Intrusion of seawater into coastal aquifers is rampant, in Lebanon as well as the Mediterranean basin, due to high extraction rates and low recharge. Due to this rising salinity, household are compelled to seek alternate sources causing water expenditures to exceed 6.5% of incomes, significantly higher than the worldwide averages ( Alameddine et al., 2018 ).

The hydrogeological context of Lebanon is complex and poorly researched in light of the decades-long calamities that never seem to abate, as such, it is beyond the reach of this paper to contemplate elucidation. However, it would suffice to point out that said hydrogeology comprises ten or so aquifers predominantly karstic in nature, and the ones that intersect the 225 km long coastline are subject to the Ghyben-Herzberg principle.

The principle was put forward by Willem Ghijben and Alexander Herzberg at the turn of the twentieth century. They derived said analytical solution to approximate the behavior of seawater intrusion, which is based on a number of broad assumptions that often does not apply to all field cases.

Simply put, when an aquifer crops out beneath the sea, ocean water may enter it under certain conditions. Sea water will be at such a depth that the overlying column of fresh groundwater will exactly balance a column of heavier sea water, according to said principle.

Hence, under static conditions, if the freshwater has a specific gravity of 1.0 and seawater a specific gravity of 1.025, the interface between the heavier sea water and the overlying freshwater in the area is pushed 40 meters below sea level for every meter that the water table stands above sea level. This is a very important point because it means that if the height of the water table above sea level is known, it is possible to calculate the depth to which freshwater is present as in Figure 1 below.

With the above in mind, Shaban (2015) , postulates that there are no less than 100,000 wells strewn across Lebanon, pumping groundwater at an average rate of no less than 10 liters per day, most being unlicensed. UNDP on the other hand, estimates that there are no less than 80,000 wells across Lebanon with an alarming density of about 8 per square kilometer, the majority of which are also unregistered ( UNDP, 2014 ). With the above in mind, all wells along the Lebanese coastline are subject to the repercussions of the Ghyben-Herzberg principle.

Additionally, an unhindered influx of Syrian refugees into Lebanon since 2011, topped with recurrent periods of drought have placed tremendous stress on an already dwindling resource. These concurrent stressors have inadvertently exacerbated the overall quality of freshwater in Lebanon, demonstrated by an outbreak of cholera that spread like wildfire, from refugee camps, and engulfing the entire nation, killing no less than 50 persons in 2022.

With the above in mind, supply of freshwater to the populated cities of Lebanon like coastal Beirut, has for decades forced the water authorities to adopt rationing to just a few hours per week, leaving civilians to resort to unsustainable measures such as over-pumping of ground water, and relying on dubious water vendors in the shape of tankers and bottled water.

Despite the urgency of these societal and environmental challenges, a better understanding of the impacts of seawater intrusion on different sectors and potential mitigation measures are inadequate.

As such, this paper attempts to identify the extent of salinization across the country’s different water sources, with the aim of recommending immediate measures to abate the root-cause of it i.e. seawater intrusion, at least for the immediate future. To this end, existing literature related to seawater intrusion impacts in Lebanon was reviewed, proposing some viable and readily implementable mitigation measures.

Owing to the fact that the endeavor of this paper was an initiative undertaken by like-minded water pundits, with limited resources, the aim of the survey is to simply highlight the severity of salinization using portable equipment. A comprehensive national water quality monitoring program is the inevitable solution, to be carried out by the Lebanese government, namely the Ministry of Energy & Water.

Sampling and testing of water sources began across Lebanon in the summer of 2023 ( Figure 1 ) and continues to the present day, using several portable LaMotte Salt/TDS/pH/Temperature TRACER Pocke Tester.

Tests were carried out in accordance with ASTM, 2019 guidelines, D4448-01 Standard Guide for Sampling Groundwater Monitoring Wells. The test results of the campaign are summarized in the Appendix.

Water sources were analyzed in-situ for temperature, and Total Dissolved Solids (TDS), thus minimizing errors and costs as opposed to laboratory testing. TDS values are determined by multiplying the conductivity measurement by a known conversion ratio factor. The meter allows the selection of a conversion ratio factor that is typically between 0.5 and 0.7. The stored ratio factor will briefly appear in the lower temperature display when the meter is first turned on or when changing the measurement function to TDS.

