Monitoring well interception with fractures in clayey till.
When using monitoring wells for investigation of contaminant sources in clayey till, there is a high risk that fractures may cause mobile contaminants to bypass the monitoring wells. This paper indicates that the probability of interception between monitoring wells and hydraulic conductive fractures is often significantly less than 50%. Based on a field experiment and application of a calibrated discrete fracture matrix diffusion numerical model (FRAC3Dvs), the paper also evaluates pesticide-monitoring results for different positions of monitoring well screen relative to fractures. For well screens situated 0.25 and 2 m from a conductive fracture, the first concentrations of the pesticide metabolite (2,6 dichlorobenzamide, "BAM") would be measured two years and 18 years, respectively, after the contaminant had been transported into an underlying aquifer. In this way, underlying aquifers may be subjected to contamination by downward moving contamination without being observed in monitoring wells in the till.
Jørgensen
Peter R
PR
Technical University of Denmark, Institute of Environment and Resources, DK-2800, Lyngby, Denmark. pej@er.dtu.dk
Klint
Knud Erik S
KE
Kistrup
Jens P
JP
D000538:Aluminum Silicates; D002138:Calibration; D000077215:Clay; D004784:Environmental Monitoring / Q000379:methods*; D008962:Models, Theoretical; D012989:Soil Pollutants / Q000032:analysis*; D014872:Water Movements; D014873:Water Pollutants / Q000032:analysis*
D000538:Aluminum Silicates; D012989:Soil Pollutants; D014873:Water Pollutants; D000077215:Clay