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The Washington Suburban Sanitary Commission takes water from the
Patuxent and Potomac Rivers. The water from the Patuxent River/Rocky
Gorge Reservoir is pumped to the Patuxent Water Filtration Plant in
Laurel, Maryland. The water from the Potomac River is pumped to the to
the Potomac Water Filtration Plant in Potomac, Maryland.
The Patuxent Plant
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"Let's Get Together"
The Rocky Gorge Reservoir is created on the Patuxent River by the T. Howard Duckett
Dam. Water is pulled through large intake screens in the reservoir to keep
out fish and large debris, and then pumped to the filtration plant. Before
entering the plant, chemicals, such as lime and ferric chloride or
aluminum sulfate, are added to create 'floc', a gelatinous sticky
substance that absorbs color out of the water and surrounds solid
particles in the water. Turning fine particles into larger ones is called
coagulation.
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"The Flocculation
Zone"
Big paddles gently
mix the water, causing the small floc particles to bump up against each
other and stick together to form bigger, heavier particles (the size of
snowballs!). This mixing process is called flocculation.
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"Settle Down There!"
After mixing, the water is passed into a settling basin or tank. As the
water quiets down, the large, heavy particles drop down to the bottom of
the basin. This is called sludge and is withdrawn from the bottom of the
basin, leaving the water on top cleaner and ready for more filtering. The
sludge is mixed with lime to stabilize it and the results are called
'biosolids', which can
be used to help fertilize landfills. (For more information on Biosolids
Recycling, click here).
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"Bleached"
Prior to going through further filtration, chlorine is added to the water.
Chlorine is used to kill any harmful bacteria and make the water safe to
drink. It also removes substances, like manganese and iron, which make
the water look funny and give it unpleasant tastes and odors. Lab
technicians at the plants constantly monitor the amount of chlorine
in the water and make sure it stays at safe levels. As a matter of
fact, our water quality experts at the plants constantly monitor the
water every step of the way to make sure we produce good safe drinking
water.
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"On To The Beach - Or At Least, The Sand Filters"
The filters in the plant have many layers. The first layer is gravel,
which sits on a perforated steel plate. On top of that are several
layers of sand. On top of that is a layer of anthracite coal. Water is
passed through these filters to remove any remaining 'floc'. These
filters are kept clean by a process called "backwashing", where
water is pumped backwards through the filter and the residual is siphoned
off to a special tank.
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"Just Hold On There!"
After leaving the filters, the water is pumped into filtered water storage
reservoirs. Right before it enters the filtered storage, quicklime is
added to adjust the pH and alkalinity in the water. This controls
corrosion in the pipes. Fluoride is also added to protect your teeth
from cavities!
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"All Pumped Up and Ready To Go!"
After processing is done, the water is stored to water storage. There
it waits to be pumped out through the series of pipes and water mains
to your home and community.
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The Potomac Plant
"Me Too! Me Too!"
The Potomac Plant processes water
much the same way as the Patuxent Plant, except that water is taken from the
Potomac River. Since this is a flowing river, a special little dam (weir) was
built across it to make sure there was always a pool of water to draw from,
especially when there is a drought. Once the water is pulled through the large
intake screens to keep out fish and large debris, large pumps then pump the
water 140 feet up the hill to the plant. From then on, the water filtration
process is basically the same. |
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