Elevated arsenic concentrations have been reported in a drinking water and irrigation-supply aquifer of Stuarts Point, New South Wales, Australia. Arsenic occurrence in such aquifers is potentially a major issue due to their common use for high yield domestic and irrigation water supplies. Ten multi-level piezometers were installed to depths of approximately 30 m in the sand and clay aquifer. Sediment samples were collected at specific depths during drilling and analysed for chemical and mineralogical composition, grain size characteristics, potential for arsenic release from solid phase and detailed microscopic features. From this data, a full geomorphic reconstruction allowed the determination of source provenance for the aquifer sediments. The model proposed herein provides evidence that the bulk of the aquifer was deposited under intermittent fluvial and estuarine conditions; and that all sediments derive from the regional arsenicmineralised hinterland. More than 200 groundwater samples were collected and analysed for over 50 variables. The heterogeneity of the aquifer sediments causes redox stratification to occur, which in turn governs arsenic mobility in the groundwater. The bulk of the aquifer is composed of fluvial sand deposits undergoing reductive dissolution of iron oxides. Arsenic adsorbed to iron oxide minerals is released during dissolution but re-adsorbs to other iron oxides present in this part of the aquifer. The deeper, more reducing fluvial sand and estuarine clay groundwaters have undergone complete reductive dissolution of iron oxides resulting in the subsequent mobilisation of arsenic into groundwater. Some of this arsenic has been incorporated into iron sulfide mineral precipitates, forming current arsenian pyrite sinks within the aquifer. The extraction of groundwater from the aquifer for irrigation and drinking water supply induces seawater intrusion of arsenic-rich estuarine water, bringing further dissolved arsenic into the aquifer. A greater understanding of the source, sinks and mobilisation of arsenic in this aquifer contributes to our broad understanding of arsenic in the environment; and allows aquifer specific management procedures and research recommendations to be made. Any coastal or unconsolidated aquifer that has sediments derived from mineralised provenances should consider monitoring for arsenic, and other potentially toxic trace elements, in their groundwater systems.

The Patonga Claystone, a red bed facies in the Narrabeen Group of the Sydney Basin, is one of the most unfavorable rock units in the basin from a geotechnical point of view. This rock unit is composed of sandstone, siltstone, mudstone and claystone. One of the unfavorable characteristics is the low shear strength, which causes instability of cut slopes; another is its slaking-prone behaviour. Numerous measurements of geotechnical properties, along with extensive mineralogical and geochemical determinations, were carried out to identify cause of this slaking behaviour. Key techniques were the use of quantitative X-ray diffractometry for mineralogical analysis, and the determination of slake durability index and related properties to evaluate the slaking behaviour under both standard and more extended conditions. Standard (two cycle) slake durability test results indicate a range from low to high slake durability index values, with some mudstone samples having very low durability and some sandstones having very high slake durability indices. Jar slake test results indicate that the rock samples break rapidly and/or develop several fractures (Ij = 4) in an as-received state, but degrade to a pile of flakes or mud (Ij = 1) if the samples are oven dried before testing. The results for jar slake testing of oven-dried material are comparable, for individual samples, to those obtained from the more comprehensive slake durability tests. The mineralogy of the samples was evaluated by quantitative X-ray diffraction techniques using the Rietveld-based Siroquant processing system. Comparison to independent chemical data show a generally good level of agreement, suggesting that the mineralogical analysis results are consistent with the chemical composition of the individual rock samples. Good correlations were also obtained between clay mineralogy determined from orientedaggregate XRD analysis of the &lt2 micron fraction and the results from powder diffractometry and Siroquant analysis of the whole-rock samples. Evaluation of the slake durability characteristics and other geotechnical properties in relation to the quantitative mineralogy suggests that quartz and feldspar form a rigid framework in the rocks that resists the disruptive pressures that cause slaking. Expansion of the clay minerals by various processes, including the incorporation of water into the interlayer spaces of illite/smectite as well as changes in pore pressures associated with entry of water into micro-fractures in the clay matrix, are thought to produce the disruptions that cause slaking and degradation. An abundant clay matrix also reduces the strength of the rock materials, probably because of the less rigid nature of the clay minerals relative to the quartz and feldspar particles. As well as the mineralogy, the loss on ignition (LOI) and water absorption percentage were found to provide good indicators of longer-term slaking behaviour. Both properties are also related to the overall clay content. Rock samples with water absorption values of &lt10, 10-15 and &gt15% behave as highly durable, intermediate and less durable materials respectively. Rocks with LOI values of greater than 5% by weight behave as less durable rock materials, at least for the strata encompassed by the present study. The water absorption and LOI values were also used to develop a predictive model of slake durability characteristics for the different rock materials in the Patonga Claystone, providing a relatively simple basis for predicting longer-term stability in a range of geotechnical studies.

