Ahtna conducted an Expanded Site Inspection (ESI) to investigate locations on the former Plattsburgh Air Force Base (AFB) installation where the release of PFAS attributable to Air Force actions may pose an unacceptable risk to human health.

ESI activities were focused on inspecting dissolved PFAS plumes in groundwater that may impact groundwater used as drinking water. ESI work was completed under a UFP-QAPP approved by the Air Force, NYDSEC, NYDOH, and the EPA. Ahtna managed field activities and reporting, including:

• Install a variety of borings in multiple hydrostratigraphic units (such as sand, till, and fractured bedrock) to collect soil samples and install groundwater-monitoring wells
• Perform geophysical logging and hydraulic profiling at multiple locations to improve the understanding of bedrock fractures and hydraulic conductivity
• Advance borings and wells, and conduct vertical aquifer sampling to understand the migration pathways of PFAS in groundwater
• Sample newly installed and existing groundwater monitoring wells using low-flow techniques and a variety of pumping scenarios
• Collect surface water samples from multiple locations (streams, drainage ditches, and storm drains) as an approximate measure of groundwater concentrations in the up-gradient drainage area
• Prepare a 3-dimensional Conceptual Site Model (CSM) using advanced software that incorporates historical data from previous characterization and investigation activities at the former AFB, and new data generated or updated during the ESI