Geohazard Evaluation of Bukit Merah/ Malaysia using Geospatial Information Technique

Geospatial technology (that includes Remote Sensing and Geographical Information System GIS) has opened up opportunities for qualitative analyses of sinkholes distribution with multi thematic maps to define the relationship of GIS database. Kinta Valley have been deteriorating dramatically as a result of changes that had occurred in the past and continues due to the close relationship between the fast rate of lateral urbanization and extensive dimensional expansion of surface mining and quarrying activities, where sinkholes are the main crux of the geohazard in Kinta Valley. Geospatial information system for sinkholes had been established using pictorial, tabular and ancillary data to build a relational GIS database. The application is capable of analyzing an entire data set of sinkholes to create sinkholes distribution map. The objective of this paper is to highlight the value of Geospatial Information System as a tool to define sinkhole distribution and change detection for geohazard evaluation. Keywords: Geospatial, Karst, Sinkholes distribution, Geohazard, Malaysia

A Comparative Analysis of Groundwater Vulnerability and PFAS Contamination in Maine

As more information is learned regarding the long-term health effects of per- and polyfluoroalkyl substances (PFAS), increasing regulatory measures are being taken to protect the public from these chemicals. States like Maine are on the forefront of such legislation, banning land-applied biosolids in 2022 for fear of PFAS contamination, with plans to halt sales of all unnecessary PFAS products in the state by 2030. The state has conducted some testing of groundwater supplies, but the near-ubiquitous nature of PFAS in manufacturing indicates contamination may be widespread. To prioritize testing in Maine’s most vulnerable aquifers, a groundwater susceptibility map has been developed using a modified form of the EPA’s DRASTIC model. The model uses geological, atmospheric, and land use data to estimate the relative vulnerability of groundwater across the state. Additionally, a heatmap of potential PFAS sources was created, where each site was assigned a risk score based on the upper magnitude of PFAS contamination associated with its industry. These maps were compared with state PFAS test results to determine the validity of each method. Regional vulnerability trends were found which indicate karst features, coarse glacial/fluvial deposits, volcanic geology, and urban development are signs of high groundwater vulnerability. Density of potential PFAS sources was also found to be highest around urban centers, with PFAS test data affirming the relationship. Recommendations are made for best management practices guided by the models, such as protection of the most vulnerable aquifers via rezoning and building factories on impermeable geologies. Future model development is encouraged with more robust datasets and additional fine-tuning of the statewide Depth to Groundwater, Depth to Bedrock, and Hydraulic Conductivity maps

A model ensemble generator to explore structural uncertainty in karst systems with unmapped conduits

Karst aquifers are characterized by high-conductivity conduits embedded in a low-conductivity fractured matrix, resulting in extreme heterogeneity and variable groundwater flow behavior. The conduit network controls groundwater flow, but is often unmapped, making it difficult to apply numerical models to predict system behavior. This paper presents a multi-model ensemble method to represent structural and conceptual uncertainty inherent in simulation of systems with limited spatial information, and to guide data collection. The study tests the new method by applying it to a well-mapped, geologically complex long-term study site: the Gottesacker alpine karst system (Austria/Germany). The ensemble generation process, linking existing tools, consists of three steps: creating 3D geologic models using GemPy (a Python package), generating multiple conduit networks constrained by the geology using the Stochastic Karst Simulator (a MATLAB script), and, finally, running multiple flow simulations through each network using the Storm Water Management Model (C-based software) to reject nonbehavioral models based on the fit of the simulated spring discharge to the observed discharge. This approach captures a diversity of plausible system configurations and behaviors using minimal initial data. The ensemble can then be used to explore the importance of hydraulic flow parameters, and to guide additional data collection. For the ensemble generated in this study, the network structure was more determinant of flow behavior than the hydraulic parameters, but multiple different structures yielded similar fits to the observed flow behavior. This suggests that while modeling multiple network structures is important, additional types of data are needed to discriminate between networks

Controls on Speleogenesis in the Upper-Mississippian Pennington Formation on the Western Cumberland Plateau Escarpment

Much of the pioneering work on caves of the Cumberland Plateau (province spanning Tennessee, Kentucky, Alabama, and Georgia) has been stratigraphically located within the Mississippian Bangor and Monteagle Limestones, wherein some of the region’s largest and most spectacular caves occur. Of interest to the understanding of this karst landscape, but severely underrepresented in the literature thereof, are caves and karst features in a heterogeneous sequence of clastics and carbonates known collectively as the Pennington Formation (Upper Mississippian). This work consisted of a regional study of Pennington caves on the western Cumberland Plateau escarpment (Alabama and Tennessee), and a case study of Pennington caves in Savage Gulf State Natural Area (Grundy County, Tennessee). The objective of this research was to determine controls on speleogenesis in the Pennington Formation, using cave geomorphology, dye tracing, and GIS to explore lithologic, hydrologic, and structural influences on karst processes. This resulted in a conceptual model for speleogenesis in the Pennington Formation, with the major controls being: 1) direct and diffuse recharge from the caprock, undersaturated with respect to calcite; 2) thin, horizontally bedded limestones sandwiched by shales and other insoluble rocks; and 3) networks of stress release fractures oriented parallel to major stream valleys. Our present understanding of the Cumberland Plateau could be advanced by further study of karst dynamics in the Pennington Formation

Comparative Microbial Community Dynamics in a Karst Aquifer System and Proximal Surface Stream in Northwest Arkansas

