Remediation of coal-mine drainage by a sulfate-reducing bioreactor: A case study from the Illinois coal basin,USA

This study reports changes in coal-mine drainage constituent concentrations through an anaerobic SO₄-reducing bioreactor monitored over a 3-a period. The purpose of the study was to identify and monitor over time the biogeochemical mechanisms that control the attenuation of toxic compounds in the mine drainage. This information is needed to investigate bioreactor performance and longevity. The water treated at the case example site, the Tab-Simco Mine, was highly acidic with an average pH of 2.9, a net acidity of 1674 mg/L CaCO₃ equivalent-CCE, and high levels of dissolved ${\text{SO}}_4^{2-}$, Al, Fe and Mn. The results of this study indicated that the treatment system increased the pH of the acid mine drainage (AMD) to 6.2 and decreased the median acidity to 22.7 mg/L CCE, ${\text{SO}}_4^{2-}$ from 2981 to 1750 mg/L, Fe from 450.6 to 1.76 mg/L, Al from 113 to 0.42 mg/L, and Mn from 36.4 to 23.3 mg/L. Geochemical modeling indicates that the bioreactor discharge is saturated with respect to the minerals alunite, gibbsite, siderite, rhodochrosite, jarosite, and Fe hydroxide precipitates. The observed trends also include seasonal variations in ${\text{SO}}_4^{2-}$ reduction and a general decline in the amount of alkalinity produced. The average δ³⁴S value of the ${\text{SO}}_4^{2-}$ in the untreated AMD was +7.3‰. In the bioreactor, δ³⁴S value of ${\text{SO}}_4^{2-}$ increased from an average of +6.9‰ to +9.2‰, suggesting the presence of bacterial SO₄ reduction processes. Preliminary results of a bacterial community analysis show that DNA sequences corresponding to bacteria capable of SO₄ reduction were present in the bioreactor outflow sample. However, these sequences were outnumbered by sequences similar to bacteria capable of reoxdizing reduced sulfur species. This study illustrates the dynamic nature of metal removal in SO₄-reducing bioreactor-based treatment systems.     

Hydrogeologic controls on lake level: a case study at Mountain Lake, Virginia, USA

Mountain Lake in Giles County, Virginia, USA, has a documented history of severe natural lake-level changes involving groundwater seepage that extends over the past 4,200?years. The natural lake was full during a large part of the twentieth century but dried up completely in September 2008 and levels have yet to recover. The objective of the study was to understand the hydrogeologic factors that influence lake-level changes using a daily water balance, electrical resistivity, water sampling and geochemical analysis, and well logging. Results from the water balance demonstrate the seasonal response to precipitation of a forested first-order drainage system in fractured rock. The resistivity surveys suggest discrete high-permeability areas may provide pathways for lake drainage. Imagery, well logs, and field observations appear to confirm the presence of a fault which crosses the Eastern Continental Divide to the east of the lake that had not previously been discussed in literature on the lake; the position of the lake within local and intermediate groundwater flow systems is considered. Historical data suggest that either significant precipitation or artificial intervention to mitigate seepage would be required for lake-level recovery in the near future.     

Dissolved metals and associated constituents in abandoned coal-mine discharges,Pennsylvania, USA. Part 1: Constituent quantities and correlations

