Je. Landmeyer et al., ASSESSMENT OF NATURAL ATTENUATION OF AROMATIC-HYDROCARBONS IN GROUNDWATER NEAR A FORMER MANUFACTURED-GAS PLANT, SOUTH-CAROLINA, USA, Environmental geology, 34(4), 1998, pp. 279-292
Citations number
30
Categorie Soggetti
Water Resources","Environmental Sciences","Geosciences, Interdisciplinary
Shallow, anaerobic groundwater near a former manufactured-gas plant (M
GP) in Charleston, South Carolina, USA, contains mono- and polycyclic
aromatic hydrocarbons (MAHs and PAHs, respectively). Between 1994 and
1997, a combination of field, laboratory, and numerical-flow and trans
port-model investigations were made to assess natural attenuation proc
esses affecting MAH and PAH distributions. This assessment included de
termination of adsorption coefficients (K-ad) and first-order biodegra
dation rate constants (K-bio) using aquifer material from the MGP site
and adjacent properties. Naphthalene adsorption (K-ad = 1.35 x 10(-7)
m(3)/mg) to aquifer sediments was higher than toluene adsorption (K-a
d = 9 34 x 10(-10) m(3)/mg), suggesting preferential toluene transport
relative to naphthalene. However, toluene and benzene distributions m
easured in January 1994 were smaller than the naphthalene distribution
. This scenario can be explained, in part, by the differences between
biodegradation rates of the compounds. Aerobic first-order rate consta
nts of C-14-toluene, C-14-benzene, and C-14-naphthalene degradation we
re similar (-0.84, -0.03, and 0.88 day(-1), respectively), but anaerob
ic rate constants were higher for toluene and benzene (-0.002 and -0.0
0014 day(-1), respectively) than for naphthalene (-0.000046 day(-1)).
Both areal and cross-sectional numerical simulations were used to test
the hypothesis suggested by these rate differences that MAH compounds
will be contained relative to PAHs. Predictive simulations indicated
that the distributions of toluene and benzene reach steady-state condi
tions before groundwater flow lines discharge to an adjacent surface-w
ater body, but do discharge low concentrations of naphthalene. Numeric
al predictions were ''audited'' by measuring concentrations of naphtha
lene, toluene, and benzene at the site in early 1997. Measured naphtha
lene and toluene conentrations were substantially reduced and the area
l extent of contamination smaller than was both observed in January 19
94 and predicted for 1997. Measured 1997 benzene concentrations and di
stribution were shown to be relatively unchanged f rom those measured
in 1994, and similar to predictions for 1997.