WK Dickson provided planning, environmental assessment, permitting coordination, funding assistance, engineering design, and construction administration for the construction of a new 6-MGD raw water intake, the expansion of the town’s existing WTP from 3-MGD to 4.5-MGD, planning for Phase II WTP expansion, and construction of 12 miles of 24-inch water transmission main.
At the selected intake site, numerous design alternatives were evaluated. An infiltration gallery was selected as it would not result in any permanent negative impacts to aesthetics, recreation, or stream flow. In addition, the town was able to increase the capacity of their existing WTP from 3- to 4.5-MGD by increasing filter rates at the plant and making other necessary operation and maintenance upgrades. Improvements included upgrades to the existing flocculators, rapid mixers, settling basin, filters, chemical feed equipment, the addition of onsite generation of chlorine disinfectant to replace chlorine gas, and a second clearwell.
These improvements expand the capacity of the plant while keeping it in operation on a very constrained site. Due to significant elevation gains from the intake and water treatment plant, a booster pump station was proposed along the raw water transmission main to mitigate extremely high pressures and pump horsepower requirements at the raw water intake pump station. Our team conducted a transmission main system head curve evaluation with field testing prior to selection and sizing of the pumps.
At the raw water intake pump station, three vertical turbine raw water pumps rated at 2-MGD each were provided to convey the water to the proposed booster pump station. A maximum of two raw water pumps operate at any given time, leaving the third raw water pump as a redundant backup. An additional vertical turbine pump rated at 4-MGD was provided for backwashing the infiltration gallery.
Routing of the raw water main was coordinated extensively with the NCDOT, as several segments were installed under the pavement of secondary state roads. After much due diligence, geotechnical investigations, and alternative analysis, NCDOT agreed to allow approximately six miles of the raw water main to be installed within the median of New US Hwy 421. The project included several open cuts of tributary streams and five crossings of the South Fork of the New River by horizontal directional drilling.
WK Dickson assisted the town in acquiring a $1.8 million USDA-RD grant, a $32.5 million USDA-RD low interest loan, and $450,000 loan from the NC Rural Center to make the project possible.
This project received the ACEC North Carolina Grand Conceptor Award.