Gotham JA Miele, Sr, PE

Water conservation cleans Long Island Sound, RL Swanson, DJ Tonjes

Marine vessels serving New York City, W Goyzueta, J Chen, K Byrnes, R Ferro

Line stops avoid bypass in pumping station, F Gallo

Pilot biological nutrient removal, B Bodniewicz, K Mahoney

Enhanced beach protection — 2000, FJ Oliveri, F Loncar, M Ellis

Telemetering in New York, S Rozelman, S Aziz

Job order contracting, MP Quinn, P Schrayer

Operational benefits of celebrating Water Week, RE Adamski, H Einsohn, M Keating, A Lamarche, B Olivieri

CSO signage: expanded notification, S Rozelman, P Lutz, F Loncar

Brooklyn student wins water prize

Executive director's message, P Cerro-Reehil

People and places

Summer 2001 — Vol. 31, No. 2

by Frank Gallo, PE

The Manhattan Pumping Station (13th Street), owned and operated by New York City's Department of Environmental Protection, serves about one-third of Manhattan. The station pumps sewage at an average dry-weather flow of 170 MGD and peak capacity of 400 MGD. It serves 4,162 acres of land supporting 446,000 residents and 1.3 million people who work in the drainage area. The drainage area is serviced by 180 miles of sewers and 40 regulators. It includes the neighborhoods of the Upper East Side, Midtown, the Lower East Side, Greenwich Village, and the Financial District.

Wastewater enters the pumping station through two 108-inch diameter interceptors. The two flows combine in a junction chamber just outside the pumping station. Flow then enters the forebay area, is separated into four screening channels, and then flows into the wet well.

Wastewater from the wet well is drawn by five main sewage pumps into a discharge header. The flow from the main header area is discharged into a surge tank and continues to flow beneath the East River through a tunnel that is 8½-ft in diameter, 7500 ft long, and 300 ft deep. The wastewater is treated at the Newtown Creek Water Pollution Control Plant located in Greenpoint, Brooklyn.

Click here to view Figure 1 in a new window. Move the window to view text simultaneously.

Figure 1 shows the layout of the wet well and the general piping arrangement. Each of the five main sewage pumps is equipped with a 60-inch diameter isolation gate valve on the suction side and a 42-inch air-actuated cone valve on the discharge, which functions as both a check and a gate valve. The main sewage pumps themselves have been in operation since start-up of the station in 1976 and normally require overhaul for the impeller and wear ring replacement after 35,000 hr of operation.

The need for a shutdown

To perform required maintenance of the main sewage pumps, the 60-inch isolation gate valve on the pump's suction side must be closed to isolate the pump from the wet well. Main Sewage Pumps Nos. 1 and 2 could not be serviced because the suction gate valves were unable to seal, thus preventing the isolation of these two pumps from the wet well. If maintenance of the pumps was attempted without the capability to isolate the suction line with the valve, wastewater would flood the pumping station.

When problems with the suction valves were first identified, it became apparent that the valves had to be replaced. An in-house design to replace the two valves and actuators was initiated. The contract was awarded to Spectraserv of New Jersey for $660,000.

To carry out this work, NYCDEP proposed a 96-hr shutdown of the Manhattan Pumping Station to allow replacement of the valves for Pumps Nos. 1 and 2. The shutdown would result in a bypass or direct discharge of wastewater into the Hudson and Lower East Rivers through the numerous combined sewer outfalls which serve the pumping station. NYCDEP began discussions with the New York State Department of Environmental Conservation (NYSDEC) to obtain a permit for the required bypass in early 1996.

NYCDEP intended a shutdown of the pumping station in March 1996 to replace the suction valves under the contract at that time, but discussions with NYSDEC were not concluded by the end of March. The valve replacement effort was postponed until the winter of 1997 because bypasses are permitted between October 31st and March 31st only. This schedule limits the potential water quality effects to the time of year when recreational uses are at a minimum.

Delays

Discussions with NYSDEC were resumed in the fall of 1996; however, because of engineering complexities, the planned shutdown did not occur.

The 96-hr shutdown was rescheduled and approved by NYSDEC for Saturday, February 15, 1997. It was planned during the Presidents' Day holiday weekend when water use would be reduced; thus, dry weather flows would be lower than usual and bypassing minimized.

The shutdown was approved providing no rain was forecast. Notices were published in local Manhattan newspapers informing residents of the planned shutdown and requesting that water conservation practices be followed to limit the dry weather bypass.

