The investigation comes years after a September 2004 petition was filed with the CEC by Ecojustice and Waterkeeper Alliance, representing a number of NGOs. It claimed the US Environmental Protection Agency failed to enforce the Clean Water Act (CWA), leading to mercury pollution in water bodies by coal fired power plants.

The investigation to gather facts from NGOs, government and technical sources will examine permits for forty coal fired plants in ten US states. CEC will also look into Total Maximum Daily Load (TMDL) calculations.

A draft factual record will be prepared by June 2009 and shed light on whether the EPA allowed for ongoing point source discharges of mercury into US waterways and neglected to account for mercury that falls back to earth from coal power air emissions.