water

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

Ido Negev 1,*, Joseph Guttman 1 and Wolfram Kloppmann 2 1 Mekorot, National Water Company, Tel Aviv 6713402, Israel; [email protected] 2 BRGM, French Geological Survey, Orleans, France; [email protected] * Correspondence: [email protected]; Tel.: +972-3-623-0653

Academic Editor: Pieter J. Stuyfzand Received: 31 October 2016; Accepted: 12 January 2017; Published: 24 January 2017

Abstract: 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.

Keywords: stable water isotopes; SAT; desalination; effluent

1. 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 18O/16O and 2H/1H 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 [1–3]. 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., [4–7]). 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.

Water 2017, 9, 73; doi:10.3390/w9020073 www.mdpi.com/journal/water Water 2017, 9, 73 2 of 16

Collection and analysis of available δ18O and δ2H values published in various studies indicate that each of the abovementioned natural water sources has a typical isotope composition, as will be further discussed in the results section. During the last decade, an important source of desalinated water has been added to the National Water Carrier as five new desalination plants went into action: Ashkelon (capacity of 120 million cubic meter per year [CM/year], 2005), Palmahim (45 MCM/year, 2007, and 90 MCM/year since 2013), Hadera (145 MCM/year, 2009), Soreq (150 MCM/year, 2013) and Ashdod (100 MCM/year, 2015). Thus, since 2015 desalinated water has contributed more than 60% of the water in the NWC, and has nearly reached 100% in the Dan Region during significant periods of the year. Previous studies have shown that the isotopic composition δ18O and δ2H of the raw, Mediterranean Sea water is preserved during the desalination process, and hence also characterizes the desalinated product [6–8]. The Dan Region Wastewater Reclamation Plant (Shafdan plant), established during the 1970s, provides a centralized, high quality solution for the sewage of the most populated area in Israel. The plant collects the sewage of the Tel-Aviv Metropolitan area (Dan Region) and neighboring municipalities, treats it, and afterwards recharges it into a defined coastal aquifer section for a complementary Soil Aquifer Treatment (SAT). In this way, the Shafdan plant treats about 135 MCM/year of raw sewage from seven municipalities, industrial areas, and approximately 1.5 million inhabitants. The sewage is treated to a level of secondary effluents using a Mechanical Biological Treatment Plant (MBTP), prior to infiltration in the SAT ponds. The recharge and the SAT process takes place in the coastal Quaternary sandstone aquifer (the Coastal Aquifer), one of the major freshwater sources of Israel. During flow process of the secondary effluent through the vadose zone and the aquifer, most of the biodegradable organic matter, suspended solids, bacteria, viruses, phosphorus, heavy metals and other ions are removed from the effluents by a combination of geochemical, physical, and biological processes (e.g., [9–17]). Retention time in the aquifer (saturated zone), estimated using a flow-transport numerical model developed and calibrated by Mekorot, ranges between 0.5 and 60 months, and is strongly dependent on the spatial flow regime and on the distances between the wells and their associated recharge ponds [17]. The aquifer section utilized for the SAT treatment is dynamically isolated from the nearby main coastal aquifer by the flow regime management, controlled by the operation of dozens of infiltration ponds and hundreds of surrounding recovery wells (RW) [9,13,14,18]. The recovered effluents after SAT are characterized by excellent quality for most of the measured parameters, and are significantly better than any other treated wastewater in Israel. According to the Israeli health regulations, the recovered Shafdan water (after SAT) is suitable for unrestricted irrigation of any crop [9,16,17]. Nevertheless, a rise of manganese concentrations in recovery wells since 2001 needs to be coped with [12]. To maintain the necessary separation between the Shafdan basins and the regional aquifer, and to avoid any breakout and contamination of fresh water wells by effluents, a proper hydrological management and an extensive monitoring system are required. The traditional and simplest way to track the spatial extension of the recharged effluent is to measure the concentrations of conservative tracers such as chloride in observation and recovery wells. In places where the difference between the pristine aquifer water (50–150 mg-Cl/L) and the reclaimed water (230–280 mg-Cl/L) is large enough, the chloride concentration is a suitable tool for tracing the effluent front in the aquifer and for estimating mixing ratios (MR) of effluent and freshwater. However, down-stream, where the effluents are diluted to less than 30% and the chloride concentration decreases, chloride can no longer be used as a reliable tracer [19–21]. Moreover, the chloride tracer has very limited use in specific areas that are located east of the Shafdan basins and are characterized by high salinity, in some cases higher than 300 mg-Cl/L, unrelated to the Shafdan recharged effluents [21]. In these cases, state-of-the-art geochemical and environmental tools are needed. A new tracer that was discovered in the past few years takes advantage of the inert and conservative behavior of carbamazepine (CBZ), an antiepileptic drug which is present in the sewage Water 2017, 9, 73 3 of 16 as a micro-pollutant and is being recharged to the aquifer with the effluents. Previous studies proved the CBZ to be a useful tracer in the Shafdan system, especially down-stream where the effluents are Water 2017, 9, 73 3 of 17 diluted. It was shown that in these areas CBZ can be used for MR calculations of less than 5% [18–23]. However,CBZ to CBZ be a useful is limited tracer to in lessthe Shafdan diluted system, areas especially (MR > 80%) down and‐stream for where prediction the effluents purposes, are diluted. due to its unstableIt was concentrations shown that in in these the rechargedareas CBZ can effluents be used [21 for]. MR calculations of less than 5% [18,19–23]. TheHowever, present CBZ research is limited hypothesized to less diluted that areas the (MR massive > 80%) amounts and for ofprediction desalinated purposes, water due added to its each year tounstable the National concentrations Water in Carrier the recharged should effluents affect [21]. the supplied water isotopic composition, as well as the isotopicThe composition present research of thehypothesized associated that effluents the massive treated amounts by the of Shafdan desalinated plant. water The added objectives each of this studyyear to were the National to examine Water the Carrier applicability should affect of the the water supplied isotopes water 18isotopicO and composition,2H as a quantitative as well as tool: the isotopic composition of the associated effluents treated by the Shafdan plant. The objectives of (1) for tracing the spatial distribution of the recharged effluents in the Shafdan basins; and (2) for this study were to examine the applicability of the water isotopes 18O and 2H as a quantitative tool: examination of the relationship between different water sources in the water–sewage–effluent system, (1) for tracing the spatial distribution of the recharged effluents in the Shafdan basins; and (2) for that is,examination between theof the different relationship water sourcesbetween indifferent the Israeli water National sources Waterin the Carrier, water–sewage–effluent between the NWC and thesystem, Shafdan that is, plant, between and betweenthe different the water Shafdan sources plant in and the Israeli the SAT National recovery Water wells. Carrier, between the NWC and the Shafdan plant, and between the Shafdan plant and the SAT recovery wells. 2. Materials and Methods 2. Materials and Methods 2.1. Sampling Program 2.1. Sampling Program In order to verify the research hypothesis, an extensive survey was conducted, including sampling and analysisIn order of water to verify collected the research from recovery hypothesis, wells, an fromextensive pipe survey connections was conducted, of the NWC including and from desalinationsampling plants. and analysis The mainof water research collected took from place recovery in the wells, area from of the pipe Soreq connections recharge of the basin, NWC located and at the northernfrom desalination part of the plants. Shafdan The main plant. research The aquifertook place in in this the area area isof subdividedthe Soreq recharge into four basin, sub-aquifers, located at the northern part of the Shafdan plant. The aquifer in this area is subdivided into four sub‐aquifers, A to C (Figure1). The main SAT activity, as well as the freshwater pumping, takes place in sub-aquifer 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 B. In some places, the recharged water reaches also lower unit (sub‐aquifers C). Some of the recovery wellswells penetrate penetrate several several sub-aquifers sub‐aquifers and and hencehence technically technically connect connect and and exploit exploit all of all them. of them.

