Hey Judy- I'm no chemist, but I've done a fair amount of looking into soil lead. In general, I think the main hazard from soil lead is dust, either in the air or on produce or hands that get into people's mouths. The main strategies for reducing airborne dust are dilution or encapsulation. If, for instance, you assume that the 500ppm EPA residential limit on soil lead is a reasonable target, then diluting, say, the top six inches of soil with enough additional soil and compost to bring the level within bounds is one way to do it. In your case, adding 8 inches of material and tilling it in would do that job. Also, note that just because your average lead level for the garden is 1146ppm doesn't mean that's the level everywhere. On a former building lot, you will tend to see very high levels around the perimeter of the building(s) and lower levels elsewhere. Encapsulation means you put something between the contaminated soil and your crops, hands, and lungs. Mulched or grassed pathways handle part of that problem. Raised beds handle the rest. Somebody has a list of crops that tend to take up lead. If you are going to plant them, your beds should be deep, like the 1-foot beds your neighbors use. Relying on physical barriers may be chancy, unless you use concrete. Phytoremediation seems to work, although it is hard to get seed for the most effective plants. They will clean the top six inches of soil pretty well in a season or two. The drawback is that they don't go much deeper than that. They are good for reducing risk of airborne dust, but not the risk of contact with crops or hands. Lawn grass is apparently a pretty good way to reduce surface dust, particularly if you collect and dispose of clippings from mowing. Just growing the grass reduces dustiness, and the plants take up some lead. Other than that, people should know that detergent really works to remove lead and other nastiness from produce. They even sell some special produce detergent in supermarkets. As long as the problem is surface contamination of produce, washing is important. All that being said, a case can be made that the only appropriate treatment for lead contamination is removal and replacement of soil. To do that effectively, you need to know where the lead is. Unfortunately, just because you know there is lead in the top six inches of soil doesn't mean that's the only place it is. There is a great piece of equipment called an XRF - ground penetrating x-ray - that will measure lead levels as you go, and some health departments have them. It's probably not an appropriate investment for your local community garden group. Removal and replacement can be very expensive and difficult, and the "soil" you get back may not be as good as what you started with. Nonetheless, removal is the only way to know for sure that the lead threat is gone. Here in Hartford, we test soil for lead before we commit to starting a new garden, and we try to avoid sites with high levels. Regardless of the test outcomes, we try to tell people to assume there is some lead in their soil and to act accordingly. Good luck. JH
Jack N. Hale Executive Director Knox Parks Foundation 75 Laurel Street Hartford, CT 06106 860/951-7694 f860/951-7244 -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of [EMAIL PROTECTED] Sent: Monday, May 09, 2005 3:56 PM To: [EMAIL PROTECTED] Subject: [cg] need advice on site with high lead Hi, I'm organizing a vacant lot community garden in Washington DC (size 60'x70'). Unfortunately, the soil test results came back from UMass with the following lead levels: extracted lead=151ppm, estimated total lead=1146 ppm. We need advice on how to approach gardening in this lot. A couple of garden in the area with high lead (don't know how high) chose to create raised beds, about 1" deep and use new soil. They didn't seal off the bottom. And I don't think they've tested their food. I don't have enough technical knowledge to know if this is a safe approach. Whole thing is making me plenty nervous. We would like to use phyto-remediation to make it possible to safely grow food in the lot before resorting to sealed raised beds. I would welcome all of your advice and ask if there are research scientists in the Washington DC metro area that we could contact directly for additional help. Sincerely, Judy Tiger FYI, here is the remaining info from soil test results: - soil pH 7.6 - buffer pH 7.4 - nitrogen N03-N=4ppm - nitrogen NH4-N=1ppm - organic matter: 6.6% (desirable range 4-10%) - phosphorus - 11 ppm - potassium - 151 ppm - calcium - 5689 ppm - magnesium - 117 ppm - cation exchange capacity 30.6 meg/100g - percent base saturation K=1.3, Mg=3.2, Ca=95.6 - micronutrient levels all normal - extractable aluminum 27 ppm ______________________________________________________ The American Community Gardening Association listserve is only one of ACGA's services to community gardeners. To learn more about the ACGA and to find out how to join, please go to http://www.communitygarden.org To post an e-mail to the list: [EMAIL PROTECTED] To subscribe, unsubscribe or change your subscription: https://secure.mallorn.com/mailman/listinfo/community_garden ______________________________________________________ The American Community Gardening Association listserve is only one of ACGA's services to community gardeners. To learn more about the ACGA and to find out how to join, please go to http://www.communitygarden.org To post an e-mail to the list: [EMAIL PROTECTED] To subscribe, unsubscribe or change your subscription: https://secure.mallorn.com/mailman/listinfo/community_garden
