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Ian Cartwright - One of the best experts on this subject based on the ideXlab platform.
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environmental isotopes as indicators of inter aquifer mixing wimmera region murray basin southeast australia
Chemical Geology, 2010Co-Authors: Tamie Renee Weaver, Ian Cartwright, Dioni I Cendon, Ian SwaneAbstract:Abstract Complex groundwater flow systems in confined Aquifers that result from geological structures, stratigraphic changes, or the absence of efficient aquitards are difficult to constrain using physical parameters alone. Despite a relatively simple aquifer configuration, the distribution of groundwater total dissolved solids (TDS) concentrations, δ13C values, 87Sr/86Sr ratios, and 14C activities (a14C) in groundwater in the Wimmera region of the southern Murray Basin implies that considerable inter-aquifer flow has occurred. Given the presence of both silicate and carbonate Aquifers, δ13C values and 87Sr/86Sr ratios are the key parameters that demonstrate inter-aquifer flow. Locally, between 40 and 95% of water from one aquifer has infiltrated the underlying aquifer homogenising many aspects of the groundwater geochemistry. Groundwater residence times estimated from a14C range from modern to > 30 ka and the distribution of 14C residence times confirm that inter-aquifer flow is regional scale and long term. Recharge of the deepest Aquifers occurs across a broad region and not solely at the basin margins. Vertical leakage rates are ~ 6–10 × 10−3 m/year and long-term recharge rates 0.1–0.2 mm/year (
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distinguishing groundwater flow paths in different fractured rock Aquifers using groundwater chemistry dandenong ranges southeast australia
Hydrogeology Journal, 2005Co-Authors: Sarah Tweed, Tamie Renee Weaver, Ian CartwrightAbstract:Major ion geochemistry is used to qualitatively interpret groundwater residence times within an aquifer, and the extent of mixing between Aquifers with distinctive mineralogy. In conjunction with hydraulic heads and stable isotope geochemistry, flow paths and inter-aquifer exchange are defined in a fractured-rock aquifer system in the Dandenong Ranges, southeast Australia. Stable isotopes indicate modern seasonal recharge throughout the system. At high elevations in the sub-catchment, which includes both marine Silurian-Devonian sedimentary and Tertiary basalt Aquifers, Cl is derived primarily from cyclic salts, and differences in mineralogy result in groundwater from the basalt aquifer having higher TDS contents (123–262 mg/L) and (Ca+Mg)/Na ratios (0.9–1.3) than groundwater from the sedimentary aquifer (TDS: 55–79 mg/L; (Ca+Mg)/Na: 0.1–0.2). At low elevations, in areas of local groundwater discharge, the more regional flow system in the Silurian-Devonian sediments contains additional Cl from water–rock interaction and has distinctly higher TDS contents (517–537 mg/L). Differences in groundwater chemistry between the Aquifers and between shallower and deeper flow systems highlights areas of inter-aquifer mixing. This is particularly important for aquifer vulnerability where groundwater quality in the deeper aquifer may be impacted by surface activities.
Andre Ellis - One of the best experts on this subject based on the ideXlab platform.
