Contaminant Fate and Reactive Transport in Groundwater - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 872

stoichiometric ratio (number of moles of acceptor needed to degrade 1 mole of
donor). Maier and Grathwohl ( 2006 ) report a similar empirical correlation:

C D γ
C A

0.3

0.5 M 2
α T

L = (19.20)

In the same plot the dependence of the plume length on biodegradation rate
constant is shown (triangles). The reaction kinetics have a strong influence on
steady state plume length as long as the reaction is slow and acts as limiting fac-
tor (lower portion of the plot). When the degradation rate is fast, the supply rate
of electron acceptor to the plume by transverse mixing becomes the limiting pro-
cess and the plume length turns out to be independent of the biodegradation rates.
Biodegradation kinetics also determines the shape of the contaminant plume and
the consumption of electron acceptors, as can be observed from the results of the
simulations shown in Fig. 19.10 . Simulations of toluene transport and aerobic degra-
dation were performed using two different degradation rate constants. With fast,
almost instantaneous degradation kinetic, the steady state plume is shorter and the
vertical gradients of electron donor and acceptor do not overlap. When the degra-
dation rate constant was set to a lower value, a longer plume was computed as well
as the overlapping of the toluene and oxygen vertical gradients. This overlapping
indicates that, in the second case, the degradation rate and no more the transverse
mixing is the limiting factor for the overall biodegradation.
Also the amount and quality of the infiltrating water from the surface affects
the fate and transport of contaminant plumes in shallow groundwater systems. The
recharge enhances the dilution of the plume and acts as a new source of electron
acceptors and nutrients, which adds a positive effect on the overall biodegradation
capacity of the aquifer. Simulations were performed with the composition of the

10 − 10 mol L − 1 s − 1 )andaslow

Fig. 19.10 Simulated toluene plumes assuming a fast ( k = 5 ×

10 − 12 mol L − 1 s − 1 ) biodegradation rate constant and corresponding vertical profiles of
toluene and oxygen at a longitudinal distance of 100 m

( k = 1 ×