draft calculation of natural background levels, threshold values … · 2014. 12. 30. · water and...
TRANSCRIPT
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DRAFT
Calculation of natural background levels, threshold values and
dilution for groundwater according to the proposed
methodology in the groundwater body “Southern Vienna
Basin” in Austria
Claudia Schramm, Andreas Scheidleder, Dietmar Müller, Franko Humer, Irene Zieritz,
Johannes Grath, Irmgard Plank, Günter Eisenkölb
UMWELTBUNDESAMT – Federal Environmental Agency Austria
SUMMARY
In the frame of the EU project BRIDGE the Austrian groundwater body “GK100024 Southern Vienna Basin” was chosen as a case study within WP4.
In a first step the groundwater body was characterised. Groundwater itself, drinking water and surface water were found to be relevant receptors in the Southern Vienna Basin.
According to the proposed tiered approach (Deliveralbe D15) natural background levels (tier 1), receptor based threshold values (tier 2) and dilution with surface water (tier 3) was acquired. Drinking water quality standards and ecotoxicological standards were used as reference values.
Attenuation of pollutants due to (bio)geochemical reactions (tier 4) was not considered in the Austrian case study.
Abbreviations WFD: Water Framework Directive GWD: Draft Groundwater Directive NBL: Natural Background Level TV: Threshold Value LOD: Limit of Detection LOQ: Limit of Quantification DWD: Drinking Water Directive DF: Dilution Factor EQS: Environmental Quality Standard REF: Reference Value not av.: not available
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CONTENT OF THE CASE STUDY REPORT AUSTRIA
SUMMARY ..................................................................................................................... 1
1. Introduction ................................................................................................................ 3
2. CHARACTERISATION OF THE GROUNDWATER BODY ................................ 3
2.1 Physical and hydrogeological description ........................................................................... 3 2.1.1 Geographical boundaries .............................................................................................. 3 2.1.2 Climate.......................................................................................................................... 4 2.1.3 Water balance ............................................................................................................... 4 2.1.4 Geology......................................................................................................................... 5 2.1.5 Hydrogeology ............................................................................................................... 5
2.2 Identification of pressures ................................................................................................... 8 2.2.1 Groundwater abstraction............................................................................................... 8 2.2.2 Artificial recharge ......................................................................................................... 8 2.2.3 Pollution........................................................................................................................ 9
2.3 Conceptual model................................................................................................................ 9
2.4 Natural background levels – national approach ................................................................ 10
2.5 Review of impacts ............................................................................................................. 11 2.5.1 Monitoring network (groundwater and surface water) ............................................... 11 2.5.2 Effects of abstraction on groundwater quantity .......................................................... 11 2.5.3 Effects of abstraction on groundwater quality ............................................................ 11 2.5.4 Effects of abstraction on dependent ecosystems......................................................... 12 2.5.5 Effects of artificial recharge........................................................................................ 12 2.5.6 Effects of pollutant pressures on groundwater quality................................................ 12 2.5.7 Effect of groundwater induced pollutant pressures on dependent ecosystems ........... 13 2.5.8 Pollutants selected for threshold methodology evaluation ......................................... 13
3. THRESHOLD VALUES TO ASSESS THE CHEMICAL STATUS OF THE GROUNDWATER................................................................................................... 13
3.1 Application and evaluation of the proposed threshold methodology ................................ 13 3.1.1 Tier 1: Assessing the Natural Background Levels (NBLs) with the proposed pre-
selection method ......................................................................................................... 13 3.1.2 Tier 2a Option 1: Calculation of Threshold Values for the receptor Groundwater itself
.................................................................................................................................... 16 3.1.3 Tier 2a Option 2: Calculation of Threshold Values with the maximum permissible
addition (MPA) approach for the receptor groundwater itself.................................... 18 3.1.4 Calculation of the dilution factor for the receptor surface water ................................ 20
4. CONCLUSIONS ...................................................................................................... 22
4.1 Comments and conclusion on BRIDGE data pre-selection and NBL estimation ............. 22
4.2 Comments and conclusion on the selection of Reference (REF) values ........................... 22
4.3 Comments and conclusion on the derivation of threshold values (TVs)........................... 23
4.4 GENERAL CONCLUSION.............................................................................................. 23
5. REFERENCES ......................................................................................................... 23
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1. Introduction
The “Southern Vienna Basin” is located in the south-east of Vienna.
It contains one of the largest groundwater reservoirs in Europe, the so called “Mitterndorfer Senke” and is hence of utter importance for the drinking water supply the eastern part of Austria.
According to Art. 5 of the Water Framework Directive the groundwater body GK100024 Southern Vienna Basin has not been reported to be at risk.
Nevertheless water abstractions and agriculture are a relevant pressure in the Southern Vienna basin. Contaminated sites put a risk the groundwater quality of the Southern Vienna Basin, mainly due to chlorinated hydrocarbons.
2. CHARACTERISATION OF THE GROUNDWATER BODY
2.1 Physical and hydrogeological description
2.1.1 Geographical boundaries
The Southern Vienna Basin is a single, shallow groundwater body. The mean altitude is 235 meters above sea level (adria), ranging from 133 up to 494 meters.
The total area of the Southern Vienna Basin is 1228 km2. The maximal length and width is 72 and 30 km, respectively.
More than 85% of the area is situated in the federal province Lower Austria (1048 km2), the rest in the area of the province and city of Vienna (173 km2) and a small area of 7 km2 belongs to the Province of Burgenland.
The groundwater body belongs to the Sub river basin “Donau unterhalb Jochenstein (DUJ) [PL100004]” and the river basin “Donau [EZ100002]”.