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

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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 Water 2017examination, 9, 73 of various isotopes and chemical compounds as a potential tracer for the Shafdan4 of 16 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 Twomonitoring sampling wells, campaigns most of them were 2–3 times conducted (Figure 2). during The sampled the years wells 2010–2011 were carefully and chosen 2014. to The be first campaignlocated (2010–2011) at various distances was part from of the a France–Israeli recharge ponds, bilateral and yet to research be as similar program, as possible and includedfrom the the examinationtechnical ofand various hydro‐geological isotopes andaspects. chemical A limited compounds sampling as campaign a potential that tracerincluded for only the Shafdanthe systemShafdan [25,26 effluents]. The second and 3 observation campaign waswells conducted was conducted by Mekorot during winter in order 2013. to validate the conclusions and the predictionsEach campaign of included the first sampling campaign. of secondary In each effluents campaign, from we the sampled outlet of the 17 MBTP to 21 (PS recovery‐6) and and from recharge ponds. Samples were also taken from two desalination plants (Palmahim and Hadera) monitoring wells, most of them 2–3 times (Figure2). The sampled wells were carefully chosen to be and from specific points along the National Water Carrier, in order to represent the isotopic locatedcomposition at various of the distances Dan Region’s from supplied the recharge freshwater ponds, (Figure and 2). yet Each to be campaign as similar also as included possible specific from the technicalsampling and hydro-geologicalprograms (sub‐experiments) aspects. A to limited evaluate sampling the contributions campaign of that individual included sources only and the Shafdanthe effluentseffects and of secondary 3 observation processes wells such was as conducted evaporation during or seasonal winter variations, 2013. as listed in Table 1.

Figure 2. Experiment setup and the sampling program implemented in the study: (a) Schematic Figure 2. Experiment setup and the sampling program implemented in the study: (a) Schematic layout layout of the Israeli National Water Carrier with the locations of Hadera and Palmahim desalination 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) plantsEnlarged (DSPs) map and of the the ShafdanShafdan area plant. and Bluethe Soreq triangles recharge represent basin. Red the triangles freshwater represent sampling effluents points; (b) Enlargedsampling map points. of Black the Shafdan dots represent area and recovery the Soreq and observation recharge basin. wells Redthat were triangles sampled. represent effluents sampling points. Black dots represent recovery and observation wells that were sampled. Table 1. General description of the sub‐experiments conducted during the campaigns. Table 1. General description of the sub-experiments conducted during the campaigns. Examined Effect Campaign Setup and Remarks Seasonal effects on the isotopic The first sampling campaign was divided into 2 parts: September 2010 compositionExamined of the Effect recovered 2010–2011 Campaign(summer) and February 2011 (winter). The two Setup sub and‐campaigns Remarks were water (after SAT) conducted at the same wellsThe or firstat hydro sampling‐geologically campaign equivalent was wells. divided into Seasonal effects on the isotopic (1) By simultaneous sampling2 parts: from September PS‐6 (MTBE 2010 outlet) (summer) and from and the recharge pond on 14 September 2010. Effluent sampling of the recharge compositionEvaporation of the effects recovered on the isotopic water 2010–2011 February 2011 (winter). The two sub-campaigns pond was taken at the end of the day, ~6 h. After beginning of flooding. (aftercomposition SAT) of the recharged 2010–2011 were conducted at the same wells or at (2) By continuous sampling of the recharge pond during flooding on 19 effluents, during the recharge period hydro-geologically equivalent wells. September 2010 (beginning of flooding) and on 20 September 2010 (end of flooding). (1) By simultaneous sampling from PS-6 (MTBE (1) On 21 February 2011 and onoutlet) 7 February and from 2013 effluents the recharge were sampled pond on The effect of the Sea of Galilee and from the Shafdan during a14 period September when no 2010. water Effluent was supplied sampling from the of the Evaporationthe desalinated effects water on the on isotopicthe 2010–2011, lake to the NWC. recharge pond was taken at the end of the compositionisotopic composition of the recharged of the 2013 and 2014 2010–2011(2) On 25 February 2014 effluentsday, were ~6 h. sampled After beginningfrom the Shafdan of flooding. during a effluents,Shafdan during effluents the recharge(see Section period 3.3) period when no water(2) wasBy supplied continuous from the sampling Hadera DSP of the and recharge from the pond SOG to the NWC. during flooding on 19 September 2010 (beginning of flooding) and on 20 September 2010 (end of flooding). (1) On 21 February 2011 and on 7 February 2013 effluents were sampled from the Shafdan The effect of the Sea of Galilee and during a period when no water was supplied the desalinated water on the isotopic from the lake to the NWC. 2010–2011, 2013 and 2014 composition of the Shafdan effluents (2) On 25 February 2014 effluents were sampled (see Section 3.3) from the Shafdan during a period when no water was supplied from the Hadera DSP and from the SOG to the NWC. Water 2017, 9, 73 5 of 16

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 (Figure2). Each campaign also included specific sampling programs (sub-experiments) to evaluate the contributions of individual sources and the Water 2017, 9, 73 effects of secondary processes such as evaporation or seasonal variations, as listed5 of 17 in Table1.

