Chemical evolution of acid precipitation in the unsaturated zone of the Pennsylvanian siltstones and shale of central Ohio

The North Appalachian Experimental Watershed in Coshocton, Ohio, USA has recorded average pH of precipitation of 4.7 over a 30-year period. The area lies within the Pennsylvanian siltstones and shale, dominated by aluminosilicates and <5% calcite. A study was conducted to determine the evolution of acid deposition through an unsaturated to saturated zone composed of siltstone and shale in an isolated hill, precluding lateral flow and seepage. The results from water–rock chemical reactions modeled using PHREEQM demonstrate the percolating precipitation water is neutralized to pH 7.5 within the top 1.5 m. The model suggests that, along with calcite, dissolution of albite, illite, and kaolinite are the dominant mechanisms of neutralization. The cation exchange capacity of the siltstone and shale, in the range 54.6–386 meq/100 g, appears to be a function of high organic carbon content of 2.0–3.2%. While cation exchange is responsible for some of the Na⁺ in solution, it is not the primary source of Ca²⁺, Mg²⁺, or K⁺ ions. Exchange onto clays is occurring, but is secondary to exchange on organic matter. Chemical composition of groundwater perched within a coal seam is controlled by oxidation and dissolution of pyrite, returning pH to approximately 4.0.     

Hydrochemical characteristics and pollution potential of Uluova aquifers,Elazığ, Turkey

The study area is in the southeastern part of the city of Elaz between 38°17–38°43 latitudes and 38°36–39°07 longitudes. Formations of Paleozoic, Mesozoic and Cenozoic age comprise confined and unconfined aquifers. Unconfined aquifers are represented by Na-Cl and Na-HCO₃ type waters while confined aquifers are characterized by Ca-HCO₃, Mg-HCO₃ and Na-HCO₃ type waters. Due to sodium pollution, as a result of irrigation from waters of Hazar lake in the plain, as well as intense use of artificial fertilizer and improper storage of animal fertilizers, NH₄-N, NO₃-N and total PO₄-P pollution are detected in waters of the unconfined aquifer. Organic material contents in waters of well nos. S₂₇, S₂₉ and S₃₂ completed in the unconfined aquifer are above 3.5 mg/l of Turkish Standard Institute (TSE), (266) standard. In confined aquifers, total PO₄-P pollution in four wells and NH₄-N pollution in three wells were observed to be above the TSE (266) standard.     

Assessment of water quality and pollution of the Lake Seyfe basin, Kırşehir, Turkey

Lake Seyfe is located in a closed basin near K?r?ehir in the central Anatolian region, Turkey. The aim of this study is to evaluate the groundwater quality and effects of lithogenic contamination carried out in the Lake Seyfe basin, which is represented by various lithologies and groundwater types. Seyfe, Horla and Akp?nar springs are recharged through marbles at the western and southwestern of the basin are ultimately and discharged into the K?z?l?rmak Formation and Lake Seyfe. The waters of deep wells drilled into the marbles are of bicarbonate type (type I) in the Ca²⁺–Mg²⁺–HCO₃ ^? and Ca²⁺–HCO₃ ^? facies. Özlühüyük spring and waters from most of trenches and shallow wells, which are fed by the K?z?l?rmak Formation, have a mixed (type II) composition in the Ca²⁺–Mg²⁺–HCO₃ ^?–Cl^? facies. Groundwater in the alluvium and K?z?l?rmak Formation along Lake Seyfe has a salty (type III) character in the Na⁺–Cl^? facies. The main reasons of formation and change of the groundwater salinity and hydrochemical facies in the Seyfe basin are causing the various (a) lithogenic pollution and heterogeneity of the K?z?l?rmak Formation, (b) salinity of the upper soil zones, and (c) evaporation of the trench and channel waters open to the atmosphere. Considering parameters such as sodium hazard, specific conductivity, bicarbonate and carbonate hazards, waters in the study area are generally suitable for agricultural usage.     

High-resolution study on the hydrochemical variations caused by the dilution of precipitation in the epikarst spring: an example spring of Landiantang at Nongla,Mashan, China

In addition to rainfall, high-resolution measurements of water level, pH, specific conductivity and temperature of Landiantang epikarst spring at Nongla, Mashan county in Guangxi Province, China were recorded in summer rainy season by using a data logger with time interval of fifteen minutes. Water from the spring issues along a karst conduit. During the rainstorms in summer, it was found that the pH and temperature of Landiantang spring increased while its specific conductivity decreased. As HCO₃ ⁻, Ca²⁺ and Mg²⁺ are the dominant ions, linear relationships between concentrations of those ions and specific conductivity were developed. According to the ion concentrations from the linear relationships, the saturation indexes of calcite (SI_C), the saturation indexes of dolomite (SI_D) and CO₂ partial pressure (Log ) of the spring were calculated. Results indicated that the Log of the spring during the rainstorms was lower than that without rain, and its SI_C and SI_D was also lower. Combined with the characteristics of the epikarst zone, it was inferred that the above results were caused by the dilution of rainwater, because overland flow with high pH (due to neutralization of carbonate rock dusts in the air to rainwater) and low specific conductivity traveling through the conduit rapidly during rainstorms, showed greater influences on the hydrochemical variations of the epikarst spring.     

