Methyl tertiary butyl ether (mtbe)

The effectiveness of remediation methods is directly linked to the physical and chemical characteristics of the constituent of concern. Because MTBE behaves differently in soil and water than other petroleum constituents, the choice of an effective remediation technology may be different when MTBE is present with other fuel contaminants at a site.

In soil, MTBE's very high vapor pressure and a low affinity for sorption to soil responds well to soil vapor extraction (SVE) and low-temperature thermal desorption (LTTD), typically without any costs beyond those needed for remediating other petroleum constituents. But because MBTE moves rapidly from the soil into the groundwater, SVE or LTTD must be used soon after a release. High oxygen content facilitates the biodegradation of MTBE. Bioremediation methods for soil treatment (e.g., bioventing, biopiles) may be effective if the appropriate microbes are available (ITRC 2005).

Because spills of conventional gasoline typically move slowly through groundwater and are biodegraded over time, many are left in place to undergo bioremediation at no cost other than monitoring and temporarily replacing the water supply. MTBE, however, moves rapidly with groundwater and can render groundwater unpotable at low levels (20 µg/L to 40 µg/L, EPA 1997). Therefore, spills involving MTBE may require much more aggressive management and remediation than do spills of conventional gasoline.

Pump and treat often can be an effective remediation technology for MTBE because the compound does not adsorb significantly to soil. As a result, fewer aquifer volumes are required to remove all of the MTBE than are required to remove other slowly desorbing petroleum hydrocarbons. Because of its high solubility, most of the MTBE mass can dissolve quickly into groundwater, making pumping an efficient method for removing large quantities of the contaminant (EPA 2004). As with petroleum hydrocarbons, however, diffusion is also a factor controlling the remediation timeframe. If micropores exist within the aquifer that are not readily influenced by groundwater flow, transfer of a contaminant from the micropores to the macropores will occur through the slow process of diffusion, which means that pump and treat will not always be an efficient remediation method for MTBE contamination (ITRC 2005, Rasa et al. 2011).

The physical and chemical properties of MTBE limit the selection of ex situ treatment methods. MTBE is not a good candidate for removal via granular activated carbon (GAC) because it does not adsorb significantly to carbon (EPA 2004). A 1991 American Petroleum Institute study (API Publication No. 4497) determined that air stripping alone was the most cost-effective technology for remediating water containing 20 ppm MTBE down to a level of 10 ppb, though MTBE's high solubility means that air strippers must use a higher volume of air than is required for other petroleum contaminants, such as benzene. MTBE remediation can require more extraction wells and associated equipment (e.g., pumps, lines) than for other fuel contaminants because MTBE may travel farther and faster than the rest of the plume, resulting in a larger plume size. UV-catalyzed oxidation with hydrogen peroxide has been used to treat water and off-gases. Air sparging also has shown some promise, though the method typically is appropriate only in homogeneous sands, and also could require greater volumes of air to volatilize the MTBE than do other petroleum-related contaminants. Air sparging also enriches the oxygen content of the groundwater, which can enhance MTBE as well as BTEX aerobic biodegradation. When used as a biodegradation aid, considerably less air is needed than when trying to volatilize the MTBE (ITRC 2005).

Bioreactors have also been found to be effective for treating MTBE (Hicks et al. 2014, ITRC 2005). Bioreactors generally are used in either suspended growth or attached growth configurations. In Suspended Growth Bioreactors—including plug flow, completely mixed or continuously stirred tank reactor, batch and sequencing batch, activated sludge, and membrane bioreactors—cells are suspended within the reactor unit. Typically, contaminated water is circulated within an aeration basin or passed through an aerated column or pipe (ITRC 2005).

In Attached Growth Bioreactors ("fixed-film" or "immobilized cell" reactors)—including fluidized-bed, fixed/packed bed, trickling filter bioreactors, and rotating biological contactors—cells are established on an inert substrate. Attached growth reactors may retain slow-growing bacteria that wash out from suspended growth reactors (ITRC 2005).

MTBE is biodegradable under both aerobic and anaerobic conditions through the use of biostimulation (introduction of oxygen or other additives) or bioaugmentation (ITRC 2005, Salanitro 2000, and Bruce et al. 2013). For example, biobarriers consisting of oxygen bubbled through the groundwater and a bioaugmented oxygen "curtain" bubbled through the groundwater in a zone perpendicular to groundwater flow were successful in reducing MTBE concentrations to acceptable levels. The unaugmented treatment zone had a significant lag time (>200 days), while significant decreases of MTBE were noted in the bioaugmented zone in 30 to 60 days (Johnson et al. 2003). For more information on biobarriers, see Johnson et al. 2004.

In situ chemical oxidation also can be an effective technique for some MTBE plumes; as with other chemical contaminants, the size of the plume to be remediated will determine its cost effectiveness (ITRC 2005). Table 1 provides a summary of oxidants and their properties.

