Quantification of dissolved organic matter in pore water of the vadose zone using a new ex-situ positive displacement extraction

Chemical Geology 466 (2017) 263–273

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Quantification of dissolved organic matter in pore water of the vadose zone using a new ex-situ positive displacement extraction

MARK

Alexander Sopliniaka, Roy Elkayama,b, Ovadia Leva,⁎ a b

Casali Center of Applied Chemistry, The Institute of Chemistry, The Hebrew University of Jerusalem, Jerusalem 9190401, Israel Mekorot, Israel National Water Company. LTD., Israel

A R T I C L E I N F O

A B S T R A C T

Keywords: Dissolved organic carbon (DOC) Pore water extraction Mobile-immobile model Depth profiles Soil-Aquifer Treatment (SAT) Wastewater treatment Breakthrough curves

Quantification of dissolved organic carbon (DOC) in pore water is vital for understanding the transport of solutes and the fate of contaminants. However, the extraction of pore water from saturated soils, and even more so, from unsaturated soils without an artificial increase in the DOC content is challenging. To this end, we have established a methodology for pore water extraction from unsaturated and saturated soils based on the displacement of the pore water from cores withdrawn from the ground by direct-push drilling machines. The displacement extraction is performed by introducing distilled water at the top of a liner filled with soil core and collecting the displaced eluent from the bottom. This positive displacement extraction (PDE) method was compared to pore water extraction by centrifugation for the analysis of DOC. Method validation was carried out with various DOC levels using different flow rates and three different soil types: sandy, sandy-clayey and clayey. The limit of detection for the suggested method was < 0.22 mg L− 1 for all soil types, and for all studied saturation levels (> 15%) under flow rates lower than 1 mL min− 1. Extraction by centrifugation gave biased, unacceptable results throughout the studied DOC range (0–25 mg L− 1). Detailed parametric dependence by mobile – immobile modeling showed that for most soils and saturation levels collection of the first 10% of the pore water initially present in the core will introduce a bias of less 8% in DOC. For clayey soils with an exceedingly high immobile water fraction, a pedotransfer parameter estimation or comprehensive column tests should be carried out in order to estimate accurately the collectible water fraction and assure accurate prediction of the DOC level. Field studies that were carried out in a Soil Aquifer Treatment system provided 30 m deep DOC profiles with < 1.5 m spatial resolution, a resolution that is unattainable by alternative techniques.

1. Introduction Mobility and availability of nutrients and contaminants in soil are largely determined by their dissolved and dispersed portions in the pore water (Gregory, 2006; Hillel, 2003; Kirkham, 2005). Except for few cases, such as on-site determination of pH and dissolved oxygen by selective sensors (Topp et al., 2000; Vieweg et al., 2013; Westerman, 1990) and partition sampling by absorption sensors (Wu and Gschwend, 1986), the analysis of the solutes requires preliminary extraction of the pore water prior to laboratory analysis (Di Bonito et al., 2008). The analysis of dissolved organic carbon is often a challenging task since the concentration of the target species in the solid phase exceeds the dissolved concentration by several orders of magnitude (Kalbitz

et al., 2000; Lal and Shukla, 2004). Shear forces exerted during the extraction process disrupt the soil and artificially increase the concentration of solutes and solute-bearing colloids in the aqueous phase (Kaplan et al., 1993; Puls, 1990). The former is important only when equilibrium between the adsorbed and free forms was not attained prior to the sampling, whereas the latter can introduce positive bias even after equilibration (Sillanpää, 2014; Thurman, 1985). The organic content in soil is mostly > 0.1%wt, whereas the DOC of effluents and surface water is in the range of 10− 3 wt% (Hillel, 2003; Xu et al., 2013), and thus even leaching of a very small fraction of the soil organics would introduce unacceptable bias, e.g., 1% leaching would double the observed DOC. Extraction techniques of pore water from the vadose zone can be classified as those involving field sampling of soil and field extraction of

Abbreviations: BTC, breakthrough curve; CDE, convection-dispersion equation; DOC, dissolved organic carbon; IBTC, inverse breakthrough curve; MIM, mobile-immobile model; PD/ PDE, positive displacement extraction – pore water extraction by its displacement with distilled water.; SAT, soil-aquifer treatment; WWTP, wastewater treatment plant ⁎ Corresponding author. E-mail address: [email protected] (O. Lev). http://dx.doi.org/10.1016/j.chemgeo.2017.06.017 Received 25 October 2016; Received in revised form 25 May 2017; Accepted 14 June 2017 Available online 16 June 2017 0009-2541/ © 2017 Elsevier B.V. All rights reserved.

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Nomenclature C0, C Cm, Cim D, Dm De Kd Ks L n Pe R S t Vg VW Vx

z α α′

initial/solute concentration (M L− 3) solute concentration in the mobile/immobile phase (M L− 3) dispersion coefficient (L2 T− 1) in the bulk and in the mobile domain effective diffusion coefficient (L2 T− 1) distribution coefficient (L3 M) hydraulic conductivity (L T− 1) column length (L) an index of the soil water retention function (dimensionless) Peclet number, Lνm/Dm retardation factor (dimensionless) saturation level defined as θ/ε (%) time (T) bed volume, the geometrical volume of the core (L3) initial solute-bearing water volume in the core (L3) collectable volume of a breakthrough curve at a concentration cutoff percentile x

ε θ θm, θim θr θs λ, λm ν, νm ρb Ω

distance (L) mass transfer coefficient (T− 1) scale parameter inversely proportional to the mean pore diameter (L− 1) porosity, void fraction (L3 L− 3) total water content per unit volume (L3 L− 3) water content in the mobile/immobile phase per unit volume (L3 L− 3) residual water content per unit volume (L3 L− 3) saturated water content per unit volume (L3 L− 3) dispersivity in the bulk and in the mobile phase (L) pore water velocity, bulk and mobile phase velocities (L T− 1) solid bulk density (M L− 3) θim/ε, immobile water fraction defined as immobile water content/void fraction (%)

