Groundwater Hydrology Homework #6 Due: Wed., October 24, 2001

Fit a Peclet number to the lab data using the BTC spreadsheet.

What is the dispersion coefficient?

The dispersivity?

Show the expected plot of C/C
0
vs pore volumes for a chemical that has a k d
of 0.2 L/kg.

Using the Domenico model on the spreadsheet to do problem 6-10.

Plot C/C
0
versus distance.

Determine C at 200 m.

Let the data from 6-10 be one case.

Show another case where there is degradation with a half-life of four years.

Show another two cases with Pe = 10 for the longitudinal dispersion, and
 transverse
=1/3
 long and
 vertical
= 1/10
 long
with and without degradation.

Which variable has the most affect on concentration?

Do Problem 6-6.

10 kg of MTBE is spilled into 50 m 3 of saturated aquifer with a porosity of 0.35. A well is 1000 m downgradient of the spill. The hydraulic conductivity of the aquifer is 0.15 m/day and the hydraulic gradient is 0.012. MTBE sorbs to the aquifer material with a distribution coefficient of k d
= 0.1.
Assuming no degradation, use the BTCfit spreadsheet to plot the approximate concentration of MTBE at the well as a function of time.

At a remediation site, natural attenuation is being evaluated as the remediation alternative. Sampling data from 13 monitoring wells sampled on June 1, 2000 show an average concentration of 16 mg/L benzene. Moment analysis on the data indicates that there is a total of 213 kg of benzene at the site.
The sampling data from March 3, 2001 indicate that there is a total of 152 kg of benzene at the site.

Assuming that the mass is lost through biodegradation, what is the degradation rate constant?

What is the half-life of benzene at the site?

When would you predict that the average concentration would be below the cleanup level of 0.1 mg/L?