While a power plant can be liable under the Act for discharging pollutants into navigable waters via hydrologically connected groundwater, the pollution in this instance was from the landfill and settling pools connected with the site, which were not a "point source" covered by the Act.
Parallel provisions in state permit should be construed reasonably and in a manner congruent with the federal regulations.
http://www.ca4.uscourts.gov/opinions/171895.P.pdf
Since 2011. An occasional commonplacing of the U.S. Circuit Courts of Appeal.
Neither an authoritative statement of the law nor legal advice. Quick work.