Phytoremediation has been used at sites having MTBE contamination. It relies on multiple processes to accomplish the removal of contaminants from shallow groundwater. Each of these processes is affected by different chemical properties as well as site-specific conditions. The biodegradability of MTBE affects treatment processes in the rhizosphere, where the conditions support an abundance of metabolically active bacteria and fungi that may enhance contaminant degradation. The relatively high solubility and low organic partition coefficients of oxygenates generally limits significant removal through phytostabilization but facilitates removal through root uptake. In addition, volatility and Henry's Constants may affect the removal through phytovolatilization (EPA 2004, ITRC 2005).

Under certain circumstances, monitored natural attenuation may be a useful technique for addressing MTBE releases (ITRC 2005); however, MNA is appropriate only in conjunction with source control and remediation of high concentrations. LNAPL is removed prior to implementing MNA, and in many cases active remediation of high dissolved concentrations will be necessary prior to MNA. MNA limited in application to the fringes of the plume may be appropriate with other active remediation technologies in the source area (ITRC 2005). For further information on MNA of MTBE, see Zeeb and Wiedemeier 2007, Wilson et al. 2005, and Davis and Erickson 2004.

Under its MTBE Demonstration Project, EPA sponsored three MTBE treatment technology demonstrations on fuel-contaminated groundwater at Naval Base Ventura County, Port Hueneme, California, from 2000 through 2002. The demonstrations examined propane biostimulation, high-energy electron injection (E-Beam), and the HiPOx advanced oxidation process. Links to the reports are provided on this page.

General Information

Comparative Treatment Study of MTBE and Alternative Fuel Oxygenates
C.D. Adams, J. Sutherland, and J. Kekobad.
Missouri Petroleum Storage Tank Insurance Fund, 69 pp, 2002.
Contact: Craig Adams, adams@umr.edu

Comparison of air stripping, carbon adsorption, hydrogen peroxide/ozone advanced oxidation, and hydrogen peroxide/UV advanced oxidation treatment processes for MTBE at the pilot scale under a variety of treatment conditions to develop key design parameters used to calculate estimated treatment costs. Also compared the treatability and associated costs of treating alternative fuel oxygenating agents.

Degradation and Removal of Methyl tert-Butyl Ether
Q. Hao, X.-R. Xu, S. Li, J.-L. Liu, Y.-Y. Yu, and H.-B. Li.
International Journal of Environment and Bioenergy 1(2):93-104(2012)

Evaluation of MTBE Remediation Options
R.A. Deeb, A.E. Flores, A.J. Stocking, S.E. Thompson, M.C. Kavanaugh, D.N. Creek, and J.M. Davidson.
National Water Research Institute, Center for Groundwater Restoration and Protection, Fountain Valley, CA. 150 pp, 2004

Provides an evaluation and case study summaries of a range of strategies and technologies applicable to MTBE remediation: pump and treat, soil vapor extraction, multiphase extraction, air sparging, in situ chemical oxidation, bioremediation [Note: this bioremediation information is dated; please refer to newer resources], natural attenuation, advanced oxidation processes, synthetic resin sorbents, thermal processes, phytoremediation, and chemical reduction.

Groundwater Remediation Strategies Tool
American Petroleum Institute, Publ. No. 4730, 80 pp, 2003.

This guide provides strategies for focusing remediation efforts on 1) the change in MTBE mass flux in different subsurface transport compartments (e.g. the vadose zone, smear zone or a zone within an aquifer of interest) and 2) the change in remediation timeframe.

Level 2 Remediation Action Plan, AA Discount, 181 West Kings Highway, Center Hill, Florida
Florida Department of Health, 140 pp, 2018

The 181 West Kings Site is an active petroleum gas and convenience store. A past discharge led to the removal of four 6,000 gal USTs, associated piping, and ~155 tons of surrounding soils in a 1500 ft² excavation area to a depth of 13 feet. Groundwater sampling results for wells MW-5R and MW-8R in 2014 and MW-5I and MW-8I in 2017 tested positive for BTEX and MTBE. In February 2018, two 8-hour soil vapor extraction and air sparging tests were conducted at the site using mobile, trailer-mounted systems. Results indicated successful remediation and were used to design a system for full-scale remediation.

MTBE Fact Sheet #2: Remediation of MTBE Contaminated Soil and Groundwater
U.S. EPA, Office of Underground Storage Tanks. EPA 510-F-97-015, 5 pp, 1998.

MTBE Remediation Handbook
Moyer, Ellen and Paul T. Kostecki (eds.).
Springer, New York. ISBN: 1-88494-029-3, 712 pp, c2004. [Originally published by Amherst Scientific Publishers in 2003.]

