Field Demonstration of Electro-Scan Defect Location Technology for Condition Assessment of Wastewater Collection Systems

Abstract

A USEPA-sponsored field demonstration program was conducted to gather technically reliable cost and performance information on the electro-scan (FELL -41) pipeline condition assessment technology. Electro-scan technology can be used to estimate the magnitude and location of potential leaks along a pipeline, helping utilities better understand and control sources of infiltration/exfiltration. It directly measures leak potential, independent of external conditions that are temporal in nature (e.g., seasonal, wet weather). Its use of direct measurements provides a quantitative analysis of leak potential without relying on visual observation. The field demonstration was conducted in Kansas City, MO in August 2010 in areas of the collection system with known operational issues due to root intrusion and inflow/infiltration (I/I). The project was part of a USEPA research program “Innovation and Research for Water Infrastructure for the 21 st Century.” The program was implemented by the USEPA Office of Research and Development to generate science and engineering knowledge to help utilities reduce the cost and improve the effectiveness of operation, maintenance, and replacement of aging drinking water and wastewater treatment and conveyance systems. This paper provides an overview of field demonstration results for the electro-scan (FELL-41) technology and compares them to observations obtained using traditional in-line closed-circuit television (CCTV) inspection. Electro-scan technology uses the variation of electric current flow through the pipe wall to identify pipe defects that are potential leaks. The standard practice is fully described in the ASTM standard F2550-06. It can be used in non-conductive (i.e., non-ferrous) gravity sanitary and combined sewer mains, and service laterals. The field demonstration was carried out in an area with small diameter (8-in. and 10-in.) vitrified clay pipe. Electro-scanning was performed under fully surcharged conditions, which was accomplished by using a sliding pipe plug in conjunction with a jet truck. Technology performance was measured in terms of versatility, accuracy, repeatability, and inspection time/production rate. Results were compared to a baseline condition assessment completed using traditional in-line CCTV inspection. The evaluation of the total cost included factors such as planning, mobilization, field inspection, and reporting. Electro-scanning identified an average of 17 defects per pipe segment, although most were determined to be small defects (defined as anomalies with an amplitude of 1 to 4). It identified more leakage-related defects than CCTV and in some cases, detected different defects than CCTV. Electro-scanning technology did not detect all line breaks identified by CCTV, some of which may be stressed areas that may progress toward leakage. Electro-scanning can provide information on leak potential that is complementary to CCTV observations. While CCTV provided visual identification of pipe features, electro-scanning results were used to interpret defect severity and to better understand whether a defect poses a serious infiltration or exfiltration problem.