K = 3.0 x 10^-5m/s

dh/dl = 0.002

effective porosity = 0.23

dispersivity () = 10m

dispersivity in the y is 1/5^th that in the x direction

dispersivity in the z is 1/10^th that in the x direction

D* = 1 x 10^-9m²/s

Calculate the contaminant concentration in a ground-water sample collected from a well 15 meters down gradient after 1 year. The well has a total depth of 14 meters and is screened from 13 to 14 meters depth. The well is offset laterally from the center of the tank by a distance of 5 meters. When you want to confirm your answer, click answer for the value.

For your convenience, I include the appropriate expression here:


    
     
where:
C_o = source concentration [M/L³]
C = concentration [M/L³]
x = distance from the source in the direction of flow
y, z = orthogonal distances from the center of the plane source
= average linear velocity of ground water [L/T ]
t = time since continuous concentration release began [ T ]
D_x, D_y, D_z = dispersion coefficients in the x, y, & z directions [L²/T ]

Note: dispersivity varies with scale of plume migration, as well as, direction and each dispersivity is multiplied by the velocity in the x direction

erf = the error function ERF
erfc = the complimentary error function ERFC

FOR DOWNWARD SPREADING ONLY, substitute Z for Z/2

FOR NO SPREADING IN THE z DIRECTION, increase CO/8 to CO/4 and omit the erf terms for z.

Calculate your answer, being extremely careful with respect to using consistent units and noticing how the answer is expressed (e.g. as Concentration or relative Concentration, then check yourself by deciding whether the answer is reasonable, and visiting the key.