1. Deriving groundwater quality thresholds in the Vouga river basin (Portugal) applying BRIDGE methodology
M. T. Condesso Melo, C. M. Ordens, C. Sena, M. A. Marques da Silva
A t l a n t i c O c e a n N km
Aveiro

2. Geology of the Vouga river basin
Precambrian-Early Paleozoic bedrock units are overlain by the Meso-Cenozoic sedimentary cover (Jurassic limestone, Triassic and Cretaceous sandstone, and Quaternary sands and gravel) N
Precambrian-Early Paleozoic bedrock
A t l a n t i c O c e a n
A t l a n t i c O c e a n
Vouga River
Basin
Quaternary sands
& gravel
Cretaceous sandstone
Triassic sandstone
Jurassic limestone

3. Surface water bodies in the Vouga river basin
River Vouga and its tributaries, ‘Pateira de Fermentelos’ lagoon, ‘Ria de Aveiro’ lagoon’ & Atlantic ocean N
Vouga River
A t l a n t i c O c e a n
Ria de Aveiro
lagoon
A t l a n t i c O c e a n
Vouga River
Basin
Pateira de Fermentelos
lagoon

4. Special protection areas in the Vouga river basin
Ria de Aveiro lagoon, a shallow coastal lagoon
with both marine and estuarine waters.
A t l a n t i c O c e a n
S. Jacinto Dunes Natural Reserve (wintering area for thousands of aquatic birds and has been classified as Special Protection Area under the EC Directive on the Conservation of Wild Birds).
Pateira de Fermentelos lagoon a shallow freshwater lagoon.

5. Main defined groundwater bodies in the Vouga river basin
Cretaceous sandstone aquifer
A t l a n t i c O c e a n

6. Main defined groundwater bodies in the Vouga river basin
Cretaceous sandstone aquifer, Quaternary sand and gravel aquifer
A t l a n t i c O c e a n

7. Main defined groundwater bodies in the Vouga river basin
Cretaceous sandstone aquifer, Quaternary sand and gravel aquifer, Jurassic karstic aquifer
A t l a n t i c O c e a n

8. GWBs selected for threshold definition in the Vouga river basin
Quaternary sand and gravel (GWB1) aquifer and Cretaceous sandstone aquifer (GWB2)
A t l a n t i c O c e a n
Confining layer
Quaternary aquifer
Cretaceous aquifer
confined
phreatic
GWB 2
GWB 1

9. Main groundwater receptors of each groundwater body
GWB1 (Quaternary sand and gravel aquifer), GWB2 (Cretaceous sandstone aquifer)
A t l a n t i c O c e a n
phreatic
GWB 1 Quaternary aquifer
Dependent Aquatic Ecosystems > Irrigation > Industry > (Drinking water)
Confining layer
Drinking water > Industry > (Dependent Aquatic Ecosystems)
confined
GWB 2 Cretaceous aquifer

10. Factors influencing groundwater quality
Main pressures on groundwater quality of both GWBs (Article 5)
GWB1 (Quaternary sand and gravel aquifer), GWB2 (Cretaceous sandstone aquifer)
dilution, attenuation
age
Factors influencing groundwater quality
natural
agriculture
industry
pumping
human impact
salinity
redox
Confining layer
GWB 1 Quaternary aquifer
GWB 2 Cretaceous aquifer
confined
phreatic
Fe, Mn
Heavy metals, organics F
Cl, SO4, Na
NO3, K, SO4, Heavy metals
Cl, SO4, Heavy metals
Cl, Na

11. Nitrate Vulnerable area
Main pressures on groundwater quality of both GWBs
Pressure AGRICULTURE GWB1 Quaternary sand and gravel aquifer & GWB2 Cretaceous sandstone aquifer
Nitrate Vulnerable area

12. Pressure INDUSTRY GWB1 Quaternary sand and gravel aquifer
Main pressures on groundwater quality of both GWBs
Pressure INDUSTRY GWB1 Quaternary sand and gravel aquifer

