Fh. Chapelle et al., MEASURING RATES OF BIODEGRADATION IN A CONTAMINATED AQUIFER USING FIELD AND LABORATORY METHODS, Ground water, 34(4), 1996, pp. 691-698
Rates of biodegradation were measured in a petroleum hydrocarbon-conta
minated aquifer using a combination of field and laboratory methods. T
hese methods are based on tracking concentration changes of substrates
(both electron donors and accepters) or final products of microbial m
etabolism over time. Ground water at the study site (Hanahan, South Ca
rolina) is anoxic, and sulfate reduction is the predominant terminal e
lectron accepting process. Laboratory studies conducted with sediment
cored from the site showed that C-14-toluene was mineralized to (CO2)-
C-14 with a first-order degradation rate constant (k(tol)) of -0.01 d(
-1) under sulfate-reducing conditions, Under nitrate-amended, Fe(III)-
amended, or nonamended (methanogenic) conditions, toluene was not sign
ificantly mineralized, C-14-Benzene was degraded at low but measurable
rates (k(ben) = -0.003 d(-1)) under sulfate-reducing conditions where
as degradation under methanogenic conditions was negligible, These res
ults illustrate the extreme sensitivity of laboratory-measured biodegr
adation rates to terminal electron-accepting conditions, and show the
necessity of carefully matching experimental conditions to in situ con
ditions. Concentration decreases of toluene along aquifer flowpaths, w
hen the uncertainty of ground-water Bow velocities was considered, ind
icated k(tol) values ranging from -0.0075 to -0.03 d(-1). Concentratio
n decreases of sulfate and concentration increases of dissolved inorga
nic carbon (DIC), when normalized for assumed stoichiometric oxidation
of toluene coupled to sulfate reduction, yielded a k(SO4) range of -0
.005 to -0.02 d(-1), and a k(DIC) value range of +0.00075 to +0.003 d(
-1). Because both laboratory and field methods have numerous sources o
f uncertainty, a combination of these methods is the most appropriate
procedure for evaluating biodegradation rate constants in contaminated
ground-water systems.