Doing the Dirty Work

Dec. 11, 2003
Tips for proper sewage assessment/clearance

Microbiological contamination of water is responsible for numerous outbreaks of gastrointestinal illness that occur every year in the United States. Most of these outbreaks are a result of sewage contamination.

Contamination of water, soil and other material can occur from raw sewage overflows, leaking sewer lines and septic tanks, partially treated wastewater and land application of sludge. The greater the sewage contamination and exposure to people, the higher the risk of contracting ear, nose and throat infections and stomach upsets such as diarrhea.

Consequently, it is often necessary to test areas suspected of sewage contamination, or after sewage remediation, to provide data assessing the potential for health risk and / or the successful removal of sewage contamination.

What do I need to test for?

Some laboratories recommend testing for total coliforms, fecal coliforms and fecal Streptococcus as indicator organisms for sewage contamination. However, the presence of many of these organisms is not indicative of fecal contamination and so these tests provide suggestive, but not definitive, evidence of sewage contamination. It is better to test for the specific indicator organisms E.coli, and species within the genus Enterococci, to indicate fecal contamination, thereby providing the best available data on possible contamination.

Coliform bacteria belong to the family Enterobacteriaceae and include Escherichia coli as well as the genera Enterobacter, Klebsiella and Citrobacter. A subset of total coliforms called fecal coliforms includes Escherichia coli and some Klebsiella species. Klebsiella can occur in nonenteric environments and have been isolated from environmental samples in the apparent absence of fecal pollution.

Consequently, total and fecal coliforms are not necessarily indicative of fecal or sewage contamination. However, E. coli, a member of the fecal coliform group, is a part of the indigenous fecal flora of warm-blooded animals and its occurrence is considered a specific indicator of fecal contamination and the possible presence of enteric pathogens.

Similarly, fecal Streptococcus includes many species like E. faecalis, E. faecium, E. avium, S. bovis, E. gallinarum and S. equines. The presence of some of these species are not true indicators for fecal contamination. A subgroup of fecal streptococci recently recategorized to the genera Enterococcus includes E. faecalis, E. faecium, E. gallinarum and E. avium are valuable indicators for determining the extent of fecal contamination. The most rigorous tests for determining fecal contamination, test for the specific indicator organisms, E. coli and Enterococcus species.

How do I sample to test for sewage contamination?

Proper sampling procedures (use of gloves, clean sampling equipment, etc.) must be followed or contamination may produce false positives resulting in needless anxiety, re-testing and remediation. An area suspected of sewage contamination can be sampled using a swab, typically on a defined area, such as 1 cm 2. Similarly, a bulk sample of the area can be sampled for sewage contamination. To test non-potable water for suspected sewage contamination, allow water from taps or pumps to flow two to three minutes before taking the sample. Collect 250 ml water in sterile bottles and follow proper sampling precautions while collecting the sample suspected of sewage contamination.

How do I submit the sample?

Bacterial testing is time sensitive. Samples should arrive at the laboratory within 24 to 30 hours from the time of sampling. Store samples at approximately 4°C (place the samples on cold pack or in a refrigerator until shipment to the lab) and ship the samples using a cold pack. Samples that get too warm may produce inaccurate test results. The sample should be accompanied by a completed chain of custody for analysis.

How is the sample processed in the laboratory?

Upon receipt at our laboratory, the samples are processed as follows: The samples are checked against the chain of custody, logged into the database, prepared for analysis by a trained technician, and analyzed by an analyst following strict standard operating procedures and quality controls. Our database has been developed in house to facilitate sample tracking, automated report generation and data storage for future reference.

The samples are processed using the standard protocols for testing E. coli and Enterococcus species provided in the EPA's Improved Enumeration Method for the Recreational Water Quality Indicators: Enterococci and Escherichia coli and the Standard Methods for the Examination of Water and Wastewater (20th Edition). Data are reported semi-quantitatively indicating the presence or absence of E. coli and Enterococcus species in the sample.

How do I interpret the results of the test?

Bacteriological tests look for the presence of bacteria such as E. coli and Enterococcus group (E. faecalis, E. faecium, E. gallinarum and E. avium) that specifically indicate contamination with sewage. The presence of the Enterococcus group in the sample tested indicates the contamination of the sample with fecal material. Coliform bacteria occur naturally in soil and in intestines of humans and animals. E. coli is one type of fecal coliform that is indigenous to the intestines of humans and animals. Their presence in the sample tested is indicative of fecal contamination. The majority of E. coli types do not cause human illness. E. coli O157:H7 is one specific subset of E. coli that can cause serious illness.

Where can I get more information?

For further information on sewage contaminated problems and other microbiological testing needs, please feel free to contact us at 1-866-888-MOLD (6653), or you can email us at [email protected].

Dave Gallup, chief executive officer, Environmental Microbiology Laboratory Inc., became president of EML in 1997, and has focused on growing the company as a leader in the IAQ industry by recruiting and training the most experienced microbiologists in the nation, and developing and implementing systems and processes to ensure that EML consistently provides the highest quality and service.

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