Integrated Assessment of Groundwater Vulnerability and Drinking Water Quality in Rural Wells: Case Study from Ceanu Mare Commune, Northern Transylvanian Basin, Romania

Abstract

Groundwater contamination by nitrates (NO₃⁻) and nitrites (NO₂⁻) is an urgent problem in rural areas of Eastern Europe, with profound public health and sustainability implications. This paper presents an integrated assessment of groundwater vulnerability and water quality in rural wells in the Ceanu Mare commune, Cluj County, Romania—a representative area of the Northern Transylvania Basin, characterized by diverse geological structures, intensive agricultural activities, and incomplete public water infrastructure. This study combines detailed hydrochemical analyses, household-level studies, and geological context to identify and quantify key factors influencing nitrate and microbial contamination in rural wells, providing a comprehensive perspective on water quality challenges in the central part of Romania. This study adopts a multidisciplinary approach, integrating detailed geotechnical investigations conducted through four strategically located boreholes. These are complemented by extensive hydrogeological and lithological characterization, as well as rigorous chemical and microbiological analyses of nearby wells. The results reveal persistently elevated concentrations of NO₃⁻ and NO₂⁻, commonly associated with inadequate livestock waste management and the proximity of manure storage areas. Microbiological contamination was also frequent. In this study, the NO₃⁻ levels in well water ranged from 39.7 to 48 mg/L, reaching up to 96% of the EU/WHO threshold (50 mg/L), while the NO₂⁻ concentrations varied from 0.50 to 0.69 mg/L, exceeding the legal limit (0.5 mg/L) in 87% of the sampled wells. Ammonium (NH₄⁺) was detected (0.25–0.34 mg/L) in all the wells, below the maximum allowed limit (0.5 mg/L) but indicative of ongoing organic pollution. All the well water samples were non-compliant for microbiological parameters, with E. coli detected in 100% of cases (5–13 CFU/100 mL). The regional clay–marl substrate offers only limited natural protection against pollutant infiltration, primarily due to lithological heterogeneity and discontinuities observed within the clay–marl layers in the study area. This research delivers a replicable model for rural groundwater assessment and addresses a critical gap in regional and European water safety studies. It also provides actionable recommendations for sustainable groundwater management, infrastructure development, and community risk reduction in line with EU water directives.

1. Introduction

Water is an essential yet limited resource [1,2] whose quality directly affects both human health and ecosystems [3]. Agricultural, industrial, and urban activities significantly contribute to the pollution of both surface and groundwater resources through the input of nutrients, heavy metals, and toxic compounds [4,5], all of which are influenced by geological structure and region-specific anthropogenic activities [2,5]. Groundwater quality is significantly influenced by factors such as soil composition, livestock density, fertilizer application, and wastewater discharge [6]. Soil texture influences the degree of retention or transfer of pollutants: sandy soils favor the rapid migration of nitrogen compounds, while clayey soils act as natural barriers [7,8]. Livestock activities carried out in the proximity of water sources, especially the storage of animal manure, contribute significantly to nitrate contamination, with concentrations exceeding 100 mg/L being reported in wells located less than 100 m from such sources [9], as well as ammonium contamination (>0.5 mg/L) and microbiological indicators, including E. coli, especially in areas with high water tables and permeable soils [10,11]. In addition, the intensive use of nitrogen fertilizers in quantities exceeding the threshold of 170 kg N/ha/year has been correlated with high levels of nitrates in groundwater, up to 120 mg/L, especially in hydrogeologically vulnerable areas [12].

NO₃⁻ contamination—primarily originating from agricultural fertilizers and improper livestock waste disposal—has been recognized as a leading threat to groundwater safety and human health [13,14]. This issue is further exacerbated by traditional farming practices, such as the frequent placement of animal stables and manure storage platforms (manure storage area) in close proximity to wells, as well as the absence of modern sewage systems in many rural areas [15,16,17]. The transformation of NO₃⁻ into NO₂⁻ within the human body can lead to a range of diseases and is associated with an increased risk of gastric cancer [17,18]. Nitrogen cycling processes in soil and aquifers fundamentally control the distribution of nitrogen forms found in groundwater used for human consumption (Figure S1). Organic nitrogenous matter in soils is degraded by ammonification, a microbial process that releases ammonium (NH₄⁺). In the presence of oxygen, NH₄⁺ is converted by nitrification—a two-step process—first into NO₂⁻ and then into NO₃⁻. Under anaerobic conditions, NO₃⁻ can be converted by denitrification into gaseous forms (N₂, N₂O), thus reducing the nitrogen load in the aquifer. The balance of these processes depends on soil composition, oxygen levels, microbial activity, and the input of nutrients from agricultural or domestic activities [13,19,20,21].

