25 Pa. Code § 73.15 - Percolation tests
Percolation tests shall be conducted in accordance with the following procedure:
(1)
Number and location. Six or more tests shall be made in
separate test holes spaced uniformly over the proposed absorption area
site.
(2)
Results.
Percolation holes located within the proposed absorption area shall be used in
the calculation of the arithmetic average percolation rate.
(3)
Type of hole. Holes
having a uniform diameter of 6 to 10 inches shall be bored or dug as follows:
(i) To the depth of the proposed absorption
area, where the limiting zone is 60 inches or more from the mineral soil
surface.
(ii) To a depth of 20
inches if the limiting zone is identified as seasonal high water table, whether
perched or regional; rock formation; other stratum; or other soil condition
which is so slowly permeable that it effectively limits downward passage of
effluent, occurring at less than 60 inches from the mineral soil
surface.
(iii) To a depth 8 inches
above the limiting zone or 20 inches, whichever is less, if the limiting zone
is identified as rock with open joints or with fractures or solution channels,
or as masses of loose rock fragments including gravel with insufficient fine
soil to fill the voids between the fragments, occurring at less than 60 inches
from the mineral soil surface.
(4)
Preparation. The bottom
and sides of the hole shall be scarified with a knife blade or sharp-pointed
instrument to completely remove any smeared soil surfaces and to provide a
natural soil interface into which water may percolate. Loose material shall be
removed from the hole. Two inches of coarse sand or fine gravel shall be placed
in the bottom of the hole to protect the soil from scouring and clogging of the
pores.
(5)
Procedure for
presoaking. Holes shall be presoaked, according to the following
procedure, to approximate normal wet weather or in-use conditions in the soil:
(i)
Initial presoak. Holes
shall be filled with water to a minimum depth of 12 inches over the gravel and
allowed to stand undisturbed for 8 to 24 hours prior to the percolation
test.
(ii)
Final
presoak. Immediately before the percolation test, water shall be
placed in the hole to a minimum depth of 6 inches over the gravel and
readjusted every 30 minutes for 1 hour.
(6)
Determination of measurement
interval. The drop in the water level during the last 30 minutes of
the final presoaking period shall be applied to the following standard to
determine the time interval between readings for each percolation hole:
(i) If water remains in the hole, the
interval for readings during the percolation test shall be 30
minutes.
(ii) If no water remains
in the hole, the interval for readings during the percolation test may be
reduced to 10 minutes.
(7)
Measurement. After the
final presoaking period, water in the hole shall again be adjusted to
approximately 6 inches over the gravel and readjusted when necessary after each
reading.
(i) Measurement to the water level
in the individual percolation holes shall be made from a fixed reference point
and shall continue at the interval determined from paragraph (6) for each
individual percolation hole until a minimum of eight readings are completed or
until a stabilized rate of drop is obtained whichever occurs first. A
stabilized rate of drop means a difference of 1/4 inch or less of drop between
the highest and lowest readings of four consecutive readings.
(ii) The drop that occurs in the final period
in percolation test holes, expressed as minutes per inch, shall be used to
calculate the arithmetic average percolation rate.
(iii) When the rate of drop in a percolation
test is too slow to obtain a measurable rate, the rate of 240 minutes per inch
shall be assigned to that hole for use in calculating the arithmetic average
percolation rate. The absorption area may be placed over holes with no
measurable rate when the average percolation rate for the proposed absorption
area is within the limits established in §
73.16 (relating to absorption and
spray field area requirements), Table A.
(iv) When a percolation test hole is dry at
the end of a 10 minute testing interval, that hole may not be used in the
calculation of the arithmetic average percolation rate. If 1/3 or more of the
percolation test holes are dry at the end of a 10 minute testing interval, the
proposed absorption area may not be designed or installed over these holes
unless the local agency determines that an anomaly caused the fast percolation
rate and a retest of the area is within the acceptable percolation rate limits.
If no anomaly is discovered, the local agency may accept the percolation test
results from the remaining holes if the results are supplemented with the
results of additional percolation testing conducted outside of the area in
which the dry percolation holes were found.
Notes
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