It is part of the ecoregion for rivers and lakes “11.Hungarian Lowlands” and partly “4. Alps” and the ecoregion for coastal waters “7. Black Sea”.
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Fig. 1: Map of the groundwater body GK100024 Southern Vienna Basin
2.1.2 Climate
The mean annual air temperature in the Southern Vienna Basin is 8 to 10 °C.
The average of the annual precipitation is about 570 mm. In the southern part of the groundwater body values up to 700 mm can be reached.
The seasonality of the monthly precipitation shows its maxima in June in the central and southern part of the Southern Vienna Basin. In the northern part the maxima of the monthly precipitation occurs in July.
2.1.3 Water balance
The climatic water balance in the groundwater body is mainly negative according to data from 1961 to 1990. Only the south-western part of the Southern Vienna Basin and narrow bands along the rivers show a positive water balance.
The mean annual potential evapotranspiration in the Southern Vienna Basin is between 625 and 650 mm. The mean annual actual evapotranspiration ranges from 400 mm in the northern part of the case study area up to 625 mm in the south (using water balance data).
The mean annual depth of runoff in the case study area is less than 250 mm (using water balance data).
Table 1: Annual average in mm of water balance components
Precipitation ETP pot. ETP act. Runoff
500 - 700 mm 625 - 650 mm 400 - 625 mm 0 - 250 mm
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2.1.4 Geology
The Southern Vienna Basin was formed as a pull-apart basin between the Alps and the Karpat mountain range. It was filled during tertiary times by thick, mainly marine sediments. Above these quaternary fluviatile channel and basin sediments can be found. The sandy gravel formations of the Pleistocene are relevant water resources. The so called “Mitterndorfer Senke” for example has a length of approximately 50 km and a width ranging from 15 to 20 km and is one of the largest groundwater reservoirs in Europe.
Upper confining layers in the Southern Vienna Basin are siltic humic top soils.
At the western fringe of the basin middle till coarse grained water-bearing Pannonian sediments are present.
2.1.5 Hydrogeology
The aquifer consists mostly of gravel and sand. Local moraines are developed. According to the aquifer typology defined in WP2 the groundwater body can be described with Sands and Gravels.
The mean thickness of the aquifer is 30 m, ranging from 2 to 150 m. The groundwater-depth varies between 0 and 70 m. Up to 25% of the groundwater body are covered with an upper confining layer. The mean sum of upper confining layers is 2 m and consists mainly of siltic humic top soils. The hydraulic conductivity ranges from 0.0002 to 0.01 m/sec, with a mean value of 0.003 m/sec.
Fig. 2: Simplified hydrogeology and depth to water table
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2.1.5.1 Delineation and type of groundwater body
In the west the Southern Vienna Basin is surrounded by the carbonates of the Northern Calcareous Alps of Austria. In the south the elevation of the “Bucklige Welt” defines the geological boundary. The northern boundary results from the watershed of the river Danube. The eastern geological limits are the elevations of the “Arbesthaler Hügelland”, the “Leithagebirge” and the “Rosaliengebirge”.
2.1.5.2 Hydrodynamics
According to a groundwater model (SIMULTEC, 1996) groundwater inflow from the West to the Mitterndorfer Senke is about 1.5 m³/s. Groundwater recharge from precipitation has the same dimension, whereas the infiltration of surface water is calculated between 3 and 4 m³/s. Hence, the majority of the annual groundwater recharge in the Mitterndorfer Senke is formed by surface water alimentation, for example from the rivers Schwarza, Piesting, Leitha, Warme Fischa (fig. 3 and 7).
The exfiltration of groundwater is an important factor for several rivers and creeks, in particular for the rivers Fischa and its tributaries. The amount of exfiltration depends on the groundwater level. The average yearly sum of exfiltration of groundwater into surface water is about 5.5 m³/s.
Fig. 3: Zones with exfiltration of groundwater
The mean annual fluctuation of the groundwater table in the groundwater body is 2.5 m. In the southern part the mean annual fluctuations of the groundwater table show values more than 10 m.
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Fig. 4: Potentiometric map of the study area with indication of rivers and main groundwater flow directions
2.1.5.3 Hydrogeochemistry
The southern part of the groundwater body shows mainly alkaline earth-carbonatic dominated groundwater. In the northern part the groundwater tends to show sulfatic evolution.
Fig. 5: Characterization of groundwater hydrochemical evolution along flowpath
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2.1.5.4 Groundwater receptors
The main receptors are groundwater itself, drinking water and surface water. In the groundwater body there are 12 drinking water protected areas (some for existing, some for future water supply).
In the Southern Vienna Basin there are 5 Natura 2000 areas. Only a little part of one of them is WFD relevant (fig. 5).
The quality standards for the tiered method to refer to are drinking water standards and national surface water EQS.
Fig. 6: Map with location of protected areas
2.2 Identification of pressures
Potential anthropogenic pressures on groundwater are present in form of water abstractions, agricultural activities and contaminated sites.
2.2.1 Groundwater abstraction
In the investigated area water abstraction points with a daily extraction of at least 2 m3
were investigated, which amounted in a number of 114 water abstractions with at least 2 m3 per day. The water abstraction is dominated by industrial use with a total daily amount of about 6000 m3 and wells with about 4000 m3 per day. 300 m3 are abstracted for agricultural use and 50 m³ at four springs.
2.2.2 Artificial recharge
According to Article 5 of the WFD there is no relevant artificial recharge of groundwater in the investigated area.
