Evaluation of Groundwater Hydrochemistry in Egbeagu Amansea, Anambra State, Nigeria for Sustainable Water Management

Groundwater, one of the largest freshwater resources, serves as the primary provision of drinking water globally [1]. Given the high population density in urban areas, there is likelihood of groundwater contamination [2], which could subsequently threaten the health of thousands of people. Consequently, management of water resources and its related studies have placed a high priority on providing potable and palatable water [3]. Therefore, it is crucial to determine the status of groundwater quality and evaluate its suitability for drinking [4]. Assessing groundwater quality ensures compliance with standards such as the World Health Organization (WHO) Guidelines for Drinking-Water Quality [5] and the Nigerian Industrial Standard [6].

Groundwater chemistry is shaped by natural processes and human activities during its movement from recharge to discharge zones [7], [8], [9]. These processes include mineral dissolution, ion exchange, and anthropogenic contamination from activities such as improper waste disposal, excessive extraction of groundwater, and agricultural runoff with high concentration of fertiliser [10], [11]. Moreover, leachates from pit latrines and septic systems can infiltrate and contaminate groundwater sources, hence compromising their quality [12].

The hydrochemistry of groundwater is also influenced by chemical properties of recharged water, reactions between water and minerals, rock-water interactions, geochemical formations, and intermixing of water [13]. For instance, while soil horizons act as natural filters attenuating contaminant migration, elevated concentrations of metals could occur if minerals in the earth crust leach into groundwater [14]. The geology and geographic configuration of an area affect the inherent chemical quality of groundwater [15]. Hydrochemical evaluations of groundwater flow systems are generally based on the availability of data on groundwater chemistry [16].

Groundwater serves as a critical source of potable water within the Egbeagu Amansea. However, excessive extraction of groundwater in the region poses potential threats to the quality and sustainability of these groundwater resources. From the literature, there is no study on the hydrochemical characteristics of the groundwater in this specific area. This lack of information hinders effective groundwater management and exposes the population to potential health risks associated with contaminated water. This study aims at evaluating the hydrochemical characteristics of groundwater in the above-mentioned region.

The study was conducted in a small village of Egbeagu Amansea, Awka North local government of Anambra State, Nigeria. Egbeagu Amansea is among the five villages in Amansea rural community and lies approximately between latitude 06 16' 16.91631"N and longitude 07 07'34. 01516"E. The inhabitants of this community rely mainly on their stream, known as Amaowelle, for domestic activities. The stream (06 15' 05.86739"N, and 07 08' 21.68037"E) is located at the lower course of Ezu river [17]; in this connection, few commercial boleholes were drilled in the strategic locations within the area. The region experiences a tropical savannah climate with distinctly wet and dry seasons, receiving an average annual rainfall of approximately 1,800 mm. Geologically, Awka North is underlain by the Imo shale formation and the Bende-Ameki formation, which influence the hydrogeological characteristics of the groundwater system. The map of the study area is shown in Figure 1.

A total of eight groundwater samples were collected from seven boreholes (BH1, BH2, BH3, BH4, BH5, BH6, and BH7) and one hand-dug well (WL3) located in Egbeagu Amansea. The boreholes and the well were purged by pumping water for 5-10 minutes to ensure representative groundwater was collected. Sterile 1-liter polyethylene bottles were rinsed with the groundwater to be sampled before collection. Two sets of samples were collected at each point: One for physicochemical analysis (pH, EC, TDS, total hardness, carbonate, fluoride, nitrate, sulphate, and chloride) and another for cation analysis (calcium, potassium, sodium, and magnesium). Samples for cation analysis were acidified with 2-3 drops of concentrated nitric acid (HNO$_3$) to a pH $<$ 2 to preserve metal ions. Samples were labelled with identification number, date, and time, and stored in a portable cooler at 4°C for analysis within 24-48 hours to minimize degradation.

To ensure balanced coverage of the entire small village, seven boreholes and a hand-dug well (at close proximity to BH3) were purposively selected to represent aquifer types in the area.

This study was intended to be a preliminary assessment of the groundwater in the Ebeagu-Amansea community. As shown in the map of Figure 1, Egbeagu is geographically a confluence settlement. Samples were collected in the wet season between June and July 2025 to account for either infiltration of polluted surface runoff to the hand-dug well or intrusion from nearby rivers into the boreholes. Sampling was done by the grab method, which involved collecting a single sample from each source at a given time, an approach considered reliable for assessing physical, chemical, and microbiological properties of the drinking water [18]. At the well and boreholes, bottles were rinsed three times before sampling; water was allowed to flow for about 2–3 minutes before collection.

