Provide a description and/or references pertaining to: the conceptual model, a list of key variables and/or parameters, the model structure, and governing equations:

IWEM uses EPACMTP to model the WMU and structural fill sources, and an external roadway source module to model the roadway source. IWEM also relies on EPACMTP to model subsurface fate and transport of contaminants leaching from WMU, structural fill, or roadway sources. In addition, IWEM utilizes EPACMTP’s Monte Carlo capabilities to account for variability that occur in climate conditions, soil types, and subsurface characteristics.