Investigating the quality of groundwater in Ibeju-Lekki Local Government Area, Lagos State

ABSTRACT This study assessed the groundwater quality in the rapidly urbanizing peri-urban region of the Ibeju-Lekki Local Government Area in Lagos State, Nigeria, during the rainy season. This study employed a two-stage sampling technique to select representative sampling locations, including boreholes and hand-dug wells. Seven towns in Ibeju-Lekki were sampled for this study. A total of 14 sampling points were chosen for the analysis of 15 water parameters, which included five physical parameters (NTU, TCU, E.C. TDS and TSS), eight (8) chemical parameters (pH, T.H. Ca, Mg, Cl-, NO3-, SO42- and Fe), and two (2) microbial parameters (E.Coli count and BOD) after standard procedures. The data obtained were subjected to statistical analysis using Python to assess correlations between the physicochemical parameters. The results were compared with water quality standards set by the World Health Organization (WHO) and the Nigerian Standard for Drinking Water Quality (NSDWQ). In addition, a water quality index (WQI) was calculated to provide a single numerical expression of the overall water quality. The findings revealed variations in the quality of borehole and well water, with some parameters exceeding the recommended standards, such as magnesium and iron concentrations. The presence of elevated turbidity, total dissolved solids (TDS), and electrical conductivity (E.C.) in well water indicated potential contamination sources. The study also demonstrated the significance of understanding physicochemical parameter correlations in groundwater quality assessment. The WQI results emphasized that groundwater is suitable for various purposes, including animals and other domestic and agricultural purposes. However, the paper recommended routine monitoring and thorough treatment to address the high magnesium (Mg) and iron (Fe) levels in both borehole and well water sources.


