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Grey Water Filter
The GWF unit is a lightweight durable plastic unit, which is easy to handle on site, and does not require heavy lifting gear. It is suitable for underground and supported above ground installation, as long as it is protected from earth pressure and hydraulic forces, which can float it out of the ground in certain conditions.
The GWF Grey Water Filter is designed to use pine bark chip to filter contaminants, which clog normal filters and are unpleasant to clean. The major contaminants are body fats, hair and soap scum. The filtered liquid is then passed through a gravel filter. The GWF tank is used in conjunction with an SDC or PDC Dosing chamber and an LPP Kit for dispersal into an evapo-transpiration field.
Because the tank is approximately one third full of heavy material, with airspace above, and is free draining, it is vulnerable to side pressures and must be supported by a timber enclosure, back-filled with fine drainage metal or scoria.
- Under-house installation
- If the tank is installed in an enclosure underneath the house, and is not susceptible to rain water or flooding by surface flows, or a rising water table, the risk of floating is minimal. The requirement for side support is particularly important in heavy soils.
Back-filling should be undertaken with care, and consolidated to ensure that the risk of voids is minimised, particularly under the sloping bottom of the tank., where the drainage metal fill and soil inside the tank need support.
In free draining sandy soil situations, sand can be used for back-filling, but should be avoided in heavier soils.
- External installation, on sloping ground
- In this situation the enclosure is exposed to rain, and surface flow storm-water. Provision for free drainage of the enclosure is vitally important. We suggest that one end or side of the GWF unit be dug into the slope, (depending on the degree of slope), so that the sides of the enclosure extended above ground level on the low side to contain the fill.
In sandy soil, the buried end of the GWF tank will also need a retaining wall. In heavy clays this will not be necessary. In both cases the back and sides of the containment should be drained using 100 mm Draincoil.
Shade-cloth over this followed by about 100 mm of good quality topsoil will provide a good medium for plant growth.
- External installation on flat ground
- This situation carries the highest risk of flooding of the containment, and careful drainage of the enclosure is essential. This implies that there must be somewhere down-slope to drain the water to or a free draining substrate. If not, the use of the GWF unit may not be recommended. These factors will be considered in the design stage of your system, and we may recommend alternatives such a concrete tank with ground anchors.
- Planting
- To fit the finished installation into your landscape we suggest planting the area of the containment around the access hatch with selected native plants.
Careful selection of plants, particularly Carex spp (native grasses), flaxes, coprosmas, particularly prostrate varieties, and native Toetoe do a good job of fitting the installation into the natural environment. If they are thickly planted, at a rate of 2 per square metre for G2 size or 1 per square metre for G3 size and weeded for the first year, they will crowd out weeds leaving an easy care addition to your landscaping.
We suggest you extend the planting beyond the line of the containment, and introduce curves to soften the edges, and selection of plants for height will soften the vertical aspect.
If your containment extends above ground level, the walls can be covered with ground covering plants such as Coprosma Repens.
Please bear in mind that the planting around your VERM unit containment is cosmetic and serves no treatment function. In the establishment phase the plants will need normal garden care, particularly watering in dry weather. Plant growth can be improved by applying a small quantity of slow release fertiliser such as Magamp at planting time.
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