Exam Study Guide - January 2021

Licensing exams can be challenging. Our Exam Study Guide helps you prepare by presenting questions similar to those on an actual exam. You can find many more sample questions on the TPO website at www.tpomag.com/study.

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By Rick Lallish

While performing the daily walk-through at an aerated lagoon treatment plant, you notice surface bubbling throughout the primary lagoon, except in one area. In this area, the surface is calm and uninterrupted. What is the most probable problem?

A. Blue-green algae has taken over the lagoon

B. Diffuser is plugged or fouled

C. Filamentous bacteria have begun to take over

D. Riprap has failed in this area

Answer: B. Visual inspections are very important in any type of treatment facility. In a lagoon system using aeration, the surface turbulence will tell the operator many things about the plant’s performance. A calm area over a diffuser usually means the diffuser is plugged or fouled. Heavy surface turbulence or a geyser of water usually indicates a broken diffuser. Troubleshooting a plant is very important part of an operator’s daily duties. More information may be found in the Office of Water Programs, Operation of Wastewater Treatment Plants, Volume 1, 8th edition, Chapter 8.


By Drew Hoelscher

How do you calculate the running annual maximum residual disinfectant level (MRDL) average for chlorine?

A. Average the highest distribution system chlorine residuals from each month for 12 months

B. Average the lowest distribution system chlorine residuals from each month for 12 months

C. Average the highest and lowest distribution system chlorine residuals from each month for 12 months.

D. Average the four most recent quarterly distribution system chlorine residual averages.

Answer: D. MRDL is a running annual average that is computed quarterly. The first step is to average the chlorine residuals reported during the monthly bacteriological sampling period. The monthly averages for the quarter are then averaged so that a current running annual average can be computed by averaging the four most recent quarters. The MRDL for chlorine is 4.0 mg/L.

About the authors

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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