During drought periods the plant may briefly provide up to 90% of the Occoquan Reservoir inflow.
The UOSA 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).
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 for Fairfax Water. 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 far cleaner than the stream sources of surface water inflow into the Occoquan Reservoir.
The plant’s rated capacity is 54 million US gallons per day.