Spatial Variability of Contaminant Transport in a Fractured Till, Avedøre Denmark

Abstract

A field experiment shows that rapid downward migration of solutes and microorganisms can occur in a fractured till. A solute tracer, chloride, and a bacteriophage tracer, PRD-1, were added to groundwater and allowed to infiltrate downwards over a 4 × 4 m area. Chloride was detected in horizontal filters at 2.0 m depth within 3-40 days of the start of the tracer test, and PRD-1 was detected in the same filters within 0.27 - 27 days. At 2.8 m depth chloride appeared in all the filters, but PRD-1 appeared in only about one-third of the filters. At 4.0 m depth chloride appeared in about one-third of the filters and trace amounts of PRD-1 were detected in only 2 of the 36 filters. Transport rates and peak tracer concentrations decreased with depth, but at each depth there was a high degree of variability. The transport data is generally consistent with expectations based on hydraulic conductivity measurements and on the observed density of fractures and biopores, both of which decrease with depth. Transport of chloride was apparently retarded by diffusion into the fine-grained matrix between fractures, but the rapid transport of PRD-1, with little dispersion, indicates that it was transported mainly through the fractures.

The implications of groundwater velocity variations on microbial transport and wellhead protection – review of field evidence

“…Evidence from studies in several hydrogeological environments is presented in Table 1. The results of field studies are supported by numerical modelling which shows that, as the heterogeneity Horizontal transport of f2 bacteriophages slightly faster (Â 1.6-1.9) than bromide over 1-3 m [30] Horizontal transport of stained, indigenous bacteria (32 m day À1 ) slightly faster than bromide (25 m day À1 ) [31] Glacial till (fissured) Vertical transport of PRD-1 coliphage (7.4 m day À1 ) >10 faster than chloride (0.7 m day À1 ) over 2 m [32] Horizontal transport of PRD-1 and MS-2 phage (2.5 to >5 m day À1 ) >35 faster than bromide (0.01-0.07 m day À1 ) over 4 m [25] Chalk (fissured) Horizontal transport of bacteriophages (2 wild coliphage, Serratia marcescens) more rapid (2.4 km day À1 ) than bulk groundwater flow over 366 m [33] Horizontal transport of bacteriophage (Serratia marcescens) ($2 km day À1 ) and MS-2 coliphage ($150 m day À1 ) more rapid than bulk groundwater flow over 2-3 km [34] Granite (fractured) Horizontal transport of Bacillus stearothermophilis more rapid (1 m day À1 ) than bulk groundwater flow over 29 m [35] Horizontal transport of Escherichia coli (90 m day À1 ) $9 faster than bromide (11 m day À1 ) over 12.7 m [36] of porous media increases, microbial (and colloidal) transport can be facilitated to the extent that the arrival of these tracers precedes that of conservative tracers [37,38]. Sets of groundwater flow velocities via linked groundwater pathways in unconsolidated and fissured media are represented conceptually in Fig.…”

Differential transport and dispersion of colloids relative to solutes in single fractures

“…Experimental studies in both porous [1][2][3][4] and fractured (e.g., [5][6][7]) media have demonstrated that the average transport velocity of colloid tracers may be larger than that of both water molecules and molecular-scale conservative tracers. This phenomenon is commonly referred to as differential transport.…”

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).…”