In Romania, access to safe drinking water sources in rural areas remains limited compared to urban environments [22]. In 2018, only 47% of the rural population had access to safe water sources, and approximately 22% benefited from public water supply networks [23], a percentage that increased to 57% in 2023, representing the lowest rate in the European Union (EU) [24]. Although recent investments have resulted in partial improvements (60–65% safe access in 2022), approximately 70% of rural households continue to rely on individual sources, such as wells and boreholes [25], which are frequently vulnerable to chemical (NO₃⁻, heavy metals) and microbiological (coliform bacteria, E. coli) contamination [24,26,27]. Local studies have reported significant excesses of the maximum allowable NO₃⁻ limits in more than 42% of well water samples, while contaminants such as iron, manganese, arsenic, and nickel have also been detected, particularly in areas affected by industrial activity [27,28,29].

Surface waters in rural areas are affected by diffuse agricultural pollution (excessive nutrient loading) and the direct discharge of untreated wastewater due to the lack of wastewater treatment plants, thus impacting both local health and ecosystems [28]. Groundwater remains the main source of drinking water for rural communities, with 91% of groundwater bodies reported as having good chemical status in 2021. However, 9% exhibited concentrations of NO₃⁻ exceeding the maximum allowable limits, primarily originating from diffuse agricultural and domestic sources [29]. During the period of 2020–2022, 9% of monitoring points indicated NO₃⁻ levels above 50 mg/L, while 14% were within the alert range (25–50 mg/L), according to the thresholds established by European Directive (EU) 2020/2184 and Romanian Law No. 458/2002 [30,31,32]. Pollution is more frequently observed in shallow groundwater layers, which are directly exposed to surface infiltration [23]. Although authorities have intensified monitoring and marking of non-compliant sources, and pilot projects for water filtration and public education have been implemented in certain regions [24], the absence of public water supply and sewerage networks continues to pose risks to both public health and the quality of aquatic ecosystems [23].

Ensuring access to safe, high-quality drinking water is a cornerstone of sustainable development and public health, enshrined in Sustainable Development Goal 6 (SDG 6) and the EU policy agenda [33,34]. However, in rural Eastern Europe, this goal remains elusive due to the convergence of complex geological structures, agricultural intensification, inadequate wastewater management, and fragmented infrastructural development. The Northern Transylvanian Basin exemplifies these challenges, where shallow phreatic aquifers serve as the primary drinking water source for millions but are acutely vulnerable to diffuse and point-source pollution.

Recent official reports, including those from the Cluj Public Health Directorate (DSP), have documented chronic surpassing of NO₃⁻ and NO₂⁻ limits in rural wells across Cluj County, with the Ceanu Mare commune repeatedly highlighted as a critical zone of non-compliance [35,36,37,38]. Numerous regional and national studies have highlighted the vulnerability of shallow groundwater in the Transylvanian Plain and its rural settlements [37,39]. Yet, most analyses remain sectoral, focusing either on geological stratigraphy, chemical quality, or anthropogenic pressures in isolation. There is a marked shortage of integrated, multidisciplinary studies that combine geological, hydrogeological, chemical, and statistical analysis at the micro-regional scale—an approach essential for both scientific understanding and evidence-based policymaking.

Moreover, while the European Union’s Water Framework Directive and related policies mandate continuous monitoring and remediation of groundwater quality, there remains a significant gap between legislative intent and on-the-ground implementation in rural Romania. Addressing this disconnect requires detailed, locally grounded research that can both inform local action and contribute to the international scientific discourse.

This article responds to these challenges by presenting a comprehensive, multidisciplinary case study of groundwater vulnerability and rural well water quality in the Ceanu Mare commune, Cluj County. The objectives are as follows:

i.

Characterize the local and regional geological structure and its influence on aquifer vulnerability;

ii.

Systematically analyze the chemical and microbiological quality of well water in the proximity of key hydrogeological investigation sites;

iii.

Quantify the statistical relationships between water quality, livestock density, and proximity to pollution sources;

iv.

Provide a replicable model and operational recommendations for sustainable water management and public health protection in rural agricultural contexts.

The novelty of this research lies in its integrative design: by explicitly correlating stratigraphic structure, detailed chemical and microbiological analyses, and socio-environmental risk factors, it addresses both scientific and practical needs at the interface of geology, hydrology, rural development, and health policy.

2. Study Area and Regional Context

2.1. Geographical Setting

The Ceanu Mare commune is located in the southeastern part of Cluj County, Romania, at the juncture of the sub-Carpathian hilly region and the Transylvanian Plain (46°37′50″ N–46°41′00″ N latitude, 23°56′45″ E–24°02′00″ E longitude). The commune includes several rural villages, of which Hodăi-Boian serves as the focal point for this study (Figure 1). The topography is dominated by gently undulating hills (350–430 m above sea level), dissected by ephemeral valleys and small watercourses. The landscape supports a mixed land-use system, with arable crops, hay meadows, pasture, and dispersed household gardens [36].

