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Evapotranspiration
(ET) systems are ideal in locations where the annual
evaporation rate exceeds the annual precipitation rate. The
effluent flows from the pretreatment unit to the sand bed
underlaid with an impermeable liner. Capillary action in the
fine sand causes the effluent to rise to the surface and escape
through evaporation while at the same time, vegetation transports
the wastewater from the root zone to the leaves where it is
transpired as a relatively clean condensate. The design allows
for complete wastewater evaporation with no discharge. Evapotranspiration-absorption
(ETA) systems are similar to ET systems. However these systems
are unlined and designed for use where soils are fairly impenetrable,
but not entirely so. The ETA system disposes of wastewater
in the same evaporation/transpiration manner but also allows
effluent to trickle slowly into the underlying ground.
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