On Friday afternoon on February 14, hours before the planned shutdown, NYCDEP was informed that the State of New Jersey planned to block the bypass in federal court that night. New Jersey officials were concerned with effects of the bypass on shellfishing beds in Raritan Bay. In response to the concerns of the State of New Jersey and its Governor, NYCDEP agreed to cancel the shutdown and place the planned replacement of the pump valves on hold.

The planned bypass received extraordinary political and media attention. The New York City Council's Committee on Environmental Protection conducted a hearing regarding the issue. As a result of the hearing, NYCDEP agreed to examine alternate methods which would minimize the bypass.

Alternatives and solution

Based on NYCDEP's commitment to the City Council, alternative repair plans were investigated:

• The possibility of installing a balloon in the
line was considered; however, this option was ruled out because of the dangers involved in plugging a diameter of 60 inches. A failure of the balloon in a pipe of this size would result in the loss of life, loss of equipment, and would necessitate a pumping station shutdown for an extended time.
• Also considered, was the possibility of freezing
the pipe. Again, due to the large pipe diameter involved and the limited space available, this option was considered infeasible.
• Finally, a method was identified which allowed
for continuous operation of the pumping station during the valve replacement procedure with no bypassing of sewage. This plan incorporated a new technology consisting of drilling, tapping, and installing a folding isolation plug into the pump's suction pipe. TDW Services of Naperville, Illinois specializes in using this method and had successfully applied it in other areas including the chemical, petroleum, and gas industries. An investigation by NYCDEP engineers showed that this technology could be applied to wastewater facilities.

Line-stopping method

The line stopping method involves welding a stopple fitting around the pipe. This is a tee type of fitting with a flanged connection in the branch of the tee. The following steps implement this solution:

— A temporary "sandwich" valve is installed on the fitting.
 
— A "hot tap" machine is secured to the sandwich valve, and the tap is made through the valve.

Figure 2. Flanged stopple fitting welded around pipe

Figure 3. Sandwich valve and plug cutter.

— A hole is drilled into the pipe under pressure without spilling the contents of the pipe.   Figure 4. Hot tapping in progress. Sandwich valve is at bottom; cutting machine on top.
— The cut pipe segment, or coupon, is then removed, and the valve on the fitting is closed.   Figure 5. View of removed pipe segment (coupon).
— The tapping machine is then removed, and the plugging machine is installed on the sandwich valve.   Figure 6. The plugging machine is lowered into position.
— A folded stopple plug is installed in the pipe. This plug is designed to unfold and create a seal as it makes contact with the wall of the pipe.   Figure 7. View of folding stopple plug after installation and with existing piping removed.
— Upon verification of the seal, the existing 60-inch valve is removed and replaced with the new valve.   Figure 8. New 60´´ valve being delivered to work site.
— Upon installation of the new valve, the stopple plug is removed and a completion plug inserted to close the opening.   Figure 9. The new 60´´ valve is lowered into place.

— A blind flange is installed to secure the completion plug.

Click here to see Figure 10 in a new window.

As shown in Figure 10, a wet tap and isolation line stop was needed at Location 1 to isolate the 60-inch gate valve for Pump No. 1. An additional problem was apparent in isolating Pump No. 2. As shown in Figure 10, the 42-inch pipe on the discharge side of Pump No. 1 prevented the installation of a line stop in the suction pipe of pump No. 2. This problem was solved by installing an additional line stop at Location 2.

With line stops installed at Locations 1 and 2, the 42-inch discharge pipe between these line stops could be temporarily removed, allowing access to the 60-inch suction pipe of Pump No. 2. A line stop was added at Location 3, which allowed for the replacement of the valve of Pump No. 2.

Results

Ultrasonic measurements taken on the removed 42-inch pipe section between Locations 1 and 2 revealed that the pipe was excessively worn and in need of replacement. Rather than reinstall the existing segment previously removed, it was decided to install a new 10-ft section of 42-inch pipe.

Faced with the seemingly impossible task of replacing two 60-inch valves without a shutdown, NYCDEP engineers researched other industries and found a suitable technology. Adapting this technology to the specialized needs of New York City's wastewater treatment operations has enabled NYCDEP to replace these valves successfully without bypassing any sewage.
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Frank Gallo, PE is Chief of the Mechanical Engineering Section in the Bureau of Wastewater Treatment of the New York City Department of Environmental Protection, Phone 718-595-4866.