Subscripts m im

mobile phase immobile phase

An alternative set of methodologies for pore water extraction involves collection of the soil and extraction of the pore water by aggressive techniques. Pressure filtration (squeezing) and centrifugation of sampled soils are frequently used, which, however, involve sample homogenization and repacking into a centrifugation vial or pressure filtration cell (Fares et al., 2009; Gamerdinger and Kaplan, 2000; Litaor, 1988; Schrum et al., 2012; Tyler, 2000; Zabowski and Ugolini, 1990). Soil suspension in synthetic water, equilibration, and displacement of the pore water is an alternative method, which, however, extracts both adsorbed and dissolved species (Andersen et al., 1992; Celorie et al., 1988; Yin et al., 2002). All these methods involve excessive sheer force and interference of the solid phase. We had to face the challenges of pore water extraction and analysis during our studies of processes in the vadose zone of the aquifer recharge system of the effluent of the Shafdan wastewater treatment plant (Section 2.5). Depth profiling of the DOC in the vadose zone of water recharge systems was measured only by low resolution, due to the need to install a large number of samplers (Graham, 1989; Laws et al., 2011; Quanrud et al., 2003). In this article we introduce a novel methodology based on directpush rigs (Geoprobe™ (“Direct-Push Series Drilling Machines,”, 2016)) that allows collection of minimally disturbed soil samples from the unsaturated zone. The pore water in the soil-filled liners can then be washed by distilled water and the initial elution volume can be collected and analyzed. We validate the methodology by quantification of the DOC in effluents at different saturation levels under different experimental conditions and show that the inverse breakthrough curves (IBTC) fit the mobile-immobile model (MIM) well. The newly introduced methodology is demonstrated for high resolution profiling of DOC in the vadose zone of a Soil Aquifer Treatment system. A single day of sampling is sufficient to probe a 30-m deep DOC profile of a Soil Aquifer Treatment (SAT) system. Mathematical modeling shows that for most soils collection of < 10% of the initially present pore water for DOC analysis will yield an accurate DOC analysis. A general methodology for the estimation of the allowable volume of sample that should be collected from the core is presented.

the pore water from the ground. Each of these methodologies has been proven useful for some applications, but all suffer from substantial flaws that call for the development of an alternative approach. Passive samplers, which are also called free drainage samplers, such as the passive capillary lysimeters (e.g., Decagon Devices™ (“Decagon Devices,”, 1983)), collect drainage, which can be sent for laboratory analysis. These systems do not apply external pressure and thus sample only the macropore water, which makes the passive technique rather limited, since water content in the deep vadose zone may be very close to residual water (Dorrance et al., 1991; Fares et al., 2009; Van der Velde et al., 2005). The spatial resolution of the passive samplers is limited only by the number of samplers that are installed in the field, but since the installation at deep locations is expensive and manpower demanding, the spatial resolution of the concentration profiles is limited. Active samplers apply tension for sample withdrawal and therefore are more versatile. Carefully designed suctions cups have a tailored capillary pore size, which allows immobile pore water extraction, as well (Di Bonito et al., 2008; Dorrance et al., 1991; Graham, 1989; Grossmann and Udluft, 1991). Active samplers became the method of choice for the collection of water from shallow locations. The Rhizon™ samplers, which employ macroporous suction cups and external vacuum, are probably the most popular method for sediment pore water extraction nowadays. The Rhizon™ samplers became a basis for modification and improvement, e.g., by combining them with a portable electrophoresis device (Torres et al., 2013). However, sampling of hydrophobic contaminants such as polyaromatic compounds can be biased by adsorption to the high surface area filters and the release of organics from the filters (Di Bonito, 2005; Eijkelkamp Soil and Water company, 2003). This adsorption bias is obviously larger for microporous suction cups due to their higher suction tension. In addition, the application of excessive vacuum induces migration of colloids and clogging of the suction cup, and higher suction pressure (lower vacuum) results in slow flux and low sampling volumes (Ankley and Schubauer-Berigan, 1994; Gamerdinger and Kaplan, 2000; Grossmann and Udluft, 1991). Moreover, as with passive samplers, the spatial resolution of depth profiling of contaminants is limited by the cost of a large number of installed samplers. Finally, even with active samplers, the extraction of large volumes sufficient for trace organics analysis is slow, and, thus, it is impractical to extract microporous pore water by these devices (Di Bonito et al., 2008; Dorrance et al., 1991; Fares et al., 2009).

2. Material and methods 2.1. Materials and reagents Laboratory experiments were carried out with effluents from the 264

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2.3.1.2. Soil centrifugation. Centrifugal forcing of the pore water from the soil was carried out using the homemade setup described in Fig. 1C. 50 mL Falcon™ tubes were equipped with 3 mm PVC holey disks and a 40-mesh stainless steel net. The disk was supported by the bottom cone of the Falcon tube. Centrifugation was conducted using MRC™ MDCEN302 centrifuge at 6000 rpm for 3 min. Water was collected from the bottom of the tube by a syringe. For clayey saturated soils the process was repeated up to four times to collect most of the pore water.

Shafdan wastewater treatment plant (WWTP), Rishon LeZion, Israel. Characteristics of the secondary treated effluents are described in Table A1 in Appendix A. 2.1.1. Tested soils The validation tests were conducted using three different soils (Fig. 1B) with largely different permeabilities and soil characteristics, representing different layers of the Shafdan SAT vadose zone: A) Sandy soil (collected from a depth of 2 m), B) Sandy – clayey soil (from 8.5 m) and C) Clayey soil (from 15.5 m). Table 1 depicts the relevant physical and hydraulic characteristics and composition of the tested soils.

2.4. Physical and hydraulic soil properties 2.4.1. Water content and density Soil water content was determined according to ASTM D2216-10. Volumetric water content is derived by measurements of soil bulk density ρb, which was conducted while the soil was still within the liner according to ASTM D7263-09.

2.2. Liquid phase methods All experiments were carried out at a temperature of 20 ± 1 °C, a pressure of 695 ± 5 Torr and a relative humidity of 47.5 ± 2.5%. 2.2.1. Laboratory validation of the pore water extraction for DOC analysis 2.2.1.1. Principle. Geoprobe™ cores were collected from the Shafdan SAT and the cores were cut into sections of desired lengths. The core sections were then equilibrated with secondary treated effluent (STE) by pumping effluent-distilled water mix through the liners, using peristaltic pumps, until equilibrium was reached. Then, water was allowed to leach out and the set saturation level was attained by nitrogen flashing for several minutes. Afterwards, the cores were connected to the extraction setup and elution tests were conducted under controlled conditions. Each elution test was repeated three times (triplicates). 1 mL eluents were collected at the set elution time for each experiment and the average DOC and its standard deviation were used to construct the inverse break through curves. The samples were filtered and analyzed for DOC. Different DOC values were achieved by dilution of the STE with distilled water. High DOC concentrations in water were achieved by evaporation of the effluents with a rotary evaporator to achieve up to 25 mg L− 1 DOC.

