The Use of Stable Water Isotopes as Tracers in Soil Aquifer Treatment ( SAT ) and in Regional Water Systems

This study examines the feasibility of tracing and quantifying the progress of different water sources along the water–effluent–SAT (Soil Aquifer Treatment) chain using 2H and 18O isotopes. The research was conducted at the Dan Region Reclamation Plant (Shafdan), which reclaims ~135 MCM/year of effluent for irrigation. Water samples representing different stages along the chain were taken in two surveys during 2010–2011 and 2014. δ18O and δ2H values were used for mixing ratios (MR) calculations, and compared with calculated MRs using chloride and carbamazepine concentrations. The results showed a relative enrichment of 18O and 2H in the Israeli water system compared to the regional groundwater, due to the addition of massive quantities of desalinated water. A linear correlation for δ2H vs. δ18O with a slope of 4.5 was found for the different freshwater sources and their mixing products, suggesting evaporation-mixing effects. MR values indicate on the spreading of new type of effluent originating from desalinated water in the aquifer. A dilution model explains the isotopic compositions in the water system and of the Shafdan effluents. Water isotopes have an advantage over other tracers, due to the ability to predict their ratio in the supply system and in the effluent, based on mass balance calculations and on knowledge of water supply volumes.


Introduction
The use of stable isotopes as markers for tracing after the spreading, processes and reactions of various materials in the environment and the water cycle has been commonplace for many years [1,2].The fractionation of the water molecule stable isotopes 18 O/ 16 O and 2 H/ 1 H under natural moderate temperature conditions is affected mainly by phase transformations, notably evaporation-condensation and freezing-melting processes due to temperature and pressure changes.This, together with their intrinsic association to the water molecule and their relatively inert behavior in other processes, makes these isotopes ideal for tracking different sources of water bodies during transport and mixing processes [1][2][3].However, in many studies that applied the stable isotopes of water to assess contamination processes or managed aquifer recharge (MAR), only the qualitative or semi-quantitative aspects of "fingerprints" of mixing between different sources could be demonstrated (e.g., [4][5][6][7]).The main reason for this is the lack of unambiguous definition of end-member composition, which did not enable quantitative estimations.Specifically, in Israel, neither in the Shafdan plant nor in any other recharge (MAR) project, stable water isotopes have been used for mass balance calculations.
Water supply in Israel is broadly based on a centralized system known as the National Water Carrier (NWC).The NWC collects its water from three major natural water sources: Lake Kinneret (Sea of Galilee (SOG)) in the north, and the Coastal and Mountain aquifers in the central part of Israel.
CBZ to be a useful tracer in the Shafdan system, especially down-stream where the effluents are diluted.It was shown that in these areas CBZ can be used for MR calculations of less than 5% [18,[19][20][21][22][23].However, CBZ is limited to less diluted areas (MR > 80%) and for prediction purposes, due to its unstable concentrations in the recharged effluents [21].
The present research hypothesized that the massive amounts of desalinated water added each year to the National Water Carrier should affect the supplied water isotopic composition, as well as the isotopic composition of the associated effluents treated by the Shafdan plant.The objectives of this study were to examine the applicability of the water isotopes 18 O and 2 H as a quantitative tool: (1) for tracing the spatial distribution of the recharged effluents in the Shafdan basins; and (2) for examination of the relationship between different water sources in the water-sewage-effluent system, that is, between the different water sources in the Israeli National Water Carrier, between the NWC and the Shafdan plant, and between the Shafdan plant and the SAT recovery wells.

Sampling Program
In order to verify the research hypothesis, an extensive survey was conducted, including sampling and analysis of water collected from recovery wells, from pipe connections of the NWC and from desalination plants.The main research took place in the area of the Soreq recharge basin, located at the northern part of the Shafdan plant.The aquifer in this area is subdivided into four sub-aquifers, A to C (Figure 1).The main SAT activity, as well as the freshwater pumping, takes place in sub-aquifer B. In some places, the recharged water reaches also lower unit (sub-aquifers C).Some of the recovery wells penetrate several sub-aquifers and hence technically connect and exploit all of them.[24]).
Water 2017, 9, 73 4 of 16 Two sampling campaigns were conducted during the years 2010-2011 and 2014.The first campaign (2010-2011) was part of a France-Israeli bilateral research program, and included the examination of various isotopes and chemical compounds as a potential tracer for the Shafdan system [25,26].The second campaign was conducted by Mekorot in order to validate the conclusions and the predictions of the first campaign.In each campaign, we sampled 17 to 21 recovery and monitoring wells, most of them 2-3 times (Figure 2).The sampled wells were carefully chosen to be located at various distances from the recharge ponds, and yet to be as similar as possible from the technical and hydro-geological aspects.A limited sampling campaign that included only the Shafdan effluents and 3 observation wells was conducted during winter 2013.
Water 2017, 9, 73 4 of 17 Two sampling campaigns were conducted during the years 2010-2011 and 2014.The first campaign (2010-2011) was part of a France-Israeli bilateral research program, and included the examination of various isotopes and chemical compounds as a potential tracer for the Shafdan system [25,26].The second campaign was conducted by Mekorot in order to validate the conclusions and the predictions of the first campaign.In each campaign, we sampled 17 to 21 recovery and monitoring wells, most of them 2-3 times (Figure 2).The sampled wells were carefully chosen to be located at various distances from the recharge ponds, and yet to be as similar as possible from the technical and hydro-geological aspects.A limited sampling campaign that included only the Shafdan effluents and 3 observation wells was conducted during winter 2013.
Each campaign included sampling of secondary effluents from the outlet of the MBTP (PS-6) and from recharge ponds.Samples were also taken from two desalination plants (Palmahim and Hadera) and from specific points along the National Water Carrier, in order to represent the isotopic composition of the Dan Region's supplied freshwater (Figure 2).Each campaign also included specific sampling programs (sub-experiments) to evaluate the contributions of individual sources and the effects of secondary processes such as evaporation or seasonal variations, as listed in Table 1.Table 1.General description of the sub-experiments conducted during the campaigns.

Examined Effect
Campaign Setup and Remarks Seasonal effects on the isotopic composition of the recovered water (after SAT)

2010-2011
The first sampling campaign was divided into 2 parts: September 2010 (summer) and February 2011 (winter).The two sub-campaigns were conducted at the same wells or at hydro-geologically equivalent wells.
Evaporation effects on the isotopic composition of the recharged effluents, during the recharge period 2010-2011 (1) By simultaneous sampling from PS-6 (MTBE outlet) and from the recharge pond on 14 September 2010.Effluent sampling of the recharge pond was taken at the end of the day, ~6 h.After beginning of flooding.(2) By continuous sampling of the recharge pond during flooding on 19 September 2010 (beginning of flooding) and on 20 September 2010 (end of flooding).
The effect of the Sea of Galilee and the desalinated water on the isotopic composition of the Shafdan effluents (see Section 3.3) 2010-2011, 2013 and 2014 (1) On 21 February 2011 and on 7 February 2013 effluents were sampled from the Shafdan during a period when no water was supplied from the lake to the NWC.(2) On 25 February 2014 effluents were sampled from the Shafdan during a period when no water was supplied from the Hadera DSP and from the SOG to the NWC.Each campaign included sampling of secondary effluents from the outlet of the MBTP (PS-6) and from recharge ponds.Samples were also taken from two desalination plants (Palmahim and Hadera) and from specific points along the National Water Carrier, in order to represent the isotopic composition of the Dan Region's supplied freshwater (Figure 2).Each campaign also included specific sampling programs (sub-experiments) to evaluate the contributions of individual sources and the effects of secondary processes such as evaporation or seasonal variations, as listed in Table 1.

Analytical Procedures
Chemical analyses included measurement of salinity (Cl, EC) in all samples.In part of the samples, mainly during the first campaign, major ions (Ca, Mg, Na, K, HCO 3 , SO 4 , and B), nitrogen species (NO 3 , NH 4 , and NO 2 ), Redox parameters (DO, ORP, Mn, and Fe) and other parameters (pH, temperature, DOC, alkalinity, UV and metal concentrations) were also measured.This was done for quality control and comparison purposes, and is not discussed further in this paper.Analyses were conducted by the central laboratory of Mekorot using standard methods.
Potential tracers for mixing ratio (MR) calculations, including Cl, CBZ and the stable isotopes of water molecule ( 18 O and 2 H), were measured at all wells.CBZ concentrations were measured in the central laboratory of the Israeli Water Authority.Measurements were done using liquid chromatograph equipped with tandem triple quadruple mass spectrometer LC/MS/MS according to the EPA method 1694, which enable limit of quantification (LOQ) of 0.1 ng/ L [20].The oxygen and hydrogen isotopes (expressed as δ 18 O and δ 2 H values in ater 2017, 9, 73 5 of 17 .

Analytical Procedures
Chemical analyses included measurement of salinity (Cl, EC) in all samples.In part of the amples, mainly during the first campaign, major ions (Ca, Mg, Na, K, HCO3, SO4, and B), nitrogen pecies (NO3, NH4, and NO2), Redox parameters (DO, ORP, Mn, and Fe) and other parameters (pH, emperature, DOC, alkalinity, UV and metal concentrations) were also measured.This was done for uality control and comparison purposes, and is not discussed further in this paper.Analyses were onducted by the central laboratory of Mekorot using standard methods.
Potential tracers for mixing ratio (MR) calculations, including Cl, CBZ and the stable isotopes of ater molecule ( 18 O and 2 H), were measured at all wells.CBZ concentrations were measured in the entral laboratory of the Israeli Water Authority.Measurements were done using liquid hromatograph equipped with tandem triple quadruple mass spectrometer LC/MS/MS according to he EPA method 1694, which enable limit of quantification (LOQ) of 0.1 ng/ L [20].The oxygen and ydrogen isotopes (expressed as δ 18 O and δ 2 H values in ‰ vs. the VSMOW standard) were measured y two separated labs.Samples from the first campaign (2010-2011) were analyzed by the BRGM otope laboratory on a Finnigan MAT 252 mass spectrometer following the gas-water equilibration echnique with CO2 for oxygen isotopes [27] and with H2 for hydrogen isotopes [28].Analytical ncertainty, based on replicate analyses of international and laboratory standards, are ±0.8‰ for δ 2 H nd ±0.1‰ for δ 18 O.Water and effluent samples from the second campaign (2014 and 2013) were nalyzed by the IT 2 laboratory (Waterloo, ON, Canada) on CRDS, Model L1102-i (Piccaro, Santa lara, CA, USA) for both oxygen and hydrogen isotopes.The instrument was configured with a nique vaporization module that converts the liquid water sample to the vapor phase in a flash rocess at 140°C.The vapor was then delivered into the CRDS cavity for analysis.This process voided any possible fractionation processes that may have occurred with other liquid/vapor ransitions such as nebulizers.Typical precision for δ 18 O and δ 2 H are ±0.1‰ and ±0.6‰, respectively.ll results were corrected and reported against the Vienna Standard Mean Ocean Water (VSMOW).ll in-house standards were calibrated every six months by VSMOW, GISP and SLAP (The IAEA ternational standards).All samples were analyzed in duplicates at both laboratories, with internal hidden standards or control.