Introduction
For home water supplies, more than 60% of Nigerians rely on groundwater (Omole, 2011(Omole, , 2013)).Most residences rely on their own supplies rather than municipal water supplies (Omole & Ndambuki, 2015).Self-supply of water, however, frequently results in abuse and turmoil due to improper planning and laws (Omole, 2011;Omole & Ndambuki, 2015).In Nigeria, poor town planning has led to the proximity of family houses and industry (Omole & Isiorho, 2011).Industrial pollution, including effluent discharges, frequently affects drinking water sources and other aspects of human existence (Adewumi, Ogbiye, Longe, & Omole, 2011).Natural contaminant deposits exist in groundwater (Glynn & Plummer, 2005).However, anthropogenic activities and the interaction between surface and groundwater can also result in groundwater pollution.Heavy metal pollution from manufacturing, metallurgy, paints and chemicals, and other related industrial operations is a type of pollutant that can harm drinking water supplies.Because of inappropriate wastewater management, contaminants such as nitrates, nitrites, and sulfate can harm drinking water sources (Omole, Ndambuki, & Balogun, 2015).Therefore, it is crucial to test water quality to protect the public's health regularly.
An unfavorable change in groundwater quality caused by human activity is known as pollution.Many factors, including urbanization, increased industrial activity, intensive farming and an over reliance on fertilizers in agricultural production, cause these changes.It is common knowledge that a polluted environment harms the health of people, animals, and plants (Rueedi, Cronin, & Morris, 2009).With the rise in water demand suitable for particular uses and meets the desired quality, there is a need to define water quality.Poor water quality and unsanitary living conditions can negatively impact health (Chavan, Lokhande, & Rajput, 2006).Therefore, maintaining water quality at acceptable levels is crucial for effectively using water resources.Water quality must be regularly monitored to ensure the long-term viability of groundwater resources.The main objective of such an evaluation is to obtain a complete picture of the spatial distribution of groundwater quality and the changes that occur, either naturally or because of human intervention (Wang, Guan, & Aral, 2009).
The effects of urban development on water supply may be of greater significance.The relationship between hydrology and land use is a topic of interest worldwide.This is because water resources, including rain, rivers, the sea, and groundwater, are among the environmental resources most at risk from overuse or pollution, both of which are aggravated by human activities on the world's surface (Ghouli et al., 2009).Residential and commercial projects are replacing undeveloped land.Unplanned changes in land use have become a significant issue.Most land use changes occur randomly and illogically, with little regard for how they will affect the ecosystem.This is especially true in the region of Lagos, which has become a megacity.
Infrastructure development and urbanization are major problems for the government and the public.One of the most important needs of the people, both now and in the future, is the provision of potable water.Due to pollution, the city's surface water cannot be used.In the heavily industrialized and densely populated Ikeja suburb, there are around 2000 companies, the bulk of which dump their effluents into streams.The water quality of the rivers exceeds the WHO and Federal Environmental Protection Agency norms regarding pH, turbidity, fecal coliforms, BOD, total suspended solids, and heavy metals.The city's residents rely on groundwater for a consistent supply of drinkable water.Therefore, groundwater must be used sustainably, monitored, and safeguarded.This study examined groundwater quality in and around the fast-growing city of Lagos.This study primarily investigated the features of groundwater as represented by its component parameters.In addition, water portability was assessed in this study by comparing its quality with established international criteria.Groundwater's potential and quality make it a valuable economic resource and a need for human existence.However, because the effluent from discharges or runoff from solid waste disposal sites typically moves vertically downwards, the deterioration in major cities and urban centers due to population explosion urbanization and industrialization results in large volumes of effluent discharge that may affect the groundwater quality (Rosenthal, Guttman, Sbel, & Moller, 2009).
Therefore, this study is motivated by the fact that a substantial portion of the Lagosian population relies on groundwater for their domestic water supply due to the limitations of municipal water sources.However, this reliance on groundwater is accompanied by challenges arising from improper planning, industrial pollution, and natural and anthropogenic contaminants.This study acknowledges the need to evaluate and maintain water quality, given its direct impact on public health.In addition, it recognizes the growing concerns related to urbanization, land use changes and industrial activities, which can significantly affect groundwater quality.
Ibeju Lekki, the focus of this research, is a diverse area characterized by various communities, including cities, villages, and other settlements.These communities represent a broad spectrum of urban and rural environments, each with unique water usage patterns and challenges.To provide context for our study, it is crucial to understand the distributions of these communities and their respective water supply needs and constraints.The climate of the Ibeju Lekki area plays a fundamental role in shaping the groundwater resources and quality.Situated in the coastal region of Lagos, the area experiences a tropical monsoon climate with distinct wet and dry seasons.Understanding the local climate is essential as it influences the availability and movement of groundwater, and it can affect the vulnerability of water sources to contamination.
This study builds on existing literature by highlighting the challenges and environmental factors unique to Lagos State, where urban development and industrialization have created new dynamics for groundwater quality.For example, Soladoye and Ajibade, 2014 discovered highly variable groundwater quality in Lagos State, with parameters often exceeding local (NSDWQ) and international (WHO) standards, emphasizing the unsuitability of groundwater for drinking purposes in the region (Akoteyon & Soladoye, 2011) assessed the groundwater quality in Eti-Osa, revealing that several key parameters, including TDS, Fe, and Mg, exceeded the recommended limits and highlighted the heterogeneity of groundwater quality in the area.Omole et al. 2017 examined groundwater quality on a faith-based campus, where cadmium concentrations raised significant health concerns (Awoyemi, Achudume, & Okoya, 2014) monitored water quality parameters in the Majidun-Ilaje Area of Ikorodu and concluded that borehole water was generally suitable for various purposes.
In contrast, hand-dug wells and surface water showed variations above permissible limits (Balogun, Akoteyon, & Adeaga, 2012) assessed the impact of land use on groundwater quality in Lagos, revealing that a substantial portion of water samples were unsuitable for drinking, mainly because of high pH, total dissolved solids, chloride, total hardness, and nitrate levels.These studies underscore the significance of evaluating groundwater quality in Lagos State and its implications for public health and environmental sustainability.
The contributions of this study lie in its in-depth assessment of the spatial distribution of groundwater quality, considering both natural and human-induced changes.This holistic approach, along with the comparison of water quality against international standards, offers a comprehensive view of the groundwater status in the region.By doing so, it contributes to filling gaps in the existing literature, providing a valuable resource for policymakers and stakeholders seeking to ensure the sustainable use and protection of this critical water resource.This study bridges the gap between the broader concerns about groundwater quality in Nigeria and the challenges posed by rapid urbanization and industrialization in the Ibeju-Lekki area.

Study area
The Ibeju-Lekki Local Government Area, situated in Lagos State, Nigeria, as shown in Figure 1, is a rapidly urbanizing peri-urban region characterized by substantial residential development and population growth.Covering an area of approximately 646 square kilometers, it accounts for a quarter of Lagos State's total landmass and has a population of 117,481, according to the 2006 census (Olajide, Agunbiade, & Bishi, 2018).The area experiences a humid tropical climate with distinct wet and dry seasons and high relative humidity throughout the year.The vegetation includes lowland rainforests, freshwater swamp forests, and agricultural tree crop plantations.The geology is marked by sand, sandy clay, lignite, and recent-quaternary alluvium, and a double rainfall pattern influences the region (Sojobi, Balogun, & Salami, 2016).Its relief and drainage systems are characterized by numerous lagoons and waterways, constituting approximately 22% of the territory.Socioeconomic activities range from small-scale agriculture and local crafts to modern commerce, with a predominant issue of severe poverty due to limited employment opportunities and low education levels, particularly in indigenous areas.

