English Abstract An in situ experiment using an injection/withdrawal
system was done with five pesticides (atrazine, 1,3-dichloropropene,
dinoseb, mecoprop and propachlor) at a location in Schaijk. Pesticides and
a tracer (chloride) were injected at 7 m below surface and withdrawn again
at the same depth 1.5 m downstreams. Sorption of pesticides was found to
be of little importance: only atrazine showed retardation by a factor of 1.3
three pesticides (1,3-dichloropropene, dinoseb and propachlor) disappeared
from the system ; their halflife times were 10 d, 1.3 d and 20 d
respectively. Mecoprop showed no reaction at all. The computercode PULS
which was developed for the interpretation of in situ experiments proved to
be appropriate for approximating sorption and tranformation constants both
for the in situ experiment in Schaijk and for experiments performed earlier.
With the simulation package METROPOL a good agreement was found between
measured and calculated breakthrough curves.