| dc.description.abstract | The vulnerability to pollution and hydrochemical variation of groundwater in the mid-west karstic
lowlands of Ireland were investigated from October 1992 to September 1993, as part of an EU
STRIDE project at Sligo Regional Technical College. Eleven springs were studied in the three
local authority areas of Co. Galway, Co. Mayo, and Co. Roscommon. Nine of the springs drain
locally or regionally important karstic aquifers and two drain locally important sand and gravel
aquifers. The maximum average daily discharge of any of the springs was 16,000 m3/day.
Determination of the vulnerability of groundwater to pollution relies heavily on an examination of
subsoil deposits in an area since they can act as a protecting or filtering layer over groundwater.
Within aquifers/spring catchments, chemical reactions such as adsorption, solution-precipitation
or acid-base reactions occur and modify the hydrochemistry of groundwater (Lloyd and
Heathcote, 1985). The hydrochemical processes) that predominate depend cm the mineralogy of
the aquifer, the hydrogeological environment, the overlying subsoils, and the history of
groundwater movement.
The aim of this MSc research thesis was to investigate the hydrochemical variation of spring
outflow and to assess the relationship between these variations and the intrinsic vulnerability of
the springs and their catchments. If such a relationship can be quantified, then it is hoped that the
hydrochemical variation of a spring may indicate the vulnerability of a spring catchment without
the need for determining it by field mapping. Such a method would be invaluable to any of the
three local authorities since they would be able to prioritise sources that are most at risk from
pollution, using simple techniques of chemical sampling, and statistical analysis.
For each spring a detailed geological, hydrogeological and hydrochemical study was carried out.
Individual catchment areas were determined with a water balance/budget and groundwater
tracing. The subsoils geology for each spring catchment were mapped at the 1:10,560 scale and
digitised to the 1:25,000 scale with AutoCad™ and Arclnfo™. The vulnerability of each spring
was determined using the Geological Survey's vulnerability guidelines. Field measurements and
laboratory based chemistry analyses of the springs were undertaken by personnel from both the
EPA Regional Laboratory in Castlebar, Co. Mayo, and the Environment Section of Roscommon
Co. Council. Electrical conductivity and temperature (°C) were sampled fortnightly, in the field,
using a WTW microprocessor conductivity meter.
A percentage (%) vulnerability was applied to each spring in order to indicate the areal extent of
the four main classes of vulnerability (Extreme, High, Moderate, and Low) which occurred
within the confines of each spring catchment. Hydrochemical variation for the springs were
presented as the coefficient of variation of electrical conductivity. The results of this study show
that a clear relationship exists between the degree of vulnerability of each catchment area as
defined by the subsoil cover and the coefficient of variation of EC, with the coefficient of
variation increasing as the vulnerability increases. The coefficient of variation of electrical
conductivity is considered to be a parameter that gives a good general reflection of the degree of
vulnerability occurring in a spring catchment in Ireland's karstic lowlands. | en |
