Leach Fields & Septic Systems

This technical reference covers the secondary stage of an on-site wastewater system, the disposal field, built as an EPIC leach line: an open-bottomed, double-walled chamber surrounded by washed sand and set on the compacted trench floor in place of the conventional stone trench and perforated pipe.

It is organised around three questions that govern every on-site field: how much liquid can leave the structure each day, how long that rate is sustained, and where the dissolved nitrogen goes. Parts I to III give the physical and biological answers: why a conventional stone field fails, how the EPIC leach line is configured, and the biology and chemistry of septic tank effluent in the profile.

Part IV turns those answers into a sizing procedure, with the design basis, soil interface geometry, sizing tables, worked examples and the EPIC percolation test. Part V covers the three configurations and how to choose between them, field alternation through a leachate switching vault, tree-pit blackwater irrigation, the sand filter, grey-water separation and estate layouts. Part VI covers installation, setbacks, commissioning, operation, comparative performance and the field record.

The design basis follows the work of Jonas Z. Sipaila, inventor of the EPIC chamber, and uses the United States Public Health Service percolation bands. The document states that application rates, setbacks and field areas are set by the health authority with jurisdiction, and that nothing in it overrides a local code. An annex of thirteen full-size plates is laid out for printing and site use.