Here are the answers to the Sept. 24, 2020 edition of TPO's Exam Study Guide:

1. While performing a 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 issue?

The answer to this question is B. Performing visual inspections is very important no matter what form of treatment facility. In a lagoon system using aeration systems, the surface turbulence will tell the operator many things about the performance of his/her plant. A calm area over a diffuser will usually mean the diffuser is plugged or fouled. A 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.

2. Using the data in the table, what sample is most likely representing the oldest water?

The correct answer is C. TTHMs (chloroform, bromodichloromethane, dibromochloromethane, and bromoform) are a byproduct of chlorine reacting with naturally occurring organics in drinking water. These byproducts are typically monitored on a quarterly basis due to their known adverse health effects at elevated concentrations. The current MCL for TTHMs is 0.08 mg/L or 80 ug/L and is calculated by averaging the most recent quarterly results at each sample location. This method is referred to as a locational running annual average (LRAA). At least one sample location must be selected to represent the oldest water in the distribution system because TTHMs usually increase in concentration the longer chlorine is in contact with the organics. 



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