performed with a pumping well completed within the waste. The efficiency of the well in controlling off‐site leachate migration is questioned because field observations strongly suggest that the nearby former Francon quarry is diverting local ground water flow. To address this issue, four additional hydraulic control options are considered: (1) increased pumping at the existing waste well; (2) new pumping wells in the rock on the eastern limit of the site; (3) new injection wells in the rock on the eastern limit; and (4) combination of new injection wells at the same location and new water supply wells upgradient of the landfill. We evaluated the four hydraulic control options at the CESM using two coupled models: (1) a decision model based on an objective function weighting the risk, costs, and benefits of each option translated into dollar units; and (2) a numerical ground water flow model to represent the effect of operational conditions and ascertain success. Decision analysis offers a quantitative unbiased tool to evaluate the potential and relative cost of each option, but qualitative considerations and judgment still must be used for a complete evaluation. Our analysis confirms that scenario 4, which was the intuitively favored option, represents the best containment strategy.
An Evaluation of Horizontal Recirculation Using Single‐Well Tests, Pumping Tests, Tracer Tests, and the Colloidal Borescope
Authors: Korte Nic , Kearl Peter M. , Siegrist Robert L. , Muck Maureen T. , Schlosser Robert M.
Published: February 2007

Extensive hydrodynamic testing was performed as part of a program to evaluate horizontal recirculation as a means of removing contaminants from thin, interbedded aquifers. Two test sites, each containing a pair of horizontal recirculation wells, were evaluated using various hydraulic tests. Results of these evaluations showed that ground water was intercepted more than 100 feet beyond the wells, and that the hydraulic gradient increased by more than two orders of magnitude. Aquifer heterogeneity, however, controlled the efficiency and uniformity of ground water flow. Heterogeneity was assessed with a variety of techniques. Bromide tracer tests and the colloidal borescope provided the most useful data. For example, at an uncontaminated site, the leading edge of the bromide tracer traversed the 100 feet between the injection and extraction wells in 21 hours, and the peak bromide concentration was observed in 2.6 days, compared with the four days predicted by a pumping test. The resulting maximum velocity calculation was consistent with measurements made with the borescope in preferential flow zones. Data obtained from a highly contaminated location indicated that assessments of aquifer heterogeniety are further complicated by the presence of DNAPL. Very low flow occurred in a highly contaminated zone, despite the fact that lithologic descriptions indicated that this region contained permeable sand and gravel.
A County‐Level Assessment of Ground Water Contamination by Pesticides
Authors: Shukla Sanjay , Mostaghimi Saied , Shanholt Vernon O. , Collins Michael C. , Ross Burton B.
Published: February 2007

A pesticide screening model was integrated with a geographic information system (GIS) for evaluating the ground water vulnerability to pesticide contamination in Albemarle County, Virginia. The attenuation factor (AF). an index of pesticide mass emission from the vadose zone, was used to evaluate the relative contamination potential of 70 pesticides used in the county. Results for only three pesticides—atrazine, dicamba, and lindane—are discussed in this paper. Spatial (land use, soils, and hydrogeology) and relational (soil and pesticide properties) data layers were combined with the AF model within the GIS environment for spatial computation of AF for actual and 2 m ground water depths. For each pesticide, a ground water vulnerability map with five contamination potential categories (high, medium, low, very low, and unlikely) was generated, based on the spatial distribution of AF for each cell size of 0.27 acre (0.11 ha). To consider the variability in pesticide transport, model simulations were performed for “maximum,”“average,” and “minimum” scenarios of pesticide leaching. Under the average leaching scenario (2 m depth), the three pesticides were found to have very low to low levels of contamination potential in some areas. For maximum leaching scenario (2 m depth), contamination potential of these three pesticides increased to low to medium levels. When actual ground water depth was used, no significant contamination potential was indicated by any of the three pesticides. The modeling approach was evaluated using the data from a limited monitoring study in Albemarle County. Although agreement between the model prediction and actual pesticide detection was observed, extent of the data was not sufficient enough to draw firm conclusions about the model's success in predicting contamination potential. A sensitivity analysis of the methodology revealed that significant uncertainty can be involved in predicting the county‐scale contamination potential. To make better use of this study, it is recommended that a comprehensive pesticide monitoring be undertaken in Albemarle County.
Free‐Product Recovery of Petroleum Hydrocarbon Liquids
Authors: Charbeneau Randall J. , Johns Russell T. , Lake Larry W. , McAdams Michael J.
Published: February 2007

