Spatial assessment of groundwater quality for drinking In Souk El Arbaa, Morocco

There is a higher demand for fresh water in Morocco's semi-arid regions due to less rainfall, population growth, and increased industrial and agricultural activities. It is important to use groundwater resources efficiently and take steps to prevent contamination (Mohammed et al. 2020; El Mountassir et al. 2021; Ez-Zaouy et al. 2022; Hilal et al. 2024). The best way to address groundwater pollution is to implement strategies to mitigate it early on. Protecting and managing groundwater requires specific plans and guidelines that focus on certain areas to prevent contamination. To safely use and develop groundwater, it is necessary to have a thorough understanding of the aquifer system and hydrological conditions in the area, which can be used to create a map that shows vulnerability to groundwater pollution (Marques et al. 2019).

Understanding the quality of groundwater is as important as its quantity because it is the main factor determining its suitability for drinking, domestic, agricultural, and industrial purposes (Darwesh et al. 2019; Darwesh et al. 2020). It relies heavily on groundwater in the water supply to the population, whether in urban or rural areas, and whether it is in humid areas or arid and semi-arid areas, and therefore must be protected from pollution. Natural and anthropogenic effects, including local climate, geology, and irrigation practices, influence water quality (Alhumairia & Rahalb 2023).

Groundwater vulnerability is crucial for understanding how the physical environment can protect groundwater from pollutants and assessing the sensitivity of different zones to prevent contamination (Bera et al. 2021). Addressing groundwater pollution is challenging due to the risk of contamination from human activities and land use, with varying levels of susceptibility across different areas (Olojoku et al. 2017). Assessments of groundwater vulnerability are essential for sustainable development and preserving groundwater resources (Majandang & Sarapirome 2013).

The chemical character of any groundwater determines its quality and utilization. The quality is a function of the physical, chemical, and biological parameters and could be subjective since it depends on a particular intended use.

Groundwater plays a key role in providing water for drinking, agriculture, and industry. Groundwater is used in the production of around 40% of the world's food, and it is dependent on one-third of the world's population. An already constrained water supply is in danger due to the growing global economy, population, and infrastructure (Bhat et al. 2018; Kumar et al. 2022). Water quality assessment is more crucial than water quantity assessment and provides crucial data for water management planning, especially in relation to drinking water (Naser et al. 2017; Li et al. 2018).

Nitrates, commonly used in agriculture as fertilizers, are a major source of groundwater pollution (Al-Aizari et al. 2020). They do not naturally occur in groundwater and can indicate the movement of contaminants. Evaluating the vulnerability of groundwater to pollution is crucial for ensuring clean water supplies and reducing negative impacts. Many models and techniques have been created and used worldwide to assess and map groundwater threats (Ekwere & Edet 2017; Shah et al. 2021; Mkumbo et al. 2022).

Morocco has an arid and semi-arid climate, with vastly different precipitation patterns depending on the season and location.

Although groundwater in Morocco is a significant component of the nation's hydrological legacy, it is contaminated by urban, industrial, and agricultural activities. Water supplies in Morocco are scarce. The annual amount of renewable water in Morocco is predicted to be 29 billion m³; in 1998, it was 1,044 m³ per person, but by 2020, it only be 786 m³ per person/year.

After 2025, Morocco is predicted to have a water scarcity (less than 500 m³/inhabitant/year), as it is already under water stress (less than 1,000 m³/inhabitant/year) (Bzioui 2004; El Khodrani et al. 2016).

The Gharb region's coastal water resources are becoming more and more polluted because of artisanal, industrial, agricultural, and urban growth. Recent growth in the area has led to a rise in water consumption as well as the creation of various contaminated sites. Morocco's western area is crucial to the agricultural output of the nation HCP (2013).

In the Souk El Arbaa area in northwest Morocco, traditional methods are used for well digging; when water is at a depth of less than 10 m, manual drilling is employed with axes and shovels. At 30 m minimum depth, a drilling rig is widely used by local farmers. The depths of the wells in the area ranged between 3 and 42 m. In addition to the use of natural fertilizers to fertilize soil (animal waste residues), farmers also use synthetic fertilizers.