Provides an overview of MTBE history, properties, occurrence, and assessment, followed by a survey of applicable remediation technologies—soil vapor extraction, bioventing, air sparging, in situ chemical oxidation, aerobic and anaerobic in situ bioremediation, phytoremediation, pump and treat, and monitored natural attenuation—and over a dozen remediation case studies.

Overview of Groundwater Remediation Technologies for MTBE and TBA
Interstate Technology and Regulatory Cooperation Work Group MTBE and Other Fuel Oxygenates Team.
Interstate Technology Regulatory Council (ITRC), 131 pp, 2005.

Technologies For Treating MtBE and Other Fuel Oxygenates
U.S. EPA, Office of Superfund Remediation and Technology Innovation, Technology Innovation Program
EPA 542-R-04-009, 109 pp, 2004

• Download Appendix A (9.8MB/108pp/PDF)
• Download Paper 'Application and Performance of Technologies for Treatment of MTBE and Other Oxygenates' (187K/12pp/PDF)

This report provides an overview of the treatment technologies used to remediate groundwater, soil, and drinking water contaminated with MtBE and other fuel oxygenates. The treatment methods discussed include air sparging, soil vapor extraction, multi-phase extraction, in situ and ex situ bioremediation, in situ chemical oxidation, pump-and-treat, and drinking water treatment. Information in the report can be used to help evaluate those technologies based on their effectiveness at specific sites. The report summarizes available performance and cost information for these technologies, examples of where each has been used, and additional sources of information.

Case Study Databases

MTBE Treatment Profiles

Contains information about completed and ongoing applications of treatment for MtBE in drinking water and media at contaminated sites. [The profiles database is updated at irregular intervals; the last update was completed in February 2013.]

Cost and Performance Case Studies from the Federal Remediation Technologies Roundtable

The FRTR Remediation Case Study Searchable Database provides capability to search all 342 case studies by keyword and category, including media/matrix, contaminant type, primary and supplemental technology type, specific site name, or state.

Cost Studies

Cost of In situ Treatment of Fuel Oxygenates
Fiedler, L. and M. Berman.
2003. National Ground Water Association Conference on Remediation: Site Closure and the Total Cost of Cleanup, 13-14 November 2003, New Orleans. 12 pp.

This paper was developed from an analysis of the costs for 162 ongoing and completed full-scale cleanup projects described in the MtBE Treatment Profiles case study database.

An Estimate of the National Cost for Remediation of MTBE Releases from Existing Leaking Underground Storage Tank Sites
Frank Sweet et al.
Association for Environmental Health and Sciences, Amherst, MA. 46 pp, 2005.

In-Situ Bioremediation of MTBE in Groundwater. ESTCP Cost and Performance Report
Environmental Security Technology Certification Program. ESTCP Project CU-0013, 43 pp, 2003.

In-Situ Remediation of MTBE Contaminated Aquifers Using Propane Biosparging: Cost and Performance Report
Naval Facilities Engineering Service Center, Port Hueneme, CA. Environmental Security Technology Certification Program (ESTCP) Project CU-0015. NFESC-TR-2230-ENV, 59 pp, 2003

Prediction of Groundwater Quality Down-Gradient of In Situ Permeable Treatment Barriers and Fully-Remediated Source Zones: ESTCP Cost and Performance Report
Environmental Security Technology Certification Program (ESTCP), Project ER-0320, 39 pp, 2008

A Review of Cost Estimates of MTBE Contamination of Public Wells
American Water Works Association, Denver, CO. 33 pp, 2005.
Contact: AWWA, 303-794-7711

Biological Methods

Aerobic MTBE Biodegradation in the Presence of BTEX by Two Consortia under Batch and Semi-Batch Conditions (Abstract)
M. Raynal and A. Pruden.
Biodegradation 19(2):269-282(2008)

This study explores the effect of microbial consortium composition and reactor configuration on MTBE biodegradation in the presence of BTEX. MTBE biodegradation was monitored in the presence and absence of BTEX in duplicate batch reactors inoculated with distinct enrichment cultures: These results demonstrate that MTBE bioremediation in the presence of BTEX is feasible, and that culture composition and reactor configuration are key factors.

Assessment of Post Remediation Performance of a Biobarrier Oxygen Injection System at a Methyl Tert-Butyl Ether (MTBE)-Contaminated Site, Marine Corps Base Camp Pendleton, San Diego, California
Neil, K., T. Chaudhry, K.H. Kucharzyk, H.V. Rectanus, C. Bartling, P. Chang, and S. Rosansky.
ESTCP Project ER-201588, 284 pp, 2017

This project was conducted to evaluate the long-term performance of natural attenuation of MTBE after shutdown of a biobarrier system. The long-term impact of the biobarrier system on formation permeability was assessed via slug tests. In addition to evaluating data collected using conventional monitoring techniques, this project applied metagenomics and metaproteomics to improve the understanding of long-term impacts of the remedy on biodegradation at the site.

