Lowari Tunnel Water Quality Evaluation: Implications for Tunnel Support, Potable Water Supply, and Irrigation in Northwestern Himalayas, Pakistan

Abstract

Water ingress is a common and costly problem in tunnel construction, and understanding the hydrogeological characteristics of a site is crucial for mitigating its effects. This study presents a detailed analysis of the water ingress problems experienced during the construction and operation stages of the Lowari Tunnel in Khyber Pakhtunkhwa, Pakistan, and evaluates the suitability of the water for various purposes. The study found that the water quality varied significantly, depending on the geological conditions and water quantity, with the south portal of the tunnel dominated by Mg cations and bicarbonate anions. The water was found to be suitable for tunnel support systems, including concrete and steel installations, with negligible corrosion observed over the study period. However, the water coming out of the tunnel at the south portal was found to be unsuitable for drinking due to its low pH value. The Wilcox plot classified the water samples as excellent for irrigation, which could benefit local agriculture in the area. The findings of this study can provide valuable insights into the hydrogeological characteristics of the Lowari Tunnel, contributing to the design and construction of similar infrastructure projects in the region. Furthermore, these insights can help improve access to safe and reliable water sources for local communities.

1. Introduction

Mountain tunnels are susceptible to water ingress, which can impede tunnel excavation progress and compromise the safety of the support system, leading to partial or complete failure. Water ingress is affected by geological structures such as weak zones, faults, and joints, which connect to aquifers [1,2]. Sources such as joints (51%), faults (30%), pipelines (16%), and cavities (3%) contribute to a 45% disaster risk factor for water ingress in tunnels constructed using the drill and blast technique, such as the New Austrian Tunneling Method (NATM) [3,4]. In addition to geological structures, the inflow of water is influenced by the characteristics of the aquifer, drainage pattern, catchment area, and precipitation frequency. The presence of icicles, ice, and water ponding can further disrupt tunnel operations and pose safety risks [5,6,7]. Instances of such occurrences include the Beijing Metro Line 10 Tunnel, where equilibrium groundwater forced its accumulation, leading to a 24 m × 14 m × 12 m erosion, and the Chang-Ji Expressway and Taipei-Ilan Tunnels, where sudden groundwater inflow impeded excavation and led to collapse [8,9,10,11]. Likewise, dynamic loads during seismic activity can also cause fractures in rock formations, which can provide pathways for water to enter tunnels. Additionally, seismic activity can cause ground movement, which can disrupt drainage patterns and increase the amount of water that flows into tunnels [12,13,14,15].

To ensure the long-term sustainability of tunnel construction projects, it is critical to conduct both quantitative and qualitative analyses of the tunnel water [16,17]. While pre-grouting is effective in managing minor water ingress in tunnels, it is essential to carry out a thorough investigation and establish an efficient drainage system to handle significant water inflows. In cases where the water ingress is extensive, a combination of surface cleaning, grouting, and waterproofing methods are employed to restore the tunnel’s structural integrity [4,18,19,20,21]. Damage to tunnels due to water seepage depends on the quantity and quality of water [8]. Concrete lining is carried out for strengthening tunnel walls and tunnel crowns to counter the water pressure and prevent water seepage and surface settlement in a tunnel [22]. Water in tunnels with an excessive amount of sulfate alters the composition of cement, weakens the bond between the aggregate and cement paste, and results in cracks [23,24]. In Switzerland, high chloride levels in the water continue to cause concrete to corrode [25]. Water infiltration in concrete structures can lead to the breakdown of its components, causing the growth of microorganisms that can induce the movement of foundations [26]. The presence of dissolved chlorides from sources such as deicing salts and seawater can permeate solid concrete and come into contact with steel, leading to corrosion in the presence of oxygen and moisture [27]. Similarly, the occurrence of chlorides and carbonates, along with a drop in alkalinity, can cause damage to the external bitumen layer and the ingress of dissolved gases. In addition to corrosion, metals may dissolve in water that is low in dissolved salts and high in specific ions, such as calcium, magnesium, sodium, and potassium [28]. Several instances of damage and corrosion in tunnels have been reported due to high levels of sulfate and acidic groundwater conditions, indicating the significance of water quality in maintaining the integrity of rock supports and concrete structures in tunnels [29,30].

