DURANGO, TEXAS – The City of Durango stopped using biodiesel in its fleet because engines were becoming contaminated with an unidentified sludge, reports The Durango Herald. The city’s transit manager reported that a city director had sent a sample of the sludge to a lab for analysis. About 40,000 gallons of the 42,000 gallons of fuel used by the city last year were biodiesel. The city fleet has since gone to an all-diesel fleet. The city is not completely abandoning the use of biodiesel, but is putting it on hold until the sludge problem is solved, according to the report. The city is considering other fuel alternatives such as E-85 and hydrogen fuel cells.