Showing papers in "Ground Water Monitoring and Remediation in 1998"
TL;DR: RT3D as mentioned in this paper is a general purpose, multispecies, reactive transport code, which uses MODFLOW to simulate flow and several MT3D sub-programs to simulate advection and dispersion.
Abstract: In this paper, the details of RT3D, a general purpose, multispecies, reactive transport code, are presented. The code uses MODFLOW to simulate flow and several MT3D sub-programs to simulate advection and dispersion. A set of reaction modules were developed and incorporated into RT3D to simulate various types of multispecies reactive transport. This new computer model can be used for analyzing different types of subsurface contaminant reactions, microbial metabolisms, and microbial transport kinetics. Details of the model and numerical solution procedure are presented. The numerical formulation of the code is general enough to allow description of any type of reaction with any number of mobile/immobile species. Several example problems are presented to test the performance of the code, and to illustrate its features. The presented numerical model is shown to be a useful tool for analyzing different types of subsurface bioremediation systems. Prediction based on this model can be used for screening remediation alternatives including natural attenuation and/or for forecasting contaminant exposure levels and environmental risks at sensitive, downgradient receptors.
246 citations
TL;DR: In this paper, the authors measured methyl tert-butyl ether (MTBE) and benzene in a shallow, sandy aquifer contaminated by a mid-1980s release of gasoline containing fuel oxygenates.
Abstract: Methyl tert-butyl ether (MTBE) and benzene have been measured since 1993 in a shallow, sandy aquifer contaminated by a mid-1980s release of gasoline containing fuel oxygenates. In wells downgradient of the release area, MTBK was detected before benzene, reflecting a chromatographic-like separation of these compounds in the direction of ground water flow. Higher concentrations of MTBE and benzene were measured in the deeper sampling ports of multilevel sampling wells located near the release area, and also up to 10 feet (3 m) below the water table surface in nested wells located farther from the release area. This distribution of higher concentrations at depth is caused by recharge events that deflect originally horizontal ground water flowlines. In the laboratory, microcosms containing aquifer material incubated with uniformly labeled 14C-MTBE under aerobic and anaerobic. Fe(III)-reducing conditions indicated a low but measurable biodegradation potential (<3%14C-MTBW as 14CO2) after a seven-month incubation period, Tert-butyl alcohol (TBA), a proposed microbial-MTBE transformation intermediate, was detected in MTBE-contaminated wells, but TBA was also measured in unsaturated release area sediments. This suggests that TBA may have been present in the original fuel spilled and does not necessarily reflect microbial degradation of MTBE. Combined, these data suggest that milligram per liter to microgram per liter decreases in MTBE concentrations relative to benzene are caused by the natural attenuation processes of dilution and dispersion with less-contaminated ground water in the direction of flow rather than biodegradation at this point source gasoline release site.
112 citations
TL;DR: In this paper, 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.
Abstract: 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.
104 citations
TL;DR: The influence of sorption on biodegradation is quantified here by defining a bioavailability factor, Bf, and challenges facing environmental engineers are to develop a better understanding of these processes at both laboratory and field scales.
Abstract: The low bioavailability of hydrophobic organic compounds (HOCs) is one of the key sources of uncertainty in the implementation of in situ bioremediation. Bioavailability of HOCs in the subsurface is affected by sorption/desorption processes in two important ways. First, sorption causes high organic concentrations in microporous regions and impermeable zones to which bacterial access is obstructed. Second, because desorption and immobile zone diffusion must occur before biodegradation can proceed, the overall rate of bioremediation can be limited or even controlled by these mass transfer processes, not by the activity of the degrading microorganisms. Rate models that couple sorption/desorption--related mass transfer processes and biodegradation have been successfully applied to laboratory results and are beginning to offer some insight into the problem. Specifically, the influence of sorption on biodegradation is quantified here by defining a bioavailability factor, B{sub f}. However, many questions remain and predictive modeling is elusive, especially in the context of complicated heterogeneous natural systems. Challenges facing environmental engineers are to develop a better understanding of these processes at both laboratory and field scales and ultimately to use such understanding toward the development of more effective and economical remediation technologies.
