many cases, homes are located too far from each other to make a
community wastewater collection and treatment system economical.
Here, wastewater is handled onsite using a "miniature treatment
plant" consisting of a septic
tank and drain field.
Wastewater is delivered to the septic tank, a concrete box with
a capacity of ~1000 gallons, where grease and large solids which
would clog the drain field are trapped. Over time, much of the solid
material is converted to a liquid form and passes to the drain field.
Solids remaining in the septic tank must be removed by pumping every
drain field consists of perforated
plastic pipes placed in a layer of gravel. Organic matter is broken
down by aerobic bacteria in the gravel and underlying soil and
the treated water trickles into the groundwater. In constructing
a home treatment system, it is important that water trickle or
percolate through the soil at a rate which will not lead to formation
of ponds of wastewater on the ground. Septic tanks are also located
to avoid contamination of the home's well water.