Geostatistical tools for better characterization of the groundwater quality [Elektronische Ressource] : case studies for the coastal quarternary aquifers in the Nam Dinh area/Vietnam / vorgelegt von Hoang Duc Nghia

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GEOSTATISTICAL TOOLS FOR BETTER CHARACTERIZATION OF THE GROUNDWATER QUALITY – CASE STUDIES FOR THE COASTAL QUATERNARY AQUIFERS IN THE NAM DINH AREA/VIETNAM I n a u g u r a l d i s s e r t a t i o n zur Erlangung des akademischen Grades doctor rerum naturalium (Dr. rer. nat.) an der Mathematisch-Naturwissenschaftlichen Fakultät der Ernst-Moritz-Arndt-Universität Greifswald vorgelt von Hoang Duc Nghia geboren am 01, January, 1977 in Hue, Vitnam Greifswald, 2008 Dekan: .................................................................................................................... 1. Gutachter : .................................................................................................................... 2. Gutachter: .................................................................................................................... Tag der Promotion: ................................................................................................................ Erklärung Hiermit erkläre ich, daß diese Arbeit bisher von mir weder an der Mathematisch-Naturwissenschaftlichen Fakultät der Ernst-Moritz-Arndt-Universität Greifswald noch einer anderen wissenschaftlichen Einrichtung zum Zwecke der Promotion eingereicht wurde.
Publié le : mardi 1 janvier 2008
Lecture(s) : 21
Source : UB-ED.UB.UNI-GREIFSWALD.DE/OPUS/VOLLTEXTE/2008/493/PDF/NGHIATHESIS_2008.PDF
Nombre de pages : 143
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GEOSTATISTICAL TOOLS FOR BETTER
CHARACTERIZATION OF THE GROUNDWATER
QUALITY – CASE STUDIES FOR THE COASTAL
QUATERNARY AQUIFERS
IN THE NAM DINH AREA/VIETNAM




I n a u g u r a l d i s s e r t a t i o n

zur

Erlangung des akademischen Grades

doctor rerum naturalium (Dr. rer. nat.)

an der Mathematisch-Naturwissenschaftlichen Fakultät

der

Ernst-Moritz-Arndt-Universität Greifswald


vorgelt von

Hoang Duc Nghia

geboren am 01, January, 1977

in Hue, Vitnam

Greifswald, 2008


































Dekan: ....................................................................................................................


1. Gutachter : ....................................................................................................................

2. Gutachter: ....................................................................................................................


Tag der Promotion: ................................................................................................................
Erklärung






Hiermit erkläre ich, daß diese Arbeit bisher von mir weder an der Mathematisch-
Naturwissenschaftlichen Fakultät der Ernst-Moritz-Arndt-Universität Greifswald noch einer anderen
wissenschaftlichen Einrichtung zum Zwecke der Promotion eingereicht wurde.
Ferner erkläre ich, daß ich diese Arbeit selbständig verfaßt und keine anderen als die darin
angegebenen Hilfsmittel benutzt habe.




