Evaporation - Transpiration septic system design & regulation: this document uses the New York State wastewater treatment standard for individual household septic systems (Appendix 75-A) to provide an example of state regulated design and installation of evaportion-transpiration septic systems.

Design Regulations for Evaporation-Transpiration (ET) and Evapo-Transpiration Absorption (ETA) Septic Systems Design Criteria

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Tafgard soil based wastewater treatment systems - developed in Japan by Taisei Kogyo Co., Ltd., this system uses a combination of a five-chamber waste treating septic tank designed by Taisei, effluent disposed-of by an evaporation-transpiration system through a Tafgard geotextile and aerated soil (effluent spread horizontally and upwards from distribution piping). The Taisei septic tank utilizes a chain of bacteria, protozoan, metazoans and various kinds of enzymes.

For details about evaporation / transpiration septic system design, construction, and repair,

see EVAPORATION-TRANSPIRATION SEPTIC SYSTEMS. Citation of this article by reference to this website and brief quotation for the sole purpose of review are permitted. Use of this information at other websites, in books or pamphlets for sale is reserved to the author.

[Regulation and System Design Criteria for Raised Septic Systems, Septic Mound Systems, Intermittent Sand Filter Bed Systems, Evaporation-Transpiration Septic Systems, Evaporation-Transpiration Absorption Septic Systems, and Other Alternative Septic Systems] Effective Date: 12/01/1990

(1) Evaporation/Transpiration/Absorption Septic Systems - General

ET systems rely on the upward movement of moisture through the soil, surface vegetation and into the air rather than absorption into the soil. ETA systems also use the absorptive capabilities of the soil and are less dependent on evaporation and transpiration.

(2) Site Requirements for Evaporation, Transpiration-Absorption Type Septic Systems

(i) All systems previously discussed, except intermittent sand filters, have been determined to be unacceptable for the planned building site.

(ii) An expansion area equal to or greater than 50% of the required basal area shall be available on the site.

(iii) All minimum vertical and horizontal separation distances can be maintained as described in Table 2 from both the edges of the basal area and the designated expansion area.

(iv) An environmental assessment determines that the development of the site with this system is consistent with the overall development of the area and will cause no adverse environmental impacts.

(3) Design Criteria for Evaporation, Transpiration-Absorption Type Septic Systems

(i) The designer must consider all of the items listed below and be able to document from reliable sources (i.e., National Weather Service, Soil Conservation Service) the parameters used and show that the net outflow from the system exceeds the inflow without the exposure of sewage or partially treated sewage on the surface of the ground:

• Total rainfall and snowfall.
• The percentage of the rainfall and snowfall that will infiltrate into the soil and the percentage that can be expected to runoff the system.
• The annual land evaporation rate of the area.
• The vertical rise of water than can be expected in the soil due to capillary action.
• The amount of transpiration expected from the surface vegetation.
• The permeability of the underlying soil and the impact the system will have on the groundwater level.
• (ii) The design must provide for a trench depth that is not greater than 30 inches below the surface.
• (iii) Pressure distribution of effluent throughout the system is required.

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Continue reading  at EVAPORATION-TRANSPIRATION SEPTIC SYSTEMS or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

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