Sampling locations
The study employed for this research is a reconnaissance study of the survey type, focusing on the rainy season in Nigeria, which typically spans from June to September 2022.The choice of the rainy season for this research is significant because rainfall during this season can introduce various contaminants into groundwater, including dissolved minerals and pollutants washed from the surface.Hence, conducting the research during this period was deliberate because it allowed the researcher to gain valuable insights into the groundwater quality in Ibeju-Lekki during a season of heightened environmental impact.
A reconnaissance survey of the study area was conducted before the sample collection to select the specific sampling locations.The basis for selecting the sampling locations was to ensure a representative sample of the groundwater sources in the area.A two-stage sampling technique was employed.In the first stage, a purposive random sampling technique was used to select seven (7) locations, namely Bojije, Eleko, Ibeju, Lakowe, Awoyaya, Elerangbe, and Abijo.These locations were chosen because they have a significant presence of hand-dug wells and boreholes, which are common groundwater sources in the region.In the second stage, a simple random sampling technique was used to select two sampling points (one hand-dug well and one borehole) from each previously chosen location.This approach ensured that we obtained a diverse representation of the groundwater sources in Ibeju-Lekki.In total, 7 hand-dug wells and 7 boreholes were selected, making up 14 sampling points.This selection process was designed to capture a variety of groundwater sources in the study area, providing a comprehensive assessment of groundwater quality during the rainy season.

Sampling collection
The coordinates of the sampling points were recorded using the Global Positioning System (GPS) Garmin Channel 72 model.Identification numbers were allotted to each sampling point in this study, and the numbers were used in the discussions instead of the actual names of the locations.The water samples were collected in clean 1.5-liter plastic jars with screw caps, packed in a cooler containing ice, and transported to a standard laboratory (Central Research Lab) for further analysis within 24 hr of sample collection.Fifteen (15) water parameters were considered for the study.The parameters were divided into physical, chemical, and microbial parameters.Five (5) physical parameters, including turbidity (NTU), color (TCU), electrical conductivity (E.C.), total dissolved solids (TDS), and total suspended solids (TSS), eight (8) chemical parameters, including pH, total hardness (T.H.), calcium (Ca), magnesium (Mg), Chloride (Cl-), Nitrate (NO 3 − ), Sulfate (SO 4 2- ) and Iron (Fe), and two (2) microbial parameters, i.e.E.Coli count (a type of fecal coliforms) and biological oxygen demand (BOD), were analyzed to provide valuable insights into the groundwater quality.

Analytical methods
Analytical methods were employed to comprehensively assess the water quality, covering the physical, chemical and microbial parameters.The pH, TDS, and E.C were determined using a Hanna Multi-parameter instrument (HI 9812-5).Before analysis, the instrument was calibrated, and readings were obtained from the water samples after rinsing the probe.Cl − estimation was performed using the argentometric method, which is suitable for relatively clear waters containing 0.15-10 mg of Cl − .In this method, potassium chloride (K 2 CrO 4 ) was used as an indicator to detect the endpoint of the silver nitrate (AgNO 3 ) titration of Cl − .Various interferences, such as Bromine (Br − ), Iodine (I − ), and Cyanide (CN) were considered, and special reagents, including aluminum hydroxide Al(OH) 3 suspension and hydrogen peroxide (H 2 0 2 ), were used to remove interferences.The concentration of Cl − in the samples was calculated on the basis of the volume of AgNO 3 solution used in the titration.TSS was also determined using an Ohaus Pro weighing balance.The filter paper was initially weighed, and then 50 ml of the water sample was filtered.After drying, the weight of the filter paper and residue was measured to calculate the percentage of TSS.For mineral analysis, samples were ashed at 550°C, and the resulting ash was processed with HCl and filtered.The minerals were determined using an atomic absorption spectrophotometer (AAS PG Instrument Model 990FG) and expressed in ppm (mg/100 g).Ca and Cl − were determined spectrophotometrically using a UV/Vis Spectrophotometer model 752N.The BOD was typically measured by first incubating a water sample in the dark at a controlled 20°C temperature for 5 days with microbial activity.After the incubation period, the remaining dissolved oxygen (DO) in the sample was measured, and BOD was calculated based on the difference in DO concentrations before and after incubation.Microbial assessment involved autoclaving the media and inoculating sterilized nutrient agar plates with 100 μL of the water sample.The plates were incubated at 35°C for 24 hrs, and colony-forming units (CFU) were counted and recorded as an indicator of microbial presence.

