DETROIT — The U.S. Environmental Protection Agency and the state announced a plan on Tuesday to treat the groundwater contamination at the former Electro-Plating services facility that was determined to be the source of a green ooze leak last year. The treatment will begin next month, by injecting chemicals into the soil and treating the contaminants in place. Since groundwater naturally migrates through the soil, the chemicals used to treat the pollutants will flow through the injection areas between the Electro-Plating Services building in Madison Heights and Interstate 696. The plan creates a long-term management process that will protect residents and natural resources. The extent of the contamination remains undetermined.