The state Department of Ecology has fined Tidewater Barge Lines Inc. $18,000 for spilling 40,000 gallons of fertilizer in the Columbia and Snake rivers in April. Investigators with Ecology found that two of Tidewater’s steel tank barges weren’t adequately maintained and allowed urea ammonium nitrate, a liquid fertilizer known to be corrosive to steel, to spill on three separate occasions. The Vancouver-based company’s first spill occurred between April 11 and 21, when 16,600 gallons of fertilizer escaped into the waterway during transfer and storage operations at the Tidewater Snake River Terminal in Pasco due to a corroded tank in one of the company’s barges.The second spill occurred between April 20 and 24 when a barge moved and moored on the Columbia River near Vancouver spilled 22,100 gallons of urea ammonium nitrate due to the barge’s corroded storage tank. Tidewater spilled a third time during a transport operation on the Columbia, again near Vancouver, on April 28. About 950 gallons were released due to damage to the barge storage tank’s shell.