Bioaugmentation for MTBE Remediation (Abstract)
C.L. Bruce, J.P. Salanitro, P.C. Johnson, and G.E. Spinnler.
Bioaugmentation for Groundwater Remediation, Stroo, Leeson, and Ward, eds., Springer, New York. SERDP-ESTCP Environmental Remediation Technology, Volume 5, Chapter 10. p 289-312, 2013

Although MTBE and TBA were originally perceived to be highly recalcitrant, indigenous microorganisms have proven capable of effective aerobic treatment, given sufficient oxygen, and it also has proven possible to create stable and robust zones of oxygenation even in relatively complex lithologic systems. This chapter briefly describes three bioaugmentation pilot tests and four field implementations at full scale. Lessons learned in the course of MTBE/TBA bioremediation research include: (1) site delineation is critical, (2) sufficient oxygen delivery is a common limitation, (3) biostimulation is usually sufficient, though a time lag may be experienced, (4) bioaugmentation activity can persist for years in situ, (5) typical co-contaminants must be considered, (6) effective treatment typically requires a minimum of 6-12 months, and (7) large numbers of bacteria may be needed for effective treatment.

Biodegradation of Methyl Tert-Butyl Ether by Isolated Bacteria from Contaminated Soils to Gasoline
A. Kariminik,, J. Amini, and K. Saeidi. International Research Journal of Applied and Basic Sciences 5(12):1566-1569(2013)

Three bacterial species from gasoline-contaminated soils were isolated that were capable of degrading MTBE as a sole carbon and energy source. The degradation rates of MTBE in 500 ppm concentration after 20 days with Micrococcus luteus, Bacillus subtilis, and B. megaterium was 93.2%, 60%, and 97.97%, respectively. The findings indicated that these bacteria were successfully adapted on MTBE and potentially can offer a suitable and efficient method to treat MTBE contaminated environments.

Biodegradation of MTBE by Bacteria Isolated from Oil Hydrocarbons-Contaminated Environments
B. Lalevic, V. Raicevic, D. Kikovic, L. Jovanovic, G. Surlan-Momirovic, J. Jovic, A.R. Talaie, and F. Morina.
International Journal of Environmental Research 6(1):81-86(2012)

Bioremediation of MTBE, Alcohols, and Ethers
Victor S. Magar, et al. (eds.).
Sixth International In Situ and On-Site Bioremediation Symposium, Volume I.
Battelle Press, Columbus, Ohio. 249 pp, c2001.

Biotreatment of Groundwater Contaminated with MTBE: Interaction of Common Environmental Co-Contaminants
X. Wang and M.A. Deshusses.
Biodegradation 18(1):37-50(2007)

In a study of a lab-scale biotrickling filter for groundwater treatment inoculated with a microbial consortium degrading MTBE, individual or mixtures of BTEX compounds were transiently loaded in combination with MTBE. The results indicated that single BTEX compound or BTEX mixtures inhibited MTBE degradation to varying degrees, but none of them completely repressed the metabolic degradation in the biotrickling filter. TBA, a frequent cocontaminant of MTBE had no inhibitory effect on MTBE degradation. The bacterial consortium was stable and showed promising capabilities to remove TBA, ethylbenzene and toluene, and partially degraded benzene and xylenes without significant lag time. The study suggests that it is feasible to deploy mixed bacterial consortia to degrade MTBE, BTEX, and TBA at the same time.

Comparison of Biostimulation versus Bioaugmentation with Bacterial Strain PM1 for Treatment of Groundwater Contaminated with Methyl Tertiary Butyl Ether (MTBE)
A. Smith, K. Hristova, I. Wood, D.M. Mackay, E. Lory, D. Lorenzana, and K.M. Scow.
Environmental Health Perspectives 113(3):317-322(2005)

After lab studies revealed that bacterial strain PM1 rapidly and completely biodegraded MTBE in groundwater sediments, PM1 was tested in an in situ field study at Port Hueneme Naval Construction Battalion Center, Oxnard, CA. Two pilot test plots (A and B) in groundwater located downgradient from an MTBE source were intermittently sparged with pure oxygen. Plot B was also inoculated with strain PM1. MTBE concentrations upgradient from plots A and B initially varied temporally from 1.5 to 6 mg MTBE/L. Six months after treatment began, MTBE concentrations in monitoring wells downgradient from the injection bed decreased substantially in the shallow zone of the groundwater in plots A and B, thus even in the absence of the inoculated strain PM1. In the deeper zone, downstream MTBE concentrations also decreased in plot A and to a lesser extent in plot B. Difficulties in delivery of oxygen to the deeper zone of plot B, evidenced by low DO concentrations, were likely responsible for low rates of MTBE removal at that location. A naturally occurring bacterial strain with >99% 16S rDNA sequence similarity to strain PM1 was detected in groundwater collected at various locations at Port Hueneme, including outside the plots where the organism was inoculated. Addition of oxygen to naturally occurring microbial populations was sufficient to stimulate MTBE removal at this site. In some cases, however, inoculation with an MTBE-degrading culture may be warranted.