13. Pressure INDUSTRY GWB1 Quaternary sand and gravel aquifer
Main pressures on groundwater quality of both GWBs
Pressure INDUSTRY GWB1 Quaternary sand and gravel aquifer

14. Pressure ABSTRACTION GWB2 Cretaceous sandstone aquifer
Main pressures on groundwater quality of both GWBs
Pressure ABSTRACTION GWB2 Cretaceous sandstone aquifer
background

15. Selected elements for threshold derivation (based on Article 5)
based on Article 5 and risk assessment analysis
phreatic
Quaternary aquifer
EC, Cl, SO4, NO3, As, B, Cd, Ni, Pb, Zn
Confining layer
confined
Cretaceous aquifer
Cl, SO4, NO3, As, B, Cr, F, Ni, Pb, Zn

16. Natural Background Definition
number of sampling points available for each groundwater body
(time series very limited; values below detection limit replaced by max D.L.)
phreatic
Quaternary aquifer
From the initial 129 groundwater samples:
47 groundwater samples (NO3-N< 2.3 mg/L)
43 groundwater samples (Cl < 250 mg/L)
Confining layer
From the initial 93 groundwater samples:
75 groundwater samples (NO3-N< 0.01 mg/L
60 groundwater samples (Cl < 250 mg/L)
confined
Cretaceous aquifer

17. Natural Background Levels (NBL)
GWB 1
GWB 2
Confining layer
Quaternary aquifer
Cretaceous aquifer
confined
phreatic

18. Approach used to derive the threshold values for the GWB:

19. GWB 1. Quaternary sands & gravels
Threshold value (TV) derivation based on P0.90
Receptor: Crop irrigation
  GWB 1. Quaternary sands & gravels
SEC Cl
SO4
NO3 As B Cd Ni Pb Zn
microS/cm
mg/L
microg/L
NBL (P90.0)
933 91 64
3.6
4.29
0.40
0.03
3.60
0.71
25.0
REF (Max recommended values for irrigation)
1000 70
575
50.0
10.0
0.30
500
5000
2000
TV (Tier 2) Case 1
966
7.1
Case 1: NBL≤REF then TV=(REF+NBL)/2
TV (Tier 2) Case 2
128
7.3
0.05
7.19
1.41
Case 2: NBL<(REF/3) then TV=2xNBL
TV (Tier 2) Case 3
Case 3: NBL>REF then TV=NBL
TV (Tier 2)

20. GWB 2. Cretaceous Sandstone
Threshold value (TV) derivation based on P0.90
Receptor: Drinking water supply
 GWB 2. Cretaceous Sandstone
SEC Cl
SO4
NO3 As B Cr F Ni Pb Zn
microS/cm
mg/L
microg/L
NBL (P90.0)
1050
170
124
0.02
9.3
0.33
1.22
0.93
4.37
0.49
93.1
REF (DWS)
2500
250 50
10.0
1.00
50.0
1.50
20.00
25.00
3000.0
TV (Tier 2) Case 1
1775
210
187
9.7
0.67
1.21
Case 1: NBL≤REF then TV=(REF+NBL)/2
TV (Tier 2) Case 2
0.04
2.43
8.75
0.99
186.2
Case 2: NBL<(REF/3) then TV=2xNBL
TV (Tier 2) Case 3
Case 3: NBL>REF then TV=NBL
TV (Tier 2)

21. Conclusions
Developed Bridge methodology was of easy application in the Portuguese case study, and the results showed that may be used for both groundwater body status assessment and to limit pollution;
It does provides very low TV for nitrate because of the pre-selection method;
Tier 2, Case 2 and Case 3 are supposed to be the ones to protect GWB natural background levels, but the factor applied in case 2 is indeed arbitrary, it maybe 1 or greater;
Between 10 and 20% of the samples in GWB1 exceeded one of the TV defined, while in GWB2 there were less than 5% of the samples;
It would be important to develop environmental quality standards for groundwater itself as a receptor;
Further investigation on groundwater-surface water interaction is required to take into account the impact on aquatic ecosystems.