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EPA On-line Tools for Site Assessment Calculation


The old seepage velocity and travel time calculator determined the advective travel time. This calculation accounted for transport due to advection and sorption only. Because of widespread biodegradation of petroleum hydrocarbons and dispersion in aquifers, the advective travel time can come long after the first arrival time of a contaminant at a receptor. To avoid this situation the one-dimensional transport calculators have been revised to calculate the first arrival times.

Try instead:

Continue below for the seepage velocity calculation.

Seepage Velocity
Seepage Velocity Calculation
See bottom of page for equations solved.

Input Parameters
Site Name
Distance Unit
Time Unit
Fraction Organic Carbon
Hydraulic Conductivity (K)
Upgradient Location (x1,y1)
Downgradient Location (x2,y2)
Head unit
Upgradient Water Level (h1)
Downgradient Water Level (h2)


Intermediate Results
Hydraulic Conductivity (K)
Bulk Density (rb)
Retardation factor (R)
Gradient (i)

Main Result
Seepage Velocity (qs = v)
Retarded Seepage Velocity (qs/R)

seepage velocity q s = v = -K i / q

qs = v = seepage velocity [L/T]
K = hydraulic conductivity [L/T]
i = hydraulic gradient [L/L]
q = porosity [L/L]

retardation factor R = 1 + rbkd /q

R = retardation factor
rb = bulk density = rs(1-q)
rs = solids density
q = porosity
kd = (soil) distribution coefficient = foc Koc
foc = fraction organic carbon
Koc = organic carbon/water partition coefficient
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