Abraham J. Amiel

Characterization of suspended particles collected in groundwater under natural gradient flow conditions

Microscale Eulerian variations in the flux, mineralogical composition and size of suspended particles have been found in a contaminated sandy aquifer under natural gradient flow conditions ( ) during an 8-month study period. Particle variability has been detected along a 16-m saturated section of the aquifer at a scale of centimeters and meters in the vertical and horizontal dimensions, respectively. The average concentration of particles in groundwater varied between 1 and 40 mg/L, but high concentrations of up to 5000 mg/L were determined in specific 3-cm vertical intervals of the aquifer. The particles were primarily composed of CaCO3 (11–57%), quartz (7–39%) and clays (8–43%). Most of the particles were within the 140–3000 nm size range with size modes varying from 310 to 660 nm. The large amounts of suspended particles are considered to be related to high inputs of dissolved organic carbon into groundwater, from sewage effluents which have been used for agricultural irrigation since the early 1960s. As a result of organic matter biodegradation in the saturated zone, anoxic conditions developed and the pCO2 content of groundwater increased dramatically (pCaCO2 = 10−1.8 to 10−1.3 atm). It is postulated that part of the carbonate cement of the rocks dissolved and detrital CaCO3, quartz and clay were released as colloidal particles. Part of the clay particles could have also been transported through the unsaturated zone into groundwater after mobilization from surface layers as a result of the intermittent input of water of different chemical quality. In the prevailing anoxic conditions of groundwater at the study site (dissolved oxygen concentrations of <1 mg/L) colloidal stability is enhanced by organic matter coating of particles.

Application of a multi-layer sampler based on the dialysis cell technique for the study of trace metals in groundwater

Abstract Most studies of metals in groundwater involve sample filtration. A water sampling technique based on dialysis cells has an advantage of in situ separation of particulate (colloidal) matter from the fluid, thus avoiding overload of the membrane during laboratory filtration. A series of laboratory and field experiments were carried out with a multi-layer sampler based on the dialysis cell technique. Results show that (1) the time of equilibration for Cu and Mn is within 2 d, (2) dialysis cells do not absorb these metals, and (3) the metal content measured in the dialysis cells is much lower than that in water taken by bailer and filtered in the laboratory. Measurements of metal profiles in the water table zone of the phreatic Coastal Plain Aquifer of Israel show both vertical and horizontal variations in Mn content which can be related to changes in pH due to biological activity in this aquifer.

Distribution of metals in a polluted aquifer: A comparison of aquifer suspended material to fine sediments of the adjacent environment

Abstract Metal concentrations were determined for groundwater suspended matter from a site in the coastal aquifer of Israel which has been irrigated with secondary sewage effluents since the 1960s. Suspended matter was collected from the aquifer saturated zone by pumping and by a multi-layer sampler. Fine sediments were collected from both the unsaturated and saturated zones of the contaminated aquifer, as well as from an adjacent uncontaminated environment. Ag, Cu, Fe, Mn and Zn were leached from the samples in three sequential chemical extractions which are taken to represent the carbonate, organic and oxide phases. Comparison of the aquifer samples to those of the adjacent environment showed that Fe and Mn are primarily enriched in non-mobile fine sediments and not in suspended matter, whereas the concentrations of Zu, Cu and Ag show up to an order of magnitude enrichment in the mobile suspended matter in groundwater. The enrichment of these metals in the suspended matter indicates that metals from sewage effluents and agricultural activities have reached the groundwater.

Determination of in situ metal partitioning between particulate matter and ground water

the extracts operationally represent metals in the carbonate, oxide and organic fractions. Groundwater and extracts were analyzed for metals by both flame and furnace atomic absorption spectroscopy. Spike recoveries for all analyses ranged between 90-110~ Percent carbonate and organic matter in each sample was determined by thermal gravimetric analysis, and percent oxide was calculated from AI, Fe and Mn concentrations [9]. The chemical characteristics of the water profile are shown in Fig. 2. Figure 3 shows that particulate matter from the uppermost sampling interval is distinctly enriched in many metals: the trend is demonstrated by Cu, Pb and Zn in all fractions, Cd and Mn in oxide and organic fractions, and Ag in the oxide fraction. Aluminium noticeably increases with depth for the oxide fraction. The profiles of dissolved metals in groundwater (Fig. 4) show that metals are distributed homogeneously downwell for Ag, Cu and Fe, but surface-enriched for AI, Cd, Zn. Dissolved-metal concentrations were averaged for four depth intervals corresponding to the four separate

Scavenging effects of Fe-hydroxide-coated sand in phreatic aquifers

Abstract Sand grains coated with Fe-hydroxide were compared to uncoated sand grains as an absorbant filtration media for the treatment of metal-bearing waters. Coated and uncoated sand grains were placed into dialysis cells of a multilayer sampler and then placed into a research well. After two months of exposure, the samples were retrieved and analyzed for Cr, Pb, Ni, Cd, Mn and Co concentrations. Transmitted light and scanning electron light microscopy showed that the coating prevailed in the field and was not removed. Only Cr showed significant enrichment on the coated material compared to the uncoated material, indicating that the exposure of the Fe-coated surface to groundwater was sufficient for preferential scavenging of Cr from the water. The eight-fold enrichment of Cr may be related to its oxidation state of +3, thereby readily permitting substitution into the Fe 3+ position in the coating material. The rest of the studied metals were only slightly enriched in the coated grain.

Tracing the influx of sewage from a leaky sewer into a very thin and fast-flowing aquifer

Abstract Water parcels of different chemical composition were detected in a 1 m thick and up to 17 m/d fast-flowing groundwater system using a multi-layer sampler based on the dialysis cell technique. The parcels result from the infiltration of sewage effluents and also probably due to the leaching of sewage sludge from the agricultural land surface. Samples obtained at depth intervals as small as 3 cm in a natural gradient flow field revealed relative high concentrations and variable vertical profiles of Na + , NO 3 − , HCO 3 − , SO 4 2− and DOC 9 m downstream of the infiltration pipe. A pump used to obtain water samples during a 2 year period, in the same research field, proved to be an inadequate sampling technique to trace the movement of sewage effluent.

On the natural variability of trace-metal content of particulate matter in a deep aquifer☆

Abstract A multilayer sampler (MLS) has been used in a deep phreatic aquifer to collect particulate matter transported by a natural gradient flow field. The trace-metal content (Fe, Mn, Cu, Zn, Ag) associated to the carbonate, organic and oxide fractions of the particulate matter has been characterized by Eulerian variability at a microscale level (