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2.2.3 Pollution
2.2.3.1 Diffuse sources
According to CORINE Landcover 2000 land use consists mainly of agricultural areas (~63 %), urban area (~26 %), forest and natural areas (~10 %) and water (0.6 %).
2.2.3.2 Point sources
28 contaminated sites are located in the Southern Vienna Basin. Five of them are significant according to Article 5 of the WFD. They are all situated in the northern part of the groundwater body, in the industrial area in the south of Vienna.
There are no sewage treatment plants without channels or streams receiving the effluent from a waste water treatment plants.
Fig.7: Maps of pressures 2.3 Conceptual model
The Southern Vienna Basin is a shallow, unconfined groundwater body in the south-east of Vienna. During tertiary it was filled by thick, mainly marine sediments. Above these quaternary fluviatile channel and basin sediments can be found. These sandy gravel formations are important water resources. Parts of the area are drinking water protected areas for existing and future water supply.
Groundwater flow was simulated for the Mitterndorfer Senke, a groundwater resource of utter importance in the case study area, which covers main parts of the groundwater body. The majority of the annual groundwater recharge is formed by surface water alimentation, mainly in the south of the Southern Vienna Basin. Exfiltration of groundwater is an important factor for several rivers and creeks in the northern part of the groundwater body, in particular for the rivers Fischa and its tributaries.
According to CORINE Landcover 2000 land use consists mainly of agricultural areas (~63 %), urban area (~26 %), forest and natural areas (~10 %) and water (0.6 %).
Pressures on the groundwater body include groundwater abstraction, diffuse pollution by agricultural activities and point sources of pollution by contaminated sites.
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Receptors for groundwater in Southern Vienna Basin are groundwater itself, drinking water and surface water.
2.4 Natural background levels – national approach
GEOHINT is an Austrian-wide assessment of regionalized, hydrochemical background concentrations in shallow groundwater bodies which has been performed by the Geological Survey of Austria in 2004, under contract to the Federal Ministry for Agriculture, Forestry, Environment and Water Management.
The assessment was based on hydrochemical and geochemical data of research / technical reports and monitoring programmes from federal and provincial authorities and data from CORINE Landcover and geological surveys. The derivation of NBLs was carried out with geostatistical, hydrogeological and hydrochemical methods. The Background Concentration of a groundwater body was established as the highest value of the measured data without anthropogenic impact. Values below the limit of quantification or the limit of detection were replaced by zero.
Approach for groundwater bodies with adequate data:
• Check of plausibility of the data-base
• Exclusion of anthropogenic influenced data (in addition: principal component analysis)
• Statistical analysis of the data based on groundwater bodies
• Derivation of NBLs for several parameters on the spatial base of groundwater bodies
• Classes of natural background levels per parameter over Austria were used for visualisation of the results (maps)
Approach for groundwater bodies with a lack of data:
• Data from lithologic similar Groundwater bodies nearby
• Geochemical Analysis (not statistically, but expert reports)
Table 2: National natural background levels (GEOHINT) Parameter NBL from the
national Aproach
Parameter NBL from the
national Aproach
Aluminium 31 µg/l Magnesium 40.8 mg/l Ammonium 0.09 mg/l Manganese 0.044 mg/l Arsenic 4.1 µg/l Nickel 3.7 µg/l Lead 3 µg/l Nitrate 23.3 mg/l Boron 0.037 mg/l Nitrite 0.08 mg/l Cadmium 0.2 µg/l Phosphate 0.05 mg/l Calcium 133.6 mg/l Potassium 7.7 mg/l Chloride 32.1 mg/l Sodium 21.9 mg/l Chrome 3.5 µg/l Sulphate 79.7 mg/l
Iron 0.47 mg/l Water hardness
18.5 °dH
Copper 4.1 µg/l Electric Conductivity
910 (µS/cm) at 25°C
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2.5 Review of impacts
2.5.1 Monitoring network (groundwater and surface water)
In Austria standardised water quality monitoring based on legal provisions started in 1991. The monitoring programme covers groundwater in porous media, groundwater in karst and fractured (fissured) rock and surface water (rivers). The main goals are to assess the current status of the Austrian waters on the basis of a sound and reliable database and to detect negative developments at an early stage. Based on this programmes of measures can be introduced to reverse a negative development.
Groundwater sampling sites are distributed all over the groundwater areas. The location of the monitoring sites for surface water was chosen to cover the potential risk of the most important settlement areas and industrial zones.
For both groundwater and surface waters the duration of a monitoring cycle is 6 years and comprises for:
- groundwater: an initial investigation period of one year covering an extended number of parameters (parameter block 1 and 2 and selected parameters of block 3 – for the definition of blocks see below) and five years period of repeated investigation. The latter comprises the minimum requirement (= parameters of block 1) and parameters which appeared to be relevant based on experience from the initial investigation period.
- surface water (rivers): initial investigation period for two years covering an extended number of parameters and four years period of repeated investigation. The latter comprises the minimum requirement (= parameters of block 1) and parameters which appeared to be relevant based on experience from the initial investigation period.
Groundwater is monitored four times a year, running waters generally 12 times a year. At selected transboundary river monitoring sites investigations are carried out every two weeks. Both biological water quality and river sediments are investigated once a year in accordance with the Austrian Ordinance on Water Quality Monitoring.
In the case Study Area the Groundwater Monitoring Network consists of a total of 141 sampling sites in porous media, which where monitored from 1991 to 2005 (end of the reviewed dataset) at least occasionally. From 1997 to 2005 54 groundwater sampling sites were monitored continuously once in a quarter of a year, and additional 26 sites were monitored continuously at least once in half a year.
