ELR Citation: ELR 20141
No(s). 04-2151 (10th Cir. Jul 6, 2005)

The court upheld the U.S. Environmental Protection Agency 's (EPA's) approval of New Mexico's water quality standards. The applicable regulation includes a revised enforcement exemption for some pollutants that result from irrigation and flood control facilities, and environmental advocacy groups argued that the regulation violates the Clean Water Act (CWA). Because EPA originally determined that the regulation could be interpreted as violating the CWA, the state sent EPA a letter containing its interpretation of the regulation such that it complied with the CWA. EPA then approved the regulation based on that interpretation. Despite the groups' arguments to the contrary, EPA did not act arbitrarily or capriciously in determining that the regulation was ambiguous. Nor did EPA arbitrarily or capriciously rely on the state's interpretation of that regulation, particularly since it reserved the right to revoke its approval if New Mexico interpreted the regulation in the future in a way that would not comply with the CWA.