Thursday, November 7, 2013

Water and Sewage in Loudoun County

In the past generation Loudoun County has grown from a predominantly rural area with a few small towns like Middleburg, and Leesburg to a booming high density suburb. The population has exploded to an estimated 336,000 in 2013. With people comes human waste-sewage. Under the terms of an agreement dating back to the first development of the Dulles Airport area the sewage from Loudoun County that was not handled by private septic systems was pumped to be treated by the District of Columbia’s sewage treatment plant.

The District of Columbia's sewage system, one of the oldest in the United States is located on the southernmost tip of Washington DC and called the Blue Plains Advanced Wastewater Treatment Plant. While there are larger sewer treatment plants, that remove the solids and bacteria, the modern day Blue Plains also has Tertiary Treatment to remove nitrogen and phosphorus making Blue Plains the largest advance treatment plant in the United States. The plant sits on 150 acres and has a rated average daily capacity if 370 million gallons per day and a peak wet weather capacity of 1,076 million gallons a day. The system needs such a large storm rated capacity to accommodate the old central city combined sewer system that overflows with predictable regularity during large storms. Blue Plains is under a consent order from the Environmental Protection Agency, EPA, to meet new effluent limits for total nitrogen released and better control of the system during storms.

These problems and distance limited the long term ability of Blue Plains to treat waste water from Loudoun County. Today, 13.8 million gallons per day of the wastewater Loudoun County Service Authority (Loudoun Water) collects from the sewer system gets treated at Blue Plains Treatment Plant. Though that is still most of the waste water, Loudoun Water began treating waste water in Loudoun County in 2008. This was carefully tested and studied because Loudoun Water’s discharge is upstream of the of drinking water intakes for the three major Washington area water utilities, Washington Aqueduct, Fairfax Water, and Washington Suburban Sanitary Commission. These utilities serve over three million people in the Washington, D.C. region. While sewage treatment discharges upstream of drinking water intakes are not uncommon in Virginia, a more stringent set of regulations were developed for the Washington D.C. metropolitan area drinking water supplies. The goal of the regulation is to provide an even higher level of assurance that the drinking water supply for the millions of regional residents is protected. The Dulles Watershed Regulation specifies:
  • The number of sewage treatment plants is limited to two and ownership is specified;
  • The two sewage treatment plants must be a minimum of 10 miles upstream of a drinking water intake or proposed intake;
  • The effluent limitations are very stringent, far exceeding what might otherwise be required to protect water quality standards and exceeding effluent standards that have been achieved elsewhere. 
Loudoun Water began planning more than a decade ahead of the need and were able to work with Virginia Tech‘s Department of Civil and Environmental Engineering, the Occoquan Watershed Monitoring Laboratory, to develop a treatment strategy and pilot the program to demonstrate its effectiveness. Loudoun Water staff and its consulting team presented their findings in May, 2001.

After demonstration of the technology, Loudoun Water built the Broad Run Water Reclamation Facility (Broad Run), a state-of-the-art plant that treats wastewater to the limits of today’s technology. In 2008, Loudoun Water began collecting more wastewater than they could send to Blue Plains, and the Broad Run plant went on-line on May 2, 2008, meeting permit requirements on the very first day. The facility discharges to Broad Run, a tributary to the Potomac River, can treat up to 11 million gallons a day and has demonstrated the waste water technology of the future as well as a water resource management strategy emphasizing water reuse.
From Loudoun Water web site- Broad Run

The Broad Run plant uses preliminary screening/grit removal, primary clarification, fine screening (2 mm), flow equalization, a membrane bioreactor, and activated carbon and UV disinfection. The membrane bioreactors are dispersed in twelve membrane tanks. Membrane filtration eliminates the need for clarifiers and settling tanks, and results in improved water quality that enables water reuse. The first water reuse projects in the county have been completed. So far Loudoun Water has installed over 30,000 feet of reclaimed water pipe called “purple pipe” to two data centers and the National Rural Utilities Cooperative Finance Corporation located along Route 28. These customers receive reclaimed water for irrigation, cooling towers and other non-potable uses, in order to meet LEED (Leadership in Environmental and Energy Design) criteria and other environmental and economic goals (recycled water is cheaper). Waste activated sludge from the Broad Run plant is centrifuge thickened, combined with primary sludge for stabilization in anaerobic digesters, and centrifuge dewatered prior to land application. Loudoun Water is proactively planning for the future of their region.

There are sections of Loudoun County that are not served by Loudoun Water. These area are either served by private well and septic system or community systems. As Loudoun County was expanding, developers began building free standing Community Water and Wastewater Systems. These systems provide water to a rural development, village or hamlet and may also provide wastewater treatment utilizing what is called a packaged treatment facility. Treated wastewater is discharged either on site (to a drip irrigation field) or to local streams and rivers. These packaged systems are limited and have a permitted capacity of about 170 gallons per day of waste water per house that should not be exceeded. Loudoun County's Comprehensive General Plan does not allow central water and sewage service into the Rural Policy Area. To get this changed would require a Comprehensive Plan Amendment (CPAM).

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