**Input**

*x (downgradient location of interest): * ** **

**t (time of interest): **

**Co (constant source concentration): **

**v (groundwater velocity): **

Go to groundwater velocity calculator

**D (dispersion): **

**R (retardation factor): **

**Go to retardation calculator**

****KEEP UNITS CONSISTENT****

**Results:**

*Concentration****: **

*** Concentration will have same units as Co**

**Example**** (from Fetter, 1994):**

A landfill is leaking leachate with a chloride concentration of 725 mg/L, which enters an aquifer with the following properties:

Hydraulic conductivity = 3.0 x 10^{-3} cm/s

dh/dl (hydraulic gradient) = 0.0020

Effective porosity = 0.23

Dispersion = 2.4 x 10^{-7} m^{2}/s

Compute the concentration of chloride in 1 y at a distance 15m from the point where the leachate entered the groundwater. Chloride has a retardation factor of 1.0.

**Solution:**

Determine the groundwater velocity:

v_{x} = K(dh/dl)/n_{e} (click to go to velocity calculator)

v_{x} = 3.0 x 10^{-5} m/s x 0.0020/0.23 = 2.6 x 10^{-7} m/s

Using all this data, and converting the time from 1 year into 3.15 x 10^{7} seconds, the concentration at 15 m would be approximately 30 mg/L.

* Reference*

Fetter, C.W. (1994). Applied Hydrogeology, Third Edition. Published by Prentice-Hall Inc., New Jersey, USA.