Fairfax Water's Griffith Water Treatment Plant

from Fairfax Water

Last Friday I had the opportunity to tour the Fairfax Water Frederick P Griffith , Jr Water Treatment Plant on the northern edge of the Occoquan Reservoir in Lorton, Virginia. I had never visited the plant before and was really delighted to have the opportunity to tour the facility with a group from the Potomac Watershed Roundtable. We were fortunate enough to have Chad Coneway, the Manager of the Griffith facility act as our tour guide.

Fairfax Water is 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 residents (1.13 million retail customers and 988,000 people through their wholesale customers - Prince William Service Authority, American Water and Loudoun Water).

The Frederick P Griffith , Jr Water Treatment Plant was completed in 2006 to replace a series of older water treatment facilities. It’s design capacity is 120 million gallons of water a day, but it can be expanded to 160 million gallons a day if regional water demand grows. Despite growing population in the region, water demand from Fairfax Water has remained fairly level for over 25 years as water conservation habits and appliances have been adopted regionally and Loudoun has built a water treatment plant that draws directly from the Potomac River.

The Griffith plant is operated by a team of operators in a control room with two rows of screens that monitor operations and water parameters watching for an unusual or out of parameter. The Griffith plant does testing in the process to ensure that the water treatment operations remain consistently within parameters. As Mr. Coneway pointed out there is no ability to dump a “bad batch” of water. Around 100 million gallons of water is treated every day at Griffith and it all has to be good.

The Fairfax Water Quality Laboratory which is housed in the Corbalis Plant monitors the water from both the Potomac River and Occoquan Reservoir throughout the water treatment process and at various points in the distribution system for almost 300 parameters including the Federal Safe Drinking Water Act, SDWA primary and secondary contaminants for which there exist maximum contaminants limits and also for a list of emerging contaminants such as Endocrine Disrupting Compounds (EDCs), Pharmaceuticals, and Personal Care Products (PPCPs) that have been found in water nationally. Fairfax Water tests their source and treated waters for a list of 25 substances, hexavalent chromium and perchlorate have recently been added to the list.

The technology used for chemical analysis has advanced to the point that it is possible to detect and quantify nearly any compound known to man down to less than a nanogram per liter or parts per trillion (1/1,000,000,000,000), but Fairfax Water and all water treatment plants are struggling to get ahead of PFAS regulations. In the meantime, research has shown that using the combination of ozone and granular activated carbon filtration that is used by Fairfax Water is very effective in removing broad categories of personal care products and pharmaceuticals as well as the more dangerous Cryptosporidium organism from the source water. Though, no method of filtration is 100% effective all the time.

The Griffith plant also uses an unusual water quality monitoring system. Blue gill fish are part of an aquatic biomonitoring system. A water-monitoring device electronically analyzes the behavior of eight captive young bluegill fish to detect the presence of chemical toxins or other contaminants. The system uses bluegills because the fish are both sedentary and because there exists a large database showing how various toxins affect them. Although adult bluegills can grow to be over a foot long, the system relies young fish that are generally no longer than four inches. It requires that they remain in the chamber, unfed, for two-to-three-week tours and then are retired to the aquariums to breed more bluegills.

Water from Fairfax Water is distributed through approximately 4,000 miles of water pipes in to the homes and businesses in Fairfax County. On average, Fairfax Water produces 160 million gallons of water per day from both the Corbalis plant and the Griffith plant. The combined total capacity of both plants is 345 million gallons/day. The system must be sized to deliver the peak demand on a hot summer day when everyone is doing laundry and watering their lawns and everything else we do with water on hot summer days. This past summer the peak demand day was 238 million gallons. The peak demand day ever was 259.1 gallons of water delivered. To ensure the continuation of water supply during droughts, Fairfax finalized a regional drought response plan in 2001 that included a low flow allocation agreement with the members of the Interstate Commission on the Potomac River Basin, ICPRB. In addition, Fairfax bought the rights to 14 billion gallons of water from the Jennings Randolph Reservoir. Planning for the future Fairfax Water has obtained the Vulcan Quarry in Lorton. It will be converted to a reservoir in phases and continue to operate. Phase I 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.

