i MINISTRY OF EDUCATION AND TRAINING HANOI UNIVERSITY OF MINING AND GEOLOGY HOANG VAN HOAN SALT WATER INTRUSION IN QUATERNARY SEDIMENT IN NAM DINH AREA Specialty: Engineering geology Code: 62.52.05.01 SUMMARY OF DOCTORAL THESIS ON GEOLOGY Hanoi, 2014 ii This thesis has been completed at: Department of Hydrogeology, Faculty of Geology Hanoi University of Mining and Geology SUPERVISORS: 1: Assoc Prof Dr Pham Quy Nhan, Hanoi University of Natural Resources and Environment 2: Assoc Prof Dr Flemming Larsen, Geological Survey of Denmark and Greenland Judge 1: Assoc Prof Dr Doan Van Canh Vietnam Association of Hydrogeology Judge 2: Assoc Prof Dr Nguyen Van Hoang Vietnam Academy of Science and Technology Judge 3: Assoc Prof Dr Nguyen Hong Duc National University of Civil Engineering Shall be defended before the State level Thesis Assessment Council held at: Hanoi University of Mining and Geology at…… hours, on … … The Thesis can be further referred to at: National Library of Vietnam Or Library of Hanoi University of Mining and Geology INTRODUCTION Background of the thesis Vietnam has a coastline of over 3,260 km and many coastal areas where are high population, important economic and transportation of the country Located in the south east of the Red River Delta, in some districts of Nam Dinh and Ninh Binh provinces exist ground water lens in Cenozoic sediments Groundwater resources are being exploited to serve the dining, living and production of local people Potential exploitable reserves is smaller than demand and water level tends to get significantly lower (0.5 ÷ 0.7 m/year) The risk of saltwater intrusion has taken place due to the exploitation of groundwater In order to sustainable management groundwater resources It is necessary to study the distribution, shape, quality and quantity changes of the fresh water lens extraction in the area Purpose and tasks Purpose: To study the formation of freshwater lens; To determine the current status of fresh/saltwater in the Quaternary sediments in Nam Dinh area; To identify mechanisms of saltwater intrusion in Pleistocene aquifer (qp); To assess the mechanisms impact of salinization process Tasks: To study geological and hydrogeological structure that affect the formation of freshwater lens; To analyze and assess the current state of fresh/saltwater distribution based on the hydrogeological parameters and geophysics observations; To study salinity distribution in lowly permeable marine sediment and its influence to the Pleistocene aquifer; To identify saltwater intrusion mechanisms of freshwater lens in Pleistocene aquifer; To develop a mass transport model and to predict saltwater intrusion Target and study area Target: Groundwater in Pleistocene aquifer in Nam Dinh area; Study area: Freshwater lens in the Pleistocene aquifer at Nam Dinh city and related areas Project activities Determine the current status of saline groundwater distribution; Do sampling and analyze the surface, groundwater, precipitation and seawater samples; Identify mechanisms of saltwater intrusion in Pleistocene aquifer; Interpret the geophysical and hydrogeologic data; Conduct drilling, undisturbed soil sampling and squeeze pore water; Conduct drilling boreholes, and aquifer test; Develop solute transport models and make prediction of salt intrusion Approach and methodology Approach: - Practical approach; - Access to previous research results; - Access to the evaluation methods of modern investigation Methodology: - Hydro-geochemical method/hydrodynamics: Assess the salinity and evaluate hydrogeological parameters of the aquifer; - Geophysical method: determine the formation conductivity; - Isotopic method: determine the age and origin of groundwater; - Modeling methodology: forecast groundwater salinization; - Discussion: discuss and learn from the experts Scientific and practical significance of thesis Scientific significance: The thesis contributes to better understanding the process, the origin and recharge source of freshwater lens Mechanisms of saltwater intrusion and the role of these mechanisms in the process of salinization have characterized The correlation between the hydrogeological- geophysical parameters, and isotope composition has established and applied in the study area The obtained correlation therefore is applicable for other areas that have similar hydrogeological conditions Practical significance: The thesis has identified the current state of the saline groundwater distribution, and predict changes of salinity intrusion in the study area The obtained results provide valuable information to the managers, policy-makers and scientists for exploiting and sustainable use of precious groundwater resources Research objectives Objective 1: Freshwater in Pleistocene aquifer in Nam Dinh area is formed in evolution of geology and hydrogeology of area; the freshwater lens are continuously recharged by freshwater from lower aquifers in the west and northwest of Nam Dinh area Objective 2: Freshwater lens in the Pleistocene aquifer of Nam Dinh area is intruded saltwater due to the difference in hydraulic head between salt and freshwater zones from the north and