2.4.2. Hydraulic conductivity Hydraulic conductivity under saturation, Ks, was measured using the setup of Fig. 1 using a 10 m head tank and measurement of the water flow rate after saturation was reached (Hiscock, 2005; Lal and Shukla, 2004). 2.4.3. Soil organic matter content Organic matter content was measured according to ASTM D297400. 2.4.4. Soil texture The particle size distributions of different soil fractions were determined by sieving according to ASTM D422-63. 2.5. Field test site Field studies were carried out in the Shafdan water recharge

2.3. Liquid phase tests Geoprobe™ PVC liners were collected from clayey, sandy and sandyclayey layers of the vadose zone below the infiltration basins of the Shafdan SAT. A set length of the core was cut and sealed at both sides by Delrin™ stoppers, held in place by Teflon™ O-rings (Fig. 1A). Inlet and outlet stainless steel ball valves were attached to the upper and bottom holders, and a third ball valve gas inlet was installed in a T connection at the inlet side. Silicon tubing, a peristaltic pump (MasterFlex easy-load™ model 7518-10), and a 500 mL plastic container were used for spiked effluent circulation through the liner. Circulation rate was set at 0.1–1 mL min− 1. Periodic sampling and analysis of DOC assured that equilibration was achieved. Usually, equilibration was attained after < 100 bed volumes were circulated through the core. 2.3.1. Extraction of pore water Extraction of pore water was done using two different methods: centrifugation and column leaching. 2.3.1.1. Positive displacement extraction (PDE) test. The equilibrated core (Fig. 1A) was connected to a 5 L distilled water container by a 10 m long Teflon™ tubing (0.9 cm in diameter). The container served as a constant-height head tank. We demonstrate that the concentrations of DOC in the first portion of the IBTC are equal to the DOC in the pore water and provide a simple way to determine pore water DOC, and thus only the first portion of eluted water should be sampled for analysis. The tests were carried out using 30 cm sections of clayey (B, C) and sandy (A) soils, respectively. Flow rates were tested in the range between 0.25 and 10 mL min− 1. Three water saturation levels were tested: 15% (soil A), 20% (soil B), 25% (soil C), 50%, and 90%.

Fig. 1. Liquid phase extraction setups. A. Column leachate system – composed of a section of PVC liner sealed at it ends by inlet and outlet Delrin™ caps held in place by two Teflon O-rings and equipped with stainless steel valves. B. cores of soil type A–C, representing (A) sandy, (B) sandy clayey, and (C) clayey soils. The liner is sealed at both ends with plastic caps. An empty liner section is also shown. C. Soil centrifugation setup. The Falcon tubes are equipped with holey disks and 40 mesh flat strainers supporting the soil sample. Water is collected below the holey support.

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Finally, we conclude with results of field studies in a SAT system and demonstrate a practical application. According to the proposed method the DOC of a minimally disturbed soil can be evaluated based on the whole IBTC or by analysis of the DOC in the first portion of water emanating from the bottom of the core. The amount of water that can be collected for analysis is therefore a pertinent practical question whose answer depends on the initial water hold up in the examined core as well as on soil hydraulic parameters and elution speed. The fraction of water that can be collected for DOC analysis (Vx) out of the initial water holdup (Vw) is the most important parameter from the experimental point of view. Collection of an excessive volume for analysis would inevitably lead to a dilution error, and underestimation of the DOC, whereas collection of too small a volume may cause analytical errors in the instrumental determination of the DOC in the sampled volume. In Appendix B we present a detailed parametric analysis of the dependence of Vx/Vw and the associated dilution bias on the hydraulic and solute parameters. We have chosen to examine the effect of all these parameters by analysis of the IBTCs by MIM, which provides a comprehensive description of the stagnant water portion in soils. The drawback of MIM is the large number of variables that are needed in order to evaluate the IBTC. Appendix B describes the dependence of Vx/ Vw and dilution bias on the hydraulic parameters, S and θim/ε (the latter is denoted as Ω, immobile water fraction), the transport parameters Dm, Kd, α and the operational parameter, Peclet number (Pe).

Table 1 Soil characteristics. Soil type

Sand%

Silt%

Clay%

Organic matter %

ρb (gr cm− 3) Bulk density

Ks (cm day− 1) Hydraulic conductivity

A B C

93 60 19

7 10 14

– 30 67

0.05 0.20 0.36

1.58 1.58 1.45

529 ± 10 14.0 ± 0.4 1.5 ± 0.2

lagoons. The Shafdan WWTP treats over 130 Mm3 of domestic wastewater from the 2 million inhabitants of the Tel Aviv Metropolitan Area. The process involves mechanical and biological treatment with nitrification/denitrification followed by surface spreading aquifer recharge of the effluent. The percolation lagoons are flooded for 24 h by the effluent, after which the lagoons are allowed to dry for 2–3 days. The water table is at −36 to −40 m below the bottom of the lagoons. The water flows horizontally in the saturated zone and is reclaimed after a retention time of approximately three years for irrigation. The percolation lagoons are located in the coastal aquifer of Israel along the Mediterranean Sea coast. The aquifer is phreatic Pliocene-Pleistocene aquifer, comprising of predominantly calcareous sandstone interlaced by intercalations of clay, silt and loam layers. The aquifer overlies impermeable shales of the Saqiye group at a depth of 100–150 m below ground level (Herman and Idelovitch, 1987; Icekson et al., 2015; Idelovitch and Michail, 1984).

3.1. Practical working ranges for collection of water volumes

2.5.1. Soil core collection Soil core collection was performed in a percolation lagoon 24 h after the field flooding ended. The sampling was done by Direct Push VTR 9700 rig from AMS Technologies™. The rig pushes cylindrical PVC liners of 3.8 cm in diameter and 1.5 m long. The liner is then withdrawn with the soil core to the surface. Sampling was done down to 30 m below the ground (“Direct Push Series Drilling Machines,”, 2016).

Fig. 2A and B summarize the calculated permissible working ranges for all presented soil types (sandy, sandy clayey and clayey), represented by the areas beneath the various curves for collection volumes of 10, 25, 50 and 70% of the initial water content, Vw, for Peclet number, Pe = 30 (frame A) and 300 (Frame B). The former is the lowest Pe value within the range of an acceptable bias of < 10%, and the latter represents the average Pe number in our studies. The dilution bias by collection of the indicated permissible volume for analysis is shown in the various points on the boundary curve, and it is readily seen that it is mostly < 8%. The curves show that there is a trade-off between Ω and S; the permissible range of Ω increases with increased initial saturation level.

2.6. Analytical measurements and instruments 2.6.1. DOC quantification DOC samples were filtered with a 0.22 μm filter and then quantified using a Shimadzu TOC-V CPH E200V Total Organic Carbon analyzer according to EPA method 5310. The instrumental limit of quantification (LOQ) was 0.1 mg L− 1 for a signal-to-noise ratio (S/N) = 10.