The use of water from tunnels for domestic and agricultural purposes has been explored as a potential solution to water scarcity in certain regions [31,32]. However, due to the potential for the water to be contaminated with harmful substances, it is crucial to assess its quality before incorporating it into existing water supply infrastructure [33]. The water may contain various contaminants, including dissolved minerals, organic matter, and microorganisms, which can affect its suitability for various applications [34]. Additionally, the water quality may vary over time, depending on the geological, hydrological, and operational conditions of the tunnel system [35]. Therefore, appropriate measures are taken to monitor and maintain the quality of water from tunnels to ensure its safe and sustainable use for domestic and agricultural purposes [36]. To assess the corrosive effects and suitability for drinking and irrigation, Piper diagrams and Wilcox plots are utilized. The Piper diagram interprets the hydrochemical data and represents the composition of the sample [37]. It is a graphical representation of water chemistry that can be used to identify the dominant cation and anion species present in the water, including the presence of dissolved salts and ions that can cause corrosion in metal structures such as concrete linings, rock bolts, and other supporting structures [38,39]. If the water chemistry indicates high chloride levels, measures such as cathodic protection or corrosion inhibitors can be used to protect metal structures from corrosion [40]. The Wilcox diagram is a graphical tool that helps to determine the suitability of water for irrigation purposes by analyzing the water’s salinity and sodicity levels. It plots the water’s sodium adsorption ratio (SAR) against the total dissolved solids (TDS) concentration to classify water into different irrigation classes based on its potential effects on soil structure and plant growth [41]. Water with high TDS and SAR values can negatively affect soil structure and crop yield. The SAR level can cause soil dispersion and reduce water infiltration rates, while high TDS levels can cause salt accumulation in the soil and plant tissues [42].

Previous studies have primarily focused on the quantitative analysis of tunnel water, neglecting its qualitative aspects. This study provides a comprehensive analysis of the hydrological conditions in the Lowari Tunnel, including both quantitative and qualitative analyses of tunnel water. The study also assesses the suitability of tunnel water for drinking and irrigation purposes, which is an important consideration for the sustainable use of tunnel water.

2. Study Area

The Lowari Pass in Khyber Pakhtunkhwa, Pakistan, is situated at an altitude of 3100 m and is characterized by heavy snowfall, landslides, rockfalls, and snow avalanches, which make road construction and maintenance challenging and costly. To overcome these challenges, an approximately 8.5 km long and 87.2 m² cross-sectional area road tunnel was constructed, crossing through various geological formations, such as granite, granite biotite, metasediments, meta-igneous, meta-volcanic, and shear zones. Tunnel construction began in 1975, paused in 1977, and resumed in 2006, with a breakthrough in 2009, and operation commencing in 2017. The south and north portals of the tunnel are located at 35°18′59.39″ N and 71°50′08.17″ E, and 35°22′41.11″ N and 71°47′05.19″ E, respectively. The tunnel has a south-to-north slope of 1.8% and a maximum overburden of 1100 m, and experiences significant water infiltration during the snowmelt period between April and September, as well as due to excessive rainfall, localized flooding, spring divergence, and disturbance of underground aquifers [43]. The drainage pattern of the Lowari Tunnel and surrounding area is illustrated in Figure 1. The Dare and Daro streams pass over the Lowari tunnel, resulting in increased water ingress inside the tunnel when sheared zones, minor faults, fractures, and jointed rock strata are present. In the vicinity of the Lowari Tunnel’s south portal, small tributaries join the main Lowari Stream, which flows southwards toward Dir. At the north portal area, the Sharai, Tranger, and Gatus streams converge to form the Ashret stream, which joins the Kunar River before flowing northwest toward Chitral.

3. Materials and Methods

This research involved comprehensive assessments of the water quality in the Lowari Tunnel throughout its construction and operation stages (Figure 2). During the construction stage (2006–2009), the entire length of the tunnel was thoroughly examined to assess the groundwater conditions. The tunnel drive was subdivided into dry, damp, dripping, and flowing sections, and dewatering quantities were recorded during excavation. The water quality was also analyzed (February 2007) to ensure its suitability for drinking purposes. Likewise, during the operational stage, discharge measurements were taken at both the south and north portals of the tunnel during the summer (July 2021) and winter seasons (January 2023). The tunnel water was assessed for its susceptibility to corrosion and its usability for drinking and irrigation. These evaluations were crucial for ensuring the safe and effective operation of the Lowari Tunnel.