2.2. Analytical Procedures2.2. Analytical Procedures Chemical analysesChemical included analyses measurement included of measurement salinity (Cl, ofEC) salinity in all (Cl, samples. EC) in allIn samples. part of Inthe part of the samples, samples, mainly duringmainly the during first thecampaign, first campaign, major ions major (Ca, ions Mg, (Ca, Na, Mg, K, Na, HCO K,3 HCO, SO43, ,and SO4 ,B), and nitrogen B), nitrogen species (NO3, species (NO3, NH4NH, and4, andNO2 NO), Redox2), Redox parameters parameters (DO, (DO,ORP, ORP, Mn, Mn,and andFe) and Fe) andother other parameters parameters (pH, (pH, temperature, temperature, DOC,DOC, alkalinity, alkalinity, UV and UV andmetal metal concentrations) concentrations) were were also also measured. measured. This This was was done done for for quality control quality control andand comparison comparison purposes, purposes, and and is isnot not discussed discussed further further in in this this paper. paper. Analyses Analyses were were conducted by the conducted by the centralcentral laboratory laboratory of of Mekorot Mekorot using using standard standard methods methods.. Potential tracers forPotential mixing tracersratio (MR) for mixingcalculations, ratio (MR)including calculations, Cl, CBZ includingand the stable Cl, CBZ isotopes and the of stable isotopes of water molecule (18waterO and molecule 2H), were ( 18measuredO and 2H), at wereall wells. measured CBZ concentrations at all wells. CBZ were concentrations measured in werethe measured in the central laboratorycentral of the laboratory Israeli ofWater the Israeli Authority. Water Authority. Measurements Measurements were weredone doneusing using liquid liquid chromatograph chromatograph equippedequipped with with tandem tandem triple triple quadruple quadruple mass mass spectrometer spectrometer LC/MS/MS LC/MS/MS according according to to the EPA method the EPA method 1694,1694, which which enable limit of quantificationquantification (LOQ)(LOQ) ofof 0.10.1 ng/ ng/ LL [[20].20]. TheThe oxygenoxygen and and hydrogen isotopes hydrogen isotopes(expressed (expressed as asδ δ1818OO andand δδ22H values in ‰ vs. the VSMOW standard) were were measured measured by two separated by two separated labs.labs. SamplesSamples from from the the first first campaign campaign (2010–2011) (2010–2011) were were analyzed analyzed by theby the BRGM BRGM isotope laboratory on isotope laboratorya on Finnigan a Finnigan MAT MAT 252 mass 252 mass spectrometer spectrometer following following the gas-water the gas‐water equilibration equilibration technique with CO2 for technique with COoxygen2 for oxygen isotopes isotopes [27] and [27] with and H2 forwith hydrogen H2 for isotopeshydrogen [28 isotopes]. Analytical [28]. uncertainty, Analytical based on replicate uncertainty, basedanalyses on replicate of international analyses of international and laboratory and standards, laboratory are standards,±0.8 forare δ±0.8‰2H and for± δ0.12H for δ18O. Water and ±0.1‰ for δ18andO. Water effluent and samples effluent from samples the second from campaignthe second (2014 campaign and 2013) (2014 were and analyzed 2013) were by the IT2 laboratory analyzed by the IT(Waterloo,2 laboratory ON, (Waterloo, Canada) on ON, CRDS, Canada) Model on L1102-i CRDS, (Piccaro, Model Santa L1102 Clara,‐i (Piccaro, CA, USA) Santa for both oxygen and Clara, CA, USA) forhydrogen both oxygen isotopes. and The hydrogen instrument isotopes. was configured The instrument with a uniquewas configured vaporization with module a that converts unique vaporizationthe module liquid water that sampleconverts to the the liquid vapor phasewater insample a flash to process the vapor at 140 phase◦C. The in vapora flash was then delivered process at 140°C. intoThe thevapor CRDS was cavity then for delivered analysis. into This the process CRDS avoided cavity anyfor possibleanalysis. fractionation This process processes that may avoided any possiblehave occurredfractionation with processes other liquid/vapor that may transitions have occurred such as with nebulizers. other liquid/vapor Typical precision for δ18O and transitions such asδ nebulizers.2H are ±0.1 Typicaland ±precision0.6 , respectively. for δ18O and All δ2H results are ±0.1‰ were and corrected ±0.6‰, and respectively. reported against the Vienna All results were correctedStandard and Mean reported Ocean against Water (VSMOW). the Vienna AllStandard in-house Mean standards Ocean wereWater calibrated (VSMOW). every six months by All in‐house standardsVSMOW, were GISP calibrated and SLAP every (The six IAEA months international by VSMOW, standards). GISP and SLAP (The IAEA international standards).All samples were analyzed in duplicates at both laboratories, with internal hidden standards All samples werefor control. analyzed in duplicates at both laboratories, with internal hidden standards for control. 3. Results and Discussion 3. Results and Discussion 3.1. Isotopic Composition of the Shafdan System 3.1. Isotopic CompositionThe of the results Shafdan for System the isotopic composition and concentrations of Cl and CBZ are given in Table2. 2 18 The results forA the typical isotopic correlation composition diagram and of concentrationsδ H vs. δ O forof Cl the and Shafdan CBZ are system given (Figure in Table3a) 2. and for the Israeli A typical correlationwater diagram system of sources δ2H vs. (Figure δ18O for3b) the is given Shafdan in Figure system3. (Figure 3a) and for the Israeli water system sources (FigureExamination 3b) is given of seasonal in Figure effects: 3. Samples from recovery wells were taken during summer 2010 and winter 2011 (Table1). 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.

