Landfills, specifically, are built to be as isolated from the environment as possible[1], will generally kills most anything inside and reduces the rate of decomposition.
Admittedly, that is being a bit pedantic, the question would still seem to hold if you were talking about traditional waste dumps, I have no idea about the environmental makeup of those. Although my understanding is that the number of dumps, in the U.S. at least, has dramatically decreased of the last few decades.
Admittedly, that is being a bit pedantic, the question would still seem to hold if you were talking about traditional waste dumps, I have no idea about the environmental makeup of those. Although my understanding is that the number of dumps, in the U.S. at least, has dramatically decreased of the last few decades.
[1] https://en.wikipedia.org/wiki/Landfill