northeast area; and also due to recharge from overlying low permeability (marine sediment) layer through complex chemical and physical processes, in which diffusion process and density flow play as major roles The scientific contributions of the thesis - The results of chemical analysis, isotopic compositions were used in combination with results of borehole geophysics to determine the variation of conductivity versus depth and also to analyze the impact of its processes to the Pleistocene aquifer - The thesis has applied geophysics methods and hydrogeological methods to determine the current status of the distribution of saltwater in the aquifer and marine sediments - The correlation between the chemical composition (Cl-, TDS) and geophysical parameters (conductivity, resistivity of formation) has been determined This correlation will be used for determining and assessing groundwater quality through geophysical parameters Data sources 9.1 Data collection: Available data and information related to thesis were collected, including published papers and final project reports 9.2 Laboratory and field studies results for the thesis only: The thesis mainly used data sources and field results carried out by the author and collaborators as following: Investigation results of the current status of saline groundwater distribution by the transient electromagnetic sounding (TEM), (61 points) and shallow boreholes (22 boreholes); Geophysical borehole logging results: 16 boreholes; Results of aquifer tests in qp aquifer: 03 pumping boreholes; The results of hydrochemical analysis: 59 groundwater samples and 27 pore water samples; The results of stable isotopic analysis: 87samples), radioactive isotopes (32 samples) and isotopes of inert gas (8 samples); Monitoring water quality and groundwater levels 10 Structure of thesis This thesis consists of 160 pages, including 20 tables, 94 figures and 122 references Structure of the thesis is as follows: Introduction Chapter 1: Overview of groundwater salinization study Chapter 2: The formation of the freshwater lens Chapter 3: Current state of saline distribution Chapter 4: Mechanism of saltwater intrusion in Pleistocene aquifer Chapter 5: Assessment and prediction of saltwater intrusion Conclusions and recommendations 11 Acknowledgements This thesis was completed at the Department of Hydrogeology, Faculty of Geology, Hanoi University of Mining and Geology, under the scientific supervision of Assoc Prof Dr Pham Quy Nhan and Assoc Prof Dr Flemming Larsen During the study period, written thesis, the author has received encouragement and guidance of subcommittee hearted guide The author also always get the help from scientists such as: Assoc Prof Dr Nguyen Van Lam, Assoc Prof Dr Kim Ngoc Nguyen, Assoc Prof Dr Doan Van Canh, Assoc Prof Dr Phan Ngoc Cu, Dr Dang Dinh Phuc, Dr Dang Duc Nhan, Assoc Prof Dr Nguyen Van Dan, Assoc Prof Dr Nguyen Van Hoang, Dr Vu Kim Tuyen, Dr Nguyen Thi Thanh Thuy, Dr Duong Thi Thanh Thuy, MSc Kieu Thi Van Anh, Prof Dieke Postma, Dr Frank Wagner, Assoc Prof Dr Christiansen V Anders, MSc Vu Long Tran, MSc Dang Tran Trung, MSc Nguyen The Chuyen, MSc Tran Thanh Le and colleagues in the VietAS project as well as many officials Scientifics expertise Again, the author would like to express my sincere gratitude for all these valuable help! Chapter - OVERVIEW OF GROUNDWATER SALINIZATION STUDY 1.1 Overview of groundwater salinization studies in the world The synthesis and analysis of scientific works published research salinization in the world showed that, all the studies were combined using different methods to solve a particular problem, such as to assess the current state, determine the cause, General comments: The cause of groundwater salinization in different areas can be varied, depending on its geological, hydrogeological conditions and geological evolution These studies have used different methods to determine the mechanisms of the process groundwater salinization, Synthesis of studies can be divided into main methods, including: Hydro-geochemical/hydrodynamics methods; Isotopic methods; Geophysical methods; Modeling methods 1.2 Overview of groundwater salinity intrusion in Vietnam Pollution of groundwater sources have been interested by scientists in Vietnam, as there are many topics, study of this issue Groundwater salinity intrusion occurs in coastal plains, dunes and islands due to human activities and natural environment factors General comments: The saltwater intrusion studies are often combined in the evaluation report of groundwater resources, mainly survey, demarcation survey of saltwater boundaries with TDS=1g/l and counting the time and speed movement of boundaries on the basis of geological and hydrogeological conditions in the study area with exploitation recharge requirements On the other hand, studies have also issued a warning about the possibility of saline into the exploitation works Synthesis of studies can be classified into main methods, including: Hydro-geochemical/hydrodynamics methods; Geophysical methods; Numerical modeling methods 1.3 History of studies on geology and hydrogeology in study area The studies