The Griffith Plant draws its water from the Occoquan Reservoir down the hill. The Occoquan Reservoir is fed by the Occoquan River which receives on average over 30 million gallons a day of the treated discharge of the Upper Occoquan Sewage Authority treatment plant. (The peak for that plant is 54 million gallons a day.) A significant portion of the flow (especially during dry periods) into the reservoir is recycled sewage. This treated wastewater is from areas supplied by the Corbalis plant or lake Manassas. In addition, the reservoir receives stormwater runoff, precipitation from the Occoquan Watershed which covers portions of Loudoun, Fairfax, Fauquier, and Prince William counties and feeds the streams and creeks that feed Bull Run and the Occoquan River.

Bars and giant screens on the pipes are used to prevent the intake of trash, debris and fish. Potassium permanganate (KMnO4) is added to the water at the intake to control taste and odors, remove color, prevent biological growth within the water treatment plant, and remove iron and manganese. The raw water is then pumped to the Griffith plant where is treated in a series of slow and elegantly simple steps to produce clean and clear drinking water.

Once at the plant the water is pumped to the first of a series of continuously monitored water chambers where the pH is adjusted by adding either caustic soda or sulfuric acid and the primary coagulant, polyaluminum chloride. This coagulant is used to remove small particles of dirt suspended in the water by causing them to stick to one another aided by the coagulant polymer. The water moves from the first water chamber where it is mixed through a series of chambers (which are really just a series of open rectangular water pools) with slower and slower mixing to allow the particles to coagulate into larger and larger particles until dirt floc is formed. Finally, the water arrives in the sedimentation basins that are not mixed at all and the floc is allowed to settle to the bottom of basins by gravity where they are removed. The floc is filtered out pumped to the quarry where the water separated out. Mr. Coneway call the sediment basins the workhorses of the plant.

The next step in the water treatment process is ozonation, the infusing of the water with ozone gas and the first of two disinfection steps. This step is still very much leading edge in water treatment technology. Ozone is the only chemical made on site, and is highly effective in eliminating the Cryptosporidium bacteria and other naturally occurring microorganisms present in water. Unlike ultraviolet and chlorine disinfection systems, there is no re-growth of microbes after ozonation. This step improves the taste and smell of the water. Ozonation also reduces the formation of trihalomethanes (chlorine breakdown products) because of the reduction of organic materials in the water before chlorination. Fairfax water converts liquid oxygen to ozone by an electrical discharge field created in a series of tanks. I was able to  be able to see the purple corona in the one operating tank. The Griffith plant has the capacity to treat a much higher level of cryptosporidium bacteria than is typically found in the Occoquan Reservoir.

Ozonation is followed by filtration through granular activated carbon. One cup of GAC has the surface area of about 25 football fields (1,300,000 square feet). Billions of pores in GAC absorb the organic substances removing them from the water and is very effective in removing biological and physical impurities that occur in broad categories of personal care products and pharmaceuticals from the water. Slow flow through the filter tanks improves the effectiveness of the filtration. The filter water wash, all runoff from the plant and the water from the dewatering process are reclaimed and returned to the raw water control chamber. The GAC is regularly backwashed, but lasts about 20 years before it has to be replaced. Mr. Coneway told us that the cost to replace the GAC in each bay is currently around $400,000.

The final steps in the water treatment process is the second disinfection, fluoridation and the addition of a ammonium hydroxide to adjust the pH slightly to prevent corrosion of piping and fixtures in customer homes to prevent the leaching of lead into water. Nine months of the year Fairfax Water uses chloramine (created by mixing sodium hypochlorite and ammonia) as the final disinfection step. However, during April, May and June of every year Fairfax Water flushes the entire 3,200 miles of water main and uses chlorine during that time to disinfect the delivery network. Flushing the water system entails sending a rapid flow of water through the water mains. As part of the flushing program, fire hydrants and valves are checked and cleaned. Flushing of the water distribution system is performed to remove sediment in pipes and helps to keep fresh and clear water throughout the distribution system. Chlorine is used as the disinfectant during this time so that after the system is flushed, a chlorine residual is maintained in the distribution system to provide a persistent disinfectant to prevent the re-contamination of water before your water tap.