Introduction

Adequately managed on-site wastewater systems are a cost-effective and long-term option for meeting public health and water quality goals in rural areas.Decentralized systems currently serve approximately 25 Percent of the U.S. population, and approximately 37 percent of new development.

For most of the 20^th century, wastewater management entailed either large municipal centralized treatment facilities for highly populated areas, or conventional onsite systems (septic tanks with soil absorption or cesspools) for rural areas. 

Less than one-third of the land area in the U.S. has soil conditions suitable for conventional soil absorption systems.  Numerous innovative alternatives to the conventional septic tank and soil absorption system have evolved in response to the demand for an environmentally acceptable and economical means of disposing domestic wastewater onsite and into the restrictive soil conditions common in many areas. 

The treatment and disposal of wastewater takes place in three principle areas or categories: (1) The treatment device (or black box), (2) The disposal device, (3) the in-situ soil.  There is significant ambiguity regarding what is a treatment device and disposal device.  For the purpose of this document the definitions are:

·        Treatment Device – A constructed discrete device or system that increases water quality through physical, biological or chemical means independent of receiving soils.

·        Disposal Device – A constructed device or mechanism that maximizes the natural soil simulative capacity.  (All treatment takes place in or at the soil interface.  If no significant treatment is expected to occur outside the soil boundary, the device is purely disposal).

As mentioned above, in addition to the treatment taking place Soil – Suitable soil is an effective treatment medium for effluent treatment.  The soil consists of billions of microorganisms, including bacteria, protozoa, fungi, molds and other organisms.  These organisms interact with the minerals, organic matter, water and gases that comprise the soil.  This complex community along with the physical structure of the soil itself provide the mechanisms by which the wastewater is purified as it percolates through the soil and returns to the underlying groundwater, or is taken up by plants or evaporated.

Because of the enormous variations in temperature, soils, water use, availability of filtration media and climate throughout the world, no single design has been used everywhere.  Instead, different treatment and disposal alternatives can be combined to produce optimum solutions for particular sites.  New treatment technologies are being developed, but the basic principles of wastewater treatment remain constant.  The complexity of the system required for a particular site varies with the infiltrative capacity of the soil, geology, and climate, topography of the site and regional rules and regulations. 

.          The following document reports on a variety of on-site systems, both treatment and disposal devices, but by no means covers all systems currently in use or presently being developed.  The treatment devices and disposal devices have not been specifically separated in the document therefore it is up to the reader to understand the differences in treatment and disposal devices.  This document reports on system uses, process descriptions and design criteria as well as necessary operation and maintenance and system advantages vs. disadvantages. 

This manual enhances the proposed rule, which may be in effect as early as January 1, 2000, by reporting on a variety of on-site systems that will be designed per the revised rules.  This document is continuously expanding and evolving along with the proposed rules.  We have and will continue, with your help, to resolve ambiguities and inconsistencies found here or in the rule.