of geology and hydrogeology in Nam Dinh are always associated with the study of the history of Red River Plain, besides at least 20 projects have been done in the area of Nam Dinh The topics and projects have showed overall picture of geological and hydrogeological conditions in Nam Dinh Chapter - THE FORMATION OF THE FRESHWATER LENS 2.1 Study area The study area is located in southeastern of Rid River Delta Plain, including Nam Dinh and Kim Son provinces, Yen Mo, Yen Khanh, Gia Vien district belong to Ninh Binh province 2.2 Geological characteristics of the study area 2.2.1 Stratigraphic characteristics 2.2.1.1 Stratigraphic characteristics Nam Dinh area Proterozoic Eonothem Proterozoic formations is Song Hong formation, widely distributed in the study area Composition: gneis mineral biotite, sillimanite, garnet Mesozoic Eonothem The Mesozoic formation consists mainly in the Triassic, the composition is limestone, brightly colored, clay limestone, on the western of study area in Ninh Binh province Cenozoic Eonothem - Neogen system - Pliocene series Including the Vinh Bao and Tien Hung formations Sediment composition consists of mainly small to medium sand interbedded with gravel and slity clay Quaternary System Lower Pleistocene stage - Le Chi formation (amQ11lc) The sedimentary of Le Chi formation is not exposed in surface but can met in the majority of boreholes in the study area Lithological composition including silt, fine sand, silty-clay Distribution depth of formation from 79m to 132.8m The thickness varies from 4m to 26.2m Middle Pleistocene stage - Ha Noi formation (a, amQ12-3hn) The sedimentary of Hanoi formation is widely distributed in the study area Lithological composition mostly sand and gravel with ranging from blue-gray to yellow-gray Upper Pleistocene stage - Vinh Phuc formation (a, am, mQ13vp) the sedimentary of upper Pleistocene in the study area is Vinh Phuc formation Composition is mainly of sand, silt sand and silty clay Lower-middle Holocene stage - Hai Hung formation (mQ21-2hh) The sediments of the Hai Hung formation is divided into types of origin Lithological composition is sand, silt sand with organic matter Upper Holocene stage - Thai Binh formations (Q23tb) Thai Binh formation is subdivided into two parts Sediment composition is mainly of fine-grained sand and silty clay 2.2.1.2 Stratigraphic characteristics of continental shelf Marine sediments belong to tidal estuary sedimentary in this study due to tidal Composition is composed mainly of coarse sand, fine sand, silt and clay, fine grain which gradually towards the sea 2.2.2 Structural Characteristics 2.2.2.1 Geological structural characteristics of Nam Dinh area In the study area exist two major fault systems that are perpendicular to each other and extend in northwest - southeast (NW-SE) and northeast - southwest (NE-SW) directions 2.2.2.2 Structural characteristics of geology in western study area In addition to the characteristics of the geological formations in the Cenozoic and pre-Cenozoic, the area was covered with Quaternary sediments with different geological structures The faults system extend in two directions: NW-SE and NE-SW, and the tectonic activities have divided the area into the lift and drop blocks 2.2.2.3 Geological structure characteristics of the continental shelf of study area The study area is located in the northwestern area of the Red River sedimentary basin, where there are many major faults oriented NW-SE 2.3 Hydrogeological characteristics 2.3.1 The aquifers 2.3.1.1 Aquifer of upper Holocene sediments Distributed throughout the all plain area, components of aquifer include sand, silty sand of Thai Binh formations 2.3.1.2 Aquifer of lower Holocene sediments This aquifer is not evenly distributed throughout the study area, not exposed on the surface Components of aquifer include sand, silty sand, silty clay of Hai Hung formation 2.3.1.3 Pleistocene aquifer Describe aquifers distributed throughout the delta area, lithological composition of aquifer include fine sand, coarse sand and gravel of Vinh Phuc, Hanoi and Le Chi formation 2.3.1.4 Pliocene aquifer 11 of rain, river water and water from bedrock, freshwater in Bao Vinh, Hanoi and Le Chi aquifers - In the late Pleistocene, about 14,000 to 15,000 years BP, sea levels began to rise again, beginning Flandrian transgression period, the Pleistocene sediments begin immersion by sea water in Nam Dinh - The Holocene transgression, reaching a maximum value in 6,000 years BP period When transgression occur, fine-grained sediments were deposited, they will prevent sea water from the Pleistocene aquifer before and become confine aquifer - The degradation in the Holocene, about 4,000 years BP the sea level begins dropping, while the hydraulic gradient in the aquifer increased due to the height difference between the supplying sources from the western bedrock formations and Quaternary sediments increased, fresh water flow prevail and replace saltwater in aquifer 2.5 Groundwater recharge for freshwater lens of study area 2.5.1 Methodology Application of isotopic techniques combine to study the structure of geology and hydrogeology