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Unsaturated zone travel time to groundwater on a vulnerable site
Richards, Karl G. Coxon, Catherine E. Ryan, Michael
Richards, Karl G.
Coxon, Catherine E.
Ryan, Michael
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2005
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Karl Richards, Catherine E. Coxon & Michael Ryan (2005): Unsaturated zone travel time to groundwater on a vulnerable site, Irish Geography, 38:1, 57-71
Abstract
A bromide (Br) tracing experiment was conducted to ascertain unsaturated zone
travel time to groundwater on a site with a karstified limestone aquifer overlain
by a thin free-draining overburden. Br tracer was applied to areas surrounding
two boreholes; soil solution and groundwater Br concentrations were monitored.
Bromide was first detected after eight and 34 days in the soil solution and
groundwater. The quick break-through of the applied Br in the soil solution and
groundwater indicates the presence of preferential flow in the soil at this site.
The time to maximum groundwater Br concentration supports a dominant
matrix flow path through the overburden and then preferential flow through the
unsaturated limestone bedrock. The results indicated that the transport of conservative
contaminants, such as nitrate, can be expected to occur in a single
recharge season. The occurrence of preferential flow raises concerns over rapid
transport of non-conservative contaminants such as faecal coliforms and this
merits further investigation.