Coliform sampling is a surprisingly difficult and frustrating endeavor. The reason: a hold time of 6 hours. I sample for coliform during stormwater events, and the race against the clock while working in the pouring rain can cause a lot of stress. I know many others who feel the same way. Many-a-times I hear someone exclaim, ?What?s so important about coliform samples anyway?!?
I?m so glad you asked?.
Coliform sampling is necessary to determine whether sewage may be contaminating your waterway, lake, or water supply. Coliform is present in great numbers in human feces but also exists in animal manure, soil, and detritus (material derived from dead plants and animals). It should be noted that coliform, in and of itself, does not usually pose a danger to humans. However, it may indicate the presence of pathogens that exist along with it. There are a number of tests available to analyze for coliform, and it can be difficult to know which ones are the best indicators for your water sources. I hope to shed some light on that here. Since labs often have different method numbers for these analyses, I?ll list the methods by name.
This gives a count for the total amount of coliform found in your sample and does not distinguish between fecal and non-fecal. It?s basically an indicator of whether or not the water has come into contact with plant or animal life. As such, this is not a recommended test if you are sampling for the health of recreational waters. However, it is recommended for sampling drinking water, as its presence often indicates contamination of the water supply from an outside source or that disinfection is not working properly.
This gives a coliform count that is more specific to mammal feces. Until recently, it has been the recommended analysis for determining whether recreational waters have come into contact with sewage. However, studies confirming that some bacteria groups (such as klebsiella) in fecal coliform tests are associated with other sources, such as paper and textile mills, have led some state and federal regulators to consider E-Coli analyses as better indicators of sewage in recreational and fresh waters.
Escherichia Coli (E-Coli)
Since E-Coli are coliform bacteria specific to fecal matter from mammals, the EPA considers this method the best indicator for the presence of sewage in recreational and other fresh waters.
Fecal streptococci and enterococci
Okay, so this isn?t a coliform (it?s a genus of lactic acid bacteria), but nevertheless, Enterococcus, a subgroup of fecal streptococci indentified in 1984, generally occurs in the digestive systems of mammals. Enterococci have the ability to survive in salt water, making them an excellent indicator of water health along beaches and in estuaries. In 2004, Enterococcus replaced fecal coliform as the federal standard for water quality at public beaches.
I hope that this helps you select the appropriate analyses for coliform sampling. It is also important to remember to check with your state-specific regulatory agency, as many have their own criteria for coliform sampling.
Written by: Chris Hollinger