Kirk Hatfield

Field‐scale evaluation of in situ cosolvent flushing for enhanced aquifer remediation

A comprehensive, field-scale evaluation of in situ cosolvent flushing for enhanced remediation of nonaqueous phase liquid (NAPL)-contaminated aquifers was performed in a hydraulically isolated test cell (about 4.3 m × 3.6 m) constructed at a field site at Hill Air Force Base, Utah. This sand-gravel-cobble surficial aquifer, underlain by a deep clay confining unit at about 6 m below ground surface, was contaminated with a multicomponent NAPL as a result of jet fuel and chlorinated solvent disposal during the 1940s and 1950s. The water table within the test cell was raised to create a 1.5 m saturated flow zone that contained the NAPL smear zone. The cosolvent flushing test consisted of pumping about 40,000 L (approximately nine pore volumes) of a ternary cosolvent mixture (70% ethanol, 12% n-pentanol, and 18% water) through the test cell over a period of 10 days, followed by flushing with water for another 20 days. Several methods for assessing site remediation yielded consistent results, indicating that on the average >85% mass of the several target contaminants was removed as a result of the cosolvent flushing; NAPL constituent removal effectiveness was greater (90–99+%) in the upper 1-m zone, in comparison to about 70–80% in the bottom 0.5-m zone near the clay confining unit. Various interacting factors that control the hydrodynamic sweep efficiency, and the NAPL removal effectiveness during cosolvent flushing in this unconfined aquifer are discussed.

Use of humic substances to remediate polluted environments : from theory to practice

Preface. Introduction. Contributors. Part 1. Remedial properties of humic substances: general considerations and problems in addressing needs of environmental remediation. 1. Remediation chemistry of humic substances: theory and implications for technology I.V. Perminova, K. Hatfield. 2. Soil organic matter and protective functions of humic substances in the biosphere D.S. Orlov and L.K. Sadovnikova. 3. Chemical stoichiometry and molecular level mechanisms as support for future predictive engineering calculations, D.S. Gamble et al. Part 2. Complexing interactions of humic substances with heavy metals and radionuclides and their remedial implementation. 4. Interactions of humic substances with trace metals and their stimulatory effects on plant growth A. Kaschl, Y. Chen. 5. Influence of UV-oxidation on the metal complexing properties of NOM F.H. Frimmel et al. 6. Role of humic substances in the complexation and detoxification of heavy metals: case study of the Dnieper reservoirs P.N. Linnik, T.A. Vasilchuk. 7. Complexation of radionuclides with humic substances V. Moulin. 8. Humic acids as barriers in actinide migration in the environment S.N. Kalmykov et al. 9. The use of humates for detoxification of soils contaminated with heavy metals O.S. Bezuglova, A.V. Shestopalov. Part 3. Sorptive-partitioning interactions of humic substances with organic ecotoxicants and their implementation for remediation technologies. 10. Utilization of immobilized humic organic matter for in-situ subsurface remediation G.U. Balcke et al. 11. The use of aqueous humic substances for in-situ remediation of contaminated aquifers D.R. Van Stempvoort et al. 12. Advantages of in situ remediation of polluted soil and practical problems encountered during its performance J.F. De Kreuk. 13. Wastewater treatment using modified natural zeolites P. Princz et al. Part 4. Impact on physiological functions of living organisms and on microbial transformations ofecotoxicants. 14. Mitigating activity of humic substances: direct influence on biota N.A. Kulikova et al. 15. Cytogenetic effects of humic substances and their use for remediation of polluted environments A. Gorova et al. 16. Influence of metal ions on the activity of soil humics-enzyme complexes S. Jorobekova et al. 17. Microbial redox reactions mediated by humus and structurally related quinines J. A. Field, F.J. Cervantes. 18. Enhanced humification of TNT H. Thomas, A. Gerth. 19. Commercial humates from coal and their influence on soil properties and initial plant development O.S. Iakimenko. 20. Impact of humic substances on plants in polluted environments: implications for phytoremediation technologies M.M. Kharitonov et al. Part 5. Quantifying structure and properties of humic substances and example studies on design of humic materials of the desired properties. 21. Molecular level structural analysis of natural organic matter and of humic substances by multinuclear and higher dimensional NMR spectroscopy N. Hertkorn, A. Kettrup. 22. Understanding capillary electrophoretic separation processes to characterize humic substances and their interactions with pollutants Ph. Schmitt-Kopplin, A. Kettrup. 23. Ozone application for modification of humates and lignins M.M. Ksenofontova et al. 24. Synthesis, metal-binding properties and detoxifying ability of sulfonated humic acids M.V. Yudov et al. Author Index. Subject Index.

