1. Polychlorinated biphenyls (PCBs) are a widespread sediment contaminant. To sequester this

contaminant, an "active cap" consisting of an adsorbent material can be used (Fig. 1). A study

was published in 2006 by Murphy et al. to compare the performance of different types of cap

material: sand, coke, and activated carbon.

(a) Plot in Excel or another spreadsheet software the breakthrough curve for Cout(t)/Cin vs. t

exiting the 1.25 cm capping layer, if there is no degradation (see next page for example

spreadsheet setup). The range on the time axis for your plot should be selected to clearly

observe when complete breakthrough has occurred - note the time scales may be

extremely different (by several orders of magnitude) for the three different capping

materials; therefore, prepare three separate plots for sand, coke, and activated carbon.

Write a sentence explaining the differences in the time to breakthrough for the three

materials, in terms of the advection-dispersion-adsorption parameters in Table 1.

(b) Repeat part (a) if PCB has a half-life of 50 years and undergoes 1st order decay

(biodegradation) in the capping layers. Plot the Cout(t)/Cin vs. t results onto the same plot

that you made in part (a) for each capping material. Write a sentence explaining the trend

in the final (steady-state) concentration that exits the capping layer for the three different

materials when the degradation reaction is included.