Formatted Title
Design, Construction, and Commissioning Risks: Engineering Challenges and Lessons for a Large Groundwater Extraction and Conveyance System
Background/Objectives
At an active chemical manufacturing facility (the Site) in North Carolina, a groundwater remedy comprising a 6,000-foot-long barrier wall, 68 well groundwater extraction system, and treatment system was installed to reduce per- and polyfluoroalkyl substances (PFAS) loading from groundwater flow from under the Site to receiving water bodies. The objective of this remedy is to intercept groundwater and prevent groundwater migration around, above or under the barrier wall and then convey the captured water to a treatment plant where it is to be treated to 99% removal efficiency of PFAS indicator compounds. The project regulatory deadlines required the remedy to be operational within 3 years which required extensive planning. The process included baseline investigations, establishing basis of design, completing the design, constructing, commissioning, and startup, all amidst the COVID-19 global pandemic.
Approach/Activities
Pre-design investigations collected subsurface geological and hydrogeological data relevant to the design of the barrier wall and groundwater extraction and conveyance (GWEC) system was used to inform the design basis for the remedy. Additionally, a groundwater flow model was developed to develop the design parameters for the remedy.
The basis of design identified two water bearing units, a shallower surficial aquifer unit and a deeper aquifer unit for the groundwater remedy. The design consisted of an extraction system with 68 wells: 52 in the deep aquifer and 16 in the surficial aquifer with projected total flow rates of up to 1,000 gpm. The extraction well network and conveyance system were designed to be upgradient of the barrier wall and approximately 8500 feet (~1.6 miles) long, extending beyond either end of the 6,000-foot barrier wall with extensive supporting mechanical, electrical, and communication infrastructure.
The GWEC design basis and design package was completed in approximately one year followed by construction and commissioning the following year to meet schedule milestones. With the groundwater remedy comprising of several interactive components, it was necessary to sequence activities to avoid conflicts that affect commissioning and remedy performance assessment. Coordination between the various parties implementing the groundwater remedy including engineers of record, contractors, and stakeholders and sequencing of activities with ongoing supply chain shortages presented challenges throughout the design and construction phases. Several tools including construction QA/QC, management of change, effective data management, scheduling charts, commissioning and startup plans, and risk registers were used to successfully execute and deliver the GWEC remedy on schedule and in conformance with the design. Design and planning for the groundwater remedy was not just limited to the commissioning and startup phase but extended into projected O&M activities and their synergistic effect on the groundwater remedy.
Results/Lessons Learned
This case study highlights the challenges of designing and implementing a large groundwater extraction system under very aggressive timelines, with evolving regulatory requirements and milestones, and completing this scope of work during a global pandemic. This case study will also address the importance of managing project expectations and mitigating construction and contractual risk during the design, procurement, and construction phases and the tools that were employed for a successful project.