TREATMENT FACILITIES
Section 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.
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thanks Brian for sharing
ReplyDeleteI think soil needs to have perfect soil absorption power to have a septic system
Hope to see more post related to Septic design Sudbury