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RE: need advice on site with high lead

  • Subject: RE: [cg] need advice on site with high lead
  • From: "Jack Hale" jackh@knoxparks.org
  • Date: Mon, 9 May 2005 17:16:48 -0400

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: community_garden-admin@mallorn.com
[mailto:community_garden-admin@mallorn.com]On Behalf Of Grow19@aol.com
Sent: Monday, May 09, 2005 3:56 PM
To: community_garden@mallorn.com
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


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______________________________________________________
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:  community_garden@mallorn.com

To subscribe, unsubscribe or change your subscription:  https://secure.mallorn.com/mailman/listinfo/community_garden





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