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2.2. 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. Water 2017, 9, 73 Potential tracers for mixing ratio (MR) calculations, including Cl, CBZ and the stable isotopes of 6 of 16 water molecule (18O and 2H), were measured at all wells. CBZ concentrations were measured in the central laboratory of the Israeli Water Authority. Measurements were done using liquid Table 2. Cl,chromatograph CBZ and isotopic equipped compositions with tandem of freshwater,triple quadruple effluent mass and spectrometer recovered LC/MS/MS effluents according in the study. to the EPA method 1694, which enable limit of quantification (LOQ) of 0.1 ng/ L [20]. The oxygen and Location Location Type Water Typehydrogen Sampling isotopes Date (expressed Cl (mg/L) as δ18O and CBZ δ (ng/L)2H valuesδ 2inH ‰ vs. SMOWthe VSMOWδ18 standard)O vs. SMOW were measured Notes DSP-Hadera Desalination plant Freshwaterby two 23/02/2011separated labs. Samples 14 from theNM first1 campaign 10.0(2010–2011) were analyzed 1.5 by the BRGM DSP-Palmahim Desalination plant Freshwaterisotope 22/02/2011laboratory on a Finnigan 63 MAT 252 NM mass spectrometer 9.7 following the gas 1.5‐water equilibration SYS-Lincoln Local water system Freshwatertechnique 23/02/2011 with CO2 for oxygen 39 isotopes NM [27] and with H 1.72 for hydrogen isotopes−0.1 [28]. Analytical − − SYS-Bar Ilan Main water system Freshwateruncertainty, 23/02/2011 based on replicate 41 analyses of NM international and1.8 laboratory standards,0.8 are ±0.8‰ for δ2H PS-6 Plant outflow Effluents 14/09/2010 260 NM −4.1 −1.4 Samples were taken from PS-6 and from the 18 Soreq-1: 103/2 Recharged pond Effluentsand ±0.1‰ 14/09/2010 for δ O. Water 260 and effluent NMsamples from the− 4.2second campaign (2014−1.4 and 2013)recharge were pond to study the effect of evaporation PS-6 Plant outflow Effluentsanalyzed 21/02/2011 by the IT2 laboratory 223 (Waterloo, 837 ON, Canada) −on8.2 CRDS, Model L1102−2.0‐i (Piccaro, Sea Santa of Galilee (SOG) is off PS-6 Plant outflow EffluentsClara, CA, 07/02/2013 USA) for both NMoxygen and hydrogen NM isotopes.−2.1 The instrument was−1.6 configured with SOG isa off PS-6 Plant outflow Effluentsunique 25/02/2014vaporization module NM that converts NM the liquid water−5.6 sample to the vapor−2.4 phase in a SOG flash and Hadera DSP are off PS-6 Plant outflow Effluents 25/03/2014 209 1132 −0.3 −1.2 process at 140°C. The vapor was then delivered into the CRDS cavity for analysis. This process Yavne-2: 5102 Recharged pond Effluents 19/09/2010 280 NM −5.9 −1.7 Continuous flooding to study the effect Yavne-2: 5102 Recharged pond Effluentsavoided 20/09/2010 any possible fractionation 276 processes NM that may− have5.5 occurred with− 1.5other liquid/vaporof evaporation Shoreq T-1 Observation Well SATtransitions 08/05/2014 such as nebulizers. 134 Typical precision 2 for δ18O and−20.4 δ2H are ±0.1‰ and− ±0.6‰,4.7 respectively. Shoreq T-2 Observation Well SATAll results 08/05/2014 were corrected and 128 reported against 36 the Vienna− 10.8Standard Mean Ocean−2.8 Water (VSMOW). − − Shoreq T-27/1 Observation Well SATAll in‐house 10/07/2014 standards were 272 calibrated every 684 six months by9.1 VSMOW, GISP and2.3 SLAP (The IAEA Shoreq T-5 Observation Well SAT 10/07/2014 89 74 −12.7 −3.2 Shoreq T-61 Observation Well SATinternational 26/03/2014 standards). 268 1010 −2.7 −1.1 Shoreq T-62/1 Observation Well SATAll 26/03/2014 samples were analyzed 201 in duplicates 1166 at both laboratories,−0.5 with internal−0.9 hidden standards Shoreq T-71d Observation Well SATfor control. 26/03/2014 88 20 −15.0 −3.8 Shoreq T-71s Observation Well SAT 26/03/2014 197 188 −7.5 −2.6 − − Soreq t-1a Observation Well SAT3. Results 30/04/2013 and Discussion NM NM 19.4 5.0 Soreq t-2a Observation Well SAT 30/04/2013 NM NM −20.0 −5.0 Soreq t-3 Observation Well SAT 30/04/2013 NM NM −20.3 −5.0 Soreq T-61 Observation Well SAT3.1. Isotopic 21/02/2011 Composition of the 250 Shafdan System 1030 −7.3 −1.8 Dan 1 Recovery Well SAT 08/05/2014 290 1900 −10.1 −3.1 The results for the isotopic composition and concentrations of Cl and CBZ are given in Table 2. Dan 14a Recovery Well SAT 08/05/2014 163 446 −12.2 −3.5 2 18 Dan 21a Recovery Well SATA typical 25/03/2014 correlation diagram 153 of δ H vs. δ 380O for the Shafdan−13.5 system (Figure 3a)−3.6 and for the Israeli Dan 25 Recovery Well SATwater system 25/03/2014 sources (Figure 248 3b) is given 1096 in Figure 3. −11.1 −3.1 Dan 2a Recovery Well SAT 25/03/2014 152 482 −12.3 −3.4 Dan 33 Recovery Well SAT 25/03/2014 258 1158 −2.8 −1.4 Dan 5 Recovery Well SAT 25/03/2014 264 1236 −5.2 −1.9 Dan 6 Recovery Well SAT 25/03/2014 260 1236 −4.8 −2.0 Dan 7 Recovery Well SAT 25/03/2014 209 650 −10.4 −2.8 Dan 8 Recovery Well SAT 25/03/2014 246 860 −7.7 −2.3 Dan-16a Recovery Well SAT 21/02/2011 277 870 −12.2 −2.7 Dan-17a Recovery Well SAT 14/09/2010 240 NM −14.1 −3.4 Dan-17a Recovery Well SAT 21/02/2011 246 1296 −14.1 −3.1 Dan-24 Recovery Well SAT 14/09/2010 289 NM −12.3 −3.0 Dan-24 Recovery Well SAT 21/02/2011 291 1337 −12.6 −2.8 Dan-2a Recovery Well SAT 14/09/2010 164 NM −15.4 −3.6 Dan-2a Recovery Well SAT 21/02/2011 160 299 −15.2 −3.5 Dan-32 Recovery Well SAT 14/09/2010 280 NM −10.1 −2.6 Dan-32 Recovery Well SAT 21/02/2011 278 1174 −10.2 −2.3

