Ahmed, Nasir

Bhuiyan, Md Abdul Quaiyum

Hermans, Thomas

Islam, Mazeda

Karim, Md Masud

Sarker, Md Mizanur Rahman

Van Camp, Marc

Walraevens, Kristine

English

Ghent University Academic Bibliography

Hydrochemical Characteristics of Multilayer Dupi Tila Aquifer System Beneath Dhaka Mega City, BangladeshMazeda Islam1, 2, Marc Van Camp1, Thomas Hermans1, Md. Mizanur Rahman Sarker1, 2, Md. Abdul Quaiyum Bhuiyan3, Nasir Ahmed3, Md. Masud Karim3 and Kristine Walraevens11Laboratory for Applied Geology and Hydrogeology, Department of Geology, Ghent University, Belgium2Department of Geological Sciences, Jahangirnagar University, Savar, Dhaka, Bangladesh3Bangladesh Atomic Energy Commission, Dhaka, Bangladesh1. IntroductionAround 20 million people are living in Dhaka with a growing rate of 4.2 percent per year. Major part of the water supply is depending on groundwater from the Plio-Pleistocene fluvio-deltaic sands of the Dupi Tila Formation. Massive abstraction from the aquifer by water-wells has been causing a significant aquifer dewatering and huge drop in groundwater level upto 89 m PWD (Public Works Department) datum beneath the part of the city. The resulting depression cone is thought to prompt recharge from rivers and surrounding area.Fig. 1: Historical Evolution:Groundwater and Surface Water Supply and Demand with the Expansion of Dhaka City, Bangladesh.(Source: DWASA, 2016)1 2 3 4 5 6 7 8 9 10 111953 1959 1963 1971 1971 -1985 1990 1996 2000 2010 2013 2015 2016Growth expansion and development of Dhaka city-First master plan -Water demand for 0.58 x106peopleEstablishment of Dhaka WASAIndependence of Bangladesh: -2 x106population-47 deep tube wells (DTWs)-50 x106m3/yr DTWsinstalled in Upper Dupi Tila aquifer (UDA) near the rivers -216 DTWsin UDA-510 x106 l/d->5 times than 1970-2nd master plan -1st plan for 10 x106inhabitants-10 x106 population-308 DTws-deficit 380 x106 l/d- Drawdown to -65 m PWDWater supplied 1990 x106 l/d-Water demand 2180 x106 l/d-560 DTWs- 4 surface water treatment plants(SWTP). Supplycapacity 2250 x106/l/d-644 DTWsand 4 SWTPSupplycapacity 2420 x106 l/d-DTWs 7024 SWTP. -16 x106 population - Supply capacity2450 x106 l/d-760 DTWs and 4 SWTP. 2. Aim of the StudyThe present work investigates groundwater chemistry inthe multilayer Dupi Tila aquifer using hydrochemical data,stable isotopes along with physico-chemical parameters.3. Hydrostratigraphy: Aquifer System➢ Upper Dupi Tila Aquifer (UDA): Upper part mainlycomposed of fine sand to medium sand and lower part medium sand to coarse sand occasionally with gravel.Average bottom depth is 142.5.➢ Middle Dupi Tila Aquifer (MDA): Mainly composed of medium sand to coarse sand  with gravel. Averagebottom depth 254.5 m. ➢ Lower Dupi Tila  Aquifer (LDA): Predominantlycomposed of fine sand to medium sand . Avg. bottom  depth is 385 m. 4. HydrographMirpur Area (UDA): Fig. 4a✓ Seasonal fluctuation and no falling trend up to 1985✓ Lowest Groundwater level (GWL): - 65.06 m PWD (2010), ✓ Sharp decline rate: 5.4 m/year (2000-2005). ✓ Relatively stable after 2010-2016✓ Recovery GWL 2017 to - 60.84 m PWD (5 m rise).Gulshan Area(UDA) : Fig. 4b✓ Lowest GWL: - 72 m PWD (2018)✓ Highest decline rate: 4.1 m/year (2000-2005).Sutrapur Area (UDA) : Fig. 4c✓ Due to proximity of Buriganga river ,GWL was very much different.✓ Lowest GWL: -14.2 m PWD (2010)✓ Relatively stable from 2000 to 2010 in UDA.Sabujbagh Area (UDA) : Fig. 4d✓ Lowest GWL: -62.8 m PWD (2009)✓ Maximum decline rate: 2.8 m/year (2000-2005)5. Piezometric MapsUDA❑ 1985 (Fig. 5a)▪ Depression in South central part down to -10 m PWD▪ Most of the area : -1 m PWD❑ 2017 (Fig. 5b)▪ Lowest GWL (depression cone) down to - 80 m PWD▪ Peripheral part: -50 m PWDMDA❑ 2005 (Fig. 6a)▪ Shape and extent of depression showed sporadicpattern.▪ Lowest GWL in southeast side down to -36.82 m PWD❑ 2017 (Fig. 6b)▪ Lowest GWL (depression cone) down to -65 m PWD▪ Peripheral part: -35 m PWD6. Hydrochemical Characteristics➢ Relative abundance of the ions Ca2+ > Na+ > Mg2+ > K+ > Fe2+ > NH4+ > Mn2+ and      HCO3– > Cl- > SO42- > NO3- > PO43- > NO2-.➢ Low mineralization water (EC: 161-835 (µS/cm – 25°C), TDS: 119-550 (mg/l) and neutral pH (pH: 7.11-7.81). ➢ Waters are mostly CaHCO3 (86%) and 17% NaHCO3 types(Fig. 7) localized in two zones due to infiltration of rain wateror anthropogenic pollution.