Constructed in 1968, the City of Bellingham’s Water Treatment Plant (WTP)
has a capacity of 24 million gallons a day (MGD) of treated water with one
filter off line for backwashing. Over the years, the plant has been updated to include computer controls and
the latest in water treatment technology. The WTP uses what is known
as an in-line or contact filtration process in which a chemical that aids or
enhances the coagulation process is added just prior to filtration. This
type of treatment is preferred for high-quality source water like that found
Lake Whatcom serves as the drinking water source for Bellingham with additional
water rights coming from the Middle Fork of the Nooksack River via the
Deming Glacier on Mt. Baker. Lake water travels two-thirds the length
of Lake Whatcom by gravity were it enters a submerged intake, then into a
gate-house and finally a screen house. In the screen house, fish and debris
are removed and chlorine is added.
Chlorine helps with the
coagulation process and prevents algae growth in the pipes carrying
a pipeline conveys the water to the WTP.
At the WTP, the 66-inch diameter pipeline bifurcates, or divides, into
two, 48-inch diameter pipelines that lead to two rapid mixing basins. Water
flows from the basins into a common filter applied water channel for
distribution to the filters. These large filters consist of anthracite
coal, silica sand, and an under drain system.
Following gravity filtration through the multimedia filters, the filtered
water flows into a 1 million gallon reservoir located inside the plant
called the clear well. The water then flows into a 16 million gallon
reservoir for disinfection
and distribution into the water system. The reservoir provides contact
time with the chlorine prior to distribution. Alum and a cationic polymer that cause microscopic impurities
in the water to clump together are added at the WTP. These larger particles
are more easily removed by filtration.
Finally, soda ash is added to raise the pH of the treated water to help
protect the 410 miles of water mains and our water customer’s plumbing.
Powdered, activated carbon is occasionally added for taste and odor control.
Last, water quality tests are performed every day before the water leaves the
The City of Bellingham operates a state-certified laboratory at the WTP.
Extensive water quality monitoring is conducted of the treated water at the
plant, and throughout the distribution system. Treated water quality is
monitored continually by on-line instrumentation and regularly analyzed for
more than one hundred sixty (160) constituents. There are roughly
ninety (90) designated sampling stations that are used to monitor water
quality throughout the city each month.
For more information about treated water quality and monitoring programs,
please contact the Technical Supervisor at the Operations Division of the
Public Works Department.
Particulate impurities in water result from land erosion, pickup of
minerals and the decay of plant material. Additional impurities can be
added by airborne contamination, industrial discharges and by animal wastes.
For these reasons, surface water sources are likely to contain suspended and
dissolved organic (plant or animal origin) and inorganic (mineral) materials
and biological forms, such as bacteria and plankton.
These particulates (commonly called suspended solids) cover a broad size
range. Larger-sized particles such as sand and heavy silts can be
removed from water by slowing down the flow to allow for simple gravity
settling. These particles are often called SETTLEABLE SOLIDS.
Settling of larger-sized particles occurs naturally when surface water is
stored for a sufficient period of time in a reservoir or lake.
Smaller-sized particles, such as bacteria, fine clays and silts, do not
readily settle. Water treatment is required to produce larger particles that
are settleable. These smaller particles are often called NONSETTLEABLE
SOLIDS or COLLOIDAL MATTER.
The purpose of the coagulation and flocculation is to remove particulate
impurities, especially non-settleable solids and color, from the water being
treated. Non-settleable particles in water are removed by the use of
COAGULATING chemicals. The mixing of the coagulant chemical and the
raw water is commonly referred to as flash mixing. The primary purpose
of the flash mix process is to rapidly mix and equally distribute the
coagulant chemical throughout the water. The reaction between the
colloidal matter with the coagulating chemical occurs within seconds, and
the first results are the formation of very small floc particles. When
pieces of floc clump together, they form larger, heavier floc which can
settle out and/or be removed by filtration.
the WTP there are six granular media filters with a total surface area of
3,360 square feet. Each filter has two cells, which are controlled by one
rate-of-flow effluent control valve. Each cell is backwashed separately
using a pumped backwash system. Filter media is considered “mixed” because
there are different constituents in place which aid in removing
In Bellingham, our filter media consist of 31 inches of anthracite and 11
inches of silica sand. This filter media is supported by AWI stainless steel under drains.
Each filter cell has three wash water troughs and two rotary arm surface
wash sweeps. The sweeps are used during the cleaning of the filter to help
remove trapped solids within the filter media. The filters are also equipped
with a filter-to-waste system. This system is used to remove the
higher filter effluent turbidities which will occur during the first few
minutes at the beginning of a filter run. Filtering-to-waste for this
period makes sure that only the cleanest water is delivered to customers.
The WTP produces drinking water continuously, and with the help of many
storage reservoirs stationed throughout the city. The reservoirs store
twice the daily average demand for the City and are used to supply the peak
water demands during the day. The storage reservoirs are refilled at
night when the water demand is lower. Typically, on a warm summer day the
water demand goes up in the afternoon and drops off around midnight.
The production rates at the plant average between 8 million gallons per day
during the winter months and up to 20 million gallons per day in the summer.
Seasonal fluctuations in water use are a large reason why water
conservation is so important. Each year, City customers consumed 67% of the
available water stored in Lake Whatcom. Water stored in Lake Whatcom
is used most during the summer when the water demand is the greatest and
there is less rainfall to help replace the water used. The good news
is that City water customers are doing their part to conserve.
In the late 1990’s, 34% of the total water used in a year was
consumed in the summer months. Today, that percentage has dropped to 30%, mainly due to water conservation. Visit the
conservation webpage for information and tips.
purpose of the filtration process is the removal of the particulate
impurities and floc from the water being treated. Floc removal is
accomplished by contact with the media grains (sand, coal or other granular
substance) throughout the depths of the filter. After initial coating or
conditioning of the media surfaces with floc at the beginning of the
filtration cycle, subsequent applications of floc will build upon the
material previously deposited on the media surface. Over a period of
time (several hours) the floc material accumulates in the filter media bed
to the point where the impurities start to break through causing higher
turbidity on the filter effluent, or clog up the filter to a point where the
flow is reduced significantly. At this point the filter must be
cleaned by backwashing.
Backwashing is the process of reversing the flow of water through the
filter media to remove the entrapped solids. The backwash flow rate is
usually 10 times higher then the filtration rate in order to expand, or
fluidize, the media in order to release the entrapped solids. This
process may use two to four percent of the process water to clean the
Filter unit design, filter media type and thickness play a role in
determining filter removal efficiency. Dual media filters have
lighter, larger diameter grains in the top layer of the filter which stop
the larger particles. Smaller particles are usually stopped further
down in the filter media. The larger grain size in the anthracite coal layer
of a dual media filter permits greater depth penetration of solids into the
anthracite. This coal layer provides larger solids storage volume in
the filter. The sand layer below the anthracite is used as a
protective barrier against breakthrough.
Administration and Control
State certified plant operators are on duty 24 hours a day to monitor and
control the treatment process. The plant is fully automated and has a
state-of-the-art computer system which provides operators with accurate and
The City has a number of educational material available on the topic of
water quality and water treatment.
Tours for individuals or community groups can be arranged by contacting
the Chief Operator in the Operations Division of the
Public Works Department.
Over the last several years, the City of Bellingham has developed and
implemented an extensive and highly successful
public education program
focusing on the City's water supply. The program targets schools, civic
groups, drinking water customers, watershed residents and other community
interests, with the goal of increasing public awareness of water resources,
water quality, and water conservation issues.