# Solution Exercise 2

Assume one-dimensional flow for the purpose of calculations and consider the rate of *S* consumption in a 1 L cube of aquifer material (10 cm x 10 cm x 10 cm).

Determine the amount of *S* in the 1 L aquifer cube which weighs:

We know *S* is 0.02 percent of the dry material by weight, so:

*NO*_{3}^{–}*–**N* flux through the cube is determined as follows.

From Equation 14, 1 M of *NO*_{3}^{–}*–**N* will consume 10/14 M *S*:

Given that there is 0.36 g *S* in each 1 L cube of aquifer, each cube has sufficient *S* to support autotrophic denitrification of a plume for 0.052 years as shown below.

= =

Thus, the *NO*_{3}^{–}*–**N* plume will advance 10 cm every 0.052 yr, or one could say it can consume all *S* from 19.2 cubes each year (1/0.052=19.2), which is a rate of *NO*_{3}^{–}*–**N* plume advance of 192 cm/yr. Another way to calculate the advance rate is as follows.