5    REMEDIATION OF GMC-CENTRAL FOUNDRY
DIVISION-DEFIANCE FOUNDRY HAZARDOUS
WASTE SETTLING BASIN
Ajit K. Chowdhury, Senior Chemical Engineer
Richard C. Krueger, Project Engineer
Michael A. Warner, Project Engineer
RMT, Inc.
Madison, Wisconsin 53708
Thomas R. Wirth, Senior Environmental Engineer
General Motors Corporation
Central Foundry Division
Defiance, Ohio 43512
INTRODUCTION
General Motors Corporation —Central Foundry Division —Defiance (CFD —Defiance) operates a
ferrous foundry in Defiance, Ohio. Particulate emissions from the cupola operations are collected by
wet cap and venturi scrubber emission control systems. The wastewater from the emission control
systems is conveyed to a settling basin, and the effluent is reused in the plant. The accumulated sludge
in the settling basin has been periodically removed by hydraulic dredging, and disposed in an on-site,
state-approved, solid waste landfill.
In the process of complying with NPDES regulations and Federal Metal Molding and Casting
Effluent Guidelines, several sludge samples from different parts of the basin were collected and
analyzed. Slightly more than half of these samples released lead in the EP Toxicity test above the
hazardous waste criterion of 5.0 mg/L.
CFD —Defiance notified the United States Environmental Protection Agency (USEPA) and the
Ohio Environmental Protection Agency (OEPA) that the basin contained EP-Toxic sludge. As a
result, CFD —Defiance and the OEPA negotiated a consent order for management of the sludge.
To prevent generation of new hazardous sludge, an in-line wastewater treatment system was
installed upstream from the basin to treat the incoming solids. For remediation of the hazardous
solids in the basin, a continuous treatment process using a hydraulic dredging system with in-line
addition of phosphoric acid was developed by RMT, Inc and implemented by CFD —Defiance. The
EP-Toxic sludge in the basin (approximately 400,000 cubic yards) was remediated with this system
(slurried and treated) to render the sludge nonhazardous, according to an OEPA-approved "Closure
Plan" for achieving RCRA clean closure. The basin remained in use during the remediation process.
BENCH-SCALE TREATABILITY TESTING
Several composite samples of the basin sludge, with initial EP-Toxicity lead concentration varying
from 8 to 38.5 mg/L, were treated with different chemical additives to evaluate various treatment
possibilities for rendering the sludge non-EP-Toxic. The bench-scale treatability tests were designed to
test the following variables:
• Concentration of solids in test slurry.
• Type and dosage of chemical additive.
• Final treated slurry pH.
• Additives for control of final slurry pH.
Treatment additives evaluated during initial screening included:
• Phosphates (three forms)
• Magnesium hydroxide (two grades)
45th Purdue Industrial Waste Conference Proceedings, © 1991 Lewis Publishers, Inc., Chelsea, Michigan 48118.
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