LAB AND FIELD-MEASUREMENTS OF THE HYDRAULIC CONDUCTIVITY OF CLAYEY SILTS

Various lab and held experiments were conducted to determine the verti cal hydraulic conductivity of two highly compressible, organic-rich cl ayey silts (Holocene marsh sediments Klei and gyttja). Constant-head p ermeameter tests in the lab show an increase in measured hydraulic con ductivity with sample size by a factor of 5 (Klei) and 20 (gyttja). On a field scale, six different methods were tested: (1) evaluation of t he propagation of the tidal wave from the aquifer into the silts; (2) aquitard reaction test; (3) evaluation of aquifer drawdown; (4) slug t est; (5) evaluation of vertical profiles of measured organic contamina nt concentrations in the silts; (6) evaluation of benzene concentratio ns measured in aquifer wells. Porous cup pressure cells instead of pie zometers must be used to measure relatively fast changes of hydraulic head in these low-permeability media. Comparison of the results is ham pered by spatial heterogeneity.