 percolation Site conditions and alternative systems Recommended septic tank capacities Septic tank inside dimensions Commonly required liquid waste system setback distances Head loss due to friction in PVC pipe Square feet of trench bottom area required by the Uniform Plumbing Code Square feet of bottom area recommended by the Manual of Septic Tank Practice Square feet of bottom area recommended by the Environmental Protection Agency Absorption areas for seepage pits Recommended mound interior absorption sys- tem configurations Application rates for various mound fills Natural soil infiltration rates Correction factors for natural ground slope Flow rates through holes of various diameters Recommended lateral distribution pipe diam- eters Irrigation efficiencies for various soils Loading rates for elevated sand filters ET water budget ETA system loading capacities Wastewater characteristics Water volumes associated with grey water sys- Residential water use by activity Introduction In nature, all living things use resources and produce wastes. The wastes of each group of organisms represent resources for another group of organisms, SO that materials are recycled and reassimila- ted. We are now learning that our health is totally dependent on the health of the environment and its cycles, that accumulations of wastes can cause severe environmental pollution, and that wastes should be recycled whenever possible. It used to be said that a stream would cleanse itself in 10 miles of flow. This distance generally was maintained between settlements along rivers SO that the waste from an upstream settlement would not be consumed by those downstream. But, as population densi- ties grew, the capacity of rivers and streams to assimilate the wastes and cleanse the water was exceeded, resulting in the accumulation of wastes in a deteriorating environment. Now communities using rivers and streams for water supplies must treat the water exten- sively because chances are that some proportion of the flow entered the water channel 