A GREY WATER WETLAND IN SANDFORD, TASMANIA
Background
My wife and I live on a 4 ha level property in Sandford, Tasmania 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 in six tanks while toilet and kitchen waste go to a septic tank. Grey water from the laundry, hand basins, bath and shower 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. This system has been in operation for 15 years, since the house was built.
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. I was aware that untreated grey water is not particularly beneficial to native vegetation and trees.
We have a dam (actually a water hole) about 80 metres from the house. A community of frogs inhabits it, along with beetles and other water creatures. There are reeds and rushes around it and some floating plants.
A few months ago I put a T junction in the outlet pipe near the house, with taps and a non-return valve, and extended the 20mm irrigation pipe to the dam. However, when the water emptied into the dam I realised that this approach was a mistake and reluctantly went back to the previous system.
Research and Planning
When I told my son about my dilemma he mentioned that there was a seminar on 22 October - “2006 Environmental Home Expo Talks Program” that included a session by Nigel Jones* “Managing Waste Water”.
Unfortunately, I was not able to attend the seminar but I phoned him later to ask for advice and suggestions as to the best approach for a home-owner to re-use grey water.
Nigel suggested that a constructed wetland might be appropriate for our needs and offered to visit us to provide some advice.
On his first visit of three, Nigel recommended a site for the wetland and how water should be directed into the pit and allowed to drain away after being processed.
I also looked up various sources on the internet, including:
“Greywater Treatment Systems” by Sustainable Living Tasmania;
“Household Greywater Wetlands” by the Amphibian Research Centre;
and Mobbs, Michael, 1998. "Sustainable House: Living for Our Future." Marrickville, NSW Choice Books.
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 5 m long, 3 m wide and 800mm deep.
* Nigel Jones – Specialising in environmentally appropriate homes, services and surroundings, passive and active solar heating, traditional and alternative forms of construction.
7 Oakleigh Avenue, Taroona Tas 7053 Phone 03 6227 9097.
email n.jones@bigpond.com.
Construction
The site chosen for the wetland was next to the dam to allow the treated water to flow into it.
At the same time as having the wetland pit excavated I took the opportunity to have the dam enlarged by having a large amount of clay removed and increasing the capacity by about 60% in the process.
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 and 2m wide lengths of Forticon were placed across the base and up the sides of the pit. The purpose of the Forticon was to provide a warning that the liner was just underneath if an excavation is necessary in the future.
The water inlet consisted of 20mm irrigation pipe which led 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 about 0.5 cubic metres of 14mm blue metal.
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, without blue metal being able to enter the pipe.
A load of 14mm blue metal was placed near the outlet point. The remainder of the pit was filled with 14 cubic metres of 7mm blue metal.
Where the pond liner and Forticon overlapped the top edge this was trimmed back and covered with soil to improve its appearance.
As the pit has now filled, taking about three weeks to achieve, about 80 wetland plants have been planted in the blue metal. No water is visible at the surface but saturation occurs about 60mm down.
Plants that have been used are:
Juncus filicaulis
Juncus krausii
Juncus pauciflorus
Neopaxia australasica
Carex appressa
Carex longibrachiata
Xyris operculata.
I avoided using Phragmites australis because I was advised that it is a very aggressive plant and in time could damage the pond liner. Other people I spoke to consider that this could not happen.
Operation
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.
In view of this I have purchased a new Davey D42A submersible sump pump but I have not yet summoned up the courage to actually get into the pit and instal it. When I do this I will also take the opportunity to clean out any sludge that might have accumulated over the years. [I have now installed the new pump. I was worried about the quality of the air in the pit as I cleaned out the sludge and held my breath as I scraped the muck into a bucket. I realise this does not comply with OH & S requirements but it was the best I could manage. The pump is working beautifully.]
It is too early to determine if the new wetland will do what I believe it is capable of achieving – that is, to treat the grey water to an extent that it will not harm the living creatures in the dam. However, initial indications are encouraging - no smell from the water going into the dam and the dam level is being maintained through dry conditions here.
As I also use the dam water through a network of irrigation piping 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
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. I am also indebted to Nigel Jones, who has provided his advice and expertise to me at a nominal charge and to my son, Matthew, for his considerable help by assisting in filling the pit with blue metal.
Monitoring/Follow-up
As this is still basically a work-in-progress, it is too early to give any information at this stage. However, I presume the proof of whether it works or not will be the extent to which my dam remains healthy enough to support a viable frog population without any smell or mosquito problems.
Contact
email address - Back to Tony's Trips Website