At approximately 4pm on Wednesday, January 22nd, contractors working at the wastewater treatment plant on Martin Street accidentally spilled a small amount of Mercaptan while refilling a tank. Mercaptan is also known as methanethiol and is a harmless but pungent-smelling gas that is added to natural gas, which is colorless and odorless, to make it easier to detect. As a result of the odor from the spill, the City and Excel Energy received many calls from residents reporting a gas leak. While the amount of the spill was small (about half a gallon), the odor was detectable over a large area. Mercaptan is noticeable in tiny quantities smaller than one part per million, and there is no toxicity associated with those very low levels. A City civil engineer was on site to supervise the cleanup. The odor may remain noticeable for several hours, but poses no risk to the public.