ONWASA Sanitary Sewer Rehab

Town of Richlands, NC

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The Town of Richlands sanitary sewer system is operated by the Onslow County Water and Sewer Authority (ONWASA).  A moratorium on new sewer connections imposed by NC Department of Environment and Natural Resources (NCDENR) due to hydraulic overloads associated with infiltration/inflow (I/I) prompted the Town, and subsequently ONWASA, to investigate strategies for I/I reduction.

Rivers was engaged to conduct a system-wide I/I analysis utilizing sub-basin flow monitoring meters.  An analysis report was compiled in which three sub-basins were designated as being subjected to excessive I/I in accordance with NCDENR criteria and recommended for further study.

Performance of a Sanitary Sewer Evaluation Survey (SSES) – Phase I followed the I/I analysis and focused on the three sub-basins.  Tasks included nocturnal preliminary flow observation and nocturnal instantaneous flow monitoring which isolated pipelines within the sub-basins exhibiting excessive I/I by NCDENR criteria and thus cost-effective for rehabilitation.  The three sub-basins were smoke tested, identifying numerous potential sources of direct rainwater entry into the system from manholes and defective services, including on private property.  A SSES-Phase II consisted of closed circuit television (CCTV) inspection of the designated “excessive” I/I pipelines to observe the conditions of underground pipelines that would impact ability to rehabilitate pipelines by interior lining methods.  Rivers provided video interpretation of findings and refined recommendations for sewer rehabilitation.

The final phase included design and construction of the recommended rehabilitation techniques.  The scope of the rehabilitation construction included: 1,1,00 LF of sewer mains repairs; 300 LF of sewer replacement; 11,000 LF of sewer main liner; replacement of associated service connections with laterals to new clean-outs at the right-of-way lines, and; repairs to 102 manholes.  Services provided by Rivers for this phase included funding assistance, design surveys, detailed engineering design, regulatory permit acquisition, easement mapping, construction administration and construction inspection.