MTBE and Private Water Wells in Pennsylvania

This information 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 human-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 MTBE get into groundwater?

MTBE in the environment can result from releases to air, surface water, and groundwater. When released into the air, MTBE can mix with rain or snow that may eventually carry MTBE to groundwater or to streams. Alternatively, gasoline spills may directly contribute to MTBE contamination of groundwater and surface water. Because MTBE moves easily through soils and is water soluble, it can easily contaminate groundwater aquifers. Once in groundwater, 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 on preliminary data, the EPA draft drinking water lifetime health advisory for MTBE is estimated to fall within the range of 20 to 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, hich means it is a possible candidate for future regulation.

How common is MTBE in groundwater wells?

A national study by the U.S. Geological Survey detected MTBE in 27 percent of urban wells and 1.3 percent 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 percent of the thirty 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 extension office.

EPA's Safe Drinking Water Hotline: 1-800-426-4791

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MTBE and Private Water Wells in Pennsylvania

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