After a preliminary site assessment, due diligence and other preparation, the area chosen for the percolation test requires drilling of 4-6 borings and additional borings for one or more observation wells to confirm soil character, depth and groundwater conditions.
My nephew helper is young and determined. He only works with me one or two days per year but reminds me of what it is like to have energy and youth (and I only have to pay him off with baseball cards and money for Leggoland).
Testing has a time sequence to determine the fall of water in the nominal six inch diameter test hole (measured in minutes per inch of fall). Measurements are carefully done and sometimes I use an electronic measuring device. Testing of borings deeper than 5 feet are best done with a distant reading "Rube Goldberg set-up" such as a weighted float tied to fish line and a foot or so portion of a tape near a surface platform. The objective is to be consistently accurate.
With loose soils, it is necessary to use inserts so as to not have the sidewalls of the boring cave and invalidate the test. I use perforated six inch diameter plastic flower pots pushed gently to the bottom with a four inch plastic pipe.
The actual procedure (which I wrote when employed by the County) can be read in its entirety at www.sdcounty.ca.gov
Go to this URL and under "Quicklinks", right click on "A-Z Services"; then scroll to the "E" Section and right click on "Environmental Health". Right click "waste and then "septic systems". Look for the section called "Useful Information" and right click "Design Manual for Onsite Wastewater Systems"; then scroll to page 21.