After spending decades and millions of dollars rehabilitating sewer pipes across its service area, a large coastal County in Florida realised its legacy pipe inspection programme was failing to reduce excessive and unwanted infiltration. In January 2020, the County requested a 1 day field demonstration of Focused Electrode Leak Location (FELL) pipe inspection for selected pipes in its gravity collection system. The field demonstration was performed by Electro Scan, Inc. with assistance from County collection system staff. Demonstration results indicated that FELL technology could be helpful in supporting the County’s ongoing planning and rehabilitation prioritisation to reduce I/I
In August 2020, the county engaged Electro Scan to perform a FELL inspection programme comparing equal lengths of three (3) pipe categories including:
- A 50-year old unlined vitrified clay pipe (VCP)
- A newly installed Cured-In-Place Pipe (‘new CIPP’)
- Some approximately 15 year old CIPP liners (‘old CIPP’) to evaluate its efficacy to
support improved rehabilitation strategie
A total of 92 pipes were inspected using FELL, with a total project distance of 24,646 linear feet (7,512 m). 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 and federal, state, and County health & safety guidelines for the COVID-19 pandemic. After each scan was complete for individual pipe segments, data was immediately uploaded to Electro Scan’s Critical Sewers®
cloud-based application for processing and reporting.
Field operations show the physical arrangement to conduct a FELL gravity sewer inspection.
Electro Scan provided turnkey services with its field crew and inspection vehicles to complete the investigation. Remarkably, the 50 year old unlined VCP performance for controlling I/I was 2½ times more effective than the newly rehabilitated CIPP liners. Given this significant finding, a priority can be set to inspect all remaining unlined VCP to identify precisely which pipes do and do not require further attention at this time. By finding a substantial quantity of VCP not requiring rehabilitation, the County can be poised to avoid significant capital expenditures that could exceed several million dollars.
Unlined VCP showed superior performance regarding potential I/I flow rates than either of the CIPP rehabilitated pipes. Since each pipe type represents approximately ⅓ of the total project distance, the summary results can be compared directly. Older CIPP showed better performance than newer CIPP liners. Of the total potential I/I flows, the VCP contributes just over 20% of potential infiltration, while older CIPP contributed over 30% and new CIPP contributed nearly 50% in the study area. The chart below depicts relative I/I contribution
for each pipe type. Notably, the unlined VCP shows superior overall performance relative to the CIPP rehabilitated pipes, regardless of age.
For all pipes inspected, 36% of pipes contributed to 70% of the potential I/I flows. This data allows precisely targeting rehabilitation or repair priorities to only those pipes contributing to the most potential I/I. On a relative basis, a significantly smaller number of VCP pipes require rehabilitation to meet similar I/I reduction targets than either class of CIPP lined pipes. A side-by-side comparison was also performed between FELL and legacy CCTV inspection results. By stark contrast, FELL documented 1,188 individual infiltration defects, compared to just 34 defects identified by CCTV inspection.
Importantly, FELL inspection found 74% of customer taps were defective, compared to only 3% documented using CCTV inspection. New fiscal challenges for all utilities create an essential need to maximise available capital resources. This study shows that most recently lined sewer pipes using CIPP rehabilitation are contributing to more infiltration than 50 year old pipes. Utilities cannot accept ‘business as usual’ methods to approve work that does not reduce unwanted infiltration, driving up costs to rate payers.