Upscaled modeling of complex DNAPL dissolution.

A straightforward, upscaled DNAPL mass dissolution model is developed using relatively simple input consisting of characteristic dimensions and saturations of a DNAPL accumulation. Multiple accumulations are aggregated into a single source zone volume. Physically, the dissolution process is a combination of flow through the mass (advective component) and flow around the mass (dispersive component). The contribution of each component is based on initial characteristic length scales and the average initial saturation. Changes over time with the depletion of mass are captured with a changing relative permeability and a power law relationship for the fraction of initial mass remaining. The utility of the upscaled process model is demonstrated with data from three studies: numerical simulation of multiple pools, two-dimensional test cell experiments with mixed architecture and with heterogeneous soil, and a controlled field study of multicomponent DNAPL release and depletion. Use of the model successfully reproduced the observed multistage mass discharge in each study and illuminated the governing processes. The power law exponent was relatively constant for the various conditions and relative permeability changes were integral to the success. The numerical and experimental studies were run to complete mass depletion which the upscaled model matched. The input parameters are minimal and are found in typical DNAPL source zone characterization data.

Corrosion of unexploded ordnance in soil-field results.

Unexploded ordnance (UXO) are found on 400 000 Ha of land across 1400 different sites in the United States. In many cases, UXO contain high explosives posing a risk to groundwater quality. This paper provides results from a field survey of 14 inactive Army ranges distributed throughout the mainland United States. Metal samples and adjacent soil were collected from 161 UXO. Soil samples were analyzed for a variety of chemical and physical properties. Metal samples were analyzed for pitting corrosion. Climate data were also compiled. Of these analyses, only rainfall correlated with extent of corrosion. Samples had been buried from the Civil War era through the 1990s. Photographs taken in the field illustrate that corrosion occurs more rapidly on the underside of a UXO. Field observations also revealed that low-order detonations and UXO are difficult to distinguish in the field. The deepest individual pit measured on any of the 161 metal samples was 2400 microm. Low rainfall environments had shallower average pit depths (590+/-130 microm)than moderate and high rainfall environments, which produced deeper average pit depths (940+/-90 microm). The UXO studied in this effort were not a significant source of explosives to the unsaturated soil environment.