Controlled release, blind test of DNAPL remediation by ethanol flushing

A dense nonaqueous phase liquid (DNAPL) source zone was established within a sheet-pile isolated cell through a controlled release of perchloroethylene (PCE) to evaluate DNAPL remediation by in-situ cosolvent flushing. Ethanol was used as the cosolvent, and the main remedial mechanism was enhanced dissolution based on the phase behavior of the water-ethanol-PCE system. Based on the knowledge of the actual PCE volume introduced into the cell, it was estimated that 83 L of PCE were present at the start of the test. Over a 40-day period, 64% of the PCE was removed by flushing the cell with an alcohol solution of approximately 70% ethanol and 30% water. High removal efficiencies at the end of the test indicated that more PCE could have been removed had it been possible to continue the demonstration. The ethanol solution extracted from the cell was recycled during the test using activated carbon and air stripping treatment. Both of these treatment processes were successful in removing PCE for recycling purposes, with minimal impact on the ethanol content in the treated fluids. Results from pre- and post-flushing partitioning tracer tests overestimated the treatment performance. However, both of these tracer tests missed significant amounts of the PCE present, likely due to inaccessibility of the PCE. The tracer results suggest that some PCE was inaccessible to the ethanol solution which led to the inefficient PCE removal rates observed. The flux-averaged aqueous PCE concentrations measured in the post-flushing tracer test were reduced by a factor of 3 to 4 in the extraction wells that showed the highest PCE removal compared to those concentrations in the pre-flushing tracer test.

Changes in contaminant mass discharge from DNAPL source mass depletion: Evaluation at two field sites

Changes in contaminant fluxes resulting from aggressive remediation of dense nonaqueous phase liquid (DNAPL) source zone were investigated at two sites, one at Hill Air Force Base (AFB), Utah, and the other at Ft. Lewis Military Reservation, Washington. Passive Flux Meters (PFM) and a variation of the Integral Pumping Test (IPT) were used to measure fluxes in ten wells installed along a transect down-gradient of the trichloroethylene (TCE) source zone, and perpendicular to the mean groundwater flow direction. At both sites, groundwater and contaminant fluxes were measured before and after the source-zone treatment. The measured contaminant fluxes (J; ML(-2)T(-1)) were integrated across the well transect to estimate contaminant mass discharge (M(D); MT(-1)) from the source zone. Estimated M(D) before source treatment, based on both PFM and IPT methods, were approximately 76 g/day for TCE at the Hill AFB site; and approximately 640 g/day for TCE, and approximately 206 g/day for cis-dichloroethylene (DCE) at the Ft. Lewis site. TCE flux measurements made 1 year after source treatment at the Hill AFB site decreased to approximately 5 g/day. On the other hand, increased fluxes of DCE, a degradation byproduct of TCE, in tests subsequent to remediation at the Hill AFB site suggest enhanced microbial degradation after surfactant flooding. At the Ft. Lewis site, TCE mass discharge rates subsequent to remediation decreased to approximately 3 g/day for TCE and approximately 3 g/day for DCE approximately 1.8 years after remediation. At both field sites, PFM and IPT approaches provided comparable results for contaminant mass discharge rates, and show significant reductions (>90%) in TCE mass discharge as a result of DNAPL mass depletion from the source zone.