3.1. Construction Stage

Water ingress into mountain tunnels can be challenging to predict based solely on surface geological conditions [44]. To better understand the hydrological conditions of the Lowari Tunnel during its excavation, extensive mapping was carried out. This assessment considered the source and quantity of water ingress, water characteristics (such as color and odor), and the potential impact of water on the surrounding rock formation. The excavation of the tunnel encountered significant amounts of water from both the north and south portals, as shown in Figure 3A. In April 2007, heavy water ingress was observed at chainage 1 + 923 in the compacted and jointed granite and gabbro, as seen in Figure 3B. To manage the water seepage at the dripping and flowing stations, grouting was applied to seal the cracks, and plastic pipes were installed to divert the flowing water into the main drainage system of the tunnel. The tunnel was divided into dry, damp, dripping, and flowing stations, and their relationship with the geological conditions was studied. Natural water outflows were observed over a 3875 m stretch along the north drive, from chainage 4 + 634 to 8 + 509, which flowed towards the north portal. In contrast, along the south drive, water encountered during excavation, covering a 4634 m stretch from chainage 0 + 000 to 4 + 634, was diverted to a pond at chainage 0 + 590, due to the tunnel face acting as a barrier. To ensure proper drainage, the accumulated water was then pumped towards the south portal using appropriate pumping systems, as depicted in Figure 3B. To gather data on water flow rates, Elster water flow meters were installed in the vicinity of the pond from 10 April 2007 to 14 January 2009.

The provision of potable water for workers in the Lowari Tunnel was facilitated by positioning a plastic water tank at station 1 + 662 on the south drive. A water quality assessment was subsequently conducted on 2 February 2007 to determine its suitability for drinking purposes. For the chemical analysis, water samples were collected in polythene bottles, pre-washed three times with the sampled water (APHA 2005), labeled, and stored in a refrigerator at 4 °C. Various water quality parameters were analyzed during the study period using specialized equipment. The pH, electrical conductivity, total dissolved solids, and total suspended solids were measured using the CONSORT C931, Belgium, while chlorine, nitrates, sulfates, and total hardness levels were determined using the DR 2800 spectrophotometer, USA. The concentration levels of calcium, magnesium, sodium, and potassium were analyzed using an Analyst 700 atomic absorption spectrometer from Perkin Elmer, Waltham, MA, USA, following acidification of the water sample. Finally, the total alkalinity was determined through titration methods adapted from the APHA 2005.

3.2. Operation Stage

During the operation stage of the tunnel, a distinct flow pattern was observed, with water flowing towards the south portal over a 610 m stretch, from chainage 0 + 000 to 0 + 610. In contrast, a larger stretch of 7899 m, from chainage 0 + 610 to 8 + 509, saw water flowing towards the north portal. To investigate the impact of this flow pattern on the tunnel water, a study was conducted to measure the runoff from both the north and south portals on two different dates: 6 July 2021 (during the summer) and 1 January 2023 (during the winter) (Figure 4). The discharge rate in liters per second was determined by collecting water in a 24 L bucket and recording the time. Conversion factors were applied to obtain the total quantity in liters per day. A qualitative analysis was also performed to assess the water’s damaging tendency towards the tunnel support system and its suitability for drinking and irrigation purposes. To perform the water analysis, water samples were collected from both the north and south portals and subjected to analysis using the National Environmental Methods Index (NEMI) 2002 at the Pakistan Council of Scientific and Industrial Research, Peshawar, Pakistan. The following parameters were measured:

• Using a pH meter, we potentiometrically measured pH using the conventional hydrogen electrode method (4500-H + B);
• Electric conductivity was measured using a resistor network by the laboratory method (2510 B);
• The method (2540 C) was used to calculate total dissolved solids;
• Total suspended solids were measured using gravimetry by the solids in water method (2540 D);
• Total hardness was determined titrimetrically using the EDTA titrimetric method (2340 C);
• Calcium was determined by titration using the EDTA titration method (3500 CaB) with a color indicator;
• Magnesium was determined using the calculation method (3500 Mg/B);
• Total alkalinity was determined by the titration method (2320 B) using a pH meter;
• Chlorine was determined by iodometric method I (4500-Cl-B) using titration with color indication;
• Sodium and potassium were measured using the flame emission photometric method (3500-Na B and 3500-K B) through flame emission.