93 sampling sites were only monitored in the period from 2003 to 2005.
The Surface Water Monitoring Network consists of a total of 20 Sampling Sites.
9 Sampling Sites were only monitored in the period from 2003 to 2005.
2.5.2 Effects of abstraction on groundwater quantity
There are no effects of abstraction on groundwater quantity in the Southern Vienna Basin according to Art. 5 of the WFD.
2.5.3 Effects of abstraction on groundwater quality
There are no effects of abstraction on groundwater quality in the Southern Vienna Basin according to Art. 5 of the WFD.
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Tetrachloroethylene at the groundwater
monitoring site PG32300492
0
20
40
60
80
100
1997 1998 1999 2000 2001 2002 2003 2004 2005
Year
Te
tra
ch
loro
eth
yle
ne
in
µg
/l
Nitrate and Chloride at the groundwater
monitoring site PG32400222
0
50
100
150
200
250
1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005
Year
Nit
rate
an
d c
hlo
rid
e i
n
mg
/l
Nitrate Chloride
Ammonium, Boron and Bhloride concentrations at the
groundwater monitoring site PG32400242
0
2
4
6
8
10
12
14
16
18
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
Year
Am
mo
nia
an
d B
oro
n
in m
g/l
0
50
100
150
200
250
300
Boron Ammonium Chloride
Ch
lori
de
n i
n m
g/l
2.5.4 Effects of abstraction on dependent ecosystems
There are no effects of abstraction on dependent ecosystems in the Southern Vienna Basin according to Art. 5 of the WFD.
2.5.5 Effects of artificial recharge
There is no artificial recharge in the Southern Vienna Basin according to Art. 5 of the WFD.
2.5.6 Effects of pollutant pressures on groundwater quality
As already mentioned the Southern Vienna Basin has not been reported to be at risk according to Arc. 5 of the WFD. Anyway, there are pollutant pressures on the groundwater quality out of contaminated sites and agricultural activities. Monitoring sites may be affected by highly volatile chlorinated hydrocarbon, parameters indicating agricultural impacts and heavy metals.
Fig.8 Map of pollution distribution - Coming soon
Fig. 9 Example of time series from monitoring wells
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2.5.7 Effect of groundwater induced pollutant pressures on dependent
ecosystems
There are no effects of groundwater induced pollutant pressures on dependent ecosystems in the Southern Vienna Basin according to the WFD.
2.5.8 Pollutants selected for threshold methodology evaluation
The following pollutants were selected for threshold methodology evaluation:
• highly volatile chlorinated hydrocarbons (trichlorethylene, tetrachloroethylene, 1,1,1-trichloroethan)
• parameters indicating agricultural impacts (sulphate, phosphate, chloride, boron)
• heavy metals: copper, chrome
According to Annex V 2.4.2 of the WFD the following set of core parameters shall be monitored in all the selected groundwater bodies (surveillance monitoring:
• Oxygen content
• pH value
• Conductivity
• Nitrate
• Ammonium
The draft of the GWD comprises a minimum list of pollutants, for which Member States have to consider establishing threshold values in accordance with Article 3. This list includes the parameters arsenic, cadmium, lead, mercury, ammonium, chloride, sulphate, trichloroethylene, tetrachloroethylene and the conductivity.
Therefore these parameters were also included in the calculations.
3. THRESHOLD VALUES TO ASSESS THE CHEMICAL STATUS OF THE
GROUNDWATER
3.1 Application and evaluation of the proposed threshold methodology
According to the proposed tiered approach (Deliveralbe D15) natural background levels (tier 1), receptor based threshold values (tier 2) and dilution with surface water (tier 3) were acquired. Attenuation of pollutants due to (bio)geochemical reactions (tier 4) was not considered in the Austrian case study.
3.1.1 Tier 1: Assessing the Natural Background Levels (NBLs) with the proposed
pre-selection method
Natural background levels for the selected substances were calculated according to the proposed simplified pre-selection method (that means a median per sampling site for nitrate above 10 mg/l was used as pre-selection parameter). In addition calculations were undertaken by using not only nitrate, but also other parameters indicating
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anthropogenic impact as pre-selection parameters (like phosphate, boron, sulphate etc.). In a third version all sampling sites were excluded where synthetic substances exceeded the limit of quantification.
After pre-selection the NBLs were calculated as the concentration at the 90-percentile and the 97.7-percentile of the medians per sampling site for the selected parameters.
Values below the limit of quantification (LOQ) or the limit of detection (LOD) were replaced by half of LOD / LOQ according to the Technical Report No. 1 “The EU Water Framework Directive: statistical aspects of the identification of groundwater pollution trends, and aggregation of monitoring results. ISBN: 92-894-5639-6”.
Preliminary trend analysis / Estimation of an applicable time period for the
calculation of NBLs
As already mentioned, standardised water quality monitoring based on legal provisions started in 1991 and for most of the sites in the case study area long time series are available. In order to assess the most applicable time period for the calculation of NBLs a trend assessment was undertaken for 80 sites with continuous time series from 1997 to 2004 for nitrate (table 3).
Table 3: Results of trend assessment for nitrate for 80 groundwater sites with continuous time series from 1997-2004 in the groundwater body GK100024 Southern Vienna Basin
GK100024 Results of Trend Assessment for Nitrate
Data aggregation
level
No
Trend
Downward-
Trend
Upward-
Trend
Sum of
Sampl. Sites
Quarterly 29 12 13 54 Half yearly 17 7 2 26 Sum 46 19 15 80
At 46 sites no significant trend for nitrate was calculated. 4 sites had no trend, but anyway were not included in all three periods, because the median for nitrate was sometime below, sometimes above 10 mg/l.
