NAC445A.9668. Performance of percolation test.

     1. If a percolation test is performed pursuant to NAC 445A.961, the test must be performed by a qualified person, including, without limitation, a design engineer, a soils scientist or a geologist, approved by the Division or other administrative authority, and must be performed in accordance with this section.

     2. The percolation test data must be taken from a minimum of two test holes in the area of the proposed effluent absorption system. The person conducting the percolation test must:

     (a) Dig or bore the test holes to the proposed depth of the absorption system.

     (b) Ensure that the test holes have vertical sides and are not less than 4 inches or more than 12 inches in width.

     (c) Scratch the bottom and side surfaces of the test holes with a sharp or pointed instrument to expose the natural soil interface.

     (d) Remove all loose material from the bottom of the test holes.

     (e) Add at least 2 inches of coarse sand or gravel aggregate to the bottom of the test holes to prevent scouring.

     (f) Remove any soil which sloughs into the holes before or during the percolation test.

     3. To determine which percolation test procedure to follow, the person conducting the test must:

     (a) Fill the percolation hole with water to a depth of at least 12 inches over the aggregate and determine the time required for the water to seep completely away.

     (b) Fill the percolation hole with water again to a depth of at least 12 inches over the aggregate and determine if the water seeps away in 10 minutes or less and:

          (1) If water is left in the hole after 10 minutes, proceed with the presoaking procedure pursuant to subsection 4, followed by the slow percolation test procedure pursuant to subsection 5; or

          (2) If the water is completely seeped away after 10 minutes, proceed with the fast percolation test procedure pursuant to subsection 6.

     4. The presoaking procedure for the slow percolation test consists of the following steps:

     (a) Fill the percolation hole with clear water to a minimum depth of 12 inches over the aggregate.

     (b) Add clear water as required to maintain at least 12 inches of water over the aggregate in the hole for 4 hours.

     (c) Allow any water remaining in the hole after 4 hours to seep away. Do not remove the water.

     (d) Let the hole sit for not less than 16 hours or more than 30 hours before beginning the slow percolation test. Swelling of the soil may occur during this period. Do not disturb the soil.

     5. The slow percolation test consists of the following steps:

     (a) Not less than 16 hours or more than 30 hours after the end of the presoaking procedure 4-hour soaking period, fill the hole with clear water to a maximum depth of 6 inches over the aggregate.

     (b) From a fixed reference point, measure the drop in the level of the water at 30-minute intervals, for a total test time of 4 hours. If the first 6 inches of water seeps away in less than 30 minutes, the interval between measurements must be reduced from 30-minute intervals to 10-minute intervals, for a total test time of 1 hour.

     (c) Fill the hole to a maximum depth of 6 inches over the aggregate as often as necessary to prevent the hole from becoming empty during the test time.

     (d) The amount of the drop in the level of the water during the last interval of the test must be used to determine the percolation rate, except that if two successive measurements do not vary more than 1/16 inch, the test may be stopped and the percolation rate determined by the last two measurements. In any case, the minimum time in which a slow percolation test may be completed is 1 hour.

     6. The fast percolation test consists of the following steps:

     (a) Fill the percolation hole with clear water to a maximum depth of 6 inches over the aggregate.

     (b) From a fixed reference point determine, at 10-minute intervals, the extent to which the water in the hole drops over the next 1 hour. If 6 inches of water seeps away in less than 10 minutes, a shorter interval between measurements must be used, but the minimum time for the entire test is 1 hour.

     (c) Refill the hole as necessary to prevent all the water from seeping away during the 1-hour test time. The level of the water must never exceed 6 inches in depth over the aggregate.

     (d) The amount of the drop in the level of the water recorded for the final 10-minute interval must be used to determine the percolation rate.

     (Added to NAC by Environmental Comm’n by R194-07, eff. 8-26-2008)