Partitioning microbial respiration between jet fuel and native organic matter in an organic-rich long time-contaminated aquifer.

The relative importance of jet fuel biodegradation relative to the respiration of natural organic matter in a contaminated organic-rich aquifer underlying a fire training area at Tyndall Air Force Base, Florida, USA was determined with isotopic measurements. Thirteen wells were sampled and analyzed for BTX (benzene, toluene, xylene), dissolved inorganic carbon (DIC) and CH4 concentrations, and delta13C and 14C of DIC. Results range from non-detectable to 3790 ppb, 1.4-24 mM, 0.2-776 microM, +5.8 per thousand to -22 per thousand, and from 52 to 99 pmc, respectively. Residual fuel was confined to two center wells underlying the fire training area. DIC and CH4 concentrations were elevated down-gradient of the contamination, but also at sites that were not in the apparent flow path of the contaminated groundwater. DIC exhibited greatest delta13C enrichment at highest DIC and CH4 concentrations indicating that CH4 production was an important respiration mode. Radiocarbon-depleted DIC was observed at sites with high hydrocarbon concentrations and down-gradient of the site. The results indicate that while natural attenuation was not rapidly reducing the quantity of free product overlying the aquifer at the site of contamination, it was at least constraining its flow away from the spill site. Apparently under the conditions of this study, BTX was degraded as rapidly as it was dissolved.

Biogeochemical assessment of natural attenuation of JP-4-contaminated ground water in the presence of fluorinated surfactants.

The biogeochemistry of the natural attenuation of petroleum-contaminated ground water was investigated in a field study. The focus of the study was a fire training site located on Tyndall Air Force Base in Florida. The site has been used by the Air Force for approximately 11 years in fire fighting exercises. An on-site above-ground tank of JP-4 provided fuel for setting controlled fires for the exercises. Various amounts of water and aqueous film forming foams (AFFF) were applied to extinguish the fires. The sources of contamination included leaks from pipelines transporting the fuel, leaks from an oil/water separator and runoff and percolation from the fire fighting activities. Previous investigations had identified jet fuel contamination at the site, however, no active remediation efforts have been conducted to date. The goal of this study was to use biogeochemical monitoring data to delineate redox zones within the site and to identify evidence of natural attenuation of JP-4 contamination. In addition to identifying several hydrocarbon metabolites, fluorinated surfactants (AFFF) were detected down-gradient of the hydrocarbon plume.

The use of grain-size analysis with limited field data to study hydraulic conductivity variability.

The spatial variability of hydraulic conductivity is studied using grain-size data collected at a groundwater tracer test site located at Columbus AFB, MS. The study involves vertical kriging and the construction of segmented trend surfaces. It is observed that there exists some simple spatial patterns of hydraulic conductivity. Also, a possible existence of a relationship between the results obtained from grain-size data and the detrended flowmeter data are shown.

Environmental chemistry and management of hydrazine.

The recent use of 70% hydrazine-water fuel in the F-16 emergency power unit (EPU) presents problems for organizations responsible for protection of personnel and the environment because of the worldwide deployment of this aircraft and the requirement for fuel handling in a flightline environment. Hydrazine has a low vapor pressure (14 mm Hg at 25 degrees C) but still evaporation rates (16-100 mg/cm2h) from liquid pools are sufficient to generate hazardous atmospheric concentrations greater than the permissible exposure level (3 ppm) up to 2 km downwind under worst-case meteorological conditions (F Stability). In contrast to the general feeling that hydrazine degrades in the presence of atmospheric oxygen, studies show hydrazine is relatively stable in both air (t1/2 approximately 6 h) and oxygenated aqueous solutions (t1/2 approximately 5 d). The toxicity and stable character of hydrazine in the environment required quick and thorough management of any accidental spills to preclude hazards to personnel and serious environmental degradation. The Air Force has established comprehensive containment and treatment procedures which will be used in the event of inadvertent releases of hydrazine from the EPU or during handling or transport of the bulk fuel. The simple spill management procedures used to support the F-16 aircraft EPU are described.