Data analysis
The data (laboratory results) obtained were subjected to statistical analysis using Python on Jupyter Notebook.The data were subjected to Spearman's correlation for the physicochemical parameters.Spearman was used to assess associations between variables when normality assumptions were not met, making it suitable for the dataset, which includes both numeric and non-normally distributed variables such as TSS, turbidity, and NO 3 -.The results obtained were then compared with standards set by the (Nigerian Standard for Drinking Water Quality NSDWQ, 2015; World Health Organization WHO, 2008).

Water Quality Index (WQI)
The method employed for the Water Quality Index (WQI) in this study involved a systematic approach that integrated key environmental hydrogeological factors, which included fourteen trace elements (NTU, TCU, E.C, TDS, TSS, pH, TH, Ca, Mg, Cl − , NO 3 − , SO 4 2-, Fe, and BOD).Correlation analysis was first conducted to determine the strength of the relationships between these parameters, and weights (5-1) were assigned on the basis of the correlation results, with parameters exhibiting stronger correlations receiving higher weights.Relative weights were calculated by normalizing the assigned weights.Water quality standards from the WHO and NSDWQ were used to assess the quality of water samples, and the WQI was calculated based on the effective parameters for each well and borehole.The WQI allowed for a single numerical expression of overall water quality, facilitating the evaluation of groundwater suitability for drinking.

Description analysis
Table 1 provides a comprehensive set of descriptive statistics for various groundwater parameters in the Ibeju-Lekki Local Government Area, Lagos State.The Mg content in borehole water sources ranges from 11.17 to 17.21 mg/L, with a mean of 14.46 mg/L.In well water sources, the Mg content varied from 14.57 to 15.61 mg/L, with a mean of 15.12 mg/L.This suggests that boreholes tend to have slightly lower Mg levels than wells.The Fe contents in borehole water ranged from 0.01 to 0.74 mg/ L, with a mean of 0.32 mg/L.In well water, the Fe content ranges from 0.07 to 0.50 mg/L, with a mean of 0.32 mg/L.The iron concentrations were relatively low and exhibited little variation between the two sources.In borehole water sources, Ca concentrations vary from 3.97 to 4.85 mg/L, with a mean of 4.55 mg/L.Well water sources show a broader range, from 3.14 to 6.29 mg/L, with a mean of 4.48 mg/L.This suggests that calcium levels are more variable in well water, potentially due to geological differences.
Borehole water has sulfate concentrations ranging from 0.53 to 1.09 mg/L, with a mean of 0.87 mg/L.Well water exhibited a range of 0.70-0.93mg/L, with a mean of 0.74 mg/L.Both boreholes and well water sources display relatively low sulfate levels, with well water being slightly more consistent.Nitrate concentrations in both borehole and well water sources are consistently low, with a narrow range of 0.05-0.06mg/ L and means of 0.05 and 0.06 mg/L, respectively.The minimal variation in nitrate levels suggests that nitrate pollution is not a significant concern in the area.Borehole water exhibits TDS values ranging from 10.00 to 400.00 mg/L, with a mean of 194.00 mg/L.Well water has a wider range of 140.00-540.00mg/L, with a mean of 310.00 mg/L.TDS levels in well water are notably higher and exhibit more variation, possibly due to geological factors.Borehole water E.C ranges from 30.00 to 800.00 μS/cm, with a mean of 397.00 μS/cm.Well water E.C ranges from 280.00 to 1090.00 μS/cm, with a mean of 630.00 μS/cm.Well water has significantly higher electrical conductivity levels, reflecting greater variability and possibly indicating differences in the underlying geology.

