The latest installment in the Onsite Arithmetic series is a continuation of the previous problem. To see that problem, click here. 

1. What is wrong with the calculation of the average daily flow?

Here is the answer from the daily flow problem: 

Total flow: 640 cycles x 64 gallons/cycle = 40,960 gallons

Average daily flow: 40,960 gallons ÷ 120 days = 341 gallons/day

2. Would that change what you think about how this system is operating?

(Use this information from the previous problem: If the design flow was 300 gpd for the system, what does this tell you? The system is exceeding design flow by 41 gpd. Over the entire 120 days, total average is 120 days x 41 gallons/day = 4,920 gallons of additional flow; the system will eventually break if this continues. First check for leaks and extra water sources such as runoff inflow, etc., and if there are no plumbing leaks, look at flow reduction options or enlarging the system.)

If you missed it, here's a brush-up on Simple Septic Math to review first. 

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