Pollutants from water harvested from roadsides

Heya - this is my first post, but you'll be seeing a LOT of me. >_<

I live in the Sonoran desert in AZ. I have about 1/4 of an acre of land in front of my house, all sloping down away from the road, and every rainy season we get tons of water sheeting off the road into my property that I would like to harvest and use. My one concern, however, has been pollution from the road and traffic on it.

I don't know how it affects the plant life, the production trees, how to deal with it, any of that.

I have studied permaculture in bits and pieces but I'm really pretty much a newbie. Any suggestions on what to do about dealing with the pollutants or references to find out about this would be greatly appreciated! The road itself gets a fair bit of traffic, and it's made of asphalt, if that helps.

Shauna

Hi Shauna and welcome to permies!

First of all, if you live in Phoenix or Tucson, get in touch with Watershed Management Group. They have a whole program called "Green Streets" that's all about water harvesting from roadways. Water harvesting from roadways is entirely doable and running the polluted water through infiltration basins filled with woodchips and planted with native trees is a really good way to slow, sink, spread and CLEAN the water. Also check out Tucson Native and water harvesting guru, Brad Lancaster's site http://www.harvestingrainwater.com/.

As far as impacting production trees, there have been studies done and the effect is minimal if any on production trees. Mostly, biological systems do clean the water. If you are worried about pollutants reaching food trees, running the water through a bioswale that grows native grasses and trees is a great way to clean it before it goes into your orchard. And no, I wouldn't water non-woody plants with stormwater harvested from roadways.

The only thing I would add to Jenn's excellent comment is to inoculate your woodchips. Desert soils are poor habitat for fungi, although the well kept lawns in Phoenix and Tucson do support a bumper crop of Amanitas in the summer months. If you can get discarded, past-sell-date mushrooms from your local grocer, you can blend those up with some water and use that to inoculate your wood chips. That should take care of the road oils that wash off with the summer monsoon.

Leave and root veggies will absorb the pollutants and pass them on to you when you eat it.
Nuts will also pass them on to you too.

However fruits (tomatoes/blackberry/orange/etc) will not pass on the pollutants to you, even without the woodchip filter bed.

As a general rule if the food has iron/calcium/magnesium/or any metal/mineral. It will also have lead/arsenic and other pollutants.
And if the food has soil/dirt on it like potatoes/carrots then it will also pass on pollutants to you.

So only send the road water to fruit trees.
And use your "clean" water for your veggies/nut trees.

A woodchip swale is a really good idea. With the fungi trading the mineral for sugar from the trees. the trees will need to pump less water to get enough minerals.
The soil will be cooler so less water will evaporated. And you could also install a drip irrigation under it.
If some worms move in under the woodchip bed then the soil will become even more aerated.

Thank you, guys!

Jennifer - I'm very near Tucson, yes. I had heard of the water management group, but not the Green Streets. I'll go check it out!

Thank you, John, for the mushroom idea. I had no idea one could do that!

S Bengi - thank you so for the in depth 'what trees work' information. Do you know, by any chance, if legume trees act like fruit trees or like nut trees in terms of passing on pollutants? We have a lot of native legume trees (like the mesquite) that have edible legumes which I would love to harvest at last a little of. It would be very lovely if I could grow a few of them in the swales and still be able to eat them.

I did quite a few search and the native legumes like most legumes behave like nuts with alot of mineral.
It is a source of calcium, magnesium, potassium, iron, and zinc and thus also heavy metals if they are present in the soil.
http://www.foodreference.com/html/artmesquite.html

Maybe you can send a sample of the beans into the lab to see the heavy metal content.
That will set you back about $100 though

I don't know about pollutants but generally, the more active your soil is the more it can neutralize pollutants. I would maybe not put the water on the veggies but on the trees.
Actually we do have such a thing but it is very low tech and if you life in an urban area you would have to upgrade. It is simply a hole at the road side and we dug in a tube which goes into an open trench. It can be a lot of water so we have a piece of tube ready to stick vertically on the other tube if too much rain is coming , but that might not be your problem.

Oh I like that idea, Angelika - we're not in the city proper so we can mess about a bit more, thankfully. I'm trying to visualize what you describe - I'm visualizing a tube that's put in diagonally - vertically, I mean - and then maybe diagonally when compared to the road, horizontally, as well? Is that how it would be? I am not sure what you mean by another tube put on vertically, though, or how it would help, so I'm thinking maybe I'm visualizing it wrong. :-/

Oooh, thanks, Jennifer - that was quite useful. We don't have any curbs out here, but I saw the rocks embedded down low so that their tops were level with the street in a couple of the flat areas catching water - that's exactly what I needed!

Do you know if anyone has a list of what trees and shrubs Brand Lancaster used on his street when they did this? I know he put in mostly edible or medicinal plants, and was thinking that would be a great list to look at. I may simply contact the group and see if I could find out, but if there was a known list somewhere, that would be great.

I'm still feeling so energetic about this - hoping it lasts through the hard parts!

Shauna

It's pretty exciting stuff. There are plant lists online at Brad's site: http://www.harvestingrainwater.com/tucson-az-plant-lists/

I also cannot recommend hosting a co-op event at your house highly enough. It's amazing to see the transformation that takes place in just one day thanks to a bunch of enthusiastic volunteers under the guidance of a knowledgeable project coordinator. Several folks here in Phoenix (myself included), have an approved master plan for our homesite that is being implemented in stages as money allows (for materials and things like getting the plumbing for greywater systems to the exterior of the house). With the master plan in hand, your water harvesting capacity is maximized an various types of water are used for the appropriate purpose. Saves a lot on redoing stuff too!

I have wondered the same kinds of things.  Seems like Geoff Lawton or someone mentions it as being treated by swales etc.  

Thanks to those who have posted info above, good to know.  Makes sense different parts of the plants would be different.  Also the fungi stuff is fascinating......

Does anyone have links to references about this kind of stuff?