Table 9.2 Ecosystem re-entry options for on-site wastewater systems
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| Type of system |
Comments |
| Sub-surface seepage trenches and beds |
This requires sub-soils with appropriate drainage characteristics.
Groundwater levels must not be too high. |
| LPED (low-pressure effluent distribution) trenches |
Specially designed shallow and narrow trench systems
with a nested perforated dosing pipe within a drain-coil line. Used
for either deep sandy soils to distribute septic tank effluent for further
in-soil treatment, or for deep topsoil conditions overlying clay to
distribute effluent for topsoil treatment and evapo-transpiration. |
| Wisconsin mounds |
Sand-filled treatment mounds producing treated effluent
for seepage to natural ground under the base. Used on sites with high
groundwater levels and/or poorly drained soils. |
| ETS (evapo-transpiration seepage) beds |
Appropriate where soils have impeded drainage, and used
in climates with good evapo-transpiration rates and lower rainfalls.
Beds and/or surrounding spaces between beds are planted with high-transpiration
shrubs, plants and/or grasses. |
| Surface spray irrigation |
For wastewater that has received secondary treatment
(AWTS, packed-bed reactors [an upgraded intermittent sand filter], wetland)
plus disinfection via ultraviolet light or chlorine tablets. Note: Not
used for on-site applications in NZ. |
| Surface drip-line irrigation |
For wastewater that has received secondary treatment
(AWTS, packed bed reactors [an upgraded intermittent sand filter], wetland).
Drip lines are laid on the soil surface and covered with mulch or bark
or compost. Can be designed for incorporation within a landscaped area
on the lot. |
| Subsurface drip-line irrigation |
For wastewater that has received secondary treatment
(AWTS, packed bed reactors [an upgraded intermittent sand filter], wetland).
Drip lines are laid within good topsoil to depths of 50 to 100 mm. Can
be designed for incorporation within a landscaped area on the lot. |
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