Finally, you might fail to detect OBs because they break down in sunlight and may never reach your pads. Sargent and Castonguay, the authors of the OB Handbook, report that they have analyzed over 1,200 samples around the Gloucester and Ipswich areas of coastal Massachusetts and found a positive rate of about 20 percent, yet they have never had a false positive. On the other hand, false positives are not unusual in Ron Spong's experience in the upper Midwest. Monitors should be sure to do follow-up testing of all positive results to determine whether they can be traced to a human source. Storm runoff or combined sewer overflows.
Human wastewater is present, likely associated with storm runoff or combined sewer overflows.
Like any other monitoring program, OB monitoring needs a study design. Selection of sampling locations will depend on what your questions are. You may choose sites that are representative of a stream reach, or you may want to isolate problems by bracketing suspected pollution sources. Monitoring the presence or absence of OBs tells you just that. It doesn't tell you anything about the presence or concentration of bacteria, for example.