Leak Stabilization Of The Delaware Aqueduct

Authors:

  • Eileen M. Feldman, Vasyl Kravchyk, Marc Santos, Joseph Sesto, Megan Messmann, P.E., Paul Rush, P.E. Ben Stanford, PhD

The Delaware Aqueduct supplies approximately 50% of New York City’s daily water demand and is the world’s longest continuous concrete-lined tunnel at 85 miles in length. Inspections of the Delaware Aqueduct via an aquatic underwater vehicle have revealed that hairline cracks with a characteristic size of 0.10-1.0 mm have formed in the concrete walls of some sections the Rondout West Branch (RWB) Tunnel portion of the aqueduct. These cracks have resulted in an estimated leakage rate of 5 to 35 million gallon per day.

The purpose of this paper is to report on a project that is evaluating a method for controlling leaks by chemically stabilizing the water supply before entering the RWB Tunnel. The chemical stabilization strategy includes the addition of calcium and carbon based treatment chemicals to increase pH and alkalinity and supersaturate the Rondout Reservoir water entering the Delaware Aqueduct with calcium carbonate. Once stabilized, the aqueduct water has the propensity to form a calcium carbonate based surface scale in small cracks along the tunnel liner. A flow-through demonstration facility was constructed and operated for 12 months to evaluate the ability of multiple chemical combinations to autogenously seal leaking cracks. The pilot facility employed three (3) 2,400-ft long pipe loops to replicate full-scale conditions including tunnel velocity and travel time to leak locations in the Delaware Aqueduct. Purpose-designed crack test units were installed along each pipe loop to simulate the performance of hairline cracks at various locations in the tunnel liner.

This paper will discuss the novel, in-situ chemical stabilization strategy and the pilot-scale tests performed to confirm the proof of concept for surface deposition of calcium carbonate scale. Results will include crack unit pressure and flow data to demonstrate scale deposition and leakage reduction rates; surface analysis with X-ray diffraction and scanning electron microscopy to confirm healing throughout crack length by a robust calcium carbonate scale; and water quality analysis of the raw water supply and chemically stabilized solutions to observe supersaturation strength through the pipe loop. The results of this study will be used to assess (1) the efficacy of chemical stabilization strategies in mitigating the aggressiveness of Rondout Reservoir water; and (2) the potential for calcium carbonate scale deposition to seal existing system cracks. Outcomes of the study are relevant to aging infrastructure and concrete water transmission systems experiencing leakage.

For more information, contact the author at efeldman@hazenandsawyer.com.

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