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Bryan Swistock, Extension Associate, School of Forest Resources
Information presented in this fact sheet is condensed from U.S. Geological Survey and U.S. Environmental Protection Agency publications. What is MTBE?
MTBE (short for methyl tert-butyl ether) is a man-made volatile organic compound (VOC) that is added to gasoline in some parts of the United States to reduce air pollution emissions from automobiles. MTBE is volatile so it readily escapes into the air and smells like turpentine. It is soluble in both gasoline and water. How does it get into ground water?
MTBE in the environment can result from releases to air, surface water, and ground water. When released into the air, MTBE can mix with rain or snow that may eventually carry MTBE to ground water or to streams. Alternatively, gasoline spills may directly contribute to MTBE contamination of ground water and surface water. Because MTBE moves easily through soils and is water soluble, it can easily contaminate ground water aquifers. Once in ground water, MTBE is slower to decay than other gasoline components like benzene.
What are the potential health effects?
EPA tentatively classifies MTBE as a possible human carcinogen. There is presently no federal drinking water standard for MTBE because few controlled studies have been conducted to determine its health effects. Based upon preliminary data, the EPA draft drinking water lifetime health advisory for MTBE is estimated to fall within the range of 20-200 µg/L. This range gives the maximum amount of MTBE that should be allowed in drinking water. Until more research is available, the safest approach would be use 20 µg/L as an approximate drinking water standard. Many people can smell or taste MTBE in water before it reaches this concentration. MTBE concentrations below the health advisory are not expected to cause any adverse effects over a lifetime of exposure but more research is needed. MTBE is also on the EPA's Drinking Water Priority List which means it is a possible candidate for future regulation.
How common is MTBE in ground water wells?
A national study by the U.S. Geological Survey detected MTBE in 27% of urban wells and 1.3% of agricultural wells but very few wells had MTBE above 20 µg/L (the estimated lower limit of the EPA draft drinking water health advisory level). In Pennsylvania, sampling has been generally restricted to agricultural wells in the Lower Susquehanna River Basin. Here, MTBE was detected in 13% of the 30 farm wells tested but the concentrations were very low with a maximum of 1.3 µg/L.
Should I test for MTBE in my well?
Most homeowners with private wells probably do not need to test for MTBE. Homeowners with wells located near underground gasoline storage tanks or where gasoline spills are known to have occurred may want to have their water tested for MTBE. You can expect to pay about $100 to have your water tested for MTBE at a commercial water lab. A list of state certified water-testing laboratories near you is available from your county Cooperative Extension office.
EPA's Safe Drinking Water Hotline 1-800-426-4791
Additional Information on MTBE