..........................................................................................................................................14 1 Objectives and Deliverables ....................................................................................................16 1.1 Objectives........................................................................................................................16 1.2 Deliverables.....................................................................................................................16 2 Introduction ............................................................................................................................18 2.1 General overview on the Arsenic crisis in Bangladesh ...................................................18 2.1.1 Arsenic in the (hydro)geological and (hydro)geochemical context ............................19 2.1.2 Mobilisation of Arsenic...............................................................................................22 2.1.3 Arsenic speciation in groundwater .............................................................................24 2.2 The test site at the Titas hospital complex ......................................................................25 2.2.1 Local geology and sediment geochemistry at Titas .....................................................26 2.2.2 Local groundwater chemistry and water tables ..........................................................30 2.2.3 Local climate conditions and the water balance .........................................................31 3 Methodology ...........................................................................................................................36 3.1 Methods in the field........................................................................................................37 3.1.1 Monitoring of the hydro-geochemistry at test site Daudkandi...................................37 Cornelia Härtig Master Thesis page 3 of 150 3.1.2 Water levels at the test site.........................................................................................44 3.1.3 Aquifer tests................................................................................................................44 3.1.4 Water tables at irrigation wells...................................................................................48 3.1.5 Well head positions and elevation of the land surface adjacent to wells ....................49 3.1.6 Field injection spike....................................................................................................50 3.2 Analytical methods used in laboratory ...........................................................................52 3.2.1 Determination of TIC and DOC..................................................................................52 3.2.2 Analysis of anions and cations with IC.......................................................................52 3.2.3 Flouride determination with an ion sensitive probe...................................................54 3.2.4 Speciation and totals of As and P with AEC-ICP-MS and ICP-MS ............................54 3.3 Methods of data handling ...............................................................................................55 3.3.1 Error of the analysis and Conductivity check.............................................................55 3.3.2 Limit of detection (LOD) and limit of quantitation (LOQ).........................................56 3.3.3 Statistical methods ......................................................................................................58 3.3.4 Hydraulical permeability K based on grain size analyses............................................59 3.3.5 Transmissivities T and hydraulical permeability K based on aquifer tests..................60 3.3.6 Actual evapotranspiration in 2007..............................................................................62 3.3.7 Map of Titas geography and irrigation wells...............................................................63 3.3.8 Contour map of land surface elevation .......................................................................63 3.3.9 Modelling with Visual Modflow.................................................................................64 4 Results and Discussion.............................................................................................................65 4.1 Hydraulic properties of the subsurface at the test site ....................................................65 4.1.1 Results of water table measurements at the test site...................................................65 4.1.2 Results of the Aquifer tests .........................................................................................66 4.1.3 Conceptual model of the subsurface ...........................................................................69 Cornelia Härtig Master Thesis page 4 of 150 4.1.4 Levelled water tables at irrigation and test site wells .................................................70 4.1.5 Potential evaporation (PE) and actual evapotranspiration (AET)...............................72 4.1.6 Stationary flow modelling...........................................................................................72 4.2 Groundwater chemistry at the test site...........................................................................78 4.2.1 Quality evaluation of the analyses ..............................................................................78 4.2.2 Depth-dependent variation of the groundwater chemistry........................................88 4.2.3 Seasonal changes of the groundwater chemistry ......................................................111 4.3 Influence of pumping tests on water chemistry............................................................117 4.3.1 On-site parameters during water withdrawal...........................................................117 4.3.2 Effects of water withdrawals on Arsenic and other water quality parameters .........119 4.4 Injection spike...............................................................................................................120 4.4.1 Spike Solution ...........................................................................................................120 4.4.2 Results of the Injection Spike Test............................................................................121 5 Recommendations .................................................................................................................125 Bibliograhy ....................................................................................................................................127 Appendixes ....................................................................................................................................130 Cornelia Härtig Master Thesis page 5 of 150 LIST OF TABLES Table 1 Characterization of typical Arsenic rich Holocene groundwaters in the Bengal basin 21 Table 2 Summary of Lissner’s Investigations on sediment samples from the Titas core drilling (Lissner, H., 2008).........................................................................................................27 Table 3 Measurement devices for pH, Electrical conductivity EC, electromotive force EMF (redox potential EH), Oxygen concentration O2conc and saturation O2sat, temperature T ......................................................................................................................................39 Table 4 On-site parameters measured photometrical with the HACH DR/890 colorimeter listed together with the applied HACH analysis methods, their concentration ranges, quantitation limits (LOQ), absolute standard deviations (ASD) and known interferences (information derives from the HACH-manuals in Appendix C4) ................................41 Table 5 Sample denotation, sampling conditions and subsequent usage of the water samples, taken during each monitoring ......................................................................................43 Table 6 Technical data of the utilized pumps............................................................................45 Table 7 Pump-wells, primary and secondary piezometers during pump tests ..........................47 Table 8 Identified peaks, retention times (RT) with ion chromatography (see Appendix B4).53 Table 9 Query structure and conclusion for the analysis ..........................................................56 Table 10 Determination of the detection limit, the graphical representation derives from (Merkel and Planer-Friedrich, 2002)..........................................................................................57 Table 11 Limits of Detection for the laboratory parameters ......................................................57 Table 12 Relation between U and the proportional constant C ..................................................60 Table 13 Considering, whether the prerequisite conditions for Theis recovery method are fulfilled. Both, pumping time tp and recovery time t’ must be greater than 25r2/T and 500r2/T and D2S/2T, respectively (tp-pumping time, t’-recovery time, T-transmissivity, r-well radius, S-Storativity, Ss-Specific storage, D – saturated aquifer thickness) .......62 Table 14 Factors for the calculation of real evapotranspiration from Titas agricultural low-land (factors for partial inundation are rough estimates, basing on the field surveys in these months).........................................................................................................................63 Table 15 Results from evaluation of recovery data from the pumping tests at the 85, 115 and 280 ft wells with Theis Recovery Method as described by Krusemann and de Ridder (2000). (The saturated thickness of the deep aquifer (280 ft well) is insecure, thus the res