Comparison of univariate and transfer function models of groundwater fluctuations

Seasonal autoregressive integrated moving average (SARIMA) univariate models and single input-single output transfer function (SARIMA with externalities or SARIMAX) models of groundwater head fluctuations are developed for 21 Upper Floridan aquifer observation wells in northeast Florida. These models incorporate empirical relationships between rainfall input and head response based on historical correlations and cross correlations between these two time series. The magnitude of the forecast error terms indicates that the SARIMA and SARIMAX models explain an average of 84–87% of the variation observed in the monthly piezometric head levels for 1-month lead forecasts. Thus the models account for the dominant processes which affect temporal groundwater fluctuations. Both the SARIMA and SARIMAX models provide unbiased forecasts of piezometric head levels; however, the SARIMAX models produce more accurate forecasts (i.e., smaller forecast probability limits) than the SARIMA models, particularly as lead time increases. Modeling efforts reveal consistent model structures over the study region, with local hydrologic and geologic conditions causing site-specific variability in the time series model parameters.

Optimal estimation of residual non–aqueous phase liquid saturations using partitioning tracer concentration data

Stochastic methods are applied to the analysis of partitioning and nonpartitioning tracer breakthrough data to obtain optimal estimates of the spatial distribution of subsurface residual non–aqueous phase liquid (NAPL). Uncertainty in the transport of the partitioning tracer is assumed to result from small-scale spatial variations in a steady state velocity field as well as spatial variations in NAPL saturation. In contrast, uncertainty in the transport of the nonpartitioning tracer is assumed to be due solely to the velocity variations. Partial differential equations for the covariances and cross cpvariances between the partitioning tracer temporal moments, nonpartitioning tracer temporal moments, residual NAPL saturation, pore water velocity, and hydraulic conductivity fields are derived assuming steady flow in an infinite domain [Gelhar, 1993] and the advection-dispersion equation for temporal moment transport [Harvey and Gorelick, 1995]. These equations are solved using a finite difference technique. The resulting covariance matrices are incorporated into a conditioning algorithm which provides optimal estimates of the tracer temporal moments, residual NAPL saturation, pore water velocity, and hydraulic conductivity fields given available measurements of any of these random fields. The algorithm was tested on a synthetically generated data set, patterned after the partitioning tracer test conducted at Hill AFB by Annable et al. [1997]. Results show that the algorithm successfully estimates major features of the random NAPL distribution. The performance of the algorithm, as indicated by analysis of the “true” estimation errors, is consistent with the theoretical estimation errors predicted by the conditioning algorithm.

REMEDIATION CHEMISTRY OF HUMIC SUBSTANCES: THEORY AND IMPLICATIONS FOR TECHNOLOGY

An overview is given of the interactions encountered between humic substances (HS), ecotoxicants, and living organisms in the context of environmental remediation. The most important interactions identified include: binding interactions affecting chemical speciation and bioavailability of contaminants; interfacial interactions altering physical speciation or interphase partitioning of ecotoxicants; abiotic-biotic redox interactions that influence metabolic pathways coupled to pollutants; and finally direct and indirect interactions coupled to various physiological functions of living organisms. Because humics are polyfunctional, they can operate as binding agents and detoxicants, sorbents and flushing agents, redox mediators of abiotic and biotic reactions, nutrient carriers, bioadaptogens, and growth-stimulators. It is shown that these functions possess significant utility in the remediation of contaminated environments and as such humic-based reactions pertinent to permeable reactive barriers, in situ flushing, bioremediation, and phytoremediation are examined in detail. Finally, this chapter introduces the novel concept of “designer humics” which are a special class of customized humics of the reduced structural heterogeneity and of the controlled size. They are developed and deployed to carry out one or more of the above in situ functions in an optimum manner and for the purpose of enhancing the efficacy of one or more remediation technologies. Designer humics possess specified reactive properties obtained by chemical modification and cross-linking of the humic backbone. This new class of reactive agents portend new opportunities for achieving enhanced remediation and for quantifying remediation performance. The latter is described in the context of the passive flux meter technology developed for direct measuring fluxes of contaminants and biomass.

