FRACTURE APERTURE MEASUREMENTS AND MIGRATION OF SOLUTES, VIRUSES, ANDIMMISCIBLE CREOSOTE IN A COLUMN OF CLAY-RICH TILL

A series of ground-water flow and tracer experiments were performed on an undisturbed column of fractured clay-rich till, 0.5 m diameter by 0.5 m long, in a pressure-controlled cell. The measured hydraulic cond uctivity of the sample was 1.0 to 1.2 X 10(-6) m/sec and the average h ydraulic gradient during the tracer experiments ranged from 0.45 to 0. 49. The experiments clearly show that ground-water flow and contaminan t migration through the sample is primarily controlled by fractures an d root holes. Tracer experiments using a solute (chloride), colloid-si zed bacteriophage (PRD-1 and MS-2) and uncharged latex microspheres, i ndicated very fast transport rates of 4 to 360 m/day. These rates are similar to fracture flow velocities calculated on the basis of the mea sured bulk hydraulic conductivity of the column, and measured fracture spacing, using the cubic law for flow through parallel-walled fractur es. Fracture aperture values calculated from the ground-water flow dat a (35 to 56 mu m) are of the same magnitude as values calculated from the breakthrough of tracers (13 to 120 mu m). Aperture values calculat ed for fractures (1 to 94 mu m) and root holes (2 to 188 mu m), on the basis of measured immiscible creosote entry pressures, are also compa rable with these values. The injected creosote, a DNAPL, penetrated mo st of the visible and a few invisible fractures and root holes, indica ting that, for this till, fractures and root holes are important condu its for the transport of DNAPL's.