Exam Study Guide - July 2021

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By Rick Lallish

The MPN method for fecal coliform testing has become one the most common methods for testing. What is a disadvantage for MPN fecal coliform analysis?

A. Sample toxins are diluted

B. Samples cannot be analyzed by membrane filtration

C. Difficult to interpret, either by observation or gas emission

D. Results are not very accurate and have a high probability of false positives

Answer: D. It is important for operators to understand the many types of laboratory procedures and analysis so that they can properly operate a wastewater treatment facility. Fecal coliform testing is required on most if not all NPDES permits. MPN has become the most common method. The advantages of MPN are ease of interpretation, sample toxins are diluted, and it is very effective on highly turbid samples, and samples that cannot be analyzed by membrane filtration. However, the method has distinct disadvantages that need to considered, such as the amount of time to get the results (up to 48 hours), the requirement for more glassware and media, probable false positives and sometimes inaccurate results. More information may be found in the OWP, CSU-Sacramento textbook: Operation of Wastewater Treatment Plants Vol. 2, (seventh ed.), Chapter 16 and Bacteriology, Microbiology for Beginners (Nisha Rijal). 


By Drew Hoelscher

In the distribution of potable water, where is the beginning of the service line located?

A. At the meter

B. At the curb stop

C. At the corporation stop

D. Where the line enters the building

Answer: C. Corporation stops are threaded either directly into the distribution main or a service saddle. The corporation stop is then connected to the service line, which provides water to the customer. It is recommended that the service line be installed in an S-curve down from the tap so that the line has plenty of slack to allow for earth settlement and pipe expansion/contraction. In addition, the service line should be buried at a depth below the maximum frost line for freeze protection.

Rick Lallish is water pollution control program director and Drew Hoelscher is program director of drinking water operations at the Environmental Resources Training Center of Southern Illinois University Edwardsville.  


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