|Alexandria's Combined Sewer Area|
Like many old cities in the United States, Alexandria, Virginia has an area of the City, mostly around Old Town that has a Combined Sewer System. This combined system is a piped sewer system in which there is one pipe that carries both sanitary sewage and stormwater to the local wastewater treatment plant. This was how sewer systems were commonly built in the days before waste water treatment systems. There was no need to consider capacity of waste water treatment plants, because there were none. This was a time when sanitation was simply moving sewage out of the city to the rivers and streams. Back then one piping system was cheaper and adequate for the job.
However, today when sewage is treated by waste water treatment plants, the rain water that falls in the street and enters the storm water drains is combined with the sanitary waste water entering the sewers from homes and businesses. The combined flow can overwhelm the waste water treatment plant. The water coming from the combined sewer system is the most dilute. It has already had rainwater mixed in with the sewage. So, to protect the sewage system as a whole, the combined sewage and rainfall is released into the local creeks in a controlled and planned fashion out of the “Combined Sewer Overflows” which are release locations permitted and monitored by the regulators.
The U.S. Environmental Protection Agency (EPA) requires that each city have a Long Term Control Plan to address its combined sewer system overflows. In Virginia that program is managed by the Department of Environmental Quality (DEQ). Alexandria has been operating its combined sewer system under an approved Long Term Control Plan since 1999. Nonetheless, these overflows impact local water quality and over the years these regulations have been tightened. The Virginia Department of Environmental Quality (VDEQ) determined that Hunting Creek, Cameron Run, and Holmes Run watersheds where Alexandria is releasing the mixed stormwater and sewage water exceeded water quality standards for E. coli bacteria and put a limit on the amount of E. coli that can be released. This limit is called a Total Maximum Daily Load (TMDL) is the maximum amount of a pollutant that a waterbody can receive during a storm and still meet water quality standards. The City was issued a new combined sewer system discharge permit in 2013 that requires Alexandria to update its Long Term Control Plan by August 2016 to meet the Hunting Creek E. coli limit no later than 2035.
Alexandria has submitted its plan that is a combination reducing stormwater flow, increasing system storage and separating the stormwater from the sanitary sewer system as areas are redeveloped. Specifically, Alexandria’s long term plan calls for the following:
- Construction of a 1.6 million gallon storage tunnel in the area of Hooffs Run. This tunnel will be 10-feet in diameter and be approximately 1/2 mile in length. Construction activities would be limited to a few tunneling shafts, but is still estimated to cost $80,000,000-$120,000,000.
- Construction of a 3 million gallon storage tank at the south end of Royal Street. This is estimated to cost $35,000.000-$53,000,000
- Utilize green infrastructure to reduce stormwater runoff as a complementary strategy to be implemented citywide. This is estimated to cost $5,000,000-$7,500,000.
- Targeted sewer separation as a complementary strategy to be done as a condition of redevelopment in the Old Town area. These targeted separations are estimated to cost $5,000,000-$7,500,000.
- Other potential opportunities including evaluating incentives for private property owners, including rebates for installation of water-saving fixtures to reduce overall sewage flow.
The total cost of the combined sewer long term control plan is estimated to be $125,000,000-$188,000,000. This strategy of a Storage Tunnel for Hoofs Run and Storage Tank at Royal Street complemented by green infrastructure was selected as the preferred strategy because it had the lowest capital and operating costs, and was determined by stakeholders to be least disruptive to the community . These projects will be funded by issuing bonds which are paid back through the sanitary sewer rates. Currently, the average household in Alexandria pays $45-50 per month on their sewer bill. Studies are underway to determine the impact of these projects on the sewer rates, but preliminary estimates by the city indicate that the expected impact will be an increase of $10-$15 per month on the monthly sewer bill for these projects. These increases to the billing will be implemented over time.
These project when implemented will address the TMDL on Hunting Creek, Cameron Run, and Holmes Run watersheds, however; there is another combined sewer overflow at the end of Pendleton Street. This outfall discharges into Oronoco Bay, which is a Virginia waterway that is tidally influenced by the Potomac River. The Potomac River and Oronoco Bay are not part of the Hunting Creek TMDL and currently there is no regulatory requirement to reduce overflows there. However, because it is part of the combined sewer system, it is subject to the EPA’s existing Long Term Control Plan approved in 1999. Additionally, sewer separation and stormwater controls are a requirement of redevelopment in the combined sewer areas.
So, following the implementation of Hunting Creek, Cameron Run, and Holmes Run watersheds infrastructure projects and the Old Town North Small Area Plan, the City will reassess the need for additional controls at Pendleton Street.