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a multi isotope δd δ18o 87sr 86sr and δ11b approach for identifying saltwater intrusion and resolving groundwater evolution along the western caprock escarpment of the southern high plains new mexico
Applied Geochemistry, 2010Co-Authors: Jeff B Langman, Andre EllisAbstract:Abstract Declining water levels in arid and semi-arid regions increase an aquifer’s vulnerability to natural and anthropogenic influences. A multi-isotope ( δ D, δ 18 O, 87 Sr/ 86 Sr, and δ 11 B) approach was used to resolve the geochemical evolution of groundwater in a declining aquifer in a semi-arid region of the southwestern USA as groundwater composition reacts to source-water mixing, cross-formational flow including saltwater intrusion, water–rock interaction, and likely agricultural recharge. Sub-Aquifers or local flow systems are present in the Southern High Plains aquifer along the Western Caprock Escarpment in New Mexico, and the study site’s local flow system contains a Na–Cl, high dissolved-solids groundwater that flows from the escarpment until it mixes with a high quality regional aquifer or regional flow system. The local flow system contains water that is similar in composition to the underlying, upper Dockum Group aquifer. Saltwater found in the upper Dockum Group aquifer likely originates in the adjacent Pecos River Basin and crosses beneath or possibly through the hydrologic divide of the Western Caprock Escarpment. Strontium concentrations of 0.9–31 mg/L and a 87 Sr/ 86 Sr range of 0.70845–0.70906 were sufficient to estimate source-water fractions, mixing patterns, and contributions from chemical weathering through mass balance inverse calculations. Boron concentrations (59–1740 mg/L) and δ 11 B values (+6.0–+46.0‰) were used to confirm source-water mixing, further evaluate water–rock interaction, and examine the influence of possible agricultural recharge. Alteration of B concentrations and δ 11 B values in an area of likely agricultural recharge indicated the loss of B and decrease in δ 11 B values likely from plant uptake, adsorption, and weathering contributions in the soil/vadose zone prior to recharge. The effectiveness of 87 Sr/ 86 Sr and δ 11 B for resolving the geochemical influences in groundwater in the Southern High Plains along the Western Caprock Escarpment allowed for the reinterpretation of the isotopic composition of water that has been shown to be highly variable in the Southern High Plains. This study shows the utility of a multi-isotope approach for resolving the geochemical evolution of groundwater in an aquifer that has a complex relationship with underlying Aquifers and the applicability of these isotopes as indicators of the alteration of source waters from natural or anthropogenic influences.
Y Zheng - One of the best experts on this subject based on the ideXlab platform.
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geochemical and hydrogeological contrasts between shallow and deeper Aquifers in two villages of araihazar bangladesh implications for deeper Aquifers as drinking water sources
Geochimica et Cosmochimica Acta, 2005Co-Authors: Y Zheng, A Van Geen, Martin Stute, R K Dhar, Zhongqi Cheng, A Horneman, I GavrieliAbstract:Sediment and groundwater profiles were compared in two villages of Bangladesh to understand the geochemical and hydrogeological factors that regulate dissolved As concentrations in groundwater. In both villages, fine-grained sediment layers separate shallow Aquifers (28 m) high in As from deeper Aquifers (40 -90 m) containing 10 g/L As. In one village (Dari), radiocarbon dating indicates deposition of the deeper aquifer sediments 50 ka ago and a residence time of groundwater of thousands of years. In the other village (Bay), the sediment is 20 ka old down to 90 m and the deeper aquifer groundwater is younger, with a residence time of hundreds of years. The shallow Aquifers in both villages that are high in As contain bomb- 3 H and bomb- 14 C, indicating recent recharge. The major and minor ion compositions of the shallow and deeper Aquifers also differ significantly. Deeper aquifer water is of the Na-HCO3 type, with relatively little dissolved NH4 (76 192 mol/L), Fe (27 43 mol/L) and Mn (3 2 mol/L). In contrast, shallow aquifer water is of the Ca-Mg-HCO3 type, with elevated concentrations of dissolved NH4 (306 355 mol/L), Fe (191 73 mol/L), and Mn (27 43 mol/L). In both villages, the quantity of As extractable from deeper aquifer sands with a 1 mol/L phosphate solution (0.2 0.3 mg/kg, n 12; 0.1 0.1 mg/kg, n 5) is 1 order of magnitude lower than P-extractable As from shallow deposits (1.7 1.2 mg/kg, n 9; 1.4 2.0 mg/kg, n 11). The differences suggest that the concentration of P-extractable As in the sediment is a factor controlling the concentration of As in groundwater. Low P-extractable As levels are observed in both deeper Aquifers that are low in As, even though there is a large difference in the time of deposition of these Aquifers in the two villages. The geochemical data and hydrographs presented in this study suggest that both Holocene and Pleistocene deeper Aquifers that are low in As should be a viable source of drinking water as long as withdrawals do not exceed recharge rates of 1 cm/yr. Copyright © 2005 Elsevier Ltd
Neal Farmer - One of the best experts on this subject based on the ideXlab platform.
