ENVIRONMENTAL THERMOGRAPHY DETERMINES CONTAMINANT TRANSPORT PATHWAYS AND GROUNDWATER SAMPLING LOCATIONS DURING SITE INVESTIGATIONS IN DELAWARE, USA

Environmental Thermography (thermal imaging of outdoor processes typically having low thermal variability [< 5^oC]) is a tool that can be extremely helpful in investigating, sampling and remediating contaminated sites. Identifying locations of groundwater discharge to streams or as subaerial springs and seeps aids in determining where to take representative water samples, provides insight into contaminant pathways and allows for sampling for pollutants at the ends of groundwater flow paths. As groundwater flow paths terminate into surface water they enter environments where sensitive ecological receptors may be impacted. Knowledge of this flow pathway informs the development of conceptual site models and helps direct sample media selection, location and extent. The technique is complementary to surface geophysics (resistivity, seismic, GPR, etc.) and well installation in characterizing aquifer systems. Groundwater discharge from preferential flow paths are the easiest to detect but the method can also be used to detect more subtle processes like diffuse groundwater discharge into a stream or estuary or from a hillslope. Site investigators used results of ground-based surveys with a handheld FLIR P45HSV thermal imager to inform environmental investigations at four complex contaminated sites in Delaware (Standard Chlorine of Delaware / Metachem, Chestnut Run, I-495 Drainage Ditch, and Del Chapel). Three of the sites are located in the Piedmont and one is located in the Coastal Plain Physiographic Province. Challenges included oblique imaging, varying emissivity, noisy thermal environments (e.g. radiation from trees, bridges, houses, etc.) and groundwater discharge targets with small thermal contrasts (typically < 3-5^oC). Given these challenges, good planning is critical for a successful survey!