Recovery wells remain the principle technology for removal of free‐product hydrocarbon liquids from the subsurface. This paper presents simple models for estimating hydrocarbon recovery rates using wells and vacuum‐enhanced systems. Use of LNAPL volume balance between LNAPL recovery rate and formation free‐product volume leads to development of algebraic equations that can be used to estimate recovery times. Selection of model parameters is discussed, model comparisons are made, and applications are presented for design and analysis of recovery systems using wells. Model validation is also discussed.
Oxidation of Binary DNAPL Mixtures Using Potassium Permanganate with a Phase Transfer Catalyst
Authors: Seol Yongkoo , Schwartz Franklin W. , Lee Sangsuk
Published: February 2007

Phase transfer catalysts (PTCs) can enhance the oxidation of pure DNAPLs using potassium permanganate by facilitating reactions in the organic phase. This study examined the influence of pentyltriphenylphosphonium bromide (PTPP) as a PTC on the rate of permanganate (MnO4‐) oxidation of DNAPLs in pure phases and mixtures. Kinetic batch experiments with trichloroethylene (TCE), 1,1,2‐trichloroethane (TCA), tetrachloroethylene (PCE), 1,1,2,2‐tetrachloroethane (TECA), and their mixtures, (1:1, v/v) were performed in test tubes to assess reaction rates. The disappearance of MnO4‐ was quantified by capturing digital images pf the tubes. This rapid photographic monitoring approach was validated by comparison with an UV‐Vis spectrometer method. The PCE/TCA mixture was selected to examine the impact of relative contents of a component in the binary mixture on the MnO4‐ disappearance. The comparative rates of MnO4‐ consumption for pure phases were TCE > TECA > PCE > TCA. PTPP increased MnO4‐ consumption rates, especially for TCE and TECA as pure, phases. The consumption rates of mixtures without PTPP were lower than those including the pure phases. However, due to their high extraction capability for PTPP‐MnO4‐ ion pairs, TCA and TECA appeared to increase the MnO4‐ consumption significantly when they were mixed with TCE or PCE, The increase in consumption rates with PTPP was most remarkable with the mixture of PCE and TCA. Chloride concentration showed faster increases for the mixtures with relative PCE contents ranging about 5 % to 90%, maximum at about 50% PCE, than for pure phases of PCE and TCA when the PTC assisted the reactions. The PTC appears to be promising in its ability to increase oxidation rates of DNAPL mixtures.
DNAPL Characterization Methods and Approaches, Part 1: Performance Comparisons
Authors: Kram Mark L. , Keller Arturo A. , Rossabi Joseph , Everett Lorne G.
Published: February 2007

Contamination from the use of chlorinated solvents, often classified as dense nonaqueous phase liquids (DNAPLs) when in an undissolved state, represents an environmental challenge with global implications. Mass‐transfer limitations due to rate‐limited dissolution can lead to long‐term aquifer persistence for even small volumetric fractions. The identification of DNAPL source zones located beneath the water table is critical to ultimately achieve site remediation and aquifer restoration. This paper provides a comparison of the advantages and disadvantages of many of the methods being used for detecting and delineating DNAPL contaminant source zones. The objective is to determine which options are best to pursue based on site characteristics, method performance, and method costs. DNAPL characterization methods are grouped into approaches, which include site preparation, characterization, and data‐processing activities necessary to design an effective remediation system. We compare the different approaches based on the level of chemical and hydrogeologic resolution, and the need for additional data requirements. Our findings can be used to assist with selection of appropriate site remediation management options.
Diffusive Oxygen Emitters for Enhancement of Aerobic In Situ Treatment
Authors: Wilson Ryan D. , Mackay Douglas M.
Published: February 2007

