Onsite Wastewater Treatment

In areas where houses are spread apart, it is often more economical to treat wastewater onsite. This generally means through the combination of a septic tank, sand mound, and drainfield. There are also systems that are capable of treating water more effectively called Advanced Treatment Units, or ATUs.

The Septic Tank

Let’s start with the basics. A septic tank is a one- or two-compartment tank, usually made out of concrete, where solids are able to settle, and the liquid portion is able to pass through. Septic tanks are a form of anaerobic treatment, meaning treatment in the absence of oxygen, and therefore give off an odor. Septic tanks need to be pumped every few years.

The Sand Mound

After the liquid leaves the septic tank, at least in central PA, it generally flows through a sand mound. Sand mounds are those manmade hills you see in some people’s lawns. Here, the water filters through sand where it is further treated before moving to the drainfield.

The Drain Field

Liquid leaving the sand mound will generally pass through a distribution box, or d-box, where the liquid will be split up into several paths in the drain field. A drain field is simply an area that allows water to seep into the ground at a certain rate, which is verified by a percolation test, or perc test for short.

Advanced Treatment Units

There are several units that can treat water better than the conventional septic/sand combination. These units generally rely on aeration or filtration. The water leaving these units is clear and odorless. Since little pollution is carried to the drainfield, the lifespan of the drainfield is increased. If the ATU performs well, the drainfield should never need to be replaced.

In Pennsylvania, only ATU’s that are certified by the National Sanitation Foundation’s (NSF) Standard 40 may be installed. The NSF/ANSI Standard 40 test is controlled over 6 months, sampling both influent and effluent from a unit. In order to pass as a Class I system, a unit must average below 30 mg/L TSS and BOD, two metrics used to determine wastewater strength.