Upper Occoquan Sewage Authority

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, VA 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 Millard H. Robbins Water Reclamation Plant is a state-of-the-art plant that includes primary-secondary treatment and the following advanced waste 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).

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 Table 1 are among the most stringent in the State of Virginia and possibly in the United States.

Table 1: UOSA Permit Limits

Parameter	Limit
Flow, mgd	54
E. coli, number/100 mL	< 2
Chemical oxygen demand, mg/L	10.0
Turbidity, NTU	0.5
Total Suspended Solids, mg/L	1.0
Total Phosphorus, mg/L	0.1
Surfactants, mg/L	0.1
Total Kjeldahl Nitrogen, mg/L	1.0
Dissolved Oxygen, mg/L	Greater than 5.0
Dechlorination Chlorine Residual, mg/L	Non detect