Aerobic biodegradation can be enhanced within contaminant plumes by elevating typically low dissolved oxygen (D.O.) levels using materials or devices that passively release oxygen. We have developed passive devices that provide a uniform, steady, long‐term source of oxygen by diffusion from pressurized polymeric tubing and report test results under lab and field conditions. Lab flow‐through reactor tests were conducted to determine the diffusion coefficient (D) of oxygen through four readily available tubing materials. Oxygen diffusion was greatest through Tygon® 3350 platinum‐cured silicone (D = 6.67 ± 10‐7 cm2/sec), followed by 2075 Ultra Chemical Resistant Tygon (1.59 ± 10‐7 cm2/sec), 2275 High Purity Tygon (5.11 ± 10‐8 cm2/sec), and low‐density polyethylene (LDPE; 1.73 ± 10‐8 cm2/sec). Variable‐pressure release tests with LDPE resulted in very close estimates of D, which confirmed that mass transfer is controlled by diffusion and that the concentration gradient is a valid approximation of the chemical potential driving diffusion. LDPE emitter devices were designed and installed in seven 8‐inch‐diameter well screens across a portion of a gasoline plume at a former service station. With the devices pressurized to 620.5 kPag (kilopascals gauge) late in the test, steady‐state D.O. concentrations reached as high as 25 mg/L, comparing favorably to the value predicted using the mass‐transfer coefficient estimated from the lab test (26.3 mg/L). The method can also be used to release other gases for other reasons: gaseous tracers (i.e., sulphur hexafluoride, helium, and argon), hydrogen (for reductive dechlorination), or light alkanes (for cometabolic biodegradation of methyl tertiary butyl ether [MTBE] or chlorinated solvents).
Numerical Modeling of Unsaturated Flow in Wastewater Soil Absorption Systems
Authors: Beach Deborah N. Huntzinger , McCray John E.
Published: February 2007

It is common practice in the United States to use wastewater soil absorption systems (WSAS) to treat domestic wastewater. WSAS are expected to provide efficient, long‐term removal of wastewater contaminants prior to ground water recharge. Soil clogging at the infiltrative surface of WSAS occurs due to the accumulation of suspended solids, organic matter, and chemical precipitates during continued wastewater infiltration. This clogging zone (CZ) creates an impedance to flow, restricting the hydraulic conductivity and rate of infiltration. A certain degree of clogging may improve the treatment of wastewater by enhancing purification processes, in part because unsaturated flow is induced and residence times are significantly increased. However, if clogging becomes excessive, the wastewater pond height at the infiltrative surface can rise to a level where system failure occurs. The numerical model HYDRUS‐2D is used to simulate unsaturated flow within WSAS to better understand the effect of CZs on unsaturated flow behavior and hydraulic retention times in sandy and silty soil. The simulations indicate that sand‐based WSAS with mature CZs are characterized by a more widely distributed flow regime and longer hydraulic retention times. The impact of clogging on water flow within the silt is not as substantial. For sand, increasing the hydraulic resistance of the CZ by a factor of three to four requires an increase in the pond height by as much as a factor of five to achieve the same wastewater loading. Because the degree of CZ resistance directly influences the pond height within a system, understanding the influence of the CZ on flow regimes in WSAS is critical in optimizing system design to achieve the desired pollutant‐treatment efficiency and to prolong system life.
Extent of Benzene Biodegradation in Saturated Soil Column During Air Sparging
Authors: Adams Jeffrey A. , Ready Krishna R.
Published: February 2007

In situ air sparging has emerged as a popular remedial alternative to traditional pump‐and‐treat for the remediation of volatile organic contaminants in saturated soils and ground water. During air sparging, a gas, usually air, is injected into the subsurface below the lowest known point of contamination. The air induces partitioning of dissolved‐phase and free‐phase contamination into the vapor phase. Additionally, the injected air increases subsurface dissolved oxygen concentrations, potentially stimulating aerobic biodegradation. To take advantage of the ability of subsurface microbial populations to degrade organic compounds, air sparging may be implemented in a manner different from a traditional air sparging application; a technique often referred to as biosparging. This paper presents the results of a laboratory study performed to demonstrate the potential contribution of aerobic biodegradation to the attenuation of VOCs during the use of air sparging. This study included a series of controlled laboratory column tests using a soil profile subjected to biomass infiltration and a range of dissolved‐phase benzene concentrations. The test results demonstrated that, although the partitioning of NAPL‐ and aqueous‐phase benzene into the vapor phase through volatilization was the dominant removal mechanism, biodegradation could account for a substantial portion of the benzene removal during the application of air sparging. In order for considerable aerobic biodegradation to occur, however, sufficient amounts of dissolved oxygen must exist within the subsurface to serve as an electron acceptor. The presence of a soil matrix reduced the rates of biodegradation within the column tests when compared to batch reactor tests due to the discontinuous contact of the biomass, aqueous‐phase benzene, nutrients, and dissolved oxygen. Additionally, the rates of biodegradation that were observed during testing were independent of the initial aqueous‐phase benzene concentrations and the biomass concentrations selected for this study. Finally, the dissolved‐oxygen concentration was observed to be the rate‐limiting factor for biodegradation.
An Improved Method for Estimation of Biodegradation Rate with Field Data
Authors: Zhang You‐Kuan , Heathcote Richard C.
Published: February 2007

