The City of Raleigh depends on the Crabtree Creek North Bank infrastructure as one of its primary wastewater collection interceptors. With a large part of the system installed prior to 1965, many of the 30-inch, 36-inch, and 42-inch reinforced concrete pipes that make up the system were past the end of their useful life—CCTV inspection revealed several locations where the crown of the pipe had failed. Reacting quickly, WithersRavenel assisted the City with emergency repairs of approximately 7,000 LF pipe using 36-inch and 42-inch HOBAS® pipe or cured-in-place pipe (CIPP) in these sections of the project.
For another 28,000 LF of the aged-but-not-yet-failed system, WithersRavenel used a combination of rehabilitation and replacement techniques, including CIPP, slip-lining with HOBAS® pipe, and dig-and-replace with ductile iron pipe (DIP) and HOBAS® pipe, depending on horizontal and vertical construction constraints along the sewer easement. Design challenges included the proximity of existing development; maintaining parallel greenway access; multiple street crossings; rock outcrops; and NCDOT, Progress Energy, and railroad encroachments. The presence of wetlands and riparian buffers to the stream bank required WithersRavenel to perform an Environmental Assessment, Clean Water Act Section 404/401 certification, and erosion and sediment control. Withers Ravenel also assisted the City with obtaining SRF Funding from the North Carolina Division of Water Infrastructure to finance the project and incorporated state and federal guidelines into the contract documents.
In addition, WithersRavenel completed Phase I and Phase II Environmental Site Assessments (ESAs) for approximately 12,000 LF of the alignment to address an abandoned landfill, a chlorinated solvent plume, and petroleum-contaminated soils and groundwater from leaking storage tanks. During construction WithersRavenel supervised the excavation of two areas to allow slip-line material to be inserted. Soil and landfill debris was stocking and sampled, and WithersRavenel interfaced with the North Carolina Division of Waste Management’s Hazardous Waste section and the Inactive Hazardous Sites branch to classify and properly dispose of the material. Following site remediation, the 36-inch gravity wastewater line was lined in placed.
Completion of the project converted over 35,000 LF of the existing wastewater collection system from a leaking, unsafe, poor condition to excellent condition with reduced infiltration/inflow, increased capacity, and extended design life.