Wastewater collected from cities and a public corporation must ultimately be returned to receiving waters
or to the land.The complex question of which contaminants in wasterwater must be removed to protect the environmentand to what extent must be answered specifically for each ease.This requres anolyses of local conditions and needs, together with apllicatiou of scientific knowledge, ongineery judgement bared on part expenience, and consideration of the anthoritys requirements and regulations