Aerobic Septic Systems and Water Flows

Most residential aerobic wastewater systems are rated at 500 gallons per day (gpd). In a perfect world this may be true but in real life don’t bet on it.

To receive NSF certification, individual systems are tested with controlled flows over a 24 hr period. In the real world that is NOT how we use them. When we use them, it is over a 12-16 hr period and usually with most usage in the morning and in the evening. So what does that mean?

It means there will be problems if you run 500 gpd thru the system during any one day. Hydraulic overload is when too much water travels thru the system too fast. There are two problems associated with this. First is incomplete treatment of the effluent. The bacterium needs to have time to do its thing before the sprinklers come on. Second and more costly, is solids settling in the pump tank (the last compartment in the system).

Aerobic Septic System Diagram

As wastewater moves thru the system solids settle out into the trash tank and settable solids settle in the ATU. If we do not give enough time for this to happen solids will flow to the pump tank.

In most cases the intake of the pump is 10” off the bottom of the pump tank. If the solids approach this level they need to be removed, which of course isn’t free. If they are not removed the pump will try to move them thru the distribution system, causing all kinds of hate and discontent, destroying equipment, and transferring dollars from your account to someone else’s. So, how do you stop this from happening?

Monitoring of sludge levels by your maintenance provider is a start but more importantly is consistent, LOW, water flows. Spread water usage out over the day and week.

Do laundry everyday vs. ten loads on Saturday. Tankless water heaters mean limitless hot water but also mean long showers. Big Jacuzzi tubs are a big contributor to hydraulic overload. Fix leaking toilets immediately. Remove water softener regeneration flows from the drainage system.

Slow the water down! Spread the flow out! Smaller more consistent flows will save you money. Think 20 gallons per hr. vs. 500 gallons per day.

Your aerobic wastewater system is the most important appliance for the house. Treat it right and you will avoid the needless cost of repairing it.