PERCEIVED RISK AND THE SITING OF A CONTROVERSIAL ...

equirement with only the initial flow provided by the Lorena interceptor, adjustments to
the expected plant startup operations became necessary.
Specifically, the existing Lorena plant was drained by pumping flow directly from the
facility’s secondary clarifier to the new interceptor line through a newly constructed
onsite lift station, which was completed in conjunction with the interceptor project. Flow
to the Lorena plant was approximately 120,000 GPD during this period. Based on the
installed lift station capacity, it was estimated that the entire Lorena plant volume and
incoming flow could be transferred by continuous pumping within two to three hours.
The available flow from Lorena proved to be quite a challenge, considering that the total
combined volume of the new wastewater treatment plant’s biological nutrient removal
(BNR) basins is approximately 1.13 million gallons (divided between two process
trains). Moreover, each secondary clarifier has a volume of approximately 405,000
gallons, and the facility’s tertiary disc filters and ultraviolet light (UV) disinfection
system also have basins necessitating flow.
Ultimately, based on the available flow and required basin volumes, it was determined
that it would take more than a week to fill the required process units of a single treatment
train with wastewater flows coming only from Lorena. Therefore, it was decided that
plant startup would be undertaken with the basins still full of the well water used by the
contractor for equipment testing and training.
Running a single train reduces the plant’s capacity by half, or to 0.75 MGD; however,
the startup flow (and thus the facility loading) was only 16 percent of that capacity,
which is extremely low. To maintain a treatment regime that was somewhat workable,
wasting was carefully controlled,
in order to sustain a reasonable food to mass (F/M) ratio within the treatment process,
and to maximize phosphorus removal. Despite these measures, the low influent load
resulted in the production of very thin mixed-liquor sludge.
In addition, the low flow within the process meant that the water was moving extremely
slowly though the operational treatment train. This generated concerns that there might
be issues with algae growth in the anoxic basins, secondary clarifiers, and disc filter
basins where the water would be fairly quiescent. Provisions for alternate internal
recycle points were implemented by partially opening plant drains to return flow to the
onsite lift station, to allow the plant operators to keep the water within the plant
circulating.
BioWin 3.1 process modeling conducted in advance of plant startup to simulate the
modified influent flow conditions, indicated that some phosphorus removal could be
achieved within the biological process, despite the non-ideal regime; however, the model
results also implied that the mandated discharge limits for phosphorus could not be
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