The growing realization that many of the challenging questions regarding contaminant transport in groundwater must be resolved by careful field experiments, led to the convening of this symposium, which was sponsored by AGU's Groundwater Committee. The half-day symposium was held during the recent spring AGU meeting and attracted around 150 individuals.

The 13 papers presented included five invited talks. A list of authors and complete abstracts can be found in Eos (65, April 17, 1984, p. 206). Three papers discussed the results of controlled field tracer tests performed at the Chalk River Nuclear Laboratory and Borden landfill sites in Ontario, while three other papers covered tracer tests (one involving the use of heat as a tracer) at sites in Alabama and Illinois. One of the tests at the Chalk River site included the equivalent of 750,000 point measurements of iodine 131 during a natural gradient tracer test at distances as far as 40 m from the injection well. These papers demonstrated that dispersion in principle can be described by the classical advection-dispersion model provided that accurate three-dimensional velocity and permeability distributions are measured. When this is done, the resulting dispersivities are not scale dependent and are quite close to laboratory measurements. The papers also demonstrated that organic contanimants may be subject to chemical nonequilibrium processes during transport.