In addition to the use of natural fertilizers to fertilize soil (animal waste residues), farmers also use synthetic fertilizers.

The most widely used wastewater disposal method in the region is the public sewer system (43.3%), followed by septic pits (31.5%), and 5.2% of the population uses abandoned wells or public sewer systems. The present study found that 70.2% of urban areas had public sewer systems compared to 1.1% of rural areas. Septic pits are used by 48.1% of rural residences, but only 20.9% of urban households. It is also noted that wells are formed in rural areas (10%), but only 2.1% are used in urban regions (Maroc 2019). There are several types of irrigation systems used in agriculture, including drip irrigation, sprinkler irrigation, and surface irrigation. Drip irrigation is the most widely used system because it is efficient and allows precise control of water use. Sprinkler irrigation is also very popular, especially in large agricultural operations. Surface irrigation, which involves flooding fields, is used less frequently because of water conservation concerns. In this area are grown wheat, legumes, fodder, beetroot, sugar cane, and olives.

The objective of this study is to determine the suitability of the groundwater in the study area for drinking purposes.

To assess the groundwater quality for drinking, 14 groundwater samples have been collected. The samples analyzed in the field for electrical conductivity (EC), pH, total dissolved solids (TDS), and were analyzed for major cations and anions in the laboratory according to the standard methods given by the American Public Health Association APHA (2005).

The IDW tool in the Geostatistical Analyst of the ArcGIS Arc Map10.4.1 software program was used to produce the spatial distribution maps for groundwater quality based on the values of various quality parameters for drinking water.

Geostatistical Analyst Tools > Interpolation > IDW uses the measured values surrounding the prediction location to predict a value for any un-sampled location, based on the assumption that things that are close to one another are more alike than those that are farther apart.

Software of hydrochemistry (Roland SIMLER Laboratory of Hydrogeology of Avignon) was used to obtain hydrochemical facies of groundwater in the study area.

The pH values of groundwater range from 6.59 to 8.5 with an average value of 7.29 this shows that the groundwater of the study area is mainly alkaline in nature. The EC values range from 1,070 to 17,487 μS/cm with an average value of 4,050 μS/cm. TDS values range from 716,9 to 11,716 mg/l with an average value of 2,714 mg/l. Statistical summary of physical and chemical parameters of groundwater is reported in Table 1.

Table 1

Descriptive statistics of physical and chemical parameters of groundwater

Water quality parameters .	Units .	Mini .	Max .	Average .
EC	μs/cm	1,070	17,487	4,050
pH	mg/l	6.59	8.50	7.29
TDS	mg/l	716.9	11,716	2,714
T.H	mg/l	185	2,184	617
Ca2+	mg/l	46.0	607.6	166.4
Mg2+	mg/l	11.3	161.8	49.0
Na+	mg/l	25	3,453	529
K+	mg/l	2.34	89.69	14.60
Cl−	mg/l	69	6,303	954
	mg/l	27.4	729.6	198.1
	mg/l	115.9	551.6	318.2
	mg/l	126	1,327	473
	mg/l	5.556	16.380	11.535

Water quality parameters .	Units .	Mini .	Max .	Average .
EC	μs/cm	1,070	17,487	4,050
pH	mg/l	6.59	8.50	7.29
TDS	mg/l	716.9	11,716	2,714
T.H	mg/l	185	2,184	617
Ca2+	mg/l	46.0	607.6	166.4
Mg2+	mg/l	11.3	161.8	49.0
Na+	mg/l	25	3,453	529
K+	mg/l	2.34	89.69	14.60
Cl−	mg/l	69	6,303	954
	mg/l	27.4	729.6	198.1
	mg/l	115.9	551.6	318.2
	mg/l	126	1,327	473
	mg/l	5.556	16.380	11.535

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The correlation coefficient is a commonly used measure to establish the relationship between two variables. It is simply a measure to exhibit how well one variable predicts the other (Subramani et al. 2005).

