Q785. When can I use a collection efficiency (CE) of 75% from Table HH-3?

A785. Under section 98.343(c) of the rule, the collection efficiency (CE) estimated at the landfill is calculated using an area-weighted average (see Table HH-3 of this subpart) that accounts for system coverage, operation, and cover system materials.  If area by soil cover type information is not available, you may use default value of 0.75 (CE4 in table HH-3 of this subpart) for all areas under active influence of the gas collection system.  Please note that landfills with Area Type A2 as defined in Table HH-3, i.e., “Area without active gas collection, regardless of cover type,” cannot simply use the default of 0.75 for CE in Equations HH-7 and HH-8.  

The 0.75 is not an alternative to the area-weighted methodology for all landfills.  The 0.75 alternative can only be used for those that do not know the relative areas of daily, intermediate, and final soil covers (as described in Table HH-3).  It also does not apply to the entire landfill; it only applies to that portion of the landfill under active influence of the gas collection system.  If there are areas of the landfill that are not under active influence of the gas collection system, you must report that area under Area Type A2 and then use the resulting area-weighted average CE in Equations HH-7 and HH-8, even if you use the default of 0.75 for all areas under active gas collection.

Please note, the e-GGRT system uses only the values provided by the reporter for surface area by area type from Table HH-3 to calculate the area-weighted collection efficiency per the definition of the variable CE.