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.
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.