3.2. Laboratory studies of PDE of pore water Pore water extraction was carried out for each of the three target soils (A–C), at three saturation levels and six different flow rates in the range 0.25–10 mL min− 1. The full IBTCs of DOC of (the sandy) soil A are depicted in Fig. 3 for three flow rates (0.25, 1, and 10 mL min− 1 for frames A, B, and C, respectively) and three saturation levels (15%, 50%, and 90%, depicted with different symbols on the same curve). Similar results were obtained for the clayey soils (B, C), and these are depicted in Figs. A1 and A2 in Appendix A. Frames A, B, and C depict the IBTCs obtained for pore water with DOC between 10 and 15 mg L− 1, chosen as midrange examples between 0 and 25 mg L− 1 (Section 2.2). The normalized DOC concentration is depicted as a function of the number of bed volumes displaced out of the core. The average of triplicate analysis is depicted for each data point with the corresponding relative standard deviation bar. The curves in frames A–C (as well as the corresponding curves in Figs. A1 and A2) represent numerical solutions by MIM fits to the observed IBTCs by the Hydrus™ software. Solutions were fitted to 0.25 mL min− 1 IBTCs only. Table 2 summarizes the parameter values obtained from the IBTCs shown in frame A of Figs. 3, A1 and A2. The average DOC concentration values, received from the initial plateau of the different IBTCs in the range of 0–25 mg L− 1, were plotted in frames D–F in Fig. 3 (and Figs. A1 and A2 for the clayey soils) as a function of the equilibrated DOC level (0–25 mg L− 1). We received good fits to the observed DOC and equilibration DOC for 0.25 and

2.6.2. Numerical simulation A one-dimensional numerical modeling software Hydrus-1D™ (“PCProgress: HYDRUS 1-D,”, 2016; Šimůnek et al., 2008), was used to solve the Richard's equation for water flow and solute transport. In this study, the dual porosity MIM option for water flow and the MIM option were used to best fit the DOC experimental data and to estimate the parameters Dm, Kd, α, and θim. The immobile fraction size is defined in this paper by the operational parameter Ω, which equals θim/ε. Table A2 depicts the hydraulic parameters taken from the Neural Network Prediction of Hydrus™ (Rosetta Lite v. 1.1 (June 2003), Schaap et al., 2001) based on values from Table 1. Boundary hydraulic conditions were set to constant (upper) flux and seepage face (at the bottom, h = 0), and the transport boundary conditions were set to zero concentration flux at the top and zero concentration gradient at the bottom. 3. Results We start this section by presenting the modeling activity, which is imperative in understanding the PDE method and its applicable parametric domain. Then, we present the analytical studies and method validation in comparison to pore water extraction by centrifugation. 266

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0.22 mg L− 1 for soils A, B, and C, respectively. We believe that the higher noise level for clayey soil reflects the difficulty of reaching DOC saturation for clayey soil, i.e., it reflects imprecise validation testing rather than a true bias of the method. It could be noted also, that the absolute bias at high flow rates was, in all cases, positive, i.e., the observed levels were higher than the “true” DOC values, which were obtained after equilibration. The higher bias observed at high flow rates is attributed to higher shear stress, which detached colloidal particles from the soil. Most of these particles are filtered out during the DOC analysis by our 0.22 μm filtration, but particles that are smaller than the filter cutoff could still bias the analysis. Similar results were obtained by Kaplan et al., 1993, who received enhanced colloidal migration and contribution to dissolved organics under the influence of an increasing flow rate. The contribution to dissolved organics in water due to the presence of colloids is well-reported and was observed, for example, by Chiou et al., 1986 and Puls, 1990. 3.3. Pore water extraction by centrifugation Pore water extraction by centrifugation was carried out using soils A–C at saturation levels of 15% (soil A), 20% (soil B), 25% (soil C), 50%, and 90%. Fig. 4 depicts the DOC tested values after pore water extraction plotted against the equilibrated DOC values, which served as an estimate for the true value. Every data point is the average of triplicates. It can be seen that the observed values are always much larger than the equilibrated concentrations, (i.e. the true values). The standard deviation for a DOC measurement was, on average, 10.0 mg L− 1, and the average differences between the estimated values and the true values (bias) of the measurements was 12.5 ± 1.0, 16.6 ± 4.3 and 21.3 ± 5.6 mg L− 1 for soils A–C, respectively. It can be noted, that the bias increases as the soil becomes more clayey. This can be attributed to the increased organic matter content in the soil, and hence, to increased contribution of detached colloids to the observed DOC, as discussed above. The bias should grow with the increase in organic content. 3.4. Field tests of Shafdan SAT depth profile 3.4.1. Hydraulic conductivity and lithology The lithology of the working site is depicted in Fig. 5A. Sandy and calcareous layers are interrupted by clayey inter layers at − 8.5, − 12.5, − 16, and −22 m. Water infiltration through the percolation lagoon is governed by the position and width of the clayey layers, which have low hydraulic conductivity, as presented in Fig. 5B. The values of conductivity range between 2 and 5 m day− 1 for sandy soil and 10− 3–0.1 m day− 1 for clayey soil.

Fig. 2. Working ranges of water extraction for different initial conditions of saturation and immobile fractions at Peclet equal to 30 (Frame A) and 300 (Frame B). The curves correspond to a bias of < 8%, as depicted for specific points in the upper curves. The sampling volume indicated near each curve assures unbiased (< 8%) representative samples for all the working conditions below the respective curve. In frame B our data are presented for soil A (Δ), soil B (□) and soil C (○). The dotted curve in cyan represents low water collection under harsh immobile constraints, as can be seen in Table 3. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

3.4.2. DOC depth profiles IBTCs were constructed for all soils under various initial conditions, and MIM curves were fitted using Hydrus™ software. The best fit hydraulic and transport parameters are shown in Table 2 and the working points found in this study are depicted in Fig. 2B. The DOC level was then measured using the first 1 mL of water from each core. Fig. 5C and D depict the DOC concentration profiles that were obtained by the examined pore water extraction methods: PD and centrifugation. Fig. 5C depicts the PD tests and shows a descending trend in DOC concentration, which starts around 10 mg L− 1 at the topsoil, in agreement with the influent values (Table A1). The DOC level decreased from 10 to 3 mg L− 1 in the 30 m deep borehole. However, this decrease was not monotonic. First, a steep decrease in DOC level was observed until − 1.5 m where the DOC concentration was only 4.1 mg L− 1. Then the DOC concentration decrease was interrupted by a DOC plateau between − 1.5 and −6 m, and three small concentration humps are observed at −7.5, −13.5, and − 21 m. The lithological profile (Fig. 5A) shows a clayey layer slightly below or at the corresponding depths.

1 mL min− 1 flow rates (frames D and E). The deviation of the slope from 1 was 0.0192, 0.0243, and 0.0277 for soil A, 0.0253, 0.0183, and 0.0138 for soil B and 0.0194, 0.0233, and 0.0138 for soil C for a flow rate of 1 mL min− 1 at 15–25%, 50%, and 90% relative saturation. The standard deviation of the slope evaluated at 95% confidence level was always < 0.2. The R2, standard deviation, and averaged bias of all the validation fits for the range 0.25–10 mL min− 1 are depicted in Table A3, showing a gradual deterioration of the accuracy of the fit with increased flow rate. No significant deviation was found between the bias obtained at different saturation levels at the same flow rate. The method detection level (at 0.25 mL min− 1) estimated from the noise level at 0.30 mg L− 1 DOC and using S/N = 3 was 0.12, 0.19, and 267

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Fig. 3. Experimental breakthrough curves for DOC for soil A (A.–C.) and validation curves for the pore water PD (D.–F.). Data are presented for three saturation levels, 15% (circle), 50% (square) and 90% (triangle) and for flow rates equal to 0.25 (A., D.), 1 (B., E.) and 10 mL min− 1 (C., F.). Breakthrough curves were fitted with MIM using Hydrus-1D™. The whole IBTC was evaluated for each data point, but the data in frames D–F were drawn based on the initial plateau only of the IBTC curve.

