Townsend, Timothy, September 2007, #50890-05 (942 Kb).

This research report presents the results of several studies related to the advancement of construction and demolition (C&D) debris management practices. Several topics are covered, including the control of odors from C&D debris landfill gases, the recycling of engineered wood products for landscape mulch, and the recycling of concrete.

In C&D debris landfills, hydrogen sulfide (H2S) production from gypsum drywall is a major concern. The present study evaluated the attenuation of H2S at C&D debris landfills using alternative cover materials. The results showed that the alternative cover materials tested (compost,
fine concrete, lime-amended sandy soil) could attenuate H2S emissions more effectively than sandy soils. The variation in H2S emissions over time from a particular spot at a field site was studied along with a complementary lab experiment (to evaluate factors impacting the variation). H2S emission rates measured in the field ranged from zero to 1.24×10-5 mg m-2 s-1, with an average of 4.67×10-6 mg m-2 s-1. The emission rates of H2S were lower during the morning and higher in the afternoon. Results from the laboratory experiments found that soil moisture played an important role in H2S emissions. In another study, H2S migration in landfill systems was mathematically simulated using a migration model. A laboratory column experiment was conducted to compare the experimental data with model simulation results and to estimate the H2S adsorption coefficients of different cover materials.

The risks posed by engineered wood products from their use as landscape mulch was evaluated. Engineered wood products, such as plywood and oriented strand board (OSB), contain adhesive chemicals. When discarded, these wood products sometimes are ground with other wood wastes to produce landscape mulch. Synthetic precipitation leaching procedure (SPLP) results found formaldehyde and phenol concentrations in the leachates from the plywood and OSB exceeded their respective groundwater cleanup target level (GWCTL). Using the SPLP concentrations as a bench mark and extrapolating the results, it was found that a plywood fraction of greater than 7% in C&D wood could possibly result in an exceedance of the GWCTL for phenol, and a fraction greater than 24% could possibly result in an exceedance of the GWCTL for both phenol and formaldehyde. Additional investigation is warranted to determine whether size-reduced engineered wood products
pose an environmental risk when land applied following current practices.

Research was performed to determine how much concrete is generated and recycled in Florida and whether recycling could be expanded. It was found that large quantities of concrete are recycled by non-permitted "clean debris" recycling facilities and the markets look promising for increases in recycled concrete aggregate production, especially as the FDOT investigates increasing their use of the material in their projects.

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