Geology Reference
In-Depth Information
how long it takes the water surface to fall 6 in. The percolation rate is
normally reported in either inches per hour or minutes per inch, or both.
One procedure, given by Soiltest, Inc., manufacturer of the Martin
Perk-Tester, is as follows [1]:
(1) Following the presoaking period, refill the hole with water and
allow it to drop to a point below the topsoil.
(2) Place the test stand in position with the opening directly over
the hole and the stand legs pressed firmly into the soil.
(3) Set the Perk-Tester on the test stand with the binding post
situated over the curved cutout in the stand. Using the level mounted
on the tester, adjust the stand as needed.
(4) Turn the Perk-Tester on and press the test button. The meter
should read full scale. This checks the battery and amplifier circuits.
(5) Install the grounding rod down through the binding post and
well into the water. This rod must remain in contact with the water
at all times during the entire process of testing.
(6) Insert the aluminum rule through the slot in the center of the
Perk-Tester and lower it down into the hole until it penetrates the
surface of the water. As the water is penetrated, the meter should
read full scale. The rule should be adjusted so that the top edge of
the rule slot on the Perk-Tester is in alignment with a suitable inch
mark on the rule when the lower tip of the rule is only a short
distance below the surface of the water. Note that reading.
(7) Prepare a stopwatch for timing the fall of the water and watch
the meter pointer. When the water meniscus breaks away from
the tip of the rule, the meter pointer will fall to zero. Start the
stopwatch at this time.
(8) Slide the rule down into the water until it is 6 in. below the
starting point and lock it. Again watch the meter pointer and stop
the timer when it falls to zero. Record the elapsed time.
The procedure just described is for use specifically with a Martin
Perk-Tester. It is possible, however, to perform a percolation test
without using such a tester. All one needs are a timing device (e.g., a
stopwatch) and a means of measuring how far the water surface has
dropped. The latter can be determined by measuring down to the water
surface from a fixed point, using a rule or yardstick. Figure 17-2 shows
schematically how such a measurement can be made.
A procedure for conducting percolation tests, as given by the Public
Health Service and intended mainly for septic tank drain field design,
is as follows [2]:
(1) Six or more tests shall be made in separate test holes spaced
uniformly over the proposed absorption-field site.
 
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