Harford County, Maryland, found MTBE in wells near several of its filling stations beginning in 2004. This led the state of Maryland to make moves to ban MTBE.
In 2005, an Exxon-Mobil station in Fallston, Maryland, was found to be leaking MTBE into the local wells. The discovery resulted in the station being abruptly closed. Exxon-Mobil referred to the closure as a "business decision". Following the closure, MTBE levels in the area dropped.
In September 2004, Harford County placed a six-month moratorium on construction of filling stations.