THE NATURAL END OF LANDFILL LEACHATE: EXAMPLES FROM MAINE

Groundwater contamination from landfill leachate is commonly assumed to be a perennial problem. This is not necessarily so, as examples from Maine demonstrate.

Leachate composition is controlled by: 1) dissolution of soluble materials, 2) decomposition of organic materials, and 3) associated chemical interactions. For instance: 1) Salt is a common soluble material in landfilled waste. Chloride is often a primary constituent in leachate. 2) Decomposition of organic wastes uses up oxygen. This has several consequences including: dissolution of iron and manganese; genesis of methane and other landfill gases; reduced effectiveness of aerobic biodegradation of petroleum hydrocarbons; and allowing the (slow) anaerobic biodegradation of chlorinated solvents. 3) pH is generally high in landfill leachate, which limits metal mobility.

All landfills produce leachate, but only until soluble salts and decomposition are reduced to insignificant levels in the waste mass. Water quality of groundwater downgradient of several old burning dumps and closed landfills in Maine was analyzed to investigate the long-term fate of leachate. These investigations showed that: µ Burning dumps leave an archaeological record of a thin ash layer, bearing non-combustibles such as cans and bottles. µ The archaeological record of unburned, unlined landfills contains more plastic, but is otherwise similar. µ Leachate is no longer detected in groundwater downgradient of the burning dumps and unlined landfills with the exception that… µ Volatile organics, if present in the original waste, may be persistent.