I'm not Geoff, but I do have some thoughts/ideas on this. I am an environmental toxicologist/environmental health scientist as well as a permaculturist, and I live in the Inland Northwest, where lead and other heavy metal contamination can be a huge problem.
Basically, there are three main issues here that I think about; growing food, preventing exposure from other sources like air and
water, and regenerating the soil/healing the earth.
1. Growing food: I would recommend growing your food in containers, with soil you make from non-contaminated sources, especially if you are feeding kids. You can grow just about anything in containers, including fruit and some nut trees, and you can make some really nice polycultures in containers. (I do my gardening in containers on the porches of my house because I have a wildlife-rich site and it is the only way I can get to eat what I grow.) There are some good videos on Youtube for making self-watering containers, which are a very efficient use of water. If you have a problem with blowing dust that is contaminated with lead, I would recommend putting your container garden in a poly tunnel or
greenhouse to protect it.
2. Preventing exposure from air and water: Blowing contaminated dust is a big problem in some parts of the west. If that is a problem for you, as I mentioned above, I would keep my food plants in a poly tunnel so they don't collect a lot of dust ( and wash them well before eating them). I would also plant windbreaks and put up wind barriers, making sure to design them so they didn't cause dirt to be deposited where I didn't want it, like in my yard. I would also make sure that I didn't have any bare ground that could turn to dust. Depending on the source of your contamination, I would also check the lead levels in my water supply (particularly important if you have kids). And, of
course. houses with old plumbing can have lead in the water from old lead solder. I remember when I was a small child our plumber giving me a lump of lead to play with when he was soldering pipes. I think I still have it somewhere.
3. Regenerating the soil and healing the earth: Lead in the soil doesn't break down, so our choices are to try to remove it, or to sequester it so it can't move around and cause trouble. Removing it usually involves fairly heroic measures like bulldozing the contaminated soil up and trucking it away and putting it in a special landfill somewhere and then bringing in new uncontaminated topsoil. Some plants and fungi are dynamic accumulators of lead and other heavy metals but the process of using them to remove/reduce the lead in soils is relatively slow, and you have to dispose of them offsite, which means you are mining
carbon and other things from your soil as well as lead. However, lead will form stable complexes with soil organic matter, and I think that most of the time that is the best way to deal with it. ( It is worth remembering that lead can be released from being bound in the soil if the pH changes, like when you get a really acid rain.)
If I had a plot of
land that was contaminated with lead, I would start by laying down a layer of
biochar. This would help to keep the lead from migrating into upper soil levels as you build soils, and it also can provide habitat for soil life, which may need to be jumpstarted in contaminated soils. I would put down layers of organic matter in an optimum C-N ratio for composting ( I'd try to include some animal manures, as they are rich in soil-building microbes), making sure that the materials were from uncontaminated sources (test if there is any doubt), and I would put in at least one other layer of biochar as I went along. (Or you could make
compost and spread it rather than composting in place, or a combination of the two.)
I would plant with cover crops and green manures that can be slashed (not tilled in), and I would look for ones that are relatively shallow-rooted because you want to try to avoid bringing up lead from the subsoil. Grasses are excellent soil builders, and will prune their
roots in proportion to the size of their tops, so this is one place where close mowing of grass could be helpful. I would water my my soil-building plants with compost tea for additional microbial power.
If I wanted to plant some larger things like shrubs or trees to make a
perennial system that will build the soil, I would do it in a hugelkultur, the bigger the better. Sooner or later things are going to get their roots down into the contaminated subsoil, but by the time they do you
should have a good layer of topsoil to work with that is very rich in organic matter to bind any lead you do get into it. I would periodically test for lead in the leaves that are falling from the trees, and in the new topsoil you have built. A good lab should be able to tell you not only how much lead you have but also what form it is in and how stable that form is. Over time, by building the soil, you should be able to dilute the lead in the soil and to bind it with organic matter so it isn't a problem. (As they used to say, "Dilution is the solution to pollution".)
I hope this is somewhat helpful.
Good luck
Mossrose
Idaho
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