➢ Dominant control of aluminosilicates weathering on thehydrogeochemical evolution of groundwater is confirmed byCaHCO3 and NaHCO3 types water and cross plots (Fig. 7, 8& 9). Major alkaline and alkaline earth cations released fromaluminosilicates weathering.➢ HCO3- is formed from CO2 involved in aluminosilicateweathering. The increase in major cations is accompanied bya parallel increase of bicarbonate (Fig. 9).➢ Reactions (i-v)  illustrate the weathering processes which can release Ca2+ and HCO3– to groundwater.▪ 2CaAl2Si2O8 + 4CO2 + 6H2O = 2Al2Si2O5(OH)4 + 2Ca2+ + 4HCO3-..........(i)Anorthite                                 Kaolinite▪ CaMg(Si2O6) + 4CO2 + 6H2O = Ca2+ + Mg2+ + 4HCO3- + 2H4SiO4………i)Pyroxene▪ Ca2Mg5Si8O22(OH)2 + 14CO2 + 22H2O = 2Ca2+ +5Mg2+ + 14HCO3- + Amphibole                                                                    8H4SiO4…………(iii)▪ CaCO3 + CO2 + H2O = Ca2+ + 2HCO3-……….(iv)Calcite▪ CaMg(CO3)2 + 2CO2 + 2H2O = Ca2+ + Mg2+ + 4HCO3-…….(v)Dolomite➢ The average concentration (11 µg/l) of arsenic is low in all the water samples (Fig. 10) except two shallow water samples in UDA (161.88 and 383 µg/l at 14.63 and 42.67m depth respectively) in same location .➢ Very few water samples exceed guideline of WHO, 2008.7. Stable Isotopes❑ LDA water falls on and to some extent below the LMWL andGMWL (Craig, 1961): recharge from rainwater. MDA andUDA : rainfall and/or flood water (Fig. 11).❑ More depleted in river waters indicating that the river watersare composed of rainfall in the upstream catchment.❑ Enriched isotopic composition and mean d-excess of LDA is8.87‰ indicating evaporation has occurred before infiltration❑ Cl– vs δ2H plot indicates no good relationship between theorigin of GW other than river (Fig. 12).8. Conclusion✓ Huge GWL depletion in both UDA and MDA aquifers andhighest depression is observed in central part of the city.✓ Mainly CaHCO3 type water with low mineralization.✓ Aluminosilicates weathering as the primary processcontrolling groundwater chemistry.✓ Groundwater supply may not be sustainable for longpersisting period in Dhaka city because of massive declineof GWL.ReferencesCraig H (1961) Isotopic variations in meteoric waters. Science 133(3465):1702–1703DWASA (Dhaka Water Supply and Sewerage Authority) Annual Report (2015-2016), DWASA, Dhaka, Bangladesh. Piper AM (1944) A graphic procedure in the geochemical interpretation of water-analyses. Eos Trans Am Geophys Union 25(6):914–928WHO, 2008. Guidelines for Drinking-Water Quality (Electronic Resource): Incorporating 1st and 2nd Addenda, Volume 1, Recommendations, 3rd edition. WHO Library Cataloguing-in-Publication Data 668 p.806040202040608020406080 806040202040608020406080Ca Na+K HCO3 ClMg SO4H HHHHHH HHH HHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHH HHHHHHHHHHHHHHHHHHLegendLegendH SWH UDAH MDAH LDALegendDigital Elevation ModelVALUE1 - 22 - 44 - 77 - 1010 - 16River!( Upper Dupi Tila Aquifer Water Sample!( Middle Dupi Tila Aquifer Sample!( Lower Dupi Tila Aquifer Sample!( Surface Water Sample!( River Gauge Station!( BWDB Observation well location!( IWM Monitoring Well Location10th International Groundwater Quality Conference (GQ2019)Poster Session 2 (S02b + S04 + S06)9-12 September, Liège (Belgium)Fig.8: Piper Diagram (1944)AcknowledgementsThis project has received fund from Islamic Development Bank (IDB). Special thanks to Ms. Jill Van Reybrouck, Laboratory for Applied Geology and Hydrogeology, Department of Geology, Ghent University. Dhaka Water Supply and SewrageAuthority, Bangladesh Atomic Energy Commission (BAEC), Bangladesh Water Development Board (BWDB) and Geological Survey of Bangladesh (GSB), Bangladesh are also acknowledged for providing necessary data.Fig. 5: Piezometric map of UDA for a. 1985 b. 2017Fig. 2: Study area with water sample location,observation well and cross section line map.Fig. 3: Hydrostratigraphic cross sectionFig. 4: Long term hydrograph a. Mirpur b. Gulshan c.Sutrapur d. SabujbaghabcdFig. 6: Piezometric map of MDA for a. 2005 b. 2017a ba bFig. 7: Water type mapFig. 9: Cross plots of a. EC vs TDS b-e. HCO3- vs major cations f. Cl- vs NO3-Fig. 10: As vs depth plot Fig. 11: Plot of δ18O vs δ2H. Fig. 12:Plot Cl– vs δ2HaJJʹabcdabcd ef

Hydrochemical characteristics of multilayer Dupi Tila aquifer system beneath Dhaka Mega City, Bangladesh

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Hydrochemical characteristics of multilayer Dupi Tila aquifer system beneath Dhaka Mega City, Bangladesh

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