Besides the high disposal costs associated with landfill dumping – ranging from $70 to over $200 per ton – landfills pose a number of significant environmental concerns: Landfills are the second largest human-created source of methane emissions (a greenhouse gas) in the United States and account for 23% of all methane sources. Depending on the type of polymer, plastic waste can take over 1,000 years to decompose, potentially leaching harmful pollutants into the soil and water during that time. Many communities have strong feelings about the placement of landfills near residential areas. This not-in-my-backyard ("NIMBY") effect limits the number of landfills created.               Over the past 20 years, the number of active landfills in the United States has declined by nearly 80%. In 1978 there were approximately 20,000 landfills active and operating. Today there are fewer than 1,800.