.1. Isotopic Composition of the Shafdan System
The results for the isotopic composition and concentrations of Cl and CBZ are given in Table 2. typical correlation diagram of δ 2 H vs. δ 18 O for the Shafdan system (Figure 3a) and for the Israeli ater system sources (Figure 3b) is given in Figure 3.
vs. the VSMOW standard) were measured by two separated labs.Samples from the first campaign (2010-2011) were analyzed by the BRGM isotope laboratory on a Finnigan MAT 252 mass spectrometer following the gas-water equilibration technique with CO 2 for oxygen isotopes [27] and with H 2 for hydrogen isotopes [28].Analytical uncertainty, based on replicate analyses of international and laboratory standards, are ±0.8 Water 2017, 9, 73 5 of 17

Analytical Procedures
Chemical analyses included measurement of salinity (Cl, EC) in all samples.In part of the samples, mainly during the first campaign, major ions (Ca, Mg, Na, K, HCO3, SO4, and B), nitrogen species (NO3, NH4, and NO2), Redox parameters (DO, ORP, Mn, and Fe) and other parameters (pH, temperature, DOC, alkalinity, UV and metal concentrations) were also measured.This was done for quality control and comparison purposes, and is not discussed further in this paper.Analyses were conducted by the central laboratory of Mekorot using standard methods.
Potential tracers for mixing ratio (MR) calculations, including Cl, CBZ and the stable isotopes of water molecule ( 18O and 2 H), were measured at all wells.CBZ concentrations were measured in the central laboratory of the Israeli Water Authority.Measurements were done using liquid chromatograph equipped with tandem triple quadruple mass spectrometer LC/MS/MS according to the EPA method 1694, which enable limit of quantification (LOQ) of 0.1 ng/ L [20].The oxygen and hydrogen isotopes (expressed as δ 18  O and δ 2 H values in ‰ vs. the VSMOW standard) were measured by two separated labs.Samples from the first campaign (2010-2011) were analyzed by the BRGM isotope laboratory on a Finnigan MAT 252 mass spectrometer following the gas-water equilibration technique with CO2 for oxygen isotopes [27] and with H2 for hydrogen isotopes [28].Analytical uncertainty, based on replicate analyses of international and laboratory standards, are ±0.8‰ for δ 2 H and ±0.1‰ for δ 18  O.Water and effluent samples from the second campaign (2014 and 2013) were analyzed by the IT 2 laboratory (Waterloo, ON, Canada) on CRDS, Model L1102-i (Piccaro, Santa Clara, CA, USA) for both oxygen and hydrogen isotopes.The instrument was configured with a unique vaporization module that converts the liquid water sample to the vapor phase in a flash process at 140°C.The vapor was then delivered into the CRDS cavity for analysis.This process avoided any possible fractionation processes that may have occurred with other liquid/vapor transitions such as nebulizers.Typical precision for δ 18  O and δ 2 H are ±0.1‰ and ±0.6‰, respectively.All results were corrected and reported against the Vienna Standard Mean Ocean Water (VSMOW).All in-house standards were calibrated every six months by VSMOW, GISP and SLAP (The IAEA international standards).
All samples were analyzed in duplicates at both laboratories, with internal hidden standards for control.

Isotopic Composition of the Shafdan System
The results for the isotopic composition and concentrations of Cl and CBZ are given in Table 2.A typical correlation diagram of δ 2 H vs. δ 18 O for the Shafdan system (Figure 3a) and for the Israeli water system sources (Figure 3b) is given in Figure 3.

Analytical Procedures
Chemical analyses included measurement of salinity (Cl, EC) in all samples.In pa samples, mainly during the first campaign, major ions (Ca, Mg, Na, K, HCO3, SO4, and B), species (NO3, NH4, and NO2), Redox parameters (DO, ORP, Mn, and Fe) and other parame temperature, DOC, alkalinity, UV and metal concentrations) were also measured.This was quality control and comparison purposes, and is not discussed further in this paper.Analy conducted by the central laboratory of Mekorot using standard methods.
Potential tracers for mixing ratio (MR) calculations, including Cl, CBZ and the stable iso water molecule ( 18O and 2 H), were measured at all wells.CBZ concentrations were measure central laboratory of the Israeli Water Authority.Measurements were done using chromatograph equipped with tandem triple quadruple mass spectrometer LC/MS/MS acco the EPA method 1694, which enable limit of quantification (LOQ) of 0.1 ng/ L [20].The oxy hydrogen isotopes (expressed as δ 18  O and δ 2 H values in ‰ vs. the VSMOW standard) were m by two separated labs.Samples from the first campaign (2010-2011) were analyzed by th isotope laboratory on a Finnigan MAT 252 mass spectrometer following the gas-water equi technique with CO2 for oxygen isotopes [27] and with H2 for hydrogen isotopes [28].A uncertainty, based on replicate analyses of international and laboratory standards, are ±0.8‰ and ±0.1‰ for δ 18  O.Water and effluent samples from the second campaign (2014 and 20 analyzed by the IT 2 laboratory (Waterloo, ON, Canada) on CRDS, Model L1102-i (Piccar Clara, CA, USA) for both oxygen and hydrogen isotopes.The instrument was configure unique vaporization module that converts the liquid water sample to the vapor phase in process at 140°C.The vapor was then delivered into the CRDS cavity for analysis.This avoided any possible fractionation processes that may have occurred with other liqu transitions such as nebulizers.Typical precision for δ 18  O and δ 2 H are ±0.1‰ and ±0.6‰, resp All results were corrected and reported against the Vienna Standard Mean Ocean Water (V All in-house standards were calibrated every six months by VSMOW, GISP and SLAP (T international standards).
All samples were analyzed in duplicates at both laboratories, with internal hidden st for control.

Isotopic Composition of the Shafdan System
The results for the isotopic composition and concentrations of Cl and CBZ are given in A typical correlation diagram of δ 2 H vs. δ 18 O for the Shafdan system (Figure 3a) and for th water system sources (Figure 3b) is given in Figure 3.
for δ 18 O.Water and effluent samples from the second campaign (2014 and 2013) were analyzed by the IT 2 laboratory (Waterloo, ON, Canada) on CRDS, Model L1102-i (Piccaro, Santa Clara, CA, USA) for both oxygen and hydrogen isotopes.The instrument was configured with a unique vaporization module that converts the liquid water sample to the vapor phase in a flash process at 140 • C. The vapor was then delivered into the CRDS cavity for analysis.This process avoided any possible fractionation processes that may have occurred with other liquid/vapor transitions such as nebulizers.Typical precision for δ 18 O and δ 2 H are ±0.1 5 of 17 ncluded measurement of salinity (Cl, EC) in all samples.In part of the e first campaign, major ions (Ca, Mg, Na, K, HCO3, SO4, and B), nitrogen O2), Redox parameters (DO, ORP, Mn, and Fe) and other parameters (pH, ity, UV and metal concentrations) were also measured.This was done for arison purposes, and is not discussed further in this paper.Analyses were aboratory of Mekorot using standard methods.
ixing ratio (MR) calculations, including Cl, CBZ and the stable isotopes of H), were measured at all wells.CBZ concentrations were measured in the e Israeli Water Authority.Measurements were done using liquid with tandem triple quadruple mass spectrometer LC/MS/MS according to ich enable limit of quantification (LOQ) of 0.1 ng/ L [20].The oxygen and sed as δ 18  O and δ 2 H values in ‰ vs. the VSMOW standard) were measured mples from the first campaign (2010-2011) were analyzed by the BRGM innigan MAT 252 mass spectrometer following the gas-water equilibration xygen isotopes [27] and with H2 for hydrogen isotopes [28].Analytical licate analyses of international and laboratory standards, are ±0.8‰ for δ 2 H er and effluent samples from the second campaign (2014 and 2013) were ratory (Waterloo, ON, Canada) on CRDS, Model L1102-i (Piccaro, Santa oxygen and hydrogen isotopes.The instrument was configured with a ule that converts the liquid water sample to the vapor phase in a flash por was then delivered into the CRDS cavity for analysis.This process actionation processes that may have occurred with other liquid/vapor zers.Typical precision for δ 18  O and δ 2 H are ±0.1‰ and ±0.6‰, respectively.and reported against the Vienna Standard Mean Ocean Water (VSMOW).ere calibrated every six months by VSMOW, GISP and SLAP (The IAEA alyzed in duplicates at both laboratories, with internal hidden standards the Shafdan System otopic composition and concentrations of Cl and CBZ are given in Table 2. ram of δ 2 H vs. δ 18 O for the Shafdan system (Figure 3a) and for the Israeli ure 3b) is given in Figure 3. and ±0.6