The method of Buscheck and Alcantar (1995) is shown to be valid for the concentration data observed in wells along the centerline and near a source of relatively large area as compared with the lateral dispersion of the plume. When such a condition is not satisfied, the method of Buscheck and Alcantar (1995) overestimates the biodegradation rate due to its usage of a solution to a one‐dimensional advection‐dispersion equation that does not consider lateral dispersion and finite source size. It is also shown that the concentration of a two‐ or three‐dimensional plume does not always decrease exponentially with the distance from the source along a plume centerline. An improved method based on multidimensional solutions of Domenico (1987) is proposed. In using the improved method, observed concentrations are normalized by the error functions embedded in the solutions to two‐ or three‐dimensional advection‐dispersion equations for a continuous source of finite size. With the normalized concentrations and following the procedure of Buscheck and Alcantar (1995), one may estimate the biodegradation rate, which is usually smaller than that obtained with the original data. It is demonstrated with the field data presented by Buscheck and Alcantar (1995) at the Fairfax Terminal that the method of Buscheck and Alcantar (1995) indeed overestimates the biodegradation rate by 21% and 65% for a two‐dimensional plume and for a three‐dimensional plume, respectively.
Field Evaluation of the Effectiveness of Surfactant Modified Zeolite and Iron‐Oxide‐Coated Sand for Removing Viruses and Bacteria from Ground Water
Authors: Schulze‐Makuch Dirk , Bowman Robert S. , Pillai Suresh D. , Guan Huade
Published: February 2007

Field experiments were conducted to evaluate the efficiency of iron‐oxide‐coated sand (ICS) and surfactant modified zeolite (SMZ) to remove viruses and bacteria from ground water. The reactive media were employed as filter packs of a pumping well that withdrew sewage effluent from a constructed wetland at a rate of 0.72 L/min. The contact time of the pumped water with the filter pack (10 cm thick) was about two minutes. Upgradient of the pumping well, the sewage effluent was spiked with MS‐2 bacteriophage and E. coli. While the employed ICS filter pack failed to remove viruses and bacteria to a significant degree, the SMZ filter pack removed more than 99% of the viruses and 100% of E. coli from the ground water while fresh. In an additional field experiment using the same configuration but leaving the filter pack in place for more than five months, the SMZ filter pack was still removing 100% of E. coli, but failed to reduce virus numbers to a significant degree.
A Modified Radial Diagram Approach for Evaluating Natural Attenuation Trends for Chlorinated Solvents and Inorganic Redox Indicators
Authors: Carey Grant R. , Van Geel Paul J. , Wiedemeier Todd H. , McBean Edward A.
Published: February 2007

Selection of monitored natural attenuation as a ground water remedy requires that sound scientific documentation clearly illustrating the effectiveness of this remedial alternative be presented to regulatory agencies and concerned citizens. An innovative radial diagram approach is applied to illustrate natural attenuation trends for total benzene, toluene, ethylbenzene, and xylenes (BTEX) and chlorinated ethenes at a former fire training area at Pittsburgh Air Force Base, New York. A BTEX‐CAH (chlorinated aliphatic hydrocarbons) radial diagram map shows that concentrations of site contaminants are generally decreasing along the primary flowpath downgradient from the source area. This radial diagram map also suggests that there is a spatial correlation between decreasing CAH parent compound concentrations and increasing or stable daughter product concentrations. This provides secondary evidence of intrinsic biodegradation of TCE downgradient from the source area. A SEQUENCE‐Redox™ map suggests that there is a spatial correlation between trends in electron acceptor and metabolic byproduct concentrations, and the decline in total BTEX concentrations downgradient from the source area. This correlation provides secondary evidence for the intrinsic biodegradation of total BTEX in the aquifer. This study demonstrates that radial diagram visual aids can provide a clear and efficient approach for documenting natural attenuation lines of evidence, as an alternative or a complement to using multiple contour maps, tabulated data, or log‐linear plots.
Monitoring Partitioning Tracer Testing and Surfactant Flooding by In‐Line Gas Chromatography Techniques
Authors: Suva Jeff A. K. , Mariner Paul E. , Meinardus Hans W. , Ginn Jon S.
Published: February 2007