Hoang Duc Nghia

Table of content  
Contents 
CHAPTER 1 INTRODUCTION ...................................................................................................................... 1
1.1 Motivation................................................................................................................................................. 1
1.2 Why Geostatistics ?.... 2
1.3 Background and hydrogeological settings of test site: Nam Dinh Area............................................... 4
1.3.1 Study Area........ 4
1.3.2 Hydrological system and climate..................................................................................................... 5
1.3.3 Geological history............................................................................................................................ 6
1.3.4 Hydrogeological setting................................................................................................................... 7
1.4 Objective and approach............................................................................................................................. 9
1.5 Outline of the thesis.10
CHAPTER 2 CLASSIFYING WATER- TYPE GROUPS AND GRAPHICAL HYDROCHEMICAL DATA
ANALYSES .................................................................................................................................................. 12
2.1 Introduction............................................................................................................................................. 12
2.2 Methodology............ 13
2.3 Materials.................. 16
2.4 Results and discussion 18
2.4.1 Major ion comparison.................................................................................................................... 18
2.4.2 Graphical methods......................................................................................................................... 22
2.5 Conclusions.............. 31
CHAPTER 3 EXPLORATIVE STATISTICAL DATA ANALYSIS OF THE WATER .............................. 32
3.1 Introduction............................................................................................................................................. 32
3.2 Methodology............ 33
3.3 Materials.................. 34
3.4 Results and discussions........................................................................................................................... 36
3.4.1 Description data............................................................................................................................. 36
3.4.2 Exploratory data analysis and display ........................................................................................... 40
3.4.3 The quantitative variability of the groundwater chemistry due to the seasonal changes............... 43
3.5 Conclusions and discussion..................................................................................................................... 46
CHAPTER 4 TEMPORAL AND SPATIAL VARIABILITY OF THE GROUNDWATER QUALITY IN
THE COASTAL QUATERNARY AQUIFERS, THE NAM DINH AREA/VIETNAM
A CASE STUDY BASED ON KRIGING TECHNIQUES .................................................................................. 48
4.1 Introduction.............. 48
4.2 Methodology............ 49
4.2.1 Variogram....... 49
4.2.2 Kriging........................................................................................................................................... 51
4.3 Materials.................. 53
4.4 Results...................... 53
4.4.1 Variography.... 53
4.4.2 Spatial interpolation....................................................................................................................... 57
4.5 Discussion and Conclusions.................................................................................................................... 69
CHAPTER 5 CHARACTERIZATION OF THE GROUNDWATER CHEMISTRY IN THE COASTAL
QUATERNARY AQUIFERS, THE NAM DINH AREA - AN ASSESSMENT BASED ON CLUSTERING
AND PCA APPROACHES................................................................................................................................... 71
5.1 Introduction.............. 71
5.2 Methodology............ 72
5.2.1 Cluster analysis.............................................................................................................................. 72
5.2.2 Principle component analysis ........................................................................................................ 72
5.2.3 Regionalization analysis ................................................................................................................ 73
5.3 Materials.................. 73
5.4 Results...................... 74
5.4.1 Cluster analysis.............................................................................................................................. 74
5.4.2 Principle component analysis. ....................................................................................................... 79
5.4.3 Regionalization 82
5.5 Discussion and Conclusions.................................................................................................................... 86
CHAPTER 6 ASSESSING THE RISK OF ARSENIC CONTAMINATION IN THE COASTAL
QUATERNARY AQUIFERS IN THE NAM DINH AREA/VIETNAM: A CASE STUDY BASED ON
INDICATOR KRIGING ....................................................................................................................................... 88
6.1 Introduction.............. 88
6.2 Hydrogeological setting .......................................................................................................................... 89
6.3 Objectives................ 89
6.4 Results...................... 90
6.4.1 Exploratory data ............................................................................................................................ 90
6.4.1 Indicator variogram analysis.......................................................................................................... 91
6.4.2 Estimation of local dpf .................................................................................................................. 92
6.4.3 Mapping the probability of exceeding the threshold. .................................................................... 92
6.5 Discussion and conclusions..................................................................................................................... 94
CHAPTER 7 SYNTHESIS............................................................................................................................. 95
7.1 Introduction............................................................................................................................................. 95
7.2 Optimizing the data analyses on groundwater chemistry........................................................................ 95
7.3 Conclusions and discussion 97
7.4 Future perspectives on groundwater investigation and exploration of the area ...................................... 98
REFERENCES ………………………………………………………………………………………………….100
 
