Unconsolidated Materials Research Articles

Experimental investigation on the longitudinal evolution of landslide dam breaching and outburst floods

Accurate prediction of the evolution of a landslide dam that is breached due to overtopping failure is necessary to estimate the outflow hydrograph and the resulting inundation. In this study, physical flume tests on the breaching of landslide dams were conducted. A wide grain size distribution with unconsolidated dam material was used. Dam breaching was initiated by cutting a notch across the crest of the dam adjacent to the side wall of the flume. This allowed water to escape from the dam while a steady inflow of water was continuously supplied upstream. The effects of upstream inflow on the timescales and magnitudes of the peak discharges and the time to inflection point were also investigated. Experimental results reveal that the whole hydrodynamic process of dam breaching can be divided into three stages defined by clear inflection points and peak discharge. A new longitudinal evolution model is proposed. This model captures the initial increase of the soil erosion rate (of landslide dam) and its subsequent decrease along the longitudinal direction. In addition, a linear relationship between the soil erosion rate and shear stress (of water flow) was observed and this is similar to that observed in large-scale natural landslide dams. Furthermore, soil erosion resistances (of landslide dam) against water flow above are observed to increase with the concentration of entrained sediments along the flow direction.

Mach number scaling of impact craters in unconsolidated granular materials

The formation of impact craters in unconsolidated granular materials is a topic of enduring interest in solid-earth geophysics, planetary science, and several branches of engineering science. In particular, a general relationship between crater size, impact parameters, and target material properties is often sought. This paper presents a new empirical relationship, based on dimensional analysis and inspired by gas-dynamic shock physics, for the diameters of low- and high-speed impact craters in dry granular materials based on the hypothesis that surface-gravity- and shock-wave phenomena primarily set crater size. The final relationship involves the impacting object's kinetic energy and speed; the target material's density, angle of repose, and sound speed; and the gravitational acceleration at the impact location. It is formulated in terms of a dimensionless crater diameter, an algebraic combination of Froude number, Mach number, and the tangent of the target material's angle of repose, using an analogy to gas dynamics and an empirical power law for the dependence of granular-material sound speed on gravitational acceleration. The coefficient of determination for the final fit is 0.969 based on experimental impact data from 325 individual impacts spanning parametric ranges of >400 in crater diameter, 1010 in impact energy, 500 in gravitational acceleration, and 40 in target material density for two different angles of repose. The final formula provides insight into how impact energy conversion depends on Mach number and may be useful for predictive and forensic analysis of planetary impact craters and for granular-flow code validation.

Preliminary Assessment on Riverine Soil Properties of Sg. Lebir, Kelantan, Peninsular Malaysia

Soil is the unconsolidated material in which plants are rooted. Soil texture is determined by the amount of sand, silt and clay in the soil. Understanding soil properties can help to better management and minimize soil disturbance. These soils were collected for soil properties and bulk density along the 55.2km of Sg. Lebir. Soil on Earth commonly contains of various particles such as sand, silt and clay. These particles commonly classes by refer to soil textural triangle. 40g of air-dried sample diluted into 1000ml of deionised water were left until the percentage of sand, silt and clay observed then calculated as percentage. As calculated, the mean percentage of sand contained is 66%, clay 17% and silt 17%. Besides that, it was concluded that most of the soils texture along 55.2km of Sg. Lebir had a sandy loam soil with pH slightly acidic (6.08) with densities the mean is 0.24 gcm-3.

A Pleistocene Thrust Fault in Anorthosite of the Rustenburg Layered Suite near Mooinooi, North West Province, South Africa: Neotectonic Implications

Abstract The 2.056 Ma Bushveld Complex (BC) constitutes the largest layered igneous complex known. The complex forms a basin defined by strata that dip centripetally (10° to 20°). This depression presumably resulted from the load of the complex as was proposed by a number of authors. Sagging of between 460 to 740 m appears possible, resulting in flexural-slip movement. This flexural-slip manifests in many thrust faults, (mainly mapped in mines) which display reverse-slip. The research described in this paper focuses on the age of this deformation. A thrust fault was identified at Lonmin U14 Pit. Reverse slip along the fault displaced unconsolidated sedimentary material that unconformably overlies the Rustenburg Layered Suite strata. Archaeological artefacts (Acheulian hand axes) were discovered buried in this sedimentological layer and provide an age constraint of 1.25 Ma to 250 000 years. Optically stimulated luminescence (OSL) dating further constrained the age of the sedimentary material to less than 175 000 years. The youngest material deposited is a regional black clay layer. At Lonmin U14 Pit this clay layer carries a fabric that resulted from the movement of the thrust and this indicates an age significantly younger than 175 000 years.

