Status of Models for Land Surface Spills of Nonaqueous Liquids

Abstract

Executive SummaryThis report describes the status of models for predicting the spreading behavior of nonaqueous phase liquids (NAPLs) when spilled on land. NAPLs are liquids other than water and are commonly immiscible with water. Examples include diesel fuel, brake fluid, transmission fluid, and many chemical solvents. If there are adequate models available to describe spills, hydrologists can determine how the size of a spill relates to the amount spilled and how long it persists. Further, remote sensors can then be used to detect the presence of a spill on land.A NAPL spill area can often be detected by remote sensing of its vapors with infrared spectroscopy, for a period after a spill. The opportunity for sensing NAPLs having low volatility, however, may depend on the possibility of detecting directly the liquid phase, or adsorbed material, on the surface of a land spill area. Therefore, a NAPL spill model is useful to predict how large an area is produced by a spill of a certain amount and how long it remains visible for remote sensing. Only one land spill model, a simplified screening type, for NAPL spreading was found after searching the scientific literature. This model was built for the U.S. Environmental Protection Agency. It uses the theory of gravity currents from fluid dynamics to represent spill spreading, and it applies the Green-Ampt sharp front model to describe the concurrent infiltration of NAPL into the ground. This spreading model also considers component-wise evaporation of volatile petroleum liquids, but it does not treat drainage away from the surface after a spill. Predicting the drainage just beneath the surface is a critical capability for determining whether remote sensors can detect the liquid phase of a NAPL near the surface after a spill.An exact solution to the problem of coupling a gravity current of viscous liquid to its simultaneous infiltration into a porous medium was found. It derives from fluid dynamics and can be used as a paradigm for spill spreading on a flat ideally smooth surface. Test calculations of this gravity current theory revealed that the spreading area is strongly controlled by the release rate of a spill and by the subsurface permeability. A more realistic prediction of spreading under less ideal situations, however, must consider the roughness of the land surface.This report outlines the processes and mechanisms that control spill mechanics on a porous surface. It also defines physical parameters and lists sources of their values required by mathematical theory for spill phenomena. The key parameters are: iv Liquid properties: density, viscosity, interfacial tension, and vapor pressure Land properties: soil-water retention curve, permeability, surface slope, and roughness.To build a more general model for NAPL spreading over the land, two existing modeling capabilities for overland flow and multiphase subsurface flow of NAPL must be coupled. The two flow theories that must be mathematically coupled are: Saint Venant fluid dynamical equations for overland flo...

Spills on Flat Inclined Pavements

“…Calculating a one-dimensional viscous gravity current coupled to Green-Ampt infiltration was discussed and demonstrated by Simmons and Keller (2003). The model and method were extended to twodimensions with a sloping surface by using Lister's equation (1992).…”

“…For a gravity current, the spreading is controlled by the release rate of the spill and by the liquid's resistance to flow as characterized by its viscosity. This subject was discussed in a prior report (Simmons and Keller 2003).…”

An investigation into the factors influencing the detectability of oil spills using spectral indices in an oil-polluted environment

“…When oil spill occurs on a surface, the force balance between the downward pull of gravity caused by density and internal tension of the liquid may allow the oil pool to form a final spill size. A pool is considered to be a large drop of oil with a defined amount of oil held to a certain penetration depth in a surface area (Grimaz et al 2008;Simmons and Keller 2003). It also depends on the property of the oil (in the case for this study, heavy oils are used as no specific oil type is considered); the spilled oil will eventually stand a certain height or depth above the surface (Simmons, Keller, and Hylden 2004).…”

Nonlinear Regression Modeling of Hydraulic Oil Injury on a Bermudagrass Green

“…Contraction behavior may be more complex, being composed of a consortium of forces acting on residual HO. The consortium may include drainage, evaporation, and weathering processes including chemical, photochemical, and microbial transformations (Simmons and Keller, 2003). The extent of these forces would depend on environmental conditions including temperature, redox potential, organic matter content, N content, partition coefficients, and other factors such as turf management cultural practices.…”