wAbstract
@A long-term elution experiment to study the saturated transport
of pre-accumulated fertilizers by^products, was conducted within
a large tank (4~8~1.4 m) equipped with 26 standard piezometers.
Sandy sediments (35 m3), used to fill the tank, were
excavated from an unconfined alluvial aquifer near Ferrara (Northern
Italy); the field site was connected to a pit lake located in
a former agricultural field. To evaluate spatial heterogeneity,
the tank's filling material was characterized via slug tests and
grain-size distribution analysis. The investigated sediments were
characterized by a large spectrum of textures and a heterogeneous
hydraulic conductivity (k) field. Initial tank pore water composition
exhibited high concentration of nitrate (NO3-)
sulfate (SO42-) calcium (Ca2+),
and magnesium (Mg2+), due to fertilizer leaching from
the top soil in the field site. The initial spatial distribution
of NO3- and SO42-
was heterogeneous and not related to the finer grain-size content
(63Κm). The tank's material was flushed with purified tap water
for 800 days in steady-state conditions; out flowing water was
regularly sampled to monitor the migration rate of fertilizer
by-products. Complete removal of NO3-
and SO42- took 500 and 600 days,
respectively. Results emphasized organic substrate availability
and spatial heterogeneities as the most important constraints
to denitrification and nitrogen removal, which increase the time
required to achieve remediation targets. Finally, the obtained
clean-up time was compared with a previous column experiment filled
with the same sediments.
Keywords: Fertilizers; Aquifer; Pollution; Transport modeling;
Heterogeneitiesx
Introduction
Materials and methods
@Field site
@Tank set up
@Analytical methods
@Geostatistical analyses and three-dimensional visualization
@Modeling
Results and discussion
@Tank characterization
@Evolution of solute concentration distribution
@Comparison with column results
Conclusions
Acknowledgements
References