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Research and Development

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Tunnel Monitoring

The most vital resources to New Yorkers each day – water. To ensure that the community is able to enjoy fresh, crisp water each day and utilize it for necessary services, it is vital that the tunnel be monitored.

Inspection of the Rondout-West Branch Tunnel that delivers water to New York City and Upstate New York is no small task. This 45-mile long tunnel measures 13.5’ in diameter and runs through deep rock, anywhere from 400’ to 2400’ below the surface of the earth.

In the past, inspection of tunnel proved to be disruptive to New Yorkers. It required physical inspection, which called for the tunnel to be taken out of service, emptied and inspected by workers travelling on foot or by car. This is a process that takes several months that New Yorkers don’t have.

Complicating the task of inspecting this tunnel are cracks in the infrastructure which leak up to 30 million gallons of water per day, out of the normal 900 million gallon per day (mgd) delivery. This has created uncertainty about the aqueduct’s structural integrity, and ability to withstand dewatering without a collapse.

In 2003 and 2009, DEP launched an Autonomous Underwater Vehicle (AUV) — a cutting-edge, self-propelled submarine-shaped vehicle built in partnership with engineers at Woods Hole Oceanographic Institution in Massachusetts — to conduct a detailed survey of the entire 45-mile length of tunnel from Roundout to West Branch reservoirs. The AUV is a self-navigating vehicle that collects velocity, pressure and sonar data over a pre-programmed route to determine the condition of the tunnel. It is also able to take 360-degree photographs every eight feet, which allows officials to fully determine the characteristics of the leaks.

Using the AUV’s technology to inspect the tunnel only requires access at the upstream and downstream ends of the aqueduct, preventing a time-consuming and costly shut-down of the tunnel for physical inspection. Additionally, data is collected in a synchronized time-stamped format, which allows scientists to cross-reference instrument data with photos.

This cutting-edge technology has helped New York City engineers, scientists and officials to determine the exact points of weakness in the Rondout-West Branch Tunnel’s infrastructure so that it can begin work on a historic project that will repair the wear and tear that has built up over the past 50+ years. With the help of the AUV, we will work to ensure that New Yorkers are able to enjoy pristine, fresh water from the Catskill Mountains for generations to come.

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Leak Stabilization Pilot Plant

The raw water that is collected from hundreds of miles of pristine forest land in the watershed that drains to the Delaware reservoir system is referred to as “soft” water because it doesn’t have a high calcium and magnesium concentration. In most situations this is considered to be a favorable characteristic. Bathing with soap in hard water makes it more difficult to form lather and leaves a film on the skin. Clothes washed in hard water often look dingy and feel harsh and scratchy and continuous laundering in hard water can damage fibers and shorten the life of clothes by up to 40 percent. But most importantly, hard water forms a scale of calcium and magnesium minerals (limescale deposits) that can contribute to the inefficient operation or failure of water-using appliances. At home, hard water is known for causing showerheads and spray-nozzles to become blocked, bathtubs and sinks to develop a visible soap scum build up, pipes to become clogged and a decreased life of toilet flushing units. So, it’s understandable why soft water may be viewed as a preferential to hard water.

The nature of soft water, however, has one characteristic that poses a challenge to the Delaware Aqueduct. The lack of calcium and magnesium makes soft water “aggressive” which means that it can have a corrosive effect on the pipes that transmit the water, in this case the concrete lined aqueduct. So, DEP has launched a test, or pilot, facility using the raw water from the Rondout reservoir to investigate if some of the leaks can be addressed by introducing lime to the water. The expectation is that it could predictably form deposits in the aqueduct’s cracks and help seal the leaks through scale formation from within.

A previous study was done on a laboratory bench scale. The pilot facility will build on the previously completed work by performing evaluations to confirm that calcium carbonate deposition and scale formation are possible under conditions that are more representative of the Delaware Aqueduct. The pilot will provide a basis for a full-scale facility design, pending successful results, and will provide insights regarding the optimum flows and doses required for full-scale leak stabilization. The facility is currently built and has begun testing three different alternatives as illustrated in the process flow graphic.

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