Tracing shallow lateral preferential pathways of fluid movement using electrical geophysics

Assessment of gullies is essential in understanding the effects soil erosion has on resource management, urban planning, agricultural productivity and local environmental conditions. Commonly, prediction of gully head cut retreat has been disregarded due to the inherent complexities; this study proposes a method of analysing data to interpret potential pathways of Gully retreat. Through the implementation of electrical geophysics (Electrical Resistivity Imaging & Frequency Domain Electromagnetics) surveys positioned uphill of existing gullies shallow conductor’s representative of Lateral Preferential Pathways (LPP) will be detected. ERI results detected conductors uphill of the head cut at varying distances showing resistivity values of 1 -40 Qm; these identified anomalous zones were confidently linked to form an LPP. Integrated geophysical datasets were generated allowing for interpreted traces of LPP to be drawn which are representative of the future pathway of head cut retreat. Through comparing currently existing gully assessment techniques it is suggested that a combination of geophysical prediction of LPP and LiDAR data is necessary for a complete understanding of existing gullies. Based on the results of this integration, informed and targeted management decisions can be developed to remediate current landforms and mitigate future gullying.There has been recent focus placed on near surface groundwater and surface run-off flows as they have been attributed to erosion of consolidated and unconsolidated material resulting in incised surface channels referred to as gullies, which pose significant issues for agricultural productivity and local infrastructure (Beavis, 2000, Wu and Cheng, 2005). To effectively manage these erosional features through mitigation an understanding of the occurrence and future erosional pathways is required, although prediction is difficult when topographic variations are not obvious.Local hydrological conditions will determine the nature of surface flows and groundwater movement including the infiltration depth, flow direction and rate of movement, although it is generally understood that water flows through physical or chemical channels known as preferential pathways (Clothier et al., 2007). Pathways develop within a medium due to the heterogeneities in the physical properties of the material that the water is flowing through.

Envelope Widths of Volcano‐Seismic Events and Seismic Scattering Characteristics Beneath Volcanoes

AbstractVolcanoes produce highly scattered seismic wavefields, which are characterized by the scattering mean free path (l0) and the quality factor of medium attenuation for S waves (Qi). Previous studies have estimated scattering mean free paths at various volcanoes to be around 100–1,000 m, but their depth distributions remain to be determined. We estimated one‐dimensional l0 and Qi structures using the envelope widths of volcano‐seismic events at Taal (Philippines) and at Nevado del Ruiz (Colombia) in a high‐frequency band (5–10 Hz). We performed Monte Carlo envelope simulations in various one‐dimensional models, and compared the simulated and observed envelope widths. Our results indicate that a highly heterogeneous (l0 = 1,000 m) and attenuative (Qi = 100) surface layer exists to a depth of 1 km, below which l0 and Qi are comparable to those in the normal crust. The surface layer may consist of unconsolidated materials with hydrothermal fluids and/or altered clay minerals, which cause strong scattering and attenuation effects beneath these volcanoes. Our results suggest that strong heterogeneities observed at volcanoes exist only in a thin surface layer.

