updated 8/6/2008
Yes. Current landfill regulations limit the amount of leakage but do not prohibit leaks.

Landfill liners are made of soil separated by a sheet of High Density Polyethylene (HDPE), delivered in large rolls and heat welded in the field. HDPE is available thicknesses ranging from 40 mil to 120 mil. The DEC minimum standard is 60 mil. Part 360-2.13(k)(2)(i).

The DEC 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).

Leakage through the plastic liner is inevitable for a number of reasons:

"First, even the best liner and leachate collection systems will ultimately fail due to natural deterioration, and recent improvements in MSWLF [municipal solid waste landfill] containment technologies suggest that releases [of leachate] may be delayed by decades at some landfills." (Id., at p. 33345).

Second, human error may also contribute to leachate "releases due to design or operating errors (e.g., tearing of liners or disposing of wastes that are incompatible with the liner) and routine deterioration of liner." (Id., at p. 33344).

Industry argued during the development of the regulations that liners could contain landfill leachate forever. EPA disagreed:

“A liner is a barrier technology that prevents or greatly restricts migration of liquids into the ground. No liner, however, can keep all liquids out of the ground for all time. Eventually liners will either degrade, tear, or crack and will allow liquids to migrate out of the unit. Some have argued that liners are devices that provide a perpetual seal against any migration from a waste management unit. EPA has concluded that the more reasonable assumption, based on what is known about the pressures placed on liners over time, is that any liner will begin to leak eventually.”  47 Fed.Reg. (July 26, 1982), at pp. 32284-32285. See also  46 FR 11126, 11128 (1981); 53 FR 33314, 33344-33345 (1988).

Not only are landfill leaks inevitable, but dangerous chemicals present in modern consumer products make the toxicity of leachate produced by a solid waste landfill comparable to the leachate produced by a hazardous waste dump. According to EPA, "the concerns relating to failure of containment structures are the same for any landfill regardless of waste type." 53 FR at p. 33334.

This is not just a theoretical prediction.  In 1990 Virginia decided to invite commercial landfills into the state to enhance state revenues. In 1997, two of their seven new "state-of-the-art" dumps were found to have sprung leaks, according to The Washington Post: "In Amelia County, groundwater tests last year found elevated levels of lead, chromium and other substances, while another contaminant, antimony, showed up in groundwater near the Charles City landfill." Eric Lipton, "As Imported Garbage Piles Up, So Do Worries" (Wash. Post, 11/12/98).

In DuPage County, Illinois, the county government set aside $80 million to pay for post closure monitoring of a 2.2 million cubic yard municipal landfill, average in size by modern standards. Still, the landfill had to be declared a federal Superfund site to get the financing that ultimately was necessary to clean up hazardous leaks from the dump.

More resources:
Enviroweb on landfill leaks

Recycling Advocates on landfill leaks

landfill leachate 1

landfill leachate 2

landfill leachate 3

USGS, "Do Landfills Leak? -- The Norman Landfill Environmental Research Site What Happens to the Waste in Landfills? (2003)

NYSDEC photos & explanation of a
"state-of-the-art" landfill liner & components

Technical reports from NYSERDA:
"Leachate Characterization and Landfill Management Implications"
"Constructed Wetlands for MSW Landfill Leachate Treatment"

CCCC's Home Page

The Farmersville dump proposal . . .