83 citations
TL;DR: The mass of BTEX compounds in the plume diminished significantly with time due to intrinsic aerobic biodegradation, while MTBE showed only a small decrease in mass over the 16-month period as mentioned in this paper.
Abstract: In 1988 and 1989, a natural gradient tracer test was performed in the shallow, aerobic and aquifer at Canadian Forces Base (CFB) Borden. A mixture of ground water containing dissolved oxygenated gasoline was injected below the water table along with chloride (Cl-) as a conservative tracer. The migration of BTEX, MTBE, and Cl was monitored in detail for 16 moths. The mass of BTEX compounds in the plume diminished significantly with time due to intrinsic aerobic biodegradation, while MTBE showed only a small decrease in mass over the 16-month period. In 1995/96, a comprehensive ground water sampling program was undertaken to define the mass of MTBE still present in the aquifer. Since the plume had migrated into an unmonitored section of the Borden Aquifer, numerical modeling and geostatistical methods were applied to define an optimal sampling grid and to improve the level of confidence in the results. A drive point profiling system was used to obtain ground water samples. Numerical modeling with no consideration of degradation pedicted maximum concentrations in excess of 3000 μg/L; field sampling found maximum concentrations of less than 200 μg/L. A mass balance for the remaining MTBE mass in the aquifer eight years after injection showed that only 3% of the original mass remained. Sorption, volatilization, a biotic degradation, and plant uptake are not considered significant attenuation processes for the field conditions. Therefore, we suggest that biodegradation may have played a major role in the attenuation of MTBE within the Borden Aquifer.
81 citations
TL;DR: The use of surfactant solutions for the in situ recovery of residual NAPL in aquifers is increasingly considered as a viable remediation technique as mentioned in this paper, 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.
Abstract: 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 or solubilize 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 The objective of this laboratory study is first to select and characterize polymers that would be suitable for aquifer restoration Their experiments showed that among several polymers, xanthan gum is the most suitable for aquifer remediation An evaluation of 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
79 citations
TL;DR: In this paper, the authors used the ternary phase diagram to predict the general behavior of a cosolvent flood using fractional flow theory, and concluded that the one-dimensional performance of a Cosolvent Flood can be predicted largely by inspection of the Ternary Phase diagram.
Abstract: Cosolvent flooding using water miscible solvents such as alcohols has been proposed as an in situ NAPL remediation technique. This process is conceptually similar to enhanced oil recovery (EOR) using alcohols and some surfactant formulations. As a result of interest in the EOR aspects of these systems, analytical and graphical methods based on fractional flow theory were developed in the petroleum engineering literature for modeling these floods. The existing fractional flow solutions have not been used previously in environmental applications of cosolvent flooding, but they are applicable and provide many useful insights into the process. These applications are discussed, with an emphasis on explaining the mechanisms which tend to mobilize trapped NAPL during a cosolvent flood. The theory provides a simple way to predict the general behavior of a cosolvent flood using the phase diagram. It is concluded that the one-dimensional performance of a cosolvent flood can be predicted largely by inspection of the ternary phase diagram. In particular, the nature of the cosolvent flood depends primarily on the position of the cosolvent injection concentration relative to a critical tie line extension which passes through the plait point, tangent to the binodal curve.
57 citations
TL;DR: In this paper, the authors show that coarse sands are more prone to air channeling and bypassing than fine sands, and that 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.
Abstract: 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.
51 citations
TL;DR: A field study of oxygen‐enhanced biodegradation was carried out in a sandy iron‐rich ground water system contaminated with gasoline hydrocarbons, finding that increased dissolved oxygen enhanced the population of aerobes while the activity of anaerobic sulfate‐reducing bacteria and methanogens decreased.