The topology of geology 1: Topological analysis

Topology has been used to characterise and quantify the properties of complex systems in a diverse range of scientific domains. This study explores the concept and applications of topological analysis in geology. We have developed an automatic system for extracting first order 2D topological information from geological maps, and 3D topological information from models built with the Noddy kinematic modelling system, and equivalent analyses should be possible for other implicit modelling systems. A method is presented for describing the spatial and temporal topology of geological models using a set of adjacency relationships that can be expressed as a topology network, thematic adjacency matrix or hive diagram. We define three types of spatial topology (cellular, structural and lithological) that allow us to analyse different aspects of the geology, and then apply them to investigate the geology of the Hamersley Basin, Western Australia.     

Tight oil play characterisation: the lower–middle Permian Lucaogou Formation in the Jimusar Sag,Junggar Basin,Northwest China

The lower–middle Permian Lucaogou (P₂l) Formation is a “sandwich-type’’ combination of source rocks and reservoirs that is considered to be a potential tight oil reservoir in the Jimusar Sag (JS). We investigated the P₂l Formation using a designated workflow to assess its potential as a viable tight oil reservoir play using geological, petrographical, petrophysical, and geochemical characterisation of core samples. The results showed that the P₂l source rocks have a widespread distribution (up to 1500 km²), a huge thickness (up to 160 m), a relatively high abundance of organic matter (averaging 3.12 wt%), a good sapropelic quality, and a moderate thermal maturity. The reservoir consists mainly of dolomites and siltstones, predominantly characterised by secondary dissolved pores, with medium–high porosity (averaging 9.1%) and relative low permeability (averaging 0.26 mD), high abundance of brittle minerals (averaging 87.1%), and low abundance of clay minerals (averaging 11.2%) with low water sensitivity. The results demonstrate that in the JS area the P₂l Formation has great potential for tight oil production with its considerable hydrocarbon expulsion quantities, good oil storage capability, and reservoir frackability potential and provide a basis for further evaluation of the tight oil potential of the P₂l Formation in the wider Junggar Basin and for identifying similar plays elsewhere.     

Impact of seasonal variations in hydrological stresses and spatial variations in geologic conditions on a TCE plume at an industrial complex in Wonju,Korea

Spatial and temporal variations in a trichloroethylene (TCE) plume at an industrial complex in Wonju, Korea, were examined based on hydrogeological data and seven rounds of groundwater quality data collected over a year. The site has considerable vertical heterogeneities; the top layer of soil is covered by impermeable paving material at several locations, followed by a series of reclaimed or residual soil layers, and with weathered rocks to the crystalline biotite granite at the bottom. Areal heterogeneity in the surface conditions plays an important role in controlling groundwater recharge. The heterogeneity structure is influenced by complex surface conditions paved with asphalt and concrete. Owing to the presence of limited recharge area and concentrated summer precipitation events, the effects of seasonal variations on groundwater hydraulics tend to diminish with distance from the recharge area. This result was established by analysing the influence of the contrasting surface recharge conditions between the near‐source zone and the far zone, and the seasonally concentrated precipitation on the transport patterns of a TCE plume. In addition, variations in the plume's downstream contaminant flux levels were also analysed along a transect line near the source zone. The results show that the general tendency of the TCE plume contaminant concentration and mass discharges were reproducible if we account for seasonal recharge variations and the associated changes in the groundwater level. During recharge events, the TCE concentration variations appear to be influenced by leaching of the residual dense non‐aqueous‐phase liquid (DNAPL) TCE trapped in the unsaturated zone. This result shows that seasonal variations in contaminant plume near the source zone is inevitable at this site, and that these variations indicate the presence of residual DNAPL at or above the water table, at least in some isolated locations. Copyright © 2011 John Wiley & Sons, Ltd.     

