Chakravarthy said three special teams, one each for Ambur, Vaniyambadi and Tirupattur subdivisions, will track the illegal sand activities in the area. Talking about the modus operandi, he added, “The accused constructed septic tank like structures in isolated locations and put a metal sieve over them. They then dumped alluvial soil collected from nearby farms on the sieve and pumped water on it. This results in particles of less than 500 microns going through the sieve into the tank. When the tank is filled to its capacity, the sand is removed and sold.”