By performing these analyses, a comprehensive understanding of the tunnel water quality and its potential impact on the surrounding environment was obtained.

4. Results and Discussion

4.1. Constrcution Stage

Table 1. Lowari Tunnel ground water conditions during the construction stage.

Chainage	Excavation Period	Ground Water Conditions	Rock Type and Condition	Chainage	Excavation Period	Ground Water Conditions	Rock Type and Condition
0 + 000~0 + 455	Excavated	Dry	Granite, Gabrro, Granodiorite. Compacted and jointed. Local fault observed at 0 + 455 and 0 + 445 to 0 + 600	1 + 668~1 + 721	February 2007	Dry and damp	Granite, Gabrro, Granodiorite with intercalation of Amphibolite at 1 + 721–1 + 750 Compacted and jointed. Local fault observed at 1 + 839, 1 + 978
0 + 455~0 + 600	June 2006	Flowing		1 + 721~1 + 750	March 2007	Flowing
0 + 600~0 + 658	July 2006	Dry and damp		1 + 750~1 + 805	March 2007	Damp
0 + 658~0 + 669	July 2006	Flowing		1 + 805~1 + 880	April 2007	Dripping and flowing
0 + 669~0 + 780	July 2006	Dry		1 + 880~1 + 887	May 2007	Damp
0 + 780~0 + 786	August 2006	Dripping		1 + 887~1 + 923	May 2007	Flowing
0 + 786~0 + 839	August 2006	Dry and damp		1 + 923~1 + 960	May 2007	Damp
0 + 839~0 + 843	August 2006	Dripping		1 + 960~1 + 978	May 2007	Flowing
0 + 843~0 + 869	August 2006	Damp		1 + 978~2 + 030	June 2007	Damp
0 + 869~0 + 873	August 2006	Flowing		2 + 030~2 + 055	June 2007	Flowing
0 + 873~0 + 884	August 2006	Dry and damp		2 + 055~2 + 355	July 2007	Dry and damp
0 + 884~0 + 889	August 2006	Flowing		2 + 355~2 + 390	July 2007	Dripping and flowing
0 + 889~0 + 910	August 2006	Damp		2 + 390~2 + 400	August 2007	Dry
0 + 910~0 + 925	September 2006	Flowing		2 + 400~2 + 418	August 2007	Dripping
0 + 925~0 + 975	September 2006	Dry and damp		2 + 418~2 + 438	August 2007	Damp
0 + 975~1 + 021	September 2006	Dripping and flowing		2 + 438~2 + 468	September 2007	Dripping
1 + 021~1 + 055	October 2006	Dry		2 + 468~2 + 700	August–December 2007	Dry	Granite, Gabrro, Granodiorite with intercalation of Amphibolite and Rhyolite at 3 + 834 to 3 + 700. Local fault observed at 2 + 498
1 + 055~1 + 071	October 2006	Flowing		2 + 700~2 + 834	January 2008	Dripping
1 + 071~1 + 175	November 2006	Dry		2 + 834~3 + 700	June 2008	Dry and damp
1 + 175~1 + 217	November 2006	Flowing		3 + 700~3 + 900	June 2008	Dripping and flowing
1 + 217~1 + 237	November 2006	Damp		3 + 900~4 + 000	July 2008	Damp
1 + 237~1 + 246	November 2006	Flowing		4 + 000~4 + 200	August 2008	Dripping
1 + 246~1 + 258	December 2006	Damp		4 + 200~4 + 300	October 2008	Damp
1 + 258~1 + 329	December 2006	Flowing		4 + 300~4 + 325	October 2008	Flowing
1 + 329~1 + 445	January 2007	Damp		4 + 325~4 + 340	October 2008	Damp
1 + 445~1 + 459	January 2007	Flowing		4 + 340~4 + 400	November 2008	Flowing
1 + 459~1 + 619	February 2007	Dry and damp		4 + 400~4 + 634	8 November–9 January	Dry and damp
1 + 619~1 + 636	February 2007	Flowing		4 + 634~5 + 256	8 September–9 January	Dripping	Gneiness and Amphibolite
1 + 636~1 + 662	February 2007	Dry and damp		5 + 256~7 + 700	7 August–8 September	Dry and damp
1 + 662~1 + 668	February 2007	Flowing		7 + 700~7 + 828	7 July–7 August	Dripping and flowing
				7 + 828~8 + 400	7 Jan–7 July	Dry and damp
				8 + 400~8 + 509	6 September–7 January	Dripping

