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EPA On-line Tools for Site Assessment Calculation

The distribution of mass in a multiphase system depends on partitioning between the phases. The partition coefficients depend on properties of the chemical and the amounts of water, NAPL, air and organic carbon in the pore space.

Suggestion icon The mass distribution calculator only calculates the partitioning between between water, air, fuel and solids in the subsurface. Use the effective solubility calculator to determine the partitioning (concentrations) between only water and a fuel.

Mass Distribution Calculator  
Mass Distribution
Masswater = Cw Swq
MassNAPL = Cw Ko Soq
Massair = Cw Kh Saq
Masssolid = Cw Kdrb

Sw = Fraction of the pore space filled by water (water saturation)
So = Fraction of the pore space filled by NAPL (NAPL saturation)
Sa = Fraction of the pore space filled by air (air saturation)
Ko = NAPL/water partition coefficient
Kh = Henry's Law coefficient
Kd = soil/water distribution coefficient
Cw = Effective solubility
q = porosity
rb = bulk density

Effective SolubilityCw = xo S

Cw = Effective solubility
xo = mole fraction (of chemical in fuel)
S = solubility

Mole Fraction xo = (estimate) ro / ( MWo S)

ro = fuel density
MWo = average molecular weight of fuel
est. 105 g/mole for gasoline
est. 165 g/mole for jet fuel
est. 230 g/mole for diesel fuel
Site Name  
Distance Unit    
Solubility (S) mg/L  
Optional Revised Solubility (S) mg/L  
Example Fuel  
Fuel composition note:
Average Molecular Weight of Fuel (MWo)    
Percent Mass Fraction    
Effective Solubility (Cw) mg/L  
Solids density    
Fraction Organic Carbon Try 0.0001  
Water Saturation Fraction of the pore space filled with water  
NAPL Saturation Fraction of the pore space filled with NAPL  
Phase %Mass Concentration  
NAPL (Fuel) mg/L fuel
Water mg/L water
Air mg/L air
Solids mg/kg solids
Smear zone thickness  
Lens radius  
Estimated oil volume gal  
Total chemical mass kg  
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