ONS Wall Tie
Replacement

The Challenge

The aeration tanks and secondary clarifiers at both the Belmont and Southport Advanced Water Treatment plants date to the early 1980s. The original interior steel wall ties, installed to resist hydrostatic pressure on the exterior channel walls, had reached the end of their service life. Simply replacing like-for-like would have reproduced the same access and maintenance limitations for another 40 years.

The solution replaced all aging internal steel ties with new exterior support structures that are far more accessible for future inspection and maintenance. At the Belmont Aeration Channel, 189 wide-flange coated beams were installed. At the Belmont Clarifier Channel, 142 driven piles at an average depth of 30 feet were installed with concrete caps placed at 8-foot spacing. At the Southport Aeration Channel, approximately 174 wide-flange coated beams were installed at 5-foot spacing. The Southport Clarifier Channel received a combination of straight and knee piles totaling 136 driven piles.

Both plants also received crack and joint repairs, deck access ramp replacements, loading dock modifications, and exterior stair replacements as part of the broader rehabilitation. The project was completed ahead of schedule and within budget, with less than 2% change orders, zero safety incidents, and zero damage to any adjacent structures.