- Program Areas
- Energy and Water
- Environmental Restoration
- Munitions Response
- Resource Conservation and Climate Change
- Weapons Systems and Platforms
Improving Understanding of the Fate and Transport of Munitions Constituents to Enhance Sustainability of Operational Ranges
Millions of acres of land containing elevated levels of explosives and related materials in soil have been identified in the United States with costs for assessment and remediation of these sites estimated to be in the billions of dollars. Effective technologies are needed for predicting the fate and transport of munitions constituents (MC) at explosive-contaminated sites. To successfully model the fate of MCs on ranges, three key factors—dissolution rate, degradation rate, and partitioning to soil—must be understood. Because the major sources of MCs are from low-order (partial) detonation and propellant discharge, the constituents are deposited as mixtures of heterogeneous particles that affect their dissolution properties. Appropriate values of dissolution rates are essential as this is the source term for MCs in the environment. The concentration that reaches a biological receptor or a downgradient site will depend on the degradation rate of the compound and its sorption to the soil matrix. Given that MCs are highly polar compounds, high orders-of-magnitude errors result by trying to quantify sorption properties via the traditional methods applied to organic contaminants. New models supported by new data on dissolution and partitioning are required for more accurate prediction of MC fate and transport for scientifically sound risk assessments.
The overall objective of this project is to develop models supported by appropriate data that can predict (1) the dissolution and release rate of NG and 2,4-DNT from NC matrix propellant residue and (2) the partitioning of military grade RDX, HMX, TNT, NG, DNT, NQ, and mixtures of these MCs to soils of varying physical/chemical characteristics. This will require developing and using a chemical probe for determining the magnitude clay mineral binding sites and ascertaining whether irreversible binding occurs; modeling the results using polyparameter partitioning models and models for irreversible bonding; and initiating validation of the results using soils typical of those found at operational ranges. Researchers will initially validate the models developed in this project by comparing model results to those determined in soil column studies.
Adsorption/desorption of NG and 2,4-DNT will be conducted on NC particles to understand their interaction with the NC matrix through sorption and particle swelling. The kinetics of sorption and intraparticle diffusion will be determined on several types of NC particles. The partitioning of MCs will be conducted at a low water:soil ratio using extensively characterized natural soil samples. The reversibility of the sorption will be assessed by conducting two consecutive desorptions. Cesium sorption on soil will be used as a probe to evaluate the total concentration of available clay exchange sites. Partitioning modeling will be based on modern polyparameter multiphase distribution models that have demonstrated capability to deal with highly polar solutes and mineral surfaces. A multiphase model that explicitly represents sorption to organic matter; clay mineral surfaces; and Fe, Al, and Mn oxides will be developed. The partitioning model will be validated using soils from military sites representative of MC-contaminated soils, but not contaminated by explosives. The ability to predict the fate of the MCs will be preliminarily validated for military grade MCs added to columns of the soil from selected military sites. Water will be added at intervals, equivalent to rainfall for up to one year. The distribution of the MCs in the columns will be determined and compared to that predicted by the models.
Investigation of the dissolution and partitioning of MCs in natural soils will provide critical information for developing fate and transport models at contaminated sites for use in risk assessments. These models can be applied at more than 15 million acres that contain elevated levels of explosives and related materials in soil. The use of scientifically sound risk assessments will ensure sustainable use of operational ranges. (Anticipated Project Completion - 2012)
Points of Contact
Dr. Herbert Allen
University of Delaware
SERDP and ESTCP
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