Pennoni develops plan to upgrade and floodproof stormwater pumps to alleviate city’s flood risk.
By Kenneth Shine, Assoc. DBIA, CFM
Burlington City, N.J., is a proactive community that sits on the banks of the Delaware River between Philadelphia, and Trenton, N.J. Having most of its land located within the Federal Emergency Management Agency (FEMA) 100-year flood zone, good planning and design play key roles in helping the city fund the projects that will have the greatest impact to deal with the reality of climate change and sea level rise projections.
Being ready for a storm event is always on the minds of the staff and Office of Emergency Management (OEM) in Burlington City, and particularly within the Sewer & Drainage Division. The city’s staff pays constant attention to weather forecasts, and they are quick to act when storms are coming by inspecting and clearing critical drainage features and taking action to lower Kennedy Lake for the little additional storage it provides. The additional storage delivers valuable minutes to emergency responders when people need help. The existing 60-HP pump (installed in the mid-1950s) is taken to full throttle, and for storms like Hurricane Irene, which blew through in August 2011, the backup 100-HP pump (also installed in the mid-1950s) is brought online to help carry the load and prevent the city from flooding.
Pennoni was ready for the challenge when the city asked us to develop a plan to increase storage at Kennedy Lake to alleviate nuisance flooding and threats to properties that backed up to the six-acre, two-lake system along West Broad Street and West Federal Street.
The initial review revealed that the invert elevation of the lake discharge pipe was higher than the lake bottom, so dredging Kennedy Lake to increase depth would not increase storage capacity. Pennoni looked to enlarge the lake instead. Due to existing residences and commercial properties that surround the lake, an expansion would only allow for enough additional storage to handle a one-year rain event.
The engineers at Pennoni looked slightly further downstream from the lake system and identified the existing stormwater pumps, located at the city’s wastewater treatment plant. The existing stormwater pumps consisted of one 60-HP pump and one 100-HP pump. They had been installed in the mid-1950s and one of the manufacturers was no longer in business. Repair parts were no longer available for either pump, so whenever the pumps required maintenance, new parts needed to be machined and fabricated, which was costly and time-consuming.
The drainage area terminating at the pumps is almost 1,200 acres and includes the discharge from the Sylvan Lake system in Burlington Township. Under normal weather conditions, the runoff enters the Kennedy Lake system in Burlington City where it is piped to the well pump pit located at the city’s wastewater treatment plant. The aging 60-HP pump kicks on to move the water through a 54-inch force main that is 2,500 feet long, passes under the New Jersey Light Rail line (which moves commuters between Camden and Trenton all day and carries freight at night), and discharges to the Delaware River near the Burlington-Bristol Bridge.
Pennoni analyzed the existing stormwater pump components and well pump pit. In July 2012, Pennoni provided the city with a comprehensive report that recommended replacing the two existing pumps with two new state-of-the-art 150-HP pumps. The project was put on the Sewer & Drainage Department’s Capital Improvement Project list and the city began investigating how to fund the improvements.
In the wake of Hurricane Sandy, monies became available through the FEMA Hazard Mitigation Grant Program (HMGP). In 2013 the city again enlisted Pennoni, this time to assist with the grant application process. Pennoni coordinated closely with the New Jersey OEM, which was administering the grant; provided data to show the effects of the 50-, 100-, 200-, and 500-year storm events; and provided cost-benefit analysis information to demonstrate that upgrading the stormwater pumps would benefit more than 1,000 residences, commercial/retail properties, schools, and public buildings at savings from flood damage estimated for the 50- to the 500-year storms of $65 million to $81 million.
Applying for FEMA HMGP money is an on-going process, with multiple submissions that are made on an as-needed basis for FEMA to adequately assess the project. The city was notified in December 2015 that the project was approved for FEMA HMGP participation and Pennoni was authorized to proceed with the design.
The funding requirements included a caveat that all improvements connected with the stormwater pump upgrades must comply with floodproofing standards to the 500-year flood elevation. This element required that the new pump motors be installed 10-feet higher than the existing pumps. In addition, all electrical improvements leading back to the Power Building (located about 75-feet from the well pit) and within the Power Building needed to be flood-proofed to the 500-year flood level.
Again, Pennoni was up to the challenge and designed a structural platform using the existing underground concrete well pump pit as a base, saving on the costs of providing a new foundation. The electrical improvements included feeder conductors that were capable of immersion in water. The Power Building, which had a first-floor elevation to meet the 100-year flood level, was to be flood protected by sealing all cracks and seams in the basement, coating walls and floors with waterproofing paint to the 500-year flood elevation (2.8 feet above first-floor grade) and installing flood barriers at both doors and on the mechanical vent wall protrusion.
The design for the new pumps included monitoring equipment and failsafe backup systems. The available space within the existing well pump pit would not allow for two check valves, and the lag pump was designed instead with a hydraulically actuated knife valve. The two new 150-HP pumps would have variable-speed motors and be used alternately to increase their lifespans. The existing pumping capacity for the 60-HP and 100-HP pumps was 31,000 gallons per minute (gpm). One of the new 150-HP pumps could move as much as 58,000 gpm of water. The city would increase pumping capacity for current and future storm events and have a redundant system in place in case one pump went down. The engineer’s estimate for the final bid project was just under $1.5 million.
The project was bid in May 2017, with two bidders providing the exact same low-bid price of $1,289,000! The city followed New Jersey Local Public Contracts Law and awarded the project at their regular June meeting.
The preconstruction meeting was held in August 2017 and the pumps, motors, and controls were released for fabrication within a month. Structural platform components required a lengthier review period and were released for fabrication in February 2018. The temporary bypass system, which included bypassing the sanitary sewer effluent from both the Burlington City and Burlington Township wastewater treatment plants, went into operation in June 2018. Within two weeks, the old pumps had been removed, the structural platform was set, the control panels were installed, and the first new 150-HP pump was set and put into operation.
The flood mitigation project was a success at this point, with the city now having the ability to pump more water faster than they ever had! Two weeks later, installation and start-up of the second pump had been completed and the city now has a redundant system in place to protect its inhabitants and their property.
The project only required one change order for unforeseen issues, when spare conduits between the Pump Building and Power Building were found to be crushed and needed to be replaced and encased in concrete.
The Burlington City Stormwater Pump Upgrades project is a FEMA HMGP-funded project that will benefit the community for years to come by mitigating potentially catastrophic flooding that would have been caused if the aging, pre-existing pumps had failed. This project also helped the city improve its Community Rating System designation from Class 8 to Class 7, allowing flood insurance rates to be discounted by 15 percent through the National Flood Insurance Program.