|Issue Date||Summer 2007|
|Number of Articles Online||1 Articles|
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|Title||Building a Grey Water Wetland: A member's experience|
My wife and I live on a 4 ha property in Sandford, which is predominantly heavy clay. There is no mains water supply or sewerage system. Therefore, we have a total of 90,000 litres capacity rainwater tank storage while toilet and kitchen waste go to a septic tank. Grey water from the laundry, hand basins, shower and bath first go to an underground holding tank near the back door. From there a submersible sump pump empties the tank through a movable hose to the grass about 20 metres from the house. As we live in an area of very low rainfall I thought I could make better use of the water than simply draining it onto the grass.
We already had a dam about 80 metres from the house inhabited by a community of frogs, beetles and other water creatures. There are reeds and rushes around it and some floating plants. Initially I trialled diverting some of the house grey water into the dam. However, when the water emptied into the dam I realised that this approach was a mistake and I reluctantly went back to the previous system.
I sought some advice from Nigel Jones, a local builder, who specialises in building environmentally appropriate homes, passive and active solar heating and traditional and alternative forms of construction. Nigel suggested that a constructed wetland might be appropriate for our needs and offered to visit us to provide some advice.
When estimating how big the pit should be Nigel suggested that it should be able to cope with the theoretical loading provided by a family of five or six, because we have a 4-bedroom house, even though currently only my wife and I (and our terrier Topsy) occupy the house. His recommendation was for a pit 5m long, 3m wide and 800mm deep.
I also scanned the internet for further information; these sites are listed at the end of the article.
The wetland was built next to the dam to allow the treated water to flow into the dam.
The bottom of the pit was covered by a layer of sand about 50mm thick and a thick pond liner was laid in the pit. This was then covered by another 50mm layer of sand. 2m wide lengths of Forticon
The wetland pit next to the existing dam (photo) were placed across the base and up the sides of the pit. The purpose of the Forticon was to provide a warning that the actual pond liner is close if future excavation of the wetland is undertaken.
The water inlet consists of 20mm diameter irrigation pipe which leads down to the bottom of the pit at one end. This pipe was fed through a hole in an end cap that sealed a 1m length of 100mm sewer pipe. The other end was sealed. The sewer pipe had 5mm wide slots cut every 15mm to provide an even dispersion of the incoming water. This inlet was covered by blue metal.
Photo: The pit and water inlet pipe
The outlet was provided at the far end, close to the dam. A length of stormwater pipe with a grill set into the end was placed in position so that water would drain into the dam when the pit filled with water. The pit was filled with 14 cubic metres of 7mm blue metal.
Forty wetland plants have been planted in the blue metal. These include:
- Juncus filicaulis
- Juncus krausii
- Juncus pauciflorus
- Neopaxia australasica
- Carex appressa
- Carex longibrachiata
- Xyris operculate.
I am concerned that the submersible sump pump that delivers untreated water to the wetland might be working harder than it was designed to. However, it is still working after (I believe) not having been looked at for up to 15 years.
It is too early to determine if the new wetland will do the job: that is, to treat the grey water to an extent that it will not harm the living creatures in the dam. As at January 2007 there is a large amount of frog spawn around reeds following heavy rain during the previous week. If all this develops into frogs we won't be able to sleep at night for the noise!
As I also use the dam water to water various areas of the property, I want the water to be clean enough so that natives are not harmed by its use.
Costs to date have been:
- Excavation (pit and dam extension) $1,100
- Sand and blue metal $900
- Pond liner $320
- Forticon $70
- Plants $120
- Irrigation pipe and fittings $100
- New submersible sump pump $550
- Total $3,160
Clearly, these costs would have been considerably higher if I had paid a contractor to undertake the work.
If you would like any further information about this project I can be contacted by email at: email@example.com. Phone 03 6248 9117.
- Greywater Treatment Systems by Sustainable Living Tasmania;
- Household Greywater Wetlands by the Amphibian Research Centre;
- Mobbs, Michael, 1998. Sustainable House: Living for Our Future. Marrickville, NSW Choice Books.
Photo: the completed greywater wetland