An automated in‐line analytical system has been developed to provide near real‐time results for partitioning interwell tracer testing (PITT) and surfactant enhanced aquifer remediation (SEAR). The analytical methodology is based on gas chromatography (GC) with flame ionization detection and direct aqueous injection. The system was constructed from both commercially available and custom‐manufactured components that are linked electronically to facilitate autonomous operation. For the field trials presented herein, the in‐line GC method provided superior or comparable PITT and SEAR data compared to conventional sample collection followed by shipment and analysis at a commercial analytical laboratory. Analytical precolumns were shown to effectively safeguard the integrity of the analytical column, despite the consecutive analysis of more than 1000 samples per PITT or SEAR. Additionally, the use of the in‐line GC resulted in an 85% and 74% reduction in analytical costs per PITT and SEAR, respectively.
Analytical Solutions for Free‐Hydrocarbon Recovery Using Skimmer and Dual‐Pump wells
Authors: Johns Russell T. , Lake Larry W. , Obigbesan Abimbola B. , Bermudez Leonardo , Hassan M.R. , Charbeneau Randall J.
Published: February 2007

Accidental release of petroleum hydrocarbons to the subsurface may occur through spills around refineries, leaking pipelines, storage tanks, or other sources. If the spill is large, the hydrocarbon liquids may eventually reach a water table and spread laterally in a pancake‐like lens. Hydrocarbons that exist as a separate phase are termed light nonaqueous phase liquids (LNAPLs). The portion of the LNAPL that is mobile, not entrapped as residual saturation, is termed “free product.”

This paper presents new analytical solutions for the design of long‐term free‐product recovery from aquifers with skimmer, single‐ and dual‐pump wells. The solutions are for steady‐state flow, based on the assumption of vertical equilibrium, and include the effect of coning of LNAPL, air, and water on flow. The solutions are valid for soils of large hydraulic conductivity where the effect of capillary pressure on coning is small.

The results show how to estimate the maximum rate of inflow of LNAPL for skimmer wells, i.e., wells in which LNAPL is recovered with little or no water production. The paper also shows how to calculate the increase in LNAPL recovery when water is pumped by single‐ or dual‐pump wells. A simple equation is given that can be used to adjust the water rate to avoid smearing of the LNAPL below the water table.
Biological and Physical Attenuation of Endocrine Disruptors and Pharmaceuticals: Implications for Water Reuse
Authors: Snyder Shane A. , Leising Joseph , Westerhoff Paul , Yoon Yeomin , Mash Heath , Vanderford Brett
Published: February 2007

A select group of endocrine disrupters, pharmaceuticals, and personal care products was studied to determine the degree of biological attenuation in water reuse applications. Laboratory investigations involved both batch reactors using biologically active sand and continuous flow simulated aquifer storage and recovery experiments. All laboratory experiments were conducted using Colorado River water spiked with various target compounds at concentrations between 10 and 100 ng/L. Field studies were also conducted to determine the occurrence and attenuation of target compounds in water reuse applications. Two golf courses irrigated with reuse water were studied to determine if turf applications led to contamination of nearby ground water. A waste water treatment facility that uses rapid infiltration basins seasonally was also tested to determine the degree of attenuation of detectable target compounds along a subsurface flowpath. A qualitative structural activity relationship model was applied to the target compounds to predict the general rate of aerobic biological degradation. Significant attenuation of many target compounds was observed in both laboratory and field experiments. Conversely, several compounds displayed limited removal during these studies. Field experiments were limited to detectable compounds and various nonbiological removal or concentration effects that may impact data interpretations, which are discussed in this paper. The predictive model was found to be moderately accurate within the confines of the project scope.
VARIABILITY IN THE BLUBBER FATTY ACID COMPOSITION OF RINGED SEALS (PHOCA HISPIDA) ACROSS THE CANADIAN ARCTIC
Authors: Thiemann Gregory W. , Iverson Sara J. , Stirling Ian
Published: February 2007

