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Proposal for estimation of surface water bodies background levels for selected metals

Slovak Republic

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State Geological Institute of Dionýz Štúr, Bratislava________________________________________________________________

Slovak Hydrometeorological Institute, Bratislava

Slovak Water Management Authority

Institute of Hydrology SAS, Bratislava

Water Research Institute, Bratislava

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Background level means the concentration of a substance or the value of an indicator in a body of surface water corresponding to no, or only very minor, anthropogenic alterations to undisturbed conditions.

The estimation of background levels for single chemicals in groundwater is rather complicated and also „sensitive“ dilemma not only from the scientific but also from the economic point of view (implementation of WFD, river basin management plans, measures etc.).

The proposed methodology of their estimation stems from the feasibility of the input information, conceptual model and scientifically review of results in specific natural conditions of Slovak Republic.

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Estimatimation of the BL – statistical approach

o Determination of the character of the distribution of evaluated chemical element / compound (visually, histogram, testing of character of distribution)

o Censored data < 40% values below LOQ - substitution method (LOQ/2)40% - 60% values below LOQ - Kaplan-Meier´s analysis > 60% values below LOQ - meaningful value (LOQ)

o Calculation of background value (identification and elimination of

outliers). This step is individual for each element / compound and is managed by the character of the input data. After optimization

(2σ-technic, trimmed mean, x + 2σ) we recommend to use median + 2*(Median Absolute Deviation)

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Median Absolute Deviation(MAD)

1.Resistant estimator of spread (statistical point of view) 2.Suitable for geogenic and anthropogenic anomalies

detection (geochemical point of view)

The MAD is computed by first listing the absolute value of all differences |d| between each observation and the median. The median of these absolute values is than MAD.

MAD (Xi) = median |di|,

where di = Xi – median |Xi|

BL = median + 2*MAD

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Input data for estimation of the background levels in surface water bodies

• Components for background levels estimation:– selection followed EU and Slovak legislation – mainly priority and

dangerous substances– Cd, Hg, As, Pb, Ni, Cr, Zn, Cu and Al (other under preparation)

• Analytical results from the national geochemical mapping programme (statistical sampling density: 1 sample/ 4 sqr km – 10 159 samples of surface water – not the whole Slovak territory covered)

• Surface water quality monitoring network (time factor, regime variability) – 45 536 samples from time period 1995 – 2007

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Number of surface water bodies – 1826

Element

Data – SGI Data – monitoring

Number of WB with existing

measurements

Number of WB with existing

measurements (%)

Number of WB with existing

measurements

Number of WB with existing

measurements (%)

Al 1034 56,6 103 5,6

As 1048 57,4 191 10,5

Cd 1046 57,3 210 11,5

Cr 1043 57,1 145 7,9

Cu 1046 57,3 212 11,6

Hg 1047 57,3 204 11,2

Ni 217 11,9 194 10,6

Pb 1045 57,2 210 11,5

Zn 1048 57,4 220 12

Input data- National database (1995-2007)- Database of SWMA (1995-2007)- Database of State Geological Institute – unrepeated data

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Conceptual model of background levels calculation for surface water bodies

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Zlatá Baňa

Trenč. Jastrabie

Lomnický štítSkalnaté Pleso

Tatr. Lomnica

Lupčianska dol.HomôlkaStarý Hrozenkov

Slovnaft

Skalica

Chopok - Jasná

Chopok - SrdiečkoČertovica

Dobšina

Handlová

B. Studenec

Dukla

Branisko

Bratislava - Žel. st Cejkov

Červený Kláštor

Donovaly

Hajnačka

Horný Tisovník

Lehôtka p. Brehy

Lokca

Martin

Muráň

Opavská hora

Oščadnica

Patince

Pezinská Baba Plešivec

Podhradie

Pusté poleRemetské Hamre

Rochovce

Ružomberok

Slanec

Štrbské Pleso

Vojany

Vrátna dol.

Zádielska dol.

Zobor

Mapka monitorovacích stanovíšť zimných zrážok

Input data samples for BL estimation in surface water: monitoring network of the Slovak winter precipitations

(1976 - 2008)

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Input data samples for BL estimation in surface water:As distribution in the rock environment

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Input data samples for BL estimation in surface water: As distribution in soils – C horizon

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Input data samples for BL estimation in surface water: As distribution in stream sediments

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GIS system for supporting of background levels estimation

www.geology.sk1 . D escr ip tiv e s ta tis tic sls a n d

d a ta a n a ly sis

2 . Testin g o f sta tistic s m eth o d s

3 . S e lec tio n o f b est m eth o d a n d a p p lica tio n

F in a lisa tio n o f a ll e stim a ted B L fo r ea ch e lem en t

4 . C a lcu la tio n o f B L fo r ea ch W B

5 . Trea tin g o f B L in G IS

6 . S u m m a riza tio n o f W B w ith ou t d a ta

7 . Treatin g o f W B w ith o u t d a ta - a n a lo g y

8 . S p a tia l d istr ib u tio n o f a ll e s tim a ted B L

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Background level of arsenic for surface water bodies in Slovakia

As in ug/l

Mean 2.29

Median 1.6

Mode 1

Range 59

Minimum 1

Maximum 60

Count 1742

Statistics:

Histogram of As background values for surface water bodies

591 613

456

38 15 15 4 1 1 8 00

100

200

300

400

500

600

700

1 2 4 6 8 10 15 35 50 70 MoreAs in ug/l

Freq

uenc

y

General Reference Value for As in surface water (according Slovak

legislation):

30 ug/l New proposal (AA-EQS):

24 ug/l

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Example: Final proposal of background level of As for surface

water bodies in Slovakia

Legend:

Arsenic (ug/l)

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Schematic map with distribution of highest cumulative BL for selected metals

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Uncertainty in estimating the background levels

• representativeness of the monitoring network in relation to the delineation of water bodies,

• different analytical techniques used during the monitoring period 1993 - 2007,

• different levels of background concentrations estimated from water bodies with data and without data,

• the evaluation was not considered to flow, which affects the content of the elements in surface water,

• allocation of contributing surfaces, contributing to water bodies.

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Recommendations

• Analytical chemistry - application of analytical techniques and procedures for reducing LOQ and learning outcomes and processes of membrane filtration in water samples.

• Verification of estimated background levels in areas with occurrence of

mineralized zones and ore deposits .

• Determination of macro-elements background levels in surface water and characterization of basic chemical types of surface water.

• Carefully review the relationship of background levels to determine the EQS for metals and non-priority substances

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Thank you for your attention