[en] Numerous above-ground and underground oil storage tanks and underground piping present a significant ground water pollution threat when breached or deteriorated. The principal aid in cleaning up a spill on land or at sea is being able to observe it, and this opportunity is lacking in the case of the groundwater incident. A groundwater incident can be equally as damaging to the environment as a surface spill and can directly impact the public health by contaminating drinking water or creating hazardous atmospheres in cellars, storm drains, and sewers. In March 1991, when oil was found leaching from the bank of a river trench leading to the Cape Fear River, the Coast Guard Marine Safety Office (MSO) in Wilmington was able to control the oil in the trench through traditional use of booms and sorbents. The MSO was confronted with the threat of oil contaminating ground water and the challenge of locating the source. This report outlines the decisions, actions, and events surrounding the response to the groundwater contamination problem at the City Gas and Transmission facility