Septic System Installation
There are many components to a typical septic system. In planning septic system installation, it is important to consider the leach field, percolation rate, and flow rate.
Size of the Leach Field – Water must be absorbed into the leach field. Soil quality will play an important factor in determining the size of the leach field necessary for a particular septic system installation project.
Percolation Rate – The percolation rate is the time it takes for water to be absorbed into the soil of a test hole. This is measured in minutes per inch. Season changes in ground water levels will impact the proper functioning of the leach field. Absorption of more than sixty minutes per inch is considered very slow and would prevent approval for septic system installation. Absorption of one minute per inch is a very fast absorption rate and would be desirable for septic system installation.
Flow Rate – Houses built before 1979 are generally allowed 150 gallons per day per bedroom. Gallons-per-day is described as gpd. If faucets and showerheads are limited to 3 gallons per minute or less, and toilets are limited to 3.5 gallons per flush, 130 gpd is allowed per bedroom. If the house has three bedrooms, 390 gpd would be allowed. Water saving toilets use only 1 gallon per flush. Water saving toilets all 90 gpd per bedroom.
Once the percolation rate and the flow rate have been established, the following table will help calculate the necessary leach field for the property.
Septic Leach Field |
Absorption
Percolation
Minutes per Inch |
Allowable
Application Rate - Gallons
per Day per Square Foot |
1 - 5 |
1.2 |
6 - 7 |
1.0 |
8 - 10 |
0.9 |
11 - 15 |
0.8 |
16 - 20 |
0.7 |
21 - 30 |
0.6 |
31 - 45 |
0.5 |
46 - 60 |
0.45 |
Required Area (square feet) = Flow Rate (gallons per day) / Application Rate (gallons per day per square foot).
