STOCHASTIC-ANALYSIS OF CONCENTRATION MEASUREMENTS IN THE TRANSPORT EXPERIMENT AT TWIN-LAKE SITE

A procedure to identify the parameters characterizing flow and transpo rt in heterogeneous aquifers with the aid of concentration measurement s in tracer field experiments is developed. Unlike previous studies, w hich employed the measured plume spatial moments at different times an d their theoretical expressions, we rely here on breakthrough curves a nd temporal moments in order to analyze the field tests at Chalk River Site. In these experiments, breakthrough curves of a radioactive trac er were measured continuously at a large number of points in parallel control planes. We derive theoretical expressions of the temporal mome nts of the breakthrough curves by the same Lagrangian approach that wa s used previously for spatial moment. We assume a stationary random ve locity field of constant mean and relate it to the axisymmetric log co nductivity covariance by a first-order approximation in the variance, with neglect of the effect of pore-scale dispersion. The final theoret ical results relate the temporal moments to U (the mean velocity), sig ma(Y)(2) (the log conductivity variance), I-Yh (the horizontal integra l scale), and b(e) (a function of the anisotropy ratio e = I-Yv/I-Yh). By assuming ergodicity, we identify the temporal moments at the Chalk River Site experiment from measured breakthrough curves. With the aid of the theoretical results and by a best fit we could estimate U, sig ma(Y)(2), I-Yh, and I-Yh/b(e). An attempt to identify the vertical and transverse integral scales from temporal-spatial moments in the contr ol planes was not successful. We took advantage of the dense measureme nts of breakthrough curves along vertical transects (at intervals of 1 cm) in order to identify the experimental concentration two-point cov ariance. We derived a simplified theoretical expression for its depend ence on the log conductivity vertical integral scale I-Yv, which was i dentified by a best fit with experimental results. This procedure, app lied for the first time to analysis of field tests, led to the identif ication of the estimates of sigma(Y)(2), and I-Yh, as well as of their variances of estimation.