1. 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

2. Layout of presentation
Radon (focus of Rn in groundwater)
Objective of project / Phases involved
Methodology
Results & Discussions

3. 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 ?

4. Uranium decay series 238U (parent) 222Rn 206Pb (stable) 226Ra 218Po
214Bi  
238U (parent)
214Po  
234Th 
210Pb  
234Pa 
210Bi   
234U
210Po
 + 
206Pb (stable) 
230Th
 + 

5. Principal cause of radon problem
Geology

6. Genomsnittlig årlig stråldos i Sverige
Source: Statens Strålskyddsinstitut

7.  Exposure routes groundwater Construction material
Soil gas / bedrock (Granite)
groundwater

8. Regulatory limits (Sweden)
Radon in water
Radon in air
Radon > 1000 Bq/l
Gränsvärde för otjänligt
Radon: 400 Bq/m3
Riktvärde för radon i befintliga bostäder
Radon > 100 Bq/l
Gränsvärde för tjänligt med anmärkning
Radon: 200 Bq/m3
Gränsvärde för radon i nya bostäder

9. Radon problems in water
Surface water
Groundwater
Dug wells
(soil/sand aquifer)
Drilled wells
(Hard rocks)

10. 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 %

11. 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 ?

12. 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

13. Radon Emanation
Radium atom
Radon atom 
Mineral grain   
Pore 

14. Radon risk in Sweden Groundwater radon risk map of Sweden
(after Åkerblom & Lindgren, 1997)

15. (Knutsson & Olofsson, 2002)

16. Any deduction?  not always the case
Granite types of rocks with high uranium concentration
High radon concentration in water
 not always the case

17. 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.

18. 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.

19. Study area

20. Phases of the project Phase 1 Phase 2 Phase 3
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

21. 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.

22. Factors considered Elevation Derived factors 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

23. Geographical Information System (GIS)
GIS is a computer system for managing spatial data.
Purpose of GIS
Organisation
Visualisation
Spatial Query
Combination
Analysis
Prediction

24. Visualisations with GIS
Bedrocks
Soil

25. 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

26. Methodology using GIS

27. 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 ’

28. 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)

29. 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)

30. Results of statistical analyses

31. Descriptive Statistics
Statistic parameters
Number of wells
4439
Minimum radon concentration (Bq/l)
4.0
Maximum radon concentration (Bq/l)
63560
Mean radon concentration (Bq/l)
492
Median value
230
Variance
Standard deviation
1227

32. Radon concentrations in Stockholm County

33. Boxplot
Median
25%-75%
Non-outlier range

34. ANOVA - Altitude

35. Anova - Relative altitude

36. ANOVA-Bedrock

37. ANOVA- Fracture

38. ANOVA - Soil

39. ANOVA- Landuse

40. ANOVA- Uranium

41. 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.

42. Risk Variable Method Preparation Phase (Expert system)
Data collection
Statistical analyses
Expert assessment
Selection of significant variables
Determination of risk values
Determination of uncertainty values
Suming up risk and uncertainty values
Final Risk Evaluation
Preparation Phase
(Expert system)
Operational phase
(User Interface)
Define study area

43. 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)

45. Distance from fracture
Ratings after RVM
Altitude 2
Soil
Uranium 3
Landuse
Bedrock
Distance from fracture

46. An example of a risk map

47. Field Studies

48. 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 = Bq/l

49. Wells on ljusterö predominant geology is gnejsgranitoid

50. 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

51. 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)