Mahoning Creek Dam was constructed during WWII by the United States Army Corps of Engineers. The concrete gravity dam’s purpose is flood control for the tributary of the Allegheny River. The dam’s reservoir provides public outdoor recreation opportunities for boating, fishing, hiking, and camping. A detailed inspection of the dam’s service bridge in 2011 revealed the bridge’s superstructure was in critical condition. The inspection found the bridge superstructure suffered from extensive cracking and spalls. Significant alkali-silica reactivity caused delamination; deterioration was also found within the concrete from freeze-thaw. In 2012, the 70-year-old dam was retrofitted to generate hydroelectric power without addressing the service bridge issues.
A TS&L bridge report was completed in 2013, and the general recommendation was a complete replacement of the superstructure. The size and type of replacement were forecast as straightforward. However, the project provided many challenges to overcome.
Construction Cost Management (CCM) was brought on as cost estimators to the team developing design solutions for the now 80-year-old Mahoning Creek Dam’s service bridge and piers. The 139-foot concrete service bridge on five support spans supports two gantry cranes that operate the dam’s five crest gates. The project’s work scope included developing multiple solutions and required the remaining dam gates to remain operational as flood control throughout the construction.
The primary challenge for CCM in estimating the project was the location. The what of replacing the bridge was straightforward, but the where and how, less so. Access to the work area, construction laydown areas, and necessary equipment were all hurdles to be addressed. The Mahoning Creek Dam location is remote. This increased the difficulty of construction material delivery. Construction needs impacted by the location included everything from concrete mix to construction cranes and superstructure framing elements.
The nature of the project and its unique constraints required a high level of estimating experience to ensure accuracy. To address the project’s considerable cost, CCM first began by segmenting the project into phase packages that could be spread across multiple annual budgets for improved government project construction funding. Each project phase additionally had the challenge of ensuring at least two dam gates always remained in operation. CCM’s project estimator, Nishant More, developed a new estimating template unique to the Mahoning Creek Dam project to better estimate the project and help the owner understand, compare, and select the different options to meet their project budget.
Construction Cost Management estimated three different design solutions for the service bridge repair. These design options included a T-Beam that would be cast in place, a precast, a prestressed T-Beam, and a steel design option. The project estimate included challenges that were equal across the design options and unique depending on the individual design. CCM also estimated additional enhancements to the project for the owner, such as a new railing and additional site lighting, a new latch system with automated control, temporary hoist crane redundancy, and more.
CCM prepared a detailed study on Mahoning Creek and its reservoir to address site access regarding annual water levels. The report addressed the creek and reservoir’s historic water pool levels and weather patterns to suggest the best time of year to coordinate the bridge construction. CCM used the information to create a construction schedule to understand better the phasing and project duration for estimating purposes. The schedule also accounted for the number of dam gates required to stay operational throughout construction to address flooding. Upon USACE’s request, CCM estimated the alternate schedule, which was longer, and considered the severe weather conditions for construction labor. This alternative proved more expensive due to extended general conditions, escalating future pricing, and stand-by equipment.
CCM also used the water and weather report to analyze and determine favorable access points for construction. This consideration was vital for the Mahoning Creek Dam project. The dam’s location lacks adequate construction road access. Because of access challenges, all heavy equipment mobilization like construction cranes or extensive superstructure elements would need to be floated in and out of the Mahoning Creek Dam construction site.
The approved construction fund was another factor. The USACE favored the longer alternate schedule, which would have allowed more funding for construction. The plan was to repair three gates with the approved funds, with the remaining repairs as a separate procurement. The cost was estimated for demobilization, site cleanup, and again mobilizing the construction equipment for the second procurement. CCM was praised for breaking out these major costs in such detail, which provided confidence in the estimate and helped the end-user to make a sound decision for the project.
At the time of writing, the service bridge replacement is on schedule for its 2024-2025 construction. The Mahoning Creek Dam service bridge project required an unorthodox and, in some cases, entirely new estimating methodology to complete. Construction Cost Management answered the call and went above and beyond to research the project site, develop solution estimates, and delivered an estimate that accounted for the project’s proposed solutions, the dam’s operational schedule throughout construction, the budget constraints of the owner, and the unique challenges of the construction site.
CCM won the 2021 ASPE award for “Most Innovative Project” on the Mahoning Creek Dam estimation project.