Fracture Aperture Measurements and Migration of Solutes, Viruses, and Immiscible Creosote in a Column of Clay‐Rich Till

Abstract

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 conductivity of the sample was 1.0 to 1.2 × 10–6 m/sec and the average hydraulic gradient during the tracer experiments ranged from 0.45 to 0.49. The experiments clearly show that ground‐water flow and contaminant migration through the sample is primarily controlled by fractures and root holes. Tracer experiments using a solute (chloride), colloid‐sized bacteriophage (PRD‐1 and MS‐2) and uncharged latex microspheres, indicated very fast transport rates of 4 to 360 m/day. These rates are similar to fracture flow velocities calculated on the basis of the measured bulk hydraulic conductivity of the column, and measured fracture spacing, using the cubic law for flow through parallel‐walled fractures. Fracture aperture values calculated from the ground‐water flow data (35 to 56 μxm) are of the same magnitude as values calculated from the breakthrough of tracers (13 to 120 μm). Aperture values calculated for fractures (1 to 94 μm) and root holes (2 to 188 μm), on the basis of measured immiscible creosote entry pressures, are also comparable with these values. The injected creosote, a DNAPL, penetrated most of the visible and a few invisible fractures and root holes, indicating that, for this till, fractures and root holes are important conduits for the transport of DNAPL's.

Evaluation of chloride and pesticide transport in a fractured clayey till using large undisturbed columns and numerical modeling

“…A test performed [Hinsby et al, 1996] showed that the conductivity meter measurements could be directly correlated with the breakthrough of chloride (measured by specific analyses). Recorded effluent conductivities (e e) were normalized (e * ) to influent conductivities (e i) with the expression e * = (ee --e background) / (ei -e background)' Influent and effluent p H were measured using a Radiometer oe H meter.…”

Fossil rootlet biopores as conduits for contaminant transport through clay horizons: a case study of DNAPL behaviour in Severn alluvium, UK

“…Models have been developed for understanding flow through fractured heavily fractured clay horizons, using the hydraulic aperture approach (e.g. McKay et al 1999;Hinsby et al 1996 and references therein), although Jørgensen et al (1998) found that this approach did not predict DNAPL movement in column experiments. Although high numbers of biopores were discovered per square metre (see Fig.…”

“…Douglas 1986;Driese et al 2001;McKay et al 1999McKay et al , 2005McKay and Fredericia 1995;Rodvang and Simpkins 2001;Rudolf et al 1991;Shaw and Hendry 1998) and the permeability with respect to contaminants such as coal tar and coal tar distillate polycyclic aromatic hydrocarbons (e.g. Hinsby et al 1996;Vulava et al 2007). Biopores are specifically holes that occur in soils/sediments due to plant growth and/or the action of animals earth worms (Oades 1993;Edwards et al 1988).…”

The modern water interface: recognition, protection and development — advance of modern waters in European aquifer systems

“…In particular, DNAPL often result in serious contamination problems (Pankow & Cherry 1996). The DNAPL are able to penetrate fractures with apertures of only a few micrometres relatively easy (Kueper & McWhorter 1991;Hinsby et al 1996;Pankow & Cherry 1996) and furthermore, due to their high densities, they are able to sink relatively deeply into the aquifers where they may contaminate old groundwaters (Bishop et aL 1993;Lawrence et al 1996;Pankow & Cherry 1996). DNAPL source zones are capable of contaminating very large amounts of groundwater with highly toxic components.…”