The first step when you realize your lawn has chemicals and heavy metals in it is not to panic. Most people get land that is contaminated in some way, unless you clear cut the woods to build your house, which you shouldn't have done. I believe that we will need to learn how to grow food on imperfect soil, so I kind of welcome this challenge as a learning experience. One of Adam's acquaintances is a soil remediation expert, so after talking to him and doing some research of our own, here is what we've learned about nursing chemical-ridden land back to life.
Do a soil test
Know what's in your soil and in what quantities. Uconn tests for lead only, and Umass tests for lead, other metals, and optional add-ons. These tests cost money, $12 and $60 respectively. I sampled both front and back yards separately, which was useful, because they have different metal levels. Lead was low, and arsenic was 5mg in back and 15mg in front. I suspected this was due to more concentrated pesticide use in front.
As to safe arsenic levels, scientists are thoroughly in disagreement. Every state in the US has safe limits, and they range from 2mg to 40mg. Once I found that out, I threw my hands up and decided we were ok.
The soil expert said that the Umass test might be slightly inaccurate, but an accurate result could make you legally responsible for remediating the soil, which is expensive. So Uconn and Umass are great ways to generally know what's in your soil.
Raised beds are key
The soil expert was much more concerned about lead and arsenic in the soil than the historical use of Grub Ex and pesticides. He said that those substances didn't affect adult humans as much (So you can finally use that Grub Ex slip'n'slide) but arsenic and lead are dangerous. He said raised beds only 10 inches high are a safe level away from the soil. He even grows potatoes in his raised beds.
The conclusion I would make from that is that it's ok to have children dig around in raised beds, but probably not in the soil if you know it's particularly contaminated. Or at least have them wash their hands when they come in from playing. Hey, you should wash your hands too.
Choose your food crops
Lead and metals concentrate mainly in root crops, somewhat in leaf crops, and less so in fruits. So if you are concerned, grow something like tomatoes or peppers. Acidic soil makes metals more bioavailable for plants to absorb. However, if you're using a raised bed, this shouldn't be much of an issue.
Avoid old house foundations
Grow food at least three feet from old house foundations. There could be lead chips from paint there. He told a story about a person who power washed their old house and lead chips bounced into the neighbor's yard, poisoning their child. Which is not to freak you out, but just something to think about.
And molecules of heavy metals persist in the environment. Even if we rototill to loosen the soil, the lead and arsenic will bounce out, maybe onto the sidewalk, and will likely find their way back into our soil. It is simply a fact of the world we've all inherited.
Compaction is possible from years of tractors and people walking over it. Ours is extremely solid. If you want to keep your lawn, you can rent an aerator, which alleviates this. If you want to plant gardens, you can rototill or manually turn over the soil.
Most organic gardening experts oppose tillage of any kind; It fragments earthworm tunnels, destroys the structure of the soil, releases carbon into the atmosphere, and churns the living topsoil into the subsoil, where it dies.
Guess what? Chemical lawn treatments kill all of this life anyway, so your microbes are dead, and your soil structure is likely garbage as a result. So relieve that compaction by tilling before you start your organic garden. You'll create such a wonderful environment that microbes and worms will move back in.
Add organic matter
A chemical lawn is an IV drip for the grass. The soil is totally ignored, even though it is the most important element in growing healthy plants. Soil must be fed. Season after season of pushing grass up with no food will leave soil starved. You'll need to feed the soil with grass clippings, compost, chopped leaves, or aged manure. Our organic matter of choice was a humongous pile of wood chips, which we intend to compost and add to the soil. We chose this because we want to make wood chip paths through the yard as well, and we also want the entire neighborhood to know that we're maniacs.
Ok, so there are some tips if you are worried about what you or someone else has done to you soil by using Scotts 4 Step, or Weed n' Feed, or a lawn service that is not organic. And if you live in a city or suburb, industry or pollutants could have made their way into your soil. Take that soil test to determine what they are and take the above precautions.