Sampling operation at the site is as follows: The ruler is unfolded and fixed to the soil by the two pins. Eleven standard sterile polyethylene test tubes (120 mm long, 10 mm in diameter) were marked, opened, and slightly pushed, upside down, into the soil through the sampling holes of the ruler. The piston was placed over each tube and press down to its fullest extent; about 10 mm of the tube remained above the soil surface to improve the ease of withdrawing the tubes.
After the eleven tubes are driven into the soil, the piston and the ruler were removed. Each tube is hand-pulled from the soil, closed with its original sterile cap, and marked.