The correlation matrices for 12 variables were prepared (Table 2) and illustrate that EC and TDS show a high positive correlation with Cl⁻, Na⁺, total hardness, Mg²⁺, and Ca²⁺. Also, a good positive correlation is shown with K⁺ and ⁠. Total hardness shows a high positive correlation with Ca²⁺, Na⁺, K⁺, Mg²⁺, _, and Cl⁻. Mg²⁺ shows high positive correlation with Na, K⁺, and Cl⁻. Na shows a high positive correlation with Cl⁻, _, and K⁺. K⁺ shows a high positive correlation with Cl⁻ and shows a good positive correlation with ⁠. Cl shows a high positive correlation with ⁠. pH exhibits positive correlation with TDS, T.H, Ca²⁺, Mg²⁺, Na⁺, K⁺, Cl⁻, and _, and the pH exhibits negative correlation with ⁠, _, and ⁠.

Table 2

Correlation of physiochemical parameters of groundwater

.	EC (μs/cm) .	pH .	TDS .	T.H .	Ca2+ .	Mg2+ .	Na+ .	K+ .	Cl− .	.	.	.
pH	0.769
TDS	1	0.769
T.H	0.904	0.717	0.904
Ca2+	0.85	0.632	0.85	0.973
Mg2+	0.859	0.767	0.859	0.883	0.751
Na+	0.978	0.765	0.978	0.96	0.913	0.889
K+	0.797	0.75	0.797	0.933	0.918	0.804	0.884
Cl−	0.973	0.774	0.973	0.966	0.923	0.887	0.999	0.905
	0.791	0.387	0.791	0.872	0.93	0.604	0.83	0.736	0.829
	−0.151	−0.236	−0.151	−0.052	−0.058	−0.03	−0.15	−0.156	−0.162	0.056
	−0.249	−0.655	−0.249	−0.22	−0.074	−0.478	−0.269	−0.338	−0.274	0.237	0.144
	−0.477	−0.581	−0.477	−0.495	−0.438	−0.525	−0.477	−0.468	−0.48	−0.351	−0.465	0.343

.	EC (μs/cm) .	pH .	TDS .	T.H .	Ca2+ .	Mg2+ .	Na+ .	K+ .	Cl− .	.	.	.
pH	0.769
TDS	1	0.769
T.H	0.904	0.717	0.904
Ca2+	0.85	0.632	0.85	0.973
Mg2+	0.859	0.767	0.859	0.883	0.751
Na+	0.978	0.765	0.978	0.96	0.913	0.889
K+	0.797	0.75	0.797	0.933	0.918	0.804	0.884
Cl−	0.973	0.774	0.973	0.966	0.923	0.887	0.999	0.905
	0.791	0.387	0.791	0.872	0.93	0.604	0.83	0.736	0.829
	−0.151	−0.236	−0.151	−0.052	−0.058	−0.03	−0.15	−0.156	−0.162	0.056
	−0.249	−0.655	−0.249	−0.22	−0.074	−0.478	−0.269	−0.338	−0.274	0.237	0.144
	−0.477	−0.581	−0.477	−0.495	−0.438	−0.525	−0.477	−0.468	−0.48	−0.351	−0.465	0.343

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The geochemical evolution of groundwater can be understood by plotting the concentrations of major cations and anions in the Piper (1944) trilinear diagram (Piper 1944). The knowledge of hydrochemistry is essential to determine the origin of the chemical composition of groundwater (Zaporozec 1972).

The Piper diagram (Figure 2) shows that the alkaline earth cations (Ca²⁺ and Mg²⁺) exceed the alkalis cations (Na⁺ and K⁺) and the weak acids anions [(⁠⁠) as the ‘alkaline’ constituents] exceed strong acids anions [(Cl⁻and ⁠) as the ‘saline’ constituents].

The dominance of alkaline earth cations (Ca²⁺ and Mg²⁺) and weak acids anions [(⁠⁠) as the ‘alkaline’ constituents] on the chemical properties of groundwater is reported in Souk El Arbaa. This means that most of the groundwater in the study area is considered as secondary saline water (indicating the impact of anthropogenic activities), and the rest of the groundwater is considered as primary saline water (indicating the impact of the geochemical processes natural) since the study area is considered a drainage area.

The analytical results of physical and chemical parameters of groundwater were compared with the standard guideline values as recommended by the Moroccan Standards for drinking water. The number and percentage of samples exceeding the allowable limits set by Moroccan Standards are presented in Table 3.