outlines the division of the Lowari Tunnel into 62 sections, considering the different groundwater conditions encountered (dry, damp, dripping, and flowing portions), rock types (Granite, Gabrro, Granodiorite, Amphibolite, Rhyolite, Gneiss), and observed rock conditions (compactness, jointing). Table 1 shows that the flow of water in Lowari Tunnel is dependent on joints, with the greatest water ingress occurring at compacted and jointed rock boundaries. The metavolcanic portion of the tunnel has less water ingress. The water-bearing joints are oriented at an angle of +45° and are either parallel or sub-parallel in orientation. The different geological formations that the tunnel passes through are likely responsible for the variation in groundwater conditions.

Figure 5a shows the hydrological status, indicating that the majority of the tunnel (81.70%) is classified as dry and damp, while the remaining portion (18.3%) is classified as dripping and flowing. Figure 5b illustrates the dewatering process carried out during the construction stage from April 2007 to February 2009. The observed dewatering volume ranged from 5846 m³ to 115,100 m³, totaling 1,027,433 m³. The average monthly flow was measured at 46,702 m³, with an average discharge of 0.02 m³/s. In April 2007, between chainages 1 + 816.5 and 1880.5, a maximum recorded outflow of 115,100 m³ occurred due to a rise in temperature leading to snowmelt. In May and June 2007, outflows of 2045.2 m³ and 2186.5 m³, respectively, were observed at chainages 1 + 889.3 and 2 + 042. These results suggest that the water ingress into the Lowari Tunnel is seasonal. This is likely because the water ingress is caused by the seepage of water along joints and fractures in the rock. These joints and fractures are more likely to be water-bearing during periods of snowmelt or heavy rainfall. During the excavation process in 2008 and 2009, a significant reduction in water ingress was observed due to the successful grouting of water leakage points such as joints and fractures with shotcrete. This led to a noteworthy mitigation of water infiltration in the tunnel, suggesting that grouting with shotcrete proved to be an effective technique for reducing water ingress during tunnel excavation.

Table 2. Lowari Tunnel water chemistry during construction stage.

#	Parameter	Unit	Concentration	Max. Permisible Limits for Drinking Water (WHO 2017)
1	pH	--	5.21	6.5–8.5
2	EC	μS/cm	100	1400
3	TDS	mg/L	120	1000
4	Turbidity	NTU	3	5
5	Ca	mg/L	63	200
6	Mg	mg/L	14	50
7	Na	mg/L	3	200
8	K	mg/L	1.7	12
9	TH	mg/L	78	500
10	TA	mg/L	30	500
11	NO3−2	mg/L	Nil	10
12	SO4−1	mg/L	4	250
13	Cl−	mg/L	23	250

summarizes the results of the hydrochemical analysis of water samples collected from the right shoulder at chainage 1 + 662, which were compared with the 2017 World Health Organization (WHO) standards. All measured parameters were found to fall within the normal range, except for the pH value, which was observed to be low (5.21). The low pH value is attributed to the presence of CO₂ inside the tunnel, which was quantified as 14,000 ppm by [43]. According to [45], higher CO₂ concentrations are known to result in lower pH values. It is important to note that acidic water, defined as having a pH level of less than 7, can have adverse health effects such as digestive and skin problems [46,47,48].

4.2. Operation Stage

The Lowari Tunnel’s natural water discharge during its operation stage occurs due to gravity at both the north and south portals. Water discharge measurements were recorded during two different periods, specifically, on 30 July 2021, in the summer, and on 1 January 2023, in the winter. During the summer period, the total water discharge rate was 10.08 L/s, with 9.3 L/s in the north portal and 0.78 L/s in the south portal. In contrast, during the winter season, the total water discharge was lower, at 6.96 L/s, with 6.20 L/s in the north portal and 0.77 L/s in the south portal. The observed seasonal variation in water discharge is due to the snow melting process. During the construction stage, shotcrete was applied to cover water seepages originating from joints and fractures in the tunnel walls, resulting in a significant reduction in water discharge.

Table 3. Lowari Tunnel water chemistry during operation stage.

