Jul 14, 2014 1 min read

SKIPPACK (AP) – Authorities say gasoline-tainted groundwater caused the mysterious smell that led to a voluntary evacuation of about 150 homes in suburban Philadelphia.

Officials say the contaminated water got into the sump pumps of the townhouses in Skippack and caused a noxious odor.

Residents first reported the smell Sunday evening. Officials detected a chemical odor in several homes and recommended residents leave until the substance and source could be identified.

Samples analyzed by labs on Monday indicated the compound was gasoline. But Fire Chief Haydn Marriott says officials still don’t know how the gas got into the groundwater.

Residents were being allowed back into their houses on Monday. Officials say they plan to monitor affected homes in the coming days.