Siler City, North Carolina
In 1988 Hobbs, Upchurch & Associates began planning and design of an upgrade of
the 1.8 MGD wastewater treatment plant at Siler City. The plant was
experiencing severe problems caused by large peak stormwater inflow, a large
constituent of industrial water including discharge from poultry processing
plants and the relatively low flow (approaching zero at times) of the small
receiving stream.
The Town chose to seek funding through the State Revolving Loan Program
administered by the Construction Grants and Loan Section of DEM. The option
required an update of the 201 Facilities Plan, which proved to be an extremely
difficult and time consuming task because of environmental groups trying to
protect the Rocky River which received the plant discharge via Love's Creek.
A federally endangered species, the Cape Fear Shiner, raised particular
concern, because of its habitat several miles downstream of the plant
discharge. Environmental planning included time of travel stream studies,
stream macro-invertebrate populations, fish and mollusk population
investigations, and consideration of the waters' nutrient sensitivity.
Because of low receiving stream flows and the emphasis on improving the
condition of the Rocky River, Siler City was given the strictest discharge
limits presently in effect in North Carolina.
The design of the plant posed several problems, including the need for the
addition of a large volume of stormwater flow equalization; the need for a
large volume of aerobic sludge digestion; sludge thickening and sludge holding;
and the need to incorporate the oddly configured plant into the final design
while maintaining compliance during the construction period.
Extensive research was performed on nutrient removal technologies, both
proprietary and non-proprietary. Each alternative was analyzed financially to
balance the cost of capital expenditures against the operation and maintenance
costs and the expected reliability of the processes. By careful analysis of the
plant influent, HUA was able to provide a non-proprietary process at
considerable cost savings which, when augmented by chemical nutrient removal,
provides a reliable and controllable method of nutrient removal.
All existing plant basins, including clarifiers, were used in the design for
conversion into flow equalization and sludge handling facilities.
This project received a 1994 Engineering Excellence "Grand Conceptor Award"
from the American Council of Engineering Companies of North Carolina (ACEC/NC).
Project that receive this award undergo a through third part review and are
rated on requirements such as exceeding client's expectation.
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