Development of Acceptable Sulfide Concentrations in Waste, 1998 Environmental Conference Proceedings

Ishrat S. Chaudhuri & Michael Mills

ENSR Consulting and Engineering

EPA’s designation of sulfide-bearing wastes as “reactive” wastes has major implications for the pulp and paper industry with regards to disposal of such wastes. If sulfide levels are found to exceed EPA’s reactivity criteria, then these wastes need to be disposed of in hazardous waste landfills. Depending on the volume of sulfide-bearing wastes, disposal costs in hazardous waste landfills may be very high. Because of the significant cost implications of EPA’s policy, we critically evaluated the model used by EPA to develop an acceptable concentration of 500 mg H2S/kg soil, as measured by EPA’s test protocol for releasable sulfide. EPA developed an accidental release model that assumes that sulfide-bearing wastes are dumped into an acid-containing pit. The model assumes that the sulfide-bearing wastes release hydrogen sulfide, which is inhaled by a person standing at the edge of the pit. Using a very low acute toxicity threshold for H2S, EPA developed an acceptable concentration of 500 mg H2S/kg soil. Our review indicated that there are many overly conservative assumptions in EPA’s model. We developed an alternative concentration of 3850 mg H2S/kg soil by assuming that the soil is dumped in a conical pile in a landfill, and using a more realistic acute toxicity threshold for H2S. Our results indicate that EPA’s modeled concentration of 500 mg H2S/kg soil is too stringent and could result in overly expensive disposal costs. The alternative concentration of 3850 mg H2S/kg soil would reduce disposal costs, while providing adequate protection of human health.