Percolation Test - Soil Properties: Testing, Measurement, and Evaluation - page 249

Table 17-1 Typical Values and Limitations of Percolation Rates [3]

Project Slight Moderate Severe

Reservoir Less than 0.2 in./h Between 0.2 and 2.0 in./h More than 2.0 in./h

Lagoon Less than 0.6 in./h Between 0.6 and 2.0 in./h More than 2.0 in./h

Landfill Less than 2.0 in./h Less than 2.0 in./h More than 2.0 in./h

Septic tank Faster than Between 45 and Slower than

drain field 45 min/in. 60 min/in. 60 min/in.

Absorption-Area Requirements for Private Residences a [2]

Table 17-2

Percolation Rate Required Percolation Rate Required

(Time Required Absorption Area (Time Required Absorption Area

(ft 2 ) per Bedroom, b (ft 2 ) per Bedroom, b for Water to for Water to

Standard Trench, c Standard Trench, c

Fall 1 in.) Fall 1 in.)

and Seepage Pits d and Seepage Pits d (min) (min)

1 or less 70 10 165

2 85 15 190

30 e 3 100 250

45 e 4 115 300

60 e,f 5 125 330

a Provides for garbage grinders and automatic-sequence washing machines.
b In every case, sufficient area should be provided for at least two bedrooms.
c Absorption area for standard trenches is figured as trench-bottom area.
d Absorption area for seepage pits is figured as effective sidewall area beneath the inlet.
e Unsuitable for seepage pits if over 30.
f Unsuitable for leaching systems if over 60.

As related in the introduction to this chapter, percolation rates are
needed to determine whether or not a given job site will be suitable for
certain engineering projects, including reservoirs, sewage lagoons,
sanitary landfills, and septic tank drain fields. In most cases, several
percolation tests are performed at various locations throughout a
project site in order to obtain a representative value of the percolation
rate. Table 17-1 gives some typical values and limitations of percolation
rates, whereas Table 17-2 shows how percolation rates can be used in
septic tank drain field design to determine absorption areas.

SUMMARY

[1] Soiltest, Inc., Operating Instructions for Martin Perk-Tester, Evanston,

Ill., 1970.

REFERENCES

[2] U.S. Department of Health, Education, and Welfare, Public Health

Service, Manual of Septic Tank Practice, Washington, D.C., 1963.

[3] U.S. Department of Agriculture, Soil Conservation Service, Guide for

Interpreting Engineering Uses of Soils, Washington, D.C., 1971.