Catawba Raw Water Reservoir & Pump Station

Phillips was responsible for the construction of the earthen embankment dam and a raw water reservoir pump station at the plant. The dam features a cement-bentonite cutoff wall to mitigate seepage, which was installed to a maximum depth of 72 feet below the embankment's footprint. All project activities were required to be completed without interrupting the operation of the existing water treatment facilities to maintain reliable service to the Catawba River Treatment Plant’s customers. 

Phillips began work by clearing the reservoir's footprint, which was completed approximately one month ahead of schedule. Once the site was cleared, the excavation of the embankment footprint and raw water pump station commenced. As excavation progressed, each type of material was processed for future use on the embankment, which consists of several different material zones to make the core and shell. Vertical chimney and horizontal blanket drains were installed within the embankment, and Class B riprap armoring was placed on the upstream face for wave protection. A reinforced concrete emergency chute spillway was also constructed. The slope of the existing 3:1 embankment was reduced to a 4:1 slope. During this process, blanket drains were installed, and Class B riprap was placed for wave protection.

During construction, Phillips crews relied heavily on GPS to accurately place material. GPS-enabled excavators played a crucial role in building and placing the two chimney drains within the embankment. To build the drains, Phillips modified GPS-enabled excavators by attaching boxes built to the dimensions of the drains. The material for the drains was fed through the box as the excavator traced the path, allowing crews to efficiently build the drains without contaminating surrounding soils.

Phillips also installed and maintained dewatering systems, managed erosion and sedimentation controls, and developed a project-specific Stormwater Pollution Prevention Plan, as well as a National Pollutant Discharge Elimination System permit. Erosion and sediment controls consisted of permanent and temporary sediment basins, sediment tubes, and silt fence installation. A stormwater bypass was also installed during the dam construction to convey stormwater from the future impoundment while the dam was being built.

The 85′-tall concrete tower and associated bridge required mass concrete thermal control. CTL Group was contracted to design a thermal control plan for the tower foundation and walls, bridge footings, columns, and cap placements. The specification for mass concrete limited the maximum temperature after placement to 158°F and the maximum temperature differential from the interior to the exterior of the concrete to 35°F. Insulation on the exterior formwork and the concrete surface was used to control the temperature differential. Ice and placement were performed early in the morning, starting at 2 a.m., to control the maximum temperature after placement. Thermocouples were installed in each pour to monitor maximum and differential temperatures. The thermal control plan was utilized very successfully for the mass concrete. 

Materials management was also a challenge, requiring constant communication. The design of the embankment itself included five different zones. Materials for two of these zones were sourced from the site, while the other three were imported, and each of these materials had to be kept completely separate during concurrent work. Four separate crews had to work together to manage materials and ensure that another contaminated no zone of the embankment. The Phillips team had to be meticulous while importing and placing materials simultaneously. 

AWARDS

• ENR Southeast Regional Best Project Award in Water/Environment, 2019