Evaluation of in situ cosolvent flushing dynamics using a network of spatially distributed multilevel samplers

A network of multilevel samplers was used to evaluate the spatial patterns in contaminant extraction during an in situ cosolvent flushing field test. The study was conducted in an isolation test cell installed in a fuel contaminated site at Hill Air Force Base, Utah. Partitioning tracer tests, conducted before and after the cosolvent flush, were used to estimate the spatial distribution of nonaqueous phase liquids (NAPL) and the effectiveness of cosolvent flushing for removing NAPL. Samples collected during the cosolvent flushing test were used to visualize the extraction process. The results of these two analyses showed similar spatial trends in mass removal and were in general agreement with observations based on soil core data. In general, the cosolvents were more effective in the upper portion of the flow domain and had slightly lower mass removal effectiveness in the lower portion of the flow domain. In this region, tracers indicated slower transport rates and higher NAPL saturations. The spatial analysis also indicated that cosolvent was trapped in the capillary fringe increasing the time required to displace the cosolvent from the aquifer. These results demonstrate the value of spatial information for performance assessment and improving in situ flushing design strategies.

Integration of traditional and innovative characterization techniques for flux-based assessment of Dense Non-aqueous Phase Liquid (DNAPL) sites

Key attributes of the source zone and the expanding dissolved plume at a trichloroethene (TCE) site in Australia were evaluated using trends in groundwater monitoring data along with data from on-line volatile organic compound (VOC) samplers and passive flux meters (PFMs) deployed in selected wells. These data indicate that: (1) residual TCE source mass in the saturated zone, estimated using two innovative techniques, is small ( approximately 10 kg), which is also reflected in small source mass discharge ( approximately 3 g/day); (2) the plume is disconnecting, based on TCE concentration contours and TCE fluxes in wells along a longitudinal transect; (3) there is minimal biodegradation, based on TCE mass discharge of approximately 6 g/day at a plume control plane approximately 175 m from source, which is also consistent with aerobic geochemical conditions observed in the plume; and (4) residual TCE in the vadose zone provides episodic inputs of TCE mass to the plume during infiltration/recharge events. TCE flux data also suggest that the small residual TCE source mass is present in the low-permeability zones, thus making source treatment difficult. Our analysis, based on a synthesis of the archived data and new data, suggests that source treatment is unwarranted, and that containment of the large TCE plume (approximately 1.2 km long, approximately 0.3 km wide; 17 m deep; approximately 2000-2500 kg TCE mass) or institutional controls, along with a long-term flux monitoring program, might be necessary. The flux-based site management approach outlined in this paper provides a novel way of looking beyond the complexities of groundwater contamination in heterogeneous domains, to make intelligent and informed site decisions based on strategic measurement of the appropriate metrics.

Estimation of spatially variable residual nonaqueous phase liquid saturations in nonuniform flow fields using partitioning tracer data

Estimates of spatially variable residual NAPL saturations SN are obtained in heterogeneous porous media using first temporal moments of breakthrough curves (BTCs) obtained from multilevel samplers during in situ partitioning tracer tests. An approach is adopted in which the distribution of the log NAPL/water volumetric ratio (Y = ln [SN/(1 − SN∥]) and log hydraulic conductivity (F = ln K) are treated as spatially correlated random fields. A nonlinear Gauss-Newton search technique is used to identify the spatial distribution of Y that minimizes the weighted sum of the deviation of the temporal moment predictions from their measured values and the deviation of the estimate of Y from its prior estimate obtained from the temporal moments of extraction well BTCs. Sensitivities required for the algorithm are obtained using a coupled flow and transport adjoint sensitivity method. In addition to obtaining optimal estimates for the spatial distribution of Y, the method also provides the estimation error covariance. The estimation error covariance can be used to evaluate the information that may be obtained from alternate pumping and monitoring configurations for tracer tests designed to detect NAPL in the subsurface. To this end, we tested the method using two different NAPL distributions (one with a random spatially correlated field and a second that was a block of NAPL) and three different pumping configurations (a double five-spot pattern, an inverted double five-spot pattern, and a line-drive pattern). The results show that measured temporal moments are more sensitive to Y in the double five-spot and inverted double five-spot patterns, and estimates produced in these configurations are slightly superior to those produced in the line-drive pattern.