A Hydrogeological Study of Irish Holy wells

Abstract

The overall aim of the research was to characterise the hydrogeology and water chemistry of Irish holy wells. The first main research task was an analysis of the distribution of Irish holy wells (listed in a national database of 2676 wells with grid references) using a Geographical Information System (GIS). Holy wells were shown to be located in all of the main lithological groups and aquifer categories, and they occur as frequently in aquifers classed as poorly productive as they do in the regionally important aquifers. However, there is a higher density of holy wells in areas classed as having Extreme or High groundwater vulnerability than in the Moderate or Low vulnerability areas. Field surveys were then carried out at 215 holy well and five spa well sites. The surveys confirmed that the majority of holy wells are small springs and seepages, which issue from shallow unconfined aquifers where the groundwater vulnerability is often classed as Extreme or High.

A total of 238 water samples were collected for analysis from 167 holy wells and five spa wells. These included duplicates, repeat samples, and samples from four wells selected for monitoring over a 2-year period. The samples were analysed for 60 parameters, comprising major and minor ions and trace elements. As expected, the main water type was calcium-bicarbonate. Parametric and non-parametric statistical tests showed that there were significant differences in water chemistry between different lithological groups, especially between the carbonate lithologies (pure and impure limestones, sands and gravels, and mixed bedrock and gravel groups) and non-carbonate lithologies (non-calcareous sedimentary, igneous and metamorphic bedrock groups). Proximity to the sea was also a major influence on chemistry. Nitrate concentrations were above background levels in 52% of the wells, indicating that anthropogenic influences were widespread.

Reports of general or specific health cures were found for 57% of the wells surveyed and sampled. The most common of the named cures was for eye ailments. Statistical tests did not identify any linkage between the reported cure and the water chemistry in the majority of cases. However, sodium and chloride values in wells with reputations for eye cures were significantly different compared to the other wells, the median concentrations of both ions being higher in the eye wells. Eye wells were found to be more common close to the coast, where elevated sodium and chloride values would be expected in local groundwaters. The potential nutritional benefits of drinking water from holy wells were also examined, and it was shown that a water supply from a well could provide useful contributions to the recommended daily intake of calcium, magnesium and iron, especially where diets are poor.

The value of holy wells as therapeutic landscapes, heritage sites and community amenities was also examined, noting that many holy wells have been covered over or infilled over the years. The thesis ends with a set of recommendations regarding the management, protection and cataloguing of holy wells, with specific recommendations for including holy wells as County Geological Sites.