2.2. Geological and Hydrogeological Conditions

The Northern Transylvanian Basin is one of the most complex sedimentary basins in Romania, with a stratigraphic sequence that reflects successive episodes of Paleogene and Neogene subsidence, sedimentation, and tectonic deformation [19,39]. The area is characterized by thick accumulations of marls, clays, silty clays, and occasional intercalations of sands and gravels, as well as minor volcanic tuff and evaporite layers. The Miocene strata are especially prominent, consisting of alternating marls, radiolarian shales, Sarmatian marls, and clays [20,41,42].

Tectonic activity during the Alpine orogeny produced a series of gentle folds and fault zones, which locally influence the permeability and hydraulic connectivity of the aquifer system.

From a hydrogeological perspective, the region is underlain by a phreatic aquifer hosted within unconsolidated to semi-consolidated marls and silty clays, overlying compacted clay–marl sequences at depth. The shallow aquifer (4–10 m depth) is unconfined and highly susceptible to infiltration from the surface, especially along fractures and through micro-zones of enhanced permeability (e.g., sandy or gravelly interbeds) [20,41,42].

The hydraulic gradient follows the general slope of the terrain, with local groundwater flow directed toward ephemeral valley axes. The water table exhibits marked seasonal fluctuations, depending on precipitation, snowmelt, and household abstraction [27,29].

Figure 2 presents an extract from the official geological database of Romania (Geological Institute of Romania, igr.ro), corresponding to topographic sheet L-35-XIII, which covers the Ceanu Mare area and highlights the position of Hodăi-Boian village within the regional geological framework. Lithological units are classified according to the standardized lithology_200k_inspire schema. The dominant unit near Hodăi-Boian is Volhynian–Bessarabian (Miocene) deposits, primarily composed of limestone, marl, clay, sand, gravel, conglomerate, and tuffs. These deposits, shown on the map in brown/beige, typically consist of alternating marly and clayey facies with occasional sands, gravels, and volcanic tuffs, which are key to understanding local hydrogeological vulnerability and aquifer distribution. Adjacent lithological units are depicted in contrasting colors, each corresponding to specific stratigraphic codes. The use of standardized map references enables data traceability and comparability with national and European geological databases, thereby supporting rigorous spatial analysis and ensuring methodological transparency. Overall, the Volhynian–Bessarabian deposits form the essential geological substrate influencing groundwater dynamics and underpinning the analyses in this study.

2.3. Socio-Environmental and Infrastructural Context

Ceanu Mare is a typical Transylvanian rural commune, with a total population of approximately 2500 (latest census data). Households are primarily engaged in mixed agriculture, combining crop cultivation with subsistence- or semi-commercial-scale animal husbandry (cattle, pigs, poultry, sheep) [36].

Traditional settlement patterns—dispersed farmsteads with attached gardens and manure storage areas—are still prevalent. A significant proportion of the population relies on shallow, hand-dug wells for drinking water, particularly in villages not yet connected to the centralized water supply [29].

In the commune of Ceanu Mare, the average domestic water consumption is 19 L per capita per day, with values ranging from 1.5 to 107 L/person/day. In Hodăi-Boian, the average is 24 L/person/day, varying between 2 and 67 L/person/day. These figures are significantly lower than the national rural averages, underscoring major challenges in water supply and accessibility at the local level [27,43].

The commune is only partially served by a centralized public water supply system (operated by Someș Water Company), with ongoing projects aiming to expand coverage, especially in Hodăi-Boian and Iacobeni [36]. In outlying villages and isolated homesteads, private wells remain the main source of water for domestic use.

Sanitation infrastructure is generally rudimentary, with most households using pit latrines or septic tanks. Manure is commonly stored in open-air platforms, often less than 20 m from wells—contravening both national and EU guidelines, which provides for minimum sanitary protection distances between pollution sources and wells, set between 200 and 500 m [44]. Local authorities have highlighted groundwater protection as a strategic priority in the commune’s urban and environmental planning documents [36], but implementation lags due to financial and institutional constraints.

Geological vulnerability, traditional land management, and infrastructural deficits creates a context of chronic exposure to NO₃⁻, NO₂⁻, NH₄⁺, and microbiological contaminants. Reports from DSP Cluj and local health monitoring confirm repeated standard violations and occasional outbreaks of waterborne illness [38,45].

3. Materials and Methods

3.1. Selection of Study Sites

This study was designed to provide an integrative assessment of groundwater vulnerability and well water quality by combining geological, hydrogeological, chemical, microbiological, and statistical analyses. A multi-scalar approach was adopted, linking the regional context with site-specific investigations.

Four geotechnical boreholes were drilled in the village of Hodăi-Boian (Figure 3), strategically selected to capture variations in geological conditions and potential pollution gradients associated with nearby livestock operations, manure storage, and diverse land use types [46,47]. Site selection was based on field surveys, recent topographic and geological data, and input from local stakeholders (

Table 1. Coordinates of the borehole locations.