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2.2. 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. Water 2017, 9, 73 Potential tracers for mixing ratio (MR) calculations, including Cl, CBZ and the stable isotopes of 7 of 16 water molecule (18O and 2H), 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 tandemTable triple 2. quadrupleCont. 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 Location Location Type Water Typehydrogen Sampling isotopes Date (expressed Cl (mg/L) as δ18O and CBZ δ (ng/L)2H valuesδ 2inH ‰ vs. SMOWthe VSMOWδ18 standard)O vs. SMOW were measured Notes Dan-5 Recovery Well SATby two 21/02/2011separated labs. Samples 284 from the 1061 first campaign −(2010–2011)12.5 were analyzed−2.9 by the BRGM Dan-6 Recovery Well SATisotope 14/09/2010laboratory on a Finnigan 279 MAT 252 NM mass spectrometer−12.9 following the gas−‐3.0water equilibration Dan-6 Recovery Well SATtechnique 21/02/2011 with CO2 for oxygen 277 isotopes 1210 [27] and with −H12.22 for hydrogen isotopes−2.8 [28]. Analytical − − Dan-7 Recovery Well SATuncertainty, 21/02/2011 based on replicate 228 analyses of 1000 international and13.3 laboratory standards,3.2 are ±0.8‰ for δ2H NH Rishon 10 Recovery Well SAT 25/03/2014 66 353 −16.0 −4.1 18 NH Rishon 7 Recovery Well SATand ±0.1‰ 25/03/2014 for δ O. Water 86 and effluent samples 44 from the−15.4 second campaign (2014−3.7 and 2013) were NH Rishon-10 Recovery Well SATanalyzed 21/02/2011 by the IT2 laboratory 62 (Waterloo, 314 ON, Canada)− on21.3 CRDS, Model L1102−4.6‐i (Piccaro, Santa Rishon 5 Recovery Well SATClara, CA, 25/03/2014 USA) for both oxygen 86 and hydrogen 140 isotopes.−17.4 The instrument was−4.1 configured with a Rishon-5 Recovery Well SATunique 14/09/2010vaporization module 123 that converts NM the liquid water−16.4 sample to the vapor−3.8 phase in a flash Rishon-5 Recovery Well SAT 21/02/2011 114 72 −17.8 −3.8 process at 140°C. The vapor was then delivered into the CRDS cavity for analysis. This process 1 avoided any possible fractionationNote: processesNM: not measured.that may have occurred with other liquid/vapor transitions such as nebulizers. Typical precision for δ18O and δ2H are ±0.1‰ and ±0.6‰, respectively. Table 3.AllCl, results CBZ were and corrected isotopic compositionand reported against average the values Vienna of Standard different Mean types Ocean of water Water sources. (VSMOW). All in‐house standards were calibrated every six months by VSMOW, GISP and SLAP (The IAEA internationalCl (mg/L) standards). CBZ (ng/L) δ2H vs. SMOW δ18O vs. SMOW Water Source All samples were analyzed in duplicates at both laboratories, with internal hidden standards forAverage control. Stdev (n) Average Stdev (n) Average Stdev (n) Average Stdev (n) Coastal Aquifer (Cl < 200) 101 54 (27) −18.6 2.53 (27) −4.62 0.33 (27) 3. Results and Discussion Coastal Aquifer (Cl > 200) 458 240 (33) 3 1 - −17.8 2.19 (31) −4.09 0.37 (33) Coastal Aquifer (general) 297 250 (58) −18.2 2.42 (58) −4.33 0.42 (60) 3.1. Isotopic Composition of the Shafdan System Mountain aquifer 198 2 187 (36) NM - −22.1 2.80 (42) −5.36 0.37 (43) Sea of Galilee 261The results for the 18 isotopic composition NM and concentrations - of Cl and 0.88 CBZ are given 2.97 in Table (13) 2. −0.37 0.44 (13) Mediteranean Sea 3 A typical38 correlation 35 diagram (2) of δ2H vs. NM δ18O for the Shafdan - system (Figure 8.90 3a) and for 1.74 the (13)Israeli 1.74 0.19 (13) Shafdan effluents, 2010–2011 water265 system sources 28 (103)(Figure 3b) is given in Figure 3. −4.93 0.89 (4) −1.52 0.10 (4) 1071 230 (8) Shafdan effluents, 2014 218 27 (53) −1.20 1.30 (2) −1.39 0.23 (2) Notes: 1 CBZ in pristine water: according to Gasser et al. [20]; 2 For pumping wells with salinity of Cl < 1000; 3 Cl: for desalinated water only; Isotopes: desalinated and sea water.

Water 2017, 9, 73 8 of 16

Examination of evaporation effects in the recharge ponds: Various samples taken from the recharge ponds, during different hours along the recharge process, were compared (Table1). No significant differences in the δ2H and δ18O 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 δ2H vs. δ18O, 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 R2 = 0.93 (Figure3a). This slope is significantly lower than the GMWL line slope of 8. In addition, Figure3a 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. Water 2017, 9, 73 9 of 17

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

Water 2017, 9, 73 9 of 16

The secondary effluents compose the heavier end-member, with δ18O of −1.5 ± 0.1 and δ2H of −4.9 ± 0.9 for 2010–2011 campaign, and δ18O of −1.4 ± 0.2 and δ2H of −1.2 ± 1.3 for 2014 campaign (Table3). The variations for these average values are due to changes in dilution ratio between water from different sources in the NWC (Table1). For example, relatively depleted δ2H and δ18O 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 (Tables1 and2), 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 Table4 and in Section 3.3 below. The Coastal Aquifer pristine water compose the lighter end-member, with δ18O of −4.6 ± 0.3 and δ2H of −18.6 ± 2.5 in water of salinity smaller than 200 mg-Cl/L, which is typical of the Shafdan area (Table3). All the isotope composition values of the recovery and observation wells were linearly scattered between the effluent and the Coastal Aquifer end-members (Figure3a). 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: δ − δ MR(%) = NW ∗ 100 (1) δe f f − δNW

18 2 18 2 where δ represents the measured δ O or δ H in the well, δNW represents the δ O or δ H of the 18 2 pristine water (aquifer), and δeff represents the δ O or δ 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.

3.2. Isotopic Composition of the Main Water Sources and of the National Water Carrier Expanding the δ2H vs. δ18O diagram of Figure3a 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 R2 of 0.95 (Figure3b). This time the end-members are composed of the Mediterranean Sea water, either pre- or 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 [3,5,8,29–35]. The heavy end-member is composed of the Mediterranean Sea water, with δ18O of 1.7 ± 0.2 and δ2H 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 δ18O of −0.4 ± 0.4 and δ2H of 0.9 ± 3.0. On the other end, we can find the Mountain Aquifer water that represent the lighter end member, with δ18O of −5.4 ± 0.4 and δ2H of −22.1 ± 2.8, just slightly lower than the Coastal Aquifer water with δ18O = −4.3 ± 0.4 and δ2H = −18 ± 2.4 for all salinity range (Table3). The slope of the regression line is 4.5, a little smaller but not significantly different from the slope of the Shafdan system in Figure3a. 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., [29,36–38]). 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 Water 2017, 9, 73 10 of 16