determining the direction of groundwater in the Quaternary formations and earlier in order studying origin of freshwater and hydraulic relationship between aquifers * The origin of groundwater Deuterium (D or 2H) and 18O are two stable isotopes of hydrogen and oxygen and also the composition of the water molecules In the natural isotopic composition of the water will change in the phase transition * Groundwater flow determination by using radioactive isotopes The age of groundwater by isotope technique based on the decay of radioactive isotopes in the water molecular composition or in the quality or composition of the minerals dissolved in water 2.5.2 The study results 2.5.2.1 Stable isotope composition of the water samples Results analyzed stable isotopes δ2H composition changes from -72.58 to -2.12‰ and δ18O from -8.99 to -0.86‰ that showed the origin of water in aquifer from sea water and meteorological water 12 14 C 2.5.2.2 Radioactivity of C and 13C stable isotope composition Radioactivity ratio (14a) of the 14C isotope in dissolved inorganic carbon (DIC) of the water samples at different depths showed that the retention time of water in the aquifer is different Stable isotopes 13C as an indicator to determine the initial concentration of the samples 2.5.2.3 Research results and tritium isotopes of inert gas The inert gases and tritium isotopes allows to identify the residence time of water in the aquifer from to 1,500 years Resident time of ground water is longer from NW to SE 2.5.3 Analysis of results and discussion 2.5.3.1 Recharge source and origin of groundwater in study area Stable isotopes composition of water in the Pleistocene aquifer where some monitoring stations is recharged from the Neogene and Triassic aquifers Groundwater in qp aquifer has origin from rain water 2.5.3.2 Determination of groundwater flow direction base on the groundwater dating results The results of radioactive 14C isotopic composition analysis and residence time of water in the Triassic and Neogene aquifer throughout the study area showing: Residence time of water in the Pleistocene aquifer reaches the largest with 12,900 years and the shortest time is 1,100 years (fig 2.1) This freshwater in the center of the funnel has greatest residence time D GV01 100 50 0m 100 70m Q92 Present water (3H = 2,03 TU) -150 50 Q108 LK14 LK35 LK54 Q109 Q110 Q111 0m 12m 850 -50 -100 1.100 3H = 0,37 TU -50 100m 3H = 0,7 TU 3.300 67m 6.000 qp 80m tÔ nÔ 11.300 qp 150m Groundwater flow direction nÔ -200 -100 93,6m -150 7.400 nÔ 170,6m -200 tÔ -250 Fracture zone PR 248m -250 PR -300 -300 Karst and fracture aquifer; Granular aquifer; aquitard 850 - Groundwater age (year) Figure 2.1: Conceptual model of groundwater movement in study area from isotopic results (profile CD in figure 4.4) Water in the fractured, karst have directional movement NW-SE and from the west, north west toward the sea With the combination of 13 studied on geology, topography, geomorphology, and hydrogeology as well as isotopes results (14C, 3H, 39Ar/40Ar, 3He) in the monitoring points shows the trend more younger water with deeper Movement of groundwater from Triassic aquifer to Pleistocene aquifer by three ways: 1) Groundwater from Triassic aquifer recharge directly to qp aquifer; 2) From Triassic aquifer recharge to qp aquifer through Neogene; 3) From Triassic recharge to qp through Proterozoic and Neogene; Chapter - CURRENT STATE OF SALINE DISTRIBUTION 3.1 Theoretical basis of methodology The salinity of water depends on the total concentration of dissolved salts in water This is demonstrated by the ability of water conductivity Therefore, to determine electrical conductivity of water can be estimate the salinity of water characteristic 3.1.1 Resistivity of aquifer Conductivity in sedimentary rock is kind of electronic conductivity and ionic conductivity, which occurs in the mineral, or in other hand, transmission element is electron 3.1.2 The theoretical basis of transient electromagnetic method Transient electromagnetic soundings TEM study secondary field due to the eddy current induction occurs in conductive objects in the rest period of the current pulse 3.1.3 Theoretical basis of conductivity measurement Conductivity reflects the electrical capacity of the soils The essence of the method that study the phenomenon of electromagnetic induction of sediment or rock (formation) around the borehole 3.2 The TEM result 3.2.1 Location survey area The routing switch is arranged to measure the direction from the Red River to the sea; route length measurement, position measurement points and the points measured on the statement depends on results of field 14 surveys conducted before measurements to minimize, avoid noise of the surrounding environment 3.2.2 Survey results Using software SITEM/SEMDI quantitative analysis for the measured points, combining the analysis results of the chemical composition of groundwater build regression identified and verified at best limited in study area The resitivity limitation of salinity formation is 12.2 ohm.m (equal to g/L of TDS) 3.2.3 Analysis of results The first layer: resistivity value is relatively high; The