Andrea Leeson

Chlorinated Ethene Source Remediation: Lessons Learned

Chlorinated solvents such as trichloroethene (TCE) and tetrachloroethene (PCE) are widespread groundwater contaminants often released as dense nonaqueous phase liquids (DNAPLs). These contaminants are difficult to remediate, particularly their source zones. This review summarizes the progress made in improving DNAPL source zone remediation over the past decade, and is structured to highlight the important practical lessons learned for improving DNAPL source zone remediation. Experience has shown that complete restoration is rare, and alternative metrics such as mass discharge are often useful for assessing the performance of partial restoration efforts. Experience also has shown that different technologies are needed for different times and locations, and that deliberately combining technologies may improve overall remedy performance. Several injection-based technologies are capable of removing a large fraction of the total contaminant mass, and reducing groundwater concentrations and mass discharge by 1 to 2 orders of magnitude. Thermal treatment can remove even more mass, but even these technologies generally leave some contamination in place. Research on better delivery techniques and characterization technologies will likely improve treatment, but managers should anticipate that source treatment will leave some contamination in place that will require future management.

Bioaugmentation for groundwater remediation

Bioaugmentation for Groundwater Remediation: An Overview.- Dehalococcoides and Reductive Dechlorination of Chlorinated Solvents.- Production and Handling of Dehalococcoides Bioaugmentation Cultures.- Bioaugmentation with Dehalococcoides: A Decision Guide.- Bioaugmentation Considerations.- Microbial Monitoring During Bioaugmentation with Dehalococcoides.- Bioaugmentation for Aerobic Degradation of CIS-1,2-Dichlorothene.- Bioaugmentation for the In Situ Aerobic Cometabolism of Chlorinated Solvents.- Bioaugmentation with Pseudomonas Stutzeri KC for Remediation of Carbon Tetrachloride.- Bioaugmentation for MTBE.- Economics and Valuation of Bioaugmentation.- Research Needs for Bioaugmentation.- Index.

Advances in In Situ Air Sparging/Biosparging

In situ air sparging (IAS) is a technology commonly used for treatment of submerged source zones and dissolved groundwater plumes. The acceptance of IAS by regulatory agencies, environmental consultants, and industry is remarkable considering the degree of skepticism initially surrounding the technology in the early 1990s. Much has been learned and reported in the literature since that time, but it appears that practice has changed little. In particular, conventional pilot testing, design, and operation practices reflect a lack of appreciation of the complex phenomena governing IAS performance and the unforgiving nature of this technology. Many systems are poorly monitored and likely to be inefficient or ineffective. Key lessons-learned since the early 1990s are reviewed and their implications for practice are discussed here. Of particular importance are issues related to: (a) the understanding of air flow distributions and the effects of geology and injection flowrate, (b) the need to characterize air flow distributions at the pilot- and field-scale, (c) how changes in operating conditions (e.g., pulsing) can affect performance improvements and reduce equipment costs, and (d) how conventional monitoring approaches are incapable of assessing if systems are performing as designed.

Diagnosis of in situ air sparging performance using transient groundwater pressure changes during startup and shutdown

Groundwater pressure measurements during startup and shutdown of in situ air sparging (IAS) systems are used to diagnose air flow behavior below the water table. The magnitude of the pressure response provides insight into the permeability of the zone into which the air is flowing. The duration of elevated pressures during startup and reduced pressures during shutdown indicate the extent to which air is being trapped below the water table by lower-permeability layers. The pressure measurements can be easily and quickly repeated and as a result are useful for both pilot tests and for optimizing operating conditions of existing IAS systems. Whether used alone or in conjunction with other diagnostic tools, pressure measurements are an important tool for assessing IAS performance.

A Practical Approach for the Selection, Pilot Testing, Design, and Monitoring of In Situ Air Sparging/Biosparging Systems

The use of in situ air sparging (IAS) has increased rapidly since the early 1990s, and it is now likely to be the most practiced engineered in situ remediation option when targeting the treatment of hydrocarbon-impacted aquifers. To date, IAS system design has remained largely empirical, with significant variability in approaches and results. Here, the valuable knowledge gained from IAS studies and applications over the past decade has been integrated into a new paradigm for feasibility assessment, pilot testing, design, and operation. The basis for this Design Paradigm, the initial feasibility assessment, monitoring, and the overall design approach are discussed in detail here; other referenced documents contain the details of specific recommended activities. The proposed design approach is unique in that it contains two design routes; the first is a non-site-specific approach requiring minimal site characterization and testing (Standard Design Approach), while the second is a more site-specific approach (Site-Specific Design Approach).