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 Water 2017, 9, 73 5 of 17 Mountain Aquifer recharge water is also subjected to evaporation when rain storms occur under warm 2.2.climate Analytical conditions Procedures [37], but even without this component, the isotopic composition of this source does not interfere with the linear pattern. Chemical analyses included measurement of salinity (Cl, EC) in all samples. In part of the samples,3.3. Mixing mainly Ratios during in the the National first campaign, Water Carrier major and ions in the (Ca, Shafdan Mg, Na, Plant K, HCO3, SO4, and B), nitrogen species (NO3, NH4, and NO2), Redox parameters (DO, ORP, Mn, and Fe) and other parameters (pH, Mixing ratios between different water sources can be calculated based on the strong linearity temperature, DOC, alkalinity, UV and metal concentrations) were also measured. This was done for between the four main freshwater sources (Figure3b). The linear correlation enables us to run simple quality control and comparison purposes, and is not discussed further in this paper. Analyses were dilution (mixing) calculations between the different water sources in the NWC and in the Shafdan conducted by the central laboratory of Mekorot using standard methods. plant. That is, calculating the isotopic composition δ of a mixed system such as the NWC or the Potential tracers for mixing ratio (MR) calculations, including Cl, CBZ and the stable isotopes of Shafdan effluents according to the volume ratio (f ) and the isotopic composition (δ ) of each source water molecule (18O and 2H), were measured at all wells.i CBZ concentrations were measuredi in the (Equation (2)): central laboratory of the Israeli Water Authority.n Measurements were done using liquid chromatograph equipped with tandem triple δquadruple= ∑ δi · fmassi spectrometer LC/MS/MS according to(2) the EPA method 1694, which enable limit of quantificationi=1 (LOQ) of 0.1 ng/ L [20]. The oxygen and 18 18 2 2 hydrogenwhere δ isotopesrepresents (expressed the calculated as δ Oδ andO δ orHδ valuesH value in ( ‰) vs. of the VSMOW mixed system, standard) and wereδi represents measured the bymeasured two separatedδ18O or labs.δ2H valueSamples ( )from of the the fresh first water campaign source (Coastal(2010–2011) Aquifer, were Mountain analyzed Aquifers, by the BRGM SOG or isotopedesalinated laboratory water). on Assumptionsa Finnigan MAT for using252 mass the mixingspectrometer model following to calculate the the gas isotope‐water compositionequilibration of techniquethe NWC with includes CO2 no for fractionation oxygen isotopes and instantaneous, [27] and with homogenous, H2 for hydrogen mixing isotopes between [28]. the water Analytical sources uncertainty,in the line. based Additional on replicate assumptions analyses for of calculating international the and isotope laboratory composition standards, in the are Shafdan ±0.8‰ for effluents δ2H andincludes ±0.1‰ no for fractionation δ18O. Water and effluent evaporation samples throughout from the the second usage campaign of the water (2014 and and the 2013) treatment were analyzedprocess; by no the external, IT2 laboratory uncounted (Waterloo, water source; ON, Canada) and instantaneous, on CRDS, Model homogenous, L1102‐i (Piccaro, mixing between Santa Clara,NWC CA, and USA) private for wells both in oxygen the local and systems, hydrogen and betweenisotopes. different The instrument sewage sourceswas configured from the differentwith a uniquemunicipalities vaporization in the module Shafdan that MBTP. converts the liquid water sample to the vapor phase in a flash processFreshwater at 140°C. quantitiesThe vapor forwas each then main delivered source into for thethe calculationCRDS cavity of for the analysis. isotope composition This process in avoidedthe National any possible Water Carrier fractionation were taken processes from that the Mekorotmay have daily occurred database. with Mixing other calculationliquid/vapor for transitionsthe NWC such was as conducted nebulizers. by Typical a water precision supply operativefor δ18O and program δ2H are (code) ±0.1‰ that and was ±0.6‰, developed respectively. and is Alloperated results were by Mekorot, corrected as and part reported of the NWC against operating the Vienna system. Standard Freshwater Mean quantities Ocean Water for private(VSMOW). wells All(Coastal in‐house and standards Mountain were aquifers) calibrated owned every by the six municipalities months by VSMOW, were taken GISP from and the SLAP Water (The Authority’s IAEA internationalmonthly database. standards). In order to calculate the dilution ratios between different types of water sources in theAll Shafdan,samples were we assumed analyzed that in theduplicates municipal at both consumption laboratories, is first with provided internal by hidden the private standards wells for(from control. water cost considerations), and the residual is purchased from the NWC. Thus, the isotope composition of the Shafdan effluents (δshafdan) was calculated from the volume ratios between the 3.private Results wells and andDiscussion the NWC (fPW and fNWC, respectively), and from the isotopic compositions of these two sources (δPW and δNWC, respectively), as described in Equation (3). 3.1. Isotopic Composition of the Shafdan System = · + · The results for the isotopic compositionδsha f dan fandPW concentrationsδPW fNWC δ ofNWC Cl and CBZ are given in Table 2.(3) A typical correlation diagram of δ2H vs. δ18O for the Shafdan system (Figure 3a) and for the Israeli Purchased volumes of NWC water by the municipalities were obtained from the accounting water system sources (Figure 3b) is given in Figure 3. system of Mekorot (on a monthly base). The isotopic composition of each water source that was used for the mixing calculation is detailed in Table3. Water volumes data for the calculations are given in Table4. Figure4 presents the correlations between measured and calculated δ18O and δ2H 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 Table1. 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 Figure4. High deviations of

