TY - JOUR
T1 - Migration of contaminants through the unsaturated zone overlying the Hesbaye chalky aquifer in Belgium
T2 - A field investigation
AU - Brouyère, Serge
AU - Dassargues, Alain
AU - Hallet, Vincent
N1 - Funding Information:
These field experiments were performed under the scope of a research project funded by the General Division for Natural Resources and Environment from the Ministry of Environment and Agriculture of the Walloon Region in Belgium. S. Brouyère also benefited from a 4-year PhD grant provided by the National Funds for Scientific Research of Belgium. The triaxial cell measurements were performed by the Laboratory of Geomaterials (Dr. Chr. Schroeder) at the University of Liège. Measurements of physical and hydraulic properties of unsaturated formations were performed by the Agricultural Hydraulics Unit (Prof. S. Dautrebande), from the Faculty of Agronomy in Gembloux, Belgium. Nitrate was analyzed by the Center of Agronomical Research of Gembloux (Vegetal Production Department). The lenacil pesticide was analyzed by Prof. Copin from the Faculty of Agronomy in Gembloux.
PY - 2004/8
Y1 - 2004/8
N2 - This paper presents the results of a detailed field investigation that was performed for studying groundwater recharge processes and solute downward migration mechanisms prevailing in the unsaturated zone overlying a chalk aquifer in Belgium. Various laboratory measurements were performed on core samples collected during the drilling of boreholes in the experimental site. In the field, experiments consisted of well logging, infiltration tests in the unsaturated zone, pumping tests in the saturated zone and tracer tests in both the saturated and unsaturated zones. Results show that gravitational flows govern groundwater recharge and solute migration mechanisms in the unsaturated zone. In the variably saturated chalk, the migration and retardation of solutes is strongly influenced by recharge conditions. Under intense injection conditions, solutes migrate at high speed along the partially saturated fissures, downward to the saturated zone. At the same time, they are temporarily retarded in the almost immobile water located in the chalk matrix. Under normal recharge conditions, fissures are inactive and solutes migrate slowly through the chalk matrix. Results also show that concentration dynamics in the saturated zone are related to fluctuations of groundwater levels in the aquifer. A conceptual model is proposed to explain the hydrodispersive behaviour of the variably saturated chalk. Finally, the vulnerability of the chalk to contamination issues occurring at the land surface is discussed.
AB - This paper presents the results of a detailed field investigation that was performed for studying groundwater recharge processes and solute downward migration mechanisms prevailing in the unsaturated zone overlying a chalk aquifer in Belgium. Various laboratory measurements were performed on core samples collected during the drilling of boreholes in the experimental site. In the field, experiments consisted of well logging, infiltration tests in the unsaturated zone, pumping tests in the saturated zone and tracer tests in both the saturated and unsaturated zones. Results show that gravitational flows govern groundwater recharge and solute migration mechanisms in the unsaturated zone. In the variably saturated chalk, the migration and retardation of solutes is strongly influenced by recharge conditions. Under intense injection conditions, solutes migrate at high speed along the partially saturated fissures, downward to the saturated zone. At the same time, they are temporarily retarded in the almost immobile water located in the chalk matrix. Under normal recharge conditions, fissures are inactive and solutes migrate slowly through the chalk matrix. Results also show that concentration dynamics in the saturated zone are related to fluctuations of groundwater levels in the aquifer. A conceptual model is proposed to explain the hydrodispersive behaviour of the variably saturated chalk. Finally, the vulnerability of the chalk to contamination issues occurring at the land surface is discussed.
KW - Chalk
KW - Dual porosity-dual permeability
KW - Loess
KW - Saturated zone
KW - Solute transport
KW - Tracer
KW - Unsaturated zone
UR - http://www.scopus.com/inward/record.url?scp=3042715292&partnerID=8YFLogxK
U2 - 10.1016/j.jconhyd.2003.10.009
DO - 10.1016/j.jconhyd.2003.10.009
M3 - Article
C2 - 15240170
AN - SCOPUS:3042715292
SN - 0169-7722
VL - 72
SP - 135
EP - 164
JO - Journal of Contaminant Hydrology
JF - Journal of Contaminant Hydrology
IS - 1-4
ER -