Mainline Sewer Inspection

Mainline Sewer Inspection
Rapid inspection device uses acoustics

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Line assessment tool helps city find blockages in sewer

Problem: The City of Starkville, Miss., needed to quickly get a handle on blockage conditions within its 171 miles of gravity-fed sewer as part of an EPA Agreed Order on Consent (AOC) to reduce SSOs.

Solution: The City chose the Sewer Line Rapid Assessment Tool, or SL-RAT, from InfoSense, to help focus cleaning efforts around hot spot areas that had experienced SSOs or slow sewers. The unit is composed of a transmitter and a receiver. The transmitter is placed in an open manhole and transmits a sequence of tones through the air gap within the pipe. The receiver is placed in an adjacent manhole and listens for degradation in the tones it hears compared to the tones it should hear in a clean pipe. It exploits the fact that sound and water flow similarly through the free space within a pipe. The algorithms are able to quickly analyze the result and present the operator with a simple blockage assessment in real time on a scale of zero to 10. Measurements can be conducted in three minutes or less, with no flow contact, no confined-space entry and a low cost.

Result: The SL-RAT’s speed in narrowing down the segments in need of CCTV inspection made the city’s three-year AOC completion date possible. It has inspected over 200,000 feet of pipe with the unit. 877/747-3245; www.infosenseinc.com.

Advanced pipe condition assessment leads to quicker decisions

Problem: The Clark Regional Wastewater District in Vancouver, Wash., experienced H2S corrosion in its large-diameter concrete sewer pipes. Visual CCTV inspections revealed concrete spalling and a deteriorated inner cement layer. The district was unsure if these pipes had reinforcement, while it found that CCTV provided inadequate information, and age was one of the worst criteria to use in judging the condition or assumed condition of the pipes.

Solution: The district used Pipe Penetrating Radar (PPR) from SewerVUE Technology Corp. to determine the condition of two pipes ranging from 21 to 36 inches by mapping their wall thickness and rebar cover. The PPR antennas were mounted on a rubber tracked, robotic, multi-sensor inspection platform. The inspection of 4,000 feet of pipe was completed in two days while the pipes remained in service.

Result: The use of PPR and visual data provided the necessary information for the district to understand the condition of these critical trunk lines. For the 36-inch trunk, the lack of rebar signal and the concrete material scraped off during the inspections indicated poor structural condition. For the Salmon Creek Interceptor, follow-up visual observation of defects confirmed that the pipe was in poor to fair condition. 888/973-9378; www.sewervue.com.



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