Do the proposed rules allow a source to subtract the actual emissions of the equipment being replaced when calculating the NEI of the modification in the first step of the dual source calculation?
A source can subtract actual emissions (based on the definition of Actual Emission Reductions in Rule 102) of the equipment being replaced provided the new equipment is the same type as the old. For example, a boiler replacing a boiler, or an I.C. engine for an I.C. engine. Netting out is not allowed in the case of one emissions unit type ‘x’ replacing emission unit type ‘y’ under the guise they both perform the same function. For example a source would not be allowed to subtract emissions from a boiler if they were replacing it with a turbine even though both products produce steam. This is the only exception allowed under the dual source definition. As always, deductions are always allowed for all reductions in calculating the facility wide NEI. Examples of the replacement netting out policy follow (note in the following examples the replacement does not qualify for exemption under the “equivalent routine” exemption provided by Rule 202D.9). Example 1 Given: 1990 NEI = 0 (source was
