A strange fenced in mound of dirt along US 22 in Ebensburg Pa.

For 20 Plus years I have been driving thru Ebensburg on my way to Altoona when I noticed this strange fenced in square of ground with a dirt mound with in blink your eyes you will miss it. Because the field is heavily grown over with weeds. 
Intrigued I finally stopped the one day and checked it out from a far using binoculars as the field is a total swamp.
A sign on it is posted No Trespassing Beth Energy Mines  there is also a sign No Smoking  no open lights or matches .

So what is it at first glance I thought must be a hazardous waste pile which was sealed over and capped  Thinking there was a chemical company on the site but this is not the case . But seeing it was owned by a Coal mining company and knowing the nearby Bethlehem Coal mine in Revloc possibly goes under this area I am more  thinking now this was one of the rescue shafts to get miners out during and emergency or possibly even an air shaft  but it is strange the way it is capped most places use concrete cap but some do use a mound of dirt like this when sealing entrances. Why the no smoking sign. there is always the possibility of methane escaping from the old mine better safe than sorry.
So another mystery solved even if its a small one but there are so many little fenced off and mysterious little utility buildings and mounds and pits all over our state most still in use but plenty abandoned after coal and limestone etc mining operations ceased. So it is best advised not to trespass and photograph from a far to avoid problems