Borehole Location	X * (Latitude)	Y ** (Longitude)	Z *** (Altitude) m
Borehole 1	46°38′18.53” N	24°0′20.46” E	420.41
Borehole 2	46°38′33.94” N	24°0′31.10” E	406.57
Borehole 3	46°38′30.11 ”N	24°0′41.56” E	394.5
Borehole 4	46°38′18.85” N	24°0′43.11” E	401.15

* X: The geographical latitude coordinate (N/S) of the borehole location, expressed in degrees, minutes, and seconds; ** Y: The geographical longitude coordinate (E/W) of the borehole location, expressed in degrees, minutes, and seconds; *** Z: The altitude of the borehole location, expressed in m above sea level.

).

To ensure spatial representativeness, each borehole was paired with two nearby household wells (within a 50 m radius), reflecting typical well distribution patterns in central Romanian rural settings. This design allowed for both micro-scale assessment of groundwater vulnerability and direct comparison between less protected private wells and more safeguarded boreholes. The 50 m threshold was chosen to simulate realistic contamination pathways linked to domestic and agricultural practices, which constitute the main pollution sources in the area. This sampling framework supports the extrapolation of results to similar rural communities across central Romania.

Water samples were collected exclusively from wells situated in the immediate proximity (within 50 m) of the four boreholes, thus representing the most hydrogeological and contamination-relevant points for the study. Around each borehole, two nearby wells were analyzed, with their locations corresponding to households with different animal densities and land-use practices. This configuration enabled microzonal mapping of groundwater vulnerability at the household scale. A total of eight wells were sampled.

3.2. Geological and Geotechnical Investigation

Each borehole was drilled using continuous mechanical coring (Atlas Copco rotary hammer, (Atlas Copco, Stockholm, Sweden) Ø 105–64 mm), in compliance with SR EN 1997-1 and SR EN 1997-2 [48,49]. Drilling was performed in two successive sections: 0–1.8 m and 1.8–6.0 m depth. Detailed lithological logs were constructed, with laboratory analyses performed for the following factors:

-

Particle size distribution (wet and dry sieving, hydrometer methods);

-

Mineralogical composition (XRD, where feasible);

-

Plasticity and consistency (Atterberg limits).

The combined data enabled the construction of a synthetic lithological column, highlighting main stratigraphic horizons, fine fraction dominance, and potential contaminant transport pathways.

3.3. Water Sampling and Analysis

Water samples were collected exclusively from domestic wells located in the immediate vicinity (within 50 m) of the four geotechnical boreholes, ensuring the selection of points with the highest hydrogeological relevance and potential exposure to contamination sources. In total, eight wells were sampled for this study.

The sampling procedures strictly followed the guidelines outlined in SR ISO 5667-5:2009 [50] to ensure sample integrity and reliability of the analytical results. The protocol included the following steps: (i) preliminary purging of stagnant water from each well to obtain representative aquifer samples; (ii) collection of water samples in sterilized polyethylene bottles; (iii) immediate storage and transport of the samples in cooled conditions (4 ± 2 °C); and (iv) completion of laboratory analyses within a maximum of six hours after collection to prevent physicochemical or microbiological alterations.

Comprehensive chemical and microbiological analyses were carried out by national and EU standards. The evaluated parameters included NO₃⁻, NO₂⁻, and NH₄⁺ concentrations, all determined spectrophotometrically using standard methods. The Nesslerization method was specifically applied for NH₄⁺ determination. The values obtained were compared with the maximum permitted values in drinking water according to Law 458/2002: for NO₃⁻, 50 mg/L; NO₂⁻, 0.5 mg/L; and NH₄⁺, 0.5 mg/L [22].

Physicochemical parameters, such as pH (measured potentiometrically), turbidity (assessed by nephelometry), and electrical conductivity (measured by conductometry), were also determined.

The microbiological analysis included the determination of total coliform bacteria and Escherichia coli (E. coli) using the Colilert-18 method (IDEXX Laboratories, Westbrook, ME, USA)), in accordance with [11]. Microbiological quality was assessed by quantifying total coliforms and Escherichia coli using the membrane filtration technique, followed by selective agar cultivation. Viral assays were not feasible within this study.

The measurement uncertainty for NO₃⁻ and NO₂⁻ concentrations was ±5%, while for NH₄⁺, it was ±0.03 mg/L. For microbiological parameters (E. coli), the detection limit was 1 CFU/100 mL, with a measurement error below 2 CFU/100 mL.

3.4. Data Management and Statistical Analysis

All the field and laboratory data were centralized in a proprietary database. Descriptive statistics (mean, min, max, SD) were calculated for each parameter.

Pearson correlation coefficients were calculated for all the pairwise combinations of water quality indicators and potential risk factors (e.g., nitrate, nitrite, ammonium, turbidity, pH, E. coli, distance to manure platform area, number of animals per household) using IBM SPSS v27 (IBM Corp., Armonk, NY, USA). The strength of each correlation was interpreted according to the following scale: |r| < 0.3 = weak; 0.3 ≤ |r| < 0.5 = moderate; 0.5 ≤ |r| < 0.7 = strong; |r| ≥ 0.7 = very strong [51]. Potential outliers were identified and managed through standardized protocols, and the reproducibility of the analytical results was verified through duplicate sampling and laboratory cross-validation.

