Prince William Service Authority

Recently, I attended the Service Authority’s Annual Water Academy on Zoom. It was an easy way to learn about drinking water and waste water resources in Prince William County. The following is from that program and a presentation given by Don Pannell, Deputy General Manager at Prince William County Service Authority, to the Board of County Supervisors.

Utilizing current projections of water usage, the County and the Metro-Washington Council of Governments estimates that the current level of water capacity is sufficient until at least 2040. This does not take into consideration any future development of the rural crescent which has not been factored into the current projection. Depending on the level of development in the rural crescent, this date will likely occur much sooner. In addition, these projections, also, do not take into account any increase in drought due to climate change.

The Prince William Service Authority distributes about 11 billion gallons of water per year to the residents of the county that are on public water. The communities that receive their water from the Service Authority can be seen below in the blue, pink and yellow areas. The remainder of the county obtains its water from private wells.

The maximum amount of water that can be delivered by the Service Authority is 67.8 million gallons a day (MGD). The source of that water is:

• Fairfax Water: 62.4 MGD
• Lake Manassas: 5.0 MGD
• Service Authority wells: 0.4 MGD

The Occoquan Reservoir is an essential portion of the Fairfax Water supply. We are dependent on Fairfax Water for 92% of the Prince William public water supply, yet 66% of the Occoquan Watershed is in Prince William County has been unprotected from development and pollution. Fairfax preserved 21,000 acres in Fountainhead park to protect the Occoquan River and Reservoir. “On November 17, 2020, the Board issued Directive No. 20-86 for staff to develop a protection overlay district for the Occoquan Reservoir.” 

In fiscal year 2021 the average daily water demand was 30.0 MGD with the maximum day at 49.3 MGD. As you can see 92% of the water capacity for the county comes from Fairfax Water which in turn draws water from both the Potomac River and the Occoquan Reservoir. At present, less than 1% of the public water supply comes from public groundwater wells. There was a time (40 years ago) when most of the water in Prince William came from public supply wells, but that came to an end when the public wells in Manassas were discovered to be contaminated with solvents. The only groundwater study of Princes William County was done to identify the extent of the solvent contamination in 1997.

Based on growth projected that were made using the previous comprehensive plan that did not allow any public water use in the Rural Crescent or consider any change increase in duration and severity of droughts due to climate change, exiting capacity should be sufficient until 2040. However, the climate is changing and Prince William County is developing within the Rural Crescent.

Prince William Service Authority also provides waste water treatment for the public sewer customers in the county. Wastewater treatment is provided by the Fairfax run Upper Occoquan Service Authority and the H.L. Mooney AWRF plant in Woodbridge. The Service Authority treats 10.6 billion gallons of wastewater each year. Prince William has a newer separate sewer system, so we do not have combined sewer storm events. Total sewer treatment capacity: 43.8 MGD H.L. Mooney AWRF: 24.0 MGD Upper Occoquan Service Authority : 19.8 MGD. Both wastewater treatment plants are expected to expand their capacity in the future Upper Occoquan Service Authority by 2030 and Mooney by 2040.