Envirogen Propane Biostimulation Technology for In-Situ Treatment of MTBE-Contaminated Groundwater. Innovative Technology Evaluation Report
Ann Azadpour-Keeley, U.S. EPA.
EPA 600-R-02-092, 152 pp, 2002.
Contact: Ann Azadpour-Keeley, keeley.ann@epa.gov

Environmental Molecular Diagnostics: New Site Characterization and Remediation Enhancement Tools
Interstate Technology & Regulatory Council (ITRC), EMD-2, 371 pp, 2013

Factors Influencing Biological Treatment of MTBE Contaminated Ground Water
William T. Stringfellow, Robert D. Hines Jr., Dirk K. Cockrum, and Scott T. Kilkenny.
LBNL-48941, 49 pp, 2001.
Contact: William Stringfellow, wstringfellow@lbl.gov

Field-Scale Demonstration of Enhanced MTBE Bioremediation Through Aquifer Bioaugmentation and Oxygenation (Abstract)
J. Salanitro, P.C. Johnson, G.E. Spinnler, P.M. Maner, H.L. Wisniewski, and C. Bruce. Environmental Science & Technology 34(19):4152-4162(2000)

A pilot field test of in situ biostimulation and bioaugmentation was conducted on a groundwater plume of dissolved MTBE over 1500 meters long at the U.S. Navy Hydrocarbon National Environmental Test Site at Port Hueneme, CA. The test was conducted to assess the efficacy of creating an MTBE biobarrier by inoculating with a high-activity MTBE-degrading bacterial consortium (MC-100) and maintaining oxygenated conditions. Three test plots located in the MTBE-only portion of the plume included a control zone (no treatment), O2-only with intermittent gas injection, and O2 plus addition of MC-100. MTBE levels decreased in the O2-only plot to 0.01-0.1 mg/L after a lag period of 186-261 days. In the O2 plus MC-100 plot, MTBE concentrations decreased after 30 days and throughout the 261-day experiment eventually to ≤ 0.001-0.01 mg/L. TBA concentrations also declined in the bioaugmented plot to < 0.01 mg/L.

Full Scale Implementation of Sulfate Enhanced Biodegradation to Remediate Petroleum Impacted Groundwater
Cuthbertson, J. and M. Schumacher.
Proceedings of the Annual International Conference on Soils, Sediments, Water and Energy 14:181-189(2010)

Full-scale groundwater remediation using a patented sulfate-enhanced biodegradation (SEB) process was initiated in 2006 at a large former service station and bulk storage facility in Ogdensburg, NY. Applications of a concentrated solution of magnesium sulfate (Epsom salt) in water were made in 2006 (3,800 gallons) and 2007 (2,015 gallons). The SEB injections were highly successful for remediation of MTBE, as well as other petroleum constituents, although ethylbenzene was recalcitrant. The results obtained from this site represent the first field-scale demonstration of MTBE remediation utilizing this technique.

In Situ Biotreatment of TBA with Recirculation/Oxygenation (Abstract)
K.P. North et. al.
Groundwater Monitoring & Remediation 32(3):52-62(2012)

The potential for in situ biodegradation of TBA by creation of aerobic conditions in the subsurface with recirculating well pairs was investigated in two field studies conducted at Vandenberg Air Force Base. In the first experiment, a single recirculating well pair with bromide tracer and oxygen amendment successfully delivered oxygen to the subsurface for 42 days. TBA concentrations were reduced from ~500 µg/L to below the detection limit within the treatment zone and the treated water was detected in a monitoring transect several meters downgradient. Given favorable hydrogeologic and geochemical conditions, the use of recirculating well pairs to introduce dissolved oxygen into the subsurface is a viable method to stimulate in situ biodegradation of TBA or other aerobically degradable aquifer contaminants.

In Situ Bioremediation of MTBE in Groundwater
P. Johnson and C. Bruce (Arizona State Univ.); K. Miller (NFESC). Naval Facilities Engineering Service Center, Port Hueneme, CA. NFESC TR-2222-ENV, 118 pp, 2003.

In this technology demonstration, a biologically reactive groundwater flow-through barrier (the "biobarrier") is established downgradient of a gasoline-spill source zone. Groundwater containing dissolved MTBE flows to, and through, the biobarrier. As it passes through the biobarrier, the MTBE is converted by microorganisms to innocuous by-products (carbon dioxide and water). Groundwater leaving the downgradient edge of the treatment zone contains MTBE at concentrations less than or equal to the treatment target levels.