Mapping groundwater pollution vulnerability with application in a basin in southern Brazil

This study presents the criteria and conditions that supported the development of a proposed vulnerability index and its application in the Corrego do Ribeirao do Feijao Basin, which is located in the central portion of the state of Sao Paulo, southeastern Brazil. This basin was selected, because it is representative of very large areas in the south, west, and southeast regions of Brazil, is the main source of freshwater for the municipality of Sao Carlos, and has been undergoing accelerated changes due to diversified anthropogenic activities, thus increasing the number of contaminant sources. The proposed index is based on a hierarchy of information that includes a total of 46 attributes categorized into groups (4 rainfall attributes, 6 point contaminant sources, 5 non-point contaminant sources, 5 unconsolidated material 1, 4 unconsolidated material 2, 4 rock substrate 1, 4 rock substrate 2, 1 relief, 6 unconsolidated material 3, 4 rock substrate 3, and 3 groundwater), which were obtained from principles and procedures of engineering geological mapping and laboratory tests. The final vulnerability index for each land unit was obtained as a percentage using the total vulnerability index, which is the sum of the partial indices (these indices are normalized eigenvectors of the unit) and the maximum value that a unit can reach, considering the classes of maximum influence in vulnerability. The basin was divided into 29 categories controlled by engineering geological units and types of land uses, resulting in 94 land units, of which 17 were classified as Class 1, with the highest vulnerability; 41, 23, and 13 were classified as Classes 2, 3, and 4, respectively, with decreasing degrees of vulnerability. The results verify that the proposed index enables an adequate subdivision of the region and classification of the units, respecting the natural variability and the anthropogenic aspects. The attributes associated with land units and the datasheet used for data treatment permit a dynamic vulnerability analysis, because it is easier to identify and characterize the anthropogenic changes (mainly related to contaminant sources) per land unit in situ and to obtain new results that will require new control or planning measures.

Prediction of Soil Formation as a Function of Age Using the Percolation Theory Approach

Recent modeling and comparison with field results showed that soil formation by chemical weathering, from bedrock or unconsolidated material, is limited largely by solute transport. Chemical weathering rates are proportional to solute velocities. Nonreactive solute transport described by non-Gaussian transport theory appears compatible with soil formation rates. This change in understanding opens new possibilities for predicting soil production and depth across orders of magnitude of time scales. Percolation theory for modeling the evolution of soil depth and production was applied to new and published data for alpine and Mediterranean soils. The first goal was to check whether the empirical data conform to the theory. Secondly we analyzed discrepancies between theory and observation to find out if the theory is incomplete, if modifications of existing experimental procedures are needed and what parameters might be estimated improperly. Not all input parameters required for current theoretical formulations (particle size, erosion and infiltration rates) are collected routinely in the field; thus, theory must address how to find these quantities from existing climate and soil data repositories, which implicitly introduces some uncertainties. Existing results for soil texture, typically reported at relevant field sites, had to be transformed to results for a median particle size, d50, a specific theoretical input parameter. The modeling tracked reasonably well the evolution of the alpine and Mediterranean soils. For the Alpine sites we found, however, that we consistently overestimated soil depths by approximately 45%. Particularly during early soil formation, chemical weathering is more severely limited by reaction kinetics than by solute transport. The kinetic limitation of mineral weathering can affect the system until 1kyr to a maximum of 10kyr of soil evolution. Thereafter, solute transport seems dominant. The trend and scatter of soil depth evolution is well captured, particularly for Mediterranean soils. We assume that some neglected processes, such as bioturbation, tree throw, and land use change contributed to local reorganization of the soil and thus to some differences to the model. Nonetheless, the model is able to generate soil depth and confirms decreasing production rates with age. A steady state for soils is not reached before about 100 kyr.

Integrated GPR and ERT data interpretation for bedrock identification at Cléricy, Québec, Canada

Ground-penetrating-radar (GPR) and electrical resistivity tomography (ERT) are two geophysical methods widely used for shallow subsurface structure investigations. Although GPR can provide high precision information, it is very limited by the detection depth, especially when there is a medium with high conductivity. This situation is common in the Abitibi greenstone belt of Canada, where fine-grained glaciolacustrine sediments are widespread. Therefore, GPR and electrical methods were combined to investigate the undulating topography of bedrock beneath the clay, to help an infrastructure installation within an urban area. GPR measurements were carried out with four frequencies (450 MHz, 160 MHz, 100 MHz and 80 MHz) and ERT survey were accomplished using a Syscal Pro Switch from Iris Instruments, with 72 electrodes. Shallow boreholes helped in the recognition of the lithology (up to 4 m deep) and in the calibration of geophysical data interpretation. Known infrastructures (underground pipes) were used to estimate the velocity of the radar wave in the uppermost layers, which is estimated at 0.14 m/ns. The data show an unconsolidated material cover, composed of clay, sand and backfill materials, overlying a rugged bedrock surface. The present study highlighted places where the burial of new infrastructures will require rock excavation, and the observations made during the excavation carried out as part of the underground infrastructure installation work made it possible to test the validity of the geophysical measurements.

