Traditional septic systems have three main parts--the septic tank, the distribution box and the absorption field. The tank is placed closest to the home; all wastewater from the home goes there, whereupon bacteria breaks down the waste and the liquid left over decants into a watertight pipe to a distribution box located at the head of the absorption field. The distribution box divides the water evenly among the branches of the absorption field. The absorption field is a series of pipes with holes in them which pass effluent water into the soil where it is absorbed, filtered and passed down into the earth. The absorption field needs several things to function well.
An absorption field cannot just be placed anywhere. The soil in your yard must pass a percolation test. You will need to call in a contractor, inspector, health official or engineer who specializes in septic systems to help evaluate your yard. His visit will take several hours, during which time holes are dug to test the soil's absorption rate. He will classify your soil by type and determine where your field can and cannot be built. Next, he will look at the land itself.
The designer/engineer will next look at the terrain in your yard to determine which places have not only proper percolation characteristics, but also the proper grade. Absorption fields need to slope downhill in order to work properly. You will need a well-drained site that does not flood in rainy weather. The septic system designer will also have to take land usage into account.
The engineer must next look for nearby water wells, buildings, towers, sheds, trees, rock formations, shorelines, banks, creeks, roads, fences, utilities, underground power lines and pipes to insure the absorption field does not affect, nor is affected by, these structures. She must take into account vehicular and foot traffic after construction and future plans for landscaping and gardening. A garden must never be built over a septic system drain field.
You and your engineer will have to draw plans to present to your local public health authority. The size of the field is determined by the number of bedrooms in your home and how many people live there. This determines potential water usage, which is compared to the absorption rate of the soil in the drain field area to determine the size for the drain field needed. Every county has its own set of rules for how much drainage is required, so you'll have to work with your health department. The health department will have to approve the drawings before you can begin work.
Your septic system contractor will ensure all components of the system are properly installed. The absorption field will be set up in uncompacted, unsaturated soil. The soil in the field destroys pathogens, breaks down organic waste and filters the water to purify it and pass it into the groundwater. With hundreds of types of soils and an infinite number of terrain challenges, septic system construction is not a DIY project for most people. Get professional help and follow the advice of the professionals you hire.