MENLO -The city of Menlo in Guthrie County is investigating how a petroleum product entered its storm water system. A resident reported a diesel odor at the 350th Street bridge east of Pinewood Avenue, just south of Menlo, to the Guthrie County Conservation Board on Thursday. A DNR investigation found a plastic tile discharging water with a rainbow sheen and slight petroleum odor into a drainage ditch.

The tile line drains water from Menlo’s storm sewer. Unlike sanitary sewers, storm sewers do not receive any treatment before discharging into streams, rivers or lakes. The drainage ditch flows into an unnamed tributary of the North River.

The city is investigating possible sources of the fuel and has put absorbent material in the ditch to keep it from spreading. It is not known how much fuel may have entered the storm sewer.