of 17
Procedures l analyses included measurement of salinity (Cl, EC) in all samples.In part of the ly during the first campaign, major ions (Ca, Mg, Na, K, HCO3, SO4, and B), nitrogen NH4, and NO2), Redox parameters (DO, ORP, Mn, and Fe) and other parameters (pH, DOC, alkalinity, UV and metal concentrations) were also measured.This was done for l and comparison purposes, and is not discussed further in this paper.Analyses were the central laboratory of Mekorot using standard methods.tracers for mixing ratio (MR) calculations, including Cl, CBZ and the stable isotopes of le ( 18O and 2 H), were measured at all wells.CBZ concentrations were measured in the atory of the Israeli Water Authority.Measurements were done using liquid h equipped with tandem triple quadruple mass spectrometer LC/MS/MS according to od 1694, which enable limit of quantification (LOQ) of 0.1 ng/ L [20].The oxygen and opes (expressed as δ 18  O and δ 2 H values in ‰ vs. the VSMOW standard) were measured ated labs.Samples from the first campaign (2010-2011) were analyzed by the BRGM tory on a Finnigan MAT 252 mass spectrometer following the gas-water equilibration th CO2 for oxygen isotopes [27] and with H2 for hydrogen isotopes [28].Analytical ased on replicate analyses of international and laboratory standards, are ±0.8‰ for δ 2 H r δ 18  O.Water and effluent samples from the second campaign (2014 and 2013) were the IT 2 laboratory (Waterloo, ON, Canada) on CRDS, Model L1102-i (Piccaro, Santa SA) for both oxygen and hydrogen isotopes.The instrument was configured with a ization module that converts the liquid water sample to the vapor phase in a flash 0°C.The vapor was then delivered into the CRDS cavity for analysis.This process possible fractionation processes that may have occurred with other liquid/vapor ch as nebulizers.Typical precision for δ 18  O and δ 2 H are ±0.1‰ and ±0.6‰, respectively.re corrected and reported against the Vienna Standard Mean Ocean Water (VSMOW).standards were calibrated every six months by VSMOW, GISP and SLAP (The IAEA standards).les were analyzed in duplicates at both laboratories, with internal hidden standards Discussion omposition of the Shafdan System lts for the isotopic composition and concentrations of Cl and CBZ are given in Table 2. relation diagram of δ 2 H vs. δ 18 O for the Shafdan system (Figure 3a) and for the Israeli sources (Figure 3b) is given in Figure 3.
, respectively.All results were corrected and reported against the Vienna Standard Mean Ocean Water (VSMOW).All in-house standards were calibrated every six months by VSMOW, GISP and SLAP (The IAEA international standards).
All samples were analyzed in duplicates at both laboratories, with internal hidden standards for control.

Isotopic Composition of the Shafdan System
The results for the isotopic composition and concentrations of Cl and CBZ are given in Table 2.A typical correlation diagram of δ 2 H vs. δ 18 O for the Shafdan system (Figure 3a) and for the Israeli water system sources (Figure 3b) is given in Figure 3.
Examination of seasonal effects: Samples from recovery wells were taken during summer 2010 and winter 2011 (Table 1).No significant differences were found between these two sub-campaigns for Cl concentrations and for stable water isotope compositions.Thus, it can be concluded that there is no significant seasonal effect on the aquifer, and that the two sub-campaigns of 2010-2011 can be considered as one for further discussion.Seasonal effects on various chemical components in the Shafdan aquifer were examined in previous works (e.g., [16]) but never found.The reason for this is probably the moderating influence of the mixing in the aquifer on surface fluctuations and surface processes.Chemical analyses included measurement of salinity (Cl, EC) in all samples.In part of the samples, mainly during the first campaign, major ions (Ca, Mg, Na, K, HCO3, SO4, and B), nitrogen species (NO3, NH4, and NO2), Redox parameters (DO, ORP, Mn, and Fe) and other parameters (pH, temperature, DOC, alkalinity, UV and metal concentrations) were also measured.This was done for quality control and comparison purposes, and is not discussed further in this paper.Analyses were conducted by the central laboratory of Mekorot using standard methods.
Potential tracers for mixing ratio (MR) calculations, including Cl, CBZ and the stable isotopes of water molecule ( 18 O and 2 H), were measured at all wells.CBZ concentrations were measured in the central laboratory of the Israeli Water Authority.Measurements were done using liquid chromatograph equipped with tandem triple quadruple mass spectrometer LC/MS/MS according to the EPA method 1694, which enable limit of quantification (LOQ) of 0.1 ng/ L [20].The oxygen and hydrogen isotopes (expressed as δ 18 O and δ 2 H values in ‰ vs. the VSMOW standard) were measured by two separated labs.Samples from the first campaign (2010-2011) were analyzed by the BRGM isotope laboratory on a Finnigan MAT 252 mass spectrometer following the gas-water equilibration technique with CO2 for oxygen isotopes [27] and with H2 for hydrogen isotopes [28].Analytical uncertainty, based on replicate analyses of international and laboratory standards, are ±0.8‰ for δ 2 H and ±0.1‰ for δ 18 O.Water and effluent samples from the second campaign (2014 and 2013) were analyzed by the IT 2 laboratory (Waterloo, ON, Canada) on CRDS, Model L1102-i (Piccaro, Santa Clara, CA, USA) for both oxygen and hydrogen isotopes.The instrument was configured with a unique vaporization module that converts the liquid water sample to the vapor phase in a flash process at 140°C.The vapor was then delivered into the CRDS cavity for analysis.This process avoided any possible fractionation processes that may have occurred with other liquid/vapor transitions such as nebulizers.Typical precision for δ 18 O and δ 2 H are ±0.1‰ and ±0.6‰, respectively.All results were corrected and reported against the Vienna Standard Mean Ocean Water (VSMOW).All in-house standards were calibrated every six months by VSMOW, GISP and SLAP (The IAEA international standards).
All samples were analyzed in duplicates at both laboratories, with internal hidden standards for control.

Isotopic Composition of the Shafdan System
The results for the isotopic composition and concentrations of Cl and CBZ are given in Table 2.A typical correlation diagram of δ 2 H vs. δ 18 O for the Shafdan system (Figure 3a) and for the Israeli water system sources (Figure 3b) is given in Figure 3.

vs. SMOW δ 18 O
Chemical analyses included measurement of salinity (Cl, EC) in all samples.In part of the samples, mainly during the first campaign, major ions (Ca, Mg, Na, K, HCO3, SO4, and B), nitrogen species (NO3, NH4, and NO2), Redox parameters (DO, ORP, Mn, and Fe) and other parameters (pH, temperature, DOC, alkalinity, UV and metal concentrations) were also measured.This was done for quality control and comparison purposes, and is not discussed further in this paper.Analyses were conducted by the central laboratory of Mekorot using standard methods.
Potential tracers for mixing ratio (MR) calculations, including Cl, CBZ and the stable isotopes of water molecule ( 18O and 2 H), were measured at all wells.CBZ concentrations were measured in the central laboratory of the Israeli Water Authority.Measurements were done using liquid chromatograph equipped with tandem triple quadruple mass spectrometer LC/MS/MS according to the EPA method 1694, which enable limit of quantification (LOQ) of 0.1 ng/ L [20].The oxygen and hydrogen isotopes (expressed as δ 18  O and δ 2 H values in ‰ vs. the VSMOW standard) were measured by two separated labs.Samples from the first campaign (2010-2011) were analyzed by the BRGM isotope laboratory on a Finnigan MAT 252 mass spectrometer following the gas-water equilibration technique with CO2 for oxygen isotopes [27] and with H2 for hydrogen isotopes [28].Analytical uncertainty, based on replicate analyses of international and laboratory standards, are ±0.8‰ for δ 2 H and ±0.1‰ for δ 18  O.Water and effluent samples from the second campaign (2014 and 2013) were analyzed by the IT 2 laboratory (Waterloo, ON, Canada) on CRDS, Model L1102-i (Piccaro, Santa Clara, CA, USA) for both oxygen and hydrogen isotopes.The instrument was configured with a unique vaporization module that converts the liquid water sample to the vapor phase in a flash process at 140°C.The vapor was then delivered into the CRDS cavity for analysis.This process avoided any possible fractionation processes that may have occurred with other liquid/vapor transitions such as nebulizers.Typical precision for δ 18  O and δ 2 H are ±0.1‰ and ±0.6‰, respectively.All results were corrected and reported against the Vienna Standard Mean Ocean Water (VSMOW).All in-house standards were calibrated every six months by VSMOW, GISP and SLAP (The IAEA international standards).
All samples were analyzed in duplicates at both laboratories, with internal hidden standards for control.

Isotopic Composition of the Shafdan System
The results for the isotopic composition and concentrations of Cl and CBZ are given in Table 2.A typical correlation diagram of δ 2 H vs. δ 18 O for the Shafdan system (Figure 3a) and for the Israeli water system sources (Figure 3b) is given in Figure 3.Chemical analyses included measurement of salinity (Cl, EC) in all samples.In part of the samples, mainly during the first campaign, major ions (Ca, Mg, Na, K, HCO3, SO4, and B), nitrogen species (NO3, NH4, and NO2), Redox parameters (DO, ORP, Mn, and Fe) and other parameters (pH, temperature, DOC, alkalinity, UV and metal concentrations) were also measured.This was done for quality control and comparison purposes, and is not discussed further in this paper.Analyses were conducted by the central laboratory of Mekorot using standard methods.

DSP-Hadera
Potential tracers for mixing ratio (MR) calculations, including Cl, CBZ and the stable isotopes of water molecule ( 18 O and 2 H), were measured at all wells.CBZ concentrations were measured in the central laboratory of the Israeli Water Authority.Measurements were done using liquid chromatograph equipped with tandem triple quadruple mass spectrometer LC/MS/MS according to the EPA method 1694, which enable limit of quantification (LOQ) of 0.1 ng/ L [20].The oxygen and hydrogen isotopes (expressed as δ 18 O and δ 2 H values in ‰ vs. the VSMOW standard) were measured by two separated labs.Samples from the first campaign (2010-2011) were analyzed by the BRGM isotope laboratory on a Finnigan MAT 252 mass spectrometer following the gas-water equilibration technique with CO2 for oxygen isotopes [27] and with H2 for hydrogen isotopes [28].Analytical uncertainty, based on replicate analyses of international and laboratory standards, are ±0.8‰ for δ 2 H and ±0.1‰ for δ 18 O.Water and effluent samples from the second campaign (2014 and 2013) were analyzed by the IT 2 laboratory (Waterloo, ON, Canada) on CRDS, Model L1102-i (Piccaro, Santa Clara, CA, USA) for both oxygen and hydrogen isotopes.The instrument was configured with a unique vaporization module that converts the liquid water sample to the vapor phase in a flash process at 140°C.The vapor was then delivered into the CRDS cavity for analysis.This process avoided any possible fractionation processes that may have occurred with other liquid/vapor transitions such as nebulizers.Typical precision for δ 18 O and δ 2 H are ±0.1‰ and ±0.6‰, respectively.All results were corrected and reported against the Vienna Standard Mean Ocean Water (VSMOW).All in-house standards were calibrated every six months by VSMOW, GISP and SLAP (The IAEA international standards).
All samples were analyzed in duplicates at both laboratories, with internal hidden standards for control.

