Inspection Used in Florida County to Find I/I

In June 2020 Electro Scan, in cooperation with Wright-Pierce, was contracted by the Hillsborough County Public Utility Division (HCPUD), to perform an inspection on portions of the Clair-Mel City collection basin. This inspection was a part of HCPUD’s continuing inflow and infiltration (I/I) evaluations, across its entire wastewater gravity collection system.

The objective of the project was to find and quantify potential sources of I/I in the basin, then locate and prioritize the pipe segments rehabilitation needs.

Electro Scan performed a Focused Electrode Leak Location (FELL) Investigation on 117 pipe segments totaling 32,757 lf, which represents 28 percent of the total pipe in the Clair-Mel collection network. All FELL field work was conducted in conformance with ASTM F2550, Standard Practice for Locating Leaks in Sewer Pipes By Measuring the Variation of Electric Current Flow Through the Pipe Wall.

CCTV inspection was provided for 88 of the 117 pipe segments on the project for comparison of number of individual defects verified by each inspection.

The work was performed over the course of five days, Electro Scan utilized its ES-620 FELL inspection probe in combination with a jet truck to perform the inspection, the work was performed by four Electro Scan employees. The original scope of the project included 123 pipe segments, but six segments were removed from the project due to adverse site conditions. The pipe material for each segment was recorded, three different pipe materials were inspected during the project, cured-in-place pipe (CIPP), polyvinyl chloride (PVC), and vitrified clay pipe (VCP). Data from the field survey was broken down by pipe diameter, pipe material and overall length of footage scanned. Results were then organized for HCPUD’s use to determine which pipe segments were in most need of rehab.

By material, PVC was found to be responsible for the most I/I, 72.1 percent, however, it represents 70 percent of the total length of footage scanned. CIPP represents 15.4 percent of the total length scanned and 19.5 percent of the I/I. VCP represents 15.1 percent of the total footage scanned, and is responsible for 8.4 percent of the total potential I/I. These results show us that the PVC and CIPP are responsible for a greater share of the total I/I than their respective percentage of total footage scanned. Pipe segments were further categorized by total potential I/I, given as both a GPD leakage rate and a percentage of total I/I, and color coded on a “heat map”, giving HCPUD an easy to use and reference data.

For a final deliverable of tabular data, of each pipe segment organized in descending order of potential leakage rate was provided, allowing the municipality to ascertain which segments are most in need of rehabilitation. A comparison of CCTV data to the FELL results was also provided to HCPUD, this comparison was only run in the 88 pipe segments where CCTV data was available. When compared with the CCTV data, FELL uncovered a total of 1,719 individual defects, these same 88 pipes only had 34 documented defects from the CCTV reports. This selection of pipes contains 283 total customer taps, 178 were found to be defective during the FELL inspection, and only five were called out in the CCTV PACP inspection reports.

In conclusion it was found throughout this project that 42 of the 117 lines scanned were responsible for 80 percent of the potential I/I, meaning HCPUD could see an 80 percent reduction in I/I by only performing rehabilitation work on 42 pipe segments. This project gave HCPUD actionable data allowing them to selectively rehabilitate lines and optimize its I/I reduction program. All data was provided to the consulting engineer for use in their asset management platform allowing them to assist HCPUD in the analysis of the data for their I/I evaluation projects.

Nick Jackson is director of business development in the United States at ElectroScan Inc.