Iron In Groundwater around Landfills In Florida

High iron concentrations have been observed in groundwater around municipal solid waste and construction and demolition debris landfills in Florida. This study was conducted to examine the source of the iron. Specifically whether iron detected in groundwater is the result of a direct release from landfill or whether naturally occurring iron in the soil around the landfill has become mobilized in the groundwater due to landfill induced reducing conditions. Groundwater and leachate samples were analyzed for iron and geochemical parameters (pH, redox, dissolved oxygen, turbidity, ammonia, nitrate, chloride, sulfate, sulfide, carbonate, and metals etc.) from four landfills located in central and north Florida. Statistical correlation between iron and other parameters were conducted. The major solute compositions for groundwater were compared to those in the leachate using Stiff Pattern plots. Groundwater iron concentrations varied with local geology and landfill age. Iron concentrations were generally higher in groundwater down gradient of the landfill as opposed to up gradient locations. Groundwater iron concentrations showed positive correlation with reduction indicators (such as the detection of ammonia, lower redox, and neutral pH) or turbidity; but had a negative correlation with nitrate concentrations. Groundwater samples with high iron concentrations also contained relatively higher concentrations of trace metals including arsenic, barium, and zinc. Calculated iron level from the leachate did not account for the calculated iron level in the groundwater indicating that dissolved iron in groundwater is dominantly mobilized from the soil due to induced reducing conditions. The results suggest that the reduction dissolution of iron precipitates releases the bound trace metals into the solution.