Northwest Arkansas has well-developed karst systems, with numerous sinking streams and springs. Karst conduits make it easy for contaminants to enter groundwater systems, degrading the water quality and destroying fragile karst ecosystems. With the increase of urbanization, potential threats in the form of fecal contamination may prove to be more of a problem. The purpose of this research is to compare the difference between microbial communities within two different settings, a karst aquifer and a surface stream. The microbial communities within Blowing Spring Cave and Little Sugar Creek were detected and identified in water and sediment samples. Samples were also analyzed using 16s rRNA metagenomic analysis to examine microbial diversity at the genus level. The results showed diversity was greatest between the water and sediment followed by the locations. Interaction of surface and groundwater allows for the introduction and transport of microbial communities, some of which are unique to urban sources

Non-Aqueous Phase Liquid Transport and Dynamics in Simulated Karst Conduits

Flow and contaminant transport in karstic aquifers differs drastically from porous media. Little work has been done to quantify the transport dynamics of non-aqueous phase liquids (NAPLs) in karst in the lab. Some studies have 3-D printed fractures to evaluate multiphase transport at the core scale, but examination of conduit flow using this technique is lacking in the literature. This project illustrates some of the strengths and limitations of 3-D printing and using X-ray computed tomography (XRCT) to characterize flow. After testing prints made from stereolithographic resin (SLA) and polyactic acid (PLA) plastic, we decided to use acrylonitrile butadiene styrene (ABS) plastic to construct flow cells to image turbulent water-NAPL-analog flow in conduits using XRCT. To mimic conduit flow transport dynamics, printed conduit apertures are elliptical and measure more than 1 cm in cross sectional area to promote turbulent flow. Fused filament fabrication, a type of 3-D printing process used during construction, produces permeable prints. To minimize communication between the conduit and surrounding support matrix allowing reuse of flow cells, we moderately melted cores using acetone vapor. This allows dissolved plastic to fill and harden between layers making the walls impermeable. Flow of water and hydrogel beads, a potential non-toxic NAPL analog tracer candidate, was imaged with a modified XRCT scanner. XRCT images were stitched together to identify conduit irregularities, and to image beads as they move through the conduit. Future work aims to develop hydrogel beads that behave like NAPLs in the lab. As a novel technique in karst modeling, printing and imaging requires further validation. Our images do not differentiate between beads, epoxy, and plastic, making validation difficult. Future work should involve radiologic agents added to water and NAPL-analogs during experimentation to increase the contrast between water and hydrogel beads in order to clarify flow paths

Sinkhole development in the Sivas gypsum karst, Turkey

The extensive gypsum karst of Sivas, Turkey is one of the most outstanding examples of bare gypsum karst in the world. It displays a number of remarkable geomorphic features, including: (1) two stepped planation surfaces cut-across folded gypsum developed during an initial phase of slow base level deepening punctuated by periods of stability; (2) unusual deeply entrenched gypsum canyons related to a subsequent phase of rapid fluvial incision and water table lowering; (3) a polygonal karst of superlative quality mainly developed in the upper surface; (4) relict valleys disrupted by sinkholes in the lower erosional surface; (5) a large number of bedrock collapse sinkholes mostly associated with the lower surface; and (6) numerous cover subsidence sinkholes developed in the valley floors. This work analyses the spatial distribution, characteristics and evolution of the sinkholes within the broad Plio-Quaternary geomorphological and paleohydrological evolution of the epigene karst system dominated by autogenic recharge. A cartographic sinkhole inventory has been produced in an area covering 2820 km(2) with morphometric data and including 295 bedrock collapse sinkholes and 302 cover subsidence sinkholes. The different sinkhole types show a general spatial zonation controlled by the hydrogeological functioning of the different sectors: (1) solution sinkholes (polygonal karst) in the upper recharge area; (2) bedrock collapse sinkholes in the lower denudation surface and close to the base level, where well developed caves are inferred; and (3) cover subsidence sinkholes, with high densities probably associated with areas of preferred groundwater discharge. The morphology of the bedrock collapse sinkholes, varying from small cylindrical holes to large and deep tronco-conical depressions with gentle slopes reflect to geomorphic evolution of these sinkholes that reach exceptionally large hectometre-scale diameters. Their evolution, involving substantial enlargement and deepening, is attributed to the solutional removal as solute load of large volumes of gypsum by downward vadose flow. This type of morphological evolution with significant post-collapse solutional denudation differs from that observed in carbonate rocks characterised by lower solubility and erodibility. The analysis of historical imagery reveals that bedrock collapse sinkholes currently have a very low probability of occurrence and that buried cover subsidence sinkholes are used for urban development creating risk situations. (C) 2021 The Author(s). Published by Elsevier B.V

A Regional Chemical Characterization and Analysis of Groundwater in Eastern Ontario

This study utilizes 234 samples to provide a regional characterization and analysis of groundwater chemistry in eastern Ontario, Canada, where elevated TDS, Na and halogens occur in shallow groundwater. Water-types, PCA and mapping are used to investigate the processes and features controlling the chemistry. The chemical patterns are associated with glaciomarine deposits (extent, thickness) and bedrock topography, which modulate residence time and flow-path of groundwater. These determine the relative effects of recharge, ion exchange, salinization and organic breakdown on groundwater chemistry. Anomalous chemistry east of Ottawa (brackish-to-saline TDS; elevated water δ18O; elevated Na, Cl, I, CH4, pH, F) coincides with a major buried bedrock depression. Here, groundwater stagnation allows build-up of organic decomposition products and sustained residence of Pleistocene Champlain seawater with TDS up to 10400 ppm. This ambient baseline and identified natural and anthropogenic water quality threats and potential groundwater quantity issues will help support effective groundwater resource management