Hydrothermal faunal assemblages and habitat characterisation at the Eiffel Tower edifice (Lucky Strike,Mid‐Atlantic Ridge)

The Eiffel Tower edifice is situated in the Lucky Strike hydrothermal vent field at a mean depth of 1690 m on the Mid‐Atlantic Ridge (MAR). At this 11‐m‐high hydrothermal structure, different faunal assemblages, varying in visibly dominant species (mussels and shrimp), in mussel size and in density of mussel coverage, were sampled biologically and chemically. Temperature and sulphide (∑S) were measured on the different types of mussel‐based assemblages and on a shrimp‐dominated assemblage. Temperature was used as a proxy for calculating total concentrations of CH₄. Based on the physico‐chemical measurements, two microhabitats were identified, corresponding to (i) a more variable habitat featuring the greatest fluctuations in environmental variables and (ii) a second, more stable, habitat. The highest temperature variability and the highest maximum recorded temperatures were found in the assemblages visibly inhabited by alvinocaridid shrimp and dense mussel beds of large Bathymodiolus azoricus, whereas the less variable habitats were inhabited by smaller‐sized mussels with increasing bare surface in between. Larger mussels appeared to consume more ∑S compared with smaller‐sized (<1 cm) individuals and thus had a greater influence on the local chemistry. In addition, the mussel size was shown to be significantly positively correlated to temperature and negatively to the richness of the associated macrofauna. The presence of microbial mats was not linked to specific environmental conditions, but had a negative effect on the presence and abundance of macro‐fauna, notably gastropods. Whereas some taxa or species are found in only one of the two microhabitats, others, such as polychaetes and Mirocaris shrimp, cross the different microhabitats. Temperature was proposed to be a more limiting factor in species distribution than ∑S.     

An interdisciplinary approach to reservoir characterisation; an example from the early to middle Eocene Kaimiro Formation,Taranaki Basin,New Zealand

The Kaimiro Formation is an early to middle Eocene, NE-SW trending reservoir fairway in Taranaki Basin, and comprises a range of coastal plain through to shallow marine facies. A time of regional transgression is observed across the Paleocene–Eocene transition, which is linked to a general global warming trend and to regional thermal relaxation-related subsidence in New Zealand. The earliest Eocene transgressive deposits pass upwards into a series of cyclically stacked packages, interpreted as 3rd and 4th order sequences. Maximum regression occurred within the early Eocene and was followed by punctuated retrogradational stacking patterns associated with shoreline retreat and subsequent regional transgression in the middle Eocene.The Kaimiro Formation is considered a good reservoir target along most of the reservoir fairway, which can largely be attributed to a consistently quartz-rich, lithic-poor composition and reasonably coarse sand grain size. Correlations demonstrate that within the early Eocene the main reservoir facies are channel-fill sandstones overlying candidate sequence boundaries in paleoenvironmentally landward (proximal) settings, and upper shoreface/shoreline sandstones in relatively basinward (distal) settings. Middle Eocene reservoir facies are not represented in distal wells due to overall transgression at this time, yet they form a significant target in more proximal well locations, particularly on the Taranaki Peninsula.Depositional facies is one of the principal controls on sandstone reservoir quality. However, while reservoir facies have been proven along the length of the reservoir fairway, it is evident that diagenesis has significantly impacted sandstone quality. Relatively poor reservoir properties are predicted for deeply buried parts of the basin (maximum burial >4.5 km) due to severe compaction and relatively abundant authigenic quartz and illite. In contrast, good reservoir properties are locally represented in reservoir facies where present-day burial depths are <4 km due to less severe compaction, cementation and illitisation. Within these beds (<4 km) the presence of locally occurring authigenic grain-coating chlorite (shallow marine facies) and/or well-developed secondary porosity are both favourable to reservoir quality, while pervasive kaolinite and/or carbonate are both detrimental to reservoir quality.These results illustrate how an interdisciplinary approach to regional reservoir characterisation are used to help reduce risk during prospect evaluation. Assessment of both reservoir distribution and quality is necessary and can be undertaken through integrated studies of facies, sequence stratigraphy, burial modelling and petrography.     

The effect of graben structures on the migration of groundwater contaminants at an industrial site

Industrial sites present a challenge to the hydrogeological delineation of pollution sources and their impacts. When large-scale geologic structures such as grabens exist on such sites, these can have a significant impact on the hydrology and water quality distribution. At the site investigated, geophysical techniques, standard hydrogeological approaches and hydrochemical characterisation (with methods such as depth-profiling and isotopes) were used to determine the impact of a graben structure and the hydrogeological properties and consequent water quality distribution. Zones of high conductivity, corresponding with available data, were identified from the geophysical investigation and subsequent pumping tests in the area. Through hydrochemical characterisation, including isotopes, it was determined that the fault zone acts as a barrier for groundwater flow and is thus the reason for the lower levels of pollutants in groundwater beyond this feature. However, the surface water flow is not restricted by these zones, and contributes significantly to the flow and salt loads at the discharge point. The study showed that graben structures are important controls on the movement of contaminants, and that the effect of such geological features on groundwater quality distribution must be investigated using multiple methodologies to construct a feasible conceptual model of the interactions.