Special Studies: Finding Bacteria Hotspots
absence of fluorescence. Additionally, a fluorometer can be used to quantify optical brightener levels in water samples.
The usefulness of optical brightener monitoring depends on several factors including the characteristics of the water body and bacteria source(s). In some cases, naturally occur- ring organic materials in the water can create background interference. The episodic nature of laundry activities and the short time optical brighteners spend in wastewater
disposal units require multiple monitoring events. Addition- ally, brightener levels are not always linked to high bacteria levels, but instead may indicate gray water discharges, which typically have lower bacteria levels compared to black water or sewage discharges. Fecal indicator bacteria and optical brighteners have different residence times in wastewater dis- posal systems, and bacteria may be diluted below detection levels while optical brighteners remain at high levels, further limiting their usefulness in tracing illicit discharges.26
Black Water (Sewage)
Gray Water (wash water)
Can change into other nitrogen forms as the flow travels to the outfall.
Boron Color Conductivity
C C C
C C C
Ineffective in saline waters, generally highly variable.
Detergents – Surfactants
Reagent is a hazardous waste.
E. coli Enterococci Total Coliform
24- to 48-hour wait for results. Lab will need to modify dilution ratio for high bacteria concentrations.
May need to use two separate analytical techniques, depending on the concentration.
High Optical Brightener
Black water (malfunctioning septic system, sanitary sewer cross-connection)
Gray water (laundry, wash water)
Low Optical Brightener
Human or non-human sources
Potentially low or no fecal contamination
Can almost always (>80% of samples) distinguish this discharge from clean flow types (e.g., tap water or natural water). For tap water, can distinguish from natural water.
Can sometimes (>50% of samples) distinguish this discharge from clean flow types depending on regional characteristics, or can be helpful in combination with another parameter.
Poor indicator. Cannot reliably detect illicit discharges.
Table 3. Potential sources of fecal indicator bacteria based on bacteria and optical brightener levels.25
Table 4. Indicators used to detect illicit discharges in stormwater.17 Type of Discharge
Testing for other parameters
Tracking less obvious sources of con- tamination may require monitoring for other parameters, including nutrients, turbidity, ammonia, potassium, caffeine, pharmaceuticals, changes in tempera- ture, etc. As with bacteria, ammonia27 concentrations can help determine “hotspots” within the drainage network.