This time two years ago, officials from the historic city of Alexandria, VA, were jockeying with state legislators for more time to curb the sewage overflows that wash 140 million gallons of untreated sewage into the Potomac River and its tributaries each year. But since then, in an effort to meet the General Assembly’s 2025 deadline to complete the work, the city has found a way.

Like many centuries-old wastewater treatment systems in the country, Alexandria’s captures both sewage and stormwater in its pipes. To prevent sewage backups, the system was designed to divert wet-weather overflows to the nearest water body, sending untreated sewage directly into the stream or river. This has come to be known as a combined sewer overflow system.