Water 2017, 9, 73 5 of 17

2.2. 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 2H), were measured at all wells. CBZ concentrations were measured in the central laboratory of the Israeli Water Authority. Measurements were done using liquid Water 2017, 9, 73 11 of 16 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 δ18O and δ2H valuesup to 1.5in ‰ andvs. the 7.5 VSMOWfor the standard)δ18O and wereδ2H, measured respectively, were found only in the first sample taken by two separated labs. Samples from the firston campaign 14 September (2010–2011) 2010. Thiswere deviationanalyzed canby the be explainedBRGM by the difficulty to assess the effects of the isotope laboratory on a Finnigan MAT 252 massdesalinated spectrometer water following on the NWC the gas when‐water only equilibration Ashkelon and Palmahim (partially) plants were working. 18 technique with CO2 for oxygen isotopes [27] Forand the with rest H of2 for the hydrogen samples, the isotopes deviations [28]. variedAnalytical between 0 and 0.7 for the δ O, and between uncertainty, based on replicate analyses of international1 and 3.7 and laboratoryfor the δ2H. standards, In the winter are ±0.8‰ season, for δ some2H limited effect of uncounted drainage runoff and ±0.1‰ for δ18O. Water and effluent samplesduring from stormy the second days can campaign also explain (2014 part and of 2013) the deviations. were Nevertheless, the good overall agreement analyzed by the IT2 laboratory (Waterloo, ON,between Canada) calculated on CRDS, and Model measured L1102 values‐i (Piccaro, indicates Santa the conservative nature of O and H stable isotopes Clara, CA, USA) for both oxygen and hydrogenin the isotopes. water–effluent The instrument system, and,was configured consequently, with the a ability to reconstruct or to predict the isotope unique vaporization module that converts thecomposition liquid water of sample the recharged to the effluents.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 thatTable may 4. haveWater occurred volumes with from other the different liquid/vapor freshwater sources that were used for the dilution transitions such as nebulizers. Typical precision for δ(mixing)18O and calculations. δ2H are ±0.1‰ and ±0.6‰, respectively. All results were corrected and reported against the Vienna Standard Mean Ocean Water (VSMOW). Volumes (MCM/Day) at Sampling Date Water Source System All in‐house standards were calibrated every six months by VSMOW, GISP and14 September SLAP 2010(The IAEA 21 February 2011 07 February 2013 25 February 2014 25 March 2014 international standards). Coastal Aquifer 0.247 0.074 0.046 0.048 0.077 Mountain AquiferWater 2017, 9, 73 0.650 0.367 0.112 0.25312 of 17 0.183 All samples were analyzed in duplicates atLake both Kinneret laboratories, (SOG) with internal hidden0.472 standards 0.000 0.000 0.000 0.000 for control. Palmahim DSPHigh deviationsNational of Water up to 1.5‰ and0.108 7.5‰ for the δ18O 0.089 and δ2H, respectively, 0.178 were found 0.165only in the 0.169 Hadera DSP Carrier (Mekorot) 1 0.273 0.276 0.374 0.000 0.316 Soreq DSPfirst sample taken on 14 September -2010. This deviation - can be explained - by the difficulty 0.010 to assess 0.313 Sum in NWCthe effects of the desalinated water 1.75 on the NWC when 0.81 only Ashkelon 0.71 and Palmahim 0.48(partially) 1.06 3. Results and Discussion Purchased by plants were working. For the rest of0.31 the samples, the deviations 0.25 varied between 0.27 0‰ and 0.7 0.27‰ for the 0.30 municipalities δ18O, and between 1‰ and 3.7‰ for the δ2H. In the winter season, some limited effect of uncounted Coastal aquifer 0.115 0.087 0.088 0.088 0.095 3.1. Isotopic Composition of the Shafdan System drainage runoffPrivate during wells stormy days can also explain part of the deviations. Nevertheless, the good Mountain aquifer 0.019 0.019 0.021 0.021 0.022 (municipalities) 2 Sumoverall agreement between calculated 0.13 and measured 0.11 values indicates the 0.11 conservative nature 0.11 of O 0.12 The results for the isotopic composition and concentrationsand H stable of Cl isotopes and CBZ in the arewater–effluent given in system, Table and, 2. consequently, the ability to reconstruct or to Notes: 1 Daily amounts; 2 Estimated daily amounts, based on monthly data. A typical correlation diagram of δ2H vs. δ18O for the Shafdanpredict system the isotope (Figure composition 3a) and of the for recharged the Israeli effluents. water system sources (Figure 3b) is given in Figure 3.

Figure 4. Fresh water mixing assessment in the NWC and in the Shafdan for: δ18O (a); and δ2H (b). 18 2 Figure 4. FreshThe watersampling mixing point for assessment the NWC is located in the at NWCthe entrance and to in Tel the Aviv. Shafdan Samples for: for theδ ShafdanO(a); and δ H(b). The samplingeffluents point forwere the taken NWC at the is outlet located station at (PS the‐6) entrancethat pumps tothe Tel effluents Aviv. to Samples the recharge for ponds. the Shafdan effluents were taken at the outlet station (PS-6) that pumps the effluents to the recharge ponds. 3.4. 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

Water 2017, 9, 73 12 of 16

3.4. 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 practicalWater to 2017 conduct, 9, 73 reliable mixing ratio calculations using Equation (1). 13 of 17 Mixing ratio calculations for recovery and observation wells are presented in Figures5 and6 composition. The differences between these two end‐members (“new” effluent and the Coastal as a function ofAquifer) the distance made it practical of the to conduct wells reliable from mixing the recharge ratio calculations ponds. using Calculations Equation (1). of MRs were done independently fourMixing times ratio for calculations each well, for recovery using and its observation measured wellsδ are18O presented and δ in2H Figures values, 5 and CBZ6 as and chloride a function of the distance of the wells from the recharge ponds. Calculations of MRs were done concentrations.independently Figure5 represents four times for each mixing well, using ratio its calculationsmeasured δ18O and for δ2H each values, parameter CBZ and chloride according to the 2010–2011 campaignconcentrations. results. Figure Figure 5 represents6 represents mixing ratio thecalculations changes for each in parameter the mixing according ratio to the results between 2010–2011 campaign results. Figure 6 represents δthe2 changes in the mixing ratio results between 2010–2011 and 2014,2010–2011 where and 2014, MR where is calculated MR is calculated from from δ2HH values values and from and CBZ from concentrations. CBZ concentrations.

Figure 5. Mixing ratios (MR) in recovery and observation wells vs. distance from the recharge ponds. Figure 5. MixingMRs ratios were calculated (MR) in from recovery Cl, CBZ, δ and18O and observation δ2H results of the wells 2010–2011 vs. campaign. distance from the recharge ponds. MRs were calculated from Cl, CBZ, δ18O and δ2H results of the 2010–2011 campaign. Mixing ratio calculations for the 2010–2011 campaign showed significant differences between CBZ and Cl results compared to δ18O and δ2H results (Figure 5). CBZ and Cl concentrations led to Mixing ratiohigher calculations MR values, which for varied the from 2010–2011 100% to 80% campaign of effluents for showed wells in the significant range of 0 to differences1000 m between away from the recharge ponds, and from 60% to 5% for wells located 1000 to 3000 m from the ponds. 18 2 CBZ and Cl resultsLocal differences compared between to δ CBZO and and Cl MRsδ H are results mainly due (Figure to inaccurate5). CBZ Cl‐MR and calculations Cl concentrations under led to higher MR values,dilute which (low MR) varied conditions. from Mixing 100% ratios tobased 80% on δ of18O effluents and δ2H analyses for wellsyield smaller in the MR range values, of 0 to 1000 m which varied between 20% and 90% of effluents for wells located 0 to 1000 m from the recharge away from the rechargeponds, and from ponds, 35% to and 0% for from wells 60% located to 1000 5% to for 3000 wells m from located the ponds. 1000 On average, to 3000 mixing m from the ponds. Local differencesratios between calculations CBZ based and on δ18 ClO and MRs δ2H arevalues mainly reached dueabout to50% inaccurate of the mixing ratios Cl-MR that calculationswere under calculated from CBZ concentrations, which represent 18equilibrium with2 the SAT operation regime. dilute (low MR)Therefore, conditions. one can Mixingconclude replacement ratios based of about on 50%δ ofO the and previousδ H isotopic analyses signature yield with smaller the MR values, which varied between“new” isotopic 20% signature and of 90% the effluents, of effluents which occurred for wells over one located (since the 0 tooperation 1000 of m Hadera from the recharge ponds, and fromplant) 35% to five to (since 0% the for operation wells locatedof Ashkelon 1000 plant) toyears. 3000 m from the ponds. On average, mixing As mentioned before in Section 2.1, the 2014 campaign was conducted in order to verify the 18 2 ratios calculationsconclusions based from on theδ 2010–2011O and δcampaign.H values In particular, reached that about the introduction 50% of of the the mixingdesalinated ratios that were calculated fromwater, CBZ via concentrations, the National Water Carrier which to the represent aquifer is expected equilibrium to increase with mixing the ratio SAT of “new” operation regime. effluents in the recovery wells [25]. This conclusion is indeed confirmed as δ2H‐MR’s results Therefore, oneincreased can conclude from ~50% replacement to ~75% relative of to aboutCBZ‐MR’s 50% results of thein the previous main SAT‐active isotopic area (100% signature with the “new” isotopiceffluents signature based of on theCBZ) effluents, of the aquifer, which as shown occurred in Figure 6. over Assuming one (sincenegligible the effect operation of the of Hadera desalinated water until 2010 (due to weak connection of the Ashkelon plant to the Dan Region water plant) to five (sincesystem, the and operation due to low contribution of Ashkelon from plant)the Palmahim years. plant until 2013), we conclude that the 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 δ2H-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 Figure6. 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 reachedWater steady-state 2017, 9, 73 with the Shafdan SAT operation regime after about four14 of 17 years (since the operation of Haderaisotope plant).signature This of the process desalinated of “replacing”water almost reached the previous steady‐state water with the body Shafdan with SAT the new effluents affected by theoperation desalinated regime water after about is expected four years to(since continue the operation in the of Hadera next fewplant). years This process until equilibriumof with “replacing” the previous water body with the new effluents affected by the desalinated water is the operation regimeexpected is to reached.continue in the Accordingly, next few years theuntil stable equilibrium water with isotopes the operation could regime be is usedreached. as a reliable and accurate tracerAccordingly, to track the the transportstable water isotopes and spreading could be used of as the a reliable effluent and accurate in the tracer aquifer. to track the transport and spreading of the effluent in the aquifer.