3.5. Methodological Limitations

The recognized limitations include the following:

-

Focus on shallow (phreatic) aquifer; no deep boreholes due to cost/logistics;

-

Short-term (single season) sampling rather than long-term time series;

-

Variability in household cooperation and accuracy of self-reported data;

-

Microbiological testing limited to indicator organisms (no viral assays).

Nevertheless, the dataset provides a robust, representative snapshot of the region’s groundwater vulnerability and serves as a platform for future, extended monitoring.

4. Results

4.1. Geological and Geotechnical Analysis

The four boreholes drilled in Hodăi-Boian revealed a relatively homogenous lithological profile dominated by clay–marl units, interspersed with minor sandy and marly gravel horizons. The soil structure is characterized by three main layers: (i) topsoil, extending from 0.00 m to approximately −0.32 m; (ii) a layer of brown, silty clay with slight sandy content and rare marly gravel fragments, of stiff plastic consistency, extending to approximately −1.80 m; and (iii) a deeper layer of brown-yellowish, silty clay with detrital marly fragments and altered marls, also exhibiting a stiff plastic consistency, reaching a depth of −6.00 m. All the boreholes presented this stratification pattern with only minor depth variations of ±1 cm between the corresponding layers, indicating a homogeneous geological structure within the investigated area.

A synthetic lithological column (Figure 4) was compiled by integrating and averaging data from all four boreholes drilled in the Hodăi-Boian area, highlighting the main stratigraphic horizons that characterize the study site.

Particle size analyses (granulometry) confirm a dominance of fine fractions (clay 48–53%, silt 40–45%, sand <5%) in all the stratigraphic units, with only minor vertical variation.

Based on the laboratory analyses presented in

Table 2. Soil characteristics of Boreholes 1–4 at depth intervals 0–1.8 m and 1.8–6.00 m.

Soil Fractions	Subdivisions	Particle Size (mm)	Mass Percentage (%)
			Boreholes 1		Boreholes 2		Boreholes 3		Boreholes 4
			0–1.80 m	1.80–6.00 m	0–1.80 m	1.80–6.00 m	0–1.80 m	1.80–6.00 m	0–1.80 m	1.80–6.00 m
Very Coarse Soil	Large blocks	>630	0	0	0	0	0	0	0	0
	Blocks	>200–630	0	0	0	0	0	0	0	0
	Boulders	>63–200	0	0	0	0	0	0	0	0
Coarse Soil	Large gravel	>20–63	0	0	0	0	0	0	0	0
	Medium gravel	>6.3–20	0	0	0	0	0	0	0	0
	Small gravel	>2–6.3	0	0.59	0	0.57	0	0.58	0	0.60
	Coarse sand	>0.63–2	0	0.73	0	0.70	0	0.73	0	0.69
	Medium sand	>0.2–0.63	0.59	1.62	0.63	1.70	0.61	1.66	0.58	1.58
	Fine sand	>0.063–0.2	0.83	2.14	0.90	2.25	0.82	2.17	0.87	2.10
Fine Soil	Coarse silt	>0.02–0.063	11.97	12.78	12.20	13.00	12.15	12.74	11.99	12.89
	Medium silt	>0.0063–0.02	14.51	16.22	14.10	16.05	14.58	16.13	14.66	16.21
	Fine silt	>0.002–0.0063	19.24	17.53	18.95	17.40	19.14	17.40	19.07	17.40
	Clay	≤0.002	52.86	48.39	53.22	48.33	52.70	48.59	52.83	48.53

, the geological assessment was synthesized for two depth intervals—0–1.8 m (Figure 5) and 1.8–6.0 m (Figure 6)—illustrating the soil characteristics identified in all four boreholes.

The detailed particle size and compositional data indicate a substrate with low hydraulic conductivity but limited long-term resistance to persistent or point-source pollution.

The hydrogeological regime of the Hodăi-Boian area, as characterized by four strategically located boreholes and the selection of eight representative wells, provides a detailed understanding of the shallow, unconfined phreatic aquifer—the principal potable water source for local households. The aquifer is typically encountered at depths between 4.5 and 8.2 m, exhibiting seasonal fluctuations that reflect both precipitation input and anthropogenic abstraction (household use). Lithostratigraphic analysis of all four boreholes reveals a sequence dominated by marly clays and silty clays, interspersed with sporadic sandy and gravelly interbeds. These interfaces are critical, as they influence both the storage and vulnerability of groundwater resources. The marly–clay matrix, which characterizes the majority of the vertical profile, imparts a generally low hydraulic conductivity (typically in the range of 10⁻⁸ to 10⁻⁹ m/s, determined from granulometric and plasticity tests), thus theoretically retarding the vertical percolation of contaminants.

