Virginia Administrative Code › Title 12 - HEALTH › Agency 5 - DEPARTMENT OF HEALTH › Chapter 610 - SEWAGE HANDLING AND DISPOSAL REGULATIONS › Part V - Design and Construction Criteria › Article 11 - Nonpublic Drinking Water Supply Systems Utilized in Conjunction with Onsite Sewage Disposal Systems › Section 12VAC5-610-1170:2 - APPENDIX G. Percolation Test Procedure and Percolation Test Data Forms

Current through Register Vol. 40, No. 24, July 15, 2024
Definition-The percolation test is a field procedure
						conducted in the soil horizon(s) selected for installation of the proposed
						subsurface soil absorption system for the purpose of observing the rate that
						clean water will permeate the soil under saturated conditions. The test
						provides a method for approximating the actual movement of wastewater through
						the soil which will occur during operation of the subsurface soil absorption
						system.
Test Holes
1.
					 Test holes shall be located at points and depths selected by and/or approved by
					 the district or local health department.
2. The depth of the test hole shall be placed
					 in the "slowest" portion of the horizon(s) selected for installation of the
					 absorption trenches. (See § 4.03A).
3. The portion of the test hole penetrating
					 the horizon(s) selected for placement of the absorption trenches shall be 7
					 (+-) 2 inches in diameter. Minimum acceptable horizon thickness is twelve (12)
					 inches. The diameter of the test hole above the selected horizon(s) may be as
					 large as necessary to conduct the test and prepare the hole in the selected
					 soil horizon(s).
4. Test holes
					 shall, where possible, be constructed within four (4) to six (6) feet of an
					 existing profile hole.
5. A portion
					 of the material excavated from the test hole should be mounded around the test
					 hole to prevent surface water runoff from entering the hole in the event of
					 rainfall during the period preceding and continuing through the conduct of the
					 test.
6. Where indicated the bottom
					 and sidewalls of the hole shall be scarified with a sharp pointed instrument or
					 knife to remove any smeared soil surfaces. Two inches of clean course sand or
					 clean fine gravel (pea gravel) shall be added to the hole to protect the bottom
					 infiltrative surface from scouring and sedimentation.
Presoaking
1.
					 Swelling Procedure-When shrink-swell soils are suspected the soil surrounding
					 the test hole shall be saturated for at least 24 hours by keeping at least 12
					 inches of water in the hole for the 24 hour period. An additional three days
					 for swelling may be required during dry periods when cracking has occurred.
					 After completion of the swelling procedure stated above the hole shall be left
					 overnight before proceeding with the measurement procedure.
2. Saturation Procedure-All test holes not
					 subject to the swelling procedure shall be kept saturated with at least 12
					 inches of water for a 4 hour period on the day preceding the measurement of the
					 percolation rate. Residual water in the hole shall be left to provide overnight
					 soaking.
Measurement of Percolation Rate-All measurements shall
						be made from a fixed reference point.
1. Test holes with 6 inches or less of water
					 remaining after the overnight soaking period.
a. Carefully fill the hole with water to a
					 depth of 6 inches over the sand/gravel.
b. Record water surface drop every 30 minutes
					 for a 4 hour period.
c. After
					 recording the water surface drop each 30 minutes estimate if, based on the last
					 reading, the hole will go dry add sufficient water to maintain not more than
					 one (1) inch water depth over the sand/gravel at the end of the test
					 period.
d. The drop measured during
					 the last 30 minute period shall be used to compute the percolation rate for the
					 hole tested.
e. In soils where the
					 first 6 inches of water seep away in less than 30 minutes after the overnight
					 saturation period, add an additional 6 inches of water and the time interval
					 between measurements shall be taken as 10 minutes and the test run to
					 completion, i.e. hole goes dry. The drop that occurs during the final 10
					 minutes is used to calculate the percolation rate.
2. Test hole with more than 6 inches of water
					 remaining after the overnight soaking period. The water depth over the gravel
					 shall be recorded. More than 6 inches of water remaining in the hole after
					 soaking procedure is prima-facie evidence of unsatisfactory for installation of
					 a subsurface soil absorption system.
For , see Virginia Administrative Code print
						product.