Michael C. Kavanaugh

MTBE and Other Oxygenates: Environmental Sources, Analysis, Occurrence, and Treatment

The production and use of fuel oxygenates has increased dramatically since the early 1990s due to federal and state regulations aimed to improve air quality. Currently, methyl tert-butyl ether (MTBE) is the most widely used oxygenate in gasoline, followed by ethanol. Widespread use of oxygenates in gasoline has been accompanied by widespread release of these materials into the environment. This manuscript provides a review of environmental sources of MTBE and alternative oxygenates, analytical methods available for their detection in environmental samples, their occurrence in the environment with a focus on groundwater, and treatment methods for their removal from gasoline-contaminated water. Accidental gasoline releases from underground storage tanks and pipelines are the most significant point sources of oxygenates in groundwater. Because of their polar characteristics, oxygenates migrate through aquifers with minimal retardation, raising great concerns nationwide of their potential for reaching drinking water sources. As a group, fuel oxygenates present distinct analytical and sample preparation issues. Conventional procedures for the analysis of gasoline constituents have been shown to be insensitive for fuel oxy

Bioremediation of MTBE: a review from a practical perspective

The addition of methyl tert-butyl ether (MTBE) to gasoline has resulted in public uncertainty regarding the continued reliance on biological processes for gasoline remediation. Despite this concern, researchers have shown that MTBE can be effectively degraded in the laboratory under aerobic conditions using pure and mixed cultures with half-lives ranging from 0.04 to 29 days. Ex-situ aerobic fixed-film and aerobic suspended growth bioreactor studies have demonstrated decreases in MTBE concentrations of 83% and 96% with hydraulic residence times of 0.3 hrs and 3 days, respectively. In microcosm and field studies, aerobic biodegradation half-lives range from 2 to 693 days. These half-lives have been shown to decrease with increasing dissolved oxygen concentrations and, in some cases, with the addition of exogenous MTBE-degraders. MTBE concentrations have also been observed to decrease under anaerobic conditions; however, these rates are not as well defined. Several detailed field case studies describing the use of ex-situ reactors, natural attenuation, and bioaugmentation are presented in this paper and demonstrate the potential for successful remediation of MTBE-contaminated aquifers. In conclusion, a substantial amount of literature is available which demonstratesthat the in-situ biodegradation of MTBE is contingent on achieving aerobic conditions in the contaminated aquifer.

In-situ determination of field-scale NAPL mass transfer coefficients: Performance, simulation and analysis

Better estimates of non-aqueous phase liquid (NAPL) mass, its persistence into the future, and the potential impact of source reduction are critical needs for determining the optimal path to clean up sites impacted by NAPLs. One impediment to constraining time estimates of source depletion is the uncertainty in the rate of mass transfer between NAPLs and groundwater. In this study, an innovative field test is demonstrated for the purpose of quantifying field-scale NAPL mass transfer coefficients (kl(N)) within a source zone of a fuel-contaminated site. Initial evaluation of the test concept using a numerical model revealed that the aqueous phase concentration response to the injection of clean groundwater within a source zone was a function of NAPL mass transfer. Under rate limited conditions, NAPL dissolution together with the injection flow rate and the radial distance to monitoring points directly controlled time of travel. Concentration responses observed in the field test were consistent with the hypothetical model results allowing field-scale NAPL mass transfer coefficients to be quantified. Site models for groundwater flow and solute transport were systematically calibrated and utilized for data analysis. Results show kl(N) for benzene varied from 0.022 to 0.60d(-1). Variability in results was attributed to a highly heterogeneous horizon consisting of layered media of varying physical properties.

