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Hydro-geochemistry and Quality Assessment of Deep Groundwater in Shyamnagar Upazila, South-western Bangladesh

T.K. Das
Department of Environmental Science and Technology, Jashore University of Science and Technology, Jashore-7408, Bangladesh.

M.A. Mamun
Department of Environmental Science and Technology, Jashore University of Science and Technology, Jashore-7408, Bangladesh.

M.R. Shaibur
Department of Environmental Science and Technology, Jashore University of Science and Technology, Jashore-7408, Bangladesh.

Abstract/ Executive Summary:

The Shyamnagar Upazila is located in southern most part of Bengal basin, which is characterized by extensive natural geochemical activities, brackish water and huge organic deposits. The hydro-geochemical data were collected from 50 deep aquifer water samples during July, 2018 were used for evaluating water quality and to determine process that control water chemistry. The collected samples were analyzed for pH, electric conductivity (EC), total dissolve solids (TDS), salinity, total hardness (TH), Na⁺, K⁺, Ca²⁺, Mg²⁺, SO ^2-, NO ^-, PO ^-, Cl^-, and HCO ^- concentration. The results illustrated that the dominations were in the order of Na⁺>Ca²⁺>Mg²⁺>K⁺ for cations and Cl^->HCO₃ ^->PO4 ^->NO₃ ^->SO₄^2-for anions. The scatter diagram represented that Na⁺ion in groundwater comes from silicate weathering while both silicate and carbonate weathering were equally responsible for Ca²⁺ and Mg²⁺ ion. The piper diagram indicated that Na-HCO₃, mixed NaCaHCO₃ and NaCl are dominated in the hydro-geochemical facies. The Gibbs diagram showed that rock weathering was the main source of ions in groundwater, while sea water intrusion and precipitation has negligible effect on it. The Wilcox diagram indicated that most of the water sources were suitable for irrigation. The controlling factor of groundwater chemistry was mostly related to geologic factors, while the anthropogenic factors have not any significant effects.

Keywords: Coastal zone, Groundwater, Hydro-geochemistry, Quality assessment

Location: Shyamnagar upazila under Satkhira district in Bangladesh

Start Date:

End Date:

Program Area: Crop-Soil-Water Management

Commodity: Water quality

Objectives:

The aim of the study was to determine the groundwater type and hydro-geochemical process controlling the groundwater quality to determine the suitability of groundwater for drinking purpose.

Methodology:

Study Area - The study area was Shyamnagar upazila under Satkhira district in Bangladesh, which is situated in south- western corner of the country and very close to Sundorban mangrove forest and Bay of Bengal (Fig. 1). The geological position makes it hard to reach area with acute scarcity of saline free water sources. It lies between 21º36' and 22º54' N latitudes and between 88º54' and 89º20' E longitudes (Bangladesh Bureo of Statistics, 2013). The water sample were collected from six union which were selected depending on geological position, drinking water scarcity and hard to reach area. Water Sample Collection and Analysis - A total of 50 water samples were collected from deep tube well during July, 2018. The depth of all tube well varied between 450 to 600 feet’s. The samples were collected in one litter potable water bottles. At first the bottle were washed with tap water and socked in 0.1 N HNO₃ for 24 h. During sample collection the bottle were prewashed and rinsed properly with sample water to avoid contamination. Before sample collection, tube well were pumped exact times with respect to the depth of the aquifer in feet (i.e. a 500 feet tube well was initially pumped for 500 times). After collection of water sample, it was immediately carried to the Environmental Chemistry Laboratory of Jashore University of Science and Technology and analyzed. The water temperature, pH, EC and TDS were measured at the sampling site using Microprocessor pH meter (model- HANNA instrument pH 211) and conductivity meter (model- HI 8033). The measurement of Na⁺ and K⁺ were done by flame photometric method (flame photometer- PEP7). The TH, Ca²⁺, Mg²⁺ and HCO₃ ^- were analyzed by titration colorimetric method and Cl^- by Ergonometric method. The NO₃ ^-, PO₄ ^-, and SO₄^2- were analyzed by Turbid metric method with Spectrophotometer (model- UV-visible spectrophotometer, helios 949923045811) (American Public Health Association; APHA 1995). Data Analysis - The water quality data were analyzed by MS Excel 2017, SPSS version 20 and Aqua cham Version 4. Hydro- chemical classification and groundwater evaluation were discussed by using Carbonate vs Silicate Weathering, Gibbs Diagram, Piper Diagram and Wilcox Diagram. For drinking water quality assessment, the results were compared with World Health Organization (WHO), United States Environment Protection Agency (USEPA) and Bangladesh Standard and Testing Institute (BSTI) drinking water quality. The Gibbs Diagram is widely used to establish the relationship of water composition and aquifer lithological characteristics (Gibbs 1970). Gibbs ratio I (for anion) = Cl^-/(Cl^-+HCO₃); Gibbs ratio II (for cation) = Na⁺/(Na⁺+Ca⁺²), where all the ionic concentration were expressed in meq/l. The Wilcox Diagram represents the suitability of water for irrigation and domestic purposes (Wilcox 1955).

Source of Information: Int. J. Expt. Agric. 9(1):14-21(March 2019)

Article Link (Online Journal):

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

The results revealed that the deep aquifer groundwater was slightly alkaline in nature. The EC and TDS in most of the samples were within BSTI and WHO drinking water quality standard. The concentration of Na⁺, Ca²⁺, Mg²⁺ and K⁺ in two third of water samples were within drinking water quality standard. Among the anions the concentration of Cl^- and HCO ^- were the dominating species and about half of the water samples exit the prescribed drinking water quality standard of BSTI and WHO. The Na⁺ in the groundwater originated from weathering of carbonate rocks; whereas Ca⁺ and Mg²⁺ originated from weathering of both carbonate and silicate rocks. The groundwater chemistry was mainly dominated by Na⁺, Ca²⁺, Cl^- and HCO₃ ^-. The minerals in the water came from weathering of underground bedrock. On the basis of Wilcox diagram, the deep aquifer water was suitable for irrigation. The evaporation concentration and groundwater mixing had very negligible effect on chemistry of groundwater in Shyamnagar area compared to rock dissolution. The natural geochemical activities were the controlling factors of deep aquifer groundwater chemistry compared to anthropogenic activities.

Knowledge Management: Journal