Abstract

We determined the blubber fatty acid (FA) composition of 281 ringed seals (Phoca hispida) across the Canadian Arctic to make inferences about spatial, temporal, and demographic patterns of foraging. Seals were sampled in nine locations between 1992 and 2004. Regional differences in FA signatures were related to the distance between groups, with the greatest similarity occurring among seals sampled in three locations within the Beaufort Sea‐Amundsen Gulf. Seals in the western and southeastern portions of Hudson Bay also had similar FA signatures. Discriminant analysis on seventeen FAs classified ringed seals to their correct geographic region with 95% accuracy. Although location accounted for most of the variability in FA signatures, adult and juvenile ringed seals in Frobisher Bay‐Labrador Sea and Jones Sound showed significant FA differences, as did male and female ringed seals in Jones Sound and Qaanaaq. Demographic differences were not detected among ringed seals in the Beaufort Sea‐Amundsen Gulf or in western Hudson Bay. Seals off the coast of Labrador showed significant seasonal variability in FA signatures. Overall, seasonal, regional, and demographic patterns in FA signatures were consistent with differences in ringed seal diets, as inferred from stomach content and stable isotope analyses.
ASSESSING KILLER WHALE PREDATION ON STELLER SEA LIONS FROM FIELD OBSERVATIONS IN KENAI FJORDS, ALASKA
Authors: Maniscalco John M. , Matkin Craig O. , Maldini Daniela , Calkins Donald G. , Atkinson Shannon
Published: February 2007

Abstract

The behavioral and predatory patterns of Gulf of Alaska (GOA) transient killer whales (Orcinus orca) were studied between 2000 and 2005 using remote video and vessel‐based observations near the Chiswell Island Steller sea lion (Eumetopias jubatus) rookery and in the broader Kenai Fjords (KF) region of the northern GOA. GOA transient killer whales were observed on 118 d over the 6‐yr period; the median group size was two (range: 1–9). Nine predation events were observed from vessels and an additional sixteen were inferred from remote video studies; all involved Steller sea lions. Estimates from field observations suggest that fifty‐nine sea lions were consumed over the summer seasons of 2002–2005; whereas estimates based on published caloric requirements of transient killer whales would suggest a loss of 103 sea lions over the same time period. GOA transients spent a large proportion (43%) of their time resting which may be a strategy for conserving energy. Predation on sea lion pups at the Chiswell Island rookery was greatest during years when a single killer whale was foraging alone and when a 1.5‐yr‐old calf was evidently being trained to handle prey. Predation on pups was low during years when killer whales were foraging in groups and were observed and presumed to be taking mostly juvenile sea lions. Our study suggests that GOA transients are having a minor effect on the recovery of Steller sea lions in the GOA.
Tradeoff of Uncertainty Reduction Mechanisms for Reducing Weight of Composite Laminates
Authors: Acar Erdem , Haftka Raphael T. , Johnson Theodore F.
Published: February 2007

Inspired by work on allocating risk between the different components of a system for a minimal cost, we explore the optimal allocation of uncertainty in a single component. The tradeoffs of uncertainty reduction measures on the weight of structures designed for reliability are explored. The uncertainties in the problem are broadly classified as error and variability. Probabilistic design is carried out to analyze the effect of reducing error and variability on the weight. As a demonstration problem, the design of composite laminates at cryogenic temperatures is chosen because the design is sensitive to uncertainties. For illustration, variability reduction takes the form of quality control, while error is reduced by including the effect of chemical shrinkage in the analysis. Tradeoff plots of uncertainty reduction measures, probability of failure and weight are generated that could allow choice of optimal uncertainty control measure combination to reach a target probability of failure with minimum cost. In addition, the paper also compares response surface approximations to direct approximation of a probability distribution for efficient estimation of reliability.