HR: 0800h
AN: H11B-0305    [Abstracts]
TI: Effect of Embedded Sand Lenses on Transport in Till
AU: * Petersen, D L
EM: dittepe@m5.stud.ku.dk
AF: University of Copenhagen, Oster Voldgade 10, Copenhagen, DK-1350 Denmark
AU: Jensen, K H
EM: khj@geol.ku.dk
AF: University of Copenhagen, Oster Voldgade 10, Copenhagen, DK-1350 Denmark
AU: Nilsson, B
EM: bn@geus.dk
AF: Geological Survey of Denmark and Greenland, Oster Voldgade 10, Copenhagen, DK-1350 Denmark
AB: Till deposits were previously considered to provide an effective protection against contamination of underlying aquifers from surface spills or application of nutrients and pesticides. However, several investigations have now documented that fractures in the till constitute preferential pathways for contaminants thus undermining the protective nature of till. Furthermore, till often contains embedded sand lenses of varying thickness and lateral extent which also may facilitate a rapid transport of contaminants towards deeper aquifer systems. In this research we have investigated the spatial distribution of the embedded sand lenses in a till block and examined their impact on solute transport by numerical modeling. In a till block of dimensions 100m x 50 m x 8m a total 32 cone penetration tests were carried to map the presence of embedded sand lenses. The data were analyzed in a geostatistical framework using the Transition Probability Geostatistical Software (TPROGS) and on this basis a number of realizations were generated of the spatial distribution of the sand lenses in the till. These realizations were subsequently imported into the GMS modeling system for simulations of flow, particle tracking and solute transport. In the simulations a vertical head gradient was enforced over the block and no-flow conditions were specified along the vertical planes hereby focusing on the vertical transport characteristics. Flux-averaged breakthrough curves across the lower boundary were simulated following a release of tracer across the upper boundary. The simulations documented that the presence of embedded sand lenses in the till block has a significant impact on the transport pattern by causing a more rapid breakthrough and a longer tailing. The study suggests that the presence of the sand lenses leads to a further reduction in the protective capability of till deposits.
DE: 1829 Groundwater hydrology
DE: 1832 Groundwater transport
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting