System sizing starts with design flow
Design flow is usually expressed as gallons per day. Once the expected daily flow is known, the system must be sized so the tank and disposal area can handle the wastewater safely.
Basic sizing chain
- Determine the design flow.
- Identify the soil and loading rate.
- Calculate required absorptive area.
- Check layout, setbacks, slope, and reserve area.
- Confirm the system type is allowed for the site.
Common student mistake
Students often memorize one sample calculation and then force every problem into it. Instead, read the question carefully: it may ask for daily flow, total area, minimum length, or acceptable dimensions.