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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Chemical Treatment Works

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The existing chemical treatment works consist of a small
two story chemical building and a 20-foot by approximately 80-foot
open concrete reaction basin. The chemical treatment works are
located adjacent to the Delta Control Reservoir at an approximate
elevation of 5,330 feet above mean sea level. The facilities were
constructed in 1968 with the filtration plant and replaced the old
chlorinator and fluoridation houses.

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Raw water enters a five foot by six foot flash mlxlng
chamber in the chemical building from the Delta Control Reservoir.
The rate of flow is controlled by a flow tube located ahead
of a cylinder operated butterfly control valve. The pressure differ-
ential across the flow tube is converted into an electrical signal
which is used to pace the chemical feeders and rate of chlorination.
A small electrically operated service pump draws water from a tap on
the main influent line. A portion of this water may be fed into a gas
chlorinator and then into the mixing chamber. The rest of the water
pumped from the effluent line may be piped into separate dissolver
chambers where lime (Calcium Hydroide) and Alum (Aluminum Sulphate)
may be added from separate hoppers. Lime is added to partially
remove calcium and magnesium bicarbonate which cause hardness.
Alum is added as a coagulant to form chemical floc particles
that adsorb, entrap, or otherwise bring together suspended matter.

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Concentrated solutions of lime and alum are theoretically
introduced into the flash mlxlng chamber at suitable ratios for
balanced reactions to occur. From the mixing chamber, the water flows
over a weir and through four 12-inch sluice gates into the reaction
basin. The reaction basin is divided into three sections separated by
over and under weirs. The velocity of flow in the reaction basin
should be such to allow the floc particles to settle to the bottom of
the basin. At the end of the reaction basin, the upper layer of water
flows over a weir and into the main effluent pipeline and eventually
to the filtration plant. The water level below the effluent weir is
monitored and a signal is sent to the control valve on the main
influent line. The control valve is throttled to maintain a preset
level in the influent chamber.

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At frequent intervals, the particles which have settled out and
collected in the reaction basin must be flushed out. This is
accomplished by temporarily interrupting plant operation and draining
the reaction basin through strategically located 12-inch drain lines.

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A schematic diagram of
treatment works is shown in
such as sensing lines and drain

the main operations at the chemical
Figure 111-5. Secondary functions
lines have not been shown.

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