Upper Occoquan Sewage Authority

The Millard H. Robbins, Jr. Water Reclamation Plant, which is operated by the Upper Occoquan Service Authority (UOSA), is located in Centreville, Virginia and it was formerly known as the Upper Occoquan Sewage Authority. UOSA serves the western portions of Fairfax and Prince William Counties, and the Cities of Manassas and Manassas Park. The sewage treatment 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 54 million US gallons (200,000 m3) 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 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 kills; and

Generation of hydrogen sulfide in the bottoms waters of the waters of the reservoir.

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.