Meter accuracy verification was performed on a daily basis. During calibration, the meter was set in the salinity mode to perform calibration for salinity and TDS. The automatic calibration procedure recognizes the conductivity standard of 3000 ppm (3 ppt) for salinity samples within the range of 1000 to 9999 ppm salinity. Samples exceeding this range where diluted with distilled water accordingly then multiplied by the dilution factor to arrive at the estimated TDS value.

In the case of sampling and testing groundwater through wells, they were purged for at least five minutes rather than the equivalent three water columns due to the fact that in many instances, data pertaining to wells was incomplete.

The results were evaluated in accordance with the World Health Organization (WHO) Guidelines for Drinking Water Quality (2020) which stipulates a guideline of 500 mg/L (TDS) as well as other standards, including FAO’s for agriculture ( FAO, 1994 ) with a TDS not exceeding 450 mg/L, and finally the American Society for Testing and Materials ( ASTM, 2022 ) prefers potable water standards for concrete batching whenever possible.

ESRI’s ArcGIS 10.8.1 was used to generate Figure 2 of this paper. All water sources sampled in said figures are also found in the Appendix.

It is worthy to elaborate on the differences between Electrical conductivity (EC), Salinity and Total dissolved solids (TDS). EC (electrical conductivity) is a measure of a water sample’s ability to conduct electric current. It is primarily determined by the presence of dissolved salts and other inorganic substances that ionize in water. Such substances are known as electrolytes, and they conduct electricity due to their positive and negative charges.

The SI unit for conductivity is Siemens per meter (S/m). Conductivity increases with the amount of electrolytes dissolved in water up to a degree, as well as with increases in temperature.

Salinity on the other hand, is related to conductivity as it describes the total concentration of all dissolved salts in a water sample. Salinity is, therefore, commonly derived from specific conductance (conductivity and temperature) for convenience.

Lastly, Total dissolved solids (TDS) are defined as the sum of all particles that can pass through a 2-micron (0.0002 cm) filter. This includes both electrolytes (ions contributing to salinity) and any other non-ionic molecules, such as dissolved organic matter. TDS is reported as a concentration in mg/L. It was traditionally measured by evaporation, but for field measurements, it is normally derived from conductivity measurement using a TDS factor, which is approximated depending on the water type and any known sources of ions and other material.

Annual renewable water resources per capita in the Arab World is understandably among the lowest in the world, and by 2025, Lebanon’s water supply deficit will exceed 1000 MCM/year ( Korfali & Jurdi, 2011 ) placing tremendous strains on demands for water quantity and more importantly, quality.

World Health Organization (WHO) guidelines for drinking water does not express any particular health hazard from TDS concentrations exceeding 500 mg/L, however, the economic impact of aquifers degraded by seawater intrusion on Lebanon’s infrastructure is incalculable as highlighted by Alameddine et al. (2018) from accelerated corrosion of Lebanon’s infrastructure as well as deterioration of fertile soils.

An additional problem of increase in salt concentrations is a phenomenon called freshwater salinization syndrome (FSS). This syndrome is a result of direct as well as indirect effect of salts that cause other pollutants from soils, ground-waters, surface waters, and pipes to become soluble and mobile ( Cooper et al., 2014 ).

FSS with its direct and indirect effects has serious impacts on surface, ground and drinking water quality, as well as aquatic and terrestrial ecosystem function, human health, food production, and degradation of infrastructure ( Sujay et al., 2021 ).

FSS encompasses several processes such as sodification (increase in exchangeable sodium ions expressed as ESP, impacting soils by reducing their permeabilities), salinization (increase in total water ions expressed as TDS or electrical conductivity EC leading to enhanced corrosion etc.), and alkalinization or the increase in alkalinity or ability of a solution to neutralize acids through carbonates, bicarbonates etc. ( Kaushal et al., 2019 ) impacting ecosystems.

Salts alone can directly impact water quality by increasing the rate of ions mobilized from soils and pipes becoming concentrated in ground and surface waters. Nitrates for instance can be mobilized by FSS thereby leading to harmful algal blooms or HABs destroying freshwater systems as well as coastal waters ( EPA, 2022 ). Nitrates also impact infants with spikes in cases of Blue Baby Syndrome or methemoglobinemia as well as potentially increasing cases of certain cancers, namely gastric cancers ( Picetti et al., 2022 ).