4. Discussion

Table 2 MIM-fitted parameters obtained from the IBTC for 0.25 mL min− 1 and the set of experimental conditions shown in Fig. 3A. Soil types

Sat. levels (%)

Ω (%)

Dm (cm2 d− 1)

α (d− 1·10− 3)

Kd (cm3 gr− 1)

R

Soil A

15 50 90 20 50 90 25 50 90

5.55 4.87 5.48 17.71 17.24 17.49 24.01 23.60 23.19

3.82 3.76 3.87 3.68 3.97 3.94 3.83 3.96 4.13

11.11 15.43 22.12 17.22 18.57 24.31 18.12 23.81 30.89

0.008 0.010 0.010 0.010 0.011 0.010 0.014 0.015 0.016

0.9876 0.9923 0.9978 0.9866 0.9856 0.9932 0.9833 0.9899 0.9954

Soil B

Soil C

The discussion section is devoted to two issues – presentation of a general methodology to estimate the amount of water that can be collected from a core and a discussion of the Shafdan SAT DOC depth profile. Criteria for evaluation of the collectable volume: Figs. 2 as well as Figs. B2 and B3 in Appendix B present the dependence of the collectable water sample (Vx) on soil parameters. In order to calculate a Vx that would give a reasonable bias, one must evaluate the hydraulic and transport parameters of the soil-water-solute system, specific for each soil type. These parameters are the initial saturation level (S), the immobile water fraction (Ω), the Peclet number (Pe), and the exchange rate (α). Previously reported studies gave a wide range of values for these parameters for different types of soils (Table 3), which, at first glance, call for MIM analysis for each DOC measurement. However, closer scrutiny of the data ranges in Table 3 allows for certain simplifications. In all cases in Table 3, the exchange rate α corresponds to a time scale of several days, which is larger by at least an order of magnitude than the runtime of the proposed PD procedure detailed here. Therefore, the effects of the exchange rate on the amount of collectable water can be considered negligible. In addition, the reported Pe numbers are

2

The DOC profile which was obtained by centrifugation is depicted in Fig. 5D. The depth profile is dull in details. The profile starts from a very high concentration of 40–55 mg L− 1 and decreases to 20 mg L− 1 plateau at − 6 m to − 25 m, followed by an increase in DOC concentration to 35 mg L− 1 upon reaching the 30 m depth. Since the influent DOC is only around 10 mg L− 1, the profile reflects a large methodical bias, which was observed also in the method validation tests, depicted in Fig. 4. 268

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fractions for clayey soils reaching 80–95%. Ω for the rest of the soil types fall in between sandy and clayey. According to Table 3 and Fig. 2, we can conclude that collection of ≤ 10% of pore water provides sufficient amount for organic matter analysis for the vast majority of soil types except for clayey soils. For clayey soils or whenever the type of soils is unknown, site specific information, pedotransfer functions, or direct hydraulic fit to mathematical modeling can provide the hydraulic parameters that are necessary for estimation of the permissible collectable volume pore water fraction. A guidance diagram of possible pathways to calculate or estimate Vx/VW is presented in Fig. 6 for different types of soils and levels of know-how. First, an assessment of the soil texture can be carried out, since for sandy soils an estimate of Vx can be done by following the criteria mentioned above for Ω ≤ 12% and Pe = 30 (shown in pathway 1, Fig. 6). From Fig. 2A, it can be seen, that for Ω = 12%, a low estimate of Vx can be made as a function of the saturation conditions. When S ≥ 60%, Vx/VW can be taken as 0.7, for S > 30%, Vx/VW can be taken as 0.5, and for S ≤ 30%, Vx/VW can be taken as 0.1. Other approaches should be used in order to estimate the collectable water volume for other types of soils, including clayey, or when the soil cannot be classified a priori. In many sites, there is a prior estimate of the soil parameters, due to previous research efforts; for instance, our study provides a good estimate for the immobile water fraction (Ω < 24%) for the Shafdan SAT site. Pedotransfer functions were derived for many (and a rapidly growing number of) regions in the world (e.g. Goncalves et al., 2001; Holland and Biswas, 2015; Moeys et al., 2012; Pachepsky and Rawls, 2004). Pedotransfer functions provide estimates of various hydraulic and transport parameters by correlation with physical properties of the soil. The pedotransfer pathway is denoted as pathway 2 in Fig. 6. After estimating an upper bound for the immobile water fraction, two options become available: first, Fig. 2A can be used to assess the permissible collectable water volume within a range of dilution bias < 10%. Second, S, Ω and Pe can be used to simulate an inverse breakthrough curve, using a modeling software such as Hydrus™ or CXTFIT2 (Toride et al., 1995), and then Vx/VW can be calculated directly. Pathways 1 and 2 in Fig. 6 are the only pathways allowing for in papyro estimation of parameters. Alternatively, pathways 3–4 (Fig. 6) can be used, which would require either BTC or IBTC tests. BTC tests (pathway 3, Fig. 6) are experiments involving species, which are not originally present in the core. Br−, F− or nonadsorbing (anionic) dyes can be used as tracers. In such experiments, the tracer is introduced into the soil and its outflow concentration is monitored. The result is a breakthrough curve, obtained from the collection of several elutions. From this point, the curve can be fitted to MIM using software, as described above, and Vx/VW can be calculated. IBTC tests (pathway 4, Fig. 6) are experiments involving species, which are present in the pore water. These surrogate species (e.g., Cl−) replace the use of the target solute, DOC in this case, because they can be measured more easily. Vx/VW can be estimated directly from the IBTC, or the data can be fitted to MIM, as was described above (pathway 4.1, Fig. 6). A very useful surrogate is the UV254 absorbing species, since UV measurement is easy and nondestructive, and the samples that were used for UV analysis can be reused for the DOC tests. Another option for IBTC tests is to measure the DOC in the outlet itself (pathway 4.2, Fig. 6); this would provide an inverse breakthrough curve and Vx/Vw can be estimated directly from the raw results. The initial DOC can then be estimated by averaging the DOC values in the plateau region of the IBTC.