Abstract: A field study of oxygen-enhanced biodegradation was carried out in a sandy iron-rich ground water system contaminated with gasoline hydrocarbons. Prior to the oxygen study, intrinsic microbial biodegradation in the contaminant plume had depleted dissolved oxygen and created anaerobic conditions. An oxygen diffusion system made of silicone polymer tubing was installed in an injection well within an oxygen delivery zone containing coarse highly permeable sand. During the study, this system delivered high dissolved oxygen (DO) levels (39 mg/L) to the ground water within a part of the plume. The ground water was sampled at a series of monitors in the test zone downgradient of the delivery well to determine the effect of oxygen on dissolved BTEX, ground water geochemistry, and microbially mediated biodegradation processes. The DO levels and Eh increased markedly at distances up to 2.3 m (7.5 feet) downgradient. Potential biofouling and iron precipitation effects did not clog the well screens or porous medium. The increased dissolved oxygen enhanced the population of aerobes while the activity of anaerobic sulfate-reducing bacteria and methanogens decreased. Based on concentration changes, the estimated total rate of BTEX biodegradation rose from 872 mg/day before enhancement to 2530 mg/day after 60 days of oxygen delivery. Increased oxygen flux to the test area could account for aerobic biodegradation of 1835 mg/day of the BTEX. The estimated rates of anaerobic biodegradation processes decreased based on the flux of sulfate, iron (II), and methane. Two contaminants in the plume, benzene and ethylbenzene, are not biodegraded as readily as toluene or xylenes under anaerobic conditions. Following oxygen enhancement, however, the benzene and ethylbenzene concentrations decreased about 98%, as did toluene and total xylenes.
29 citations
TL;DR: In this article, a seven month bioremediation field trial to monitor biodegradation rates of weathered diesel non-aqueous phase liquid (NAPL) contaminating a shallow sand aquifer was conducted.
Abstract: 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.
28 citations
TL;DR: A GIS‐based methodology has been developed to design a ground water monitoring system and implemented for a selected area in Mae‐Klong River Basin, Thailand and makes it possible to choose the best monitoring network from various alternatives based on the prioritization of decision factors.
Abstract: A GIS-based methodology has been developed to design a ground water monitoring system and implemented for a selected area in Mae-Klong River Basin, Thailand. A multicriteria decision-making analysis has been performed to optimize the network system based on major criteria which govern the monitoring network design such as minimization of cost of construction, reduction of kriging standard deviations, etc. The methodology developed in this study is a new approach to designing monitoring networks which can be used for any site considering site-specific aspects. It makes it possible to choose the best monitoring network from various alternatives based on the prioritization of decision factors.
TL;DR: In this paper, an analytical model was developed to predict the removal of volatile organic compounds (VOCs) from ground water by air sparging (AS) using a completely mixed reactor subject to removal of dissolved contaminants by volatilization, advection, and first-order decay.
Abstract: An analytical model was developed to predict the removal of volatile organic compounds (VOCs) from ground water by air sparging (AS). The model treats the air sparging zone as a completely mixed reactor subject to the removal of dissolved contaminants by volatilization, advection, and first-order decay. Nonequilibrium desorption is approximated as a first-order mass transfer process. The model reproduces the tailing and rebound behavior often observed at AS sites, and would normally require the estimation of three site-specific parameters. Dimensional analysis demonstrates that predicting tailing can be interpreted in terms of kinetic desorption or diffusion of aqueous phase contaminants into discrete air channels. Related work is ongoing to test the model against field data.
TL;DR: In this article, an impact drive point method is described for emplacing piezometers in a cobble river bottom where this has previously been difficult without the use of drilling rigs.
Abstract: An impact drive point method is described for emplacing piezometers in a cobble river bottom where this has previously been difficult without the use of drilling rigs. To force the drive point piezometers through cobble, the vibrational impact of an air-powered hammer was carried directly to the drive point by the use of an internal drive rod. After insertion to depth, the drive rod was removed from the lower portion of the piezometer and a standpipe was added to extend the piezometer above the river level. Piezometers installed in this way have permitted water quality analysis and dynamic measurement of vertical potentials in cobble sediments ranging in size from 2.5 to >30 cm and the method has been successfully used in the Columbia River, USA, and Toess River, Switzerland. This innovative method provides information on the hydrodynamics of pore water in highly permeable, cobble deposits that are common in high-energy river and lake bottoms. Piezometers installed using the internal drive rod method facilitate the assessment of the temporal and spatial dynamics of recharge and discharge at the ground water/surface water interface and analyses of the ecological connectivity between the hyporheic zone and surface water of rivers and streams. This informationmore » will lead to improved management decisions related to the nation`s ground water and surface water supplies.« less
TL;DR: Based on the experimental results, it would be advantageous to use a high UG2 biosurfactant concentration, a high pore water velocity, and possibly a flow interruption of more than 15 h in order to reduce the injected volume and the duration of the treatment required.