Elevated arsenic concentrations have been reported in a drinking water and irrigation-supply aquifer of Stuarts Point, New South Wales, Australia. Arsenic occurrence in such aquifers is potentially a major issue due to their common use for high yield domestic and irrigation water supplies. Ten multi-level piezometers were installed to depths of approximately 30 m in the sand and clay aquifer. Sediment samples were collected at specific depths during drilling and analysed for chemical and mineralogical composition, grain size characteristics, potential for arsenic release from solid phase and detailed microscopic features. From this data, a full geomorphic reconstruction allowed the determination of source provenance for the aquifer sediments. The model proposed herein provides evidence that the bulk of the aquifer was deposited under intermittent fluvial and estuarine conditions; and that all sediments derive from the regional arsenicmineralised hinterland. More than 200 groundwater samples were collected and analysed for over 50 variables. The heterogeneity of the aquifer sediments causes redox stratification to occur, which in turn governs arsenic mobility in the groundwater. The bulk of the aquifer is composed of fluvial sand deposits undergoing reductive dissolution of iron oxides. Arsenic adsorbed to iron oxide minerals is released during dissolution but re-adsorbs to other iron oxides present in this part of the aquifer. The deeper, more reducing fluvial sand and estuarine clay groundwaters have undergone complete reductive dissolution of iron oxides resulting in the subsequent mobilisation of arsenic into groundwater. Some of this arsenic has been incorporated into iron sulfide mineral precipitates, forming current arsenian pyrite sinks within the aquifer. The extraction of groundwater from the aquifer for irrigation and drinking water supply induces seawater intrusion of arsenic-rich estuarine water, bringing further dissolved arsenic into the aquifer. A greater understanding of the source, sinks and mobilisation of arsenic in this aquifer contributes to our broad understanding of arsenic in the environment; and allows aquifer specific management procedures and research recommendations to be made. Any coastal or unconsolidated aquifer that has sediments derived from mineralised provenances should consider monitoring for arsenic, and other potentially toxic trace elements, in their groundwater systems.

The Patonga Claystone, a red bed facies in the Narrabeen Group of the Sydney Basin, is one of the most unfavorable rock units in the basin from a geotechnical point of view. This rock unit is composed of sandstone, siltstone, mudstone and claystone. One of the unfavorable characteristics is the low shear strength, which causes instability of cut slopes; another is its slaking-prone behaviour. Numerous measurements of geotechnical properties, along with extensive mineralogical and geochemical determinations, were carried out to identify cause of this slaking behaviour. Key techniques were the use of quantitative X-ray diffractometry for mineralogical analysis, and the determination of slake durability index and related properties to evaluate the slaking behaviour under both standard and more extended conditions. Standard (two cycle) slake durability test results indicate a range from low to high slake durability index values, with some mudstone samples having very low durability and some sandstones having very high slake durability indices. Jar slake test results indicate that the rock samples break rapidly and/or develop several fractures (Ij = 4) in an as-received state, but degrade to a pile of flakes or mud (Ij = 1) if the samples are oven dried before testing. The results for jar slake testing of oven-dried material are comparable, for individual samples, to those obtained from the more comprehensive slake durability tests. The mineralogy of the samples was evaluated by quantitative X-ray diffraction techniques using the Rietveld-based Siroquant processing system. Comparison to independent chemical data show a generally good level of agreement, suggesting that the mineralogical analysis results are consistent with the chemical composition of the individual rock samples. Good correlations were also obtained between clay mineralogy determined from orientedaggregate XRD analysis of the &lt2 micron fraction and the results from powder diffractometry and Siroquant analysis of the whole-rock samples. Evaluation of the slake durability characteristics and other geotechnical properties in relation to the quantitative mineralogy suggests that quartz and feldspar form a rigid framework in the rocks that resists the disruptive pressures that cause slaking. Expansion of the clay minerals by various processes, including the incorporation