THE 1978 BORDEN TRACER EXPERIMENT - ANALYSIS OF THE SPATIAL MOMENTS

A reanalysis of the 1978 tracer experiment at Borden, Ontario, is perf ormed using spatial moments. The tracer experiment involved the unifor m injection of chloride ions into an aquifer, and the resulting plume was allowed to migrate under natural gradient conditions. Detailed mon itoring of the evolving plume was then performed in three dimensions. The work of Sudicky et al. (1983) showed that the solute cloud evolved as two plumes owing to variations in hydraulic conductivity at the si te. In this paper we compute the zeroth through the fourth spatial mom ents of the plume in the lower hydraulic conductivity zone. From these moments the solute mass of the plume, the velocity of the center of m ass, the dispersion, the skew, and the kurtosis of the plume are calcu lated. These results are compared with the results of Sudicky et al. a s well as with the theoretical results of Gelhar et al. (1979) and Naf f (1990). Our computed plume velocity and apparent horizontal transver se macrodispersivity are in agreement with the estimates of Sudicky et al.; however, our apparent longitudinal macrodispersivity estimate ex ceeds that of Sudicky et al. by a factor of 2. The apparent horizontal transverse macrodispersivity obtained is also quite similar to that o f Freyberg (1986). At early times, the plume is found to be positively skewed as well as platykurtic. This supports the findings of Gelhar e t al. and contradicts those of Naff.