#	Parameter	Unit	Summer		Winter		Max. Permisible Limits for Drinking Water (WHO 2017)
			South Portal	North Portal	South Portal	North Portal
1	pH	--	5.22	7.51	5.83	5.83	6.5–8.5
2	EC	μS/cm	56	359	120	100	1400
3	TDS	mg/L	34	241	60	50	1000
4	Turbidity	NTU	2	3	2.13	3.07	5
5	Ca	mg/L	17	87.39	12.9	70.6	200
6	Mg	mg/L	14	33.01	2.3	3.7	50
7	Na	mg/L	3.40	37.4	34.8	49.3	200
8	K	mg/L	1.30	2.3	3.237	3.641	12
9	TH	mg/L	31	120.4	1.86	0.93	500
10	TA	mg/L	31.25	136	300	250	500
11	NO3−2	mg/L	Nil	Nil	Nil	Nil	10
12	SO4−1	mg/L	3.8	10.9	3.33	1.33	250
13	Cl−	mg/L	12	30	47.925	21.3	250

depicts the hydrochemical analysis of the water samples collected from both the north and south portals, with measured parameters compared to the 2017 World Health Organization (WHO) standards.

The results of the water analysis indicate that most of the parameters examined in the south and north portals fall within the permissible ranges for drinking water according to WHO 2017 standards, except for the pH level. The pH of the water samples collected from the south portal during summer and winter was 5.22 and 5.83, respectively, indicating an acidic nature. Similarly, at the north portal, the pH of the water was measured to be 5.83 during winter, while, in summer, the pH showed a higher value of 7.51. The acidic pH of the water in the south portal may be due to the presence of dissolved carbon dioxide that can make the water taste sour. The electric conductivity, total dissolved solids, total hardness, calcium, magnesium, total alkalinity, chlorine, sodium, potassium, and sulfate concentrations are significantly higher in the north portal as compared to the south portal. This difference is attributed to the longer drainage stretch of the north portal, which is responsible for the relatively high concentration of these parameters.

Figure 6a,b presents the results of the Piper diagram and the Wilcox plot, respectively, which provide a comprehensive assessment of the physicochemical characteristics of water extracted from the Lowari Tunnel. The Piper diagram is commonly used to identify water facies, which are a combination of lithology, chemical kinematics, and flow patterns [49]. The hydrochemistry of the samples showed significant variation in both seasons, with Mg being the dominant cation in the south portal during the summer season. In contrast, the north portal samples were plotted in the mixed zone, indicating a lack of dominance by any cation. For the winter season, Na + K showed dominance over other cations at the south portal, while Ca was the dominant ion at the north portal. Additionally, bicarbonate was the dominant anion in both seasons and portals. The diamond plot in the Piper diagram was used to assess the hydrochemical facies of water [50,51]. The majority of the samples showed Ca-Mg-HCO₃ as the dominant hydrochemical facies, with the only exception being a sample collected from the south portal during the winter season, which was plotted in the mixing zone. It could also be inferred from the Piper diagram that weak acids exceeded strong acids in all the samples, except for one sample collected from the south portal during the winter season, where alkaline-earths were dominant in comparison to alkalis. This may indicate the meteoric nature of waters with a low residence time, mainly dominated by rock weathering [52].

The Wilcox plot, a well-established tool for assessing the suitability of water for agricultural purposes based on Na% and EC, was also utilized to classify the samples extracted from the Lowari Tunnel. Excessive amounts of Na in water may adversely affect soil properties and nutrient uptake by plants. EC is a good measure of the salinity hazards posed by irrigation waters. Notably, all the samples were rated “excellent” according to the Wilcox plot classification [53]. This is a positive indication for farmers who require high-quality water for their crops, as it ensures that the water is not only safe but also suitable for irrigation. The results of this study align with previous research on the physicochemical properties of groundwater in mountainous regions, which have been found to be rich in species such as calcium, magnesium, and bicarbonate [54,55].

A comparison of water parameter values between the construction and operational stages of the Lowari Tunnel for the south drive reveals no significant difference in total hardness. The value is slightly higher during the construction stage due to increased Ca concentrations (total hardness is the sum of calcium and magnesium concentrations). Electric conductivity is higher in the Lowari Tunnel’s water during the construction stage. In general, conductivity decreases with increased filtration, which reduces the number of dissolved solids. The alkalinity and magnesium concentrations of the Lowari Tunnel water show only slight variation between the construction and operational stages. The nitrates were found to have the same concentration in both stages, while the concentration of sulfates was slightly higher during the construction stage than in the operational stage. These findings demonstrate the importance of understanding the relationship between geology and hydrology in tunnel construction, as well as the influence of filtration on water quality. The observations in this study align with previous research [56,57], emphasizing the significance of this study.

