Upper Occoquan Sewage Authority
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The Millard H. Robbins, Jr. Water Reclamation Plant, which is operated by the Upper Occoquan Service Authority (UOSA), is located in
Centreville, Virginia Centreville is a census-designated place (CDP) in Fairfax County, Virginia, United States and a suburb of Washington, D.C. The population was 73,518 as of the 2020 census. Centreville is approximately west of Washington, D.C. History Colonia ...
and it was formerly known as the Upper Occoquan Sewage Authority. UOSA serves the western portions of
Fairfax Fairfax may refer to: Places United States * Fairfax, California * Fairfax Avenue, a major thoroughfare in Los Angeles, California * Fairfax District, Los Angeles, California, centered on Fairfax Avenue * Fairfax, Georgia * Fairfax, Indiana * Fa ...
and
Prince William William, Prince of Wales, (William Arthur Philip Louis; born 21 June 1982) is the heir apparent to the British throne. He is the elder son of King Charles III and his first wife Diana, Princess of Wales. Born in London, William was educat ...
Counties, and the Cities of Manassas and
Manassas Park Manassas Park is an independent city (United States), independent city in the U.S. state of Virginia. As of the 2020 United States Census, 2020 census, the population was 17,219. Manassas Park is bordered by the city of Manassas, Virginia, Manas ...
. The
sewage treatment Sewage treatment (or domestic wastewater treatment, municipal wastewater treatment) is a type of wastewater treatment which aims to remove contaminants from sewage to produce an effluent that is suitable for discharge to the surrounding envir ...
plant includes primary-secondary treatment and the following advanced wastewater treatment processes: chemical clarification, two-stage recarbonation with intermediate settling, multimedia filtration, granular activated carbon adsorption, chlorination for disinfection and dechlorination. The plant’s rated capacity is per day (mgd).


Discharge permit

UOSA operates under a Virginia Pollutant Discharge Elimination System (VPDES) Permit, which is issued by the Department of Environmental Quality (DEQ). The Permit limitations listed in the table below are among the most stringent in the State of Virginia and possibly in the United States. :UOSA Permit Limits :


Effects on Occoquan Reservoir water quality

The
Occoquan Reservoir Occoquan Reservoir is a reservoir in northeast Virginia, southwest of Washington, D.C., straddling part of the boundary between Fairfax County and Prince William County, west of Alexandria. It is formed by the Occoquan Dam on the Occoquan River ...
is a component in a water supply system that currently serves over 1.4 million residents of Northern Virginia. During the suburban expansion of the Northern Virginia region in the 1960s, the reservoir’s water quality degraded, resulting in: * Massive algal blooms (including blue-green algae of the genus cyanobacter) due to over enrichment with plant nutrients; * Periodic episodes of taste and odor in the finished drinking water; * Low dissolved oxygen levels; * Periodic
fish kill The term fish kill, known also as fish die-off, refers to a localized die-off of fish populations which may also be associated with more generalized mortality of aquatic life.University of Florida. Gainesville, FL (2005) ''Plant Management in Fl ...
s; and * Generation of
hydrogen sulfide Hydrogen sulfide is a chemical compound with the formula . It is a colorless chalcogen-hydride gas, and is poisonous, corrosive, and flammable, with trace amounts in ambient atmosphere having a characteristic foul odor of rotten eggs. The unde ...
in the bottoms waters of the waters of the reservoir.Virginia Tech. "An Assessment of the Water Quality Effects of Nitrate in Reclaimed Water Delivered to the Occoquan Reservoir, OWML, Manassas, VA." April 2005. In 1968—1969 a study conducted by Metcalf and Eddy, under the auspices of the State Water Control Board, determined that water quality deterioration in the reservoir was caused by substandard wastewater discharges from 11 secondary wastewater treatment plants and non-point sources of pollution. Following the commissioning of UOSA, the water quality of the Occoquan Reservoir has greatly improved. UOSA discharges a highly nitrified reclaimed water into Bull Run, which is a major tributary of the reservoir. Research conducted by the Occoquan Watershed Monitoring Laboratory (OWML) has shown that the nitrate in the UOSA reclaimed water has benefited the reservoir water quality specifically by: * Preventing the release of sediment bound phosphorus; * Reducing the release of ammonia from reservoir sediments; * Preventing the reduction of sulfate to sulfide in the bottom layers of the reservoir; * Possibly preventing the release of manganese (II) from sediments; and * Maintaining green algae and diatoms species dominance and preventing the proliferation of less desirable blue-green algae. According to OWML’s research, phosphorus releases are prevented when, in the absence of molecular oxygen in the lower levels of the reservoir, nitrate acts as an alternate terminal electron acceptor for certain bacteria delaying the onset of anaerobic conditions and inhibiting the release of iron-bound phosphorus from the sediments. During this process the nitrate is converted to nitrogen gas, which is released to the atmosphere. This is a fortuitous process that occurs because, during periods of thermal stratification, the waters of Bull Run enter the reservoir at lower temperatures than the surface waters causing the high nitrate water to sink to the oxygen-deficient lower reservoir depths. The Virginia DEQ recognizes the water quality protection benefits of the UOSA nitrified discharge on the Occoquan Reservoir in State permits.


