In 1980, the U.S. Environmental Protection Agency (EPA) dtermined that "mercury can migrate from municipal solid waste landfills in harmful concentrations and reach human drinking water sources located over a mile from the landfill in significant concentrations, i.e., concentrations exceeding allowable mercury in drinking water. 

Actual site data from recent and on-going studies support the Agency’s conclusion that mercury is present in significant concentrations in both leachate and groundwater at non-hazardous waste landfill sites, including municipal solid waste landfills, and has migrated off-site to drinking water sources (in some instances in concentrations exceeding Federal drinking water standards). This conclusion is sufficient to warrant continued regulation of spent lamps containing mercury as hazardous waste."

EPA developed the Toxic Characteristic Leaching Procedure to determine the toxicity of waste.  TCLP is designed to simulate the leaching a waste will undergo if disposed in a sanitary landfill.  This test includes mercury. lead, cadmium, and other hazardous materials.  Passing this test for mercury, for instance, requires a yield of less than 0.2 milligrams per liter upon completion of the test.

TCLP Testing of Spent Lamps