Municipalities regulated under the EPA Phase II final rule for municipal separate storm sewer systems (MS4s) are required to identify and eliminate illicit discharges within their municipal boundaries. Illicit discharges can come from a variety of different sources, and in residential communities, they are most often from direct and indirect connections between the sanitary and storm sewer systems.
Tracking down and identifying the sources of illicit discharges in a storm sewer system can be a very expensive and time-consuming process, often requiring multiple investigative techniques before finding the source. The traditional tools include analytical sampling, video inspection, manhole inspections, dye testing, and smoke testing.
In 2007, national environmental engineering and consulting firm Malcolm Pirnie Inc. was awarded a contract to track down the sources of fecal coliform bacteria discharging from the storm sewer system to the Bronx River in Yonkers, NY. There are 13 sub-drainage areas within the Bronx River drainage area that have shown to be polluted with fecal coliform and require further investigation. One of the main goals of the project is to identify the sources of fecal coliform pollution as cost-effectively as possible, to ensure that there is enough funding to adequately address each of the sub-drainage areas. Lessons learned from each sub-drainage area investigation are used to adjust the investigation methodology, and the inspection team is always looking for new tools and techniques to improve upon the approach and to reduce costs. One new tool–a high-resolution infrared camera–was recently evaluated for the investigation with very favorable results.
Innovative Application of New Technology
Aries Industries recently introduced a high-resolution infrared camera for water and sewer pipe inspections. This camera displays variations in temperature graphically using a spectrum of colors and shading. The red end of the color spectrum represents warmer temperatures and blue represents cooler temperatures. The camera is also equipped with a non-contact thermometer that the camera operator can use to measure the actual temperature of the water or sewer pipe, just by focusing the camera on the area of interest. The camera was developed to help contractors locate sewer and water service connections once a pipe has been lined with a cured-in-place liner as part of a repair. Malcolm Pirnie saw this new technology as a potential new tool for identifying direct and indirect connections between the sanitary sewer and the storm sewer by observing variations in the temperature of water entering the storm sewer system from building service connections.
Aries Industries agreed to allow a series of tests be performed for this new application. In spring 2010, the infrared camera was placed in the storm sewer at locations that had been previously identified, using traditional technology, as either having a direct pipe connection to the sanitary sewer or an indirect connection though a broken sewer service connection. During the evaluation, the operator moved the infrared camera to the problem areas in the storm sewer to look for variations in temperature at building connections from the use of hot tap water, from biological growth on the sewer service connections, or from slight differences between the temperature of the groundwater that had infiltrated in the pipe versus tap water that had been sitting in pipes in conditioned building space.
The results from the experiments were very exciting. During a traditional sewer video inspection, water is often observed discharging from a service connection, as shown in Figure 1. If the flow is steady as the camera passes the connection, it is often assumed to be from groundwater infiltration. The infrared camera allows the operators to look for changes in temperature, as shown in Figure 2. The red color represents warmer temperatures, which are confirmed using the non-contact thermometer. The image shown on Figure 1 was taken using a traditional inspection camera. The operator then switched to the infrared camera to show that this was in fact an illicit connection, as shown in Figure 2.
Another limitation of traditional video inspection equipment is that the camera operator may not be able to identify a problem unless the illicit discharge is occurring as the camera passes the service connection. The next experiment involved evaluating whether hot water use would leave residual heat on the storm sewer main, so that a problem could be identified after the hot water stopped flowing. For this experiment, the infrared camera was placed in a sanitary sewer in front of a service connection for a restaurant. Hot water was run from a restaurant kitchen sink for five minutes and then turned off. The temperature at the service connection was monitored for 12 minutes, and during that time there was no water use in the restaurant.
Figure 3 shows the residual temperature on the service connection when the hot water was turned off. The blue number on the bottom left corner of the screen shows that the service connection was 60°F at 11:34. Figure 4 shows that the temperature in the pipe 12 minutes later had only dropped 10 degrees to a temperature of 50°F. Graphically, the color went from bright yellow, representing a hotter temperature, to a mix of red and yellow, showing a decrease in temperature. The temperature in the storm sewer pipe that day was 42°F, so there was still eight degrees of residual heat in the pipe after 12 minutes. In future experiments, the service connection will be observed until there is no discernable difference in temperature to determine how long an operator has to identify an illicit connection after an active discharge has stopped. During the course of experiments, the infrared camera also detected a delta between cold tap water and the temperature of the groundwater that infiltrated into the storm sewer.
Valuable Results
The results of this experiment show that an infrared sewer camera is a very effective tool in the identification of illicit connections in storm sewers, and it could prove to reduce the level of effort and costs by streamlining the trackdown process and possibly reducing the number of techniques needed to find the sources of illicit discharges. The infrared camera experiments in the city of Yonkers indicate that direct active connections to the sanitary sewer are very easy to detect; the residual heat from illicit connections can be used to locate those illicit connections, even if they are not presently active; and cold tap water discharging through illicit connections can also be detected using the infrared camera. Indirect connections that result in a dripping service connection were not picked up with the infrared camera, although an indirect connection with a steady flow could be noticeable with the camera. Using the infrared camera for this type of application will be most successful in residential areas in the morning as residents are getting ready for work and in the evening when they return from work and are using water. Likewise, the greatest success in commercial areas will be achieved during business hours.