A Comparative Geophysical Study of the Sedimentary-Metamorphic Contacts in the Douala and Kribi-Campo Sub-Basins of Cameroon

The magnetotelluric method has been used in this work to compare the nature of the sedimentary-metamorphic contacts of the Douala and Kribi-Campo sub-basins in Cameroon. The results show that the sedimentary-metamorphic contact zones for the two sub-basins, marked by a subsidence of the low resistivity materials on the sedimentary formations and uplift of the high resistivity materials characterized by intrusive bodies of higher values of resistivity on the metamorphic formations, are structurally similar,. However, the very low values of resistivity of rocks in the Douala sub-basin is suggestive of high porosity, permeability and high level of saline ions dissociation leading to high conductivity. These rocks should be of unconsolidated sediments for the sedimentary formation and gneiss for the metamorphic formation. On the contrary, the very high values of resistivity for rocks in the Kribi-Campo sub-basin indicate the absence of free mobile electrons and ions and low porosity, permeability and non-conductivity. The sedimentary formation of this sub-basin should be composed of limestone and conglomerates rocks with some gneissic and unconsolidated granitic materials. The rocks in the metamorphic formation should be completely granitic in nature. The shallow depth of penetration of only 4 km of telluric current in the Douala sub-basin is enough evidence that the tectonic events responsible for the emplacement of this contact zone were limited to the earth crust. On the other hand, in the Kribi-Campo sub-basin the tectonic events should have originated from within the earth mantle as the depth of penetration of telluric current attains 150 km.

Evaluation and application of the optical image profiler (OIP) a direct push probe for photo-logging UV-induced fluorescence of petroleum hydrocarbons

The presence of free phase petroleum fuels in the subsurface (often called light nonaqueous phase liquids/LNAPL) is a hazard in almost every town and city in the modern world. Leaking underground storage tanks and the resulting contamination and hazards have proven to be a challenge to investigate and remediate. One issue is adequately characterizing the presence and spatial extent of LNAPLs in the subsurface. Experience has shown that conventional soil coring methods and groundwater monitoring methods are fraught with limitations that can lead to significant errors in the estimation of the amount and spatial distribution of LNAPLs in the subsurface. This leads to the development of inaccurate conceptual site models and costly errors in remedial actions. A new direct push logging tool, the optical image profiler (OIP), has been developed to obtain high resolution site characterization data to more accurately define the presence and extent of LNAPLs in unconsolidated materials. The OIP system uses a downhole ultraviolet light-emitting diode to induce fluorescence of fuel LNAPL. A small complimentary metal–oxide–semiconductor camera mounted inside the probe behind a sapphire window captures photographic images of visible range fluorescence as the probe is advanced by direct push methods. In situ images of subsurface fuel fluorescence have not previously been available to the investigator and may further the understanding of LNAPL behavior. The OIP software also provides a log of percent area fluorescence (%AF) based on analysis of the images. An electrical conductivity (EC) dipole on the probe provides a log of bulk formation EC that is often a good indicator of formation lithology. The information presented here explains the basic design and operation of the OIP system in the field. Bench tests confirm the capability of the OIP system to detect a range of petroleum fuels. Field studies with the tandem EC and %AF logs are used to identify LNAPL and its migration pathways in the subsurface. These capabilities can improve the management and remediation of LNAPL-impacted sites and reduce long-term costs associated with cleanup and closure.

