Is there a rule of thumb on acres required for drainage field depending on flow rate?
The size of the drainage field depends on the soil loading rate, whether or not we are going to take a field reduction for using chambers in the drainage field, and if there is a perimeter drain on the project. We take the flow rate, divide by 0.25, multiply by 0.75, multiply by 4, and then divide by 43,560 to get acres. Example: 5,000 gpd / 0.25 x 0.75 x 4 / 43,560 = 1.38 acres (0.25 is the soil loading rate, 0.75 is a reduction factor for the ADS chambers if allowed. If no reduction is allowed then it would be 1.84 acres – it depends what county you are in and if they allow a reduction. The 4 multiplier takes into account spacing between the absorption fields and perimeter drain. If no perimeter drain is required, the field will be significantly smaller. If the loading rate is higher, say 0.5, than obviously the field will be half the size as a field with a 0.25 loading rate).
