Over the last decade Pennsylvania has seen the share of its electricity coming from coal decline from 57% to 48%. That decline of 15% means that Pennsylvania is just a bit above coal's approximately 44% national market share.
Gas grew in the same period from just 2% of Pennsylvania's power to 13%. That is strong growth, but puts Pennsylvaia well below the 24% of electricity that gas provides nationally. Pennsylvania also had 8,000 megawatts of new gas plants built from 2000 to 2008. But most of those gas plants ran about 30% of the time due to high gas prices making them uneconomic.
Shale gas production that has rocketed up and now provides 30% of all gas has caused gas prices to fall from $13 for a thousand cubic feet to now $4.
Given the huge gas supply in Pennsylvania and today's low gas prices, no excuse exists for running old coal plants without pollution controls. Such plants emit toxic pollution like mercury and arsenic, soot and smog causing pollution. Clean them up or switch to gas.