Isotopic Composition of the Shafdan System
The results for the isotopic composition and concentrations of Cl and CBZ are given in Table 2.A typical correlation diagram of δ 2 H vs. δ 18 O for the Shafdan system (Figure 3a) and for the Israeli water system sources (Figure 3b) is given in Figure 3.Chemical analyses included measurement of salinity (Cl, EC) in all samples.In part of the samples, mainly during the first campaign, major ions (Ca, Mg, Na, K, HCO3, SO4, and B), nitrogen species (NO3, NH4, and NO2), Redox parameters (DO, ORP, Mn, and Fe) and other parameters (pH, temperature, DOC, alkalinity, UV and metal concentrations) were also measured.This was done for quality control and comparison purposes, and is not discussed further in this paper.Analyses were conducted by the central laboratory of Mekorot using standard methods.
Potential tracers for mixing ratio (MR) calculations, including Cl, CBZ and the stable isotopes of water molecule ( 18O and 2 H), were measured at all wells.CBZ concentrations were measured in the central laboratory of the Israeli Water Authority.Measurements were done using liquid chromatograph equipped with tandem triple quadruple mass spectrometer LC/MS/MS according to the EPA method 1694, which enable limit of quantification (LOQ) of 0.1 ng/ L [20].The oxygen and hydrogen isotopes (expressed as δ 18  O and δ 2 H values in ‰ vs. the VSMOW standard) were measured by two separated labs.Samples from the first campaign (2010-2011) were analyzed by the BRGM isotope laboratory on a Finnigan MAT 252 mass spectrometer following the gas-water equilibration technique with CO2 for oxygen isotopes [27] and with H2 for hydrogen isotopes [28].Analytical uncertainty, based on replicate analyses of international and laboratory standards, are ±0.8‰ for δ 2 H and ±0.1‰ for δ 18  O.Water and effluent samples from the second campaign (2014 and 2013) were analyzed by the IT 2 laboratory (Waterloo, ON, Canada) on CRDS, Model L1102-i (Piccaro, Santa Clara, CA, USA) for both oxygen and hydrogen isotopes.The instrument was configured with a unique vaporization module that converts the liquid water sample to the vapor phase in a flash process at 140°C.The vapor was then delivered into the CRDS cavity for analysis.This process avoided any possible fractionation processes that may have occurred with other liquid/vapor transitions such as nebulizers.Typical precision for δ 18  O and δ 2 H are ±0.1‰ and ±0.6‰, respectively.All results were corrected and reported against the Vienna Standard Mean Ocean Water (VSMOW).All in-house standards were calibrated every six months by VSMOW, GISP and SLAP (The IAEA international standards).
All samples were analyzed in duplicates at both laboratories, with internal hidden standards for control.

Isotopic Composition of the Shafdan System
The results for the isotopic composition and concentrations of Cl and CBZ are given in Table 2.A typical correlation diagram of δ 2 H vs. δ 18 O for the Shafdan system (Figure 3a) and for the Israeli water system sources (Figure 3b) is given in Figure 3.

vs. SMOW Notes
Dan

Analytical Procedures
Chemical analyses included measurement of salinity (Cl, EC) in all samples.In part of the samples, mainly during the first campaign, major ions (Ca, Mg, Na, K, HCO3, SO4, and B), nitrogen species (NO3, NH4, and NO2), Redox parameters (DO, ORP, Mn, and Fe) and other parameters (pH, temperature, DOC, alkalinity, UV and metal concentrations) were also measured.This was done for quality control and comparison purposes, and is not discussed further in this paper.Analyses were conducted by the central laboratory of Mekorot using standard methods.
Potential tracers for mixing ratio (MR) calculations, including Cl, CBZ and the stable isotopes of water molecule ( 18O and 2 H), were measured at all wells.CBZ concentrations were measured in the central laboratory of the Israeli Water Authority.Measurements were done using liquid chromatograph equipped with tandem triple quadruple mass spectrometer LC/MS/MS according to the EPA method 1694, which enable limit of quantification (LOQ) of 0.1 ng/ L [20].The oxygen and hydrogen isotopes (expressed as δ 18  O and δ 2 H values in ‰ vs. the VSMOW standard) were measured by two separated labs.Samples from the first campaign (2010-2011) were analyzed by the BRGM isotope laboratory on a Finnigan MAT 252 mass spectrometer following the gas-water equilibration technique with CO2 for oxygen isotopes [27] and with H2 for hydrogen isotopes [28].Analytical uncertainty, based on replicate analyses of international and laboratory standards, are ±0.8‰ for δ 2 H and ±0.1‰ for δ 18  O.Water and effluent samples from the second campaign (2014 and 2013) were analyzed by the IT 2 laboratory (Waterloo, ON, Canada) on CRDS, Model L1102-i (Piccaro, Santa Clara, CA, USA) for both oxygen and hydrogen isotopes.The instrument was configured with a unique vaporization module that converts the liquid water sample to the vapor phase in a flash process at 140°C.The vapor was then delivered into the CRDS cavity for analysis.This process avoided any possible fractionation processes that may have occurred with other liquid/vapor transitions such as nebulizers.Typical precision for δ 18  O and δ 2 H are ±0.1‰ and ±0.6‰, respectively.All results were corrected and reported against the Vienna Standard Mean Ocean Water (VSMOW).All in-house standards were calibrated every six months by VSMOW, GISP and SLAP (The IAEA international standards).
All samples were analyzed in duplicates at both laboratories, with internal hidden standards for control.

Isotopic Composition of the Shafdan System
The results for the isotopic composition and concentrations of Cl and CBZ are given in Table 2.A typical correlation diagram of δ 2 H vs. δ 18  O for the Shafdan system (Figure 3a) and for the Israeli water system sources (Figure 3b) is given in Figure 3.

Analytical Procedures
Chemical analyses included measurement of salinity (Cl, EC) in all samples.In part o samples, mainly during the first campaign, major ions (Ca, Mg, Na, K, HCO3, SO4, and B), nitr species (NO3, NH4, and NO2), Redox parameters (DO, ORP, Mn, and Fe) and other parameters temperature, DOC, alkalinity, UV and metal concentrations) were also measured.This was don quality control and comparison purposes, and is not discussed further in this paper.Analyses conducted by the central laboratory of Mekorot using standard methods.
Potential tracers for mixing ratio (MR) calculations, including Cl, CBZ and the stable isotop water molecule ( 18O and 2 H), were measured at all wells.CBZ concentrations were measured i central laboratory of the Israeli Water Authority.Measurements were done using li chromatograph equipped with tandem triple quadruple mass spectrometer LC/MS/MS accordin the EPA method 1694, which enable limit of quantification (LOQ) of 0.1 ng/ L [20].The oxygen hydrogen isotopes (expressed as δ 18  O and δ 2 H values in ‰ vs. the VSMOW standard) were meas by two separated labs.Samples from the first campaign (2010-2011) were analyzed by the BR isotope laboratory on a Finnigan MAT 252 mass spectrometer following the gas-water equilibr technique with CO2 for oxygen isotopes [27] and with H2 for hydrogen isotopes [28].Analy uncertainty, based on replicate analyses of international and laboratory standards, are ±0.8‰fo and ±0.1‰ for δ 18  O.Water and effluent samples from the second campaign (2014 and 2013) analyzed by the IT 2 laboratory (Waterloo, ON, Canada) on CRDS, Model L1102-i (Piccaro, S Clara, CA, USA) for both oxygen and hydrogen isotopes.The instrument was configured w unique vaporization module that converts the liquid water sample to the vapor phase in a process at 140°C.The vapor was then delivered into the CRDS cavity for analysis.This pro avoided any possible fractionation processes that may have occurred with other liquid/v transitions such as nebulizers.Typical precision for δ 18  O and δ 2 H are ±0.1‰ and ±0.6‰, respecti All results were corrected and reported against the Vienna Standard Mean Ocean Water (VSMO All in-house standards were calibrated every six months by VSMOW, GISP and SLAP (The I international standards).
All samples were analyzed in duplicates at both laboratories, with internal hidden stand for control.

Isotopic Composition of the Shafdan System
The results for the isotopic composition and concentrations of Cl and CBZ are given in Tab A typical correlation diagram of δ 2 H vs. δ 18  O for the Shafdan system (Figure 3a) and for the Is water system sources (Figure 3b) is given in Figure 3.  Examination of evaporation effects in the recharge ponds: Various samples taken from the recharge ponds, during different hours along the recharge process, were compared (Table 1).No significant differences in the δ 2 H and δ 18 O values were found.Thus, it can be concluded that the effect of evaporation during the recharge process on the fractionation of the stable water isotopes is negligible for the Shafdan case, and that mixing and dilution processes dictate the isotopic compositions in the aquifer.
A scattered plot of δ 2 H vs. δ 18 O, based on the results of the isotopes compositions in the secondary effluents and in the SAT recovery wells, show a significant linear correlation with a slope of 4.9 and R 2 = 0.93 (Figure 3a).This slope is significantly lower than the GMWL line slope of 8.In addition, Figure 3a clearly shows that the Shafdan system is dominated by two discrete end-members: the secondary recharged effluents on the heavier end, and the pristine aquifer water on the lighter end.All the isotope composition values of the recovery and observation wells were linearly scattered between the effluent and the Coastal Aquifer end-members (Figure 3a).Assuming no fractionation processes take place during the SAT process, and considering the conservative behavior of the water isotopes, this pattern represents a mixing line between the recharged effluents and the native water, where the isotope composition in each well is affected only by mixing of these The secondary effluents compose the heavier end-member, with δ 18 O of −1.5 ± 0.1 and δ 2 H of −4.9 ± 0.9 for 2010-2011 campaign, and δ 18 O of −1.4 ± 0.2 and δ 2 H of −1.2 ± 1.3 for 2014 campaign (Table 3).The variations for these average values are due to changes in dilution ratio between water from different sources in the NWC (Table 1).For example, relatively depleted δ 2 H and δ 18 O values were measured in the effluent on 21 February 2011 and on 25 February 2013.These values can be explained by the shutoff of the SOG and the Hadera desalination plant during these periods (Tables 1 and 2), accompanied by increasing contributions from the Mountain Aquifer wells in order to compensate for water shortage in the NWC.More details regarding the variations in water amounts between different water sources are given in Table 4 and in Section 3.3 below.
The Coastal Aquifer pristine water compose the lighter end-member, with δ 18 O of −4.6 ± 0.3 and δ 2 H of −18.6 ± 2.5 in water of salinity smaller than 200 mg-Cl/L, which is typical of the Shafdan area (Table 3).
All the isotope composition values of the recovery and observation wells were linearly scattered between the effluent and the Coastal Aquifer end-members (Figure 3a).Assuming no fractionation processes take place during the SAT process, and considering the conservative behavior of the water isotopes, this pattern represents a mixing line between the recharged effluents and the native water, where the isotope composition in each well is affected only by mixing of these two end-members.Accordingly, a mixing ratio (MR) in each well is directly correlated to its isotope composition, and can be calculated as follows: where δ represents the measured δ 18 O or δ 2 H in the well, δ NW represents the δ 18 O or δ 2 H of the pristine water (aquifer), and δ eff represents the δ 18 O or δ 2 H of the Shafdan effluents.It is important to note that δ can be replaced by concentration values of any conservative tracing marker that is valid for the Shafdan system, such as Cl or CBZ.