List of figures 

Fig. 1.1 The outline map of the Nam Dinh area ..................................................................................... 4
Fig. 1.2 Cross section from Vu Ban to Hai Hau 5 3 Relationship between the monthly mean rainfall and actual evaporation................................. 6
Fig. 1.4 Relationship between annual rainfall and actual evaporation.................................................. 6
Fig. 1.5 Quaternary geology and topography of the Red River delta and adjacent areas. ................... 7
Fig. 1.6 The variation of water levels at the national monitoring wells ................................................. 8
Fig. 1.7 The decreasing of water levels at the national monitoring wells .............................................. 9
Fig. 2.1 Different water types................................................................................................................ 15
Fig. 2.2 The frequency of charge balance error .................................................................................. 17
+Na
Fig. 2.3 Frequency plot of ratio ..................................................................................... 18 + −Na + Cl
+Na
Fig. 2.4 frequency plot of ratio........................................................................................ 19 + −Na + Cl
2 +Ca
Fig. 2.5 The difference of the ratios in groundwater of the Holocene........................ 19
2 + 2 −Ca + SO
Fig. 2.6 Major ion percentage of seawater......................................................................................... 20
2 +Mg
Fig. 2.7 Frequency representing different ...............................................................20
2 + 2 +Ca + Mg
2 +Mg
Fig. 2.8 The various ratios of the Pleistocene aquifer ............................................. 21
2 + 2 +Ca + Mg
+K
Fig. 2.9 The frequency of ratio........................................................................................ 22 + +Na + K
Fig. 2.10 Piper plot representing various groups of groundwater-types........................................... 23
Fig. 2.11 Piper plot representing various groups of groundwater-types ............................................ 23
Fig. 2.12 Piper plot representing various water-types ........................................................................ 24
Fig. 2.13 Piper plot representing major components .......................................................................... 25 14 Pip 25
Fig. 2.15 Piper plot representing various water-types for the Pleistocene aquifer . ........................... 26
Fig. 2.16 Hydrogeochemical section of the Pleistocene . .................................................................... 27 17 Hythe Pleistocene aquifer from West to East ............................ 28
Fig. 2.18 Site map representing the relative proportions of the six major ions................................... 29 19  Site.................................. 30
Fig. 3.1 The location distributions of samples ..................................................................................... 35
Fig. 3.2 Histograms representing original and log-transformed data................................................. 41 3 Histograms representing original........................................................................................... 42
Fig. 3.4 Statistical distribution of measured elements as box-plots for both aquifers......................... 44 5 Comparison of the short term variation ................................................................................. 45
Fig. 4.1 Omni-directional variograms and fitted models..................................................................... 54
Fig. 4.2 Directional variograms and fitted models on chloride and EC levels.................................... 55
Fig. 4.3 Variograms and fitted models on log(Cl), log(Fe) and pH variables..................................... 56 4 Kriging maps showING locally spatial distribution of the chloride (Cl) concentration ........ 59
Fig. 4.5 Temporal and spatial distribution of calcium and bicarbonate ............................................. 60
Fig. 4.6 Kriging maps and error maps show the temporal and spatial distribution of the iron ......... 61
Fig. 4.7 Comparison of the difference between isotropic estimation and anisotropic estimation ...... 64
Fig. 4.8 Kriging maps showING the spatial variability of chloride and iron concentrations ............. 65
Fig. 4.9 Temporal and spatial variability of EC as obtained from three datasets ............................... 66
Fig. 4.10 Kriging maps and error maps of the pH variable ............................................................... 67
Fig. 4.11 Kriging maps representing the distribution of the three groundwater groups .................... 68
Fig. 5.1 Dendrogram based on agglomerative hierarchical clustering.............................................. 75
Fig. 5.2 Scatter-plot representing the spatial distribution of the classes............................................. 76
Fig. 5.3 Scatter-plot repre 77
Fig. 5.4 Scatter plot representing ththe classes 78
Fig. 5.5 Regionalization of the principal components for the shallow groundwater........................... 83 6 Region ofor the Holocene aquifer ................................. 84
Fig. 5.7 Regionalization of components ......................................................................... 85
Fig. 6.1 Histograms of arsenic values measured for the Holocene aquifer......................................... 90
Fig. 6.2 Isotropic indicator variograms for the Holocene and Pleistocene aquifers........................... 91
Fig. 6.3 E-type and probability maps of exceeding 10 μg/l ................................................................. 93

List of tables 


Table 2.1 Simple groundwater classification based on TDS........................................................... 13
Table 2.2 Source-Rock deduction analysis ..................................................................................... 14
Table 2.3 Materials used in the entire thesis................................................................................... 17
Table 3.1 Different quantiles of all parameters collected in both campaigns RS 1999 and DS 2000
representing the frequency of ions concentration . ......................................................... 37
Table 3.2 SS 2000 hntration .......................................................... 38
Table 3.3 Range of groundwater chemistry for the Holocene aquifer ............................................ 39
Table 3.4 groundwater chemistry for the Pleistocene aquifer ......................................... 40
Table 4.1 Parameters of the fitted models for Kriging estimation in some chemical variables of the
Holocene aquifer ............................................................................................................. 57
Table 4.2 f the fitted models for Kriging estimation under the assumption of
isotropy………….............................................................................................................. 57
Table 4.3 Parameters of the fitted models for Kriging estimation based on anisotropic variogram
models… …………………………………………………………………………………………57
Table 5.1 R-mode varimax rotated factor matrix for 7 measurements in shallow groundwater
samples……………………................................................................................................ 79
Table 5.2 r 11 measurements in the Holocene aquifer... 80
Table 5.3 R-mode varimax rotated factor matrix for the Pleistocene aquifer................................. 81
Table 6.1 Parameters of fitted indicator variogram models for arsenic in both aquifers............... 91
 
