The Fairfax County James J. Corbalis Jr. Water Treatment Plant

On Thursday, April 26, 2012 I went up to Fairfax County near Herndon to see the Corbalis Water Treatment Plant, the newer of the two Fairfax Water treatment plants and visit with Melissa Billman, the Water Quality Laboratory & Regulatory Compliance Manager and Jeanne Bailey, the Public Affairs Officer for Fairfax Water. Combined they have more than half a century experience in Water Treatment Pants and Compliance and were kind enough to take the time to share their knowledge and experience. Fairfax Water is one of the 25 largest water supply companies in the nation supplying drinking water to 1.7 million Virginians, 900,000 of whom reside in Fairfax County. Twenty percent of all Virginians who are served by public water get their water either directly or indirectly from Fairfax Water. Loudoun Water, Prince William Service Authority, Virginia American Water, the town of Herndon, Fort Belvoir, and Dulles airport all obtain some or all of their water from Fairfax Water.

The Corbalis Water Treatment Plant also houses the Fairfax Water Quality Laboratory built in 2005 and using the state-of-the-art gas chromatography and laboratory equipment that reminded me that I studied chemistry in the Stone Age. The Water Quality Laboratory tests 15,000 samples of water each year and tested for 67,000 parameters including 3,240 samples tested throughout the year for coliform bacteria alone. Each and every month 270 samples are tested for coliform bacteria for the Virginia Department of Health, VDH.  All this testing is done to ensure that the water delivered to  their customers meets or exceeds all regulatory standards and that the water supply delivered to their 1.7 million customers is the best possible drinking water with today’s knowledge and technology.

The Water Quality Laboratory monitors the water from 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. In 2011 Fairfax water found minuscule traces (parts per billion or parts per trillion) of 2,4-D, TCEP, DEET, Monensin, Simazine, Atrazine,hexavalent chromium and perchlorate in the finished water.

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). The guiding principal of toxicology is that there is always a dose below which no response occurs or can be measured. So if the concentration of the contaminant was low enough there would be no toxic reaction and a trace amount of a substance does not necessarily represent a health risk. Fairfax Water as one of the largest (top 25) water utilities in the nation gathers and provides some data to federal and state regulators that may determine the future changes in the SDWA. 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.

  

After Melissa Billman showed us the laboratories and their equipment, Jeanne Bailey led the plant tour. Ms. Bailey once worked in this plant, starting when the plant was brand new and delivered 50 million gallons of water a day in 1982. Now the Corbalis Water Treatment Plant can deliver 225 million gallons of water a day and is planned to be expanded to 300 million gallons a day years from now when the fourth and final phase of the plant is finally built. The plant was conceived and planned to be built in phases.  The Corbalis plant is the newer of the two Fairfax Water Treatment Plants. Water from Fairfax Water is distributed through approximately 3,200 miles of water mains to the county’s homes and businesses. 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 100 degree day when everyone is doing laundry and watering their lawns and everything else we do with water on hot summer days.  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. 

The Corbalis Plant draws its water from the Potomac River four and a half miles away. There are two water intakes-one near the shore and the other mid-stream, which ever intake has better water quality is the one that is used.  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 Corbalis 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 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 well 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 thickened by the addition of a polymer, filtered, dewatered by pressure and ultimately used as a lovely agricultural soil amendment.

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 was added at the Corbalis plant in 2000 and used this way is still very much leading edge in water treatment technology. Ozone 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 within a series of tanks. Viewed just right, you should be able to see the purple corona during the process, but I did not see it.

Ozonation is followed by filtration through granular activated carbon and sand. 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 as well as the more dangerous Cryptosporidium organisms 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 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 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.

Building the plant in phases has allowed Fairfax water to modify their water treatment process and stay in the forefront of water treatment. Yet, Fairfax Water delivers water to their customers significantly below the national average cost of water, has the lowest retail water rates in the region and has a repair and replacement program that responds not only to the water main breaks, but is designed to replace the entire water supply and distribution system ever 75 years. Many thanks to Melissa and Jeanne for their time and a very interesting afternoon.