second layer: play role the transition layer ; The third layer: a very small resistivity value, from 0.6 to 2.2 ohm.m; The fourth layer: large range of resitivity, lower resitivity gradually from west to east; The fifth layer: resistivity value is relatively high, from 12÷35ohm.m 3.3 Geophysical borehole results 3.3.1 Borehole logging location The logging boreholes measurement evenly distributed in the study area, with 16 monitoring boreholes 3.3.2 The determination results From the measurement results, analyze the chemical composition of pore has demonstrated the ability to vary the conductivity of the sediments depends on the pore water saturation 3.4 Hydrogeological boreholes investigation results The results of hydrogeological boreholes to establish the pair correlation between regression and resistivity values Also to assess the status of the saltwater distribution in aquifer 3.5 Analyzed results of chemical composition of pore water The analysis results of 27 samples of pore water was squeeze from marine sediments, evenly distributed in depth, at 02 sampling locations VietAS_ND02 VietAS_ND01 and clarified the chemical composition, the ability to identify the correlation of pore water conductivity and the electrical conductivity of the formation with a high correlation coefficient 15 (R = 0.9262), this result indicates that the electrical conductivity of marine sediments in Nam Dinh area is dominated by the pore water The highest value of TDS of pore water distributed in the middle of marine sediment layer and lower value toward the surface and bottom layer The maximum value reached more than 37g/L (fig 3.1) H G Figure 3.1: Hydro-geochemical cross-section of TDS concentration distribution of pore water (profile in figure 4.4) 3.6 Summary of saltwater distribution determination Results composite materials research suggests Nam Dinh area: - Upper Holocene aquifer (qh2) have TDS relatively large, the vast majority of the value is greater than 1g/L; - Lower Holocene aquifer (qh1) is salty entirely; - The boundaries of salinity in Pleistocene aquifer in the north and northeast of the region; - The survey results show that fine-grained sediments (clay, silty clay) have very high TDS, and distributed over the entire area of research and TuyÕn mặt cắt descending on the top and bottom of layer.AB A 0m LK47 LK48 Q229N LK53 Q228A LK54 Q227A LK55 Q226N qhÔ qhÔ -50 -50 qhÊ qhÊ qp TÔ 150 -100 110 qp 120 140 -150 nÔ nÔ 170 151 155 170 -300 nÔ 150 -150 -200 -200 -250 0m qhÔ 66 -100 B Q225A LK63 TÔ PR 248 PR Figure 3.2: Conceptual model of salinity distribution (profile in figure 4.4) -250 -300 16 Chapter - MECHANISM OF SALTWATER INTRUSION IN PLEISTOCENE AQUIFER 4.1 Solute transport in groundwater 4.1.1 The processes of solute transport 4.1.1.1 Advection process Advection is just a fancy word for the movement of mass entrained in the flow Solute advection is dissolved substances process by subsurface flow 4.1.1.2 Dispersion process a Mechanical dispersion process Mechanical dispersion is the process of solute that moves through the pore environment b The process of hydrodynamic dispersion The process of hydrodynamic dispersion consists of two different processes that combine mechanical dispersion and molecular diffusion Parameters characterizing is called the coefficient of hydrodynamic dispersion (DL and DT) 4.1.1.3 Molecular diffusion process When there are differences in differential concentration, calculations in thesis base on Fick's law in sedimentary environment 4.1.1.4 The hydro-geochemical processes relevant The other related process can occur: The reaction acid/base, the association of ions into the neutral element, the redox reactions, the process of precipitation, dissolved, the process of absorbing and releasing (ion exchange process) 4.1.2 Characteristic of salinity movement in groundwater 4.1.2.1 Effect of density to the distribution of saline Effect of liquid density to the spatial distribution according to the relationship: H = 40h 4.1.2.2 Solute transport by the difference in density Solute transport of density differences mainly affected by gravity Darcy's law for solute transport by the effects of density is calculated 17 basis, quantitative assessment of saltwater intrusion to the Pleistocene aquifer by lower permeability layer (marine origin) 4.2 Mechanism of saltwater intrusion in the Pleistocene aquifer 4.2.1 The general concept and study-oriented for mechanism of saltwater intrusion in the Pleistocene aquifer in study area 4.2.1.1 The general concept Mechanism of saltwater intrusion is the way of saltwater intrude into freshwater body in aquifer or freshwater lens, increasing the concentration of salt in aquifers or freshwater lens 4.2.1.2 Study-oriented for mechanism of saltwater intrusion in the Pleistocene aquifer Base on reference to study the mechanism of saltwater shows oriented study is appropriate to clarify the following: 1) In the study area exist any salt sources? 2) Distribution of salinity source compared to study aquifer? 