List of abbreviations 

K: Hydraulic conductivity [m/d]
DS: Dry Season
RS: Rainy Season
TDS: Total Dissolved Solid [mg/l]
EC: Electrical Conductivity [ μS/cm]
ΣFe: Total Iron [mg/l]
CA: Cluster Analysis
PCA: Principle Component Analysis
RA: Regionalization Analysis
OK: Ordinary Kriging
IK: Indicator Kriging
Ani-variogram: Directional Variogram
Omni-variogram: Omni Directional Variogram, calculated independently of direction
a: Range of influence (spatial correlation) [Length]
2C : Nugget Effect [data unit ] 0
th 2C : Sill of i structure [data unit ] i
Ani-ratio: Ratio of Anisotropy
Sph: Spherical variogram model
Exp: Exponential variogram model
Est: Estimate
Est_var: Estimation variance

 
Summary 

The primary objective of this study is to practically apply geostatistical tools that can help
to improve an evaluation of groundwater quality for a particular area. The Nam Dinh area, an
2area of 70 x 70 km , located in the Southern part of the Red River Delta, was selected as a
source for different data sets to be used as case studies. A set of geostatistical tools has thus
been applied to the different real data sets which were collected from the coastal Quaternary
aquifers in the different campaigns. This gives us a yardstick by which the success of a
specific approach can be measured. Throughout the thesis a series of the case studies are, in
turn, represented in order to get insight into and an understanding of what various
geostatistical tools can do and, more importantly, what their shortcomings are.
There are nine different methods of data analyses use in this thesis, which include: (1)
Major Ion Comparison, (2) Graphic Plots, (3) Exploratory Statistical Data Analysis, (4)
Variogram Analysis, (5) Spatial Estimation Using Kriging, (6) Cluster Analysis, (7) Principle
Component Analysis, (8) Multivariate Regionalization Analysis, and (9) Contamination Risk
Mapping Using Indicator Kriging.
First, major ion comparison and graphic analysis are performed in order to get a general
hydrogeochemical view of the collected datasets, before stepping into a further geostatistical
approach. By these analyses, various groundwater types are observed and a general
hydrochemical trend is visualized using Stiff- and Piper diagrams as well as site maps. The
major ion ratios in relation to TDS concentration are compared to investigate the origin of
water. It is demonstrated that a mixing process of fresh-brackish-saltwater interactions
governs the groundwater chemistry in both aquifers. A general trend of increasing major ion
concentrations from southeast to northeast and from west to east of the Nam Dinh area in the
Pleistocene aquifer is detected. The fresh groundwater (< 1000 mg/L) in the Pleistocene
aquifer is of Na-Ca-Mg-HCO type, whereas the dominant water-types in the Holocene 3
aquifer and in the remaining part of the Pleistocene are Na-Cl and Na-Mg-Cl. Within the
Holocene aquifer to two water-types are heterogeneously distributed in space. Contrastingly
in the Pleistocene aquifer the Na-Ca-Mg-HCO fresh water body can clearly be distinguished 3
from the saline water.
Second, a statistical exploratory data analysis is applied to describe the important features
of the data by which the character of a specific hydrogeochemical variable might be
recognized. Deviations from the Gaussian probability model are detected and appropriate
transformations for a formal analysis in geostatistics are selected. Since the Theory of
Regionalized Variables (Mathéron 1971; short term: Geostatistics) assumes Gaussian
distribution the hydrochemical variables used here are checked for normality. These analyses
show that although the data are facing some problems such as outliers and they are very
positively skewed at the linear scale, this can effectively be minimized by transforming the
data to log-scale. However, for trace elements (e.g., Al and F) other transformations would
have been necessary. The extreme values of several well known trace elements such as F and
Al that still remain high in the dataset after log-transformation can, however, cause
undesirable effects in the spatial estimation using Kriging and in principle component
analysis, respectively. In consequence, these variables have not been considered in these
analyses. Moreover, the results of these analyses show that the range of the major ions for
both aquifers varies largely. The concentrations of Na, Mg, and Cl ions in the Holocene
aquifer are, in general, higher than those in the Pleistocene aquifer. Except for a large number
of analyses in the Pleistocene, taken from wells in the Southern part of the Nam Dinh area,

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