Increased salinity (often expressed as TDS) would render coastal aquifers unsuitable for public supply with only a 2% contamination ( Bear, 1999 ). Normally, a 1% mixing would triple groundwater salinity or TDS, while 5% mixing would increase salinity to the guideline limit of 450 mg/L ( Bear, 1999 ). Hence once freshwater resources are degraded by salt contamination, it will take decades for aquifers to recover, and if positive groundwater recharge conditions are not re-established, they may never do so.

The TDS values summarized in the Appendix and labeled into three groups, namely groundwater (expressed as wells and springs), tap water (municipal supply), and surface runoff (rivers and streams).

To begin with, groundwater TDS results, especially with coastal sources clearly indicate contamination by seawater in several wells in Saida (99), coastal Chouf (30), and Keserouane (39). As for Greater Beirut, the severity of seawater intrusion has been long established by the author’s doctoral dissertation undertaken between 2004-08 and again in subsequent articles, that measured groundwater

quality including TDS in a multitude of wells indicating severe seawater contamination ( Saadeh, 2008 ).

As for the tap water provided by local public utilities, most notable include Beirut (#45) at about 2200 mg/L, Jbail (#57 & #59) at 2300 and 2050 mg/L respectively, and Baabda (#95) at a staggering 5500 mg/L, all of which deleteriously exceeding permissible guidelines for drinking water, concrete batching and agricultural irrigation.

Lastly, surface runoff (streams, rivers etc.) like those measured in samples #14 and #55, are generally still within acceptable guidelines for TDS of 500 mg/L as per drinking water, concrete batching and irrigation.

Once freshwater has been afflicted with elevated Salinity/TDS ( Korfali & Jurdi, 2010 ), like most metropolitan centers along Lebanon’s coastline, combating these effects may take decades to undo, as per notable studies including Bear (1999) , and again Barlow (2003) . Even though, aquifer recharge is often employed for contaminated coastal aquifers worldwide, only potable water standards should provide a reference point for recharging said aquifers, a commodity which is already acutely scarce in Lebanon and the region.

By no means are the following recommendations a panacea for ensuring water efficiency and quality for any Integrated Water Resources Management Plan (IWRM), nevertheless, experts alike agree that they are integral to any successful water management plan, from the eminent Tony Allan (2011) to Klaus Balke and many others.

The results of the ongoing water quality campaign, sharply focus the deleterious effect of seawater intrusion on Lebanon’s most precious water resource, groundwater, however, more alarming is the fact that elevated values of TDS have now been detected in all major coastal cities, namely Beirut, Saida, Tripoli and Byblos (Jbeil) alike.

Any water management strategy is by no means a “one size fits all” approach, and each has to be fine-tuned to its required set of goals, nevertheless, the aforementioned recommendations are a fundamental step in the right direction. As such, this paper emphasizes first and foremost the urgency for the implementation of an updated national comprehensive integrated water resources management plan (IWRM) with immediate enforcement ensuring that coastal aquifers are disencumbered by the Ghyben-Herzberg principle. This will decouple the impacts of salinization from coastal aquifers on which the majority of Lebanon’s population relies.

All of Lebanon’s aquifers, on the other hand, must also be protected by adopting the recommended three protection zones coupled by a metering the nation’s entire water supply network from source to tap. Only then can water conservation proceed in tandem with water efficiency.

As a final note, the late eminent professor Tony Allan warns that “wherever we irrigate, society always runs out of water”, a declaration that will certainly not bode well with agriculture pundits.

Lebanon, and the Middle East continues to rely heavily on irrigation, consuming around 70% of its renewable freshwater resources, to that end, an improvement of only 10% in irrigation efficiency could potentially double the resources available for public water supply according to TWORT’s, an avenue well worth pursuing in Lebanon and the region, where agricultural practices remain stubbornly adamant to proven and efficient irrigation methods.

This study took time and effort of countless hours to bring to fruition, which would not have been possible without the unwavering support of friends, colleagues and the generosity of the Lebanese folk.