Old Dumps and ATVs, In Our Back Yard

(Via Stef at the DEP...)

Spring and warm weather is here, and many of you will be hopping onto an All Terrain Vehicle (ATV) to enjoy the outside and maybe “boldly go where you’ve never gone before”. Remember to obtain landowner permission before straying from established and marked trails, and be on the lookout for small, lush, green hills that look a little too perfect, a little too symmetrical than what you are used to seeing. There is a good chance that a hill like this is an old dump with a protective covering on top of it, and the wheels of your ATV - even if you don’t mean to - can do a lot of damage to this hill and unleash buried pollutants.

Here is why the hill is there in the first place, and how the wheels of an ATV can damage it.

One big problem with old dumps is rain falling on them. The rain falls on top of the old dump, seeps down through the soil and old garbage and washes the nasty chemicals and other pollutants from the garbage into the ground and surface water. This process is called “leaching”, and old dumps are “capped” to minimize this problem.

The dump (or landfill) is typically covered with a “cap” to keep as much rainwater and melting snow as possible from reaching the old garbage. This cap usually consists of a thick layer of soil (clay) that has a “low permeability” (does not let much water get through). Sometimes the cap included a “geosynthetic (flexible plastic) membrane” over the clay, which was then covered by a layer of gravel, and then a layer of soil planted with grass seed. The geosynthetic membrane is impermeable (rain water does not go through it), while the gravel directs water away from the impermeable geosynthetic membrane and toward the outer edges of the “cap”. The soil and grass, the top layer, evaporate water back into the atmosphere and keeps the gravel layer in place, which - in turn - keeps the geosynthetic membrane in place.

A capped dump or landfill with a healthy covering of long grass in the spring and summer may look durable, but looks can be deceiving. The cap is actually quite fragile and the tires of ATVs and dirt bikes can easily do a number on it and damage it. The layer of topsoil and grass seed is typically only 6 inches thick. A spinning tire from a stuck ATV can go through this thin layer in no time, especially after a rain. Also, repeated travel on the same trail destroys the protective grass. Once the protective layer of soil and grass is gone, the gravel layer is quickly washed away by erosion, which then exposes the fragile clay layer or geosynthetic membrane. The geosynthetic membrane is no match for a rainstorm and is quickly dislodged, allowing rain into the old dump and leaching of the old pollutants to occur.

So avoid those hills that are often right next to the transfer station and keep pollutants out of our back yard and under a “cap”, which is where they belong.

This column was submitted by Peter Moulton, an Environmental Engineer with the Maine Department of Environmental Protection’s (DEP) Bureau of Remediation and Waste Management. In Our Back Yard is a weekly column of the DEP.