19 sites showed a significant downward trend. At two of these sites the median for nitrate exceeded 10 mg/l when using all data, but the median was < 10 mg/l when using the time periods 97-05 respectively 00-05. The other 17 sites were above respectively below 10 mg/l nitrate in all three time periods.
15 sites had a significant upward trend, but the level of nitrate was above 10 mg/l in all three time periods.
Conclusion: The selection of the time period for NBL calculation should be discussed with regard to possible trends in nitrate-concentrations. Because of trends in the nitrate concentrations the number of sampling sites, that are included in the NBL assessment, may vary for different time periods. For the Austrian case study the time period 1991-2005 was selected for the further assessment of NBLs.
Additional minimum requirements for NBL-Calculation according to Deliverable 15:
Samples with an incorrect Ion balance (>10 %) had been eliminated.
There were no data from hydrothermal or salty aquifers.
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Exclusion of sites due to indicator substances:
- According to D15 sites with a median for nitrate above 10 mg/l were excluded (in addition one site with a median for ammonium > 0.5 mg/l was eliminated) è Version 1
- Further exclusion of sampling sites with considerable concentrations of boron, potassium, phosphate, chloride, sulphate (indicators for anthropogenic impacts) and continuous concentrations of synthetic substances above LOQ (pesticides, chlorinated hydrocarbons) è Version 2
- Further exclusion of all sites with concentrations of synthetic substances above the limit of quantification (LOQ) è Version 3
Table 4 comprises an overview of the number of sites which remained for the assessment of NBL for each of the three versions and time periods.
Table 4: Overview of the number of sites for each of the three versions and the time periods 1991-2005 / 1997-2005 / 2000-2005 (fat: time period chosen for NBL calculation)
Number of sampl. sites
Samples excluded because of incorrect ion balance
Sampling Sites used for NBL calculation
Version 1 141 / 129 / 103 2.9 % / 2.5 % / 2.2 % 25 / 24 / 20 Version 2 141 / 129 / 103 3 % / 1.8 % / 2.9 % 13 / 11 / 7 Version 3 141 / 129 / 103 15 % / 0 % / 0 % 1 / 3 / 2
Comparison of the results of the three versions
Version 1:
The results proved that the pre-selection method with a nitrate as indicator is not strong enough for the exclusion of all anthropogenic influenced sampling sites.
Version 2:
The pre-selection criteria for nitrate is amended by including other parameters than nitrate as indicator for anthropogenic impacts (boron, chloride, sulphate, potassium, ammonium). Further sampling sites with continuous concentrations of synthetic substances above LOQ were excluded. The results of version 2 seemed to provide the most applicable results concerning the exclusion of sites with anthropogenic impacts. The NBLs calculated out of version 2 were therefore used for TV-calculation.
Version 3:
Only few sampling sited have NOT been excluded from the NBL calculation.
Many sampling sites were kicked out because of the chlorinated hydrocarbons trichloroethylene, tetrachloroethylene, 1,1,1-trichlorethane and the pesticides atrazine and desethylatrazine. Beyond these parameters many sampling sites showed concentrations of MTBE exceeding the LOQ. The criteria to exclude all sampling sites with synthetic substances above the LOQ seems to be too strong for the NBL-calculation.
Comparison of the results of NBL calculation with the pre-selection method and with
national NBLs
Table 5 comprises the results of the NBL calculation with the 90- resp. 97.7-%-percentile. Furthermore the results of the 90-%-percentile and the natural background level of the national method “GEOHINT” are illustrated.
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Table 5: Natural Background Level (NBL): Comparison of the results of the NBL-calculation acc. to the pre-selection method (90 and 97.7-percentiles) and national NBLs (GEOHINT)
90 % -percentile 91-05 (vers. 3)
97.7 %-percentile 91-05 (vers. 3)
GEOHINT 90%-percentile
GEOHINT natural back-ground level
G118 PH value 7.5 7.6 7.7 7.4 G119 Oxygen mg/l 8.2 9.3 - - G140 Cadmium mg/l 0.0002 0.0002 - 0.0002 G141 Mercury mg/l 0.0001 0.0001 - - G145 Copper mg/l 0.001 0.001 0.003 0.004 G147 Lead mg/l 0.001 0.003 0.002 0.003 G148 Chrome mg/l 0.001 0.004 0.002 0.004 G150 Arsenic mg/l 0.001 0.001 0.003 0.004 G151 Boron mg/l 0.04 0.05 0.03 0.04 G152 Ammonium mg/l 0.01 0.22 0.013 0.09 G153 Nitrite mg/l 0.02 0.05 0.005 0.08 G154 Nitrate mg/l -* -* 20 23 G155 Chloride mg/l 41 50 26 32 G156 Sulphate mg/l 164 197 71 80 G159 Phosphate mg/l 0.08 0.10 0.06 0.14
G366 Electr. Conductivity (20°C) µS/cm
764 936 767 815
*: Nitrate has been used for pre-selecting data for NBL-calculation. Therefore the calculation of an NBL for nitrate is not reasonable. Anyway, the parameter is included in the table in order to demonstrate the background level for nitrate according to GEOHINT
3.1.2 Tier 2a Option 1: Calculation of Threshold Values for the receptor
Groundwater itself
The threshold values were calculated with reference to natural background levels. Drinking water standards were used as reference values (REF).