Physio-chemical parameters correlation
Table 2 presents the correlation among the physiochemical parameters of boreholes and dug wells in the study area.In the context of boreholes, Spearman's correlation matrix reveals several interesting relationships among groundwater parameters.The strong negative correlation between iron (Fe) and magnesium (Mg) at −0.79 suggests an inverse relationship, where higher iron concentrations are associated with lower magnesium concentrations.This could be indicative of geological or environmental factors affecting the mineral content of groundwater.The strong negative correlation between iron (Fe) and total suspended solids (TSS) at −0.73 implies that as iron levels rise, the presence of suspended solids in the water tends to decrease, which could be relevant for water treatment processes.Moreover, the positive correlation between pH and total dissolved solids (TDS) at 0.78 implies that more basic (alkaline) water is associated with higher dissolved solids, highlighting the potential impact of pH on water quality.Additionally, the strong positive correlation between electrical conductivity (E.C) and TDS at 0.99 indicates  a strong link between the ability of water to conduct electrical current and the concentration of dissolved solids, which could be vital for assessing water salinity and quality in boreholes.
Switching to the analysis of well water, Spearman's correlation matrix reveals its own set of intriguing relationships.The substantial positive correlation between calcium (Ca) and sulfate at 0.81 suggests a strong connection between these two ions in well water.The negative correlation between pH and total suspended solids (TSS) at −0.75 indicates that more acidic well water tends to have higher levels of suspended solids, underscoring the importance of pH in determining water quality.The positive correlation between chloride (Cl) and total hardness (TH) at 0.86 implies that increasing chloride concentration in well water is associated with higher total hardness, which could be linked to the geological composition of the aquifer.Finally, the positive correlations between BOD and several parameters (SO 4 2-, NO 3 − , and TH) suggest that higher biochemical oxygen demand is linked to increased concentrations of these constituents, indicating potential contamination sources or microbial activity in well water.These findings underscore the significance of understanding these relationships in the context of water quality assessment and groundwater management in the study area.