Abstract: Washing technologies are currently applied for the remediation of contaminated soils. The efficiency of biosurfactants produced by Pseudomonas aeruginosa strains to mobilize some hydrocarbons sorbed on soils has already been demonstrated. However, few studies have been made to define optimal procedures for the injection of these rhamnolipids in soil. This study examines (1) the efficiency of the biosurfactants produced by P. aeruginosa UG2 to mobilize pyrene from a contaminated sandy loam as compared to that of sodium dodecyl sulfate (SDS); (2) the injection procedures that might affect the efficiency of pyrene mobilization using UG2 biosurfactants; and (3) the co-transport of UG2 biosurfactants and pyrene. Based on the experimental results, it would be advantageous to use a high UG2 biosurfactant concentration, a high pore water velocity, and possibly a flow interruption of more than 15 h in order to reduce the injected volume and the duration of the treatment required. The 0.25% UG2 biosurfactant concentration greatly enhanced pyrene transport and could facilitate contaminant recovery.
Abstract: This paper contains the results of a laboratory study that was designed to compare sorption of low (mg/L) concentrations of 11 organic solutes by six polymeric materials (acrylonitrile butadiene styrene [ABS], fluorinated ethylene propylene [FEP], fiberglass-reinforced epoxy [FRE] and fiberglass-reinforced plastic [FRP], polyvinyl chloride [PVC], and poly-tetrafluoroethylene [PTFE]).
During this six-week study, ABS sorbed analytes much more rapidly and to a greater extent than did the other materials, and PVC and FRE sorbed analytes more slowly and to a lesser extent than the other materials tested.
As the study progressed, an increasing number of spurious peaks were found in the high performance liquid chromatography (HPLC) chromatograms of some of our samples, indicating that leaching of some consituents had occurred. By the end of the study, there were 11 additional peaks in the ABS samples, five in the FRP samples, and one in the FRE samples. Analysis by purge and trap gas chromatography/mass spectrometry (GC/MS) of those samples and of well water samples that were exposed to the casings for 500 hours revealed the identity of some of the leached constituents; acrylonitrile and styrene (components of ABS), chloroform and ethylbenzene (an intermediate in the production of styrene) from the ABS pipe, and toluene, 1,1,1-trichloroethane, and ethylbenzene from the FRP casing.
TL;DR: In this paper, flash vacuum stripping of trichloroethylene (TCE) from an anionic surfactant solution in a co-current packed column was studied under rough vacuum conditions.
Abstract: Volatile organic compounds (VOCs) am be removed from contaminated ground water and subsurface media by surfaclant-enhanced remediation processes. For the process to be economically competitive it is necessary to recover and reuse the surfactant from this concentrated solution. The VOC can be removed from this concentrated solution by flash vacuum stripping, leaving the surfactant solution for reuse. In this study, the flash vacuum stripping of trichloroethylene (TCE) from an anionic surfactant solution in a co-current packed column was studied under rough vacuum conditions. The presence of surfactants lead to a reduction in the overall liquid phase volumetric mass transfer coefficient (MTC) of 40 to 95%. depending on flow rate and surfactant concentration at 50°C and 16 kPa. At liquid loading rates of less than 13 cm3/cm2min, the MTC of TCE decreases rapidly with an increase in liquid loading rate, and at liquid loading rates above that, the MTC decreases slightly with an increase in the liquid loading rate. This trend may have been due to foaming. At surfactant concentrations above the critical micelle concentration, the effect of surfactant concentration was not significant at liquid loading rates less than 13 cm3/cm2min. However, beyond that rate, the MTC of TCE decreased drastically with an increase in surfactant concentration. The MTC of TCE increased with an increase in temperature. A large pressure drop (3 to 4 kPa/m) was observed across the packed bed due to foaming.
