Q780. Different daily cover materials can be used throughout the year on the working face of a landfill. The surface area can change as additional lifts of waste are added. At what point in the year should the surface area measurements be taken?

A780. 40 CFR Part 98 Subpart HH does not specify a time-frame for determining the soil cover surface areas.  We recommend that the surface areas be estimated during the first half of the reporting year because methane generation generally does not begin until the waste has been in the landfill for three to nine months.  We also recommend that the time-frame when this area determination is made be consistent from year to year.  Note that facilities reporting under Subpart TT for industrial waste landfills are specifically required to make this area determination at the start of the reporting year [see § 98.466(b)(2)]