Q784. For a facility with two landfills with separate gas collection systems and destruction devices, can I calculate a collection efficiency (CE) for each landfill gas collection and control system, or does the CE have to represent the entire facility?

A784. The  The definition of an MSW landfill in 40CFR98.6 states that a "Municipal solid waste landfill or MSW landfill means an entire disposal facility in a contiguous geographical space where household waste is placed in or on land.  An MSW landfill may also receive other types of RCRA Subtitle D wastes (40 CFR 257.2) such as commercial solid waste, nonhazardous sludge, conditionally exempt small quantity generator waste, and industrial solid waste.  Portions of an MSW landfill may be separated by access roads, public roadways, or other public right-of-ways.  An MSW landfill may be publicly or privately owned."  Therefore, all areas in which MSW waste is disposed in a contiguous geographic space are considered to be one landfill for the purposes of this rule.

While a facility may have two gas collection systems, the rule only accommodates a single value for CE to be reported and used in Equations HH-7 and HH-8.  The guidance to use a single CE for the entire facility stems from the fact that the landfill area that contains waste, but that is not impacted by the gas collection and control system must be accounted for in order to use Equations HH-7 and HH-8 (i.e., the back-calculation method to calculate methane emissions).  The area-weighted average CE method contained in the rule assumes the methane generation rate per area of the landfill is fairly uniform.  We realize that this is not a perfect representation of the landfill system, but other approaches overly complicate the equations and methodology.