TL;DR: A large-scale air sparging/soil vapor extraction (AS/SVE) project constructed within coastal plain sediments in New Jersey has demonstrated substantial progress toward remediating ground water through removal of volatile organic compounds (VOCs) as discussed by the authors.
Abstract: A large-scale air sparging/soil vapor extraction (AS/SVE) project constructed within coastal plain sediments in New Jersey has demonstrated substantial progress toward remediating ground water through removal of volatile organic compounds (VOCs). Potential concerns identified prior to project implementation regarding hydraulic mounding, reduction in hydraulic conductivity, development of air channels, and the absence of hydraulic containment were assessed and addressed through testing and operational features incorporated into the project. At the project site, AS/SVE has successfully reduced the presence of many VOCs to undetectable levels, while reducing the concentrations of the remaining VOCs by factors of two to 500. The physical agitation caused by air sparging, and incomplete transformation from sorbed and nonaqueous phases to the vapor phase, appears to temporarily increase VOC concentrations and/or mobility of dense nonaqueous phase liquids (DN APLs) within source areas at the project site, but this is addressed in terms of subsequent removal of VOCs by properly placed downgradient treatment lines and VOCs by properly placed downgradient treatment lines and DNAPL recovery wells. This case study identifies and evaluates project-specific features and provides empirical data for potential comparison to other candidates AS/SVE sites.
TL;DR: In this paper, a graphical method was devised for designing contaminant detection monitoring networks in aquifers, which eliminates bias in detection efficiency among well pairs, thereby improving the overall efficiency of a ground water monitoring network.
Abstract: A graphical method was devised for designing contaminant detection monitoring networks in aquifers. The approach eliminates bias in detection efficiency among well pairs, thereby improving the overall efficiency of a ground water monitoring network. In the equidistant configurations derived by the graphical approach, all wells are located the same distance from a landfill, but the distance is measured parallel to ground water flow, Measured perpendicular to ground water flow, there is also an equal spacing between wells in an equidistant network. A simulation model was used to compare an equidistant network to a peripheral monitoring configuration, in which wells were spaced evenly along the downgradient boundaries of a landfill. The equidistant network yielded a 12.4% higher detection efficiency and also facilitated earlier release detection. In practice, the graphical approach that yields equidistant configurations can be used to identify candidate monitoring networks to detect potential releases from landfills.
TL;DR: A full-scale ground water circulation well (GCW) system was installed and operated to demonstrate in situ remediation of soil and ground water impacted with a mixture of chlorinated and nonchlorinated organic compounds at a Superfund site in upstate New York as mentioned in this paper.
Abstract: A full-scale ground water circulation well (GCW) system was installed and operated to demonstrate in situ remediation of soil and ground water impacted with a mixture of chlorinated and nonchlorinated organic compounds at a Superfund site in upstate New York. System performance and applicability under site-specific conditions were evaluated based on the system`s ability to meet the New York State Department of Environmental Conservation (NYSDEC) cleanup goals for target compounds in ground water and soil. Contaminants from the unsaturated zone were mobilized (volatilized) by one-way vacuum extraction, and treated via enhanced biodegradation. In the saturated zone, contaminants were mobilized by soil flushing and treated by a combination of air stripping and biodegradation. An in situ aqueous phase bioreactor, and an ex situ gas phase bioreactor, were integrated into the system to enhance treatment via bioremediation. After 15 months of operation, the mass of target contaminants in soil and ground water combined had been reduced by 75%. Removal by biological mechanisms ranged from 35% to 56% of the total observed mass reduction. The in situ and the ex situ bioreactors mineralized 79% and 76%, respectively, of their target biodegradable contaminant loads. Results indicate that some mass reduction in target contaminants maymore » have been from aerobic and anaerobic processes within the circulation cell. Nonchlorinated compounds were relatively easy to mobilize and treat when compared to chlorinated compounds. The data collected during the 15-month study indicate that remediation could be accomplished at the Sweden-3 Chapman site using the technology tested.« less
TL;DR: This report provides the first evidence that DIPA is biodegraded under anaerobic conditions, and the data suggest that biodegradation may contribute to DipA attenuation under aerobic and anaer aerobic conditions in aquifers contaminated with this sour gas treatment chemical.
