HAPs To Be Regulated: Mercury Only Electric utility steam generating units are uniquely regulated by Congress under 112(n)(1)(A) EPA was required to study hazards to public health reasonably anticipated to occur from electric utility steam generating stations and then regulate as is “appropriate and necessary.” EPA identified health concerns only for mercury, therefore EPA’s authority under the MACT provisions of §§ 112(c) and (d) is limited to regulating mercury emissions only

HAPs To Be Regulated: Mercury Only Even if EPA identifies health concerns with non- mercury HAPs: Historical sampling data is insufficient to characterize HAP emissions from coal or oil fired units or to set MACT Floors EPA must collect representative data using validated methods Grouping non-mercury HAPs or designating surrogates is premature at this point

Areas of Subcategorization Fluidized bed combustors IGCC units are exempt (also are a separate category) Conventional boilers (pulverized coal & cyclone only) Coal rank (bituminous, subbituminous and lignite) Process Subcategorization Coal Chemistry differences support further subcategorization (to be discussed by West Associates)

MACT Floors MACT floors must account for the variability in mercury emissions from the best performing units Data has shown that often the “best performers” are average performers on good days UARG’s method quantifies fuel variability EPA’s method quantifies variability from sampling & monitoring, operational, plant to plant, etc. A combination of the two methods is necessary to properly account for variability.

Subcategorization Approach 1: Coal Rank SubcategoryStack Limit, lb/TBtu * Overall Reduction Bituminous2.273% Subbituminous4.231% Lignite6.547% * Limits include only a consideration of fuel variability and no other forms of variability

Subcategorization Approach 2: Coal Rank and Process SubcategoryStack Limit, lb/TBtu * Overall Reduction Bituminous - Hot3.755% Bituminous – Sat.2.263% Bituminous - Wet3.262% Subbituminous4.231% Lignite6.547% * Limits include only a consideration of fuel variability and no other forms of variability

No Beyond-the-Floor Regulation Currently no justification for regulation beyond the MACT floor. To develop a justification, EPA must: Complete IPM Runs to access the costs of regulation Use REMSAD or equivalent to understand deposition and possible health impacts Access the energy requirements of additional control Since beyond the floor controls are not commercially available, carefully access their cost and availability With reduced emissions, any justification is unlikely

New Units No additional requirements beyond what is required to meet the MACT floor for existing units and satisfy NSPS requirements. NSPS require highly efficient controls for SO2, particulate, etc. These are the controls that currently achieve the “best control” for mercury New units are subject to the same variability issues as existing units. Additional control technologies such as ACI are still developmental and not commercially available.