Methyl Tertiary Butyl Ether (MTBE)

The purpose of this section is to identify commercially available analytical and sampling methods used for detecting, measuring, and/or monitoring MTBE. The intent is not to provide an exhaustive list of analytical methods, but to identify well-established, standard methods, particularly those used for environmental samples. Check the National Environmental Methods Index (NEMI) to identify methods for MTBE not cited on this page. NEMI is a free, searchable clearinghouse of methods and procedures for regulatory and non-regulatory analyses. Sampling, analysis, and site characterization techniques for MTBE are generally the same as those used for investigating other volatile organic compounds.

MTBE behaves differently than other gasoline constituents when released into the environment, which means a remedial investigation may need to be modified to properly characterize the area of MTBE contamination. MTBE's relatively high solubility allows it to dissolve from the vadose zone into the groundwater in "pulses" that result in rapid orders-of-magnitude changes in groundwater concentrations. These pulses, which possibly are caused by the infiltration of rain water or rising groundwater levels, may necessitate frequent groundwater sampling to determine actual MTBE concentrations and levels of risk to downgradient receptors. The frequency of sampling can be determined based on the velocity of the groundwater and the number of monitoring wells (EPA 1998).

Another consideration in characterizing MTBE plumes is the potential for the plumes to dive. Because MTBE does not sorb to aquifer material and because there may be little biological degradation in some plumes, MTBE plumes can become very long. The longer the plume, the more likely that it will dive below the screen of conventional monitoring wells. Plumes can dive deeper into an aquifer by different mechanisms: they can be buried by recharge of precipitation, moving down to the aquifer from the surface, and they also tend to flow around clay layers and through sand or gravel layers. If the layers that control flow of groundwater dive into the aquifer, so will the plume (EPA 2004 and Weaver and Wilson 2000).

Given that MTBE moves at nearly the same speed as the groundwater (about twice as fast as benzene), one would expect MTBE plumes to be consistently longer than BTEX plumes; however, studies that have compared plume lengths of MTBE and BTEX have found that the majority of the plumes are about the same size, with some MTBE plumes being longer (Happel, Beckenbach, and Halden 1998, Mace and Choi 1998, and Klamath et. al 2012). ITRC (2005) suggests several reasons for the studies' findings, including the potential for biodegradation (not specifically examined in the studies), but cautions that the site characterizations might be faulty. ITRC 2005 offers the following observations:

• Because of the tendency of MTBE plumes to be narrow and long in aquifers with relatively high rates of flow, it may be necessary to collect samples at closely spaced intervals.
• Long plumes, especially in more permeable aquifers, may have a tendency to dive; therefore, it is critical to characterize oxygenate plumes both vertically and horizontally.
• At sites with heterogeneous permeabilities, MTBE plumes will tend to move with the groundwater through the more permeable layers. A monitoring well network set with 10-foot screens at the water table has the potential to miss plumes traveling at depth due to lithology.

Biodegradation can definitely occur at many MTBE sites (ITCR 2005 and Wilson, Kaiser, and Adair 2005). Microcosm studies and DNA fingerprinting are expensive tests that can be used to indicate if biodegradation is occurring or has the potential to occur. Alternatively, Wilson et al. suggest that a comparison of the ratio of MTBE concentrations to tert-butanol, a frequent degradation product, can be used to judge if biodegradation of MTBE is occurring. While analysis for biogeochemical footprints can show biodegradation and aquifer impact for a gasoline spill as a whole, they generally cannot be used as an indicator of what is happening specifically to MTBE (Wilson et al. 2005).

Analytical Methods

Analytical Methodologies for Fuel Oxygenates. Underground Storage Tanks Fact Sheet
U.S. EPA, Office of Underground Storage Tanks.
EPA 510-F-03-001, 2 pp, 2003.

Analytical Methods for Gasoline Oxygenates: the DAI-GC/MS Method
Oregon Health & Science University, Center for Groundwater Research, Beaverton, OR, web site.