However, the identification of microfractures, discontinuities, and thin sandy intercalations provides preferential flow paths, significantly increasing localized aquifer vulnerability. Such hydrogeological heterogeneity is a hallmark of the Transylvanian Basin, shaped by tectonic activity, paleoclimate oscillations, and synsedimentary processes.

The groundwater flow follows the local topographic gradient and is generally directed toward ephemeral stream valleys, facilitating the lateral spread of contaminants in areas where the terrain permits. Vulnerability hotspots are observed where shallow groundwater coincides with high pollution risk—specifically, near manure storage areas, and where the clay–marl aquitard is thinner or disrupted by preferential pathways.

Although the low-permeability clay–marl strata offer superficial protection, persistent and diffuse pollution sources—primarily livestock manure—combined with shallow water tables and seasonal recharge contribute to the gradual yet significant migration of contaminants. Stratigraphic “windows” or preferential flow paths intersecting with surface contamination sources can facilitate rapid pollution propagation.

4.2. Chemical Quality of Well Water: Patterns, Exceedances, and Spatial Risk

The analytical results of the water from the wells adjacent to the boreholes reveal a troubling and spatially coherent pattern of contamination. In all the sampled wells, the NO₃⁻ concentrations ranged between 39.7 and 48 mg/L, remaining below the World Health Organization (WHO), Romanian, and EU threshold of 50 mg/L [10,11,12,31] (Figure 7), while the NO₂⁻ levels varied from 0.5 to 0.69 mg/L, exceeding the maximum admissible limit of 0.5 mg/L in most cases (Figure 8). The omnipresence of NO₃⁻exceedances, with a spatial gradient matching proximity to animal husbandry and manure storage, underscores chronic overloading of the aquifer system by agricultural practices. The pattern is aggravated in wells adjacent to active livestock stables.

The NH₄⁺ concentrations determined in the samples taken from the eight wells were in the range of 0.25–0.38 mg/L, values that do not exceed the maximum allowed limit of 0.5 mg/L (Figure 9), according to national and EU standards [31,52,53]. However, the constant presence of NH₄⁺ in these concentrations may indicate a possible anthropogenic influence or processes of decomposition of organic matter in the catchment area, suggesting the need for continuous monitoring to prevent possible future increases. Episodes of NH₄⁺ elevation reflect recent or ongoing organic contamination, likely related to manure leaching or poorly managed septic effluents.

The pH values determined in the analyzed groundwater samples range between 6.9 and 7.4 (Figure 10), falling within the limits recommended for drinking water by the World Health Organization (6.5–8.5) and the legislation in force at the national and EU levels [10,11,12,30,31]. This range suggests a weakly alkaline to almost neutral character of the water, corresponding to the natural conditions of the local aquifer environment. Maintaining the pH in this range is favorable from the perspective of the chemical stability of the water, reducing the risk of corrosion in the transport and distribution infrastructure, as well as possible adverse effects on the health of consumers.

The turbidity values recorded in the water samples from the eight wells ranged from 2.5 to 4.1 NTU (Figure 11). Although these values remain below the 5 NTU limit set by the WHO and European legislation for drinking water [10], elevated turbidity may still signal suspended particles or colloidal matter. Such values can affect both the aesthetic quality of the water (taste, color) and the efficiency of disinfection processes, suggesting possible sources of physical or biological contamination in the catchment area.

The electrical conductivity values in the analyzed water samples range between 395 and 451 µS/cm (Figure 12), which indicates a water quality within the typical range for unpolluted groundwater or slightly influenced by moderate anthropogenic activities. According to the specialized literature, these values suggest a relatively low concentration of total dissolved substances, which is favorable for the use of water for drinking and agricultural purposes.

Lower pH values (slight acidification) in wells closest to livestock may indicate acidifying processes linked to organic decomposition. Turbidity follows a similar spatial pattern, reinforcing the mechanistic link between livestock density and water quality degradation. While all the values fall within permissible limits, higher conductivities in the most contaminated wells suggest cumulative mineral and organic input from anthropogenic sources. The overlap of elevated chemical levels and infrastructure deficits positions these wells as key nodes in the local risk network, demanding targeted intervention.

To directly illustrate the impact of livestock density and proximity to manure platforms on groundwater quality, we analyzed the variation in NO₃⁻, NO₂⁻, NH₄⁺, and E. coli concentrations according to (i) the number of animals kept at each household and (ii) the distance from each well to the nearest manure platform.

As shown in Figure 13, there is a clear positive trend between the number of animals and the concentrations of NO₃⁻, NO₂⁻, and E. coli in well water. Wells belonging to households with more livestock consistently show elevated levels of these pollutants. Similarly, Figure 14 demonstrates a strong negative association between the distance to manure platforms and the concentrations of key pollutants: wells located less than 20 m from manure storage areas exhibit the highest concentrations of NO₃⁻, NO₂⁻, NH₄⁺, and E. coli.

