When 20 years of drilling, sampling, monitoring, and remediation efforts failed to reveal the origin of LNAPL seeps at a coastal refinery, Aestus’ GeoTrax Survey™ joined the investigation. Both marine and upland electrical resistivity images were taken to evaluate LNAPL migration in more detail and formulate a more accurate CSM.
The prevailing CSM posited that the source of the LNAPL seep was shallow LNAPL-saturated filter clays. This assumed that LNAPL migration would primarily occur at or near the static groundwater table (see Pre-Aestus CSM graphic). Aetsus’ high-resolution electrical images showed there was more to the story.
GeoTrax Survey™ images were able to track the migration of LNAPL through the subsurface to its discharge points along the coast. Both marine and upland electrical imagery revealed preferential flowpaths originating within deeper coarse-grained alluvium than previously thought. Targeted confirmation drilling guided by GeoTrax Survey™ images verified the presence of LNAPL at deeper depths – more than 10 ft below the static groundwater level measured in site monitoring wells.
Electrical images served as the remedial linchpin, as they revealed that upland LNAPL impacts were diving, migrating laterally at depth through coarser-grained materials, and then rising to discharge along the adjacent shoreline (see Post-Aestus CSM graphic).
For 20 years, the source of an LNAPL seep remained elusive. After electrical imagery was leveraged to update the CSM, targeted pumping of the seep sources resulted in seep elimination within 4 years.
Even coastal environments can’t stop GeoTrax Survey™ from helping you solve the mystery of your LNAPL seep! Have you performed characterization work in these challenging environments? What have you learned that has helped make your project a success?
