Enhanced Field Inspections of Closed Landfills Using Aerial Orthophotography in Illinois

Most closed landfills in Illinois are inadequately lined former dumps with thin earthen covers. Customary walkover inspections of these legacy landfills can overlook defects in the cover and surrounding area that increase threats to human health and water resource quality. Publicly available aerial orthophotography and light detection and ranging (lidar) data were interpreted for 10 closed, managed landfills in Illinois. Visible and near-infrared data were enhanced by histogram stretching, normalized difference vegetation index, iron oxide index, and images draped over lidar data to improve recognition of defects and features of interest. Image interpretation keys were used and confidence levels assigned to create previsit maps showing deformation features, including depressions and dimples that collect runoff, gullies eroding into earthen covers, slope instability, wet and barren spots that may be outlets for leachate seeps, and vegetation anomalies that can indicate outgassing. Defects on inspection maps were ordered for on-site reconnaissance. Changes observed from comparing historical and current imagery and geographic information system–based defect-tracking databases can provide a basis for scheduling maintenance and prioritizing repairs for sustainable postclosure and custodial landfill management.