esm222_11_multiphase

esm222_11_multiphase - ESM 222 Typical Spill Scenario...

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1 © Arturo A. Keller ESM 222 Multiphase Flow 2 © Arturo A. Keller Typical Spill Scenario 3 © Arturo A. Keller Multiphase Flow ± NAPL enters the subsurface, either as a spill or as a leak ± Travels down some distance in the NAPL (oily) phase until ± it is spread out too thin ± it reaches a barrier for flow. 4 © Arturo A. Keller Multiphase Flow ± The barrier may be an impermeable layer (e.g. clay or bedrock) ± In the case of LNAPL (e.g. most hydrocarbons - gasoline, diesel fuel), the barrier can be the top of the water table ± Forms a “pool” which then spreads laterally 5 © Arturo A. Keller Multiphase Flow ± DNAPLs (e.g. chlorinated solvents, PCBs, many pesticides) will continue travelling through the aquifer until they find a clay layer or bedrock ± If there is still enough DNAPL left, it spreads out horizontally until it either is spread too thin or it finds a new pathway (e.g. fracture in bedrock or clay) 6 © Arturo A. Keller Typical Spill Scenario
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7 © Arturo A. Keller Multiphase Flow ± At the same time NAPL travels downward, it begins to volatilize ± Surrounding vapor phase becomes saturated with organic vapors and these begin to diffuse away from the source ± Soil vapor flow through advection is small unless we actively promote flow. 8 © Arturo A. Keller Multiphase Flow ± Once NAPL reaches the capillary fringe and then the water table, it begins to dissolve ± LNAPLs have a relatively small contact area with water and are typically relatively insoluble (except Benzene - a potential carcinogen), so transfer to the water phase is slow ± If the water table rises and falls due to seasonal rainfall and drying, then NAPL is smeared and the contact area increases. 9 © Arturo A. Keller Multiphase Flow ± DNAPLs, which go right through the aquifer, present a greater interfacial contact area and thus the rate of dissolution may be greater ± Rate at which the NAPL disappears depends on solubility of NAPL constituents, as well as groundwater flow velocity 10 © Arturo A. Keller Multiphase Flow ± In either case, sorption also occurs. The flowing NAPL phase is separate from the immobile organic fraction associated with the soil. ± Contaminants may sorb from ± NAPL to soil ± water to soil ± vapor to soil. 11 © Arturo A. Keller 12 © Arturo A. Keller Multiphase Flow ± Groundwater flowing past the NAPL dissolves more and more NAPL ± Forms a “dissolved plume” of contaminants, which moves with the water flow and also disperses out ± Due to mass transfer limitations, the plume is
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This note was uploaded on 08/06/2008 for the course ESM 222 taught by Professor Keller during the Spring '08 term at UCSB.

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esm222_11_multiphase - ESM 222 Typical Spill Scenario...

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