According to Deliverable 15 the following 3 cases were distinguished:
CASE 1: NBL ≤ REF:
Where the NBL is below the REF value the TV is set as the concentration that is half of the difference (50%) between NBL and the reference value higher than the NBL:
TV = (REF + NBL) / 2
CASE 2: NBL<one third of REF:
Where NBL is considerably below REF then limit the TV to twice the NBL:
TV = 2 x NBL
CASE 3: NBL ≥ REF:
Where the NBL is higher than the reference value the TVs are equal to NBL itself:
TV = NBL
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This approach does not allow establishing a threshold value for synthetic substances as these have a natural background of zero.
Table 6 provides the results of the TV calculation for both the 90- and the 97.7-% percentile. Furthermore the calculation of TVs was undertaken with national NBLs from GEOHINT. In Austria the ordinance on groundwater threshold values (BGBl. 502/91, 213/97, 147/02) provides national threshold values for groundwater for several parameters and an algorithm for data aggregation on the spatial base of a groundwater body. The results of the calculations according to Deliverable 15 were compared with existing national groundwater threshold values resp. drinking water standards.
Table 6: Results of TV-calculation based on NBLs and drinking water standards - comparison of results based on NBLs from version 3 / 91-05 and NBLs from GEOHINT
Drinking Water Directive
National Groundwater Threshold Values / Drinking Water Standards
NBL 90% Percentile
NBL 97.7% Percentile NBL (Geohint)
Case TV Case TV Case TV Cadmium mg/l case2 0.0003 case2 0.004 case2 0.0004 0.003 / 0.005 Copper mg/l case2 0.002 case2 0.002 case2 0.008 0.06 / 2 Lead mg/l case2 0.002 case2 0.006 case2 0.006 0.03 / 0.025 Chrome mg/l case2 0.002 case2 0.008 case2 0.007 0.03 / 0.05 Arsenic mg/l case2 0.002 case2 0.002 case1 0.01 0.03 / 0.01 Boron mg/l case2 0.08 case2 0.10 case2 0.07 0.6 / 1 Ammonium mg/l* case2 0.02 case1 0.36 case2 0.18 0.3 / 0.5 Nitrite mg/l case2 0.04 case1 0.07 case1 0.09 0.06 / 0.1 Nitrate mg/l case2 19 case2 19 case1 37 45 / 50 Chloride mg/l case2 82 case2 100 case2 64 60 / 200 Sulphate mg/l case1 207 case1 224 case2 159 not av. / 250 Electr. Conductivity. (20°C) µS/cm case2 1529 case1 1718 case2 1630 not av. / 2500
* It should be discussed to chart the parameter ammonium (examine aerobic / anaerobic aquifers separately)
For mercury and phosphate the TV calculation was not possible, because there is no drinking water standard available.
Conclusion: For the Austrian case study most threshold values are calculated with case 2 (NBL<1/3 of Reference Value; TV= 2 x NBL). The resulting TVs are generally lower than national Groundwater Threshold Values. In the following two examples are given:
e.g. Boron
NBL = 0.04 mg/l and REF DWD = 1 mg/l TVBRIDGE = 0.08 mg/l National Groundwater-Threshold Value acc. to the Ordinance: 0.6 mg/l
e.g. Copper
NBL = 0.001 mg/l and REF DWD = 2 mg/l TVBRIDGE = 0.002 mg/l National Groundwater-Threshold Value acc. to the Ordinance: 0.06 mg/l
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Table 7 comprises a comparison of the number of sampling sites where the annual arithmetic mean 2004 exceeds the TVs out of the Bridge-Methodology with different NBLs (90- and 97.7%-Percentile), the TVs calculated with the Bridge-Methodology but with national NBLs from GEOHINT and national threshold values.
Table 7: Number of sites with an arithmetic mean 2005 exceeding the Bridge – TV in the case study area respectively the TVs calculated with the Bridge Methodology based on the national
NBLs (GEOHINT) and national threshold values Number of Sampling Sites with a Mean 2004 exceeding the TV out of
Parameter Bridge TV-Method; NBL 90% Percentile
Bridge TV-Method; NBL 97.7% Percentile
Bridge TV-method, NBL from Geohint (nat. approach)
National Threshold Values
Cadmium mg/l 1 / 84 0 / 85 0 / 85 0 / 85 Copper mg/l 14 / 71 14 / 71 0 / 85 0 / 85 Lead mg/l 0 / 85 0 / 85 0 / 85 0 / 85 Chrome mg/l 7 / 78 0 / 85 0 / 85 0 / 85 Arsenic mg/l 4 / 81 4 / 81 0 / 85 0 / 85 Boron mg/l 28 / 64 24 / 68 33 / 59 1 / 91 Ammonium mg/l
15 / 77 4 / 88 5 / 87 4 / 88
Nitrite mg/l 10 / 82 3 / 89 2 / 90 4 / 88 Nitrate mg/l 42 / 50 40 / 52 24 / 68 18 / 74 Chloride mg/l 11 / 81 9 / 83 14 / 78 16 / 76 Sulphate mg/l 10 / 82 10 / 82 17 / 75 not av.
0
20
40
60
80
100
120
140
160
180
Cadmium Copper Lead Chrome Arsenic Boron Chloride
Bridge-TV (NBL 90% Perc.) Bridge-TV (NBL 97.7% Perc.) Bridge-TV (NBL Geohint) National Groundwater Standard
Fig. 10 Comparison of the results of TV-calculation with the method proposed in option 1 based on different NBLs and drinking water standards - comparison of results based on NBLs from the
90- and 97.7-%-percentile and NBLs from GEOHINT
3.1.3 Tier 2a Option 2: Calculation of Threshold Values with the maximum
permissible addition (MPA) approach for the receptor groundwater itself
With the maximum permissible addition (MPA) – approach TVs are calculated based on the NBL and MPAs out of a suitable reference value, normally a surface water EQS or ecological criteria:
TV = NBL + MPA
19
For organics the accounting would be the MPC, which is the maximum permissible concentration, representing a tolerable risk level for 5 % of the species (protection of 95 % of species).