Assessing the Current and Future Impacts of the Disposal of Chromated Copper Arsenate-Treated Wood in Unlined Landfills

Abstract Several states have recently considered altering disposal requirements for chromated copper arsenate (CCA)-treated wood waste, particularly Florida, where CCA-treated wood waste is disposed in unlined construction and demolition (C&D) debris and Class III municipal solid waste (MSW) landfills. The primary concern is the potential for CCA-treated wood waste to elevate arsenic levels in groundwater downgradient of the disposal sites. To address this concern, we evaluated the impact of past disposal practices of these wastes in unlined Florida C&D and Class III landfills by conducting a statistical analysis of two sets of groundwater data compiled by the Florida Department of Environmental Protection (FDEP). The databases contain water quality data from C&D and Class III landfills in Florida covering 15 yr of record from February 1992 through February 2007 and together provide the most complete datasets to evaluate this issue. Comparative statistics of the different population groups in the databases showed that the arithmetic mean concentrations of total arsenic were in most cases higher in background wells than in wells downgradient of the landfills. The statistical analysis indicates that past disposal of CCA-treated wood in C&D and Class III landfills in Florida has not increased arsenic levels downgradient of the landfills. Policy decisions regarding the continued disposal of CCA-treated wood waste as a nonhazardous waste in unlined landfills must therefore be based on a scientifically sound assessment of potential future impacts. Quantitative predictions of future impacts are difficult and pose several scientific challenges. Therefore, future management decisions should be based on a more accurate and comprehensive risk analysis that assesses the risks and benefits of different alternatives and takes into account the natural attenuation capacity of soils and aquifer solids for arsenic and the practical limitations of managing this waste stream as a hazardous waste.

Advanced Diagnostic Tools

In the past decade, the advent of innovative diagnostic tools has improved site assessment and remediation practices. This chapter discusses five diagnostic tools that are particularly important for chlorinated solvent source zone remediation: multi-level monitoring systems; rock matrix characterization techniques; mass flux/mass discharge measurements; compound-specific isotope analysis; and molecular biological tools. The discussion includes descriptions of each diagnostic tool, a value of information analysis to help practitioners determine when the tools will be useful and cost effective, and practical recommendations for use of each tool.

Environmental Fate and Transport of Alternative Gasoline Oxygenates

Rula A. Deeb—Malcolm Pirnie, 180 Grand Ave., Suite 1000. Oakland, CA 94612, USA, rdeeb@pirnie.com, Telephone: (510) 808-3020, Fax: (510) 451-8904; Maryline Laugier—Malcolm Pirnie, 180 Grand Ave., Suite 1000. Oakland, CA 94612, USA, mlaugier@pirnie.com, Telephone: (510) 808-3034, Fax: (510) 451-8904; Michael C. Kavanaugh—Malcolm Pirnie, 180 Grand Ave., Suite 1000. Oakland, CA 94612, USA, mkavanaugh@pirnie.com, Telephone: (510) 808-3000, Fax: (510) 451-8904

Natural Attenuation Versus Active Remediation at MTBE-Impacted Sites

Due to the wide occurrence of MTBE (Methyl tertButyl Ethanol), uncertainties regarding the reliance on biological processes for remediation at gasoline-contaminated sites have increased over the past several years. Contrary to early reports of MTBE and TBA (tert-butyl alcohol) recalcitrance, a review of recent literature and on-going laboratory and field studies suggests that MTBE and TBA are biodegradable by a wide range of microorganisms. Mixed and pure bacterial and fungal cultures have been shown to partially degrade or completely mineralize both compounds. While in some instances MTBE and TBA were degraded in aquifer microcosms from gasoline-contaminated sites, evidence suggest that bioattenuation of MTBE in subsurface environments is mostly site-specific. Specifically, their biotransformation rates in the field appear to be correlated to dissolved oxygen concentrations and groundwater velocities. In some cases, MTBE and TBA were degraded following the introduction of exogenous laboratory-grown MTBE-enriched cultures. Preliminary results from field studies where bioenhancement and bioaugmentation remediation schemes were applied suggest that such techniques have a strong potential for success. The objectives of this study are to review laboratory and field studies addressing the biodegradation of MTBE and TBA and to evaluate our current understanding of the factors limiting MTBE bioattenuation in the environment. Important parameters for optimizing MTBE and TBA biodegradation rates and limitations that may impede the application of successful bioremediation schemes will be discussed. Several key issues will be reviewed in some detail including the potential accumulation of rate limiting intermediates during MTBE degradation, the effect of cocontaminants on MTBE biotransformation rates and the observed dependency of MTBE and TBA biodegradation on dissolved oxygen concentrations. Finally, bioattenuation will be compared to in situ conventional and emerging technologies for MTBE and TBA removal in the context of effectiveness for all contaminants of concern, reliability, risk reduction potential and cost.