Last week I went through the example calculations for determining operating volume and gallons per inch in a rectangular tank. Now put those examples to use and answer the following questions. 

A rectangular septic tank has the following dimensions: 7 feet long; 4 feet wide; and 5 feet deep.

1. What is the operating volume of this tank in gallons?
2. What are the gallons per inch of tank volume?
3. If the flow is 600 gallons, what is the detention time in this tank? Is the tank large enough?
4. If the sludge depth is 10 inches and the scum depth is 5 inches should this tank be pumped?

Answers are posted here. 

This article is part of a series of practice problems for installers:

• Onsite Arithmetic: Is This Tank Large Enough?
• Onsite Arithmetic: Cylindrical Tanks
• Onsite Arithmetic: Setting Floats
• Onsite Arithmetic: Flow
• Onsite Arithmetic: Flow - Part 2
• Onsite Arithmetic: More O&M Practice
• Pointers for Onsite Arithmetic