The groundwater samples were analysed for the following parameters: pH, electrical conductivity (EC), total dissolved solids (TDS), total hardness, calcium (Ca$^{2+}$), potassium (K$^{+}$), sodium (Na$^{+}$), magnesium (Mg$^{2+}$), carbonate (CO$_3^{2-}$), fluoride (F$^{-}$), nitrate (NO$_3^{-}$), sulphate (SO$_4^{2-}$), and chloride (Cl$^{-}$). Analytical methods followed standard procedures outlined by the American Public Health Association (APHA) [18]. The measurements of the cations and anions were performed using a 752N UV-VIS spectrophotometer and spectra AA 220$\|$S atomic absorption spectrophotometer (AAS), respectively.

The hydrochemical data were analysed using descriptive and multivariate statistical techniques, such as the Grapher software and Microsoft Excel (version 2016). Hydrochemical facies were assessed using Piper, Durov, and Stiff diagrams based on milliequivalent ion concentrations (Ca$^{2+}$, Mg$^{2+}$, Na$^{+}$, K$^{+}$, HCO$_3^{-}$ derived from CO$_3^{2-}$, Cl$^{-}$, and SO$_4^{2-}$).

Descriptive statistics (mean, standard deviation, minimum, and maximum) were calculated for each parameter to summarize the qualities of groundwater. Results were compared with the World Health Organization (WHO) guidelines and Nigerian Standard for Drinking Water Quality (NSDWQ) to assess their suitability for drinking and other purposes. Duplicate samples were analysed to assess reproducibility, with relative standard deviation (RSD) maintained below 5%. The ion balance error was calculated for each sample, with an acceptable range of ±5%.

where,

SAR = Sodium adsorption ratio

Na$^{+}$ = Sodium ion

Ca$^{2+}$ = Calcium ion

Mg$^{2+}$ = Magnesium ion

The water quality index (WQI) was calculated using the formula:

where,

$w_i$ = unit weight of ith water quality parameter

$q_i$ = quality rating (sub-index) of $i^{th}$ water quality parameter and is given as:

where,

$v_{i}$ = estimated value of ith water quality parameter

$v_{io}$ = idea value of ith water quality parameter

$s_i$ = standard permissible value of the ith water quality parameter

In most cases, $v_{io}$ = 0, except for pH and dissolved oxygen (DO)

For pH, $v_{io}$ = 7, for DO = 14.6 mg/l.

The rating of water quality using the above Eqs. (2)–(5) is shown in Table 1.

The mean pH of 7.52 indicated slight alkaline that fell within the standards stipulated by WHO (6.5–8.5) and NSDWQ (6.5–8.5). Electrical conductivity ranged from 36.7 to 185.8 $\mu$S/cm (mean 96.31 $\mu$S/cm), suggesting low mineralization below the WHO and NSDWQ limits of 1000 $\mu$S/cm (Table 2). TDS varied from 56.2 to 773 mg/L (mean 66.53 mg/L), also below the 500 mg/L guideline, and indicated good water quality. Total hardness averaged 101.23 mg/L CaCO$_3$, with a range of 74.2 to 126 mg/L to classify the water as soft to moderately hard. Major cations showed mean concentrations of 6.24 mg/L for Ca$^{2+}$, 4.97 mg/L for Mg$^{2+}$, 8.23 mg/L for Na$^{+}$, and 8.5 mg/L for K$^{+}$, all well within WHO and NSDWQ limits (75, 50, 200, and 12 mg/L, respectively). Anions included a mean SO$_4^{2-}$ of 31.06 mg/L (range of 10–49 mg/L), Cl$^{-}$ of 115.63 mg/L (range of 90–150 mg/L), NO$_3^{-}$ of 5.48 mg/L (range of 3.14–7.62 mg/L), F$^{-}$ of 0.19 mg/L (range of 0.16–0.2 mg/L), and CO$_3^{2-}$ of 166.88 mg/L (107.5–195 mg/L). In this regard, all anion levels were below the respective WHO and NSDWQ limits. Figure 2 presents a plot of the physiochemical parameters of the groundwater samples.