Isotopic Composition of the Main Water Sources and of the National Water Carrier
Expanding the δ 2 H vs. δ 18 O diagram of Figure 3a to include all the samples that were taken in this and other surveys and studies, reveals an interesting result.It clearly shows that all the sampled freshwater sources of Israel, and all the samples that were taken from different points along the NWC, are scattered along a regression line similar to the Shafdan system, with a slope of 4.5 and R 2 of 0.95 (Figure 3b).This time the end-members are composed of the Mediterranean Sea water, either preor post-desalination, and from the Mountain Aquifer water.Isotope data for the Coastal Aquifer, Mountain Aquifer, Mediterranean Sea, desalinated water and for the SOG were taken from previous studies [3,5,8,[29][30][31][32][33][34][35].
The heavy end-member is composed of the Mediterranean Sea water, with δ 18 O of 1.7 ± 0.2 and δ 2 H of 8.9 ± 1.7.Previous studies showed that water isotopes are not subjected to fractionation during the various treatments stages involved in the desalination processes [8].The Sea of Galilee water are also characterized by a relatively heavy signature, with δ 18 O of −0.4 ± 0.4 and δ 2 H of 0.9 ± 3.0.On the other end, we can find the Mountain Aquifer water that represent the lighter end member, with δ 18 O of −5.4 ± 0.4 and δ 2 H of −22.1 ± 2.8, just slightly lower than the Coastal Aquifer water with δ 18 O = −4.3± 0.4 and δ 2 H = −18 ± 2.4 for all salinity range (Table 3).
The slope of the regression line is 4.5, a little smaller but not significantly different from the slope of the Shafdan system in Figure 3a.Some studies have shown that slopes smaller than 8, which characterize the GMWL and EMMWL lines, are typical for mixing and evaporating systems (e.g., [29,[36][37][38]).In a specific study, a slope of 4.3 was measured for water systems under controlled evaporating conditions [36].Thus, the slope range of 4.5 to 4.9 that was calculated in this study suggests that evaporation had significant effect on the isotope composition of each one of the NWC water sources.This may not be surprising given the fact that at least three out of the four main freshwater sources are subjected to evaporation under similar climatic conditions.This includes the Mediterranean Sea and the derived desalinated water that is pumped relatively close to the shore line, the SOG open lake, and the recharged water of the Coastal Aquifer [32].A small fraction of the Mountain Aquifer recharge water is also subjected to evaporation when rain storms occur under warm climate conditions [37], but even without this component, the isotopic composition of this source does not interfere with the linear pattern.

Mixing Ratios in the National Water Carrier and in the Shafdan Plant
Mixing ratios between different water sources can be calculated based on the strong linearity between the four main freshwater sources (Figure 3b).The linear correlation enables us to run simple dilution (mixing) calculations between the different water sources in the NWC and in the Shafdan plant.That is, calculating the isotopic composition δ of a mixed system such as the NWC or the Shafdan effluents according to the volume ratio (f i ) and the isotopic composition (δ i ) of each source (Equation ( 2)): where δ represents the calculated δ 18 O or δ 2 H value ( Water 2017, 9, 73 5 of 17

Analytical Procedures
Chemical analyses included measurement of salinity (Cl, EC) in all samples.In part of the samples, mainly during the first campaign, major ions (Ca, Mg, Na, K, HCO3, SO4, and B), nitrogen species (NO3, NH4, and NO2), Redox parameters (DO, ORP, Mn, and Fe) and other parameters (pH, temperature, DOC, alkalinity, UV and metal concentrations) were also measured.This was done for quality control and comparison purposes, and is not discussed further in this paper.Analyses were conducted by the central laboratory of Mekorot using standard methods.
Potential tracers for mixing ratio (MR) calculations, including Cl, CBZ and the stable isotopes of water molecule ( 18 O and 2 H), were measured at all wells.CBZ concentrations were measured in the central laboratory of the Israeli Water Authority.Measurements were done using liquid chromatograph equipped with tandem triple quadruple mass spectrometer LC/MS/MS according to the EPA method 1694, which enable limit of quantification (LOQ) of 0.1 ng/ L [20].The oxygen and hydrogen isotopes (expressed as δ 18 O and δ 2 H values in ‰ vs. the VSMOW standard) were measured by two separated labs.Samples from the first campaign (2010-2011) were analyzed by the BRGM isotope laboratory on a Finnigan MAT 252 mass spectrometer following the gas-water equilibration technique with CO2 for oxygen isotopes [27] and with H2 for hydrogen isotopes [28].Analytical uncertainty, based on replicate analyses of international and laboratory standards, are ±0.8‰ for δ 2 H and ±0.1‰ for δ 18 O.Water and effluent samples from the second campaign (2014 and 2013) were analyzed by the IT 2 laboratory (Waterloo, ON, Canada) on CRDS, Model L1102-i (Piccaro, Santa Clara, CA, USA) for both oxygen and hydrogen isotopes.The instrument was configured with a unique vaporization module that converts the liquid water sample to the vapor phase in a flash process at 140°C.The vapor was then delivered into the CRDS cavity for analysis.This process avoided any possible fractionation processes that may have occurred with other liquid/vapor transitions such as nebulizers.Typical precision for δ 18 O and δ 2 H are ±0.1‰ and ±0.6‰, respectively.All results were corrected and reported against the Vienna Standard Mean Ocean Water (VSMOW).All in-house standards were calibrated every six months by VSMOW, GISP and SLAP (The IAEA international standards).
All samples were analyzed in duplicates at both laboratories, with internal hidden standards for control.

Isotopic Composition of the Shafdan System
The results for the isotopic composition and concentrations of Cl and CBZ are given in Table 2.A typical correlation diagram of δ 2 H vs. δ 18 O for the Shafdan system (Figure 3a) and for the Israeli water system sources (Figure 3b) is given in Figure 3.
) of the mixed system, and δ i represents the measured δ 18 O or δ 2 H value ( tical Procedures ical analyses included measurement of salinity (Cl, EC) in all samples.In part of the ainly during the first campaign, major ions (Ca, Mg, Na, K, HCO3, SO4, and B), nitrogen O3, NH4, and NO2), Redox parameters (DO, ORP, Mn, and Fe) and other parameters (pH, re, DOC, alkalinity, UV and metal concentrations) were also measured.This was done for ntrol and comparison purposes, and is not discussed further in this paper.Analyses were by the central laboratory of Mekorot using standard methods.tial tracers for mixing ratio (MR) calculations, including Cl, CBZ and the stable isotopes of lecule ( 18O and 2 H), were measured at all wells.CBZ concentrations were measured in the boratory of the Israeli Water Authority.Measurements were done using liquid raph equipped with tandem triple quadruple mass spectrometer LC/MS/MS according to ethod 1694, which enable limit of quantification (LOQ) of 0.1 ng/ L [20].The oxygen and isotopes (expressed as δ 18  O and δ 2 H values in ‰ vs. the VSMOW standard) were measured parated labs.Samples from the first campaign (2010-2011) were analyzed by the BRGM boratory on a Finnigan MAT 252 mass spectrometer following the gas-water equilibration with CO2 for oxygen isotopes [27] and with H2 for hydrogen isotopes [28].Analytical ty, based on replicate analyses of international and laboratory standards, are ±0.8‰ for δ 2 H for δ 18  O.Water and effluent samples from the second campaign (2014 and 2013) were by the IT 2 laboratory (Waterloo, ON, Canada) on CRDS, Model L1102-i (Piccaro, Santa , USA) for both oxygen and hydrogen isotopes.The instrument was configured with a porization module that converts the liquid water sample to the vapor phase in a flash t 140°C.The vapor was then delivered into the CRDS cavity for analysis.This process ny possible fractionation processes that may have occurred with other liquid/vapor s such as nebulizers.Typical precision for δ 18  O and δ 2 H are ±0.1‰ and ±0.6‰, respectively.s were corrected and reported against the Vienna Standard Mean Ocean Water (VSMOW).
se standards were calibrated every six months by VSMOW, GISP and SLAP (The IAEA nal standards).amples were analyzed in duplicates at both laboratories, with internal hidden standards l.