of water into the interlayer spaces of illite/smectite as well as changes in pore pressures associated with entry of water into micro-fractures in the clay matrix, are thought to produce the disruptions that cause slaking and degradation. An abundant clay matrix also reduces the strength of the rock materials, probably because of the less rigid nature of the clay minerals relative to the quartz and feldspar particles. As well as the mineralogy, the loss on ignition (LOI) and water absorption percentage were found to provide good indicators of longer-term slaking behaviour. Both properties are also related to the overall clay content. Rock samples with water absorption values of &lt10, 10-15 and &gt15% behave as highly durable, intermediate and less durable materials respectively. Rocks with LOI values of greater than 5% by weight behave as less durable rock materials, at least for the strata encompassed by the present study. The water absorption and LOI values were also used to develop a predictive model of slake durability characteristics for the different rock materials in the Patonga Claystone, providing a relatively simple basis for predicting longer-term stability in a range of geotechnical studies.

The Patonga Claystone, a red bed facies in the Narrabeen Group of the Sydney Basin, is one of the most unfavorable rock units in the basin from a geotechnical point of view. This rock unit is composed of sandstone, siltstone, mudstone and claystone. One of the unfavorable characteristics is the low shear strength, which causes instability of cut slopes; another is its slaking-prone behaviour. Numerous measurements of geotechnical properties, along with extensive mineralogical and geochemical determinations, were carried out to identify cause of this slaking behaviour. Key techniques were the use of quantitative X-ray diffractometry for mineralogical analysis, and the determination of slake durability index and related properties to evaluate the slaking behaviour under both standard and more extended conditions. Standard (two cycle) slake durability test results indicate a range from low to high slake durability index values, with some mudstone samples having very low durability and some sandstones having very high slake durability indices. Jar slake test results indicate that the rock samples break rapidly and/or develop several fractures (Ij = 4) in an as-received state, but degrade to a pile of flakes or mud (Ij = 1) if the samples are oven dried before testing. The results for jar slake testing of oven-dried material are comparable, for individual samples, to those obtained from the more comprehensive slake durability tests. The mineralogy of the samples was evaluated by quantitative X-ray diffraction techniques using the Rietveld-based Siroquant processing system. Comparison to independent chemical data show a generally good level of agreement, suggesting that the mineralogical analysis results are consistent with the chemical composition of the individual rock samples. Good correlations were also obtained between clay mineralogy determined from orientedaggregate XRD analysis of the &lt2 micron fraction and the results from powder diffractometry and Siroquant analysis of the whole-rock samples. Evaluation of the slake durability characteristics and other geotechnical properties in relation to the quantitative mineralogy suggests that quartz and feldspar form a rigid framework in the rocks that resists the disruptive pressures that cause slaking. Expansion of the clay minerals by various processes, including the incorporation of water into the interlayer spaces of illite/smectite as well as changes in pore pressures associated with entry of water into micro-fractures in the clay matrix, are thought to produce the disruptions that cause slaking and degradation. An abundant clay matrix also reduces the strength of the rock materials, probably because of the less rigid nature of the clay minerals relative to the quartz and feldspar particles. As well as the mineralogy, the loss on ignition (LOI) and water absorption percentage were found to provide good indicators of longer-term slaking behaviour. Both properties are also related to the overall clay content. Rock samples with water absorption values of &lt10, 10-15 and &gt15% behave as highly durable, intermediate and less durable materials respectively. Rocks with LOI values of greater than 5% by weight behave as less durable rock materials, at least for the strata encompassed by the present study. The water absorption and LOI values were also used to develop a predictive model of slake durability characteristics for the different rock materials in the Patonga Claystone, providing a relatively simple basis for predicting longer-term stability in a range of geotechnical studies.

