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Sunday, 15 July 2007

Copper, chrome and arsenic - oh my!

After going back and forth for ages I decided that the tanks would be installed on a bed of crushed rock instead of concrete. Cost was a factor, as was my disinclination to contribute even a few more square meters to the concrete jungle of a modern city. (Future archaeologists probably won't view this as the "information age" the way we romantically project. I think it's more likely to be known as the concrete or plastic age. But I digress...)

One disadvantage of the crushed rock option is that unless is it securely restrained it has a tendency to spread out or erode from the edges. The way I've seen people counter this is to construct a border out of sturdy wooden sleepers to contain the rock.

What I hadn't considered until I was exploring my options at the hardware ubermarket this arvo is that in order to prevent the wood from decaying - that is, being eaten by insects, fungus and bacteria the way all non-living wood naturally is - it has to be soaked in a toxic cocktail of copper, chrome and arsenic. That way the things which try and eat the wood will become sick and die, or if they're smart simply be repelled.

Now I'm having to re-think.

Partly I'm concerned about the potential for toxic effects on my family and I. The jury is officially out on whether there is a measurable risk to human health from the use of "treated" wood such as this, but remember I'm building a water supply which I intend to use on surrounding vegetable gardens. It just doesn't seem like a smart thing to do.

The other part of my concern arises from the "waste equals food" philosophy espoused in the book Cradle to Cradle. This book has had a huge influence on me and now it doesn't seem right to take a perfectly good piece of timber and turn it into something which has a short useful life and then becomes toxic waste.

I may end up pouring concrete after all.


Crazy Mumma said...

I must admit that I wouldn't use treated timber for anything after looking into the treatment process myself! Do you have a recycled materials centre nearby at all? They tend to have a great array of used hardwood timber that might suit? Or if not timber they might have bricks or pavers, or even metal offcuts of some description?

TB said...

I'm very hesitant to use untreated wood in the ground so close to my house. (See last night's post for pics.) Termites are natural, sure, but they make for rather unsustainable housing.

Metal would be hard to work with and I'd be concerned about it corroding and/or contaminating the soil.

But I was mulling over the idea of using some kind of concrete or stone blocks to form the border. Those big, ugly "Besser bricks" might work if I pound some anchor spikes down to keep them from shifting - just like I would have with sleepers but more of them.

Thanks for the suggestion.

Anonymous said...

Another option would be to create gabions, which are basically wire baskets holding the rocks. The idea is that you create large "bricks" made of stones wrapped in chicken wire and then anchor those into the ground in the same way you would the sleepers. This will have a nicer look as well. Also, you might want to explore using rubber mulch instead of rocks. The rocks are typically mined from pristine sites, whereas the rubber mulch is made from recycled tires.

TB said...

Hey there anonymous, thanks for stopping by.

Gabions sound interesting. I know a guy who's a structural engineer and I'll bounce the idea off him. My concern would be whether they're rigid enough to counter the spreading force that five tonnes of water is going to impose on the base material.

Shredded tyres I'm not so keen on. First, they're squishy when I want solid. And second they're nasty and toxic in their own special way.

Hopefully one day there might be better ways to recycle old tyres.