Aerial view of the Warren, Maine lagoon system. Photo courtesy of Woodard and Curran.

Lagoon Systems In Maine 

Systems In Maine

An Informational Resource for
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Mars Hill Wastewater Lagoon System - Mars Hill  Maine. Photo Courtesy of Wright-Pierce Engineers.
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Coliform and E. Coli Testing

(1st of 3 articles)

by Tim Loftus

   The fecal coliform group and E. coli (which is one specie of bacteria in the fecal group) are used as indicator organisms to test the effectiveness of effluent disinfection in a wastewater treatment plant. While these organisms are generally harmless to us, they do live under the same conditions that human pathogens live. Since we cannot test for every pathogen in the effluent, we test for easily detectable indicator organisms. The assumption is that if we kill the indicator organisms then we most likely kill the pathogens during effluent disinfection.

   Testing requirements for the fecal coliform group or specifically for E. coli is determined by your individual state governing body. The sampling frequency and limits will be outlined in your NPDES permit.

   The most common method of testing for the fecal coliform group and for E. coli is the membrane filtration technique. A sample of treated wastewater is filtered through a membrane filter with a pore size of 0.45 microns. The filter is placed on a specific broth designed to allow colonies of the indicator organisms to grow. After an incubation period the colonies are counted and the results are calculated. Details on how to make the broth, how to recognize a colony, and incubation temperature requirements for your indicator organisms are outlined in the test method specified in your NPDES permit. While there are many differences in testing for these indicator organisms, there are a number of aspects common to both procedures that every laboratory should address. These are outlined below.

   There is no DMR-QA study on the fecal coliform group or E. coli bacterial tests. Because of this, your quality assurance (QA) program determines the validity of these bacterial tests for reporting purposes. If you have good QA, then most likely your results will be valid. (Note that one company I know of, Environmental Resource Associates, does have fecal coliform and E. coli quantitative standards. These are not used by regulating authorities as blind checks at this time. However, you can use these for in-house QC samples.)

   There are many requirements and recommendations for a good QA program. The following list shows the most common aspects of a program that will help validate your numbers to your regulating authority.

   Training: all personnel performing bacteriological testing should be trained for the proper sampling, testing, interpreting results, and specific hygiene requirements for these analyses.

   Standard Operating Procedures (SOPs): All directions on performing the analyses, equipment and chemicals needed, what is required for QC, and how to interpret results should be clearly spelled out in a written procedure.

   Cleanliness and Sterilization of Work Area and Equipment: All areas of bacteriological testing (benches, floor, walls) should be cleaned with a disinfectant. All sample bottles, equipment, and chemicals should be autoclaved (the most common form of sterilization) for a minimum of 15 minutes at 121 C and 15 psi. Use heat tape to show these have been sterilized. Spore strips can be used to check the effectiveness of sterilization.

   Record Keeping: Record daily the temperatures of any incubator ovens and water baths (using a NIST traceable thermometer, of course!), autoclave temperature/pressure/time, spore strip results, chemical batch dates, sampling times, dilutions, and anything else that relates to the analyses.

   Producing valid results is the most important aspect of being a lab analyst. Since bacteriological testing has a whole set of different challenges than physical and chemical testing, itís important to incorporate all measures available to assure reliable and accurate results. The second article in this series will address general sampling, QC, and sample dilutions. A third article will review calculating the geometric mean for NPDES reporting purposes.

   The information in this article is based on general test methods that are used throughout the New England area for NPDES monitoring of the fecal coliform group and for E. coli. As usual, check your federal, state, and local regulations. You may have additional regulations or reporting requirements that you must meet.

  If you have any questions, suggestions, or comments, please contact NEWEA Lab Practices Committee Chair Phyllis Arnold Rand at (207) 782-0917 ( or Tim Loftus at (508) 949-3865 (



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