WA6 Fate and Effects of Energetic Compounds
202 Oregon Ballroom
8:00 AM - 12:00 PM, Wednesday
() Nitroaromatic Pollutant Migration at VAAP Site: Bench-Scale Sorption and Leachability Studies.
Zhang, C1, Law, M1, Deeb, R2, Hughes, J, 1 University of Houston-Clear Lake, Houston, Texas, USA2 Malcolm Pirnie, Inc., Emeryville, California, USA
ABSTRACT- In the last several years, we have successfully demonstrated bioremediation of soils highly contaminated with explosives using anaerobic and aerobic strategies at the bench, pilot and field scales. The objective of this bench soil column study was to determine whether natural attenuation is a feasible option for soils lightly contaminated with explosives compounds. Natural attenuation incorporates in-situ contaminant stabilization or destruction using physical, chemical, and biological means. Under certain circumstances, it is the preferred and may be the only cost-effective remediation strategy. Using aquifer materials from Volunteer Army Ammunition Plant (VAAP), this study was to obtain sorption and leaching parameters that are essential to assess natural attenuation processes. Results from this study indicate that: (1) The soil-water partitioning coefficients (Kd) of 2,4-DNT, 2,6-DNT and TNT are small (2.80 - 4.96), implying a low retardation factor (R) in the range of 10 - 18. (2) Conventional models using Kow underestimate the Koc values of nitroaromatic compounds (NACs) due to the specific sorption mechanisms of clays in the VAAP soil. (3) Desorption of DNTs and TNT from an aged VAAP soils can be described by a two-compartment kinetic model -- an almost instantaneous (in minutes) desorbing fraction (67-90%) followed by a relatively slow desorbing fraction in the timeframe of hours to days. (4) Leaching of these nitroaromatic compounds is dependent of the initial concentration in the soil. Under the worst-case scenario of simulated sandy aquifer and intensive rainfall, 2,6-DNT and TNT depleted rapidly within 30 days (approximately 5 pore volumes) from a contaminated VAAP loamy soil. The low Kd values associated with high aqueous solubilities and desorption rate imply that the high bioavailability of TNT and DNTs could favor the biological attenuation of nitroaromatic pollutants at the VAAP site. The partition coefficients higher than predicted from hydrophobic partitioning theory indicate that additional retardation mechanisms exist and conventional groundwater plume modeling and management should take into account of the clay contents which could be attributed to the specific affinity of NACs to the prevailing clayed soils at the VAAP site.
Key words: natural attenuation, biodegradation, leaching and sorption, explosives