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HSSM. H ydrocarbon S pill S creening M odel U.S. EPA – 1994 Non-Aqueous Phase Liquids – especially LNAPLS. NAPL Migration Basics. Residual Saturation 1-D movement Impact of non-homogeneities Spreading at the Water Table (LNAPL). Idealized View of NAPL transport in Vadose Zone.
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HSSM Hydrocarbon Spill Screening Model U.S. EPA – 1994 Non-Aqueous Phase Liquids – especially LNAPLS
NAPL Migration Basics • Residual Saturation • 1-D movement • Impact of non-homogeneities • Spreading at the Water Table (LNAPL)
Idealized View of NAPL transport in Vadose Zone • Conservative
KOPT Module • NAPL transport from surface to Water Table • Known Flux, Specified Duration (qo) • Run-off? Qo > Keo • Known Volume over Specified Depth • Is Volume Oil/Volume Voids > retention capacity • Ponded LNAPL for given duration
Kopt Module • Uniform Water Saturation • Neglect of Capillary Gradient: Sharp Front • Relative Permeability of NAPL • Two Component Mixture • LNAPL (soluble and sorbing) • Chemical Constituent (soluble in water and NAPL, sorbing)
KOPT – movement of constituent • Movement due ONLY to advection (of water and NAPL) • No Dispersion • Impact on Groundwater via dissolution of oil lens at water table, and movement of constituent dissolved in aqueous phase
OILENS • Simulates radial spreading of LNAPL phase at water table and dissolution of chemical constituent • Typical Formation Shape
Transient Source Gaussian Plume Module • 2-D (vertically averaged) solution of advection-dispersion equation • Depth of plume is based on vertical dispersion plus vertical advection due to impact of recharge through oil lens
Example Problem #1 • Gasoline Arrival Time at Water Table • Run only the KOPT module • Hydrologic Properties • Hydrocarbon Phase Parameters • Hydrocarbon Release • Output Provides Saturation Profiles
Example Problem #2 • Transport of Gasoline Constituents (Benzene) to Receptor Wells