[1] A study on water infiltration and groundwater recharge was conducted in the coastal plain, Israel. The study implemented a novel development, flexible time domain reflectometry sensors (FTDR), which enabled the continuous monitoring of water content at selected points through the entire vadose zone. Data on water content variation with time and depth was collected throughout the rainy season of 2004/2005 at two sites. One site was located in a sand dune area with a 21 m thick vadose zone; the other was located in an undeveloped urban area with an 8.4 m thick vadose zone. The lithology of both sites consisted of unconsolidated sand with silt and clay interbeds. The resultant data allowed tracing of the infiltration progress through the entire vadose zone. Each large rain event initiated an infiltration wave that propagated into the vadose zone and pushed the wetting front farther down. The wetting front appeared to progress in a step-like pattern, controlled by the frequency of large rain events and followed by a slower drainage process. Clay interbeds did not seem to prevent or significantly delay progress of the wetting front down to the groundwater. The apparent wetting front signal reached the groundwater table at 21 m below land surface (bls) only 3 months after the first significant rain event. Groundwater recharge was calculated from the variations in vadose zone water storage. An increase in vadose zone water storage was attributed to an infiltration event, while a reduction in water storage was attributedto a draining process.

This study focuses on water flow and solute migration through unsaturated fractured chalk in an arid area. The chalk underlies a major industrial complex in the northern Negev desert, where groundwater contamination has been observed. Four drydrilling holes were bored through the vadose zone. Core and auger samples, collected at 30-to 50-cm intervals, were used for chemical and isotopic analyses, enabling the construction of the following profiles: (1) a tritium profile, to estimate the rate of water flow through the unsaturated zone; (2) oxygen 18 and deuterium profiles, to assess the evaporation of water at land surface before percolation, and in the upper part of the vadose zone after infiltration; and (3) chloride and bromide profiles, as tracers for inert solutes and pollutants. The tritium and bromide profiles showed the rate of infiltration through the unsaturated matrix to be very slow (1.6-11 cm/yr). The chemical and isotopic data from the core holes suggested that the pore water changes characteristics with depth.Close to land surface, the pore water is strongly evaporated (15180 = +5.94%0) and highly concentrated (--•29 meq CI/100 g rock), but changes gradually with depth to a more dilute concentration (-4 meq Cl/100 g rock) and isotopically depleted composition (151•O = -4.4%o), closer to the isotopic composition of precipitation and groundwater. Nearby monitoring wells have shown anthropogenic contribution of heavy metals, organic compounds, and tritium (Nativ and Nissim, 1992). A conceptual model is proposed in which a small portion of the rainwater percolates downward through the matrix, while a larger percentage of the percolating water moves through preferential pathways in fractures. The water flowing through the fractures penetrates the matrix across the fracture walls, where it increases the tritium concentrations, depletes the stable isotopic composition, and dilutes the salt concentrations. The observed rapid downward migration of tritium and heavy metals through the profuse fractures makes the chalk inefficient as a hydrologic barrier. •J,•a,,l•,,11 LI•JII, 11 ari Ll•Jllari I i •,.71 LI •,Cl LIII•,11 L and isolation of hazardous waste has been operating there since 1975. The aridity of the area (50-200 mm precipitation/ ,,, J LEGEND O Sands 8, AlLuvium (Ouat. Hotoc.) Ku Kurkor (Ouot. Pteist) NATIV ET AL.: WATER RECHARGE AND SOLUTE TRANSPORT 261 207-225, 1992. Zimmermann, U., D. Ehhalt, and K. O. Munnich, Soil-water movement and evapotranspiration: Changes in the isotopic composition of the water, in Isotopes in Hydrology, Proceedings of the IAEA Symposium, Vienna, pp. 567-585,

Water percolation and solute transport through an unsaturated sandy formation were investigated using a vadose‐zone monitoring system that enables in situ, continuous, real‐time monitoring of the percolating water. Measurements of the temporal variations in vadose‐zone water content as well as continuous monitoring of the vadose‐zone pore water allowed detailed tracking of the propagation velocities of the wetting front and determination of the flow patterns governing solute transport. It has been shown that the chemical composition of mobile flowing water along the vadose zone is not in equilibrium with the total soluble solute potential of the sediment. This phenomenon is usually attributed to a flow mechanism controlled by preferential flow. Wetting‐front propagation patterns, as monitored continuously during four rainy seasons throughout the entire vadose zone, as well as a tracer experiment, showed relatively uniform wetting‐front propagation with no direct evidence for significant preferential flow. Contradictory observations of matrix and preferential flow as governing mechanisms led to conceptualization of the percolation process as pore‐scale dual‐domain flow.

Abstract. Flow through a natural fracture crossing unsaturated chalk in an arid region was investigated in a field experiment using a specially designed experimental setup. The setup allowed complete control of the flow domain inlet and outlet. Water flux into and out of the fracture was measured in small segments of the fracture openings, and flow trajectories were identified using seven fluorobenzoic acid tracers. A 5 day percolation experiment on a 5.3 rn long fracture showed significant spatial and temporal variability of the flow regime. Flow through fracture openings did not reach a steady state either in individual segments or across the entire flow domain, although the boundary conditions were kept relatively steady for the entire duration of the experiment. Flow trajectories within the fracture plane varied over time; however, most of the flow was confined to small sections of the fracture. Over 70% of the flux was transmitted through <20% of the studied fracture openings. Observations from the tracer tests suggest that flow paths can coexist near each other without water mixing, probably because the fracture fill generates unconnected flow paths across the main fracture void.

Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) is a common contaminant at explosives production sites. Here, we report on the use of compound-specific isotope analysis of RDX to obtain delta(15)N and delta(18)O enrichment factors during biodegradation in batch cultures. A new preparation method has been developed based on RDX purification using thin-layer chromatography. RDX is then subjected to an elemental analyzer coupled with an isotope-ratio mass spectrometer (EA-IRMS). The precision of the method shows standard deviations of 0.13% per hundred and 1.18% per hundred for delta(15)N and delta(18)O, respectively, whereas the accuracy of the method has been checked routinely, adhering to external standards. The method was applied to RDX samples subjected to biodegradation under aerobic or anaerobic conditions. Enrichment factors under aerobic conditions were -2.1% per hundred and -1.7% per hundred for delta(15)N and delta(18)O, respectively, and under anaerobic conditions, -5.0% per hundred and -5.3% per hundred for delta(15)N and delta(18)O, respectively. The results of this study provide a tool for monitoring natural attenuation of RDX in a contaminated environment.