Hydro G Final report - Kildare.ie

Hydro-G FINAL REPORT
3.3.2. Hydrochemical Interpretative Summary
The physiochemical monitoring carried out in situ revealed significant differences in water
characteristics throughout the site during two sampling occasions (10/12/2007 & 16/01/2008) and
this suggests presence of different sources of water within the site.
It is evident that water temperatures decrease from the south to north direction, as does the electric
conductivity. The relative increase in both water temperature and EC that was recorded in the ‘irony
spring’ (monitoring point 7) suggests small leakage from the canal. In the next, further down
gradient sampling location, it was also noted that both the temperature and EC were higher in the
Upper Pond than in the Lower. In addition, lower temperature and EC in localised places around the
ponds suggest multiple sources of water at these locations, i.e cold springs which mix with warmer
water coming from the Spa Well. These cold springs are likely to originate in the shallow system,
which is expected to be cooler and less mineralised in comparison to water discharging from the
deeper system at the Spa Well. Abundance of calcite precipitated in this area and specifically around
the Lower Pond (monitoring point 18) suggests that groundwater discharges at this location.
Integration of field data suggests that while the Upper Pond is fed by the Spa Well, the Lower Pond
also has inputs from the shallow groundwater system.
Water flow on the second terrace is by flow along the ground surface, which prevented monitoring of
physio-chemical parameters.
At the third terrace, there was an abundance of water flow and sources. Water was noted to enter
from both overland flow and also from various sources directly in the ground and bedrock face.
There were two sampling points on the fourth terrace but these were located within formed surface
water channels. No direct groundwater discharge points were identified.
The drain on the Intel site at the western boundary of the Leixlip Spa site contains water at its
northern end only, which finishes at the approximate elevation of the Roman Bath (monitoring point
24). Hydrochemical data from this location suggested water originating from surface runoff.
With respect to total dissolved solids (TDS), these were found generally high at all terraces ~700-
1000 ppm and its distribution at different locations is similar to that of electric conductivities.
All the sampling locations showed alkaline conditions and were lowest in the Spa Well water.
Subsequently, lower pHs were also found in places linked to the underground discharge from the Spa
Well (monitoring points 8 and 11). Higher pH levels were found in places associated with cold
springs and that supports the hypothesis that this water originates from the shallow system which is
in contact with the alkaline bedrock. At lower terraces, the pH was generally higher.
All laboratory samples collected at the Leixlip Spa site show very high mineralisation. The ionic
balance analysis based on the hydrochemistry results showed that the majority of samples are of
sodium-chloride (Na-Cl) signature, except for one sample – the Intel drain, which presented calcium
bicarbonate character (Ca-HCO3). The sodium-chloride water signature dominates at this site
because of high concentrations of chloride delivered to the site from the Spa Well. Sodium-chloride
water is associated with older groundwater (Minerex, 1983). This type of water was found at
monitoring locations on all terraces of the site; from the discharge drain feeding from the Spa Well to
the wetland ponds area, in the Roman Bath and as far down as at the boundary between the fourth
terrace and the flood plain. The fact that all samples from the Lexlip Spa site are of the same
character suggests that majority of water originates from the Spa Well, although some dilution with
more recent, less mineralised water is evident. This is specifically reflected in decreasing chloride
Project No.: 07_136 -11-
Leixlip Spa