Nothing wrong with using slanted boards, and it may be the best approach if this is temporary. The other way would be to dig out the high side and put the soil on the low side to make a level area for the box. One advantage of that in her situation would be that the contaminated soil will be at an equal (and hopefully safe) depth throughout the bed, whereas if you level it by trimming the boards, the raised bed is deeper on one side than the other. But if it's only an inch or two it won't make that much difference.

I would think 10-12" will cover *most* of the root zone of *most* garden plants. I'm sure some go deeper, but 6" would definitely not be enough, in my opinion. I think that's a good middle ground.

I work with contaminated soil for a living, so I'm naturally curious where the lead came from and whether she knows how much is there. I would be interested in more details.

Thanks, toxcrusadr.

I thought about digging down and burying, but my concern about burying the wood is that it would just cause it to rot faster.

I should have added that I did suggest "cut and fill" as an option anyway, even if there was no actual barrier with the native soil on the "cut" end, since it would even out the levels...and lead isn't exactly mobile in the soil, right? I also suggested the option of minding what she plants on each end of the bed, and she was also amenable to that.

She had soil tests done last year, but realizes now that she wasn't as careful as she might have been about doing it in zones, so the info she has about different parts of the yard isn't quite as granular as she now wishes.

I can certainly guess the source of the lead. This is the city (not heavy-duty city, she's in a residential area with single-family homes, but city nonetheless), and I think she said her neighborhood was built about 70 years ago. Her neighborhood is quiet enough that I wouldn't guess that exhaust from leaded gas is too much of the source. Probably it's all about tightly packed old houses (and garages, and sheds) and peeling lead paint. It's a common problem around here.

She got enough granularity in last year's soil test that she knows that the bed immediately next to the house is particularly bad, so she's abandoning that for all but ornamentals. She's got other areas designated as "OK for fruiting things, not for roots crops," etc. She's hoping to be able to grow anything she wants, though.

She's got a toddler in the house, so she's trying to be extra-careful about leaded soil. In addition to the other values of the raised beds, they will also provide a barrier between the yard and a drop-off -- the edge of their yard ends in a tall retaining wall, and the neighbor's yard is much lower than theirs. I think the beds will be an excellent choice all around, considering.

Interesting! It is pretty common to see elevated lead in older areas of cities, especially next to the house where the lead paint erodes off the walls. Most places have a background level of lead in the low parts per million (it's below 10 in some parts of Missouri, but higher in the 'lead belt' where mining is actually still going on). It has to get over a couple hundred before it's considered much of a risk, so 'above background' does not necessarily mean it's a health risk. EPA considers 400 safe for home yards. MO has it set at 260.

Covering the worst areas with raised beds is a great idea.

The small, ex-mining town up the road finally finished up with the EPA hauling off and replacing their yard soil - if the owners wanted to.

At the link is the kind of concentration they had.

I garden on a slope with raised beds, and just follow the slope down the hill, lengthwise. Works rather well for watering them.

Here is a link that might be useful: thats when they dig it up and haul it off

Looks like you had a dose there david! They are doing the same thing in SW Missouri around Joplin. The entire county is a Superfund site. I think they've done 1800 yards and counting. All you can do is pile it up somewhere and cover it.