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Radon in groundwater Analysis of causes and development of a prediction methodology. Skeppström K. PhD. Student Dept. of Land and Water Resources Engineering, KTH. Layout of presentation. Radon (focus of Rn in groundwater) Objective of project / Phases involved Methodology

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Radon in groundwater analysis of causes and development of a prediction methodology

Radon in groundwater

Analysis of causes and development of a prediction methodology

Skeppström K.

PhD. Student

Dept. of Land and Water Resources Engineering, KTH


Radon in groundwater analysis of causes and development of a prediction methodology

Layout of presentation

Radon (focus of Rn in groundwater)

Objective of project / Phases involved

Methodology

Results & Discussions


Radon
Radon

  • Radioactive

  • Colourless, odourless, noble gas

  • Exists as 3 main isotopes:

  • 222Rn (uranium decay series, 238U),Half-life ( T1/2) = 3.8 days

  • 220Rn (Thorium decay series, 232Th), T1/2 = 56 seconds

  • 219Rn (Actinium decay series, 235U), T1/2 = 4 seconds

  • Cancer risk

    • 500 cases of lung cancer/year in Sweden; smokers have a higher risk.

    • Risk of developing of other cancers ?


Radon in groundwater analysis of causes and development of a prediction methodology

226Ra

222Rn

218Po

214Pb

214Bi

Uranium decay series

238U (parent)

214Po

234Th

210Pb

234Pa

210Bi

234U

210Po

 + 

206Pb (stable)

230Th

 + 



Genomsnittlig rlig str ldos i sverige
Genomsnittlig årlig stråldos i Sverige

Source: Statens Strålskyddsinstitut


Exposure routes

groundwater

Construction material

Soil gas / bedrock (Granite)

Exposure routes



Radon problems in water
Radon problems in water

Surface water

Groundwater

Dug wells

(soil/sand aquifer)

Drilled wells

(Hard rocks)


How radon in water is a problem
How radon in water is a problem?

1000 Bq/l

in water

100 Bq/m3 in air

Dish washing 95 %

Shower 60 – 70 %

Bath 30 – 50 %

Washing machine 90 – 95 %

Tap water 10 – 45 %

WC 30 %


Radon in groundwater analysis of causes and development of a prediction methodology
-

Radon in water

Radon emanated in mineral grain escape in the pore space

Recoil

Theory

Prerequisites

Presence of parent elements, 238U or 226Ra

  • Transport mechanisms

  • Diffusion

  • Convection

Pore space filled with water- Radon dissolves in the water

  • Dosimetry

  • 1000 Bq/l is dangerous

Water extracted from drilled wells (fracture water)

How is it

a problem ?


Radon in groundwater analysis of causes and development of a prediction methodology

Precipitation of 238U 234U, 230Th, 226Ra from water to surface of fracture

Leaching of 238U and 234U

Emanation of 222Rn

Content of 238U in the rock: 10ppm

222 Rn

Concentration of 222Rn in Bedrock: 0.33Bq/m3 rocks

Concentration of 222Rn in groundwater: 5 milj Bq/m3


Radon in groundwater analysis of causes and development of a prediction methodology

Radon Emanation

Radium atom

Radon atom

Mineral grain

Pore


Radon in groundwater analysis of causes and development of a prediction methodology

Radon risk in Sweden

Groundwater radon risk map of Sweden

(after Åkerblom & Lindgren, 1997)



Any deduction
Any deduction?

Granite types of rocks with high uranium concentration

High radon concentration in water

 not always the case


Radon in groundwater analysis of causes and development of a prediction methodology

Hypothesis of project

  • The hypothesis stipulates that the occurrence of radon from groundwater is governed by a number of well-defined factors ranging from:

  • Geological (bedrock, soil, tectonic structures, flow pattern and surrounding environment)

  • Chemical (oxidation reaction, other processes in water)

  • Topographical (difference in elevation and slope that determine flow pattern and renewal tendency and frequency)

  • Technical(withdrawal system & frequency which determine circulation as well as ventilation possibilities.


Radon in groundwater analysis of causes and development of a prediction methodology

Purpose of research

  • Map processes and factors influencing radon content in groundwater

  • Develop a prediction model, based on statistics, that can be used to determine areas at risk.



Radon in groundwater analysis of causes and development of a prediction methodology

Phases of the project

Using GIS and multivariate analysis of

data to assess factors affecting radon

concentration – REGIONAL LEVEL

Phase 1

Detailed study at Ljusterö to determine

spatial & temporal variation of radon

concentrations due to a range of factors.

