If flows are greater than 500 gallons per day, how should the septic tank size be determined?

The sizing of a septic tank is crucial in ensuring proper wastewater treatment and preventing system failure. When flows exceed 500 gallons per day, industry standards recommend that the septic tank size should be at least 1.5 times the estimated sewage flow. This guideline helps ensure that the tank has adequate capacity to allow for proper settling of solids and adequate retention time, which is essential for effective treatment of wastewater.

By sizing the tank to 1.5 times the daily flow, it accounts for variations in water usage, allows for the accumulation of solids without overflowing, and provides additional capacity for peak flow scenarios. This sizing strategy is particularly important for systems experiencing higher flows, as it promotes better performance and longer service life, reducing the risk of system failure or environmental contamination.

Other choices do not provide the same level of assurance or adherence to best practices. Simply using tanks of equal size does not consider the specific flow rate and can lead to under-capacity issues. Increasing capacity by a set amount, like 200 gallons, does not take into account the actual flow and may still result in inadequate sizing. Consulting an engineer is valuable when dealing with complex situations, but the guideline of 1.5 times the flow is a standard, widely accepted practice for determining