The Patonga Claystone, a red bed facies in the Narrabeen Group of the Sydney Basin, is one of the most unfavorable rock units in the basin from a geotechnical point of view. This rock unit is composed of sandstone, siltstone, mudstone and claystone. One of the unfavorable characteristics is the low shear strength, which causes instability of cut slopes; another is its slaking-prone behaviour. Numerous measurements of geotechnical properties, along with extensive mineralogical and geochemical determinations, were carried out to identify cause of this slaking behaviour. Key techniques were the use of quantitative X-ray diffractometry for mineralogical analysis, and the determination of slake durability index and related properties to evaluate the slaking behaviour under both standard and more extended conditions. Standard (two cycle) slake durability test results indicate a range from low to high slake durability index values, with some mudstone samples having very low durability and some sandstones having very high slake durability indices. Jar slake test results indicate that the rock samples break rapidly and/or develop several fractures (Ij = 4) in an as-received state, but degrade to a pile of flakes or mud (Ij = 1) if the samples are oven dried before testing. The results for jar slake testing of oven-dried material are comparable, for individual samples, to those obtained from the more comprehensive slake durability tests. The mineralogy of the samples was evaluated by quantitative X-ray diffraction techniques using the Rietveld-based Siroquant processing system. Comparison to independent chemical data show a generally good level of agreement, suggesting that the mineralogical analysis results are consistent with the chemical composition of the individual rock samples. Good correlations were also obtained between clay mineralogy determined from orientedaggregate XRD analysis of the &lt2 micron fraction and the results from powder diffractometry and Siroquant analysis of the whole-rock samples. Evaluation of the slake durability characteristics and other geotechnical properties in relation to the quantitative mineralogy suggests that quartz and feldspar form a rigid framework in the rocks that resists the disruptive pressures that cause slaking. Expansion of the clay minerals by various processes, including the incorporation of water into the interlayer spaces of illite/smectite as well as changes in pore pressures associated with entry of water into micro-fractures in the clay matrix, are thought to produce the disruptions that cause slaking and degradation. An abundant clay matrix also reduces the strength of the rock materials, probably because of the less rigid nature of the clay minerals relative to the quartz and feldspar particles. As well as the mineralogy, the loss on ignition (LOI) and water absorption percentage were found to provide good indicators of longer-term slaking behaviour. Both properties are also related to the overall clay content. Rock samples with water absorption values of &lt10, 10-15 and &gt15% behave as highly durable, intermediate and less durable materials respectively. Rocks with LOI values of greater than 5% by weight behave as less durable rock materials, at least for the strata encompassed by the present study. The water absorption and LOI values were also used to develop a predictive model of slake durability characteristics for the different rock materials in the Patonga Claystone, providing a relatively simple basis for predicting longer-term stability in a range of geotechnical studies.

The Patonga Claystone, a red bed facies in the Narrabeen Group of the Sydney Basin, is one of the most unfavorable rock units in the basin from a geotechnical point of view. This rock unit is composed of sandstone, siltstone, mudstone and claystone. One of the unfavorable characteristics is the low shear strength, which causes instability of cut slopes; another is its slaking-prone behaviour. Numerous measurements of geotechnical properties, along with extensive mineralogical and geochemical determinations, were carried out to identify cause of this slaking behaviour. Key techniques were the use of quantitative X-ray diffractometry for mineralogical analysis, and the determination of slake durability index and related properties to evaluate the slaking behaviour under both standard and more extended conditions. Standard (two cycle) slake durability test results indicate a range from low to high slake durability index values, with some mudstone samples having very low durability and some sandstones having very high slake durability indices. Jar slake test results indicate that the rock samples break rapidly and/or develop several fractures (Ij = 4) in an as-received state, but degrade to a pile of flakes or