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Special
Districts > Crestline Sanitation
District >
History
& Background
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Seeley Creek Treatment Plant The Seeley Creek WWTP is the second largest of the District's three treatment facilities with a design capacity of 0.5 mgd. This facility went through a major plant expansion in 1985 and, accordingly, it can be considered to be the newest of the three treatment plants. Seeley Creek was originally constructed in 1974 as a 0.20-mgd package activated sludge facility to treat flows from Assessment District No 5. The treatment system consisted of an in-ground circular tank containing an activated sludge aeration basin, secondary clarifier, chlorine contact chamber and digester.
Flow
Equalization - Wastewater first enters the treatment plant site
immediately upstream of the 0.1 MG flow equalization basin. At this
location, there is a bar rack and flow diversion structure. All wastewater
first passes through this bar rack and is then routed into the
equalization basin or main headworks structure. Under normal conditions,
the equalization basin is bypassed and raw wastewater is sent directly to
the main headworks structure. The flow equalization structure has not been
used except during start-up and for emergency purposes, since construction
of the plant upgrade in 1985. Pretreatment - Raw wastewater flows from the upper bar rack into a second headworks located in the main headworks structure. This structure contains a bar rack, comminutor and Parshall Flume. Once through the bar rack, solids in the wastewater are shredded by the comminutor. Downstream of the comminutor, the Parshall Flume is utilized for measuring flows. Grit is removed by hand from a raised section of the headworks structure. Primary Treatment - The 45-foot diameter primary clarifier has a side water depth of 12 feet. Although constructed from the original circular package plant, the overall design is virtually identical to that of a standard primary clarifier. Sludge from the secondary clarifier is pumped to the primary clarifier for co-settling with primary sludge. This combined sludge is then pumped into an adjacent concrete tank for temporary storage prior to being hauled to the Huston Creek WWTP. Primary skimmings accumulate in a sump prior to being pumped to the holding tank. Both sludge and skimmings pumping is accomplished by a single air-driven diaphragm pump. The sludge pumping cycle and duration are controlled via manually adjustable timers. Pumping of primary skimmings is accomplished manually. Secondary Treatment - Primary effluent flows by gravity into a 45-foot diameter trickling filter containing 12 feet of stacked plastic (cross-flow) media. The filter is covered with an aluminum dome for temperature control and to keep leaves, pine needles and snow from clogging the filter. The trickling filter is operated in a constant recirculation mode. Two submersible centrifugal pumps provide recirculation. Both pumps are constant speed pumps and are duty units used in a lead-lag mode of operation. Effluent
from the trickling filter flows by gravity into a single secondary
clarifier. The 36-foot diameter clarifier has a 14-foot side water depth.
The clarifier has a center drive sludge rake and surface skimming
mechanism. Secondary skimmings flow by gravity into a sump where they
accumulate prior to being pumped to the primary clarifier. Secondary
sludge pumping is accomplished through use of a single air-driven
diaphragm pump. The pumping system is identical in design to that of the
primary sludge pumping system. Accordingly, the pumping cycle and duration
are controlled via manually adjustable timers. Pumping of secondary
skimmings is performed manually. Effluent
Disinfection - Chlorine disinfection is accomplished in a concrete basin
of serpentine design similar to the Huston Creek chlorine contact tank.
Chlorine feed is flow-paced and also has a manual backup control. Chlorine
dilution water is supplied by plant effluent. There are two manual wall
mount chlorinators (one duty, one standby). Chlorine gas is supplied from
a one-ton tank and a standby 150-pound cylinder. The system is the same as
that described for Huston Creek. Effluent Flow Metering - Plant flow is continuously recorded in the headworks via a sonic flow meter mechanism. Solids
Handling - As stated earlier, the Seeley Creek WWTP has no on-site sludge
handling facility. All skimmings and solids are temporarily stored in the
on-site sludge storage tank prior to being hauled to the Huston Creek WWTP
for mechanical dewatering. Grit and screenings removed by hand are
combined with the Huston Creek grit and hauled to an appropriate disposal
site. Plant Water - The treatment plant has a limited supply of fresh water which is supplied from a horizontal well that flows directly into the plants water system. A steel tank located on a hill above the equalization basin was originally designed to be refilled as necessary by tanker truck when the well supply is "dry." This tank leaks badly and is unusable and therefore out of service. Potable water is provided only at the operations building for drinking purposes. |
As flow
approached design capacity, the District constructed a 0.1 MG flow
equalization basin in 1983. The flow equalization basin captured the peak
flow and released it during low flow, thus extending the overall treatment
capacity and efficiency of the treatment plant. This system served its
purpose for the next two years leading up to the 1985 construction of a
new 0.5-mgd facility. The new facility utilized a fixed film process
(i.e., trickling filter) to provide secondary treatment followed by
chlorine disinfection. This process allowed gravity flow, increased
reliability and reduced operation and maintenance costs. Solids dewatering
is accomplished at the Huston Creek WWTP. The existing 0.20-mgd package
plant was converted into a primary clarifier as part of the 1985
construction. Effluent is discharged to the Seeley Creek gravity outfall
system.