Comparison of physio-chemical parameters of the water samples with WHO and NSDWQ standards
A comparison of the physicochemical parameters of the water samples with those of the NSDWQ standard is shown in Table 3 and Figures 2-15. Figure 2 shows that the concentration (mg/L) of magnesium in the study area and at all sampling points exceeded the NSDWQ limit of 0.2 mg/L for drinking purposes.Magnesium is a constituent of hard water and one of the most abundant cationic constituents of natural water, and it depends on the geological source and chemical weathering process.In line with this finding (Akoteyon & Soladoye, 2011), assessed the groundwater quality in Eti-Osa, revealing that Mg exceeded the recommended limits and highlighting the heterogeneity of groundwater quality in the area.
Figure 3 shows that the concentrations (mg/L) of iron in borehole and well water in Bojije, Ibeju, and Elerangbe exceeded the NSDWQ limit for the concentration of iron in drinking water.Only the well type of groundwater in Awoyaya (0.45) had a concentration above the permissible limit of 0.3 mg/L for drinking.High rainfall may be necessary to increase the amount of iron in borehole water as reported by (Abubakar & Adekola, 2012) in the study conducted in Yola.Iron can be deposited in kitchen utensils, toilet bowls, and water pipes even though it is considered a secondary pollutant and has no harmful effects on human health.This can result in coloring and sediment deposits (Omole, Ndambuki, & Balogun, 2015).
Compared with the NSDWQ limit, the concentrations of Ca (Figure 4), Cl − (Figure 5), SO 42-(Figure 6), and NO 3 − (Figure 7) were below the safe limits of 300, 250, 100, and 50 mg/L for drinking at the respective sampling points in the study area.Although nitrates are naturally found in soils and water, it is very difficult for them to enter groundwater.They can enter surface water through chemical fertilizers nearby soil, natural plants, or residential wastewater leaching.Under aerobic conditions, higher sulfate concentrations may result in bowel disorders and odor (Rehman & Rehman, 2014).Figure 8 depicts that pH is a measure of hydrogen ions (H + ) and negative hydroxide ions (OH − ) in water and indicates whether the water is alkaline or acidic (World Health Organization WHO, 2008).A low acidic pH level was observed in Bojije (5.89), Eleko (6.09), Ibeju (5.15), and Awoyaya (5.75) boreholes and in Bojije (5.48), Abjio (6.12), and Elerangbe (5.55) well water samples, which indicates a slightly acidic condition.A pH value below the maximum limit of 8.0 prescribed for drinking water standards by WHO and NSDWQ was observed at all sampling points.Although low acidity is typically thought to have no direct effects on people, drinking low acidity water over an extended period of time will almost always result in mineral shortages (Islam et al., 2016).Precipitation that falls on the ground and seeps through the soil to reach the aquifer is the source of almost all groundwater.
The most common way to assess the quality of water is by measuring its total dissolved solids (TDS).Bicarbonate, carbonate, sulfate, chloride, nitrates, and other substances constitute most TDS.The total dissolved solids (TDS) (μs/cm) and electrical conductivity E.C (μs/cm), which is an indicative parameter to assess the degree of water quality, as shown in Figures 9 and 10 were below the NSDWQ prescribed limits of 500 mg/l and 1000 mg/l for drinking water purposes, except in well water sampled in Eleko (TDS = 540 and E.C = 1085), which could originate from natural sources, sewage and industrial wastewater.This implies that an increase in TDS increases the electrical conductivity of the water.The concentration and mobility of ions have a direct impact on the electrical conductivity of water.According to (Morris, Sakarya, Koh, &   O'Donnell, 2020), EC is a good indicator of dissolved ionizable materials.Eleko's high EC and TDS concentrations could be related to urban runoff, humancaused contaminants that seep into the subsurface, or discharge into nearby streams (Morris et al., 2003).
Although TDS in groundwater is often not dangerous to people, large concentrations can have an impact on those with kidney and heart conditions.
Figure 11 shows that the well water quality in the studied area is particularly abrasive.This is also applicable to some boreholes in the study area, including Bojije (456), Eleko (568), Lakowe (420), and Abijo (251).This hardness may be caused by the presence of calcium carbonates and/or magnesium, which typically causes insufficient soap lather and subsequent "scum" development as reported by Omole, Ndambuki, and Balogun (2015) in Ogun State.The presence of high magnesium content contributed to the observed high total hardness in the research area, especially in well water, even if calcium below the NSDWQ standard limit was reported in the impacted sampling stations with high total hardness (TH).The natural buildup of salts in water from contact with soil and geological formations or direct human activity pollution are the two main causes of hardness.Most individuals want water that is not too hard.When you  have a bath, it usually tastes better and removes the soap.As impurities in limestone, sulfates, chlorides, silicates, etc. of calcium, magnesium, sodium, potassium, aluminum, etc. are exposed to the water's solvent action and flow into solution, increasing the hardness (Vermani & Narula, 1995).
The turbidity (Figure 12) in the study area's borehole was higher than the NSDWQ guideline value of 5 NTU, and was also higher in the well water sampled in the study area, excluding Bojije (4.27) and Awoyaya (4.70).Plankton and other microscopic organisms, as well as suspended and colloidal debris such as clay, silt, and finely divided organic and inorganic matter, are the main contributors to water turbidity.Although turbidity typically has no direct negative impact on health, it can hinder cleaning efforts and act as a breeding ground for bacteria (Sadar, 1996).This might be a sign of disease-causing organisms such as viruses, parasites, or bacteria, which can produce symptoms such as nausea and diarrhea (Afolabi, Ogbuneke, Ogunkunle, & Bamiro, 2012).
The color (Figure 13) and total suspended solids (Figure 14) ranged from 2.67 to 4.66 and 0.05-0.70 in the sampled boreholes and wells in the study area.These values were below the NSDWQ's prescribed limits of 15 and 4 for the drinking water standard for color and total  suspended solids.The presence of colored suspended solids, fluorescence in the visible wavelength range from substances that absorb white or ultraviolet light, absorption of specific wavelengths of normal white light by dissolved or colloidally dispersed substances and preferential scattering of short wavelengths of light by the smallest suspended particles all contribute to the appearance of color in drinking water (Black & Christman, 1963).True color is assessed in water samples from which particle matter has been centrifuged out, as opposed to clear color, which is defined as color measured in water samples from which suspended matter is present.
The biological oxygen demand (BOD) levels in the groundwater of the Ibeju-Lekki Local Government Area, as indicated in Figure 15, are within the range of 0.42-2.19mg/L.BOD is a crucial parameter for assessing the quality of water bodies because it indicates the amount of oxygen required by microorganisms to decompose the organic matter present in the water.The highest BOD value was observed in the Ibeju well, with a concentration of 2.19 mg/L, whereas the lowest BOD level was found in the Elerangbe borehole, with a concentration of 0.42 mg/L.These BOD values suggest that the organic pollution and decomposition potential in the groundwater vary  across different locations within the area.Only BOD in Ibeju exceeds the 2.00 mg/L limit set by the Standards Organization of Nigeria, which is a positive indicator of the overall water quality in the region in terms of organic pollution.