Complete hydrochemical data are rarely reported for coal-mine discharges (CMD). This report summarizes major and trace-element concentrations and loadings for CMD at 140 abandoned mines in the Anthracite and Bituminous Coalfields of Pennsylvania. Clean-sampling and low-level analytical methods were used in 1999 to collect data that could be useful to determine potential environmental effects, remediation strategies, and quantities of valuable constituents. A subset of 10 sites was resampled in 2003 to analyze both the CMD and associated ochreous precipitates; the hydrochemical data were similar in 2003 and 1999. In 1999, the flow at the 140 CMD sites ranged from 0.028 to 2210 L s⁻¹, with a median of 18.4 L s⁻¹. The pH ranged from 2.7 to 7.3; concentrations (range in mg/L) of dissolved (0.45-μm pore-size filter) SO₄ (34–2000), Fe (0.046–512), Mn (0.019–74), and Al (0.007–108) varied widely. Predominant metalloid elements were Si (2.7–31.3 mg L⁻¹), B (<1–260 μg L⁻¹), Ge (<0.01–0.57 μg L⁻¹), and As (<0.03–64 μg L⁻¹). The most abundant trace metals, in order of median concentrations (range in μg/L), were Zn (0.6–10,000), Ni (2.6–3200), Co (0.27–3100), Ti (0.65–28), Cu (0.4–190), Cr (<0.5–72), Pb (<0.05–11) and Cd (<0.01–16). Gold was detected at concentrations greater than 0.0005 μg L⁻¹ in 97% of the samples, with a maximum of 0.0175 μg L⁻¹. No samples had detectable concentrations of Hg, Os or Pt, and less than half of the samples had detectable Pd, Ag, Ru, Ta, Nb, Re or Sn. Predominant rare-earth elements, in order of median concentrations (range in μg/L), were Y (0.11–530), Ce (0.01–370), Sc (1.0–36), Nd (0.006–260), La (0.005–140), Gd (0.005–110), Dy (0.002–99) and Sm (<0.005–79). Although dissolved Fe was not correlated with pH, concentrations of Al, Mn, most trace metals, and rare earths were negatively correlated with pH, consistent with solubility or sorption controls. In contrast, As was positively correlated with pH.     

Tracing the interaction of acid mine drainage with coal utilization byproducts in a grouted mine: Strontium isotope study of the inactive Omega Coal Mine,West Virginia (USA)

In order to ameliorate acidic discharge, the inactive Omega Coal Mine, West Virginia was partially filled by injection of a grout consisting of 98% coal utilization byproducts (CUB), including fluidized bed combustion ash and fly ash, and 2% Portland cement. In this study, discharge chemistry and Sr isotope ratios were determined to identify and quantify the extent of interaction between mine waters and the CUB–cement grout. Eight sampling sites were monitored around the downdip perimeter of the mine. The major and trace element chemistry of the discharges was generally not sufficient to distinguish between discharges that interacted with grout and those that did not. Elements that showed the most separation include K and As, which were elevated in some waters that interacted with CUB–cement grout. In contrast, the Sr isotope ratios clearly distinguished discharges from grouted and non-grouted areas. Discharges that bypassed the grouted portions had ⁸⁷Sr/⁸⁶Sr ratios ranging from 0.71510 to 0.71594, while two discharges that interacted with grout had ratios in the range of 0.71401–0.71456. The Treatment Inlet, which includes both grouted and ungrouted discharges, yielded intermediate isotopic ratios. Leaching experiments on CUB–cement grout, coal and surrounding rocks are consistent with the isotopic trends observed in the discharges. Based on these results, waters that interacted with grout received 30–40% of their Sr from the CUB–cement grout material. These results suggest that the grout material is chemically eroding at a rate of approximately 0.04% per year. This novel application of the Sr isotope system illustrates its ability to sensitively track and quantify fluid interaction with coal and CUB-based grout.     

Quaternary coastal lithofacies,sequence development and stratigraphy in a passive margin setting,North Carolina and Virginia,USA

