Those suspended solids in wastewater that will settle over a certain period of time and are removed in that way. Settleable solids generally remain at the bottom of an Imhoff cone which is utilized to determine the volume of sand existing in a well water sample. The settleable solids test is done to measure the total amount of solids passing through into the wastewater treatment plants, including ascertaining the quantity of sludge to be entering during the treatment process.