Farallon conducted a compliance assessment of a 16.5-acre wood waste landfill at the Bellingham International Airport, where an estimated 500,000 cubic yards of wood waste materials had been deposited between 1984 and 1992. The compliance assessment involved extensive review of historical groundwater, surface water, and leachate monitoring data collected at the landfill over a 20-year period for comparison against current MTCA cleanup levels. Based on the results of the compliance assessment, a site conceptual model was developed as a tool for future decision-making regarding leachate management and potential cleanup actions at the site. A key element of the site conceptual model was preparation of a water balance that estimated inflow and outflow components such as precipitation infiltration, groundwater flow, and leachate extraction. The site conceptual model identified primary pathways for subsurface contaminant movement beneath and adjacent to the landfill, and likely receptors.