Fig. 4. Equilibrated DOC values compared with DOC from extracted water by centrifugation for soils A, B and C (frames A.–C., respectively) at three saturation levels, 15–25% (circle), 50% (square) and 90% (triangle).

always > 30 (for L > 30 cm). Hence, when estimating the effects of dispersion on the collectable water volume, if no prior information is known, one can assume Pe = 30 as a worst case scenario (provided that L > 30 cm). The initial saturation level of the soil (S) can also be easily determined by gravimetry or Loss On Ignition (LOI) techniques. The large uncertainty, therefore, stems from the determination of the immobile water fraction, Ω, and, indeed, a broad range of values is reported for Ω in different soils (Table 3). In spite of this fact, the reported immobile water quantities have a distinct division between sandy soil, clayey soils and other soil types. It can be seen that for sandy soils the immobile water fractions are lower than 12%, and for clayey soils the values of Ω can go up to 60% for most cases. A few reported cases deal with very high values of immobile

4.1. Field studies in the Shafdan SAT A discussion of the Shafdan SAT results should address two issues: relevance to method development and interpretation of the DOC depth profile. 269

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Fig. 5. Field results for the Yavne 2 percolation lagoon. A. Lithology profile of the percolation lagoon down to − 30 m. The soil consists mostly of sand and calcareous sandstone with interlayers of clayey soil at − 8.5, − 12.5, − 16, and −22 m. B. Hydraulic conductivity profile as a function of depth, as was measured using the PD methodology. C. DOC depth profile determined by the PD method. The red dashed line represents the decreasing trend in DOC, neglecting the clay layers. D. DOC depth profile measured by soil centrifugation. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

low values of Ω are attributed to the low organic matter content (< 0.5%wt/wt) in the vadose zone of the Shafdan SAT (Table 1). Similar observations of very low levels of organics in the Shafdan SAT were reported by Lin et al., 2008 and Icekson et al., 2015. The dependence of the immobile water content on the organic matter content was established, for example, by studies of Kim and Corapcioglu, 2002; Mohawesh et al., 2014; Tabarzad et al., 2011; Totsche et al., 1997. Thus, despite the fact that MIM has never been conducted for the Shafdan SAT, or any other SAT, the range of Ω values obtained in our studies are in agreement with prevailing knowledge. The observed dispersion coefficient at a flow rate of 0.25 mL min− 1 for clayey soils B & C were slightly higher on average than for the sandy soil A (3.82 vs. 3.86 and 3.97). Similar observations were established in previous studies (e.g. Delgado, 2006; Eidsath et al., 1983; Perfect et al., 2002; Vervoort et al., 1999), suggesting that soils with finer grains and larger particle distribution have higher dispersion. For our core lengths (usually, L = 30 cm) and for a flow rate of 0.25 mL min− 1, Pe was always within a narrow range of 270–310. According to Fig. 2B and the diagram in Fig. 6, the collectable water volume from sandy soils (corresponding to the depths 0–7 m, 9–11 m, 13–15 m, and 16–21.5 m in the Shafdan SAT site) could be estimated by path 1 to allow collection of Vx/Vw < 0.5. The 1 mL samples that were collected in our studies were always well within this range. For soils B (corresponding to depths 7.5–9 m) and C (corresponding to depths 11.5–12 m, 15.5–16 m, and 21.5–22 m) we had to rely on paths 3 or 4 for estimations of Vx, since the soil was not sandy and pedotransfer functions were not available for the vadose zone of SATs. We preferred using the DOC itself rather than a surrogate or a tracer to estimate Vx (corresponding to path 4.2 in the guidance diagram). V85/Vw for the three IBTC cases that were studied in detail was in the range of 0.38–0.51, 0.58–0.83, and 0.63–0.87 for saturations 15–25%, 50%, and 90%, respectively (Figs. 5, S6 & S7) for a flow rate of 0.25 mL min− 1. In addition, Vx/Vw was also calculated based on MIM parametric fits and the values of V85/VW could be estimated independently by Hydrus™ calculations, and, as can be seen in Fig. B1, the estimates for V85/Vw were very close to the direct observations. Based on the detailed studies of the three test cases that were examined in this study and the detailed parametric dependence of the MIM fits, we could guarantee that we could use Vx/Vw < 0.38 for the Shafdan SAT, even without detailed MIM fits of all the points in the depth profile (Fig. 5). We propose that a similar algorithm can be taken for other sites as well. One can start by detailed IBTC studies of extreme cases, parameter estimates, and finally, evaluation of Vx/Vw for the

Table 3 Values of the MIM parameters α (d− 1), Ω (%), and experimental conditions for Peclet numbers (Pe). Reference

Range of α

Range of Ω

Range of Pe

Remarks

Jacobsen et al. (1992) Padilla et al. (1999) Toride et al. (2003) Van Genuchten and Wierenga (1976) Jaynes et al. (1995)

0.006–0.020

2.3–9.5

48–198

0.535–2.820 0.096–9.824 0.048–0.250

3.0–6.2 3.0–8.6 11.0–37.0

50–750 57–509 35–95

Coarse sandy soil Silica sand Dune sand Clay loam soil

0.043–0.384

51.0–95.0

NA

Saadat et al. (2012)

0.031–0.816 0.216–0.240

22.0–81.0 5.0–11.0

NA NA

0.984–1.730 1.030–1.320 NA

16.5–41.0 20.5–33.8 18.0–57.0

NA NA NA

0.019–0.132 0.024–0.055

26.4–69.6 35.1–45.9

NA NA

Beibei et al. (1992)

0.029–0.150

39.0–91.0

82–150

This study

0.011–0.022 0.017–0.024

4.9–5.6 17.2–17.7

290–299 283–306

0.018–0.031

23.2–24.0

272–293

Holland and Biswas (2015) Alletto et al. (2006)

Sandy clayey loam soil Clay loam soil Sandy loam soil Loamy soil Clay loam soil Sandy clay soil Silt loamy soil Silt clayey loam soil Clay aggregates Sandy soil Sandy clayey soil Clayey soil

4.1.1. Parameter estimation and evaluation of Vx/Vw for the Shafdan SAT First, we had to compare the parametric range with the roadmap of Fig. 6 and assess its underlying assumptions. We have carried out MIM fits of the observed IBTCs (Fig. 3 and the corresponding Fig. A1 and A2 in Appendix A). The first-order exchange rate values, α, of the Shafdan samples, were evaluated, showing that the highest exchange rate was 0.031 d− 1, corresponding to 32 days. Thus, neglecting α is justified, at least for the Shafdan SAT. The observed distribution coefficients, Kd, of the DOC based on the IBTC fits were, in all cases, lower than 0.016 cm3 gr− 1. The calculated retention factors, R, corresponding to these Kd values (Eq. [B.2]) were always < 1.05, which justifies the R = 1 assumption. Note that higher R would increase Vx, and therefore, taking R = 1 provides a worst case scenario. The immobile water fractions, Ω were always within the literature reported range (Table 3) and they were all < 24%, though soils B and C were close to the lower limits of their respective literature ranges. The 270

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Fig. 6. A guiding diagram for obtaining the permissible collectable volume. Paths in red do not require experimental evaluation of the whole IBTC.