Thermal Conduction in Deforming Isotropic and Anisotropic Granular Porous Media with Rough Grain Surface

Resistance to the heat flow in solid–solid contact areas plays a fundamental role in heat transfer in unconsolidated porous materials. In the present work, we study thermal conduction in granular porous media that undergo deformation due to an external compressing pressure. The media’s grains have rough surface, with the roughness profile following the statistics of self-affine fractals that have been shown to be abundant in natural porous media. We utilize a fractal contact model of rough surfaces in order to estimate the deformation of the contact areas, which is a function of roughness fractal parameters, the grains’ Young modulus, and the compressing pressure. For porous media saturated by a single fluid, the effects of various factors, such as the porosity, the grains’ overlap (consolidation), and shapes (circular vs. elliptical), are all studied. Increasing the compressing pressure enhances heat transfer due to deformation of the rough surface of the gains. The thermal conductivity of the medium is strongly affected by the porosity, when the grains’ conductivity is much larger than that of the fluid that saturates the pore space. Furthermore, we show that thermal anisotropy is a decreasing function of roughness deformation. In other words, granular media with rougher grains exhibit larger anisotropy as measured by the ratio of the directional thermal conductivities. Whereas in one type of granular media the anisotropy eventually vanishes at very high compressing pressure, it persists in a second model of anisotropic media that we study.

Probing the frontal deformation zone of the Chihshang Fault with boreholes and high-resolution electrical resistivity imaging methods: A case study at the Dapo site in eastern Taiwan

Not only direct fault ruptures but also later mass movement may result in complicated frontal deformation of the faults. Consequently, the deformation front or the contacts between the unconsolidated materials from the hanging wall and footwall of the thrust fault may indicate the toe of the mass movement instead of the actual fault zone. In this study, we used a combination of surface electrical resistivity imaging methods and borehole records in order to investigate the geometries of the structures in the frontal deformation zone of the Chihshang Fault at the Dapo elementary school. From the cores, we observed three different geological components at the Dapo site: the conductive Lichi mélange of the hanging wall, the colluvial gravels and the underlying fluvial-gravel layer at the footwall. The resistivity images from two parallel survey lines reveal that the position where the fault trace was thought to be is actually the toe of the slumping body's surface ruptures consisting of materials from the Lichi mélange. On the basis of the resistivity images, we also found that the actual fault plane is located on the southeastern side of the resistivity survey line near the hilltop. As a result, we conclude that mass movement induced by the inter-seismic creeping, not direct faulting, is the main factor affecting the frontal deformation zone of the Chihshang fault at the Dapo site.

Electrokinetic in situ leaching of gold from intact ore

Electrokinetic in situ leaching (EK-ISL) is a novel in situ mining technology that uses an electric field to induce the migration of lixiviants through the subsurface to extract target commodities. Based on previous experiments with fine-grained unconsolidated material, this study assesses the feasibility of EK-ISL of gold from consolidated, unfractured, low-permeability ore material. Under the initially tested laboratory conditions, substantial ionic transport through low-permeability rock was achieved by applying a constant voltage. Subsequently, synthetic gold ore was positioned in between two rock sections and gold was successfully mobilised from the synthetic ore, transported through the second rock piece and collected in the target reservoir, albeit at a fairly slow rate. EK-ISL was then applied to two different gold ore samples. Both ores consumed considerable amounts of lixiviant before gold breakthrough occurred. Within the experimental timeframe, only a trace of gold was leached from Ore Sample 1. Nevertheless, over 50% of gold was recovered from Ore Sample 2 within a month after initial breakthrough. These experiments show that EK-ISL of gold from intact rocks is feasible, and also highlight the importance of characterising the reactivity of the host rock with respect to the selected lixiviant system prior to attempting EK-ISL. It was also found that during EK-ISL the hydraulic permeability of the ore was increased as a result of the dissolution of gangue minerals, which enhanced electro-migration of ions over the investigation timeframe.