Variations in borehole and well water sample in Ibeju-Lekki
Table 4 shows the variation in borehole and well water in the study area.There was no significant variation between the Mg (p = 0.185) content in the borehole and well water.
The concentrations of magnesium in both sample points were beyond the NSDWQ limit.Researchers such as (Akujieze, Coker, & Oteze, 2003) have shown that groundwater is vulnerable to the buildup of dissolved iron and manganese under anaerobic conditions in Nigeria.
There is no significant variation between the Fe (p = 0.940) content present in borehole and well water.The iron concentrations at both sample points exceeded the NSDWQ limit of 0.3 ppm.If acidic conditions exist, high levels of iron may be anticipated in groundwater from crystalline basement regions.Because of the frequent use of dug wells to extract groundwater from the crystalline basement, elevated iron concentrations in these wells may also be caused by the presence of particle iron, particularly if the groundwater is extremely  turbid.Although below the WHO recommendation threshold, several high-iron groundwater samples were discovered by (Alagbe, 2002) in basement rocks in Northern part of Nigeria.
There was no significant variation between the Ca (0.992) content in the borehole and well water.The concentrations of calcium in both sample points were below the NSDWQ limit for drinking purposes.Similar to this finding is the research conducted in Delta State on several physicochemical characteristics of subsurface water, which revealed that borehole water contains low quantities of calcium ions (Agbaire & Oyibo, 2009).
There is a significant variation between the NO 3 (p = 0.017) content in the borehole and well water.The mean value for NO 3 contents of well (0.06) is higher than that of borehole (0.05).This finding supports that of (Malomo, Okufarasin, Olorunnio, & Omode, 1990), who found that shallow groundwater from dug wells had higher nitrate contents.If pollution sources are close by, some shallow groundwater, especially those from dug wells and dugouts, may have high concentrations of nitrate due to pollution inputs.However, not all shallow groundwater from dug wells is polluted; in fact (Alagbe, 2002), discovered in Northern Nigeria that groundwater from dug wells had lower nitrate concentrations.In unconfined aquifers, groundwater from deeper boreholes may therefore also have elevated nitrate contents.There is no significant variation between the turbidity (0.528) content present in borehole and well water.The mean values of turbidity for both groundwater (borehole = 5.54, well = 5.59) exceed the 5NTU limit of NSDWQ standard (Ofili, 2007).Contrary to this result (Aremu, Ozonyia, & Ikokoh, 2011), indicated that TDS was found to be lower in boreholes compared to well.
There is no significant variation between the color (0.528) content present in borehole and well water.The mean values of color for both groundwater (borehole = 3.40, well = 3.49) fall below the limit of NSDWQ standard.
There is a significant variation between the TSS (p = 0.000) content present in borehole and well water.The mean result of the TSS in borehole (0.29) is higher than the TSS in well (0.07) There is a significant variations between the pH (0.000) content present in borehole and well water.The pH of borehole is 5.87 while that of well is 6.63.Low pH in borehole water may be attributed to Sulfur and amino acid compounds from human and animal excreta.Similar results were found by (Eniola, Obafemi, Awe, Yusuf, & Falaiye, 2007) that showed that pH of borehole water is more acidic than well water.There is a significant variations between the TDS (0.004) content present in borehole and well water.The mean result of the TDS in borehole (188.57) is lower compared to the TSS in well (320.00).This could be a sign that well water contains more particles than borehole water, according to a study on well water conducted by (Shittu, Olaitan, & Amusa, 2008).Because of this, limestone, gypsum, dolomite, or other minerals in the soil that contain calcium or magnesium are more prevalent in well water than in the aquifer.
There is a significant variations between the EC (0.005) content present in borehole and well water.The mean value of EC in well (641.07) is higher that the EC in borehole (387.14) and in line with the result of (Aremu, Ozonyia, & Ikokoh, 2011).This expresses the level of more dissolved ions in well.
There is a significant variations between the Cl − (0.048) content present in borehole and well water.The concentration of chloride in well (56.34)compared to borehole (39.37) is higher.The presence of higher concentration of chlorides in well water could be attributed to pollutions from sewage, minerals and industrial effluents (Sameer, Hampannavar, & Purandara, 2011).
There is a significant variations between the TH (0.000) content present in borehole and well water.Well water (575.00)proves to be harder than water from borehole (320.43).The difference can be a sign that the soil contains calcium-or magnesiumcontaining minerals like dolomite, gypsum, or limestone.Since both borehole and well water samples exceed the NSDWQ standard level, they can both be characterized as hard since they make it difficult to lather up with soap when washing.However, it would be beneficial for drinking because hard water might be superior to soft water for that reason.
The BOD levels in borehole and well water samples were found to be 0.72 and 1.13 mg/L, respectively.The statistical analysis indicated a significant difference (p = 0.02) between the BOD levels in these two water sources.This suggests that the BOD in well water is higher than that in borehole water, and this difference is statistically significant.Elevated BOD levels in well water may be indicative of organic pollution and microbial contamination, making it a concerning factor for the overall quality of well water sources in the Ibeju-Lekki area.(NSDWQ), and the weights and relative weights assigned to each parameter.Notably, the assigned weights for each parameter are determined based on the correlation strength, reflecting the degree to which each parameter is interrelated.Parameters with strong correlations receive higher weights, while those with weaker or no correlations are assigned lower weights.This approach aims to emphasize the parameters that substantially influence water quality (Afolabi, Ogbuneke, Ogunkunle, & Bamiro, 2012).An interesting observation from the table is that, for both borehole and well water samples, the relative weights for most parameters are relatively uniform, with values hovering around 0.07 or 0.13.This suggests the consistent importance of parameters in assessing water quality from both sources.Moreover, the WQI results show water quality by assessing how well the water samples meet established standards, considering the relative importance of each parameter.

