Upper Trinity Regional Water District’s (UTRWD) Riverbend Water Reclamation Plant (WRP), located in north central Texas near the city of Aubrey, needed to increase its capacity from 2 million gallons per day (mgd) annual average daily flow to 4 mgd with a peak flow rate of 16 mgd. This expansion was required to keep up with the economic growth occurring to the north of the Dallas-Fort Worth metroplex. In order to increase capacity, a new influent pump station, new screening and grit removal headworks, a new sludge pump station building, modification of sequential batch reactor basins to conventional aeration basins with ballasted activated sludge, and new secondary clarifiers were required.
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Several project drivers, outlined below, would make conventional project delivery of UTRWD’s Riverbend WRP capacity upgrade difficult to achieve. These drivers included the need to accelerate the schedule for the project, ensure that the scope work was in alignment with the defined budget, and being able to obtain the treatment equipment on value-based selection process. Given these drivers, UTRWD determined that the construction management at-risk (CMAR) delivery method was the best approach for their project.
A typical design-bid-build project often requires two to three months for advertisement, assessment of bids, and award by council or board. In contrast, using CMAR enabled UTRWD to secure a guaranteed maximum price during the design phase, FAprovided them the ability to accelerate the project schedule. For the Riverbend Expansion project, UTRWD and the CMAR firm agreed to a guaranteed maximum price contract at 90% design. This agreement allowed the CMAR firm to bid out the work during final design, have all subcontractors and equipment contracted before they were given notice to proceed, and then begin construction at full speed immediately upon completion of construction documents. Construction began within 12 months of project kickoff. UTRWD preferred to avoid any early out packages or concurrent design and construction for this project. Even without using these options to accelerate the project, the CMAR delivery method reduced the overall project schedule by three months.
Scope and Budget Certainty
Like most projects, UTRWD had a set budget available for the expansion of the Riverbend WRP. The CMAR cost model allowed UTRWD to match the scope of the construction with its available budget. As an example, at 30% design, the cost model was $6M over the $31M budget. However, using value engineering and scope modifications to align the project construction cost, the project budget was maintained at $31M. Design changes resulting from the value engineering efforts included use of on-site soil, reducing the generator size by better defining essential equipment, and reducing the filter gallery improvement scope. In order for UTRWD to track and control the budget, the CMAR cost model was updated at each major design milestone.
Value-Based Selection of Equipment
The CMAR and UTRWD developed a value-based scoring system for assessing equipment which accounted for familiarity with the manufacturer representative, length of time in business, delivery time, location of service center and installation references, and ability to meet terms and conditions of the contract. Each piece of equipment was reviewed and the final equipment selection was based on best value, not simply the lowest price. The scoring system allowed UTRWD to get best value within their available budget. All equipment was bid and selected before the guaranteed maximum price, which allowed UTRWD to reduce the contingency included in the guaranteed maximum price.
Employing the CMAR method delivered a successful Riverbend Expansion project that was constructed faster than a typical design-bid-build project. It was delivered on time within the available budget. UTRWD maintained control of vendor and subcontractor selection to obtain needed materials, equipment, and workmanship that met their preferences and value expectations. The Riverbend WRP Expansion is currently 16 months into construction and is on schedule. A partial start-up milestone was met in June 2018, and full startup is expected in March 2019.