October 1, 2011. The last major stumbling block to closing the Alexandria coal-burning power plant was removed after a regional power organization determined that its operation is not needed to keep the area’s electrical grid reliable. The 62-year-old Potomac River generating plant, once considered the single biggest source of air pollution in the region, is now set to close no later than Oct. 1, 2012. The city of Alexandria and the company had announced an agreement to shutter the 62-year-old coal-fired plant in late August. But the shutdown was dependent upon whether the loss of the 485 megawatts of power the plant generates would adversely affect the region’s power grid. PJM Interconnection, a regional transmission organization that coordinates the movement of electricity in the Mid-Atlantic, concluded in a letter to GenOn it would not.