Hydrologic Investigations at Naval Air Station Jacksonville (NASJAX)
The primary ground-water contaminants of concern at OU1 are trichloroethene (TCE), dichloroethene (DCE), and vinyl chloride (VC). Starting in the 1940s, the Navy began disposing of household and sanitary waste, liquid industrial waste (oil and solvents), and demolition and construction debris at a landfill. Concentrations of TCE, DCE, and VC have been measured at two locations in creeks downgradient from OU1 from 1992 to present. At one location, the concentrations have been below the detection limit except for one sampling event in 1999. At a second location, downstream from the first, all three contaminants have been detected at low concentrations.
Ongoing biodegradation has been documented at OU1 based on the following evidence:
- decrease in concentrations of the original contaminants
- increase in the presence of daughter products
- depletion of oxygen and ferric iron
- increase in ferrous iron
- elevated hydrogen levels
An OU1 site-specific model containing 130 rows and 122 columns of active model cells was developed; the model has one layer and all cells are 25 ft on each side. Fate and transport modeling was performed using the computer code Reactive Transport in Three Dimensions (RT3D). All fate and transport model simulations began in 1945. The waste-disposal pits were simulated as specified concentration cells. The period of time that a pit acted as a source of ground-water contamination and the concentration levels at the pit were determined during model calibration. The northernmost disposal pit could have acted as a source twice-the first when the solvents were being disposed and again immediately after the free-product recovery trench was installed.
Simulations indicated that the concentration of contaminants would have reached the maximum extent by the 1970s, after which the concentrations generally declined because the pits had ceased releasing high levels of contaminants. In the southern part of the site, monitoring well MW 19, which had some of the highest levels of contamination, showed decreases for both the measured and simulated TCE and DCE concentrations from 1992 to present. To match the decline in measured concentrations, it was necessary to simulate two upgradient disposal pits as transitioning from releasing high levels of contamination prior to 1979 to releasing low levels after 1979. The linked video shows simulated movement of the TCE plume between 1945 and 2020 (16 Mb AVI video file). Complete documentation of the modeling can be found in U.S. Geological Survey Scientific Investigations Report 2007- 5043.