Lithofacies analysis is fundamental to unravelling the succession of depositional environments associated with sea‐level fluctuations. These successions and their timing are often poorly understood. This report defines lithofacies encountered within the north‐eastern North Carolina and south‐eastern Virginia Quaternary section, interprets their depositional environments, presents a model for coastal depositional sequence development in a passive margin setting and uses this understanding to develop the stratigraphy and Quaternary evolutionary history of the region. Data were obtained from numerous drill cores and outcrops. Chronology was based on age estimates acquired using optically stimulated luminescence, amino acid racemization, Uranium series and radiocarbon dating techniques. Geomorphic patterns were identified and interpreted using light detection and ranging imagery. Since lithofacies occurrence, distribution and stratigraphic patterns are different on interfluves than in palaeo‐valleys, this study focused on interfluves to obtain a record of highstand sea‐level cycles with minimal alteration by fluvial processes during subsequent lowstands. Nine primary lithofacies and four diagenetic facies were identified in outcrops and cores. The uppermost depositional sequence on interfluves exhibits an upward succession from shelly marine lithofacies to tidal estuarine lithofacies and is bounded below by a marine ravinement surface and above by the modern land surface. Older depositional sequences in the subsurface are typically bounded above and below by marine ravinement surfaces. Portions of seven depositional sequences were recognized and interpreted to represent deposition from late middle Pleistocene to present. Erosional processes associated with each successive depositional sequence removed portions of older depositional sequences. The stratigraphic record of the most recent sea‐level highstands (Marine Isotope Stage 5a and Marine Isotope Stage 3) is best preserved. Glacio‐isostatic adjustment has influenced depositional patterns so that deposits associated with late Quaternary sea‐level highstands (Marine Isotope Stages 5c, 5a and 3), which did not reach as high as present sea‐level according to equatorial eustatic records, are uplifted and emergent within the study area.     

Geochemistry of a spring-dense karst watershed located in a complex structural setting, Appalachian Great Valley, West Virginia, USA

The distribution and chemistry of the springs in the Tuscarora Creek watershed is controlled by both geologic structure and karst dissolution. The watershed is located in eastern West Virginia in the structurally complex Great Valley of the Appalachian Valley and Ridge province. The upper portion of the stream parallels strike along a mapped fault zone and is bordered by clastic rocks that comprise North Mountain. The lower reaches of the stream flow cross-strike through Cambro-Ordovician carbonates. The controlling chemical signature in the spring water is carbonate dissolution. Little evidence was seen for the recharge from adjacent clastic rocks although differences in the Ca/Mg molar ratio between springs indicated the presence of localized spring basins in headwater reaches. Na, Cl and Ca generally increased from upstream to downstream in the cross-strike reaches. Comparison of stream and cumulative spring discharge was consistent with significant groundwater base-flow contribution directly to the creek, particularly in the strike-parallel region. The largest spring in the watershed (>162 L/s) was sampled during and after a large storm event along with the adjacent creek. The creek displayed a typical dilution response with each flood pulse, whereas the spring had only a limited or delayed response. The overall chemical and thermal stability of the spring, relative to the creek, indicated the lack of significant direct hydraulic connection between the two. The conceptual model for the area includes localized flowpaths in the headwater region where the stream flow is parallel to strike and a thrust fault. In addition to the shallow localized flowpaths, a deeper, more regional flowpath likely exists for a large spring further downstream.     

煤矿采空塌陷的危险性预测评估与防治措施——以华亭矿区大柳矿井为例

煤矿开采后引发地面塌陷的危险性预测评估是煤矿地质灾害危险性评估的核心内容。以华亭矿区大柳矿井地质灾害危险性评估为例,介绍了煤矿采空引发地面塌陷危险性预测评估的基本内容及评估深度,并提出了较全面的矿区采空塌陷的防治措施,可以为矿井开采后防治地面塌陷提供指导。     

Comparison of age distributions estimated from environmental tracers by using binary-dilution and numerical models of fractured and folded karst: Shenandoah Valley of Virginia and West Virginia, USA

Measured concentrations of environmental tracers in spring discharge from a karst aquifer in the Shenandoah Valley, USA, were used to refine a numerical groundwater flow model. The karst aquifer is folded and faulted carbonate bedrock dominated by diffuse flow along fractures. The numerical model represented bedrock structure and discrete features (fault zones and springs). Concentrations of ³H, ³He, ⁴He, and CFC-113 in spring discharge were interpreted as binary dilutions of young (0–8  years) water and old (tracer-free) water. Simulated mixtures of groundwater are derived from young water flowing along shallow paths, with the addition of old water flowing along deeper paths through the model domain that discharge to springs along fault zones. The simulated median age of young water discharged from springs (5.7  years) is slightly older than the median age estimated from ³H/³He data (4.4  years). The numerical model predicted a fraction of old water in spring discharge (0.07) that was half that determined by the binary-dilution model using the ³H/³He apparent age and ³H and CFC-113 data (0.14). This difference suggests that faults and lineaments are more numerous or extensive than those mapped and included in the numerical model.     