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movement of coliform bacteria and nutrients in ground water flowing through basalt and sand Aquifers
Journal of Environmental Quality, 2001Co-Authors: James A Entry, Neal FarmerAbstract:Large-scale deposition of animal manure can result in contamination of surface and ground water and in potential transfer of disease-causing enteric bacteria to animals or humans. We measured total coliform bacteria (TC), fecal coliform bacteria (PC), NO 3 , NI-I4, total P, and POt in ground water flowing from basalt and sand Aquifers, in wells into basalt and sand Aquifers, in irrigation water, and in river water. Samples were collected monthly for 1 yr. Total coliform and FC numbers were always higher in irrigation water than in ground water, indicating that soil and sediment filtered most of these bacteria before they entered the Aquifers. Total coliform and FC numbers in ground water were generally higher in the faster flowing basalt aquifer than in the sand aquifer, indicating that the slower flow and finer grain size may filter more TC and FC bacteria from water. At least one coliform bacterium/101) mL of water was found in ground water from both basalt and sand Aquifers, indicating that ground water pumped from these Aquifers is not necessarily safe for human consumption according to the American Public Health Association and the USEPA. The NO3 concentrations were usually higher in water flowing from the sand aquifer than in water flowing from the basalt aquifer or in perched water tables in the basalt aquifer. The PO4 concentrations were usually higher in water flowing from the basalt aquifer than in water flowing from the sand aquifer. The main concern is fecal contamination of these Aquifers and health consequences that may arise from human consumption.
Z. Aziz - One of the best experts on this subject based on the ideXlab platform.
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retardation of arsenic transport through a pleistocene aquifer
Nature, 2013Co-Authors: Alexander Van Geen, Pham Thi Kim Trang, Phu Dao Manh, Kathleen A Radloff, Pham Hung Viet, Z. Aziz, Benjamin C. Bostick, Mason O StahlAbstract:Holocene Aquifers are the source of much arsenic poisoning in south and southeast Asia, whereas Pleistocene Aquifers are mostly safe; here the delayed arsenic contamination of a Pleistocene aquifer is described and modelled.
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retardation of arsenic transport through a pleistocene aquifer
Nature, 2013Co-Authors: Alexander Van Geen, Pham Thi Kim Trang, Phu Dao Manh, Kathleen A Radloff, Pham Hung Viet, Benjamin C. Bostick, Vi Mai Lan, Nguyenngoc Mai, Z. AzizAbstract:Holocene Aquifers are the source of much arsenic poisoning in south and southeast Asia, whereas Pleistocene Aquifers are mostly safe; here the delayed arsenic contamination of a Pleistocene aquifer is described and modelled. Millions of people across southeast Asia are exposed to arsenic-contaminated drinking water drawn from Holocene Aquifers, layers of sand deposited less than 5,000 years ago. By contrast, Pleistocene Aquifers, deposited about 12,000 years ago, have lower levels of contamination and are increasingly being exploited as safe sources of drinking water. This study reports the gradual penetration of arsenic into a low-arsenic Pleistocene aquifer south of Hanoi, Vietnam. Changes in groundwater flow and the redox state of the aquifer sands induced by pumping are introducing contamination from the high-arsenic Holocene aquifer. Contamination so far is limited owing to the absorption of arsenic onto aquifer sands, which delays arsenic movement by decades. Groundwater drawn daily from shallow alluvial sands by millions of wells over large areas of south and southeast Asia exposes an estimated population of over a hundred million people to toxic levels of arsenic1. Holocene Aquifers are the source of widespread arsenic poisoning across the region2,3. In contrast, Pleistocene sands deposited in this region more than 12,000 years ago mostly do not host groundwater with high levels of arsenic. Pleistocene Aquifers are increasingly used as a safe source of drinking water4 and it is therefore important to understand under what conditions low levels of arsenic can be maintained. Here we reconstruct the initial phase of contamination of a Pleistocene aquifer near Hanoi, Vietnam. We demonstrate that changes in groundwater flow conditions and the redox state of the aquifer sands induced by groundwater pumping caused the lateral intrusion of arsenic contamination more than 120 metres from a Holocene aquifer into a previously uncontaminated Pleistocene aquifer. We also find that arsenic adsorbs onto the aquifer sands and that there is a 16–20-fold retardation in the extent of the contamination relative to the reconstructed lateral movement of groundwater over the same period. Our findings suggest that arsenic contamination of Pleistocene Aquifers in south and southeast Asia as a consequence of increasing levels of groundwater pumping may have been delayed by the retardation of arsenic transport.