Determination of Fuel Ethers in Water by Membrane Extraction Ion Mobility Spectrometry (Abstract)
S. Holopainen, S., M. Nousiainen, and M. Sillanpaeae.
Talanta 106:448-453(2013)

The authors demonstrated that fuel ethers (MTBE, ETBE, DIPE, and TAME) can be quantified at mg/L level with membrane-extraction IMS. A membrane-extraction module coupled to IMS is a time- and cost-effective analysis method because sampling can be performed in a single procedure and from different natural water matrices within a few minutes. Consequently, IMS combined with membrane extraction is suitable not only for waterworks and other online applications but also in the field for monitoring the quality of drinking and natural water.

Determination of Methyl tert-Butyl Ether and tert-Butyl Alcohol in Water by Solid-Phase Microextraction/Head Space Analysis in Comparison to EPA Method 5030/8260B
Keun-Chan Oh and William T. Stringfellow.
LBNL-53866, 28 pp, 2003.
Contact: William T. Stringfellow, wstringfellow@lbl.gov

Measurement of Methyl-tert-Butyl-Ether (MTBE) in Raw Drinking Water
M.L. Davisson, C.J. Koester, J.E. Moran.
UCRL-JC-131894, 9 pp, 1999.

Method 1615: Methyl tert-Butyl Ether
NIOSH Manual of Analytical Methods (NMAM^®), 4th ed. National Institute for Occupational Safety and Health, Publication 94-113, 4 pp, 1994.

This is an air method.

Selecting Analytical Methods for the Determination of Oxygenates in Environmental Samples and Gasoline
I. Rhodes and A. Verstuyft.
Environmental Testing & Analysis, 6 pp, March/April 2001.

Test Methods for Evaluating Solid Wastes: Physical/Chemical Methods, 3rd Edition
U.S. Environmental Protection Agency, SW-846.

Method 5021, Volatile Organic Compounds in Various Sample Matrices Using Equilibrium Headspace Analysis
Method 5030B, Purge-and-Trap for Aqueous Samples
Method 5035, Closed-System Purge-and-Trap and Extraction for Volatile Organics in Soil and Waste Samples
Method 8015C, Nonhalogenated Organics Using GC/FID
Method 8260C, Volatile Organic Compounds by Gas Chromatography/Mass Spectrometry (GC/MS)

U.S. Geological Survey Laboratory Method for Methyl tert-Butyl Ether and Other Fuel Oxygenates
Jon W. Raese, Donna L. Rose, and Mark W. Sandstrom.
U.S. Geological Survey Fact Sheet FS-219-95, 1995.

Site Characterization

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

To help site managers and site consultants estimate mass flux and understand the uncertainty in those estimates, ESTCP has funded the development of a computerized Mass Flux Toolkit, free software that gives site personnel the capability to compare different mass flux approaches, calculate mass flux from transect data, and apply mass flux to manage ground-water plumes. The toolkit spreadsheet and associated documentation are available on the ESTCP contractor's website in a zipped file.

Performance Comparison: Direct-Push Wells Versus Drilled Wells
C. Reeter, J. Fortenberry, E. Lory, M. Kram.
NFESC-TDS-2087-ENV, DTIC: ADA398555, 5 pp, 2001.
Contact: Chuck Reeter, reetercv@nfesc.navy.mil

A comparison between results from direct-push installed monitoring wells and drilled monitoring wells conducted on the leading edge of a MTBE plume in a shallow semi-perched aquifer.

Site Characterisation in Support of Monitored Natural Attenuation of Fuel Hydrocarbons and MTBE in a Chalk Aquifer in Southern England
CL:AIRE Case Study Bulletin. CL:AIRE (Contaminated Land: Applications in Real Environments), London, UK. CSB1, 4 pp, 2002.
Contact: Dr. Steve Thornton, s.f.thornton@sheffield.ac.uk, or Gary Wealthall, g.wealthall@bgs.ac.uk

Strategies for Characterizing Subsurface Releases of Gasoline Containing MTBE
American Petroleum Institute, API Publication Number 4699, 116 pp, 2000.

API Publication 4699 includes a review of the chemical properties and subsurface behavior of MTBE and other oxygenated fuel additives. It also provides an overview of characterization and monitoring issues at oxygenate release sites, as well as a detailed review of the tools and techniques used for subsurface assessment. The expedited site assessment process and the use of modern direct-push tools are particularly emphasized.

