Environmental Modeling Community of Practice

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.

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
Mass_water = C_w S_wq
Mass_NAPL = C_w K_o S_oq
Mass_air = C_w K_h S_aq
Mass_solid = C_w K_dr_b

S_w = Fraction of the pore space filled by water (water saturation)
S_o = Fraction of the pore space filled by NAPL (NAPL saturation)
S_a = Fraction of the pore space filled by air (air saturation)
K_o = NAPL/water partition coefficient
K_h = Henry's Law coefficient
K_d = soil/water distribution coefficient
C_w = Effective solubility
q = porosity
r_b = bulk density

Effective SolubilityC_w = x_o S

C_w = Effective solubility
x_o = mole fraction (of chemical in fuel)
S = solubility

Mole Fraction x_o = (estimate) r_o / ( MW_o S)

r_o = fuel density
MW_o = 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

Date

Distance Unit

Chemical

Solubility (S)

mg/L

Optional Revised Solubility (S)

mg/L

Example Fuel

Fuel composition note:

Average Molecular Weight of Fuel (MW_o)

Percent Mass Fraction

Effective Solubility (C_w)

mg/L

Porosity

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