Technician occupying a confined space
            maintenance hole to install flow gauges and conductivity
            logging equipment

New methods to detect Saltwater Ingress in Wastewater Mains
T Hill, J Hearfield
Publication Date (Web): 30 January 2018

Sydney Water's wastewater system is affected by saltwater ingress (SWI) where its sewer network is located within the intertidal zones of harbour and foreshore areas. Its estimated that SWI accounts for extra flows of 1,900ML per annum and an addition 9.500 sewage pumping station hours per annum. There is increased risk of raw sewage exfiltrating to waterways during low tides from leaky sewer assets located around foreshore catchments.

Historically Sydney Water has relied on site inspections, flow gauging, conductivity logging and CCTV to detect sources of SWI. Sydney Water has developed an innovative set and retrieve video monitoring unit called SewCam, which can be deployed in maintenance holes as an additional tool in source detection investigations. This innovative piece of technology has greatly increased the speed and effectiveness of source detection of SWI. SewCam was developed internally as there was a need to conduct video monitoring within wastewater assets but there was not a camera commercially available that could withstand the environment. Hydrographers developed SewCam using four main components, GoPro camera, LED flood light, batteries and a Pelican protector case. SewCam can be installed in 45 minutes and can record up to 24 hours of continuous footage. 

SewCam is typically deployed in maintenance holes along a sewer main and can narrow down point sources of SWI in one monitoring event. Installed at strategic points within a catchment SewCam can identify SWI source from anywhere within the maintenance hole. SewCam has reduced the number of site inspections required to located SWI source and has provided video monitoring of assets during high tide that were previously unsafe to access. SewCam has replaced the need for short term flow gauging and conductivity logging to detect SWI. SewCam provides better source information for future CCTV investigations. Typical SewCam deployment and retrieval can be carried out in one week, requires no confined space entries making it a faster and safer method to detect SWI source compared to tradition detection methods. 

Comparisons of SewCam to traditional methods shows that site inspections can only be carried out during high tide periods to see ingress. SewCam can be deployed at any time when safer access is possible during low tide periods. Flow gauging and conductivity logging can provide quantitative data for flow and conductivity analysis when deployed at strategic locations within a catchment. Typical deployments is required for up to six weeks to capture multiple tidal events, requires confined space entries and requires multiple sites across the catchment and is subject to the same access issues as site inspections. SewCam can be deployed in similar locations for qualitative monitoring at lower cost. SewCam can replace the need for CCTV investigation when a point source of SWI is identified. SewCam can better inform the location of ingress for more effective CCTV investigations. 

SewCam replaced traditional monitoring techniques when investigating SWI source at four sewage pumping stations: SP0011, SP0108, SP0208 and SP0117. SewCam found point sources of SWI within maintenance holes at SP0011, SP0108 and SP0208. SewCam isolated SWI affected sections of sewer main for CCTV investigation at SP0108, SP0208 and SP0117. SewCam decreased the time it took to identify SWI source from four weeks to two weeks, eliminated the need for any confined space entry,  SewCam reduced the average monitoring cost by 82% and reduced the average monitoring hours by 66%.

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