9 Ways to Reduce Risk in Your Next Trenchless Sewer Repair Project

In order to bring your trenchless rehabilitation project in on budget with less risk, it is critical to have the right design– up front – of the bypass segment of the project.

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Here are nine key sewer bypass planning and design components to incorporate into your next trenchless sewer rehabilitation project.

Document Scope

When designing your project, determine whether a sewer bypass is truly necessary to perform the work. Less-costly trenchless technology alternatives can include employing a diversion, accessing parallel sewer lines, or using flow-through plugs.

Determine Bypass Flow

If a sewer bypass is necessary, determine bypass flow requirements in the design phase. This will help reduce price disparity between bypass subcontractor bids and will lessen the chances of paying more for an over-designed system, or conversely, experiencing the environmental impacts of and paying the price for an under-designed flow requirement. If flows are not available, a good rule of thumb is to design the bypass flow plan for the worst-case scenario.

Pinpoint Common Access Issues

Plan for access issues in advance to lessen interruption to the sewer rehabilitation project, as well as to minimize impact to surrounding areas in the community. Access issues to consider include:

• Suction and discharge. Suction access is determined by a few things, including the depth of the sewer at the suction location and the size in which to install suction tubes and/or submersible pumps. First, determine if the suction location will need modification to achieve the desired flow. For example, will you need new manholes, suction structures, or excavations? When it comes to discharge access, you need to determine if the discharge structure will accommodate the discharge piping. It’s also critical to recognize where you’re discharging to. For example, if you’re discharging into a wastewater treatment plant, transducers may be required to keep from inundating the plant with flow. 
• Discharge pipe route. This usually has the biggest impact on a sewer bypass project and thus requires careful planning and coordination. Be sure to consider any common access issues like easements, access for contractors to work and for support equipment, laydown and staging areas, and right-of-entries.
• Existing utilities. Consider all nearby utilities when planning for access, so you can prevent project redesign, limited access and permitting problems.

Identify Issues That Could Increase Project Duration

Plan a realistic sewer bypass project timeframe by thinking of issues that could affect project duration ahead of time. Common issues that can increase cost and extend impact on the community include unrealistic expectations about mobilization and demobilization time, and delays in achieving necessary access.

Calculate the Correct Bypass System Size

Calculating the correct system size during the planning stage can eliminate common issues that can derail a project, such as undersized pumps and discharge pipe, suction interference, cavitation issues, lack of pump redundancy, and ragging or debris problems. A good rule of thumb is to require bypass vendors to provide system calculations in addition to their bypass plan, and have those calculations reviewed by a qualified engineer.

Plan for Blocking of Flow

Your bypass provider should provide you with details regarding the method that will be used to block live flow, along with other critical flow-blocking plan components, including:

• The maximum surcharge head
• Details about the cabling/blocking method
• Whether a double or single plug is needed
• If lifting equipment will be on site should the plug need to be removed
• If a spare plug will be on site

Be sure to check that your provider has the appropriate training and experience to safely set and remove the plugs when required.

Prepare for Contingencies

There are plenty of variables outside your control on any trenchless sewer repair project. To help meet most bypass contingencies, answer these questions during project planning:

• Is the system designed to handle peak flows?
• Can the project be shut down during weather events?
• Has a redundancy requirement been established in the bid document?
• Who will operate the pumps?
• What is the supplier’s proximity to the project in case equipment goes down?
• Are there spare parts on site?
• Is there a sanitary sewer overflow (SSO) plan and are the supplier’s personnel trained in SSO response?

Hire the Best-Qualified Pump Supplier

It’s important that you have the best-qualified pump supplier or contractor on the project. To be sure your supplier’s experience matches the needs of the project, consider:

• Adding a degree-of-experience requirement to the bid
• Confirming the training level of the supplier’s staff who will be on the job
• Ensuring the bypass subcontractor has the resources to support the project
• Learning if the bypass subcontractor owns and maintains the equipment being used as opposed to re-renting

Ensure the Best Value

Bypass is a critical component of the overall sewer rehab project, so it’s important to control costs and maximize value. Know whether you’re working with a term contract or a defined scope. Be sure the bid items are detailed as opposed to being lumped into one line item, and break these items down on term contracts. This helps underscore value and can help reduce costs. 

Remember, an increase or decrease in any of the following is relative to the cost of the bypass:

Duration – while longer duration usually equates to more cost, a longer run time can offer the opportunity for adding value to perform necessary repairs or rehab discovered during the project.

• Flow – this is always the baseline cost for the bypass project.
• Distance – this cost is impacted by the flow design.
• Access/mobilization – this is one of the greatest cost factors and is impacted by existing site conditions.

Also, consider if it makes sense to increase the rehab footage. Pipe is cheap. Mobilization of the pumps is where most of the bypass cost is derived. If you are already on site, performing extra rehab in the line you are already bypassing will add a tremendous amount of value because it will cost more to go back later to do it.

A sewer bypass can only go two ways – good with no incidents or terribly wrong with negative environmental, financial, brand, and business consequences. Make sure to incorporate good flow control initiatives during the planning process to reduce unknown variables and ensure the success of your next trenchless sewer rehabilitation project.

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