Abstract: The potential for aerobic and anaerobic biodegradation of a sour gas treatment chemical, diisopropanolamine (DIPA), was studied using contaminated aquifer materials from three sour gas treatment sites in western Canada. DIPA was found to be readily consumed under aerobic conditions at 8°C and 28°C in shake flask cultures incubated with aquifer material from each of the sites, and this removal was characterized by first-order kinetics. In addition, DIPA biodegradation was found to occur under nitrate-, Min(IV)., and Fe(III)-reducing conditions at 28°C, and in some cases at 8°C, in laboratory microcosms, DIPA loss corresponded to consumption of nitrate, and production of Mn(II) and Fe(II) in viable microcosms compared to corresponding sterile controls. A threshold DIPA concentration near 40 mg/L was observed in the anaerobic microcosms. This report provides the first evidence that DIPA is biodegraded under anaerobic conditions, and our data suggest that biodegradation may contribute to DIPA attenuation under aerobic and anaerobic conditions in aquifers contaminated with this sour gas treatment chemical.
TL;DR: In this paper, a method is described for estimating key soil and LNAPL properties by nonlinear regression of vertical profiles of lnAPL saturation, which is relatively fast, cost effective, and amenable to quantitative analysis of uncertainty.
Abstract: A method is described for estimating key soil and LNAPL properties by nonlinear regression of vertical profiles of LNAPL saturation. The method is relatively fast, cost effective, and amenable to quantitative analysis of uncertainty. Optionally, the method allows statistical determination of best-fit values for the Van Genuchten capillary parameters (n, {alpha}{sub oil-water}, and {alpha}{sub oil-air}), residual water saturation, and LNAPL density. The sensitivity of the method was investigated by fitting field LNAPL saturation profiles and then determining the variation in misfit (mean square residual) as a function of parameter value for each parameter. Using field data from a sandy aquifer, the fitting statistics were found to be highly sensitive to LNAPL density, {alpha}{sub oil-water}, and {alpha}{sub oil-air}, moderately sensitive to the Van Genuchten n value, and weakly sensitive to residual water saturation. The regression analysis also provides information that can be used to estimate uncertainty in the estimated parameters, which can then be used to estimate uncertainty in calculated values of specific volume.
TL;DR: In this paper, traces of MTBE in ground water (>10 ppb) do not necessarily indicate recent gasoline contamination, and therefore, they do not indicate the presence of gasoline contamination.
Abstract: “Traces of MTBE in ground water (>10 ppb) do not necessarily indicate recent gasoline contamination.”
TL;DR: In this paper, five inorganic geochemical data sets with ion balances less than or equal to 5% (for different hydrogeologic basins in Mexico) were used to construct specific conductance (SC) vs. total dissolved solids (TDS) curves for each aquifer.
Abstract: Five inorganic geochemical data sets with ion balances less than or equal to 5% (for different hydrogeologic basins in Mexico) were used to construct specific conductance (SC) vs. total dissolved solids (TDS) curves for each aquifer. These curves allow one to proxy the specific conductance for inorganic water quality. The data from these five curves were integrated to form a “global” curve for Mexico. The equation that defines the line is SC = 1.40 TDS + 18. We propose that, in addition to allowing ground water monitoring, establishing a SC vs. TDS curve may be implemented to monitor drinking water supplies such as wells and reservoirs. If anomalously high values are observed, this would warrant detailed geochemical sampling.
TL;DR: In situ vertical circulation column (ISVCC) as discussed by the authors is a cylindrical containment system consisting of an instrumented steel cylinder used for experimental ground water studies in sandy aquifers.
