40 C.F.R. § 264.309
Surveying and recordkeeping
The owner or operator of a landfill must maintain the following items in the operating record required under § 264.73:
(a) On a map, the exact location and dimensions, including depth, of each cell with respect to permanently surveyed benchmarks; and
(b) The contents of each cell and the approximate location of each hazardous waste type within each cell.