Based on the water discharge rate of 803,520 L/day at the north portal of the Lowari Tunnel, this study proposes that the available water supply be used to address the water scarcity challenges faced by the nearby community of Baradam. With its 70 acres of agricultural land, 500+ residential structures, and 3000+ inhabitants, Baradam relies heavily on rainfall for farming and must travel long distances to secure drinking water. To meet the United Nations’ benchmark of 50 L per day per person for domestic usage with the available water supply, a comprehensive and efficient solution is required. In the winter regions of Pakistan, wheat and maize account for 95% of crop production, and require 180 mm of water and 4 months of growth time [58,59]. The proposed solution is to use the water flow of the Lowari Tunnel to satisfy the irrigation requirements for these essential crops. Future studies should be conducted to assess the presence of organic and microbial contamination in the water of the Lowari Tunnel. The focus can be on understanding how water quality changes over time, its impact on the tunnel structure, and the health effects of low pH levels on workers and residents. Additionally, comparing the water quality of the Lowari Tunnel with other tunnels in the region would be valuable. The findings from these studies can be used to develop a predictive model for water quality in tunnels, aiding in the design and management of tunnels to minimize water ingress and maintain optimal water quality.

5. Conclusions

This study assessed the water quality in the Lowari Tunnel during its construction stage (2006–2009) and operation stage (2021 and 2023). The study is consistent with the current trend of using a combination of qualitative and quantitative methods to assess water ingress in tunnels. The findings have important implications for the safe and effective operation of mountain tunnels and on the use of tunnel water for domestic and agricultural purposes. The important conclusions of this study are summarized below:

• During the construction stage, the dewatering process carried out from the Lowari Tunnel (from April 2007 to February 2009), successfully managed water ingress with average discharge of 20 L/s. Seasonal water ingress was observed, primarily during snowmelt or heavy rainfall periods. During tunnel excavation, the successful grouting of water leakage points, such as joints and fractures, with shotcrete significantly reduced water infiltration. For the recorded period, during its operation stage, the Lowari Tunnel experienced natural water discharge at both the north and south portals. The measured water discharge rates vared between summer and winter, with higher rates observed during summer (10.08 L/s) compared to winter (6.96 L/s). This seasonal variation in water discharge is attributed to the snow melting process;
• During the construction stage, all measured hydrochemical parameters were within the normal range except for a low pH value (5.21), attributed to a high concentration of CO₂ (14,000 ppm) inside the tunnel. In the operation stage, water analysis showed that most parameters in the south and north portals complied with WHO 2017 standards for drinking water. However, the pH levels deviated from the permissible range. The water in the south portal had acidic pH values of 5.22 (summer) and 5.83 (winter), while the north portal showed a pH of 5.83 (winter) and 7.51 (summer). The higher concentration of electric conductivity, total dissolved solids, total hardness, calcium, magnesium, total alkalinity, chlorine, sodium, potassium, and sulfate in the north portal can be attributed to its longer drainage stretch;
• Piper diagram revealed significant variation in hydrochemistry between seasons and portals. Mg was the dominant cation in the south portal during summer, while the north portal samples showed a lack of dominance by any cation. Na + K dominated in the south portal during winter, while Ca was the dominant ion in the north portal. Bicarbonate was the dominant anion in both seasons and portals. The majority of samples exhibited the Ca-Mg-HCO₃ hydrochemical facies, indicating the influence of rock weathering. The Wilcox plot classified all samples as “excellent” for agricultural purposes, ensuring the suitability of the water for irrigation without adverse effects on soil properties or plant nutrient uptake;
• These results align with previous research indicating that tunnel water is suitable for various applications, including tunnel support systems, drinking, and irrigation [60,61];
• The difference in water quality parameters between the north and south portals is attributed to the geological and hydrological factors such as surrounding rock types and groundwater conditions [62,63,64,65,66,67]. Thus, understanding local geological and hydrological conditions is essential for effective tunnel water resource management.