Flat Rock, MI — A massive, possibly century-old underground fuel oil tank has been found near a southeastern Michigan river’s tributary that had a chemical-type sheen on its surface. WXYZ-TV reports Thursday that the tank was located by a company that owns the property southwest of Detroit in Flat Rock. Flat Rock Metal said in a release that the company and the state had no record of the buried storage tank, which has an estimated capacity of 10,000 gallons. The company also said it has been on the property since the 1980s. An angler contacted authorities on Feb. 21 after noticing what looked and smelled like fuel in the river.