- Q.My excavation contractor
offered to bury my scrap drywall on site, but I've
heard buried gypsum can create a harmful gas. I've also
read that it's okay to bury small amounts if you
disperse it. Is it okay to bury drywall on site at all,
and if so, what's the proper way to do it?
A.Alex Wilson, editor
of Environmental Building News in
Brattleboro, Vt., responds: You're right that
it's not a good idea to simply bury scrap drywall
in a hole. Under oxygen-depleted conditions, such
as in a landfill or several feet underground in a
covered hole, the gypsum (calcium sulfate) in
drywall can decompose to release the noxious gas
hydrogen sulfide. This gas is hazardous at high
concentrations and an odor problem even at very low
levels. Problems have sometimes arisen when
builders have buried the scrap drywall from a
house. The rotten egg smell is not at all popular
with homeowners.
However, scrap drywall can safely be used as a
soil amendment in the oxygen-rich, active top few
inches of soil if it is properly pulverized and
applied. Drywall is composed of paper facings and
gypsum. Gypsum is often used as a fertilizer,
adding both calcium and sulfur. Along with the
benefits of the gypsum, the unbleached paper adds
tilth to soil. The following recommendations should
help you avoid problems and use drywall scrap
properly as a soil amendment:
- Only new (unpainted) drywall scrap should
be used as a soil amendment.
- The drywall should be pulverized to allow
rapid disintegration; no pieces should be
larger than 1/2 inch in diameter. Some builders
have used a brush chipper successfully to
pulverize the drywall (wear a dust mask!).
- Pulverized drywall can be spread on the
soil surface or tilled into the top layer of
soil (no more than a few inches deep).
- The pulverized drywall should be spread
evenly over the entire lot or area being
seeded.
- Pulverized gypsum may be added at rates of
up to 1 pound per square foot (22 tons per
acre), though spreading it much more thinly is
generally recommended. Gypsum's effect on soil
quality varies depending on the type of soil,
so it's best to ask your county agricultural
extension agent for guidance on how much added
gypsum is appropriate for your local soil.
- Pulverized drywall should be applied to
soil only in areas with adequate drainage and
aeration (no standing water or anaerobic
conditions).
- Finally, you should find out if there are
specific regulations in your area that address
the disposal of drywall scrap in this manner,
or if any permit is required for this
practice.
For more on the use of drywall scrap as a soil
amendment, visit the Gypsum Association website:
http://www.gypsum.org/topical.html.