Hydro G Final report - Kildare.ie

Hydro-G FINAL REPORT
5. Conclusions and Recommendations
5.1 Field monitoring and data analysis suggest that water at the Leixlip Spa site originates from
a complex groundwater system combining two sources.
5.2 The main source of water comes from a deeper, older and warmer groundwater system,
discharging through the Spa Well at the top of the first, most elevated, southern
terrace. The second is a more recent, shallow groundwater that flows through the
karstified limestone bedrock with the main groundwater discharge located in the
vicinity of the ‘filtering ponds’, which are also on the first terrace. Overland flow is
also apparent.
5.3 The majority of groundwater discharge locations were identified within the 1st terrace.
However, some discrete groundwater discharges exist also at the 2nd and 3rd
terraces. No springs were identified within the 4th or 5th terrace (floodplain).
5.4 Review of historical information revealed that the upper (1st) terrace underwent a series of
modifications which are likely to have altered the original, natural groundwater
pathways within the site. The original outflow from the Spa Well was in the north
westerly direction. The historical evidence suggests that the outflow was diverted
towards the north easterly direction in late 1970s or early 1980s. Subsequently,
water from the Spa Well flows towards the cold springs (‘filtering ponds’). The
implication of such engineering is limitation in water delivery to the western side of
the 1st terrace manifested in drying of this wet-grassland habitat. To verify this
hypothesis, further investigation is necessary and this could, for example, include
geophysical or drain camera surveys that would determine the original layout of the
Spa Well discharge pipe. It is also possible that diversion of the groundwater flow
away from the western side of the 1st terrace occurred unintentionally during sewage
works undertaken in 1980s. Knowledge of the exact location of service pipes within
the upper extent of the site would also benefit the conceptualisation of groundwater
flows at this location. If this hypothesis is confirmed, the subsequent mitigation
measures would include reengineering the pipe layout so they could allow the Spa
Well discharge to flow in north – north westerly direction. However, this will result in
a reduction of groundwater flow towards the cold springs (‘filtering ponds’) and is
likely to impact on the local ecology surrounding the ‘filtering ponds’ which have
adjusted to present conditions over time. Considering a probable local recharge of
the cold springs, redirection of the groundwater discharge from the Spa Well might
cause an increase in seasonal variation in water levels in the ‘filtering ponds’ area
and could cause seasonal drying of the fen wetland. Hydrochemical changes could
also occur. Redirection of the outflow from the Spa Well, away from the ‘filtering
ponds’, will also reduce the volume of water cascading to the second terrace at the
eastern side and this will affect distribution of water at down gradient terraces. This
is likely to be compensated by more water flowing on the western side but is likely to
lead to habitat transformations on a local scale.
5.5 Field data suggest that the Intel boundary drain does not currently act as a drainage
channel drawing groundwater from the wet-grassland habitat which has been
reported to be drying out. Data from a groundwater monitoring well on the Intel site
Project No.: 07_136 -15-
Leixlip Spa