Abstract

This paper elaborates the hydrochemical and environmental isotope (δ²H and δ¹⁸O) inferences obtained from Uddanam region, Andhra Pradesh, India. Groundwater samples collected during pre-monsoon (June 2019) showed that the quality is fresh (EC < 1539 µS/cm) and contaminants like fluoride (<1.6 mg/L) and nitrate (<49 mg/L) are present within permissible limits. The composite water quality indices for drinking (DWQI: 14.1–92.5) and irrigation (IWQI: 2.8–20.2) are found to be satisfactory. The major water types are found to be Ca–Na–HCO₃, Na–Ca–HCO₃, Na–Mg–HCO₃–Cl, Ca–Mg–HCO₃–Cl and Na–HCO₃. Three geochemical pathways are found signifying evaporite dissolution, contribution of silicate mineral weathering and base-exchange process, which is supported by estimated chloro-alkaline indices (CAI-1: −4.3 to −0.2, CAI-2: −1.03 to −0.08). Trace metal data clearly suggest that groundwater is free from any metal pollution. Dissolved silica (SiO₂) levels range from 34 to 131 mg/L and do not show any particular spatial trend. Isotope data infer that groundwater is recharged by rainwater after undergoing evaporation (δ¹⁸O: −6.0‰), which matches with that of the combined isotope signature (δ¹⁸O: −5.5‰) of SW and NE monsoon rainfall. δ¹⁸O–TDS correlations and hydrochemical facies evolution (HFE) diagram do not infer any seawater intrusion into these coastal aquifers.

Highlights

• The composite water quality indices infer good to excellent category for drinking and agriculture.

• Mineral weathering, evaporite dissolution and base-exchange reactions are the main geochemical processes.

• Dissolved silica occurrence in groundwater is sporadic.

• Isotope indicators show the signature of both SW and NE monsoons recharge to groundwater.

• Observed brackishness in groundwater is due to water – rock interaction and not due to sea water intrusion.

中文翻译：

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印度安得拉邦乌达南沿海地区部分地区地下水的主要离子，痕量金属和环境同位素特征

摘要

本文阐述了水化学和环境同位素（δ ² H和δ ¹⁸ O）推论Uddanam区域，安德拉邦，印度获得。季风前（2019年6月）收集的地下水样本显示水质新鲜（EC <1539 µS / cm），污染物如氟化物（<1.6 mg / L）和硝酸盐（<49 mg / L）在允许的范围内。饮用（DWQI：14.1–92.5）和灌溉（IWQI：2.8–20.2）的综合水质指数被认为是令人满意的。发现主要水类型为Ca–Na–HCO ₃，Na–Ca–HCO ₃，Na–Mg–HCO ₃ –Cl，Ca–Mg–HCO ₃ –Cl和Na–HCO ₃。发现了三个地球化学途径，表明蒸发岩溶解，硅酸盐矿物风化作用和碱交换过程，这由估计的氯碱指数支持（CAI-1：-4.3至-0.2，CAI-2：-1.03至-0.08） 。痕量金属数据清楚地表明，地下水没有任何金属污染。溶解二氧化硅（SiO ₂）的含量范围为34至131 mg / L，并且没有显示任何特定的空间趋势。推断地下水同位素数据由雨水再充电之后经历蒸发（δ ¹⁸ ○：-6.0‰），其与该组合同位素签名的匹配（δ ¹⁸：SW和NE季风降水的O- -5.5‰）。δ ¹⁸O-TDS相关性和水化学相演化图（HFE）不能推断出海水侵入这些沿海含水层。

强调

• 综合水质指数将饮用水和农业分类为优良。

• 矿物风化，蒸发物溶解和碱交换反应是主要的地球化学过程。

• 地下水中溶解二氧化硅的发生是零星的。

• 同位素指标显示西南季风和东北季风回补到地下水的特征。

• 观察到的咸度是由于水与岩石的相互作用，而不是由于海水的入侵。