mud (Ij = 1) if the samples are oven dried before testing. The results for jar slake testing of oven-dried material are comparable, for individual samples, to those obtained from the more comprehensive slake durability tests. The mineralogy of the samples was evaluated by quantitative X-ray diffraction techniques using the Rietveld-based Siroquant processing system. Comparison to independent chemical data show a generally good level of agreement, suggesting that the mineralogical analysis results are consistent with the chemical composition of the individual rock samples. Good correlations were also obtained between clay mineralogy determined from orientedaggregate XRD analysis of the &lt2 micron fraction and the results from powder diffractometry and Siroquant analysis of the whole-rock samples. Evaluation of the slake durability characteristics and other geotechnical properties in relation to the quantitative mineralogy suggests that quartz and feldspar form a rigid framework in the rocks that resists the disruptive pressures that cause slaking. Expansion of the clay minerals by various processes, including the incorporation of water into the interlayer spaces of illite/smectite as well as changes in pore pressures associated with entry of water into micro-fractures in the clay matrix, are thought to produce the disruptions that cause slaking and degradation. An abundant clay matrix also reduces the strength of the rock materials, probably because of the less rigid nature of the clay minerals relative to the quartz and feldspar particles. As well as the mineralogy, the loss on ignition (LOI) and water absorption percentage were found to provide good indicators of longer-term slaking behaviour. Both properties are also related to the overall clay content. Rock samples with water absorption values of &lt10, 10-15 and &gt15% behave as highly durable, intermediate and less durable materials respectively. Rocks with LOI values of greater than 5% by weight behave as less durable rock materials, at least for the strata encompassed by the present study. The water absorption and LOI values were also used to develop a predictive model of slake durability characteristics for the different rock materials in the Patonga Claystone, providing a relatively simple basis for predicting longer-term stability in a range of geotechnical studies.

Elevated arsenic concentrations have been reported in a drinking water and irrigation-supply aquifer of Stuarts Point, New South Wales, Australia. Arsenic occurrence in such aquifers is potentially a major issue due to their common use for high yield domestic and irrigation water supplies. Ten multi-level piezometers were installed to depths of approximately 30 m in the sand and clay aquifer. Sediment samples were collected at specific depths during drilling and analysed for chemical and mineralogical composition, grain size characteristics, potential for arsenic release from solid phase and detailed microscopic features. From this data, a full geomorphic reconstruction allowed the determination of source provenance for the aquifer sediments. The model proposed herein provides evidence that the bulk of the aquifer was deposited under intermittent fluvial and estuarine conditions; and that all sediments derive from the regional arsenicmineralised hinterland. More than 200 groundwater samples were collected and analysed for over 50 variables. The heterogeneity of the aquifer sediments causes redox stratification to occur, which in turn governs arsenic mobility in the groundwater. The bulk of the aquifer is composed of fluvial sand deposits undergoing reductive dissolution of iron oxides. Arsenic adsorbed to iron oxide minerals is released during dissolution but re-adsorbs to other iron oxides present in this part of the aquifer. The deeper, more reducing fluvial sand and estuarine clay groundwaters have undergone complete reductive dissolution of iron oxides resulting in the subsequent mobilisation of arsenic into groundwater. Some of this arsenic has been incorporated into iron sulfide mineral precipitates, forming current arsenian pyrite sinks within the aquifer. The extraction of groundwater from the aquifer for irrigation and drinking water supply induces seawater intrusion of arsenic-rich estuarine water, bringing further dissolved arsenic into the aquifer. A greater understanding of the source, sinks and mobilisation of arsenic in this aquifer contributes to our broad understanding of arsenic in the environment; and allows aquifer specific management procedures and research recommendations to be made. Any coastal or unconsolidated aquifer that has sediments derived from mineralised provenances should consider monitoring for arsenic, and other potentially toxic trace elements, in their groundwater systems.

