Do Landfills Leak?

Yes. Current landfill regulations limit the amount of leakage but do not prohibit leaks.

The DEP began requiring liners and leachate collection systems for landfills after December 1988, to meet minimum protections mandated by the EPA.

The regulations mandating a certain kind of "containment structure" for landfills are most relevant to this question. The regulations assume landfills will "contain" (that is, hold back) waste.

But landfills have proved ineffective in holding back all leachate, the toxic liquid produced by decomposing waste. This liquid often contains high levels of organics (suhc as methylene chloride, dichloroethylene, toluene, phenols, and benzene) and inorganic pollutants including ammonia, heavy metals and endocrine disrupting chemicals, resistent to ordinary wastewater treatment. Pre-treatment is frequently necessary before discharging leachate to a sewer or wastewater treatment plant.

EPA acknowledged this in its original notice to the public regarding these regulations. 53 Federal Register  33314-33422 (Aug. 30, 1988). There the "bathtub" or containment design was first mandated. This design requires a plastic liner bottom upon which are installed pipes to collect leachate, covered with earth. The plastic and earth layers on the bottom are "the double liner system," and the piping is "the leachate collection system." In addition, an earthen "cap" is supposed to keep the rain out, reducing the volume of leachate produced by a landfill.

However, waste still breaks down in a landfill designed this way, producing toxic leachate that gets into groundwater beneath the landfill. According to EPA, "Experience has shown that leachate generation in landfills continues long after closure.  ...Particularly for landfills designed with advanced containment systems (e.g., liners, leachate collection systems, or synthetic final caps) groundwater contamination may be delayed by many years." (Id., at p. 33344).