oxygen level until anaerobic conditions were reached at −10 m. A similar profile is observed for the DOC, but the latter uniformly declines throughout the anaerobic zone as well. 11% of the DOC was consumed in the anaerobic zone (Fig. 5C). DOC decline under oxygen-limiting conditions is mostly associated with denitrification or sulfate reduction. The first is likely to take place in the Shafdan SAT, since nitrogen mass balance indicates that minor degree of denitrification (~ 17%) takes place in the Shafdan SAT (Elkayam et al., 2015). The sulfate reduction would result in hydrogen sulfide formation, but this was never witnessed by us in the Shafdan SAT, nor is it likely to prevail in the presence of the large nitrate concentrations in the Shafdan SAT (> 6 mg L− 1 nitrate). On top of the steady DOC decline between − 6 m and −30 m, Fig. 5C shows three shallow DOC peaks at the clayey layers (− 7.5, − 13.5, and −21 m). We attribute these peaks to straining of organic rich colloids (nanoparticles) that are retained by the clayey layer, resulting in larger organic content in the clayey barriers. Additionally, the decrease in DOC level just below the clayey barrier may point to lateral convection, which, however, we have no means to assess. The DOC depth profile obtained by centrifugation is ignored altogether in this discussion as it is clearly erroneous. High resolution DOC mapping is needed in order to obtain the detailed DOC mapping that was demonstrated in Fig. 5C; lower resolution mapping that could be obtained by installation of multiple suction traps could resolve the detailed DOC profile only by installation of some 20 sampling traps, which is rarely affordable.

worst case; then the same Vx/Vw can be used for DOC sampling in all other test points. 4.1.2. Interpretation of DOC depth profile in the Shafdan SAT The second issue to be addressed here is the agreement between our Shafdan SAT depth profile and the prevailing knowledge regarding DOC in surface spreading SAT sites. The DOC depth profile (Fig. 5C) starts at the topsoil with concentrations that are close to the secondary treated effluents (Table A1), and then the DOC is reduced steeply in the first few meters from 10.0 to 4.1 mg L− 1 at − 1.5 m, corresponding to 60% removal of the initial DOC concentration. Then, the concentration decreases more slowly (as depicted by the dotted line in Fig. 5C), but it is interrupted by a few irregularities that occur near clayey barriers. The fast DOC decrease near the topsoil agrees with DOC depth profiles that were obtained for other SATs in field studies (Amy et al., 1993; Drewes and Fox, 1999; Quanrud et al., 2003; Wilson et al., 1995) and in column models (Cha et al., 2005; Quanrud et al., 1996; Suzuki et al., 2015; Westerhoff and Pinney, 2000; Xue et al., 2007; Zhao et al., 2007). A similar DOC profile, in the upper two meters of the Shafdan SAT was reported before (Icekson et al., 2015; Lin et al., 2008). The DOC depth profile is also similar to that obtained in different sites such as forest soils (Currie et al., 1996; Dosskey and Bertsch, 1997), seas, lakes, and sediments (Carlson et al., 1994; Currie et al., 1996; Maloney et al., 2005). The higher availability of oxygen and the straining of bacteria arriving from the percolation lagoons in the topsoil explain the steep DOC decline. Water retention in the organics-rich topsoil (Quanrud et al., 1996; Rooklidge et al., 2005) was indicated to contribute to the phenomenon, but we did not observe any increase of water content in the upper layer of the Shafdan SAT (not shown), and thus this mechanism seems to be unimportant for the Shafdan SAT. The DOC profile in Fig. 5C can be compared to the dissolved oxygen profile that was reported for the Shafdan SAT under similar conditions (Elkayam et al., 2015; Sopilniak et al., 2015). The dissolved oxygen profile exhibited a sharp decline from saturation levels (8.1 mg L− 1) at the topsoil to 3.9 mg L− 1 at − 1.5 m and then a gradual decrease of the

5. Conclusions A novel methodology for the extraction of pore water from unsaturated and saturated soils was developed, validated in the laboratory and applied in the field. Guidelines for the use of this methodology in the extraction of pore water from the vadose zone were developed. The method minimizes shear stresses and artificial detachment of organic colloids from the soil. Modeling of the parametric dependence of hydraulic and solute transport parameters showed that collection of 10% 271