Hydrochemical facies can be classified on the basis of dominant ions using the Piper trilinear diagram. The concentrations of major ionic constituents of groundwater samples were plotted in the Piper trilinear diagram to determine the water types (Figure 3) and illustrate the hydrochemical compositions of the eight groundwater samples. This graphical representation, comprising two basal triangles (for cations and anions) and a central diamond field, facilitates the classification of water types and inference of geochemical processes. From the cationic triangular fields of the Piper diagram, it was observed that 100% of groundwater samples fell into the no dominant type. The anion triangle revealed bicarbonate (HCO$_3^{-}$ + CO$_3^{2-}$) as the dominant anion (70–90%), reflecting carbonate dissolution in the aquifer. According to Ali and Ali [21], the concentration of bicarbonate and carbonate also affected the suitability of water for irrigation purpose. It has been hypothesized that all Ca$^{2+}$ and Mg$^{2+}$ precipitate as carbonate. This was further proposed by Eaton [22] on the concept of residual sodium carbonate (RSC) for the evaluation of high carbonate waters. Though bicarbonate aids digestion in human body and is found to have no known adverse effects on human health, it might cause kidney stones when it exceeds 300 mg/l in the drinking water and in the presence of higher concentration of calcium during dry climatic conditions [21]. The dominant bicarbonate and carbonate ions suggest natural influences, possibly due to the interaction of natural water-rock.

The other 10% of the groundwater samples fell into no dominant type. The plot of chemical data on diamond shaped trilinear diagram revealed that both alkaline earth and alkaline metal were the most dominant metals in the water samples of the study area. From the data plots, it is apparent that the total hydrochemistry is dominated by alkaline earths. The absence of samples in Na-K-Cl or saline fields underscores the character of the freshwater and rules out significant seawater intrusion or dissolution. These findings imply a geologically homogeneous aquifer system, with carbonate weathering as the primary control of water chemistry. The dominance of good quality water in this season suggests that rainfall recharge helps dilute contaminants, thereby improving groundwater quality. It also highlights relatively favorable aquifer conditions within the region.

The United States salinity (USSL) diagram in Figure 4 classifies the irrigation suitability of the eight groundwater samples (BH1, BH2, BH3, BH4, BH5, BH6, BH7, and WL3) based on sodium adsorption ratio (SAR) and electrical conductivity (EC) (Table 3). The SAR values ranged from approximately 1 to 5, classifying all samples in the low (S1) category and indicating minimal sodium hazard for soil permeability. EC values spanned 250–1000 $\mu$S/cm, thus placing samples in the low (C1) to medium (C2) categories, with BH1, BH2, BH3, BH4, BH5, and WL3 near 250 $\mu$S/cm (C1); BH6 and BH7 near 750–1000 $\mu$S/cm (C2). This suggests low to moderate salinity risk, which is suitable for most crops with good drainage. All samples fell within the S1-C1 to S1-C2 zones, indicating excellent to good irrigation water quality (Table 4).

The water quality index (WQI) was calculated using pH, TDS, total hardness, Ca$^{2+}$, Mg$^{2+}$, Cl$^{-}$, SO$_4^{2-}$, and NO$_3^{-}$, with weights assigned based on their significance to health. The mean WQI derived from the summarized data is approximately 17, thus indicating “Excellent” quality ($<$50) according to the classification ($<$50: Excellent, 50–100: Good, 100–200: Poor, $>$200: Unsuitable). All parameters were within the WHO and NSDWQ limits. The “Excellent” WQI (Figure 4) confirms that groundwater in Egbeagu Amansea is suitable for drinking and irrigation.

In the study, the consistently low TDS, EC, and WQI values indicated that the groundwater was of excellent quality for drinking. All sampled locations also met the WHO and NSDWQ standards and served as well-preserved aquifers with limited pollution. The dominance of the HCO$_3$ facies and the low levels of most ions were due to natural processes (e.g., carbonate dissolution). The C1-S1 classification in the USSL diagram confirmed that the groundwater was suitable for irrigation, and the low SAR values further indicated that the soil structure was unlikely to be adversely affected by this water when used for irrigation.

In conclusion, good water quality dominated the wet season due to recharge effects. Groundwater in this study area was considered safe without pollution from sewage discharge, industrial effluent discharge, and dense settlement. Hence, additional development and extraction could still be supported by the private sector, such as establishing the bottled-water industry for boosting the economic and sustainable utilization of groundwater resources in this locality. Moreover, the growth of food production in the state could be achieved by the government via extending the irrigated fields in this community.