Operations and Maintenance Quiz 5 – Answers

Operations and Maintenance Quiz 5 – Answers

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Here are the answers to O&M Quiz No. 5

1. T or F - A septic tank should be pumped if it is 37 percent full of sludge and scum.
Answer: True. The depth of the combined scum and sludge should be less than 25 percent of the operating depth of the septic tank. If the tank has a 60-inch operating depth, it should be pumped anytime the combined sludge and scum are 15 inches or more. This is to ensure excessive solids are not moving to the drainfield.

2. T or F - A trash trap should be watertight and remove materials that would interfere with the operation of an ATU.
Answer: True. In a previous quiz I answered this question when I pointed out a trash tank should operate like a septic tank. Anything we look for in a septic tank we should see in a trash tank; this includes being watertight. If not — just as with a septic tank — it needs to be repaired or replaced so it is watertight.

3. T or F - Thick scum is never a problem for a sludge judge when measuring scum and sludge depths.
Answer: False. Scum is a problem for a sludge judge. The larger-diameter varieties (2-inch) seem to work better. There was a research project in which some of my colleagues were trying to measure the scum and sludge in over 200 tanks and the 2-inch products worked better. Most providers use another method to determine scum thickness such as a hook with a straight shaft.

4. T or F - On-demand systems operate the pump and system more effectively than timer systems.
Answer: False. Timer systems provide much more control over when effluent is delivered for final treatment, improving treatment efficiency. In addition, knowing how long the pump runs gives a more accurate measure of effluent delivered than just a cycle counter. A timer system will spread flow out more evenly over time, which improves system operation. On-demand or socially run systems will see high flows during parts of the day — usually early morning and again in the evening  — with long periods without flow, so having flow spread out makes the systems work more efficiently.

5. T or F - A multistage pump is typically installed in a pump vault to protect it from excessive solids.
Answer: True. Multistage pumps have smaller distances between the impellers, which allows them to achieve higher heads at the same horsepower. The downside is they can be more easily impacted by solids in the effluent they are pumping. The way to protect against this is to have the pump in a pump vault. A word of caution: The pump vault has to allow the maximum discharge through the vault to the pump, so a 20 gpm vault would not work with a pump discharging 30 gpm. 

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