PROJ00001

• Contract/PO #: C153168
• Contractor Name: Delta, City of
• Contract Type: Loan
• Water District: 40
• County: Delta
• Bill Number: SB 77-35
• Loan Projects - Doc Type: Feasibility Study

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For purposes of backwashing, pressure taps on each filter
unit have been installed with transmitters to relay the signal
to a loss of head indicator mounted on the master control panel.
When the loss of head across each filter unit reaches a specified
level, a high loss alarm light is energized. Backwashing of the
filters is accomplished by drawing water from the effluent manifold
through a pressure reducing valve.

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Wash water passes through a rate of flow controller and
thence to each filter through cylinder operated valves. The rate
controller is equipped with a hydropneumatic pilot valve controller
and a rate transmitter. The pilot valve controller is connected
with a backwash water rate setter and rate transmitter which
sends a signal to the backwash indicator totalizer mounted on the
master control panel. During each backwash cycle, waste water passes
through cylinder operated valves located on each filter. Backwashing
of the filters can be done automatically or manually and each
filter unit can be backwashed independently of the others.

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Waste water from backwashing operations is presently discharged
into a local irrigation ditch. In order to comply with effluent
limitations imposed by the Environmental Protection Agency, the
City of Delta is attempting to construct facilities for collection
and recycling of backwash water. These facilities include a small
sedimentation basin and equipment to pump clarified wash water
back into the main treatment plant influent pipeline. Plans and
Specifications have been prepared and the City has received a
50 percent matching grant from the Colorado Division of Local
Governments. The City will soon award the Contract and it is
anticipated that construction will take place in the summer of
1975.

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The frequency of backwashing is
of Figures 111-8 through 111-13. Each
filter unit uses between 60,000 and 80,000

shown on
backwash
gallons on

the bottom line
cycle for each
the average.

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The monthly record of backwash water used at the filter
plant is shown in Table 111-4. The data shows that usually from
145,000 to almost two million gallons per month can be required
for backwashing the filters during the year. On the average,
approximately 7,000,000 gallons per year are used to backwash
the filters. Although this quantity is equivalent to approximately
two full days of maximum production, it is less than one percent
of the total annual production and is well within reasonable
limits for backwash losses.

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