Two of the most important elements of a treatment plant design-build project are the performance and acceptance standards associated with the start-up and commissioning of the treatment plant. Performance standards can be defined as the standards the plant needs to meet in order to operate in compliance with applicable permits over a range of typical operating conditions. Acceptance standards can be defined as the standards the design-builder must meet in order to satisfy the contractual requirements of the design-build agreement with the owner. Ideally, the performance and acceptance standards should be closely aligned. Problems can arise when contractual acceptance standards are overly conservative in relation to the normal performance standards of the facility.
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Performance and acceptance standards are arguably two of the most important provisions in the design-build agreement. Design-builders carefully review and evaluate these standards in assessing potential projects and in quantifying the project risks. If the owner doesn’t sufficiently define the performance and acceptance standards in the contract, then the owner could lack the necessary contractual recourse if the plant is not performing in the manner the owner has intended for it to perform. On the other hand, if the contract contains onerous acceptance standards that are significantly beyond the typical operating requirements of the facility or are more stringent than standard industry practice, then the owner runs the risk of deterring potentially qualified design-build teams from bidding on the project. Further, design-build teams that do bid the project may carry excessive contingency to address the risk of onerous acceptance standards.
To strike the proper balance, here are some principles that owners should consider when deciding on contractual acceptance standards for their project:
- Consider how the plant will be operated when setting the requirements. Treatment plants are a complex mix of interrelated unit processes that function as a whole. If acceptance standards are created for each individual unit process, they must take into account how the plant will operate as a system. The performance of one process affects another and it can sometimes be unrealistic to expect that every individual unit process in the train is functioning at its optimum performance at all times. Acceptance standards that require this can be difficult to achieve and not reflective of how the plant will ultimately be operated.
- Consider how the design-builder will reasonably be able to demonstrate compliance with the standards. Standards which require a performance test at the outer limits of plant design criteria such as flow, temperature, or loadings can be very expensive and physically difficult to perform. “Future” design conditions may never occur. Maximum and minimum design conditions typically occur only rarely and are unlikely to occur during the start-up and commissioning period. For example, consider projects such as those with a wet weather flow component or those with future capacity built into the design. There might not be enough available water or loading to conduct a physical test of a plant at its maximum design throughput and loading during the commissioning period. In such cases, the owner should consider other means for the design-builder to satisfactorily demonstrate compliance, such as modeling or other industry standard calculation procedures, rather than a physical test.
- Consider acceptance standards that are objective and measurable. To the extent possible, acceptance standards should be within the control of the design-builder and be able to be demonstrated using an objective and measurable test with as little subjectivity as possible. This protects both the owner and design-builder from having a subjective interpretation of the results and a disagreement as to whether the acceptance standards have been achieved.
- Utilize reasonable testing periods. Acceptance standards for individual equipment or systems should be well-defined and long enough to demonstrate the desired performance. Performance for mechanical equipment can often be demonstrated in a matter of hours while biological or chemical systems may take longer. Owners should carefully review their test periods to ensure they will be comfortable that the desired performance has been achieved while avoiding longer than necessary demonstration periods where the design-builder becomes a de facto operator for an extended period of time.
- Involve the owner’s staff in the acceptance testing process. A collaborative testing effort between the owner’s staff and the design-builder is a key component in training the operators how to run the plant and demonstrate that the facilities comply with the contract requirements. A “hands-off” approach by the owner’s staff until all acceptance standards have been met should be avoided.
By keeping these principles in mind, owners can provide proper safeguards for their project while properly apportioning the start-up risk to attract the maximum number of qualified design-build teams to bid the project. Chapter 6 of the WDBC Water and Wastewater Design-Build Handbook provides additional insight and information on best practices for planning and executing the final stages of a design-build project and successfully transitioning from construction to operations.
Scott Thibault, PE, DBIA is a Vice President in AECOM’s Water Design-Build Group. He has over 27 years water/wastewater experience, including over a dozen design-build projects.