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Consultants warn Hornwood pump station may be overwhelmed by Atlantic Gateway flows without downstream upgrades
Summary
Hazen & Sawyer told commissioners their model and field tests show the Hornwood pump station (county) pumps about 800 gpm and that adding Atlantic Gateway flows (575 gpm) plus a private 300 gpm source could exceed receiving gravity sewer capacity, risking surcharge and manhole overflows; they recommended not accepting flow until downstream upgrades are planned.
Engineering consultants Hazen & Sawyer told Anson County commissioners on June 16 that the county’s Hornwood (Kenville) pump station and downstream gravity sewer may not be able to accept additional flow from a proposed Atlantic Gateway pump station without upgrades.
Consultant Andy Larrick said pump drawdown testing at Hornwood measured an average pump rate of about 800 gallons per minute (gpm). A private textile facility already contributes roughly 300 gpm into the Hornwood wet well; Alliance Engineers’ Atlantic Gateway project proposes a pump station that would deliver about 575 gpm into the county receiving system.
"You’ve got roughly 300 gallons per minute already coming in from the Hornwood textile facility, plus they’re proposing to add an additional 575 gallons per minute," Hazen & Sawyer said. The firm’s hydraulic model indicates that sustained runs of the county pump station at near-current rates can cause surcharging of the downstream 10-inch gravity sewer, which could lead to manhole overflows and state reporting obligations.
Hazen & Sawyer recommended against accepting the Atlantic Gateway flow until Alliance Engineers provides the pump station operational schedule and hydraulic calculations showing the receiving system can handle the additional load, and until the county and Atlantic Gateway agree on a plan to improve the downstream receiving facilities (which might include upsizing force mains or enlarging the 10-inch gravity sewer to 15–16 inches in a targeted reach).
The consultants also noted uncertainty because the county does not have plans for the existing force main and lacks precise records of where it connects to the gravity system; Hazen & Sawyer said they made best-available assumptions for the model and recommended coordinated data- and operations-sharing among the county, Alliance Engineers and AEDC.
The board directed county staff to arrange a joint meeting with Alliance and AEDC (the local economic-development entity) to reconcile operational assumptions and define needed downstream improvements before any acceptance of the new flows.
Hazen & Sawyer will continue modeling once they receive Alliance’s hydraulic calculations and operating assumptions.