Abstract: 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. 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 B{sub 12} 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.
TL;DR: In this paper, a finite element model coupled with a particle tracking routine was developed to analyze the flow and transport dynamics near a high-capacity irrigation well, and 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.
Abstract: 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.
TL;DR: In this paper, a two-year pilot study involving the recharge of a ground water basin with reclaimed water was completed in the city of Los Angeles and the results showed greater than 4-log removal of coliform bacteria, up to 87% reduction in TOC, and compliance of the product water with federal and state drinking water standards.
Abstract: A two-year pilot study involving the recharge of a ground water basin with reclaimed water was completed in the city of Los Angeles. The city's Department of Water and Power is planning to initiate several ground water recharge projects using reclaimed water in the near future. One such project is the Headworks Recharge Project, the focus of this paper, Approximately 1 cfs of the Los Angeles (LA) River water comprised of 70% tertiary treated reclaimed water was recharged on a two-day wet and five-day dry cycle. The recharge water was then extracted from the basin approximately 1000 feet downgradient. Results showed greater than 4-log removal of coliform bacteria, up to 87% reduction in TOC, and compliance of the product water with federal and state drinking water standards. Model simulation showed after 15 years of recharging 3000 acre-feet per year of the LA River water and extracting about 10,000 acre-feet from the basin, the product water would contain from 5% to 15% reclaimed water. This is well below the maximum allowable limit of 20% stipulated by the California regulation.
TL;DR: In this paper, the authors used simulation to simulate ground water flow through reactive barriers of lower hydraulic conductivity than the surrounding aquifer to determine the plume capture widths, and showed that for practical values of barrier thickness and plume width, hydraulic conductivities ten-fold less than that of the aquifer can be accommodated by making the width of the barrier approximately 20% greater than the upgradient width of a plume.
Abstract: Modeling was performed to simulate ground water flow through reactive barriers of lower hydraulic conductivity than the surrounding aquifer to determine the plume capture widths. As a plume approaches such a barrier, it spreads laterally. Therefore, to intercept an entire plume, the barrier must be wider than the upgradient width of the undisturbed plume. The results indicate that, for practical values of barrier thickness and plume width, hydraulic conductivities ten-fold less than that of the aquifer can be accommodated by making the width of the barrier approximately 20% greater than the upgradient width of the plume. Barrier hydraulic conductivities one-hundred-fold less than that of the aquifer may require barrier widths up to twice the width of the upgradient plume for plumes 100 feet wide (33 m) and as little as 1.1 times for plumes 1000 feet wide (325 m). The results presented here lend support to the view that novel emplacement methods that create zones of slightly lower hydraulic conductivity than the native aquifer may be viable alternatives to the excavation-and-backfill approaches which have thus far been used for installing permeable reactive barriers.
TL;DR: In this paper, the authors describe a well design that combines a ground water well with gas sampling ports by attaching the gas sampling tubing and ports to the exterior of the casing, which reduces physical interference between the various monitoring equipment, and allows simultaneous remediation and monitoring in a single well.
Abstract: Waste disposal sites with volatile organic compounds (VOCs) frequently contain contaminants that are present in both the ground water and vadose zone Vertical sampling is useful where transport of VOCs in the vadose zone may effect ground water and where steep vertical gradients in chemical concentrations are anticipated Designs for combination ground water and gas sampling wells place the tubing inside the casing with the sample port penetrating the casing for sampling This physically interferes with pump or sampler placement This paper describes a well design that combines a ground water well with gas sampling ports by attaching the gas sampling tubing and ports to the exterior of the casing Placement of the tubing on the exterior of the casing allows exact definition of gas port depth, reduces physical interference between the various monitoring equipment, and allows simultaneous remediation and monitoring in a single well The usefulness and versatility of this design was demonstrated at the Idaho National Engineering and Environmental Laboratory (INEEL) with the installation of seven wells with 53 gas ports, in a geologic formation consisting of deep basalt with sedimentary interbeds at depths from 72 to 178 m below land surface The INEEL combination well design is easy to construct, install, and operate