User's Guide to the Collection and Analysis of Tree Cores to Assess the Distribution of Subsurface Volatile Organic Compounds
D.A. Vroblesky.
U.S. Geological Survey Scientific Investigations Report 2008-5088, 59 pp, 2008

Detecting MTBE Biodegradation

Bio-Traps Coupled with Molecular Biological Methods and Stable Isotope Probing Demonstrate the In Situ Biodegradation Potential of MTBE and TBA in Gasoline-Contaminated Aquifers (Abstract)
J. Busch-Harris et al.
Ground Water Monitoring & Remediation 28(4):47-62(2008)

Biofilms characteristic of aquifer conditions can be rapidly and efficiently collected using in situ microcosms or "bio-traps" containing Bio-Sep® beads (25% Nomex and 75% powdered activated carbon [PAC]). Bio-Sep beads can be "baited" with a variety of organic compounds by vapor-phase adsorption onto the PAC component of the beads under reduced pressure. In the aquifer, the bait or the amendment does not substantially leach into the aquifer but is available to the bacteria as a carbon source within the bead. When the organic compound is labeled with C-13, phospholipids may be extracted from bead biofilms postincubation and derived fatty acid methyl esters analyzed for C-13. Incorporation of C-13 into biomass provides proof of current in situ degradation potential.

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

Field Applicability of Compound-Specific Isotope Analysis (CSIA) for Characterization and Quantification of In Situ Contaminant Degradation in Aquifers (Abstract)
M. Braeckevelt, A. Fischer, and M. Kaestner.
Applied Microbiology and Biotechnology 94(6):1401-1421(2012)

A Guide for Assessing Biodegradation and Source Identification of Organic Ground Water Contaminants Using Compound Specific Isotope Analysis (CSIA)
D. Hunkeler, R.U. Meckenstock, B. Sherwood-Lollar, T.C. Schmidt, and J.T. Wilson.
EPA 600-R-08-148, 82 pp, 2008

When organic contaminants are degraded in the environment, the ratio of stable isotopes often will change, and the extent of degradation can be recognized and predicted from the change in the ratio of stable isotopes. Recent advances in analytical chemistry make it possible to perform CSIA on dissolved organic contaminants, including TCE and MTBE, at concentrations in water that are near their regulatory standards. This text provides general recommendations on good practice for sampling, measurement, data evaluation, and interpretation in CSIA.

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 provides recommendations on the site characterization data that are necessary to manage risk or to evaluate 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.

Mass Flux Calculations

Field Demonstration and Validation of a New Device for Measuring Water and Solute Fluxes, NASA LC-34 Site
Environmental Security Technology Certification Program (ESTCP), 172 pp, 2006

ESTCP passive flux meter (PFM) demonstration and validation projects include MTBE flux measurement at Port Hueneme, perchlorate flux at the Naval Surface Warfare Center at Indianhead, and TCE flux at NASA Launch Complex 34 at Cape Canaveral.

Field Demonstration and Validation of a New Device for Measuring Water and Solute Fluxes at Naval Base Ventura County (NBVC), Port Hueneme, CA: Revised Final Report (Version 2)
K. Hatfield, M.D. Annable, and P.S.C. Rao.
Environmental Security Technology Certification Program, NTIS: ADA468560, 113 pp, 2006

Ground-water and contaminant fluxes at NBVC were measured using passive flux meters (PFMs) at the leading edge of a MTBE plume. The objectives of the demonstration were to demonstrate the validity of the PFM and to compare flux measurements in wells reflecting different designs or construction techniques.

Mass Flux Toolkit to Evaluate Groundwater Impacts, Attenuation, and Remediation Alternatives
Environmental Security Technology Certification Program (ESTCP), 2006

To help site managers and site consultants estimate mass flux and understand the uncertainty in those estimates, ESTCP has funded the development of a computerized Mass Flux Toolkit, free software that gives site personnel the capability to compare different mass flux approaches, calculate mass flux from transect data, and apply mass flux to manage ground-water plumes. The toolkit spreadsheet and associated documentation are available on the ESTCP contractor's website in a zipped file.