Diagnostic Tools for Integrated In Situ Air Sparging Pilot Tests

In situ air sparging (IAS) pilot test procedures have been developed that provide rapid, on-site information about IAS performance. The standard pilot test consists of six activities conducted to look for indicators of infeasibility and to characterize the air distribution to the extent necessary to make design decisions about IAS well placement. In addition, safety hazards that need to be addressed prior to full-scale design are identified. Two additional pilot test activities are described in those cases where air distribution must be more precisely defined. The test activities include both chemical tests (tracking contaminant concentrations, dissolved oxygen and tracers) and physical tests (air flow rate and injection pressure, groundwater pressure response). Pilot test data from Eielson Air Force Base, Alaska illustrates implementation of the pilot test and interpretation of the data.

Helium Tracer Tests for Assessing Contaminant Vapor Recovery and Air Distribution During In Situ Air Sparging

Helium tracer tests are used as an alternative to soil-gas pressure measurements to assess the effectiveness of soil vapor extraction (SVE) systems for capturing contaminant vapors liberated by in situ air sparging (IAS). The tracer approach is simple to conduct and provides more direct and reliable measures than the soil-gas pressure approach. The tracer test described here can be used to both determine SVE system capture efficiency and to evaluate air distribution during IAS pilot tests. The tests can also be conducted on operating, full-scale systems to confirm system performance. In addition, the tests can be easily repeated, which allows system parameters to be modified and the impact of those modifications to be quickly assessed. Whether used alone or in conjunction with other diagnostic tools, helium tracer tests provide an important measure of IAS system performance.

Optimizing bioventing in shallow vadose zones and cold climates

Abstract This paper describes a bioventing study design and initial activities applied to a JP-4 jet fuel spill at Eielson Air Force Base, Alaska. The primary objectives of the project were to investigate the feasibility of using bioventing technology to remediate JP-4 jet fuel contamination in a sub-arctic environment and to determine to what degree the biodegradation rate of JP-4 soil contaminants could be enhanced by increasing soil temperature, both actively by circulating heated groundwater and passively by utilizing solar energy. Biodegradation rates at the bioventing site remained relatively high during the winter months in the active-warming test plot and were consistently higher than those observed in the passive-warming and control test plots. These studies suggest that an active-warming system operated in conjunction with bioventing is a useful method for remediating fuel-contaminated areas in cold climates.

Dispersion of Respirable Aerosols in a Fermenter and their Removal in an Exhaust System

Abstract When strains of bacteria and fungi are changed through genetic engineering and are used in industrial processes to bring about improved product yields, these new strains may expose humans to new types of RNA or DNA. Some industrial fermentation processes involve materials that are potential health hazards if aerosolized, released to the ambient environment, and inhaled by workers nearby. To study the potential release of aerosol from a fementer, a measurement system was developed to explore respirable aerosol formation characteristics and controllability. The system, which provides real-time information on the concentrations and size distributions of 0.1 to 3.0-μm-diameter residues of aerosolized liquid droplets, was used to investigate the influence of aeration rate, agitation rate, bacterial growth, and the addition of antifoaming agent on aerosol concentration in the head space and two locations in the exhaust system of an industrial pilot scale seed fermenter equipped with a mechanical foam b...

Field Test of Nonfuel Hydrocarbon Bioventing in Clayey-Sand Soil

Abstract A pilot-scale bioventing test was conducted at the Greenwood Chemical Superfund Site in Virginia. The characteristics of the site included clayey-sand soils and nonfuel organic contamination such as acetone, toluene, and naphthalene in the vadose zone. Based on the results of an earlier treatability study, an 80-ft by 80-ft (24-m by 24-m) treatment plot was established in a 35-ft (11-m) vadose zone. Air was injected at a low flowrate for 15 months. Performance monitoring included initial and final soil analysis and periodic soil gas analysis and in situ respiration tests. After beginning aeration, soil gas oxygen levels in the plot rose slowly, reaching 10% at virtually all measured locations in approximately 4 months. In situ respiration rates decreased with time indicating that the site was being cleaned. Soil concentrations of the target contaminants decreased significantly during the test, with > 98% confidence for acetone, naphthalene, benzene, chlorobenzene, and toluene, and > 90% confidenc...