3) Effect of salinity sources to the aquifer? The results of the study of geology, hydrogeology, geochemistry shows exist three main sources of salinity are: - Saltwater distributes on the surface (sea water); - Saltwater in the same Pleistocene aquifer with freshwater; - Saltwater in lower permeable marine sediments 4.2.2 Saline intrusion into Pleistocene aquifer by the influence of marine sediments 4.2.2.1 The distribution of marine sediments The distribution of the marine sediments are determined on the basis of geophysical data combined with borehole drilling materials, in order to determine the depth distribution of the layer thickness 4.2.2.2 The distribution of salinity in the marine sediment layer The results of the analysis and calculation of the salinity distribution in marine sediment has been showed in Chapter Distribution of salinity in cross-section G-H (fig 3.1) showing the highest concentration of TDS distribution in the from 20m to 30m deep (more than 37g/L) and descending toward the surface and bottom of this layer 18 4.2.2.3 Results of stable isotope composition of pore water The applied isotopic techniques to determine the possibility of mixing water in aquifers qp (meteorological origin) and sea (marine origin) in marine sediment Recently, pore water in marine sediment has both marine origin, and derived meteorology (fig 4.2) δ -8 -6 18 δ H (‰) O (‰) -4 -2 -60 -50 -40 -30 EC (µS/cm) -20 -10 0 20000 40000 60000 10 10 20 20 20 30 30 30 40 40 Depth (m) 10 Depth (m) Depth (m) 40 50 50 60 60 70 70 80 80 Pore water 60 70 (δ18O) 50 (δ2H) 80 (EC) 90 90 90 100 100 100 Figure 4.1: Distribution of stable Figure 4.2: Results of stable isotope and EC at VietAS_ND01 isotope composition 4.2.2.4 Results determined diffusion coefficient Experimentally determined diffusion coefficient of chloride in marine sediment on the basis of determining the change of NaCl concentration over time at the contact surface between and water samples The average value obtained for the study area is De = 0.6*10-9m2/s 4.2.2.5 Results of SEAWAT model Results of 1D simulation model describe the distribution of salt concentration over time with different permeability coefficient, assessing the impact of the permeability coefficient to distribution and movement of salt by diffusion and density flow 4.2.2.6 Mechanism of saltwater intrusion into Pleistocene aquifer under the influence of low permeability layer From the measurement results of borehole logging and analysis of the chemical composition of pore water as well as the correlations shows the electrical conductivity of formation is dominated by pore water; measurement results of borehole logging site can be used to determine 19 the displacement salinity of pore water in marine sediment downward qp aquifer The study results showed that salt movement influenced by two main processes are molecular diffusion and density flow, the surface layer is mainly dominated by molecular diffusion and the bottom layer is influenced by both density flow and molecular diffusion Figure 4.3: Distribution of conductivity, chloride, δ18O analysis of pore water and logging results in borehole VietAS_ND01 4.2.3 Saltwater intrusion into Pleistocene aquifer affected by hydraulic head 4.2.3.1 Grain-size analysis of Pleistocene aquifer The result of geological survey, analyze of lithology composition in Pleistocene sediments showing that, lithological composition mainly sand and gravel with porosity from 0.25 to 0.39 4.2.3.2 Hydrogeological parameters Pleistocene aquifer Results of pumping test at 03 boreholes showed that flow rate in Q227, VietAS_ND02 and VietAS_ND01 Pleistocene aquifer here is high yield, hydraulic conductivity ranged from 1,264 to 1,549 m2/day 4.2.3.3 Drawdown and flow direction in Pleistocene aquifer 20 Base on the results of the national monitoring network from 1994 to 2012 shows that groundwater level in the Pleistocene aquifer here is decreasing at rate of about 0.5 to 0.7m/yr Hydraulic gradient from saltwater to the freshwater towards the northern is 0.00042 and northeastern is 0.00039 Movement saltwater boundaries towards the center freshwater body (fig 4.4) 20 * Q221a 389 GV01 TEM profile Q222b ile of Pr B Profile C ND02 ile of Pr Q223a Salinity monitoring location A Profile D Q224a Q92 489 Q108b ND01 karst 20 Q226a karst Q225a 180 Q227a k in Q109a T 22 o f 269 Salinity boundary in qp o n Q110a Q228a l f Legend u 00 Pleistocene boreholes Ground water contouring (m) Granular aquifer Karst, fracture aquifer Sea, river Flow direction of groundwater G 60 Q229a Km 10 Figure 4.4: Hydraulic head (year 2012) and direction of groundwater flow of Pleistocene aquifer map in study area Conclusion: The main mechanisms, the dominant process saltwater intrusion into freshwater lens in Pleistocene aquifer, Quaternary sediments of Nam Dinh area includes: 1) Saline intrusion occurs vertically due to the marine sediment (clay, silt); 2) Saline intrusion occurs horizontally (in the Pleistocene aquifer) due to draw down, water level differences between saltwater and freshwater zones (fig 4.5) A Q Q 0m -50 -100 Q Q Q qhÔ qhÔ B 0m qhÔ -50 Salinity movement qp -100 TÔ 1g 1g /l /l qp nÔ -150 3g 3g /l /l nÔ -200 Salt water movement Fresh water movement -150 -200 TÔ -250 PR -250 PR -300 TDS < 1g/l zone TDS = - 3g/l zone TDS = - 8g/l zone TDS > 8g/l zone Aquitard Figure 4.5: Simulation of saltwater intrusion mechanism in the present time in Nam Dinh area (profile in figure 4.4) -300 21 Chapter - ASSESSMENT AND PREDICTION OF SALTWATER INTRUSION 5.1 Salt water intrusion in Pleistocene aquifer by marine sediment assessment 5.1.1 Saltwater intrusion due to molecular diffusion process and density flow Calculation results of the effects due to molecular diffusion and density flow ranged from 0.11 to 0.22 g/m2/yr 5.1.2 Limitation of molecular diffusion and density flow processes 5.1.2.1 Terms and conditions occurring diffusion process The molecular diffusion process in sedimentary environments stopped when the concentration gradient is 5.1.2.2 Terms and conditions occurring density flow process Density flow process does not occur in impermeable sediment when the hydraulic pressure of lower layer is greater than upper layer up to 10m 5.2 Evolution of water salinization in Pleistocene aquifer affected by exploitation 5.2.1 Calculating saltwater boundary under observation data a) Base on result of the current salinity status The most significant change occurred in the northeast region, the vibration amplitude reaches 4km for 15 years, reaching speeds of 0.27 km/yr Figure 5.1: Monitoring data of chemical composition of groundwater (monitoring location in figure 4.4) 22 b) Salinity boundary calculation by result of hydraulic gradient Determine the marginal rate of salt movement on the basis of hydraulic gradient determined from the boundary to the center of freshwater lens: northwest direction: 0.029 m/day, to the north: 0.042 m/day; northeast: 0.039 m/day 5.2.2 Prediction results of saltwater intrusion in Pleistocene aquifer by numerical models 5.2.2.1 Model of groundwater flow Based on the stratigraphic borehole survey strata of the national monitoring, results of construction monitoring works The Geological and hydrogeological parameters, model building flow under two scenarios: stable exploitation volume and increasing trend of population in study area 5.2.2.2 The model predicted the salinization of Nam Dinh In the beginning of the mass transport model obtained in 2012 with TDS originally obtained as a result of determining salinity distribution Scenario 1: Maintaining the current flow extraction saltwater intrusion assessment in 2020, 2030 and 2050 Scenario 2: Evaluation of the extraction flow increased saltwater intrusion assessment in 2020, 2030 and 2050 Results saltwater intrusion prediction based on the scenario of the flow pattern Evolution TDS concentrations at the monitoring location: The variation observed TDS concentrations over time are given for positions for regions characterized In general, all monitoring locations movements TDS has increased in both scenarios 5.3 The solution, saline intrusion restrict in the Nam Dinh 5.3.1 Remedies, salinization restrictions The main reason causing saltwater intrusion Pleistocene aquifer is differential level between the fresh and salt water zones Therefore, solutions, salinization restrictions proposed on the basis of two principles: - To reduce water level differences between the salt and the fresh; - To prevent subsurface flow from the salt to the fresh zone 23 5.3.2 Solution for groundwater exploitation and usage Solution mining and rational use of groundwater resources in the region is to convert individual forms of uncontrolled exploitation to concentrated form Concentrated groundwater extraction will help managers adjust, control operators depending on water level changes in the region and balance the demand CONCLUSIONS AND RECOMMENDATIONS Conclusions 1) The geological structure pre -Cenozoic basement in the study area is complex and divided into different lifting blocks by NW-SE and NE-SW major fault systems Those faults also played as conduits systems for recharge on which is coated by Neogene and Quaternary sediments; 2) Several saltwater intrusion processes and fluxing cycle oscillations of sea water in accordance with sediment evolution have occurred in the area during the Cenozoic The process of freshwater lens formation after beginningFlandrian transgression occurred around 4,000 years BP; 3) Strong correlation between chlorine concentration and, TDS of pore water with conductivity showed consistent with theory and certainly the basis for determining the variables change of chloride and TDS according to the results of borehole logging; 4) Applied TEM method with hydrogeological methods to determine salt-fresh water interface in Pleistocene aquifer in Nam Dinh area is appropriate with the hydrogeological conditions and shows reliable results This is one of the basic research and research-oriented on the basis of the data associated with the current state of exploitation in the region to study the mechanisms of saltwater intrusion; 5) Vertical saltwater intrusion is caused by low-permeability effect of the marine sediment The density process is dominated at the place 24 having the higher permeability (K≥10-7m/s), while the molecular diffusion process control that when lower permeability; 6) Horizontal saltwater intrusion in the