LOCAL SCALE

Phase 2

Development of risk prediction model

Phase 3


Radon in groundwater analysis of causes and development of a prediction methodology

Phase 1

  • Data collection from:

    • Swedish National Land Survey (elevation and landuse data)

    • Swedish Geological Survey, SGU (soil & bedrock geology, fractures, radiometric)

    • Municipalities (data about wells and radon content)

  • Data transformation and extraction using ArcGIS and its spatial analyst function

  • Statistical analyses including multivariate

    analysis of data.


Radon in groundwater analysis of causes and development of a prediction methodology

Factors considered

  • Elevation

  • Soil geology

  • Bedrock

  • Fracture zone

  • Landuse

  • Uranium content

Variables

  • Derived factors

  • Altitude difference

  • Predominant soil, bedrock, landuse within a certain vicinity e.g. 200 m

  • Slope of the terrain


Geographical information system gis
Geographical Information System (GIS)

  • GIS is a computer system for managing spatial data.

  • Purpose of GIS

    • Organisation

    • Visualisation

    • Spatial Query

    • Combination

    • Analysis

    • Prediction



What is my objective
What is my objective?

For each well, relevant spatial patterns need to be extracted from the factor maps

To generate continuous surfaces with a spatial resolution of 50 m

+

Derive factors

Data obtained in different formats, e.g ASCII, point vector

GIS

Software: ArcMap

Spatial analyst function

Geostatistical software

Ultra edit

software



Statistical methods
Statistical methods

  • Which method?

  • Relate radon concentration with a large number of variables

  • Variables are both qualitative and quantitative in nature

  • Non-normal distribution of many variables

  • Use of covariance and correlations ? Careful with the interpretations

    • Not much information about association between variables

    • Non-linear associations can exist

    • Very sensitive to ‘wild observations- outliers ’


Radon in groundwater analysis of causes and development of a prediction methodology

Statistical Analyses

  • Use of multivariate analysis of data

    • Each observational unit is characterised by several variables.

    • It enables us to consider changes in several properties simultaneously

    • Non normality of data (non parametrical tests)

  • Statistical Methods

    • Analysis of variance

    • Principal Component Analysis (PCA)


Pca method
PCA method

  • Eigenvectors of a variance-covariance matrix

  • Linear combinations of these variables

  • Its general objectives:

    • Data reduction (A small amount of k components account for much of the variability of the data)

    • Interpretation (may reveals relationships that were not previously suspected)





Boxplot
Boxplot

Median

25%-75%

Non-outlier range









Radon in groundwater analysis of causes and development of a prediction methodology

Summary of results

  • High radon concentration in drilled wells is related to:

    • Low altitude

    • Granite rocks

    • Close distance to fracture

    • When overlying geology is lera/silt

    • Infrequent use of wells (summer houses)

    • An overview of the terrain in the surrounding of the wells (flat or hilly) is also of interest in connection to groundwater flow tendencies and speed of flow.


Risk variable method

Data collection

Preparation Phase

(Expert system)

Statistical analyses

Expert assessment

Selection of significant variables

Operational phase

(User Interface)

Define study area

Determination of risk values

Determination of uncertainty values

Suming up risk and uncertainty values

Final Risk Evaluation

Risk Variable Method


Risk variable modelling rvm
Risk Variable Modelling (RVM)

V1 x R1 + V2 x R2 + V3 x R3 + ……….+ Vn x Rn = FRV

FRV = Final risk value

  • Where Vi= a risk value for a specific variable (-2 to +2)

    Ri = the rating of the variable (1 to 3)





Radon in groundwater analysis of causes and development of a prediction methodology

Field studies at Ljusterö

  • Why Ljusterö?

  • Number of wells = 198

    • 141 wells exceeding 500 Bq/l (71%)

    • 96 wells exceeding 1000 Bq/l (48%)

  • Radon concentration

    • Mean = 1942 Bq/l

    • Minimum = 50 Bq/l

    • Maximum = 63560 Bq/l


  • Radon in groundwater analysis of causes and development of a prediction methodology

    Wells on ljusteröpredominant geology is gnejsgranitoid


    Radon in groundwater analysis of causes and development of a prediction methodology

    What was done?

    To choose 3-4 study areas on Ljusterö, exhibiting drastic fluctuations in the radon concentration and to perfom detailed study at these locations


    Radon in groundwater analysis of causes and development of a prediction methodology

    Detailed study

    • Analysis of geology (bedrock type, fracture zones, tectonic zones and fracture filling minerals, soil type and soil depth)

    • Altitude and other terrain considerations

    • Analysis of technical factors (wells technical design, hauling system, spatial temporal extraction patterns of wells)

    • Radiometric measurements of radiation (from soil around wells as well as measurements of radiation in wells and in tap water)

    • Chemical analyses in water samples (U, Ra, Rn, fluoride and other water components)