What You Need to Know When Planning a Bypass Pumping Project
In many cases, when putting together a pipe rehabilitation project, a crucial component of the project design is what to do with the wastewater flow while the relining is taking place — all the water has to go somewhere, right?
Temporary bypass pumping can make or break a project, depending how well the bypass is designed, monitored and executed. We spoke with several leading bypass pump manufacturers and suppliers, asking for their perspective on what you need to factor in when designing this aspect of your project, as well as some areas that may be taken for granted.
All talked about how much the bypass pumping market has changed and evolved over the last few decades and what that means for the industry, with all noting how strong it is in present day. What has made the biggest impact on bypass pumping? Technology — and there has been a lot of it over the last 20 years. The technological advancements have made the bypass process more effective, cost-efficient and have given operators more reliable data. Here is just a sample of what was said.
“The bypass pumping industry has seen a vast improvement in sensor, diagnostic, remote monitoring, automation, communication and notification technology over the past five to 10 years,” says Jessada Sunhachawi, P.E., with Thompson Pump. “Pumps can now be controlled remotely over a connected desktop or even mobile apps. Automation can adjust the speeds of the pumps, in effect controlling the corresponding flowrates and provided pressures depending on the needs of the system.”
Sunbelt Rentals director of sales for pump solutions Ladd Gould concurs, noting that addition of new technologies — such as remote monitoring, flow monitoring, data logging and transducers — have made bypass system design more reliable and precise. He also says that all the evolution of the past 20 years of the trenchless industry has resulted in a change in those who provide the sewer bypass service.
“Today’s trenchless projects have more stringent requirements in order to reduce the owner’s risk,” he says. “These requirements have pushed pump providers to transition from equipment suppliers to becoming turnkey sewer bypass providers. With that progression, bypass providers have turned into subcontractors who handle the entire flow diversion, negating risk for the prime contractor.”
Xylem senior sales engineer Nate Warren points to the inclusion of non-clog impeller technology, saying it’s made the biggest impact on bypass pumping. “Traditionally, rag heavy sewers took a toll on a bypass system. In most cases, there was a need to have a technician onsite 24/7 who can manual de-rag a pump,” Warren says. “The costs to have manned bypass systems outweighs the cost of the actual pumping system rental. Although true non-clog impeller technology is not new, having them available in a portable bypass pump — whether in an automatic, self-priming diesel driven pump or electric submersible pump — is a new concept. Now that pumps can efficiently bypass heavy rag leaden sewage lines, it has dramatically cut down on labor and fuel consumption.”
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Beyond the technology evolutions, the bypass projects have become more and more complex, says Matthew Garay, fluid solutions district manager at United Rentals. While noting that telemetry has reduced waste and increased savings of resources such as fuel and labor force, there are a number of things that have added to the project’s complexity: flow rates are increasing as size or sewer diameters increase; the need for larger pumps or more pumps continues to grow while space for these systems shrinks; as repairs for sewer systems become difficult, the duration of operating bypass systems continues to get longer; and the increase in population places additional strain on systems.
Bypass pumping, while in theory is not a difficult process, does present many challenges to those who are charged with setting up and executing their inclusion in a trenchless project. So many items to consider and they all can have impactful effects on the success of a project. Among challenges is just finding qualified personnel to handle the bypass operation. Like the entire construction industry, labor continues to be at the top of the industry’s list of challenges.
“For many trenchless rehab projects, the success has hinged on the performance of the bypass, and let’s face it, [Murphy’s Law] has a habit of showing up when you least expect it” says Gould. “Therefore, it is crucial that bypass operators are qualified individuals with the proper training in the event of a failure. They should know and understand the proper response procedures to eliminate the possibility of a sanitary sewer overflow.”
Warren adds that the lowest price on a bid does not mean you will get the best outcome for your project. It comes down to having a bypass provider who knows what they are doing. “This is especially important in large metro areas where, in most cases, you can’t just pump from one manhole to another,” Warren says “Trunk sewers are deep, flows are high and vehicle traffic is heavy. Anyone can design a bypass system with a ‘bird’s eye view;’ however, understanding the total project impact — both to the owner and the public — is key to success.”
