1. Garrett Kilroy EPA Research Fellow Shannon PRB
Groundwater Risk Assessment Shannon Pilot River Basin
Working Group 2C Workshop on Groundwater
Risk Assessment
28 January 2004
Brussels
Garrett Kilroy
EPA Research Fellow
Shannon PRB
Donal Daly
Head of Groundwater Section
Geological Survey of Ireland
Environmental
Protection
Agency
Trinity College
Dublin
Funded under the ERTDI Programme
National Development Plan

2. Risk Assessment Methodology
Boundaries +
Conceptual Understanding
Description
Water Body
Delineation
Source-Pathway-Receptor Model
Emphasis on developing conceptual understanding of each GWB
Source
Pressures, Loading,
Spatial Location
Characteristics
of Pathway
(Susceptibility)
Characteristics
of Receptor
(Sensitivity)
Monitoring
Data
Risk Assessment
Information on
known impacts
Risk Assessment
Potentially
At risk
Further Characterisation
Not at Risk
At Risk

3. Use of Monitoring Data Are the data representative of the GWB?
Do the data allow trend analysis? NO
YES
Do the data indicate evidence of significant impacts on chemical status? NO
YES
Enhance existing monitoring programmes
Evaluate risk using Pressure-Pathway-Receptor Assessment
GWB probably ‘Not At Risk’
Corroborate with
Pressure-Pathway-Receptor
Assessment
Further CharacterisationRequired

4. Study GWBs
Source: GSI

5. Funshinagh GWB 354 km2 Mainly karst limestones High transmissivity
Source report and SPA
EPA hydrochemistry data
River gauging
EPA groundwater level
OSI 1:50K rivers & streams
Mapped bedrock faults
Source:
GSI
Outline of GWB

6. Nenagh GWB 756 km2 More complex geology Low transmissivity rocks
Source report and SPA
EPA hydrochemistry data
Specific dry weather flow
EPA groundwater level
OSI 1:50K rivers & streams
Mapped bedrock faults
Outline of GWB
Source: GSI

7. Risk Posed by Diffuse Pollution (e..g. nitrate)
Funshinagh and Nenagh Groundwater Bodies
Shannon Pilot River Basin

8. Methodology
Screening exercise using available GIS layers and matrices of risk factors
groundwater vulnerability + groundwater flow regime
= pathway susceptibility map
pathway susceptibility + pressure magnitude
= potential impact map
Designate risk of GWB

9. Groundwater Vulnerability
Source Data:
GSI

10. Groundwater Flow Regime
Source
Data:
GSI

11. Identifying pathway susceptibility to nitrate (& similar pollutant types)
FLOW REGIME
Karst
Fissured
Intergranular
Low Flow
GROUNDWATER
VULNERABILITY
Extreme (outcrops) E
Extreme H
High M
Moderate L
Low

12. Pathway Susceptibility
Source Data:
GSI

13. Possible derivation of thresholds for magnitude of stocking density
1991 DED Data, CSO

14. Applying Pressure Magnitude Thresholds
Source
Data:
CSO 1991

15. Combining Pathway Susceptibility to Pressure Magnitude
IMPACT
POTENTIAL
PATHWAY SUSCEPTIBILITY E H M L
PRESSURE
MAGNITUDE
High
high
moderate
low
Medium
Low
Minimal
minimal

16. Impact Potential Map 22 % High Impact Potential 1.3 % High Impact

17. Designation of GWBs ‘at risk’
% of GWB with
high impact potential
Risk Category
>30%
‘at risk’
15-30%
‘potentially at risk’
<15%
‘not at risk’
Funshinagh = 22 %
Nenagh = 1.3 %

18. Groundwater Quality Data
Data <50 mg/l, therefore GWBs not at risk?
Representative Data?
Risk assessment is required to indicate why not at risk

19. Summary Need to examine other pressure layers
Pressure thresholds need to be examined for GWBs in totality
GWBs ‘at risk’ may require subdivision
Areas of GWB which are high risk will be focus of programme of measures
Monitoring data required to validate assessment

20. Risk Posed by Abstraction
Funshinagh Groundwater Body
Shannon Pilot River Basin

21. Methodology Effective Rainfall recharge coefficient Abstraction data
Interpolation of 30yr average annual rainfall ( ) using a Triangular Irregular Network
Interpolation of evapotranspiration data
ER = Rainfall – Evapotranspiration
recharge coefficient
Definition: proportion of ER which reaches water table
Use groundwater vulnerability maps to estimate recharge coefficients
Abstraction data

22. Effective Rainfall TIN model 30yr annual rainfall
(better model required e.g. isohyetal or thiessen)
30yr annual rainfall
Rainfall – Evapotranspiration = ER
Source Data:
Met Eireann

23. Groundwater Vulnerability
Based on subsoil thickness and permeability
Used for estimating recharge coefficients, e.g.
E = 0.8
Karst/rock = 0.85
H = 0.65
M = 0.3
L = 0.1
Caveat:
Recharge coefficients require refining within vulnerability layers
soils layer required
Source Data:
GSI

24. Recharge Estimates Combine vulnerability and ER maps For each polygon:
Recharge = ER x recharge coefficent x area
Overall annual recharge to groundwater body:
(sum of polygons)
= 115,415,875 m3

25. Abstraction Pressure Known large abstractions
Total annual volume of known abstraction:
1,511,465 m3
Abstraction as % of long term annual recharge:
1.3%
Source Data:
GSI

26. Significance of Pressure
Depends on sensitivity of receptor, e.g. GW dependent terrestrial ecosystem > main river channel ecosystem
For less sensitive receptor could use:
GW abstraction impact (as % LTA recharge)
Risk Category
>30%
“at risk”
15-30%
“potentially at risk”
<15%
“not at risk”
Conclusion:
Funshinagh GWB = 1.3% of LTA
Therefore “not at risk”

27. Example of GW level fluctuations 1998 – 2003 in Funshinagh GWB

28. Thank you!