Thermal properties variations in unconsolidated material for very shallow geothermal application (ITER project)

Abstract In engineering, agricultural and meteorological project design, sediment thermal properties are highly important parameters, and thermal conductivity plays a fundamental role when dimensioning ground heat exchangers, especially in very shallow geothermal systems. Herein, the first 2 m of depth from surface is of critical importance. However, the heat transfer determination in unconsolidated material is difficult to estimate, as it depends on several factors, including particle size, bulk density, water content, mineralogy composition and ground temperature. The performance of a very shallow geothermal system, as a horizontal collector or heat basket, is strongly correlated to the type of sediment at disposal and rapidly decreases in the case of dry-unsaturated conditions. The available experimental data are often scattered, incomplete and do not fully support thermo-active ground structure modeling. The ITER project, funded by the European Union, contributes to a better knowledge of the relationship between thermal conductivity and water content, required for understanding the very shallow geothermal systems behaviour in saturated and unsaturated conditions. So as to enhance the performance of horizontal geothermal heat exchangers, thermally enhanced backfilling material were tested in the laboratory, and an overview of physical-thermal properties variations under several moisture and load conditions for different mixtures of natural material was here presented.

Genesis of Clastic Dykes and Soft-Sediment Deformation Structures in the Mamfe Basin, South-West Region, Cameroon: Field Geology Approach

This paper aims to investigate the genesis of clastic dykes and soft-sediment deformation structures in the Mamfe Basin, South West-Region, Cameroon. Results from this study portray the following: (1) The clastic dykes are extrusive and were generated from preexisting soft-sediments that penetrate fissures caused by seismic activity. It can be concluded that clastic dykes originate from seismic shacking, probably induced by volcanic-tectonic activity and magmatic dykes that cut across the Precambrian and Cretaceous formations of the Mamfe Basin. (2) The soft-sediment deformation structures (flexures, sheared foliations, anticlinal folds, load casts, and flame structures) are likely triggered by seismic shocks. The inferred influence of seismic activity results from rifting and rapid subsidence of basin-fill during the Cretaceous. Some of these soft-sediment deformation structures (SSDS) are induced by fluidization and liquefaction triggered by rapid sedimentation within tectonically active settings, as well as density variations illustrated by local occurrence of load casts with weak lateral extensions. (3) The synsedimentary features (joints, faults, filled fractures) are related to local stress triggered by gravitational sliding, because the fractures were filled by unconsolidated clastic materials.

Hydrochemical study of the Caldas Novas Thermal Complex (GO), Brazil

The city of Caldas Novas, State of Goias, Brazil, holds the largest thermal water complex in the planet not associated to with volcanism or other kinds of magmatism. Its structural control allows the fractures to be wide and deep enough so the waters can reach 1000 m depth. These waters are extracted mainly by deep wells, from the exploitation of the Paranoa and Araxa Aquifer Systems, emerging at temperatures higher than 59 °C. With a growing demand for water resources, groundwater exploration became an attractive alternative for public supply, due to its abundance, quality and low abstraction cost. In Caldas Novas, due to the population growth over the last decades and the increasing number of tourists, a disordered groundwater consumption drawdown the water levels. In order to survive, these reservoirs depend on rainwater infiltration rates to replenish the thermal springs; however, the lack of environmental management and the high risk of contamination, due to the unconsolidated materials thinness, may threaten the thermal aquifer. This study was based on the hydrochemical characterization of Caldas Novas Thermal Complex waters, including radioactive parameters, whose descriptions in the literature are still scarce. Besides, concerning the prospective increase on touristic activities, physicochemical water analyses are periodically required, being this paper a contribution for such purpose.

Real-time prediction of rain-triggered lahars: incorporating seasonality and catchment recovery

Abstract. Rain-triggered lahars are a significant secondary hydrological and geomorphic hazard at volcanoes where unconsolidated pyroclastic material produced by explosive eruptions is exposed to intense rainfall, often occurring for years to decades after the initial eruptive activity. Previous studies have shown that secondary lahar initiation is a function of rainfall parameters, source material characteristics and time since eruptive activity. In this study, probabilistic rain-triggered lahar forecasting models are developed using the lahar occurrence and rainfall record of the Belham River valley at the Soufrière Hills volcano (SHV), Montserrat, collected between April 2010 and April 2012. In addition to the use of peak rainfall intensity (PRI) as a base forecasting parameter, considerations for the effects of rainfall seasonality and catchment evolution upon the initiation of rain-triggered lahars and the predictability of lahar generation are also incorporated into these models. Lahar probability increases with peak 1 h rainfall intensity throughout the 2-year dataset and is higher under given rainfall conditions in year 1 than year 2. The probability of lahars is also enhanced during the wet season, when large-scale synoptic weather systems (including tropical cyclones) are more common and antecedent rainfall and thus levels of deposit saturation are typically increased. The incorporation of antecedent conditions and catchment evolution into logistic-regression-based rain-triggered lahar probability estimation models is shown to enhance model performance and displays the potential for successful real-time prediction of lahars, even in areas featuring strongly seasonal climates and temporal catchment recovery.