and Discussion
ic Composition of the Shafdan System esults for the isotopic composition and concentrations of Cl and CBZ are given in Table 2. correlation diagram of δ 2 H vs. δ 18 O for the Shafdan system (Figure 3a) and for the Israeli tem sources (Figure 3b) is given in Figure 3.
) of the fresh water source (Coastal Aquifer, Mountain Aquifers, SOG or desalinated water).Assumptions for using the mixing model to calculate the isotope composition of the NWC includes no fractionation and instantaneous, homogenous, mixing between the water sources in the line.Additional assumptions for calculating the isotope composition in the Shafdan effluents includes no fractionation and evaporation throughout the usage of the water and the treatment process; no external, uncounted water source; and instantaneous, homogenous, mixing between NWC and private wells in the local systems, and between different sewage sources from the different municipalities in the Shafdan MBTP.
Freshwater quantities for each main source for the calculation of the isotope composition in the National Water Carrier were taken from the Mekorot daily database.Mixing calculation for the NWC was conducted by a water supply operative program (code) that was developed and is operated by Mekorot, as part of the NWC operating system.Freshwater quantities for private wells (Coastal and Mountain aquifers) owned by the municipalities were taken from the Water Authority's monthly database.In order to calculate the dilution ratios between different types of water sources in the Shafdan, we assumed that the municipal consumption is first provided by the private wells (from water cost considerations), and the residual is purchased from the NWC.Thus, the isotope composition of the Shafdan effluents (δ shafdan ) was calculated from the volume ratios between the private wells and the NWC (f PW and f NWC , respectively), and from the isotopic compositions of these two sources (δ PW and δ NWC , respectively), as described in Equation (3).
Purchased volumes of NWC water by the municipalities were obtained from the accounting system of Mekorot (on a monthly base).The isotopic composition of each water source that was used for the mixing calculation is detailed in Table 3. Water volumes data for the calculations are given in Table 4.
Figure 4 presents the correlations between measured and calculated δ 18 O and δ 2 H values in the National Water Carrier and in the Shafdan systems.The Shafdan plant represents the mixing of different water from different sources along the water system chain, from freshwater down to sewage and treated effluent.Effluent samples from the Shafdan were taken during specific dates that represent different operation regimes of the NWC, as detailed in Table 1.Mixing calculations according to Equations ( 2) and (3) were conducted for these dates given the assumptions of no fractionations and no external (uncounted sources) effects on the isotope composition.Most of the calculated isotope compositions agree fairly well with the observed values as can be seen in Figure 4. High deviations of up to 1.5 n purposes, and is not discussed further in this paper.Analyses were atory of Mekorot using standard methods.ng ratio (MR) calculations, including Cl, CBZ and the stable isotopes of were measured at all wells.CBZ concentrations were measured in the Israeli Water Authority.Measurements were done using liquid h tandem triple quadruple mass spectrometer LC/MS/MS according to enable limit of quantification (LOQ) of 0.1 ng/ L [20].The oxygen and as δ 18 O and δ 2 H values in ‰ vs. the VSMOW standard) were measured les from the first campaign (2010-2011) were analyzed by the BRGM an MAT 252 mass spectrometer following the gas-water equilibration en isotopes [27] and with H2 for hydrogen isotopes [28].Analytical e analyses of international and laboratory standards, are ±0.8‰ for δ 2 H nd effluent samples from the second campaign (2014 and 2013) were ry (Waterloo, ON, Canada) on CRDS, Model L1102-i (Piccaro, Santa ygen and hydrogen isotopes.The instrument was configured with a that converts the liquid water sample to the vapor phase in a flash was then delivered into the CRDS cavity for analysis.This process nation processes that may have occurred with other liquid/vapor .Typical precision for δ 18 O and δ 2 H are ±0.1‰ and ±0.6‰, respectively. reported against the Vienna Standard Mean Ocean Water (VSMOW).calibrated every six months by VSMOW, GISP and SLAP (The IAEA ed in duplicates at both laboratories, with internal hidden standards Shafdan System ic composition and concentrations of Cl and CBZ are given in Table 2. of δ 2 H vs. δ 18 O for the Shafdan system (Figure 3a) and for the Israeli 3b) is given in Figure 3. comparison purposes, and is not discussed further in this paper.Analyses were ntral laboratory of Mekorot using standard methods.rs for mixing ratio (MR) calculations, including Cl, CBZ and the stable isotopes of and 2 H), were measured at all wells.CBZ concentrations were measured in the of the Israeli Water Authority.Measurements were done using liquid ipped with tandem triple quadruple mass spectrometer LC/MS/MS according to 94, which enable limit of quantification (LOQ) of 0.1 ng/ L [20].The oxygen and expressed as δ 18 O and δ 2 H values in ‰ vs. the VSMOW standard) were measured abs.Samples from the first campaign (2010-2011) were analyzed by the BRGM on a Finnigan MAT 252 mass spectrometer following the gas-water equilibration 2 for oxygen isotopes [27] and with H2 for hydrogen isotopes [28].Analytical on replicate analyses of international and laboratory standards, are ±0.8‰ for δ 2 H . Water and effluent samples from the second campaign (2014 and 2013) were 2 laboratory (Waterloo, ON, Canada) on CRDS, Model L1102-i (Piccaro, Santa r both oxygen and hydrogen isotopes.The instrument was configured with a n module that converts the liquid water sample to the vapor phase in a flash he vapor was then delivered into the CRDS cavity for analysis.This process ble fractionation processes that may have occurred with other liquid/vapor nebulizers.Typical precision for δ 18 O and δ 2 H are ±0.1‰ and ±0.6‰, respectively.rected and reported against the Vienna Standard Mean Ocean Water (VSMOW).ards were calibrated every six months by VSMOW, GISP and SLAP (The IAEA ards).ere analyzed in duplicates at both laboratories, with internal hidden standards ussion ition of the Shafdan System the isotopic composition and concentrations of Cl and CBZ are given in Table 2. n diagram of δ 2 H vs. δ 18 O for the Shafdan system (Figure 3a) and for the Israeli es (Figure 3b) is given in Figure 3.
for the δ 18 O and δ 2 H, respectively, were found only in the first sample taken on 14 September 2010.This deviation can be explained by the difficulty to assess the effects of the desalinated water on the NWC when only Ashkelon and Palmahim (partially) plants were working.For the rest of the samples, the deviations varied between 0 samples, mainly during the first campaign, major ions (Ca, Mg, Na, K, HCO3, SO4, and B), nitrogen species (NO3, NH4, and NO2), Redox parameters (DO, ORP, Mn, and Fe) and other parameters (pH, temperature, DOC, alkalinity, UV and metal concentrations) were also measured.This was done for quality control and comparison purposes, and is not discussed further in this paper.Analyses were conducted by the central laboratory of Mekorot using standard methods.
Potential tracers for mixing ratio (MR) calculations, including Cl, CBZ and the stable isotopes of water molecule ( 18O and 2 H), were measured at all wells.CBZ concentrations were measured in the central laboratory of the Israeli Water Authority.Measurements were done using liquid chromatograph equipped with tandem triple quadruple mass spectrometer LC/MS/MS according to the EPA method 1694, which enable limit of quantification (LOQ) of 0.1 ng/ L [20].The oxygen and hydrogen isotopes (expressed as δ 18  O and δ 2 H values in ‰ vs. the VSMOW standard) were measured by two separated labs.Samples from the first campaign (2010-2011) were analyzed by the BRGM isotope laboratory on a Finnigan MAT 252 mass spectrometer following the gas-water equilibration technique with CO2 for oxygen isotopes [27] and with H2 for hydrogen isotopes [28].Analytical uncertainty, based on replicate analyses of international and laboratory standards, are ±0.8‰ for δ 2 H and ±0.1‰ for δ 18  O.Water and effluent samples from the second campaign (2014 and 2013) were analyzed by the IT 2 laboratory (Waterloo, ON, Canada) on CRDS, Model L1102-i (Piccaro, Santa Clara, CA, USA) for both oxygen and hydrogen isotopes.The instrument was configured with a unique vaporization module that converts the liquid water sample to the vapor phase in a flash process at 140°C.The vapor was then delivered into the CRDS cavity for analysis.This process avoided any possible fractionation processes that may have occurred with other liquid/vapor transitions such as nebulizers.Typical precision for δ 18  O and δ 2 H are ±0.1‰ and ±0.6‰, respectively.All results were corrected and reported against the Vienna Standard Mean Ocean Water (VSMOW).All in-house standards were calibrated every six months by VSMOW, GISP and SLAP (The IAEA international standards).
All samples were analyzed in duplicates at both laboratories, with internal hidden standards for control.

Isotopic Composition of the Shafdan System
The results for the isotopic composition and concentrations of Cl and CBZ are given in Table 2.A typical correlation diagram of δ 2 H vs. δ 18 O for the Shafdan system (Figure 3a) and for the Israeli water system sources (Figure 3b) is given in Figure 3. and 0.7 samples, mainly during the first campaign, major ions (Ca, Mg, Na, K, HCO3, SO4, and B), nitrogen species (NO3, NH4, and NO2), Redox parameters (DO, ORP, Mn, and Fe) and other parameters (pH, temperature, DOC, alkalinity, UV and metal concentrations) were also measured.This was done for quality control and comparison purposes, and is not discussed further in this paper.Analyses were conducted by the central laboratory of Mekorot using standard methods.
Potential tracers for mixing ratio (MR) calculations, including Cl, CBZ and the stable isotopes of water molecule ( 18O and 2 H), were measured at all wells.CBZ concentrations were measured in the central laboratory of the Israeli Water Authority.Measurements were done using liquid chromatograph equipped with tandem triple quadruple mass spectrometer LC/MS/MS according to the EPA method 1694, which enable limit of quantification (LOQ) of 0.1 ng/ L [20].The oxygen and hydrogen isotopes (expressed as δ 18  O and δ 2 H values in ‰ vs. the VSMOW standard) were measured by two separated labs.Samples from the first campaign (2010-2011) were analyzed by the BRGM isotope laboratory on a Finnigan MAT 252 mass spectrometer following the gas-water equilibration technique with CO2 for oxygen isotopes [27] and with H2 for hydrogen isotopes [28].Analytical uncertainty, based on replicate analyses of international and laboratory standards, are ±0.8‰ for δ 2 H and ±0.1‰ for δ 18  O.Water and effluent samples from the second campaign (2014 and 2013) were analyzed by the IT 2 laboratory (Waterloo, ON, Canada) on CRDS, Model L1102-i (Piccaro, Santa Clara, CA, USA) for both oxygen and hydrogen isotopes.The instrument was configured with a unique vaporization module that converts the liquid water sample to the vapor phase in a flash process at 140°C.The vapor was then delivered into the CRDS cavity for analysis.This process avoided any possible fractionation processes that may have occurred with other liquid/vapor transitions such as nebulizers.Typical precision for δ 18  O and δ 2 H are ±0.1‰ and ±0.6‰, respectively.All results were corrected and reported against the Vienna Standard Mean Ocean Water (VSMOW).All in-house standards were calibrated every six months by VSMOW, GISP and SLAP (The IAEA international standards).
All samples were analyzed in duplicates at both laboratories, with internal hidden standards for control.