These findings are consistent with the heatmap of the Pearson correlation coefficients, confirming the statistically significant relationship between animal density, distance to pollution sources, and well water contamination in the study area.

4.3. Microbiological Quality of Well Water: Indicator Bacteria and Compliance

The total coliform concentrations in the well samples ranged from 18 to 42 CFU/100 mL, and the E. coli values ranged from 5 to 13 CFU/100 mL. These values exceed the limits allowed by Romanian and European standards [53,54], which require the total absence (0 CFU/100 mL) of these microbiological indicators in drinking water, indicating significant contamination in the sources analyzed, as detailed in

Table 3. Microbiological parameters and compliance status of wells adjacent to boreholes (Hodăi-Boian, Ceanu Mare Commune).

Well	Total Coliforms (CFU/100 mL)	E. coli (CFU/100 mL)	Compliance with Standards *
1	28	8	Non-compliant
2	35	10	Non-compliant
3	22	5	Non-compliant
4	18	3	Non-compliant
5	42	13	Non-compliant
6	39	11	Non-compliant
7	25	7	Non-compliant
8	19	4	Non-compliant

* Romanian and EU standards: 0 CFU/100 mL for E. coli and total coliforms in drinking water [53,54].

Microbial contamination is consistently highest in wells within short distance (≤20 m) from manure storage areas or unmanaged waste pits. Chronic exposure to such water sources is associated with heightened risk of gastrointestinal infections, methemoglobinemia (“blue baby syndrome”) in infants, and outbreaks of waterborne disease, threatening community health security. The endemic failure of wells to comply with microbiological standards elevates the situation to a public health emergency, requiring urgent action from both local and national authorities.

4.4. Statistical Analysis and Correlations: Risk Modeling and Predictive Insights

To quantify the linkages between anthropogenic drivers and water quality degradation, a comprehensive matrix of Pearson correlation coefficients was computed using all the field survey and laboratory data. These results are visualized as a correlation heatmap (Figure 15), allowing for rapid identification of strong and very strong associations among water quality parameters and risk factors.

Predictive regression model: To further quantify the joint effects of livestock density and proximity to manure platforms on groundwater nitrate pollution, a multiple linear regression model was developed using empirical data from all the sampled wells. The resulting equation is NO₃⁻ (mg/L) = 0.78 × Number of animals—0.23 × Distance to manure platform (m) + 42.43

This model accounts for 94% of the observed variation in nitrate concentrations (R² = 0.94), confirming the strong, additive influence of both livestock density (positive effect) and distance to manure storage (negative effect) on groundwater quality in the study area.

The structure of this model is illustrated in Figure 16 (block diagram), which summarizes the direct and inverse effects of these key variables on nitrate concentrations in rural wells.

To further substantiate the spatial relationship, a simple linear regression was performed between the nitrate concentration (NO₃⁻) in the well water and the distance from each well to the nearest manure platform. The results demonstrate a strong and statistically significant negative relationship (NO₃⁻ = −0.59 × distance + 53.45; R² = 0.77; p = 0.0042), as shown in Figure 17. This confirms that nitrate contamination decreases markedly with increasing distance from manure sources, quantitatively validating the spatial gradient observed in the field data.

5. Discussion

5.1. Regional and European Context: Comparative Analysis and Policy Relevance

The findings from Hodăi-Boian exemplify the acute vulnerability of shallow groundwater systems in rural Eastern Europe—a theme repeatedly documented in both the scientific literature and EU policy reports. The patterns of chronic NO₃⁻, NO₂⁻, and microbiological pollution observed in this study align closely with pan-European assessments by the EEA and the WHO, which highlight agricultural intensification, inadequate waste management, and infrastructural lag as root causes [10,11,12,55].

This case study advances the field by operationalizing the “multiple barrier” concept promoted in the EU Water Framework Directive, showing that geological attenuation is insufficient in isolation and must be complemented by robust socio-technical interventions.

5.2. Mechanisms and Risk Factors: Multidimensional Drivers of Pollution

A key contribution of this research lies in the dissection of causal chains linking land use, hydrogeology, and well water quality:

The conceptual diagram (Figure S1) summarizes the nitrogen cycle processes relevant to this study, namely, ammonification, nitrification, and denitrification, highlighting the links between pollution sources, subsurface transformations, and potential attenuation.

The correlation analysis revealed strong, statistically significant associations between animal density and key groundwater contaminants, including NO₃⁻ (r = 0.95), NO₂⁻ (r = 0.93), E. coli (r = 0.90), and turbidity (r = 0.87). Conversely, the distance to the manure platform was strongly negatively correlated with these parameters, highlighting the critical role of spatial proximity in pollution risk. Notably, chemical and microbiological indicators were closely linked, supporting the concept of convergent contamination sources in rural groundwater. These findings validate the multivariate risk model and reinforce the need for integrated management strategies targeting both land use intensity and spatial planning.

The prevalence of livestock and poorly managed manure platforms generates sustained, high-concentration pulses of contaminants that overwhelm even moderately protective geological barriers.

