Graduation Year

2023

Document Type

Thesis

Degree

M.S.E.V.

Degree Name

MS in Environmental Engr. (M.S.E.V.)

Degree Granting Department

Civil and Environmental Engineering

Major Professor

Mahmood Nachabe, Ph.D.

Committee Member

Mauricio Arias, Ph.D.

Committee Member

Michelle Collins, M.E.

Keywords

Infrastructure Improvement, Joint Grouting, Pipe Grading, Pipe Lining, Sanitary Sewer Overflow

Abstract

In urban coastal environments, sewer infrastructure is plagued by infiltration which seeps into aging and compromised pipes. Infiltration increases pumping costs, reduces treatment efficiency, and may trigger release of partially treated wastewater at water reclamation facilities. To restore pipes and abate infiltration, local utilities rely on structural and non-structural trenchless rehabilitation technologies. These methods are commonly used throughout the United States and the world due to their numerous benefits compared to traditional open-cut construction. However, limited data is available regarding their efficacy in reducing infiltration in sewer systems. In this study, we analysed infiltration in a small urban sewershed in Pinellas County, FL to assess the magnitude of the problem. Flow meters were deployed in different sections of the sewershed over the period of 2015 - 2016 to evaluate spatial and seasonal variabilities in infiltration. To abate infiltration, three trenchless sewer rehabilitation technologies were applied in 2019. The flow meters were re-deployed in 2021 at the same locations to compare pre- and post- rehabilitation conditions. The applied technologies were: Joint grouting, Expanded-in-Place PVC lining (EX liner), and Cure-in-Place Pipe (CIPP). Initially, average infiltration for the entire sewershed was around 2,555 gpd/mi/in during the wet season and 2,110 gpd/mi/in during the dry season Pipe rehabilitation reduced infiltration by 43% during the dry season and 49% during the wet season, but effectiveness varied by technology. Groundwater levels dropped by around 2 feet between the two monitoring periods. Accordingly, calculated infiltration was normalized. Data revealed that CIPP and EX liners were not as effective as joint grouting, probably because groundwater seeps in the space between the pipe and liner. Closed-Circuit Television (CCTV) was employed to investigate the pipes’ condition at the end of the monitoring period. CCTV showed instances of water pooling within the pipes, which is an indicator of inconsistent pipe grading. Findings suggest that poor pipe grading led to faulty joints that became the main source of infiltration. This is particularly proved by the higher efficiency of joint grouting compared to the other technologies. Additionally, the data set was used to develop a relationship between groundwater levels, pipe elevations, and infiltration to assist utilities in estimating infiltration without the need for sophisticated monitoring equipment.

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