Isotopic Composition of the Shafdan System
The results for the isotopic composition and concentrations of Cl and CBZ are given in Table 2.A typical correlation diagram of δ 2 H vs. δ 18 O for the Shafdan system (Figure 3a) and for the Israeli water system sources (Figure 3b) is given in Figure 3.
for the δ 18 O, and between 1 asurement of salinity (Cl, EC) in all samples.In part of the aign, major ions (Ca, Mg, Na, K, HCO3, SO4, and B), nitrogen parameters (DO, ORP, Mn, and Fe) and other parameters (pH, metal concentrations) were also measured.This was done for oses, and is not discussed further in this paper.Analyses were Mekorot using standard methods.(MR) calculations, including Cl, CBZ and the stable isotopes of easured at all wells.CBZ concentrations were measured in the Water Authority.Measurements were done using liquid triple quadruple mass spectrometer LC/MS/MS according to limit of quantification (LOQ) of 0.1 ng/ L [20].The oxygen and and δ 2 H values in ‰ vs. the VSMOW standard) were measured the first campaign (2010-2011) were analyzed by the BRGM T 252 mass spectrometer following the gas-water equilibration pes [27] and with H2 for hydrogen isotopes [28].Analytical es of international and laboratory standards, are ±0.8‰ for δ 2 H ent samples from the second campaign (2014 and 2013) were erloo, ON, Canada) on CRDS, Model L1102-i (Piccaro, Santa d hydrogen isotopes.The instrument was configured with a nverts the liquid water sample to the vapor phase in a flash en delivered into the CRDS cavity for analysis.This process processes that may have occurred with other liquid/vapor l precision for δ 18  O and δ 2 H are ±0.1‰ and ±0.6‰, respectively.d against the Vienna Standard Mean Ocean Water (VSMOW).ed every six months by VSMOW, GISP and SLAP (The IAEA uplicates at both laboratories, with internal hidden standards System osition and concentrations of Cl and CBZ are given in Table 2. vs. δ 18  O for the Shafdan system (Figure 3a) and for the Israeli ven in Figure 3. cluded measurement of salinity (Cl, EC) in all samples.In part of the first campaign, major ions (Ca, Mg, Na, K, HCO3, SO4, and B), nitrogen 2), Redox parameters (DO, ORP, Mn, and Fe) and other parameters (pH, ty, UV and metal concentrations) were also measured.This was done for rison purposes, and is not discussed further in this paper.Analyses were oratory of Mekorot using standard methods.ixing ratio (MR) calculations, including Cl, CBZ and the stable isotopes of ), were measured at all wells.CBZ concentrations were measured in the Israeli Water Authority.Measurements were done using liquid ith tandem triple quadruple mass spectrometer LC/MS/MS according to ch enable limit of quantification (LOQ) of 0.1 ng/ L [20].The oxygen and ed as δ 18  O and δ 2 H values in ‰ vs. the VSMOW standard) were measured ples from the first campaign (2010-2011) were analyzed by the BRGM nigan MAT 252 mass spectrometer following the gas-water equilibration ygen isotopes [27] and with H2 for hydrogen isotopes [28].Analytical cate analyses of international and laboratory standards, are ±0.8‰ for δ 2 H r and effluent samples from the second campaign (2014 and 2013) were tory (Waterloo, ON, Canada) on CRDS, Model L1102-i (Piccaro, Santa oxygen and hydrogen isotopes.The instrument was configured with a le that converts the liquid water sample to the vapor phase in a flash or was then delivered into the CRDS cavity for analysis.This process tionation processes that may have occurred with other liquid/vapor rs.Typical precision for δ 18  O and δ 2 H are ±0.1‰ and ±0.6‰, respectively.nd reported against the Vienna Standard Mean Ocean Water (VSMOW).re calibrated every six months by VSMOW, GISP and SLAP (The IAEA lyzed in duplicates at both laboratories, with internal hidden standards he Shafdan System topic composition and concentrations of Cl and CBZ are given in Table 2. am of δ 2 H vs. δ 18 O for the Shafdan system (Figure 3a) and for the Israeli re 3b) is given in Figure 3.
for the δ 2 H.In the winter season, some limited effect of uncounted drainage runoff during stormy days can also explain part of the deviations.Nevertheless, the good overall agreement between calculated and measured values indicates the conservative nature of O and H stable isotopes in the water-effluent system, and, consequently, the ability to reconstruct or to predict the isotope composition of the recharged effluents.High deviations of up to 1.5‰ and 7.5‰ for the δ 18 O and δ 2 H, respectively, were found only in the first sample taken on 14 September 2010.This deviation can be explained by the difficulty to assess the effects of the desalinated water on the NWC when only Ashkelon and Palmahim (partially) plants were working.For the rest of the samples, the deviations varied between 0‰ and 0.7‰ for the δ 18 O, and between 1‰ and 3.7‰ for the δ 2 H.In the winter season, some limited effect of uncounted drainage runoff during stormy days can also explain part of the deviations.Nevertheless, the good overall agreement between calculated and measured values indicates the conservative nature of O and H stable isotopes in the water-effluent system, and, consequently, the ability to reconstruct or to predict the isotope composition of the recharged effluents.The sampling point for the NWC is located at the entrance to Tel Aviv.Samples for the Shafdan effluents were taken at the outlet station (PS-6) that pumps the effluents to the recharge ponds.

Mixing Ratios in the Aquifer (SAT Basin)
The isotopic composition of the Shafdan effluent is directly affected by the mixing of different amounts of water with different isotopic compositions in the Israeli National Water Carrier and in the municipal sewage systems.The most dramatic effect was due to the introduction of massive amounts of desalinated water during 2010 with the beginning of the operations of the Hadera plant (145 MCM/year), and the addition of the Soreq plant (150 MCM/year) in 2013.The introduction of the desalinated water with its relatively heavy isotopic signature induced a shift in the isotopic composition of the Shafdan effluents, and led to segregation from the Coastal Aquifer pristine water The sampling point for the NWC is located at the entrance to Tel Aviv.Samples for the Shafdan effluents were taken at the outlet station (PS-6) that pumps the effluents to the recharge ponds.

Mixing Ratios in the Aquifer (SAT Basin)
The isotopic composition of the Shafdan effluent is directly affected by the mixing of different amounts of water with different isotopic compositions in the Israeli National Water Carrier and in the municipal sewage systems.The most dramatic effect was due to the introduction of massive amounts of desalinated water during 2010 with the beginning of the operations of the Hadera plant (145 MCM/year), and the addition of the Soreq plant (150 MCM/year) in 2013.The introduction of the desalinated water with its relatively heavy isotopic signature induced a shift in the isotopic composition of the Shafdan effluents, and led to segregation from the Coastal Aquifer pristine water composition.The differences between these two end-members ("new" effluent and the Coastal Aquifer) made it practical to conduct reliable mixing ratio calculations using Equation (1).
Mixing ratio calculations for recovery and observation wells are presented in Figures 5 and 6 as a function of the distance of the wells from the recharge ponds.Calculations of MRs were done independently four times for each well, using its measured δ 18 O and δ 2 H values, CBZ and chloride concentrations.Figure 5 represents mixing ratio calculations for each parameter according to the 2010-2011 campaign results.Figure 6  composition.The differences between these two end-members ("new" effluent and the Coastal Aquifer) made it practical to conduct reliable mixing ratio calculations using Equation (1).
Mixing ratio calculations for recovery and observation wells are presented in Figures 5 and 6 as a function of the distance of the wells from the recharge ponds.Calculations of MRs were done independently four times for each well, using its measured δ 18 O and δ 2 H values, CBZ and chloride concentrations.Figure 5 represents mixing ratio calculations for each parameter according to the 2010-2011 campaign results.Figure 6 represents the changes in the mixing ratio results between 2010-2011 and 2014, where MR is calculated from δ 2 H values and from CBZ concentrations.Mixing ratio calculations for the 2010-2011 campaign showed significant differences between CBZ and Cl results compared to δ 18 O and δ 2 H results (Figure 5).CBZ and Cl concentrations led to higher MR values, which varied from 100% to 80% of effluents for wells in the range of 0 to 1000 m away from the recharge ponds, and from 60% to 5% for wells located 1000 to 3000 m from the ponds.Local differences between CBZ and Cl MRs are mainly due to inaccurate Cl-MR calculations under dilute (low MR) conditions.Mixing ratios based on δ 18 O and δ 2 H analyses yield smaller MR values, which varied between 20% and 90% of effluents for wells located 0 to 1000 m from the recharge ponds, and from 35% to 0% for wells located 1000 to 3000 m from the ponds.On average, mixing ratios calculations based on δ 18 O and δ 2 H values reached about 50% of the mixing ratios that were calculated from CBZ concentrations, which represent equilibrium with the SAT operation regime.Therefore, one can conclude replacement of about 50% of the previous isotopic signature with the "new" isotopic signature of the effluents, which occurred over one (since the operation of Hadera plant) to five (since the operation of Ashkelon plant) years.
As mentioned before in Section 2.1, the 2014 campaign was conducted in order to verify the conclusions from the 2010-2011 campaign.In particular, that the introduction of the desalinated water, via the National Water Carrier to the aquifer is expected to increase mixing ratio of "new" effluents in the recovery wells [25].This conclusion is indeed confirmed as δ 2 H-MR's results increased from ~50% to ~75% relative to CBZ-MR's results in the main SAT-active area (100% effluents based on CBZ) of the aquifer, as shown in Figure 6.Assuming negligible effect of the desalinated water until 2010 (due to weak connection of the Ashkelon plant to the Dan Region water system, and due to low contribution from the Palmahim plant until 2013), we conclude that the Mixing ratio calculations for the 2010-2011 campaign showed significant differences between CBZ and Cl results compared to δ 18 O and δ 2 H results (Figure 5).CBZ and Cl concentrations led to higher MR values, which varied from 100% to 80% of effluents for wells in the range of 0 to 1000 m away from the recharge ponds, and from 60% to 5% for wells located 1000 to 3000 m from the ponds.Local differences between CBZ and Cl MRs are mainly due to inaccurate Cl-MR calculations under dilute (low MR) conditions.Mixing ratios based on δ 18 O and δ 2 H analyses yield smaller MR values, which varied between 20% and 90% of effluents for wells located 0 to 1000 m from the recharge ponds, and from 35% to 0% for wells located 1000 to 3000 m from the ponds.On average, mixing ratios calculations based on δ 18 O and δ 2 H values reached about 50% of the mixing ratios that were calculated from CBZ concentrations, which represent equilibrium with the SAT operation regime.Therefore, one can conclude replacement of about 50% of the previous isotopic signature with the "new" isotopic signature of the effluents, which occurred over one (since the operation of Hadera plant) to five (since the operation of Ashkelon plant) years.
As mentioned before in Section 2.1, the 2014 campaign was conducted in order to verify the conclusions from the 2010-2011 campaign.In particular, that the introduction of the desalinated water, via the National Water Carrier to the aquifer is expected to increase mixing ratio of "new" effluents in Water 2017, 9, 73 13 of 16 the recovery wells [25].This conclusion is indeed confirmed as δ 2 H-MR's results increased from ~50% to ~75% relative to CBZ-MR's results in the main SAT-active area (100% effluents based on CBZ) of the aquifer, as shown in Figure 6.Assuming negligible effect of the desalinated water until 2010 (due to weak connection of the Ashkelon plant to the Dan Region water system, and due to low contribution from the Palmahim plant until 2013), we conclude that the isotope signature of the desalinated water almost reached steady-state with the Shafdan SAT operation regime after about four years (since the operation of Hadera plant).This process of "replacing" the previous water body with the new effluents affected by the desalinated water is expected to continue in the next few years until equilibrium with the operation regime is reached.Accordingly, the stable water isotopes could be used as a reliable and accurate tracer to track the transport and spreading of the effluent in the aquifer.
Water 2017, 9, 73 14 of 17 isotope signature of the desalinated water almost reached steady-state with the Shafdan SAT operation regime after about four years (since the operation of Hadera plant).This process of "replacing" the previous water body with the new effluents affected by the desalinated water is expected to continue in the next few years until equilibrium with the operation regime is reached.Accordingly, the stable water isotopes could be used as a reliable and accurate tracer to track the transport and spreading of the effluent in the aquifer.