In-Situ Remediation of MTBE Contaminated Aquifers Using Propane Biosparging: Technology Demonstration Final Report, Revision 1
Environmental Security Technology Certification Program (ESTCP), 244 pp, 2003.

Methyl tert-Butyl Ether (MTBE): Its Movement and Fate in the Environment and Potential for Natural Attenuation
Air Force Center for Environmental Excellence, Brooks Air Force Base, TX. 221 pp, 1999.
Contact: Sylvia Ortega, sylvia.ortega@brooks.af.mil

MTBE and BTEX Biodegradation in a Porous Pot and a Fluidized Bed Reactor
Marie Allyson Sedran, Ph.D. thesis, University of Cincinnati. 164 pp, 2004

Any in situ biological degradation of MTBE in groundwater must take place in the presence of other gasoline contaminants. BTEX components of gasoline are often found in MTBE-contaminated aquifers. This report describes a study of the degradation of MTBE and BTEX by a porous pot reactor and a fluidized bed reactor (FBR). A mixed culture degraded both MTBE and BTEX in a continuous flow reactor with a biomass retention system (porous pot) at varying hydraulic retention times. MTBE was degraded from 75 mg/L to less than 0.001 mg/L, and each BTEX compound was degraded from 17 mg/L to less than 0.001 mg/L. A culture in an aerobic FBR with GAC as a biological attachment medium also degraded MTBE and BTEX. The FBR was run at varying empty bed contact times (EBCTs). At an EBCT of one hour, the MTBE effluent concentration averaged 0.0215 mg/L, and each BTEX compound was at an effluent concentration below 0.003 mg/L. FBR performance decreased at shortened EBCTs but continued to degrade better than 99% of all contaminants. Batch experiments were conducted with the culture from the porous pot reactor and the culture attached to the GAC in the FBR to analyze the degradation kinetics of MTBE and BTEX.

Monitored Natural Attenuation of MTBE as a Risk Management Option at Leaking Underground Storage Tank Sites
J.T. Wilson, P.M. Kaiser, and C. Adair, U.S. EPA, National Risk Management Research Laboratory, Ada, OK. EPA 600-R-04-179, 89 pp, Jan 2005

This report reviews the current state of knowledge on the transport and fate of MTBE in ground water, with emphasis on the natural processes that can be used to manage the risk associated with MTBE in ground water or that contribute to natural attenuation of MTBE as a remedy. It provides recommendations on the site characterization data necessary to manage risk or to evaluate monitored natural attenuation (MNA) of MTBE, and it illustrates procedures that can be used to work up data to evaluate risk or assess MNA at a specific site. The information is intended to allow state regulators to determine whether they have adequate information to evaluate MNA of fuel oxygenates at a site and to allow the regulators to separate sites where MNA of fuel oxygenates may be an appropriate risk management alternative from sites where MNA is not appropriate.

Natural Attenuation of MTBE in the Subsurface under Methanogenic Conditions
John T. Wilson, Jong Soo Cho, Barbara H. Wilson, and James A. Vardy.
EPA 600-R-00-006, 59 pp, 2000.
Contact: John T. Wilson, wilson.johnt@epa.gov

A Practical Approach to the Design, Monitoring, and Optimization of In Situ MTBE Aerobic Biobarriers
P.C. Johnson, K.D. Miller, and C.L. Bruce. NFESC-TR-2257-ENV, 31 pp., 2004.

Based on a gas injection-based oxygen delivery scheme, this technology establishes an oxygen-rich, biologically reactive groundwater treatment zone in situ and downgradient of a source area to reduce concentrations of aerobically degradable chemicals, such as MTBE, benzene, toluene, xylenes, and tert-butyl alcohol. Additional information: Johnson et al. 2010

Prediction of Groundwater Quality Down-Gradient of In Situ Permeable Treatment Barriers and Fully-Remediated Source Zones
P.C. Johnson, P. Dahlen, and P.M. Carlson.
Environmental Security Technology Certification Program (ESTCP), Project ER-0320, 127 pp, 2008

In situ permeable treatment barriers (more commonly referred to as a permeable reactive barriers, or PRBs) are designed such that contaminated groundwater flows through an engineered treatment zone within which contaminants are eliminated or the concentrations are reduced significantly. This project developed a practicable approach to project reasonable order-of-magnitude estimates of groundwater quality improvements with time downgradient of a PRB and used the approach while conducting detailed monitoring and characterization downgradient of a well-understood PRB site, a full-scale biobarrier to address MTBE at the Naval Base Ventura County.