Beyond the importance of having qualified personnel to handle the bypass operations, such projects also yield challenges with regards to the physical aspects, such as encountering unexpected flow levels or fluid characteristics. “Even with customized cutting or chopping action in a pump, a wise contractor should always have a plan in place to deal with clogged pumps resulting from large solids or stringy materials with high tensile strength,” says Sunhachawi. “Specifying additional backup or standby pumps that can continue to bypass the job while the contractor safely removes the clog on the primary pumps is always recommended.”
He further notes that you should also have backup or standby pumps in order to handle unexpected flow levels beyond what was specified for the job. “Always plan for worst case scenarios and keep backup or standby pumps at the ready,” he advises.
While everything about the bypass pumping operation is pertinent, there are a few components that stand out above the others to ensure that the process is successful. Garay says common design items include knowing what you’re pumping, peak flow rate, static suck lift, pump location to suction point, static discharge head, distance to discharge point and what are you pumping into. Beyond these routine components, there are few to keep in mind, such as design to limit cavitation, which he says can cause havoc on a bypass system.
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“[Also], air in the bypass system can reduce or stop flow completely,” Garay says. “Auto air release vents are critical for a consistently smooth operating bypass system …It is vital to place an auto air vent prior to any discharge into a force main, regardless of force main pressure.”
As Sunhachawi notes above, Warren reiterates the importance of having a redundant pumping system standing by. “Whether it is having only one standby pump with a single, primary pump or multiple standby pumps for a 100 percent redundant standby system, understanding how this will impact the project footprint, suction manhole and point of discharge is one of the keys to success,” he says.
Gould stresses two key areas that should be at top of your list with regards to keys to a successful bypass: flow rate and access. “Perhaps the most crucial design component to a bypass is flow,” he says. “Flow is the baseline for which the entire pumping system is created. Projects where flow has been determined in the planning and design phase and stated in the bid documents sets a baseline for all the bidders to work from.”
He explains that stating the flow requirements accomplishes the following for the prime contractor and the owner: reduces the price disparity of bypass subcontract numbers; reduces the chances of an under-designed system, which can lead to sewer spills in high flow events; and reduces the chances of paying more for an over-designed system.
With regards to access, Gould says that designers who put more thought into the access for the bypass setup will reduce unexpected cost and delays. He notes a few access components to plan for, including 1) suction access, which is dictated by the depth of the sewer at the suction location and the size in which to install suction tubes and/or submersibles, and 2) discharge access, asking yourself will the discharge location accommodate the discharge pipe or pipes?
Sunhachawi advises contractors or bidders to simply walk the job with the potential bypass provider to discuss the particulars of the project and see the jobsite firsthand. He has three questions that should be asked and answered:
- What, where and how much are you pumping?
- Has the groundwater been tested for pH or contaminants?
- What is the expected flow rate and total dynamic head required of the system?
Bypass pumping projects have a lot of moving parts and each are critical to the success and safety of the personnel involved in it, as well as the project itself. There are always some things that may get taken for granted. Our experts pointed out a few to keep in mind, including the cost of a properly designed bypass system.
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“In a pursuit to drive profitable returns, it is easy to convince ourselves of design changes that will not meet all parameters of the bypass,” Garay says. “I would not deny that it is possible to get by, however, the risk of bypass failure is substantial.”
“Understanding the actual consumed horsepower and the related fuel consumption will ensure that a project’s costs are covered,” Warren adds.
Others stress the importance of having enough access for the bypass to take place. “Many assumptions can be made or miscommunicated as to who is responsible for gaining the access, clearing and/or manhole modifications in order to install the bypass,” Gould says. “It is crucial the bypass provider and the prime contractor communicate well in advance of a project in order to eliminate many of the access unknowns.
And don’t take for granted that everyone is on the same page with regards to who is monitoring the bypass operation after the site crew has clocked out for the day or weekend, if the pumping system will be running for the duration of the trenchless project. Knowing what the assignment responsibilities are is critical, says Sunhachawi, and who, among other things, is in charge of making sure the pumps are running correctly or responsible for cleaning the strainers.
Overall, the bypass pumping market is a strong one with the need for pumps — renting or buying — continuing to surge. Without bypass equipment, a trenchless rehab project could not be completed. “Bypass is one of the most critical components to a trenchless rehab project,” Gould says. “Let’s face it, a bypass can go one of two ways: Smoothly (which is the expectation) or badly, which can cause unnecessary exposure and risk. Putting more thought into the design and execution of a project can greatly reduce risk — an unexpected cost — for the owner and prime contractor.”
Sharon M. Bueno is managing editor of Trenchless Technology.