# EPA On-line Tools for Site Assessment Calculation

 Notice 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 Date Distance Unit ft m Time Unit days years Chemical mtbe benzene toluene ethylbenzene o-xylene p-xylene m-xylene total xylenes other Porosity Fraction Organic Carbon Hydraulic Conductivity (K) ft/day m/day ft/min cm/sec gal/day/ft2 Upgradient Location (x1,y1) Downgradient Location (x2,y2) Head unit ft m Upgradient Water Level (h1) Downgradient Water Level (h2)

 Defaults
 Koc

 Intermediate Results
 Hydraulic Conductivity (K) ft/day m/day ft/min cm/sec gal/day/ft2 Bulk Density (rb) kd Retardation factor (R) Gradient (i)

 Main Result
 Seepage Velocity (qs = v) ft/day ft/yr m/day m/yr 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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