review of standards of performance for greenhouse gas emissions from new modified and reconstructed stationary sources electric utility generating units the environmental protection agency epa is proposing amendments to the rulemaking titled standards of performance for greenhouse gas emissions from new modified and reconstructed stationary sources electric utility generating units egus which the epa promulgated by notice dated 23 october 2015 i.e. the 2015 rule . specifically the epa proposes to amend its previous determination that the best system of emission reduction bser for newly constructed coal-fired steam generating units i.e. egus is partial carbon capture and storage ccs . instead the epa proposes to find that the bser for this source category is the most efficient demonstrated steam cycle e.g. supercritical steam conditions for large units and subcritical steam conditions for small units in combination with the best operating practices. the epa proposes to revise the standard of performance for newly constructed steam generating units as separate standards of performance for large and small steam generating units that reflect the agencys amended bser determination. in addition the epa proposes to revise the standard of performance for reconstructed steam generating units to be separate standards of performance for reconstructed large and small steam generating units consistent with the proposed revised standards for newly constructed steam generating units. the epa also proposes separate standards of performance for newly constructed and reconstructed coal refuse-fired egus. in addition the epa proposes to revise the maximally stringent standards for large modifications of steam generating units to be consistent with the standards for reconstructed large and small steam generating units. the epa is not proposing to amend and is not reopening the standards of performance for newly constructed or reconstructed stationary combustion turbines. the epa is also proposing to make other miscellaneous technical changes in the regulatory requirements.