A Review of Bioremediation and Natural Attenuation of MTBE
L. Davis and L. Erickson.
Environmental Progress 23(3):243-252(2004)

Role of Back Diffusion and Biodegradation Reactions in sustaining an MTBE/TBA Plume in Alluvial Media
E. Rasa, S.W. Chapman, B.A. Bekins, G.E. Fogg, K.M. Scow, and D.M. Mackay.
Journal of Contaminant Hydrology 126:235-247(2011)

An MTBE / TBA plume originating from a gasoline spill in late 1994 at Vandenberg Air Force Base persisted for over 15 years (until 2010) within 200 feet of the original spill source despite excavation of the tanks and piping within months after the spill and excavations of additional contaminated sediments from the source area in 2007 and 2008. The probable history of MTBE concentrations along the plume centerline at its source was estimated using a wide variety of available information, including published details about the original spill, excavations and monitoring by VAFB consultants, and our own research data. 2D reactive transport simulations of MTBE along the plume centerline conducted for a 20-year period following the spill suggest that MTBE diffused from the thin anaerobic aquifer into the adjacent anaerobic silts and transformed to TBA in both aquifer and silt layers. The model reproduces the observation that after 2004 TBA was the dominant solute, diffusing back out of the silts into the aquifer and sustaining plume concentrations much longer than would have been the case in the absence of such diffusive exchange. Simulations also suggest that aerobic degradation of MTBE or TBA at the water table in the overlying silt layer significantly affected concentrations of MTBE and TBA by limiting the chemical mass available for back diffusion to the aquifer.

Successful Treatment of an MTBE-Impacted Aquifer Using a Bioreactor Self-Colonized by Native Aquifer Bacteria
K. Hicks, R. Schmidt, M.G. Nickelsen, S.L. Boyle, J.M. Baker, P.M. Tornatore, K.R. Hristova, and K.M. Scow.
Biodegradation 25(1):41-53(2014)

Summary of Workshop on Biodegradation of MTBE, February 1-3, 2000
U.S. EPA, Office of Research and Development, Technology Transfer and Support Division.
EPA 625-R-01-001A, 45 pp, 2001.

Technical Protocol for Evaluating the Natural Attenuation of MtBE
Peter Zeeb and Todd Wiedemeier
API Publication 4761, 186 pp, 2007

Physical/Chemical Methods

Demonstration of the HiPOx Advanced Oxidation Technology for the Treatment of MTBE-Contaminated Groundwater
T.F. Speth, G. Swanson.
EPA 600-R-02-094, NTIS: PB2003-103275, 36 pp, 2002.
Contact: Thomas Speth, speth.thomas@epa.gov

Electrical Resistance Heating (ERH) Technology Coupled with Air Sparging and Soil Vapor Extraction for Remediation of MTBE and BTEX in Soils and Groundwater in Ronan, Montana
J. Kuhn, K. Manchester, and P. Skibicki.
Montana Department of Environmental Quality, Butte, MT. 8 pp, 2004.

Gasoline from a leaking underground storage tank located in Ronan, MT, contaminated the soil and groundwater with MTBE, BTEX, and other gasoline compounds. The contaminant plume extended beneath a busy highway. Earlier use of SVE and air sparging at the site had achieved moderate reduction of contaminant levels. In 2003, traditional air sparging and SVE were combined with electrical resistance heating, which mobilized the contaminants and allowed more effective extraction. Temperatures in the treatment volume exceeded 100 degrees C. Before treatment, soil and ground-water samples showed a significant amount of MTBE and BTEX contamination, whereas MTBE and BTEX were undetectable post-treatment.

Engineering Issue Paper: In Situ Chemical Oxidation
EPA 600-R-06-072, 2006

This issue paper was produced by the EPA Risk Management Research Laboratory and the Engineering Forum. It provides an up-to-date overview of ISCO remediation technology and fundamentals, and is developed based on peer-reviewed literature, EPA reports, web sources, current research, conference proceedings, and other pertinent information.

High Energy Electron Injection (E-Beam) Technology for the 'Ex-Situ' Treatment of MTBE-Contaminated Groundwater
Tetra Tech, Inc., San Diego, CA.
EPA 600-R-02-066, 88 pp, 2002.
Contact: Al Venosa, venosa.albert@epa.gov

In-Well Vapor Stripping Technology. Innovative Technology Summary Report
U.S. DOE, Office of Environmental Management, Office of Science and Technology.
DOE/EM-0626, 50 pp, 2002.