Plume Diving

Diving Plumes and Vertical Migration at Petroleum Hydrocarbon Release Sites
J.W. Weaver and J.T. Wilson
L.U.S.T.Line Bulletin 36, Nov 2000 [New England Interstate Water Pollution Control Commission]

MTBE Diving Plumes
U.S. EPA, National Risk Management Research Laboratory, 2004

Using Direct-Push Tools to Map Hydrostratigraphy and Predict MTBE Plume Diving (Abstract)
J.T. Wilson, R.R. Ross, and S. Acree. Groundwater Monitoring & Remediation 25(3):93-102(2005)

At a number of sites, a plume of MTBE in groundwater has dived below the screen of conventional monitoring wells and escaped detection. Two potentially applicable techniques emerging in the site characterization market are electrical conductivity logging and pneumatic slug testing performed in temporary push wells.

Plume Size

An Evaluation of MTBE Impacts to California Groundwater Resources
Anne M. Happel, Edwin H. Beckenbach, Rolf U. Halden.
UCRL-AR-130897, 80 pp, 1998.

Review of Quantitative Surveys of the Length and Stability of MTBE, TBA, and Benzene Plumes in Groundwater at UST Sites
J.A. Connor, R. Kamath, K.L. Walker, and T.E. McHugh.
Groundwater, 2014

Data from 13 published scientific surveys show the observed lengths of benzene and MTBE plumes to be relatively consistent among various regions and hydrogeologic settings, with median lengths at a delineation limit of 10 µg/L falling into relatively narrow ranges from 101 to 185 ft for benzene and 110 to 178 ft for MTBE. The observed statistical distributions of MTBE and benzene plumes show the two plume types to be of comparable lengths, with 90th percentile MTBE plume lengths moderately exceeding benzene plume lengths by 16% at a 10-µg/L delineation limit (400 ft versus 345 ft) and 25% at a 5-µg/L delineation limit (530 ft versus 425 ft). Stability analyses for benzene and MTBE plumes found 94 and 93% of these plumes, respectively, to be in a nonexpanding condition, and over 91% of individual monitoring wells to exhibit nonincreasing concentration trends. In three studies, TBA plumes were of comparable length to MTBE and benzene plumes, with 86% of wells in one study showing nonincreasing concentration trends.This paper is Open Access.

The Size and Behavior of MTBE Plumes in Texas
R.E.Mace and W.-J. Choi.
Proceedings of the Petroleum Hydrocarbons and Organic Chemicals in Ground Water: Prevention, Detection, and Remediation Conference, November 11-13, 1998, Houston, Texas, 1-12, 1998

Use of Long-Term Monitoring Data to Evaluate Benzene, MTBE, and TBA Plume Behavior in Groundwater at Retail Gasoline Sites (Abstract)
R. Kamath, J.A. Connor, T.E. McHugh, A. Nemir, M.P. Le, and A.J. Ryan.
Journal of Environmental Engineering 138(4):458-469(2012)

Analysis of long-term monitoring data for 48 retail gasoline sites indicates that MTBE plumes underlying a majority of the underground storage tank sites monitored for 5 years or longer (1) have significantly diminished in concentration over time, (2) are comparable in length to benzene plumes, (3) are, like benzene plumes, principally stable or shrinking in size and concentration, and (4) are on track to achieve remedial goals within a timeframe comparable to or faster than that of benzene plumes. TBA plumes were found to be comparable to benzene and MTBE plumes in terms of plume length; however, whereas most TBA plumes are also stable or shrinking, the percentage of TBA plumes that are currently stable or shrinking (68%) is less than that for benzene plumes (95%) or MTBE plumes (90%), likely reflecting the temporary buildup of TBA concentrations attributable to MTBE biodegradation.

Literature References

Measurement and Monitoring Technologies for the 21st Century Initiative (21M²) Literature Search
In the "needs" area of this site is a section entitled Field-Based Monitoring and Measurement Technologies for MTBE in Soil and Groundwater. This section contains abstracts and full text articles for the above topic.