Percolation Test - Soil Properties: Testing, Measurement, and Evaluation - page 246

Figure 17-2 Schemes for Making Percolation Tests [2]

(2) Dig or bore a hole, with horizontal dimensions of from 4 to 12 in.
and vertical sides to the depth of the proposed absorption trench.
In order to save time, labor, and volume of water required per test,
the holes can be bored with a 4-in. auger (see Figure 17-2).

(3) Carefully scratch the bottom and sides of the hole with a knife
blade or sharp-pointed instrument, in order to remove any smeared
soil surfaces and to provide a natural soil interface into which
water may percolate. Remove all loose material from the hole. Add