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sandy forest soil. Soil Sci. Soc. Am. J. 61, 920–927. http://dx.doi.org/10.2136/ sssaj1997.03615995006100030030x. Drewes, J.E., Fox, P., 1999. Fate of natural organic matter (NOM) during groundwater recharge using reclaimed water. Water Sci. Technol. 40, 241–248. http://dx.doi.org/ 10.1016/S0273-1223(99)00662-9. Eidsath, A., Carbonell, R.G., Whitaker, S., Herrmann, L.R., 1983. Dispersion in pulsed systems–III comparison between theory and experiments for packed beds. Chem. Eng. Sci. 38, 1803–1816. Eijkelkamp Soil & Water company, 2003. Rhizon Operating Instructions [WWW Document]. URL. https://www.eijkelkamp.com/files/media/Gebruiksaanwijzingen/ EN/m2-1921erhizonsamplers.pdf (accessed 1.7.16). Elkayam, R., Sopilniak, A., Gasser, G., Lev, O., 2015. Oxidizers demand in the unsaturated zone of a surface spreading, soil aquifer treatment system. Vadose Zo. J. 14. Fares, A., Deb, S.K., Fares, S., 2009. Review of vadose zone soil solution sampling techniques. Environ. Rev. 17, 215–234. http://dx.doi.org/10.1139/A09-010. Gamerdinger, A.P., Kaplan, D.I., 2000. Application of a continuous-flow centrifugation method for solute transport in disturbed, unsaturated sediments and illustration of mobile-immobile water. Water Resour. Res. 36, 1747. http://dx.doi.org/10.1029/ 2000WR900063. Goncalves, M.C., Leij, F.J., Schaap, M.G., 2001. Pedotransfer functions for solute transport parameters of Portuguese soils. Eur. J. Soil Sci. 52, 563–574. http://dx.doi.org/ 10.1046/j.1365-2389.2001.00409.x. Graham, D.D., 1989. Methodology, Results, and Significance of an Unsaturated-zone Tracer Test at an Artificial-Recharge Facility, Tucson, Arizona. U.S Geological Survey, Tucson, AZ. Gregory, P.J., 2006. Plant Roots Growth, Activity and Interaction with Soils, Statewide Agricultural Land Use Baseline 2015. Blackwell Publishing, Oxford, UK. http://dx. doi.org/10.1017/CBO9781107415324.004. Grossmann, J., Udluft, P., 1991. 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Jacobsen, O.H., Leij, F.J., Vangenuchten, M.T., 1992. Parameter determination for chloride and tritium transport in undisturbed lysimeters during steady flow. Nord. Hydrol. 23, 89–104. Jaynes, D.B., Logsdon, S.D., Horton, R., 1995. Field method for measuring mobile/immobile water content and solute transfer rate coefficient. Soil Sci. Soc. Am. J. 59, 352–356. http://dx.doi.org/10.2136/sssaj1995.03615995005900020012x. Kalbitz, K., Solinger, S., Park, J.H., Michalzik, B., Matzner, E., 2000. Controls on the dynamics of dissolved organic matter in soils: a review. Soil Sci. 165, 277–304. Kaplan, D.I., Bertsch, P.M., Adriano, D.C., 1993. Soil-borne mobile colloids as influenced by water flow and organic carbon. Environ. Sci. Technol. 27, 1192–1200. Kim, S.B., Corapcioglu, M.Y., 2002. Contaminant transport in dual-porosity media with dissolved organic matter and bacteria present as mobile colloids. J. Contam. Hydrol. 59, 267–289. http://dx.doi.org/10.1016/S0169-7722(02)00043-8. Kirkham, M.B., 2005. Principles of Soil and Plant Water Relations, Principles of Soil and Plant Water Relations. Elsevierhttp://dx.doi.org/10.1016/B978-012409751-3/ 50004-9. Lal, R., Shukla, M.K., 2004. Principles of Soil Physics, 1st ed. Marcel Dekker Inc. Laws, B.V., Dickenson, E.R.V., Johnson, T.A., Snyder, S.A., Drewes, J.E., 2011. Attenuation of contaminants of emerging concern during surface-spreading aquifer recharge. Sci. Total Environ. 409, 1087–1094. http://dx.doi.org/10.1016/j.scitotenv. 2010.11.021. Lin, C., Eshel, G., Negev, I., Banin, A., 2008. Long-term accumulation and material balance of organic matter in the soil of an effluent infiltration basin. Geoderma 148, 35–42. http://dx.doi.org/10.1016/j.geoderma.2008.09.017. Litaor, M.I., 1988. Review of soil solution samplers. Water Resour. Res. 24, 727–733. http://dx.doi.org/10.1029/WR024i005p00727. Maloney, K.O., Morris, D.P., Moses, C.O., Osburn, C.L., 2005. 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or less of soil water content for most soils is sufficient for accurate organic matter analysis in extracted pore water samples. This method, like any other analytical technique, comes with inherent limitations. Extractable pore water from soils with high immobile water fraction and low water content is very small, and precautions should be made to guarantee that the sampled volume is not excessive, leading to positive DOC bias. For simplicity, and due to its importance in the description of the processes in the Shafdan SAT, we have concentrated on DOC analysis in pore water, but the methodology is equally applicable to other nonadsorbing species such as inorganic anions. In addition, the applicability of the method for the determination of organic pollutants and micropollutants, having a retention coefficient greater than one, will be discussed in a separate publication. Acknowledgments We thankfully acknowledge the financial support of the Scientific Infrastructure Program of the Israeli Ministry of Science, Space and Technology (MOSST), Israel and the MOSST-Israel – BMBF-Germany Water Technology program MATAR109 (January 1st 2014 - December 31st 2016). S.A. thankfully acknowledges Teva Ph.D. scholarship. Appendices A and B. Supplementary data Supplementary data to this article can be found online at http://dx. doi.org/10.1016/j.chemgeo.2017.06.017. References Alletto, L., Coquet, Y., Vachier, P., Labat, C., 2006. Hydraulic conductivity, immobile water content, and exchange coefficient in three soil profiles. Soil Sci. Soc. Am. J. 70, 1272–1280. http://dx.doi.org/10.2136/sssaj2005.0291. Amy, G., Wilson, L.G., Conroy, A., Chahbandour, J., Zhai, W.Y., Siddiqui, M., 1993. Fate of chlorination by-products and nitrogen species during effluent recharge and soil aquifer treatment (SAT). Water Environ. Res. 65, 726–734. Andersen, M.K., Raulund-Rasmussen, K., Strobel, B.W., Hansen, H.C.B., 1992. Adsorption of cadmium, copper, nickel, and zinc to a poly(tetrafluorethene) porous soil solution sampler. J. Environ. Qual. 31, 168–175. Ankley, G.T., Schubauer-Berigan, M.K., 1994. Comparison of techniques for the isolation of sediment pore water for toxicity testing. Arch. Environ. Contam. Toxicol. 27, 507–512. Beibei, Z., Jinbang, L., Quanjiu, W., 1992. Chloride transport in an aggregated clay soil column. J. Hydrol. Eng. 20, 1–7. http://dx.doi.org/10.1061/(ASCE)HE.1943-5584. 0001227. Carlson, C.A., Ducklow, H.W., Michaels, A.F., 1994. Annual flux of dissolved organic carbon from the euphotic zone in the northwestern Sargasso Sea. Lett. Nat. 371, 405–408. http://dx.doi.org/10.1038/371405a0. Celorie, J.A., Woods, S.L., Vinson, T.S., Istok, J.D., 1988. A comparison of sorption equilibrium distribution coefficients using batch and centrifugation methods. J. Environ. Qual. 18, 307–313. Cha, W., Choi, H., Kim, J., Cho, J., 2005. Water quality dependence on the depth of the vadose zone in SAT-simualated soil columns. Water Sci. Technol. Water Supply 5, 17–24. Chiou, C.T., Malcolm, R.L., Brinton, T.I., Kile, D.E., 1986. Water solubility enhancement of some organic pollutants and pesticides by dissolved humic and fulvic acids. Environ. Sci. Technol. 20, 502–508. http://dx.doi.org/10.1021/es00147a010. Currie, W.S., Aber, J.D., McDowell, W.H., Boone, R.D., Magill, A.H., 1996. Vertical transport of dissolved organic C and N under long-term N amendments in pine and hardwood forests. Biogeochemistry 35, 471–505. http://dx.doi.org/10.1007/ BF02183037. Decagon Devices [WWW Document], 1983. URL. http://www.decagon.com/en/ (accessed 1.7.16). Delgado, J.M.P.Q., 2006. A critical review of dispersion in packed beds. Heat Mass Transf. 42, 279–310. http://dx.doi.org/10.1007/s00231-005-0019-0. Di Bonito, M., 2005. Trace Elements in Soil Pore Water: A Comparison of Sampling Methods. University of Nottingham. Di Bonito, M., Breward, N., Crout, N., Smith, B., Young, S., 2008. Overview of selected soil pore water extraction methods for the determination of potentially toxic elements in contaminated soilsoperational and technical aspects. Environ. Geochem. 213–249. Direct Push Series Drilling Machines [WWW Document], 2016. URL. http://geoprobe. com/direct-push-series-drilling-machines (accessed 1.7.16). Dorrance, D.W., Wilson, L.G., Everett, L.G., Cullen, S.J., 1991. Compendium of in situ pore-Liquid samplers for vadose zone. In: Nash, R.G., Leslie, A.R. (Eds.), Groundwater Residue Sampling Design. ACS Symposium Series 465, Washington, DC, pp. 300–331. Dosskey, M.G., Bertsch, P.M., 1997. Transport of dissolved organic matter through a

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