KS Engineers, P.C. (KSE) implemented a program of non-destructive physical testing of the Final Settling Tanks at the NYC Department of Environmental Protection’s (NYCDEP’s) Owls Head and Port Richmond Wastewater Resource and Recovery Facilities (WRRFs), and the Primary Settling Tanks at the North River WRRF. The focus of the testing was the structural integrity of the tanks, to evaluate and quantify concrete damage and deterioration such as cracks, spalls, delaminations, leaks, joint condition, efflorescence, scaling, reinforcement corrosion, and other defects. The surface condition of 100% of the tanks was observed. The majority of the concrete surfaces below the operating liquid level were checked to determine whether they exhibited severe disintegration due to corrosion and cavitation. Signs of foundation settlement or heave, and related distress, were noted. The exposed surfaces of the tanks were inspected to determine if concrete paste had been washed away from the wall and floor surfaces, leaving coarse aggregates exposed. Water leakage, ponding areas, areas of poor drainage, or other indications of water problems were noted. All defects were logged and located on the tank drawings. A total of 22 tanks were inspected at the three WRRF’s. Based on the findings of the inspections, KSE will provide recommendations for structural repairs for each set of tanks. The testing consisted of:
- “Sound testing” to help determine the defective areas in the concrete floors and walls. Sound testing is a simple, non-destructive test typically accomplished with a hammer or steel rod.
- The use of a non-destructive testing tool, e.g., a GSSI Structure Scan Min XT or a GPR device, was employed to accurately locate reinforcement in the concrete.
- The use of an Optical Rebound Hammer to non-destructively estimate compressive strength.
The eight Primary Tanks at the North River WRRF presented significant unique challenges for the inspection program. The Primary Tanks are covered, and access was only from a narrow open band at the front of the tanks. Air blowers were necessary to provide outside air into the tanks, as the plant’s odor control blowers could not be used. KSE provided portable lighting into the tank, and all personnel were required to have strapped on emergency 10-minute air supply units while in the tank. Extensive EH&S training for inspection personnel included DEP and on-site training, confined space entry, lock-out/tag-out, and OSHA certifications.
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