Elevated arsenic concentrations have been reported in a drinking water and irrigation-supply aquifer of Stuarts Point, New South Wales, Australia. Arsenic occurrence in such aquifers is potentially a major issue due to their common use for high yield domestic and irrigation water supplies. Ten multi-level piezometers were installed to depths of approximately 30 m in the sand and clay aquifer. Sediment samples were collected at specific depths during drilling and analysed for chemical and mineralogical composition, grain size characteristics, potential for arsenic release from solid phase and detailed microscopic features. From this data, a full geomorphic reconstruction allowed the determination of source provenance for the aquifer sediments. The model proposed herein provides evidence that the bulk of the aquifer was deposited under intermittent fluvial and estuarine conditions; and that all sediments derive from the regional arsenicmineralised hinterland. More than 200 groundwater samples were collected and analysed for over 50 variables. The heterogeneity of the aquifer sediments causes redox stratification to occur, which in turn governs arsenic mobility in the groundwater. The bulk of the aquifer is composed of fluvial sand deposits undergoing reductive dissolution of iron oxides. Arsenic adsorbed to iron oxide minerals is released during dissolution but re-adsorbs to other iron oxides present in this part of the aquifer. The deeper, more reducing fluvial sand and estuarine clay groundwaters have undergone complete reductive dissolution of iron oxides resulting in the subsequent mobilisation of arsenic into groundwater. Some of this arsenic has been incorporated into iron sulfide mineral precipitates, forming current arsenian pyrite sinks within the aquifer. The extraction of groundwater from the aquifer for irrigation and drinking water supply induces seawater intrusion of arsenic-rich estuarine water, bringing further dissolved arsenic into the aquifer. A greater understanding of the source, sinks and mobilisation of arsenic in this aquifer contributes to our broad understanding of arsenic in the environment; and allows aquifer specific management procedures and research recommendations to be made. Any coastal or unconsolidated aquifer that has sediments derived from mineralised provenances should consider monitoring for arsenic, and other potentially toxic trace elements, in their groundwater systems.

The Patonga Claystone, a red bed facies in the Narrabeen Group of the Sydney Basin, is one of the most unfavorable rock units in the basin from a geotechnical point of view. This rock unit is composed of sandstone, siltstone, mudstone and claystone. One of the unfavorable characteristics is the low shear strength, which causes instability of cut slopes; another is its slaking-prone behaviour. Numerous measurements of geotechnical properties, along with extensive mineralogical and geochemical determinations, were carried out to identify cause of this slaking behaviour. Key techniques were the use of quantitative X-ray diffractometry for mineralogical analysis, and the determination of slake durability index and related properties to evaluate the slaking behaviour under both standard and more extended conditions. Standard (two cycle) slake durability test results indicate a range from low to high slake durability index values, with some mudstone samples having very low durability and some sandstones having very high slake durability indices. Jar slake test results indicate that the rock samples break rapidly and/or develop several fractures (Ij = 4) in an as-received state, but degrade to a pile of flakes or mud (Ij = 1) if the samples are oven dried before testing. The results for jar slake testing of oven-dried material are comparable, for individual samples, to those obtained from the more comprehensive slake durability tests. The mineralogy of the samples was evaluated by quantitative X-ray diffraction techniques using the Rietveld-based Siroquant processing system. Comparison to independent chemical data show a generally good level of agreement, suggesting that the mineralogical analysis results are consistent with the chemical composition of the individual rock samples. Good correlations were also obtained between clay mineralogy determined from orientedaggregate XRD analysis of the &lt2 micron fraction and the results from powder diffractometry and Siroquant analysis of the whole-rock samples. Evaluation of the slake durability characteristics and other geotechnical properties in relation to the quantitative mineralogy suggests that quartz and feldspar form a rigid framework in the rocks that resists the disruptive pressures that cause slaking. Expansion of the clay minerals by various processes, including the incorporation of water into the interlayer spaces of illite/smectite as well as changes in pore pressures associated with entry of water into micro-fractures in the clay matrix, are thought to produce the disruptions that cause slaking and degradation. An abundant clay matrix also reduces the strength of the rock materials, probably because of the less rigid nature of the clay minerals relative to the quartz and feldspar particles. As well as the mineralogy, the loss on ignition (LOI) and water absorption percentage were found to provide good indicators of longer-term slaking behaviour. Both properties are also related to the overall clay content. Rock samples with water absorption values of &lt10, 10-15 and &gt15% behave as highly durable, intermediate and less durable materials respectively. Rocks with LOI values of greater than 5% by weight behave as less durable rock materials, at least for the strata encompassed by the present study. The water absorption and LOI values were also used to develop a predictive model of slake durability characteristics for the different rock materials in the Patonga Claystone, providing a relatively simple basis for predicting longer-term stability in a range of geotechnical studies.