Hydrogeologic control of shear-related fracturing in Blue Ridge basement rocks: a case study from production wells in the Marshall Metagranite,Fauquier County,Virginia (USA)

Borehole geophysical logging of four production wells completed in Precambrian metagranite in Fauquier County, Virginia (USA), was conducted to characterize stratigraphy, collect water-bearing fracture orientations and describe vertical hydraulic gradients in the vicinity of each borehole. Long-term (48–90 h) single-well pump test data were reevaluated for each well to better characterize this locally important aquifer system. Single-well aquifer test analyses indicate mid-to-late-time infinite acting radial flow conditions within the fractured rock aquifer, followed by increasing late-time contribution of stored groundwater from recharge boundaries. Later-time pump test results are believed to indicate that water-bearing fractures within the metagranite are ultimately recharged by groundwater stored within the regolith. Assumptions about the presence of a recharge boundary sourced by the regolith were tested with a simple groundwater flow model that was calibrated to observed drawdown data associated with one of the long-term pump tests. This study identifies fracturing associated with shear-related metamorphic fabrics in the wellbore and demonstrates the significance of these fractures as mechanisms for accessing groundwater. Results from this investigation indicate that shear-related metamorphic fabrics can be important structures for integrating transmissive fracture networks within the Marshall Metagranite and possibly within other Blue Ridge basement rocks possessing similar metamorphic history.

     

Seismic stratigraphy and coastal drainage patterns in the Quaternary section of the southern Delmarva Peninsula, Virginia, USA

Seismic-stratigraphic analysis of the coastal zone and inner shelf of Virginia's southern Delmarva Peninsula has revealed three geochronologically significant surfaces of post-Tertiary age that impose a relative chronostratigraphic framework on Quaternary marine transgressive and regressive events. Characteristics of these surfaces indicate that two are sequence boundaries, and one is a ravinement surface.

Lying at depths of 18–70 m (msl datum), the LP_b surface (a late Pleistocene basal unconformity) represents the sequence boundary separating the Tertiary Chesapeake Group from the overlying late Pleistocene Nassawadox Formation. High relief (approximately 50 m) on the LP_b surface is associated with large fluvial channels. Higher in the stratigraphic section, the LP_r, surface is found at depths of 6–28 m, and corresponds to a late Pleistocene transgressive, or ravinement surface. The surface dips southeastward with a regional dip of 0.04° and has local relief of less than 2 m. The LP_r surface may represent a ravinement which extended to the west side of the Chesapeake Bay prior to the development of the Nassawadox barrier spit. However, the LP_r surface may steepen between the axis of the southern Delmarva Peninsula and the Holocene lagoon to form a shoreface attached to one of several known late Pleistocene shorelines. Lying at depths of 0–20 m, the H_b surface is a basal unconformity that marks the Holocene sequence boundary. It deepens seaward, with maximum local relief of about 15 m, and has a topographic expression very similar to the present-day lagoonal drainage pattern.

Maximum thicknesses of Holocene and Pleistocene sediments (12 and 70 m, respectively) are found above channels on the H_b and LP_b surfaces. The Pleistocene channels are large and limited in number and represent high-order channels of a drainage system that drained the Piedmont and Coastal Plain. The greater density of low-order stream channels on the H_b surface suggests a relationship to much smaller drainage basins that were confined to the seaward part of the Coastal Plain east of the Delmarva Peninsula. These late Wisconsinan smaller H_b channels do not re-occupy the former drain paths of the much larger high-order LP_b channels.     

