MODELING OF PHYSICAL AND GEOCHEMICAL BEHAVIORS OF SALTWATER IN A COASTAL AQUIFER - Advances in Geosciences - page 251

MODELING OF PHYSICAL AND GEOCHEMICAL
BEHAVIORS OF SALTWATER IN A COASTAL AQUIFER
KEIGO AKAGI ∗,‡ ,TOSAOHOSOKAWA † , YOSHINARI HIROSHIRO ∗
and KENJI JINNO ∗
∗ Institute of Environmental System, Kyushu University
6-10-1, Hakozaki, Higasiku, Fukuoka, Japan
‡ [e-mail]
† Department of Urban Infrastructure, Kyushu Sngyo University
2-3-1, Matsukadai, Higashiku, Fukuoka, Japan
Groundwater quality is affected by the various reactions such as precip-
itation of dissolved ions, solid-liquid phase interaction, and the bacteria-
mediated reduction-oxidation process. The geochemical properties in coastal
aquifers are unique and important for the management of groundwater envi-
ronment. Although the studies analyzing the hydrological behaviors have been
intensively done up to now, a study of coupling both groundwater flow and
geochemical analysis is limited. In this study, the one-dimensional multicom-
ponent solute transport model which accounts for the cation exchange reaction
and the reduction reaction induced by anaerobic degradation is studied. It is
found out both through experiment and numerical simulation that the cation
exchange process is significant at the frontal part of the seawater infiltration,
while reducing process by the bacteria mediation takes places at the entire
soil column except for the top of the soil where dissolved oxygen infiltrates.
Saltwater intrusion into a coastal aquifer is a traditional but still important for
the hydro-geologists and civil engineers even at present time. Contamination of
salt is a trouble for various freshwater uses. Therefore, much attention has been
put on the movement and potential contamination. Meanwhile, the geophysi-
cal study is solely carried out. However, the consistent and accurate conclusion
will be hardly obtained due to the complicated and limited information on the
aquifer properties. In order to get a confident conclusion that can be agreed
by the researchers in various fields, an interdisciplinary approach anticipating
both hydrological and geochemical processes is indispensable.
1. Introduction
Although several computer codes are available at present to calculate the
transport of multi-chemical species in aquifers, the properties of response
of entity species are very complicated and dicult to appropriately set
the necessary soil geo-chemical parameters when many chemical elements
are involved. Specifically, bacteria-mediated reducing process in anaero-
bic condition requires the parameters representing the bacteria growth
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