Summary and Conclusions
The present work examined the feasibility of using the stable water isotopes 2 H and 18 O as tracers for tracking different freshwater and effluent sources in the Israeli National Water Carrier (NWC), in the Dan Region sewage-effluent system (the Shafdan plant), and in the aquifer during the subsequent SAT process.Two sampling campaigns were conducted through 2010-2011 and 2014 in specific points along the NWC, in the Shafdan effluents, and in a set of recovery and observation wells.Each campaign included simultaneous measurements of the water isotopes, as well as carbamazepine (CBZ) and chloride concentrations (Cl) as referent tracers for the Shafdan-SAT system.
The results of this work show, for the first time, the tremendous effect of the desalinated water on the isotopic composition of the mixed water in the NWC, in the Shafdan facility and in the SAT basins.This study also demonstrates for the first time on the linear isotopic composition relationship between the four main freshwater sources of Israel (and their mixed products), and the moderate slope regression line compared to the slopes of the meteoric water lines.These results enabled the use of the water isotopes as a conservative tracer throughout the completely manmade water cycle, starting from the freshwater sources, and all the way to the SAT system and the recovery wells.
The distinct difference in isotopic composition between the various freshwater sources, along with the data regarding volume ratios between these sources in the centralized water system, enable us to assess the isotopic composition of their mixed products in the NWC and in the Shafdan, based on simple dilution equations.The progressive enrichment of the Shafdan effluents in heavy isotopes,

Summary and Conclusions
The present work examined the feasibility of using the stable water isotopes 2 H and 18 O as tracers for tracking different freshwater and effluent sources in the Israeli National Water Carrier (NWC), in the Dan Region sewage-effluent system (the Shafdan plant), and in the aquifer during the subsequent SAT process.Two sampling campaigns were conducted through 2010-2011 and 2014 in specific points along the NWC, in the Shafdan effluents, and in a set of recovery and observation wells.Each campaign included simultaneous measurements of the water isotopes, as well as carbamazepine (CBZ) and chloride concentrations (Cl) as referent tracers for the Shafdan-SAT system.
The results of this work show, for the first time, the tremendous effect of the desalinated water on the isotopic composition of the mixed water in the NWC, in the Shafdan facility and in the SAT basins.This study also demonstrates for the first time on the linear isotopic composition relationship between the four main freshwater sources of Israel (and their mixed products), and the moderate slope regression line compared to the slopes of the meteoric water lines.These results enabled the use of the water isotopes as a conservative tracer throughout the completely manmade water cycle, starting from the freshwater sources, and all the way to the SAT system and the recovery wells.
The distinct difference in isotopic composition between the various freshwater sources, along with the data regarding volume ratios between these sources in the centralized water system, enable us to assess the isotopic composition of their mixed products in the NWC and in the Shafdan, based on simple dilution equations.The progressive enrichment of the Shafdan effluents in heavy isotopes, Water 2017, 9, 73 14 of 16 due to the massive amounts of desalinated water added to the system during the last decade, enables us to run quantitative mixing ratio calculations and to assess the spatial distribution of the effluents in the aquifer.In this work it was clearly shown that the isotopic composition of the recovery wells follow the same pattern of the CBZ and Cl concentrations; that is, reduction in calculated effluent rates with increasing distance from the recharge ponds.We could also demonstrate that the "new" effluents that are derived from desalinated water are now in the middle of a breakthrough process, replacing the "old" effluents in the aquifer.
The conclusions of this work are relevant and applicable for the Israeli water-sewage-effluent system, as well as for other places around the world.The dominance of the desalinated water in the NWC, together with the known amounts of water from other sources, assures stable and predictable isotopic trends in the Shafdan effluents and in the aquifer.The use of water isotopes for managing aquifer recharge (MAR) and for tracing the spreading of the recharged water in the aquifer can be applied worldwide.In places where desalinated or evaporated lake water bodies are recharged to the aquifers, this tool is potentially more accurate and reliable compared traditional tracers such as Cl ions.It can also be applied for tracing mixing processes in water systems in places where two or more water sources are in use.
Additional study is still needed to achieve a better understanding of the nature and mechanism of the linear correlation between the main freshwater sources of the Israeli water system, and their mixing in the NWC and in the Shafdan.Further, routine sampling and measurements in the Shafdan are highly recommended in order to verify the prediction of further isotope enrichment, and in order to trace the effluent spreading in the aquifer.

Figure 1 .
Figure 1.Cross section of the Coastal Aquifer and the area of the Soreq recharge basin (after [24]).

Figure 1 .
Figure 1.Cross section of the Coastal Aquifer and the area of the Soreq recharge basin (after [24]).

Figure 2 .
Figure 2. Experiment setup and the sampling program implemented in the study: (a) Schematic layout of the Israeli National Water Carrier with the locations of Hadera and Palmahim desalination plants (DSPs) and the Shafdan plant.Blue triangles represent the freshwater sampling points; (b) Enlarged map of the Shafdan area and the Soreq recharge basin.Red triangles represent effluents sampling points.Black dots represent recovery and observation wells that were sampled.

Figure 2 .
Figure 2. Experiment setup and the sampling program implemented in the study: (a) Schematic layout of the Israeli National Water Carrier with the locations of Hadera and Palmahim desalination plants (DSPs) and the Shafdan plant.Blue triangles represent the freshwater sampling points; (b) Enlarged map of the Shafdan area and the Soreq recharge basin.Red triangles represent effluents sampling points.Black dots represent recovery and observation wells that were sampled.

Figure 3 .
Figure 3. Water molecule isotopic compositions: (a) the Shafdan system, including the recharged effluents (PS-6 or at the ponds) and the recovery wells (RW); and (b) the freshwater sources, in the National Water Carrier (NWC) and in the Shafdan system.Isotope data for the Coastal Aquifer, Mountain Aquifer, Mediterranean Sea, desalinated water (DSP), and for the Sea of Galilee (SOG) were taken from previous works [3,5,8,29-35].

Figure 3 .
Figure 3. Water molecule isotopic compositions: (a) the Shafdan system, including the recharged effluents (PS-6 or at the ponds) and the recovery wells (RW); and (b) the freshwater sources, in the National Water Carrier (NWC) and in the Shafdan system.Isotope data for the Coastal Aquifer, Mountain Aquifer, Mediterranean Sea, desalinated water (DSP), and for the Sea of Galilee (SOG) were taken from previous works [3,5,8,29-35].

Figure 4 .
Figure 4. Fresh water mixing assessment in the NWC and in the Shafdan for: δ 18 O (a); and δ 2 H (b).

Figure 4 .
Figure 4. Fresh water mixing assessment in the NWC and in the Shafdan for: δ 18 O (a); and δ 2 H (b).The sampling point for the NWC is located at the entrance to Tel Aviv.Samples for the Shafdan effluents were taken at the outlet station (PS-6) that pumps the effluents to the recharge ponds.
represents the changes in the mixing ratio results between 2010-2011 and 2014, where MR is calculated from δ 2 H values and from CBZ concentrations.Water 2017, 9, 73 13 of 17

Figure 5 .
Figure 5. Mixing ratios (MR) in recovery and observation wells vs. distance from the recharge ponds.MRs were calculated from Cl, CBZ, δ 18 O and δ 2 H results of the 2010-2011 campaign.

Figure 5 .
Figure 5. Mixing ratios (MR) in recovery and observation wells vs. distance from the recharge ponds.MRs were calculated from Cl, CBZ, δ 18 O and δ 2 H results of the 2010-2011 campaign.

Figure 6 .
Figure 6.Mixing Ratios (MR) in recovery and observation wells vs. distance from the recharge ponds.MRs were calculated from CBZ results in the 2014 campaign (represent also the 2010-2011 campaign assuming steady-state conditions), and from δ 2 H in the 2010-2011 and 2014 campaigns (represent also MR-δ 18 O results).

Figure 6 .
Figure 6.Mixing Ratios (MR) in recovery and observation wells vs. distance from the recharge ponds.MRs were calculated from CBZ results in the 2014 campaign (represent also the 2010-2011 campaign assuming steady-state conditions), and from δ 2 H in the 2010-2011 and 2014 campaigns (represent also MR-δ 18 O results).

Table 1 .
General description of the sub-experiments conducted during the campaigns.
The effect of the Sea of Galilee and the desalinated water on the isotopic composition of the Shafdan effluents (see Section 3.3) 2010-2011, 2013 and 2014 (1) On 21 February 2011 and on 7 February 2013 effluents were sampled from the Shafdan during a period when no water was supplied from the lake to the NWC.(2) On 25 February 2014 effluents were sampled from the Shafdan during a period when no water was supplied from the Hadera DSP and from the SOG to the NWC.

Table 2 .
Cl, CBZ and isotopic compositions of freshwater, effluent and recovered effluents in the study.

Table 3 .
Cl, CBZ and isotopic composition average values of different types of water sources.

Table 4 .
Water volumes from the different freshwater sources that were used for the dilution (mixing) calculations.Notes: 1 Daily amounts; 2 Estimated daily amounts, based on monthly data.