This method does allow threshold values to be established for synthetic pollutants.
MPC and MPA values are identified in the outputs of the commission project Identification of quality standards for priority substances in the field of water quality policy (RefB4/3040/2000/30637/MAR/E1). For the Austrian case study MPAs / MPCs are given for the selected parameters cadmium, lead, tetrachlorethene and trichlorethene.
For tetrachloroethylene a national threshold value of 6 µg/l is defined. The drinking water standard for the sum of tetrachloroethylene and trichloroethylene is 10 µg/l.
Table 8: Results of TV-calculation based on NBLs (Bridge 90 %- and 97.7 %-percentile and national NBLs) and national EQS values
Parameter EQS
(national)
Bridge-NBL
90% / 97.7 /
NBL acc. to
GEOHINT
Threshold value =
EQS+NBL
Cadmiumµg/l 1 0.2 / 0.2 / 0.2 1.2 / 1.2 / 1.2
Lead µg/l 10.8 1 / 3 / 3 11.8 / 13.8 / 13.8
Mercury µg/l 1 0.1 / 0.1 / - 1.1 / 1.1 / 1
Arsenic µg/l 24 1 / 1 / 4 25 / 25 / 28
Chrome µg/l 8.5 1 / 4 / 4 9.5 / 12.5 / 12.5
Copper µg/l 8.8 1 / 1 / 4 9.8 / 9.8 / 12.8
Trichloro-ethylene
10 - 10
Tetrachloro-ethylene
10 - 10
Conclusion: The threshold values (cadmium and lead) for 'groundwater itself' calculated according to the MPA-approach with national Environmental Quality Standards (option 2) showed in general higher TVs as option 1.
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3.1.4 Calculation of the dilution factor for the receptor surface water
As already mentioned in the characterisation of the Southern Vienna Basin, groundwater from deeper lying aquifers in the southern part discharges in the northern parts of the Southern Vienna Basin and feeds surface waters, namely the river Fischa and its tributaries. Those surface waters therefore have to be regarded as relevant receptors.
There are two surface water quality monitoring sites at the river Fischa, “Haschendorf” and “Fischamend”. As concentrations of pollutants at these sites may stem from the proportion of the flow which is provided by the groundwater, the dilution factor of groundwater has to be estimated at these two sites.
The threshold value for the receptor surface water can then be calculated as:
TV = EQS / DF
Remark: With the proposed formula it is assumed that the concentration at the river upstream of the sampling site is cero and that all pollution derives from groundwater.
In Austria national environmental quality standards are defined for surface waters, which were used for the calculation of the TVs for the receptor surface water. According to the ordinance values below the limit of detection (LOD) have to be replaced by cero. Values below the limit of quantification (LOQ) have to be replaced by (LOD+LOQ)/2.
Calculation of threshold values for the receptor surface water at the site Haschendorf
The surface water quality sampling site “Haschendorf” at the river Fischa is located in the south of Southern Vienna Basin near the origin of the Fischa. The mean surface runoff at the quantitative monitoring site “Haschendorf” is about 0.4 m3/s (data from 1987 to 1997). In this section the Fischa is 100 % groundwater fed and the dilution factor therefore is 1.
Table 9 comprises the results of the calculation of threshold values for receptor surface water for the monitoring site Haschendorf.
Table 9: Results of the water quality monitoring 2005 at the site Haschendorf at the river Fischa with a Dilution Factor of 1
Parameter EQS (national)
Background
Conc.
EQS +
NBL
Threshold
value =
(EQS+NBL) /
DF
Arithmetic
Mean 2005
of the
monitored
data 2005
Cadmium 1 µg/l - 1 µg/l 1 µg/l 0
Lead 10.8 0.2 µg/l 11 µg/l 11 µg/l 0,075 µg/l
Mercury 1 µg/l - 1 µg/l 1 µg/l 0
Arsenic 24 µg/l - 24 µg/l 24 µg/l 0
Chrome 8.5 µg/l 0.5 µg/l 9 µg/l 9 µg/l 0
Copper 8.8 µg/l 0.5 µg/l 9.3 µg/l 9.3 µg/l 0.5 µg/l
21
Parameter EQS (national)
Background
Conc.
EQS +
NBL
Threshold
value =
(EQS+NBL) /
DF
Arithmetic
Mean 2005
of the
monitored
data 2005
Ammonium 0,89 µg/l - 0.89 µg/l 0,89 µg/l 8.25 µg/l
Nitrite 0,18 mg/l - 0.18 mg/l 0,18 mg/l 1.23 µg/l
Trichloro-ethylene
10 - 10 33.3 µg/l No data available
Tetrachloro-ethylene
10 - 10 33.3 µg/l No data available
For cadmium, mercury, arsenic and chrome all data are below the limit of detection and the arithmetic mean 2005 is therefore cero. For lead, copper, nitrite and ammonium the arithmetic mean values 2005 at the two sites are below the national EQS. For trichloroethylene and tetrachloroethylene no data are available at the two surface water quality sites at all.
