An investigation is ongoing on how a pipeline leaked 138,600 gallons of diesel fuel in Worth County early Wednesday morning, according to Magellan Midstream Partners L.P., the pipeline company. "It’s a big one — it’s significant," said Jeff Vansteenburg, a field office supervisor for the Iowa Department of Natural Resources. "The responsible party is Magellan, so they’ll have to bear the cost of clean up." The pipeline leaked on private agricultural land, said Karen Grimes, spokeswoman for the Iowa DNR. There is a small stream near the leak, but Grimes said no surface water has been contaminated. The Iowa DNR has not uncovered any underground water contamination.