Table 3

The number and percentage of samples exceeding the allowable limits set by Moroccan Standards

Parameters .	Moroccan Standards .	No. of wells .	No. of wells exceeding permissible limits .	Override % .	Undesirable effect .
pH	6.5–9.5	14	0	0	Taste
EC (μs/cm)	350–2,700	14	7	50
TDS (mg/L)	650–1,500	14	8	57	Gastrointestinal irritation
T.H (mg/L)	500	14	8	57	Scale formation
Ca2+ (mg/L)	100	14	9	64.28	----------
Mg2+ (mg/L)	100	14	1	7.14	----------
Na+ (mg/L)	150	14	8	57	Increases blood pressure
K+ (mg/L)	0–12	14	2	14.29	Increases blood pressure
Cl− (mg/L)	750	14	6	42.86	Salty tastea
(mg/L)	250	14	3	21.43	Laxative effect
(mg/L)	500	14	1	7.14	--------
(mg/L)	50	14	14	100	Blue baby syndrome
	2	14	14	100

Parameters .	Moroccan Standards .	No. of wells .	No. of wells exceeding permissible limits .	Override % .	Undesirable effect .
pH	6.5–9.5	14	0	0	Taste
EC (μs/cm)	350–2,700	14	7	50
TDS (mg/L)	650–1,500	14	8	57	Gastrointestinal irritation
T.H (mg/L)	500	14	8	57	Scale formation
Ca2+ (mg/L)	100	14	9	64.28	----------
Mg2+ (mg/L)	100	14	1	7.14	----------
Na+ (mg/L)	150	14	8	57	Increases blood pressure
K+ (mg/L)	0–12	14	2	14.29	Increases blood pressure
Cl− (mg/L)	750	14	6	42.86	Salty tastea
(mg/L)	250	14	3	21.43	Laxative effect
(mg/L)	500	14	1	7.14	--------
(mg/L)	50	14	14	100	Blue baby syndrome
	2	14	14	100

^aHigh concentrations of sulfate, in association with cations, such as magnesium, may have a laxative effect on people not accustomed to the water.

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With regard of groundwater quality classification in the study area according to Davis & De Wiest (1966), we found that 21.43% of groundwater samples is permissible for drinking (TDS from 500 to 1.000 mg/l), 50% of groundwater samples is useful for irrigation (TDS from 1.000 to 3.000 mg/l), and 28.57% of groundwater samples is unfit for drinking and irrigation (TDS > 3.000 mg/l).

With regard to groundwater quality classification in the study area according to Freeze & Cherry (1979), we found that 21.43% of groundwater samples is fresh water (TDS < 1.000 mg/ l), 71.42% of groundwater samples is brackish water (TDS from 1.000 to 10.000 mg/l), and 7.15% of groundwater samples is saline water (TDS from 10.000 to 100.000 mg/l).

The presence of bicarbonates in groundwater is due to dissolving carbonate-containing metals by carbon dioxide (Lower 1999). According to the Moroccan Standards, 7.14% of s groundwater samples are not suitable for drinking.

From the overall analysis, it was observed that there is a significant fluctuation in the physical and chemical parameters of the groundwater samples studied. By comparing the results obtained with the standard specifications of Moroccan, it became clear that the groundwater in the study area is unfit for drinking purposes because high amount of mg/L and is found, which exceeds the maximum quantity allowed. The high concentration of contamination at the Souk El Arbaa Basin is because the distribution of major ions largely depends on the type of geological formations in contact with the groundwater flowing through, irrigation return flow, and disposal of domestic and industrial wastewater.

Water pollution is becoming a bigger problem in Morocco because of population growth, industrialization, and increased use of agricultural chemicals. Efforts are being made to address this issue, but progress is slow. However, the study has some limitations, such as limited sampling and no consideration of seasonal variations. It is important to regularly evaluate groundwater quality to prevent further pollution and protect water quality.

All relevant data are included in the paper or its Supplementary Information.

The authors declare there is no conflict.

The authors extend their sincere thanks and gratitude to the Experience Club Office for Environmental and Water Consulting Services, Sana'a – Yemen, for its scientific and technical support in completing this research project.