MTBE Remediation Using Hollow Fiber Membrane and Spray Aeration Vacuum Extraction Technologies
M. Kram, S. Sirivithayapakorn, M. Joy, E. Lory, and A. Keller.
NFESC-CR-00-004-ENV, NTIS: ADA382396, 52 pp, 2000.
Contact: Ernest Lory, loryee@nfesc.navy.mil

PA Act 2 Closure of a Multiple-Remedy UST Site
Coll, F.R. and R.A. Moore.
Contaminated Soils, Sediments, Water and Energy: Volume 18. AEHS Foundation, Amherst , MA . ISBN-10: 0-9787640-7-2, 106-119, 2013

The Pennsylvania DEP completed remedial closure of a former gas station property where earlier fuel leaks had affected the aquifer and BTEX and MTBE threatened the drinking water supply. Remedial challenges in the source area included a large vadose zone, aquifer impacts to 90 ft, and location of the property within an existing retail operation. Within three years of installation, an in situ oxidation system combining ozone and hydrogen peroxide via the patented Perozone™ process achieved >95% reductions of UST -related contaminant concentrations in source area groundwater and promoted subsurface conditions conducive to bioremediation. Additional remedial measures included passive oxygen addition and cut-off pumping for the off-site MTBE plume. [ Note: The paper begins on page 106 in the proceedings file.]

Removal of MTBE from Drinking Water Using Air Stripping: Case Studies
R. Deeb, E. Hawley, A. Stocking, M. Kavanaugh, A. Flores, S. Sue, D. Spiers, M. Wooden, G. Crawford, and G. Garcia.
National Water Research Institute, NWRI-2006-03, 92 pp, 2006

Design, performance, and cost summary data were collected from nine packed-tower and low-profile air stripper treatment systems that address MTBE contamination in ground-water supplies in the 1990s to develop a series of cost and reliability curves and assess the accuracy of two models designed to predict the cost and performance of packed-tower and low-profile air strippers. Results indicate that a variety of different treatment train configurations can use air strippers successfully to remove a range of MTBE concentrations (i.e., from 10 to 2,400,000 ug/L). Removal efficiencies ranged from 65% to greater than 99.9%. The commercially available models predicted actual removal efficiencies within 15%.

Removal of MTBE with Advanced Oxidation Processes: Executive Summary
Michael Kavanaugh, et al.
American Water Works Association (AWWA) Research Foundation, Denver, CO. 236 pp, c2003.

All the AOP technologies evaluated in this study--ozone/peroxide, continuous wave UV/peroxide, pulsed UV/peroxide, and E beam--are capable of removing MTBE at 95% or higher efficiencies.

Technical and Regulatory Guidance for In Situ Chemical Oxidation of Contaminated Soil and Groundwater, Second Edition
Interstate Technology and Regulatory Cooperation Work Group In Situ Chemical Oxidation Work Team.
Interstate Technology Regulatory Council (ITRC), 172 pp, 2005.

Technical Report: Subsurface Injection of In Situ Remedial Reagents (ISRRs) within the Los Angeles Regional Water Quality Control Board Jurisdiction
Wilson, S., D. Clexton, C. Sandefur, et al.
In Situ Remediation Reagents Injection Working Group, 46 pp, 2009

This compilation of general tools and best practices provides a reference manual for the planning, design, and field implementation phases of ISCO projects, with a strong emphasis on safety considerations. Specific attention is given to avoiding the visible surfacing of injected ISRR materials, minimizing impact to landscaping, and ensuring no surface pathway for potential ISRR runoff.

Technology Demonstration Report: PolyGuard™, Guardian Environmental Technologies, Inc.
Eric Winkler.
Center for Energy Efficiency and Renewable Energy, Univ. of Massachusetts, Amherst. The Massachusetts Strategic Envirotechnology Partnership (STEP). 69 pp, 1999.
Contact: Eric Winkler, winkler@ceere.org

Describes a 1998 demonstration pilot of the granular absorption media that constitute PolyGuardâ„¢ to quantify its absorption potential for MTBE and other organic contaminants associated with gasoline-contaminated groundwater, evaluate its stability, and monitor its performance.

Thermal Treatment

Electrical Resistance Heating (ERH) Technology Coupled with Air Sparging and Soil Vapor Extraction for Remediation of MTBE and BTEX in Soils and Groundwater in Ronan, Montana
J. Kuhn, K. Manchester, and P. Skibicki.
Montana Department of Environmental Quality, Butte, MT. 8 pp, 2004.

Gasoline from a leaking underground storage tank located in Ronan, MT, contaminated the soil and groundwater with MTBE, BTEX, and other gasoline compounds. The contaminant plume extended beneath a busy highway. Earlier use of SVE and air sparging at the site had achieved moderate reduction of contaminant levels. In 2003, traditional air sparging and SVE were combined with electrical resistance heating, which mobilized the contaminants and allowed more effective extraction. Temperatures in the treatment volume exceeded 100 degrees C. Before treatment, soil and ground-water samples showed a significant amount of MTBE and BTEX contamination, whereas MTBE and BTEX were undetectable post-treatment.

Literature References

Technology Innovation News Survey Archives
The Technology Innovation News Survey archive contains resources gathered from published material and gray literature relevant to the research, development, testing, and application of innovative technologies for the remediation of hazardous waste sites. The collected abstracts date from 1998 to the present, and the archive is updated twice each month.