HODGES, Rex, rhodges@clemson.edu, and MURDOCH, Larry, lmurdoch@clemson.edu,   Department of Geological Sciences, Clemson Univ., 340 Brackett Hall, Box 341908, Clemson, SC 29634-1908; and NILSSON, Bertel, bn@geus.DK, and HARRAR, Bill, bwh@geus.DK,GEUS, Thoravej 8, 2400 Copenhagen, NV, Denmark

Clayey tills a few 10’s of meters thick cover 40 % of Denmark and provide rich soils for agriculture.  These tills were previously thought to protect underlying aquifers from potential contaminants released at the surface, primarily pesticides from agricultural activities.  However, macropores (fractures and bio-pores) allow for “rapid” transport of contaminants through the till to aquifers below.  Mapping of macropores in excavated pits (Klint and Graveson, 1997, 1998) clearly show the transport pathways.  The fractures occur in both vertical and horizontal sets.  The deeper fractures are attributed to glacio-tectonic forces (loading and unloading).  The shallow fractures are attributed to dessication and freeze/thaw.
    A twelve day pump test was performed in May and June of 1997 to determine the transmission properties of the system at Flakkejberg, located in east central Denmark.  The aquifer below the glacial till is 15 meters thick and is primarily a fine to medium sand with a 1.5 meter zone of fine sand at the top.  The pumping well is screened over the upper 5 meters of the medium sand, immediately below the fine sand.  The well was pumped at 331 meters3/day (60 gpm) with a resulting drawdown of 3.5 meters.  Observation wells are located in the fine sand above the pumped zone and at higher zones within the till (10 meters thick).  In order to get conductivity estimates of the till as well as the pumped aquifer, curve matching was performed using MODFLOW (GW Vistas).
    A tracer test was performed in December of 1997.  Bromide and chloride was injected by way of a covered pit.  Tracer movement was monitored through 20 samplers (from 2 to 8.5 meters deep) installed in the till directly below the center of the injection pit.  Within days of the release, a pulse was detected at the 7.25 meter level and after 4 months, a second pulse was recorded at 4 meters.  Two years after the release, the main front has yet to reach 5 meters.  Transport was modeled using FracTran, a 2D simulator for saturated GW flow and solute transport in porous or discretely-fractured porous media (Sudicky and McLaren, 1998).