an occasional water source for the Borough of Zelienople, alleging that AK Steel had failed to properly dispose of hexavalent chromium. The issue was settled in 2004, with AK Steel agreeing to pay a total of $1.2 million. In 2006, AK Steel reached a settlement to compensate for polychlorinated biphenyl (PCB) contamination in Middletown, Ohio. The settlement included cleanup work estimated to cost $12–13 million. AK Steel was listed #1 on the Mother Jones Top 20 polluters of 2010; dumping over 12,000 tons of toxic chemicals into Ohio waterways. Based on 2014 data, the Political Economy Research Institute ranked AK Steel 53rd among corporations emitting airborne pollutants in the United States. The ranking is based on the quantity (343,000 pounds) and toxicity of the emissions. At the same time, it scored well in terms of environmental justice, affecting smaller percentages of the poor and minorities than their respective percentages of the total population. In early 2015, the EPA listed the Ohio River as the most contaminated body of water in the U.S. According to the EPA's Annual Toxics Release Inventory, of the 23 million pounds of chemicals discharged into the river in 2013, more than 70 percent came from AK Steel. In 2018, AK Steel had an air and water compliance rate of over 99.99%. Middletown Works lockout Armco and the Armco Employees Independent Federation (AEIF; a labor union) had a collective bargaining agreement in place in 2004 that required AK Steel to employ 3,114 workers, a "minimum base force guarantee". The agreement also authorized AK Steel to suspend the minimum number. On January 13, 2004, AK Steel informed the AEIF that it was suspending the minimum. The union then filed a grievance contesting the suspension. An arbitrator upheld the decision by AK Steel on July 1, 2004, subject to certain limitations, through at least May 10, 2005. The union sought and was granted a new hearing, and on July 1, 2005 the arbitrator issued a comprise total workforce. As part of the agreement the arbitrator allowed AK Steel to set aside financial payments to a fund, in lieu of hiring to the minimum, the amount of which was set by the arbitrator on October 7, 2005. On September 29, 2005, the AEIF filed a lawsuit against AK Steel in the United States District Court for the Southern District of Ohio (AEIF v. AK Steel Corp.; Case No. 1:05-CV-639), in