Tracing groundwater with low-level detections of halogenated VOCs in a fractured carbonate-rock aquifer,Leetown Science Center,West Virginia,USA

Measurements of low-level concentrations of halogenated volatile organic compounds (VOCs) and estimates of groundwater age interpreted from ³H/³He and SF₆ data have led to an improved understanding of groundwater flow, water sources, and transit times in a karstic, fractured, carbonate-rock aquifer at the Leetown Science Center (LSC), West Virginia. The sum of the concentrations of a set of 16 predominant halogenated VOCs (TDVOC) determined by gas chromatography with electron-capture detector (GC–ECD) exceeded that possible for air–water equilibrium in 34 of the 47 samples (median TDVOC of 24,800 pg kg⁻¹), indicating that nearly all the water sampled in the vicinity of the LSC has been affected by addition of halogenated VOCs from non-atmospheric source(s). Leakage from a landfill that was closed and sealed nearly 20 a prior to sampling was recognized and traced to areas east of the LSC using low-level detection of tetrachloroethene (PCE), methyl chloride (MeCl), methyl chloroform (MC), dichlorodifluoromethane (CFC-12), and cis-1,2-dichloroethene (cis-1,2-DCE). Chloroform (CHLF) was the predominant VOC in water from domestic wells surrounding the LSC, and was elevated in groundwater in and near the Fish Health Laboratory at the LSC, where a leak of chlorinated water occurred prior to 2006. The low-level concentrations of halogenated VOCs did not exceed human or aquatic-life health criteria, and were useful in providing an awareness of the intrinsic susceptibility of the fractured karstic groundwater system at the LSC to non-atmospheric anthropogenic inputs. The ³H/³He groundwater ages of spring discharge from the carbonate rocks showed transient behavior, with ages averaging about 2 a in 2004 following a wet climatic period (2003–2004), and ages in the range of 4–7 a in periods of more average precipitation (2008–2009). The SF₆ and CFC-12 data indicate older water (model ages of 10s of years or more) in the low-permeability shale of the Martinsburg Formation located to the west of the LSC. A two-a record of specific conductance, water temperature, and discharge recorded at 30-min intervals demonstrated an approximately 3-month lag in discharge at Gray Spring. The low groundwater ages of waters from the carbonate rocks support rapid advective transport of contaminants from the LSC vicinity, yet the nearly ubiquitous occurrence of low-level concentrations of halogenated VOCs at the LSC suggests the presence of long-term persistent sources, such as seepage from the closed and sealed landfill, infiltration of VOCs that may persist locally in the epikarst, exchange with low-permeability zones in fractured rock, and upward leakage of older water that may contain elevated concentrations of halogenated VOCs from earlier land use activities.     

Mineralogical and ash geochemical studies of coal-mine shale and its hydrocarbon potential: A case study of shale from Makum coalfield,Northeast India

The mineralogy and geochemical studies of the coal-mine shale collected from the Tirap opencast coal-mine (Makum coalfield, Northeast India) are reported in this paper. Thermo-chemical conversion (pyrolysis) of coal-mine shale has been studied to see its hydrocarbon potential. A combined approach using X-Ray diffraction (LTA-XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) equipped with an energy-dispersive X-ray spectrophotometer (EDS), X-ray fluorescence spectrometry (XRF), thermogravimetry-derivative and differential thermogravimetric (TG-DTG and DTA) analysis is made to obtain new information on the mineralogical and geochemical studies of a coal-mine shale (CMS) sample. Gas chromatography-mass spectrometry (GC-MS) analysis is performed to evaluate the quality of the liquid fraction (tar) obtained after pyrolysis at 600°C. The shale sample is dominated by quartz, clay minerals (kaolinite and illite), sulphate bearing phase like gypsum with minor proportion of anatase, probably as artifacts of the plasma-ashing process. GC-MS analysis illustrates the presence of highly oxygenated organic components (M.W. around 94-108) and high molecular weight (M.W. 256) cyclic sulphur (e.g. octathiocane with molecular formula S₈) compounds along with the complex N-containing organic sulphur compounds (M.W. around 255-486) in the tar produced.     