Pleistocene aquifer is caused by groundwater flow from saltwater to freshwater zones This process is more dominated when the freshwater level is declined due to the increasing groundwater exploration and groundwater demand from time to time; 7) The results of groundwater flow model and prediction groundwater salinization in Pleistocene aquifer are more reliable than the results of hydrogeological parameters calculated by pumping tests rand identification of fresh-salt water boundary using different methods Recommendations 1) The distribution of freshwater lens of outer continental shelf in surface area and depth should be studied More detailed hydrogeological investigation and applied geophysical methods in hydrogeology is recommended; 2) Proper understanding the geological structure and hydrogeological characterization of freshwater lens in the north and northwest part of the Nam Dinh area is proposed A detailed work on source and recharge to freshwater lens using tracing methods and long time monitoring is also necessary; 3) The management of groundwater exploitation in the Nam Dinh area should be appropriate considered A good planning and reasonable utilization groundwater resource will improve using of valuable source of freshwater in the region 25 LIST OF PUBLICATIONS RELATED TO THESIS OF AUTHOR Hoang Van Hoan, Flemming Larsen (2007), Determination method of the effective porosity, the coefficient of permeability of the aquifer and total dissolved solids of the water by the method of borehole geophysics Case study in the northern plains, Science and Technology Journal of Mining and Geology, 20 Hoang Van Hoan Pham Quy Nhan (2008), Using the electrical geophysical methods in geology hydrology demarcation salt/fresh the qp aquifer in Pho Noi, Hung Yen, Journal of Geology, 305, (in Vietnamese) Vu Long Tran , Pham Quy Nhan , Flemming Larsen , Hoang Van Hoan (2011), Mechanism of paleo saltwater intrusion and its impact on the distribution boundary of salty in the aquifer of Quaternary sediments Giao Thuy - Nam Dinh, Science and Tech Journal of Mining - Geology, 34, 25-34, (in Vietnamese) Luu T Tran, Flemming Larsen, Nhan Q Pham, Hoan V Hoang, et al (2012), Origin and Extent of Fresh Groundwater, Salty Paleowaters and recent Saltwater Intrusion in Red River Flood Plain Aquifers, Vietnam, Hydrogeology Journal 20 Hoang Van Hoan, Pham Quy Nhan, Flemming Larsen, et al (2013), Saline water Quaternary sediments estuarine coastal area of Nam Dinh by the transient electromagnetic, Journal of Geology, 334 Hoang Van Hoan, Pham Quy Nhan, Dang Duc Nhan, Flemming Larsen et al (2013), Investigation on hydrogeological characteristics of groundwater in the Nam Dinh province by isotopic techniques, The Journal of earth sciences , 35 (2) Nguyen Van Lam, Nguyen Thi Thanh Thuy, Hoang Van Hoan (2006), Calculation of saline water boundary movement of groundwater in qp aquifers Hai Trieu, Tien Lu, Hung Yen, Scientific conference 17th Report of HUMG Hoang V H, Lassen R, Larsen F et al.(2009), Mapping of fresh and saline groundwater in coastal aquifers in the Nam Dinh province (vietnam) by electrocal and transient electromagnetic soundings, 1st APCAMM, Thailand Hoan V Hoang, Nhan Q Pham, Flemming Larsen, et al (2011), Processes Controlling High Saline Groundwater in the Nam Dinh Province, Vietnam, 2nd APCMM October, 2011, Jeju, Korea 10 Luu T TRAN, Flemming LARSEN, Hoan V HOANG et al (2011), Scenarios for distribution of different saline groundwater types in the Red River floodplain, Vietnam, 2nd APCMM October, 2011, Jeju, Korea 11 Flemming Larsen, Pham Quy Nhan, Tran Thi Luu, Tran Vu Long, Hoang Van Hoan (2012), Processes controlling the presence of of salty (paleo) groundwater in the Red River flood plain, SWIM 2012, June 17-22, Armacao, Brazil 12 Hoang Van Hoan, Pham Quy Nhan, Flemming Larsen, Tran Vu Long, Nguyen The Chuyen, Tran Thi Luu, 2012 The affect of diffusion process to salinity distribution of pore water in Quaternary marine sediments in Nam Dinh region The conference report on the 20th scientific conference of HUMG 13 Wagner, F., Ludwig, R R., Noell, U., Hoang, H V., Pham, N Q., Larsen, F., et al (2012), Genesis of economic relevant fresh groundwater resources in Pleistocene/Neogen aquifers in Nam Dinh (Red River Delta, Vietnam), EGU 12, European Geosciences Union, 22-27 April, 2012 in Vienna, Austria 14 Christoph Gerber, Roland Purtschert, Flemming Larsen, Hoan V Hoang, et al (2013), 39Ar groundwater dating of a coastal aquifer in the Nam Dinh Province, Vietnam EGU 13, European Geosciences Union, Vienna, Austria ... Denmark and Greenland Judge 1: Assoc Prof Dr Doan Van Canh Vietnam Association of Hydrogeology Judge 2: Assoc Prof Dr Nguyen Van Hoang Vietnam Academy of Science and Technology Judge 3: Assoc Prof... Canh, Assoc Prof Dr Phan Ngoc Cu, Dr Dang Dinh Phuc, Dr Dang Duc Nhan, Assoc Prof Dr Nguyen Van Dan, Assoc Prof Dr Nguyen Van Hoang, Dr Vu Kim Tuyen, Dr Nguyen Thi Thanh Thuy, Dr Duong Thi Thanh... and study area Target: Groundwater in Pleistocene aquifer in Nam Dinh area; Study area: Freshwater lens in the Pleistocene aquifer at Nam Dinh city and related areas Project activities Determine