Geogenic and Anthropogenic Chromium Contamination in Groundwater in an Ophiolitic Area, Northeastern Iran

Geology of Iran shows an ophiolitic belt around the central Iran micro-continent. One of the main ophiolite suites, with ca. 100km long and 15km wide, located northeastern Iran as Sabzevar ophiolite suite. Ultramafic rocks of this ophiolite suite, display a high concentration of chromium (1000-3000ppm) as a compatible element, especially in pyroxene group minerals. Average Chromium content of this ophiolite suite in peridotites is 2558ppm, with maximum 4525ppm (in pyroxenite) and minimum 832ppm (in dunite). Dunite layers lie underneath of these ultramafic rocks, containing chromite lenses (FeCr2O4) with 20.56wt% Cr2O3. Today, about 10 active mining sites excavate ultramafic rocks for chromite ore mineral and altered ultramafic rocks, serpentinite, dump as unconsolidated gangue materials along stream pathways. There is an unconfined aquifer just southern of this ophiolite range containing detrital altered ultramafic rocks with the high concentration of chromium minerals. In this study 23 groundwater samples, collected from unconfined serpentinite alluvium aquifer that shows cumulative increasing Cr towards south because of increasing residence time, and much more water-rock interactions. Total Cr concentrations in this aquifer are from 12 to 61µg/l, higher than normal level of Cr mentioned by WHO (2µg/l). On the other hand, discharging of chromite mine and mineral processing site, contaminate one of drinking well at Forumad village up to 61µg/l of total chromium. Although trivalent Cr is an essential nutrient, in oxidation conditions with increasing Eh and pH, it changes to chromate (CrO4-2) and dichromate (Cr2O72-) as dissolved anions which will be toxic and carcinogenic in groundwater. Based on California EPA Office of Environmental Health Hazard Assessment (OEHHA), 7.2% of total Cr is hexavalent. Recent information indicates that hexavalent chromium varies from 50% to 90% of the total chromium in many water supplies.

APXS‐derived chemistry of the Bagnold dune sands: Comparisons with Gale Crater soils and the global Martian average

AbstractWe present Alpha‐Particle X‐ray Spectrometer (APXS) data for the active Bagnold dune field within the Gale impact crater (Mars Science Laboratory (MSL) mission). We derive an APXS‐based average basaltic soil (ABS) composition for Mars based on past and recent data from the MSL and Mars Exploration Rover (MER) missions. This represents an update to the Taylor and McLennan (2009) average Martian soil and facilitates comparison across Martian data sets. The active Bagnold dune field is compositionally distinct from the ABS, with elevated Mg, Ni, and Fe, suggesting mafic mineral enrichment and uniformly low levels of S, Cl, and Zn, indicating only a minimal dust component. A relationship between decreasing grain size and increasing felsic content is revealed. The Bagnold sands possess the lowest S/Cl of all Martian unconsolidated materials. Gale soils exhibit relatively uniform major element compositions, similar to Meridiani Planum and Gusev Crater basaltic soils (MER missions). However, they show minor enrichments in K, Cr, Mn, and Fe, which may signify a local contribution. The lithified eolian Stimson Formation within the Gale impact crater is compositionally similar to the ABS and Bagnold sands, which provide a modern analogue for these ancient eolian deposits. Compilation of APXS‐derived soil data reveals a generally homogenous global composition for Martian soils but one that can be locally modified due to past or extant geologic processes that are limited in both space and time.