Water Supply and Source Water Protection

The Potomac Watershed Roundtable met last week at Fairfax Water Griffith Water Treatment Plant. The host speakers were: Greg Prelewicz, Manager-Planning for Fairfax Water and Nicki Bellezza, Watershed Protection Specialist for Fairfax Water. Mr. Prelewicz and Ms. Bellezza spoke about ensuring an adequate water supply into the future and protecting the quality of source water especially at the Occoquan Reservoir and the Griffith Water Treatment Plant.

Fairfax Water founded in Fairfax County in 1957 is now the largest drinking water provider in the Commonwealth of Virginia and one of the largest in the nation. They supply drinking water to 2 million Virginians -1.13 million retail customers through their 4,000 miles of water distribution pipes and 988,000 people through their wholesale customers - Prince William Service Authority, American Water and Loudoun Water. About 40% of the water supply comes from the Griffith Water Treatment Plant that obtains it’s water from the Occoquan Reservoir.

The Occoquan Reservoir consists of 1,400 acres containing 8.5 billion gallons of water that provides 40% of the daily water supply for Fairfax Water which in turn supplies Prince William Service Authority and a significant portion of Loudoun County. The reservoir’s water quality is a reflection of its watershed; spills, roadway runoff, stormwater carrying oil, salt and dirt are all carried into the Occoquan Reservoir. The water from the reservoir is then treated by the Griffith Water Treatment Plant and piped out to customers.

Source water protection is the first step to ensuring safe drinking remains available. By the early 1970’s Occoquan Reservoir began to experience problems with water quality and became that something had to be done to protect the water supply. Studies at that time concluded that inadequately treated sewage discharged by eleven secondary treatment plants in the Occoquan Watershed was largely responsible for the serious water quality problems in the Occoquan Reservoir. To remedy the problems, the predecessor of the DEQ adopted a comprehensive policy for the Occoquan Watershed in 1971. A principal requirement of the Occoquan Policy was the construction of a regional wastewater treatment facility to replace the eleven existing treatment plants. UOSA was created to treat the wastewater to such an extent that it could be recycled for use in the reservoir. UOSA was designed to recycle water that originated in the Potomac River and Lake Manassas into the Occoquan Reservoir. The Virginia Tech run Occoquan Watershed Laboratory continuously monitors the quality of the water.

To meet needs resulting from increases in population (both past and future) and the wastewater flows in its service area, UOSA developed an expansion program that  expanded the treatment plant capacity to 54 million gallons a day that was completed in  2005. Though the construction of UOSA was a huge step forward in restoring and maintaining water quality, it was not enough.

When the Occoquan Reservoir was first built 1957 it was located in a rural and forested area and the water was pristine. The unrelenting growth and development in this region has changed that.  When natural land is cleared to make way for commercial, residential, or industrial uses, vegetation is removed and resulted in increases in impervious which causes stormwater to flow at higher velocity and volume and damages and erodes stream banks. In addition to the damage done to streams by increased storm flows, urban/suburban runoff brings with it many types of pollution, mostly of the type that come from diffuse large geographic areas (called nonpoint source pollution). All sorts of pollutants can be carried in stormwater reflecting the land use- oil, grease, solvents, fertilizer, trace toxins from roadways, etc. The next steps to protect the Occoquan Reservoir was to develop the Occoquan Non-Point Source Program. Fairfax County down zoned 41,000 acres to 1 house per five acres or to parkland and created the Water Supply Protection Overlay District. Though 40% of the 570 square miles of the Occoquan Watershed including the headwaters of the Occoquan are in Prince William County, they did nothing to protect the Occoquan Reservoir. In addition, Prince William specifically chose not to create a Occoquan Watershed Overlay district in 2022.   

Nonetheless, Fairfax Water continues to work to improve water quality in the rivers, streams, and Occoquan Reservoir ahead of the Griffith Plant intakes. Fairfax Water is hoping in this way, despite the lack of cooperation and coordination from Prince William County it is possible to keep some contaminants out of the water and make the treatment process easier, and less expensive for all their water customers in Fairfax, Prince William and Loudoun.

Climate forecasts for the region indicate that by 2040 precipitation in the Potomac River Basin is projected to increase 8% and temperatures are forecast to increase 2.2 degrees Celsius from preindustrial times. While rainfall and storm intensity is expected to increase overall, droughts are also forecast to increase. Though water sales have been relatively flat from 1990-2020, due primarily to the expansion of water demand management in the form of more efficient water fixtures, the spread of conservation practices and reductions in water loss,  it is expected to grow in the future. Population is expanding and industrial use is growing in the form of data centers and semi-conductor chip manufacturing.

To meet the forecast demand for water and the climate uncertainties, Fairfax Water acquired the Vulcan Quarry in Lorton, VA right next door to the Griffith Plant. The Quarry will be converted to a reservoir in phases and continue to operate during phase 1 which will convert a portion of the quarry to a reservoir with storage of of about 1.8 billion gallons by 2035. Quarry operations will end with Phase II which will convert the remaining area to Fairfax Water reservoir with storage capacity of up to 15 billion gallons by 2080. 

Fairfax Water is panning for the future, but needs Prince William County to join them. The way to protect source water is land use controls (such as zoning ordinances and growth controls) Regulations, permits, and inspections. Land conservation and green infrastructure solutions utilizing plantings and open areas to manage stormwater. However, Prince William County is going in the opposite direction. Rezoning agricultural and woodland to industrial, stripping the land of natural vegetation that served as natural green infrastructure.

The entire Potomac watershed is being challenged by freshwater salinization syndrome and the expansion of roadways and impervious surfaces that require salting will make it worse. Sodium mass loading to the reservoir is primarily from watershed runoff during wet weather and reclaimed water from UOSA (where Micron Semi-Conductor discharges their process water) during dry weather, sodium concentration in the reclaimed water is higher than in outflow from the two watersheds in the current historical data, but development in the Bull Run and Occoquan watershed has been accelerating, increasing salinity. Currently, the Occoquan watershed is far less developed than the Bull Run Watershed, but Prince William is considering massive development in the watershed.  Rising salinity in the Occoquan Reservoir implies that its salt budge is out of balance and needs to change.