As part of the efforts to restore the Anacostia River and to maintain the cleanliness of the District's two rivers, government agencies have undertaken two very large tunnel projects: the Anacostia Tunnel and the Potomac Tunnel, which both unite near the rivers' confluence into the Blue Plains Tunnel, and proceed thereon to the Blue Plains Treatment Plant. Similar in concept to the nineteenth-century sewer interceptors, but substantially larger in scale, these tunnels serve as a release valve and conduit for the city's combined sewer and wastewater system, providing through their length a large reserve of space that will prevent any overflow of sewage or polluted water into the area's waterways. Construction of the Anacostia Tunnel is currently underway; environmental studies to measure the Potomac Tunnel's impact are ongoing.