3.1.4.1 Calculation of threshold values for the receptor surface water at the site
Fischamend
The surface water quality sampling site “Fischamend” at the river Fischa is in the north of the case study area, near the estuary to the Danube river. The mean surface runoff at the quantitative site “Fischamend” is about 7.6 m³/s. The total exfiltration of groundwater of the catchment area of the Fischa is approximately 5.5 m³/s (see also figure 7 with the zones of exfiltration of groundwater into surface water in the groundwater body Southern Vienna Basin).
The dilution factor for the site “Fischamend” can therefore be estimated to 0.3 or 30 %.
Dilution factor Fischamend = QGW / (QGW + Q SW) = 2.05 / 7,55 = ~ 0.3 or 30 %
Table 10 comprises the results of the calculation of threshold values for receptor surface water for the monitoring site Fischamend.
Table 10: Results of the water quality monitoring 2005 at the site Fischamend at the river Fischa with a Dilution Factor of 0.3
Parameter EQS (national)
Background
Conc.
EQS +
NBL
Threshold
value =
(EQS+NBL) /
DF
Arithmetic
Mean 2005
of the
monitored
data 2005
Cadmium 1 µg/l - 1 µg/l 3.3 µg/l 0
Lead 10.8 0.2 µg/l 11 µg/l 36.7 µg/l 0
Mercury 1 µg/l - 1 µg/l 3.3 µg/l 0
Arsenic 24 µg/l - 24 µg/l 80 µg/l 0
Chrome 8.5 µg/l 0.5 µg/l 9 µg/l 30 µg/l 0.925 µ/l
Copper 8.8 µg/l 0.5 µg/l 9.3 µg/l 31 µg/l 0.07 µg/l
22
Parameter EQS (national)
Background
Conc.
EQS +
NBL
Threshold
value =
(EQS+NBL) /
DF
Arithmetic
Mean 2005
of the
monitored
data 2005
Ammonium 0.89 mg/l - 0.89 mg/l 3 µg/l 17.25 µg/l
Nitrite 0.4 mg/l - 0.4 mg/l 1 µg/l 7.3 µg/l
Trichloro-ethylene
10 - 10 33.3 µg/l No data available
Tetrachloro-ethylene
10 - 10 33.3 µg/l No data available
For trichloroethylene and tetrachloroethylene no data are available at the two surface water quality sites at all. For Nitrite and Ammonium the mean values 2005 at the two sites are below the National EQS.
At the two surface water quality monitoring sites at the river Fischa, which is at least partly groundwater fed, no environmental quality standard has been exceeded.
4. CONCLUSIONS
4.1 Comments and conclusion on BRIDGE data pre-selection and NBL
estimation
Nitrate is in general one of the most relevant parameters concerning groundwater pollution in Austria. Therefore only few monitoring stations show a median value for nitrate < 10 mg/l. As a consequence the calculation of NBLs based on an own national approach respectively NBLs derived based on statistically results of Bridge-WP2 will be important. Furthermore it has to be recognised that for substances which are used as pre-selection parameters no sound calculation of NBLs is possible.
Besides nitrate the use of further pre-selection parameters indicating anthropogenic impacts seemed to provide the most reliable results.
The selection of the time period of measurements considered for NBL calculation should be discussed. Long time series of monitoring data already may indicate reasonable trends for any pre-selection parameter. The choice of time periods may reasonably influence how many sampling sites are to be considered for NBLs
Specific guidance on how to replace measurements below LOD / LOQ is necessary.
4.2 Comments and conclusion on the selection of Reference (REF) values
Understanding the receptor 'groundwater itself' as a resource for future uses drinking water standards would be an appropriate reference value. Regarding environmental issues the use of any agreed environmental quality standard for aquatic ecosystems might be acceptable.
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4.3 Comments and conclusion on the derivation of threshold values (TVs)
As for 'groundwater itself' as receptor most of threshold values were calculated according to case 2 of option 1 (NBL<1/3 of Reference Value; TV= 2 x NBL). The resulting TVs are consequently rather low and much lower than drinking water standards. The practicability of establishing threshold values far below drinking water standards must be discussed. Measures triggered by such threshold values might be costly but environmentally inefficient.
The threshold values (cadmium and lead) for 'groundwater itself' calculated according to the MPA-approach with national Environmental Quality Standards (option 2) showed in general higher TVs as option 1.
Regarding Tier 3 for the receptor 'surface water' the use of a dilution factor derived only according to assumptions on quantity and an estimation of the quantitative contribution of a groundwater body to a surface water body stipulates that all the dilution capacity is assigned to be filled up by one groundwater body. The fact that multiple pollutant discharges by a variety of sources are possible is neglected so far.
4.4 GENERAL CONCLUSION
The Austrian case study “Southern Vienna Basin” proofed the general applicability of the methodology. Nevertheless further discussions to refine the pre-selection approach for deriving NBLs, to establish a clear understanding and approach regarding 'groundwater itself' as a receptor and to adopt the approach regarding 'surface water' as a receptor are of importance.
5. REFERENCES
Geol. Bundesanstalt (2004): GeoHint Endbericht 2004 (Final report on geological background levels in Austria 2004). Umweltbundesamt Vienna (Environment Agency) (2005): Provision of data from the Austrian Groundwater Body-Database. BMLFUW (2005): EU WRR 2000/60/EG österr. Bericht über die IST-Bestandsaufnahme (Article 5/6 report of EU WFD). BMLFUW (2005): Wassergüte in Österreich Jahresbericht 2004 (waterquality in Austria, annual report 2004). Haidinger, R.; Reitinger, J. (1987): Grundwasserhaushalt der Mitterndorfer Senke – Grundwassererneuerung und Langzeitverhalten. TU-Wien.