A study was made in order to characterize a site in which a spill of about 5000 gallons of unleaded gasoline occurred. An anomaly was detected in one well close to the source with no free product, and the shape of the benzene plume. This plume appears not to follow the groundwater flow that occurs towards the northwest direction in a permeable aquifer within a sequence of fractured Quaternary non-consolidated and semi-consolidated volcanic ash, and tuffs. The orientation of the old and recent fractures is to the NNE and the groundwater flow direction is NNW. The water table is deep (>60 feet), with a hydraulic gradient of 0.0013.
The investigation approach included outcrop and test pit observations, soil borings, sampling, surface geophysical methods (GPR and Electric Tomography), and finally, a flow and transport groundwater model.
We conclude that the anomaly is due to a combination of the presence of caliche filling the old fractures and the recent spaced fractures (these last ones with a small aperture) caused by the actual tectonic activity, because the site is less than 800 feet from one of the main faults of the Aeropuerto graven