If you want to filtrate green ... Published December 13, 2017 14:13 by GILBERTO CRUZADO VASQUEZ, EEstudio Geologico e Impacto Ambiental de muchas carreteras en Cajamarca y en casi todo el Perú at Programa Nacional de PROVIAS If you want to filtrate green waste water through of sand layer , to be more pure the water, you must use gravey, sand and clay, but finally youmust to do analysis of midrobial testing.