Figure 6. Mixing Ratios (MR) in recovery and observation wells vs. distance from the recharge Figure 6. Mixingponds. Ratios MRs (MR)were calculated in recovery from CBZ and results observation in the 2014 campaign wells vs. (represent distance also the from 2010–2011 the recharge ponds. 2 MRs were calculatedcampaign from assuming CBZ steady results‐state conditions), in the 2014 and campaignfrom δ H in the (represent 2010–2011 and also 2014 the campaigns 2010–2011 campaign (represent also MR‐δ18O results). assuming steady-state conditions), and from δ2H in the 2010–2011 and 2014 campaigns (represent also MR-δ18O results).4. Summary and Conclusions The present work examined the feasibility of using the stable water isotopes 2H and 18O as tracers for tracking different freshwater and effluent sources in the Israeli National Water Carrier 4. Summary and(NWC), Conclusions 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 2 18 The presentspecific work points examined along the NWC, the in feasibility the Shafdan effluents, of using and thein a set stable of recovery water and isotopes observation H and O as tracers for trackingwells. Each different campaign freshwater included simultaneous and effluent measurements sources of the in water the Israeli isotopes, National as well as Water Carrier carbamazepine (CBZ) and chloride concentrations (Cl) as referent tracers for the Shafdan–SAT (NWC), in the Dansystem. Region sewage–effluent system (the Shafdan plant), and in the aquifer during the subsequent SAT process.The results Two of this sampling work show, for campaigns the first time, werethe tremendous conducted effect of through the desalinated 2010–2011 water and 2014 in specific points alongon the isotopic the NWC, composition in the of the Shafdan mixed water effluents, in the NWC, and in in the a Shafdan set of facility recovery and in and the SAT observation wells. basins. This study also demonstrates for the first time on the linear isotopic composition relationship Each campaignbetween included the four simultaneous main freshwater measurements sources of Israel (and of their the mixed water products), isotopes, and asthe well moderate as carbamazepine (CBZ) and chlorideslope regression concentrations line compared (Cl) to asthe referentslopes of the tracers meteoric for water the lines. Shafdan–SAT These results enabled system. the use of the water isotopes as a conservative tracer throughout the completely manmade water cycle, The resultsstarting of this from work the freshwater show, sources, for the and first all the time, way to the the SAT tremendous system and the effect recovery of wells. the desalinated water on the isotopic compositionThe distinct difference of the in mixed isotopic watercomposition in the between NWC, the various in the freshwater Shafdan sources, facility along and in the SAT with the data regarding volume ratios between these sources in the centralized water system, enable basins. This studyus to alsoassess demonstratesthe isotopic composition for the of their first mixed time products on the in the linear NWC and isotopic in the Shafdan, composition based relationship between the fouron mainsimple dilution freshwater equations. sources The progressive of Israel enrichment (and their of the Shafdan mixed effluents products), in heavy and isotopes, 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 to 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.

Acknowledgments: This research was supported by Mekorot and BRGM research funds, and by the Israeli-France High Council for Scientific & Technological Research within the Environment and Energy program. We wish to thank the Mekorot Shafdan team for their help and support in sampling and fieldwork, and also thank the Water Authority laboratory team for the CBZ analyses. We also wish to thank Dani Cohen (Mekorot) for his help in calculating mixing ratios in the NWC, Yoram Katz (Mekorot) for information regarding the flow model and retention time in the aquifer, and to Avihu Burg and Itai Gavrieli (Geological Survey Institute of Israel (GSI)) for their kind support throughout the study. Author Contributions: Ido Negev and Joseph Guttman conceived and designed the experiments; Ido Negev performed the experiments, analyzed the data and established the conceptual model of mixing ratios in the water system; Wolfram Kloppmann provided isotope data from the BRGM isotope laboratory and contributed to the interpretation; Ido Negev wrote the paper. Conflicts of Interest: The authors Ido Negev and Joseph Guttman are Mekorot employees, who manage and operate the National Water Carrier and the Shafdan plant. However, the subject of this research: “to search and to examine tracers for the spreading of water bodies in the water systems and in the environment”, is not an issue under conflict of interest. Thus, we hereby declare that “The authors have no conflict of interest”. In addition, “The founding sponsors had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, and in the decision to publish the results”.

Abbreviations The following abbreviations are used in this manuscript:

SAT Soil Aquifer Treatment NWC National Water Carrier (of Israel) MBTP Mechanical Biological Treatment Plant MR Mixing Ratio SOG Sea of Galilee MCM/year Million Cubic Meter per year CBZ Carbamazepine DSP Desalination Plant Water 2017, 9, 73 15 of 16

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