Related information

The UOSA plant is relatively unique in that the highly treated output from the plant supplies roughly 20% of the inflow into the Occoquan Reservoir, which provides
drinking water Drinking water is water that is used in drink or food preparation; potable water is water that is safe to be used as drinking water. The amount of drinking water required to maintain good health varies, and depends on physical activity level, a ...
used by the
Fairfax County Water Authority Fairfax County Water Authority (FCWA or more recently Fairfax Water for short) is the main water company in the Northern Virginia region of the United States, and one of the four major water providers in the Washington, D.C. metropolitan area (the o ...
. During drought periods the plant may briefly provide up to 90% of the reservoir inflow. In effect, Fairfax Water is drawing a portion of its influent from recycled sewage. UOSA has proven, indisputably, that treated plant effluent is actually far cleaner than the stream sources of
surface water Surface water is water located on top of land forming terrestrial (inland) waterbodies, and may also be referred to as ''blue water'', opposed to the seawater and waterbodies like the ocean. The vast majority of surface water is produced by prec ...
inflow into the Occoquan Reservoir. Other Fairfax County sewage treatment facilities include the Norman M. Cole, Jr. Plant in
Lorton, Virginia Lorton is a census-designated place (CDP) in Fairfax County, Virginia, United States. The population was 18,610 as of the 2010 census. History Lorton is named for a village in the Lake District National Park, Cumbria, in England. Joseph Plasket ...
. Eastern Prince William County is served by the H. L. Mooney Advanced Water Reclamation Facility in
Woodbridge, Virginia Woodbridge is a census-designated place (CDP) in Prince William County, Virginia, United States, located south of Washington, D.C.. Bounded by the Occoquan and Potomac rivers, Woodbridge had 44,668 residents at the 2020 census. Woodbridge o ...
.


History

In the 1960s, the Occoquan Watershed began its transformation from a largely rural area to a predominately urban/suburban region. This rapid growth resulted in deterioration of water quality in the nearly Occoquan Reservoir, a principal drinking water supply for Northern Virginia] In 1971, the Virginia Water Control Board, in agreement with the Virginia Department of Health, adopted a bold and innovative policy. The Occoquan Policy mandated the creation of a regional agency, the Upper Occoquan Service Authority (UOSA), to provide state-of-the-art treatment for all wastewater generated in the Occoquan Watershed, and an independent organization, the Occoquan Watershed Monitoring Laboratory, to continuously monitor the Watershed and provide advice on protective measures for the Reservoir. In 1978, the UOSA Regional Water Reclamation Plant, located on in western Fairfax County, commenced operations and replaced eleven small secondary treatment plants in the region. Since that time, water quality in the Occoquan Reservoir has steadily improved and the reliable, high-quality effluent produced by UOSA has increased the safe yield of the Reservoir. Through several expansions, the initial per day capacity of UOSA was increased to 32 mgd, and a major expansion to has been completed. After 30 years of highly successful operations, UOSA
reclaimed water Water reclamation (also called wastewater reuse, water reuse or water recycling) is the process of converting municipal wastewater Sewage (or domestic sewage, domestic wastewater, municipal wastewater) is a type of wastewater that is produce ...
is an increasingly important component of the drinking water supply strategy for the Washington metropolitan area.


Initial Construction

The expanded sewage plant was constructed over the strenuous objections of many residents, leading to a public debate known cheekily as the "Third Battle of Manassas" in reference to the
American Civil War The American Civil War (April 12, 1861 – May 26, 1865; also known by other names) was a civil war in the United States. It was fought between the Union ("the North") and the Confederacy ("the South"), the latter formed by states th ...
battles known as
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and
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Manassas.


References

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External links


Occoquan Watershed Monitoring Laboratory
Fairfax County, Virginia Manassas Park, Virginia Manassas, Virginia Prince William County, Virginia Sewage treatment plants in the United States