Hydro G Final report - Kildare.ie

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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
Hydro-G FINAL REPORT suggests that water from the deeper groundwater system on the Leixlip Spa site influences hydrochemistry at that location. 5.6 The re-wetting of the western side of the first terrace could be potentially achieved by reengineering of the surface run-off from the area upgradient from the first terrace. This area is currently hard standing with surface runoff flowing both westwards and northwards, following the topographic gradient. Rainwater is collected therefore either in the Intel drain or infiltrates into the ground at the top of the first terrace. This water could be however conserved and directed towards the western parts of the first terrace where it could seep into the, currently drying, grassland habitat. 5.7 With respect to the lowest terrace, which was reported to be drying out, the desktop review and interviews undertaken during the study have not revealed any structural changes in either local hydrology or hydrogeology. Therefore, the most probable cause of these changes is natural habitat transformation resulting from plant growth, increased evapotranspiration needs and accumulation of organic matter, which subsequently resulted in increased ground level in places. Cessation of grazing may have contributed to the vegetation overgrowth of this floodplain. 5.8 This study was executed in the months of December and January, which is a recharge period and groundwater levels are expected to be at their highest. Considering the complexity of the Leixlip Spa system combining two groundwater sources, one deep and one shallow, the relative contribution of water from these sources may differ seasonally and this can further affect hydrochemistry on a local scale. It is advised therefore that if it is decided to re-engineer the site in any way, the site’s hydrological characteristics when groundwater levels recede (summer) requires characterisation. 5.9 With respect to the future water management strategy for the Leixlip Spa site, the evidence collected suggest that alteration of the pipe network at the first, most southern, terrace may result in significant changes to the hydrological regime of the ‘filtering ponds’, which is difficult to predict quantitatively. Considering that the habitat in the vicinity of the ‘filtering ponds’ is of high ecological value, interference with the pipe layout does not seem prudent from a hydrological perspective. A management strategy is recommended for the floodplain area; however, this should focus on controlling plant growth and restricting accumulation of the organic matter. Project No.: 07_136 -16- Leixlip Spa
Page 1 and 2: HYDROLOGICAL REPORT FOR LEIXLIP SPA
Page 3 and 4: Hydro-G FINAL REPORT PROJECT TEAM D
Page 5 and 6: Hydro-G FINAL REPORT the Intel boun
Page 7 and 8: Hydro-G FINAL REPORT LIST OF FIGURE
Page 9 and 10: Hydro-G FINAL REPORT The issues to
Page 11 and 12: Hydro-G FINAL REPORT 2. Desk Study
Page 13 and 14: Hydro-G FINAL REPORT Hydrochemistry
Page 15 and 16: Hydro-G FINAL REPORT 1983 2008 Phot
Page 17 and 18: Hydro-G FINAL REPORT The general fl
Page 19 and 20: Hydro-G FINAL REPORT concentrations
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Page 25 and 26: Hydro-G FINAL REPORT FIGURES Projec
Page 27 and 28: Hydro-G FINAL REPORT 5 km Site Loca
Page 29 and 30: Hydro-G FINAL REPORT Figure 4 Site
Page 31 and 32: Hydro-G FINAL REPORT Appendix A Lei
Page 33 and 34: Hydro-G FINAL REPORT • Deteriorat
Page 35 and 36: Hydro-G FINAL REPORT Temperature, E
Page 37 and 38: Hydro-G FINAL REPORT Iron Iron conc
Page 39 and 40: Hydro-G FINAL REPORT Table 4 Result
Page 41 and 42: Hydro-G FINAL REPORT Project No.: 0
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