per inch of
sq. ft) per
sq. ft. per bedroom
(Provides for garbage grinder and automatic washing machine.)
*Unsuitable for seepage pits if over 30.
Table 1-3. Absorption area requirements for individual residences.
EXAMPLE: A 3-bedroom house on a lot where the precolation rate is 1 inch in 15
minutes requires an absorption area of 190 square feet x 3 = 570 square
feet. For trenches 2 feet wide with 6 inches of gravel below the
distribution pipe, the required total length of trench would be 570 2, or
285 feet. If this were divided into 5 equal portions (that is, 5 laterals), the
length of each line would be 285 5, or 57 feet. If the laterals are placed
6 feet apart, the width of the field will be 5 (laterals) x 2 (feet wide) = 10
feet, plus 4 (spaces between laterals) x 6 (feet) = 24 feet, or 34 feet. Thus
the size of the disposal field must be 34 feet wide x 57 feet long = 1,983
square feet, plus additional land required to maintain minimum distances
from wells, property lines, etc.
(2) Institutional requirements. Soil absorption area requirements for
institutions, business establishments, multiple-family residences, and recreation areas
vary widely. Quantities of wastewater flows vary from 60 gallons per person per day in
apartment houses to over 250 gallons per person per day in hospitals. In designing a
soil absorption system for institutional use (which would include a small military unit),
the best available data should be used to estimate the average wastewater flow. Once
the flow is determined, the soil absorption area may be determined by dividing the daily
flow by the maximum rate of wastewater application found in Table 1-4. Table 1-4 does
not include an allowance for garbage grinders and automatic washing machines. If
these applications are used, the required trench area should be increased 20 percent
and 40 percent, respectively.