Landslide characterization using active and passive seismic imaging techniques: a case study from Kerala,India

The unusually intense precipitations of the 2018 monsoon triggered numerous landslides in the Western Ghats region, southwest of India. Although the landslides caused no casualties, significant damage to property and infrastructure was observed. We present, as a case study, the results of active and passive seismic prospecting at two of those landslides with the goal of characterizing them, in a first application of shallow seismic exploration to landslides in the region. Our deployments included both sites perturbed by the landslides and unperturbed slopes adjacent to them with the purpose of identifying possible structural differences between slopes that underwent landsliding from slopes that were not affected. We analyze seismic sections obtained using the multi-channel analysis of surface waves technique and compare the results with seismic noise analyzed using seismic interferometry. We show that different analyses give similar results. The lateral variations observed in the shear-wave velocity distribution below the different profiles are well correlated with dominant frequency determined from seismic noise horizontal-to-vertical spectral ratios. Our measurements were taken after the landslides occurred. In hindsight, our results suggest that soil thickness played a major role in the triggering of landslides.

     

Estimating impacts of recurring flooding on roadway networks: a Norfolk,Virginia case study

Predicting tropical cyclone (TCs) tracks is a primary concern in TC forecasting. Some TCs appear to move in a direction favorable for their development, beyond the influence of the steering flow. Thus, we hypothesize that TCs move toward regions with high water-vapor content in the lower atmosphere. In this study, four numerical experiments, including a control experiment and three sensitivity experiments, were performed using the Weather Research and Forecasting Model, to analyze the relationship between water vapor distribution and the track of Severe Typhoon Hato (2017). Observations validated the features reproduced in the control experiment. The sensitivity experiments were conducted to explore variations in the TC track under different water vapor environments. Results indicate that the horizontal distribution of water-vapor content exerted a greater impact on the TC track than the steering flow when both factors were significant. Further analysis revealed that the TC’s movement vector was between the direction of the steering flow and the direction toward the peak of vorticity increasing area. The peaks of vorticity increasing area were close to the peaks of water vapor increasing area, which also proved the effect of water vapor distribution on the TC track. These results are expected to improve TC track analysis and forecasting.

     

Applications of particle-tracking techniques to bank infiltration: a case study from El Paso,Texas, USA

This paper presents results of a small scale study that utilized particle-tracking techniques to evaluate transport of river water through an alluvial aquifer in a bank infiltration testing site in El Paso, Texas, USA. The particle-tracking survey was used to better define filtration parameters. Several simulations were generated to allow visualization of the effects of well placement and pumping rate on flow paths, travel time, the size of the pumping influence zone, and proportion of river-derived water and groundwater mixing in the pumping well. Simulations indicate that migration of river water into the aquifer is generally slow. Most water does not arrive at the well by the end of an 18-day pumping period at 0.54 m³/min pumping rate for a well located 18 m from the river. Forty-four percent of the water pumped from the well was river water. The models provided important information needed to design appropriate sampling schedules for bank filtration practices and ensured meeting adequate soil-retention times. The pumping rate has more effect on river water travel time than the location of the pumping well from the river. The examples presented in this paper indicate that operating the pumping well at a doubled distance from the river increased the time required for the water to travel to the well, but did not greatly change the capture zone.     

基于湖积物硅藻与地球化学记录的古环境变迁反演——以桂林会仙岩溶湿地为例

通过对狮子潭柱状沉积物的放射性定年、地球化学与硅藻分析,反演桂林会仙岩溶湿地全新世的古湖沼演替,与其响应的气候变迁与人类活动记录。放射性210Pb、14C定年结果显示该湖在6 400 cal BP开始有湖积物保存,在2 700 cal BP-公元1943年间有沉积间断事件,且于公元1943年再度沉积。在6 400-5 200 cal BP,高比例的浮游型硅藻反映高水位状态,可对应到气候暖湿的中国全新世大暖期鼎盛期。在5 200-2 700 cal BP,沉积物内稀酸可溶相Ca、Mg、Sr 浓度降低,Mg/Ca、Sr/Ca值明显增加,且浮游型硅藻几乎消失,显示当时湖泊水位显著降低,气候逐渐变干。在公元1943年沉积物再度沉积,可能与战争造成人口迁徙与废耕有关。自公元1973年以来,硅藻壳片大量堆积,反映人类过度活动造成藻华的现象。湖泊沉积物内硅藻组成及沉积物的地球化学特征能够很好地反演古气候、环境变迁。