Conclusion
This study evaluated groundwater quality, specifically from boreholes and wells, in the Ibeju-Lekki Local Government Area.The quality assessment was based on a comprehensive analysis of various water quality parameters.The groundwater in the source primarily originates from hand-dug wells and boreholes, which are common and widely used groundwater sources.These sources were chosen for sampling because of their significance in providing water to the local population.The WHO and NSDWQ drinking water quality standards adopted show that TDS, Ca, SO 4 2-, NO 3 − , Cl − , color, turbidity, TSS, and TDS were below the safe limit.Mg and iron concentrations were higher than those acceptable for drinking.All groundwater samples' pH values indicated a mildly acidic state.An additional procedure was performed to identify the water parameter standards that were exceeded at each sampling station.The results demonstrate that no sample point can exist without a default.
Every place has water that surpasses established criteria in one or more parameters.Therefore, the area's groundwater is not potable.Based on the Water Quality Index (WQI) results, it is evident that boreholes and wells in the Ibeju-Lekki Local Government Area, Lagos State, exhibit similar water quality, with both scoring a WQI of 0.07, indicating good overall water quality.This implies that groundwater is suitable for various purposes, including animal and other domestic and agricultural purposes.Nevertheless, boreholes are slightly purer than wells.In addition, it was noted that the groundwater in the study area had a highly hard nature, which may be due to the presence of Ca in the water, which creates gypsum.Because drinking would help to increase the body's calcium and magnesium content, this might not be a concern.Problems would only arise when washing clothes with water because more soap would be used.Therefore, it is recommended to implement water treatment processes to address the high levels of magnesium (Mg) and iron (Fe) in both borehole and well water sources, which exceed the permissible limits for drinking water.Water treatment methods, such as filtration or chemical treatment, should be considered to improve the area's drinking water quality.

Figure 2 .
Figure 2. Comparison of mg values of the water in Ibeju Lekki with SON standard.

Figure 3 .
Figure 3.Comparison of Fe values of the water in Ibeju Lekki with SON standard.

Figure 4 .
Figure 4. Comparison of Ca values of the water in Ibeju Lekki with SON standard.

Figure 6 .
Figure 6.Comparison of SO 4 2-values of the water in Ibeju Lekki with SON standard.

Figure 5 .
Figure 5.Comparison of Cl values of the water in Ibeju Lekki with SON standard.

Figure 8 .
Figure 8.Comparison of pH Values of the water in Ibeju Lekki with SON standard.

Figure 7 .
Figure 7.Comparison of NO 3 − values of the water in Ibeju Lekki with SON standard.

Figure 9 .
Figure 9.Comparison of TDS values of the water in Ibeju Lekki with SON standard.

Figure 10 .
Figure 10.Comparison of E.C values of the water in Ibeju Lekki with SON standard.

Figure 11 .
Figure 11.Comparison of TH values of the water in Ibeju Lekki with SON standard.

Figure 12 .
Figure 12.Comparison of NTU values of the water in Ibeju Lekki with SON standard.

Figure 13 .
Figure 13.Comparison of TCU values of the water in Ibeju Lekki with SON standard.

Figure 14 .
Figure 14.Comparison of TSS values of the water in Ibeju Lekki with SON standard.

Figure 15 .
Figure 15.Comparison of BOD values of the water in Ibeju Lekki with SON standard.

Table 1 .
Descriptive statistics of groundwater sample parameters.

Table 2 .
Spearman's correlation matrix of groundwater parameters.

Table 3 .
Comparison of physio-chemical parameters of the water in Ibeju Lekki SON standard.
Table 5 offers a comprehensive overview of the key water quality parameters, the established standards by the World Health Organization (WHO) and the Nigerian Standard for Drinking Water Quality

Table 4 .
Variations in borehole and well water sample in Ibeju-Lekki.

Table 5 .
Limits of WHO, NSDWQ, assigned and relative weights for water parameters.