"Giant Shovel on I70"Ohio Strip Mine Fight: 1973 | The ...
May 31, 2017· Generally it is economic to strip mine when there is a 20:1 ratio of overburdentocoal seam, meaning, for example that a threefoot coal seam can be surface mined economically when the overburden is up to 60 feet. However, at some surface mines in Ohio, highwalls of up to 200 feet high remain where fivefootcoal seams have been extracted.
WhatsApp





