Microfractures and sandy interbeds act as “short circuits” for pollutant migration, challenging traditional assumptions about clay–marl “safety”.

The spatial congruence between high animal density, minimal buffer distances, and peak contamination confirms a predictable, replicable risk model for similar rural settings across Central and Eastern Europe.

In addition, the co-existence and chemical interrelations of nitrogen species in groundwater provide important insights into pollution sources and subsurface transformation processes.

The simultaneous presence of NO₃⁻, NO₂⁻, and NH₄⁺ in shallow groundwater reflects the complexity of nitrogen cycling in the subsurface, driven by both anthropogenic and natural processes. NH₄⁺, typically originating from the decomposition of organic matter and livestock waste, can be oxidized to NO₂⁻ and subsequently to NO₃⁻, through the process of nitrification, facilitated by aerobic microorganisms. Conversely, under reducing (anoxic) conditions, often found in zones with high organic loading or poor drainage, denitrification can occur, transforming nitrate into nitrogen gases, sometimes generating transient peaks of NO₂⁻. The detection of all three forms within the same aquifer zone may indicate overlapping redox environments, fluctuating oxygen levels, or recent pulses of organic contamination. Elevated NH₄⁺ and NO₂⁻, alongside persistent NO₃⁻, suggest incomplete nitrification or episodic shifts between aerobic and anaerobic conditions. This co-existence is particularly characteristic of rural wells impacted by animal husbandry and highlights the need for integrated management addressing both source control and aquifer vulnerability. These processes have important implications for groundwater quality, as NO₂⁻ and NH₄⁺ are regulated contaminants with acute health risks, and their persistence signals ongoing pollution and insufficient natural processes.

5.3. Policy, Management, and Operational Implications: Recommendations for Sustainable Intervention

Enforcement of minimum setbacks (≥200–300 m) between manure storage and wells and modernization of rural waste management: construction of sealed, drained manure storage and extension of public water networks.

Comprehensive, transparent monitoring: routine testing for both chemical and microbiological indicators, with public disclosure of results.

Community engagement: participatory education campaigns to shift risk behaviors and promote collective responsibility for water protection.

The integrated methodology adopted here serves as a model for other regions facing similar environmental and infrastructural constraints. Application elsewhere can inform targeted, evidence-based interventions aligned with European sustainability objectives.

5.4. Study Limitations and Future Research Directions

This study focused on shallow aquifers; deeper, potentially less vulnerable groundwater resources were not sampled.

This study only employed single-season sampling. This snapshot may underrepresent temporal variability in groundwater quality parameters, including nitrogen species, which are known to fluctuate in response to hydrological and environmental changes.

The microbiological analysis was limited to indicator bacteria; viral, protozoal, and emerging contaminants (pharmaceuticals, microplastics) require further attention.

Self-reported data on animal numbers and manure practices may be affected by social desirability bias.

Longitudinal, multi-seasonal sampling to capture variability and extreme events, as well as direct measurement of redox potential and dissolved oxygen are necessary to validate and refine the interpretations of nitrogen speciation in the subsurface. Advanced hydrogeophysical mapping to delineate fracture networks and preferential flowpaths would be advantageous.

Future studies should expand the chemical and microbiological analysis to a broader suite of pollutants.

Intervention studies should be conducted to rigorously assess the impact of new policies and technologies on groundwater safety.

6. Conclusions

This research presents a rigorous, multidisciplinary evaluation of shallow groundwater vulnerability and rural well water quality in Hodăi-Boian, Ceanu Mare commune, an emblematic rural area in the Northern Transylvanian Basin. By integrating geological, hydrogeological, chemical, microbiological, and statistical analyses, this study generates several key conclusions with direct relevance for public health, environmental policy, and the broader sustainability agenda in rural Eastern Europe.

Although the NO₃⁻ and NH₄⁺ concentrations in the well water were within the legal limits (NO₃⁻, 39.7–48 mg/L and NH₄⁺, 0.25–0.38 mg/L), none of the monitored wells complied with the drinking water standards for NO₂⁻ (0.5–0.69 mg/L; legal limit 0.5 mg/L) or for microbiological parameters (5–13 CFU/100 mL; legal limit 0), which poses a significant public health risk, especially for vulnerable groups. Frequent detection of E. coli confirms the aquifer’s vulnerability and the urgent need for action.

Effective mitigation requires coordinated measures: regulatory enforcement (e.g., minimum setbacks for manure storage), infrastructure upgrades, systematic water quality monitoring, and community education. These efforts are essential to protect rural health and comply with EU and national standards.

Spatial risk mapping highlighted that wells within 20 m of livestock or manure platforms face the highest contamination.

In summary, this study not only highlights the acute vulnerabilities facing rural groundwater resources in the Northern Transylvanian Basin but also offers a replicable and action-oriented framework for other contexts confronted with similar challenges in the nexus of environment, agriculture, and public health.