Municipal Guide To Clean Water: Conducting Sanitary Surveys to Improve Coastal Water Quality
Other source tracking techniques
Other techniques may need to be employed to identify sources of pollution and are typically conducted by trained professionals, municipal and state agency staff.
Dye testing/plumbing inspections
Conducting indoor inspections and dye tests are relatively simple. However, some property owners may be uncomfort- able and consider them to be an invasion of their privacy. For this reason, they should be done only when necessary. Dye testing is described on page 26.
Smoke testing can be used to identify stormwater cross- connections within the sanitary sewer, and to locate damaged areas of the stormwater infrastructure. Smoke is introduced by igniting specialized smoke containers and forcing the smoke into the storm drain system via a blower while field staff observe where the smoke surfaces. This approach can be used when accessing multiple properties to conduct dye testing is not feasible, or when the diam- eter of the pipe is too small for video testing (see below).
Before testing occurs, notify the public of the testing date, reason for testing, precautions to take to prevent smoke from entering homes/businesses, and what to do if smoke does enter a building. Smoke testing should not be used in sewers serving sensitive populations such as hospitals or people with asthma. A local contact number should be provided for questions and/or reporting health concerns.
Video is a useful method for investigating continuous dis- charges, but will not detect illicit connections to the storm drainage network that are not flowing at the time of the video survey. Video testing uses a mobile camera to locate the illicit discharge within the pipe. The video camera can detect cracks and other pipe damage, flows, and leaks within the pipe. This method can be expensive, unless the community already owns the equipment for sewer inspec-
tions. The video camera equipment should be selected according to the diameter and the condition of the storm sewer under investigation.17
Infrared thermography uses differences in tempera- ture to identify sewage discharges. In general, sewage discharges have a higher temperature compared to soils in the surrounding area. This is a fairly sophisticated technique that requires special infrared cameras and trained analysts. Color infrared aerial photographs also can be used to detect changes in vegetation and standing water to help locate malfunctioning subsurface wastewa- ter disposal systems.17, 28
Microbial Source racking (MST)
This advanced approach uses molecular-based methods and genetic fingerprinting to identify sources of contami- nation. Typically, MST methods are expensive, require specialized equipment and the expertise of trained micro- biologists, and are time consuming in both the field and laboratory. However, MST technology is changing quickly, with new and refined methods on the horizon. One MST method compares the ribotype profile or “fingerprint” of bacteria strains in a water sample to a genetic library of fecal bacteria sources compiled for the region. The useful- ness of such data may be watershed-specific and library matches are not 100 percent reliable.29