Modeling mass transport effects in Partitioning Inter-well Tracer Tests

Partitioning Inter-well Tracer Tests (PITTs) permit estimation of DNAPL in aquifers. In the PITT, tracers are injected at one or more wells, move across the contaminated domain, and are then extract- ed. One tracer is nonpartitioning; the other partitions between DNAPL and water, so its concentration peak at the recovery well(s) is retarded and broadened. The tracers' peak shapes and positions permit estimation of the quantity of DNAPL between the wells. H(ow)ever, mass transport kinetics affect the rate at which tracer redistributes between DNAPL and water. Also, movement of both tracers is retarded by diffusion into porous l(ow)-permeability clay, etc. These effects can confound interpretation of results. Column and two-dimensional field PITT models are described which include diffusion-limited partitioning of tracer in DNAPL and diffusion of tracers into/from clay. The dependence of tracer concentration peaks on kinetic effects is modeled. Results on the sensitivity of PITT estimates of DNAPL are examined.