Search

Hydrogeochemical processes occurring in contaminated groundwater and aquifer systems may reduce the sensitivity of boron isotopes as an indicator of hydraulic fracturing flowback fluids (HFFF) in groundwater. In this paper, based on the Chaiye-1 well (the first continental shale gas well in the northern Qaidam Basin), the hydrogeochemical processes affecting boron isotopes were analyzed in HFFF-contaminated Neogene (NG1 and NG2) and Quaternary (QG1) groundwater around the shale gas field. Then, a model for boron isotopes in HFFF-contaminated groundwater was constructed to assess the sensitivity of boron isotopes as an HFFF indicator. The results show that, limited by the range of pH values and saturation indices (SI) in HFFF-contaminated groundwater, the dissolution of alkali feldspar and precipitation of carbonate have little effect on the boron isotopes in shallow groundwater. For the NG2 aquifer system containing clay minerals, the δ11B of simulated contaminated groundwater (40.0–55.6‰) is always higher than that of the corresponding groundwater mixed conservatively (−6.4–55.6‰) due to preferential adsorption of boron isotopes onto clay minerals, indicating preferential adsorption would reduce the sensitivity of boron isotopes as an indicator of groundwater contamination from HFFF. For the scenario of HFFF contamination, when the mixing ratio of HFFF in contaminated groundwater increases by 5%, boron isotopes in Neogene (NG1 and NG2) and Quaternary (QG1) groundwater have detectable responses to HFFF contamination, suggesting δ11B is a sensitive indicator of HFFF contamination in shallow groundwater from the Dameigou Shale in the northern Qaidam Basin.

Groundwater quality in the Muling–Xingkai Plain (MXP) is closely related to food security and human health. The chemical composition of groundwater in MXP has attracted great attention. A total of 168 groundwater samples were collected in MXP, and principal component analysis, chemical ion analysis and stable isotopic analysis were used to explore key factors affecting the chemical composition and hydrochemical evolution process of groundwater. Results show sources of chemical ions in groundwater are silicate minerals, carbonate minerals and domestic sewage. Domestic sewage is responsible for groundwater with high levels of Cl−, SO42− and NO3−, but a reduction environment can lead to groundwater with a high level of NH4+ due to nitrification. Human activity and soil media together influence groundwater chemical composition. Groundwater with a high level of chemical ions is mainly collected from wells near river channels, where coarse-textured soils are overlying aquifers. The black soil far away from river channels can retard the infiltration of wastewater. Agricultural activities do not directly lead to deterioration of groundwater qualities, and agricultural non-point-source pollution does not occur in MXP. Nearly 70% of the population in MXP is living in the southern plain, where the influence of sewage on groundwater chemical composition is obvious. Thus, shallow groundwater far away from river channels is the best choice for irrigation. Some measures should be implemented to control the discharge of domestic sewage for the protection of groundwater. In addition, it is necessary to avoid the transformation of the redox environment of groundwater in the northern plain.

The deterioration of water quality in shallow groundwater systems over the past decades has attracted increased amounts of attention from hydrogeologists. Groundwater vulnerability and its changes are the factors that cause groundwater deterioration. Combining of the mean residence times (MRTs) with chemical characteristics of groundwater can be applied to understand groundwater vulnerability and its changes. The groundwater MRTs ranged from 6 to 180 years, with MRTs of 6 to 77 years in the shallow aquifer. Spatial distribution of groundwater MRTs suggested that young groundwater trended to extend. Relatively uniform MRTs and concentrations of ions were found above the main pumped well depth. High concentrations of ions (K+, Na+, Ca2+, Mg2+, HCO3−, Cl- and SO42-) were mainly distributed in the western piedmont plain areas with short turnover time but with low productivity, meaning that the aquifer is susceptible to human activities and hardly migrate out. Elevated concentrations of nitrate and others ions (such as K+, Ca2+, Cl- and SO42-) also were observed in moderately old groundwater (20

The source characterization of nitrate (NO3−) in groundwater of Muling-Xingkai Plain (MXP) and the influence of NO3− on the water environment were studied by hydrogeochemical and multivariate statistical analysis. A total of 164 groundwater samples were collected, and the samples were classified into three clusters by using hierarchical cluster analysis. Cluster 1 (C1), accounting for 13% of total samples, was mainly located in local residential zones where the top soils were the medium-textured sediments. Cluster 2 (C2) and cluster 3 (C3) were mainly located in farmlands and residential zones where the clay sediments were overlaying the aquifers. The soil media covering the aquifers was an important factor controlling the concentration of NO3− in groundwater, which determined the infiltration rate of wastewater and the redox environment of aquifers. Only the samples in C1 exceeded the WTO standards for NO3− (50 mg/L), and the samples in C2 and C3 had low NO3− concentration (less than 10 mg/L). The excessive NO3− in groundwater was observed in the shallow groundwater under local residential zones, and it was closely related to the anthropogenic activities since the 1950s. The domestic sewage was responsible for the elevated NO3− contents in the MXP. Then, it was still necessary to construct the sewage disposal system in rural areas to further protect the groundwater resource to avoid the formation of extensive nitrogen pollution. At present, NO3− in the groundwater mainly shows a fertilizer and natural rainwater origin and is not demonstrating the significant deterioration of groundwater qualities and water environment.

Water-rock interactions occurring during fracturing and flowback in shale gas reservoirs may dominate some chemical and isotopic compositions of hydraulic fracturing flowback fluids (HFFF) by imparting characteristic compositions of the continental shale to the HFFF. In this paper, a simple conservative mixing model (SCMM) and a progressive conservative mixing model (PCMM) were developed to evaluate and understand the impacts of geochemical processes on forensic indicators (δ11B, 87Sr/86Sr, and Ba/Sr) of HFFF produced from the Dameigou Shale. Application of the paired sample T-test showed that the measured values of δ11B, 87Sr/86Sr, Ba, and Sr in HFFF produced from the Dameigou Shale were all significantly (p 1.45) in HFFF. Therefore, 87Sr/86Sr and Ba/Sr show potential as indicators of continental HFFF produced from carbonate-poor shales and provide a clear distinction from rapidly-circulating shallow groundwater mainly recharged by rainwater (87Sr/86Sr: 0.70903–0.70914 and Ba/Sr

The internal fixation using metal bone plate is one of common method for the clinical treatment of fracture, it plays a role in fixation, protection and supporting of the fractured bone segments, but it also suffers high failure rates in clinical practice. This article reviewed the commonly used methods of failure analysis of bone plate, and described the research results of the failure analysis of bone plate in detail. The fatigue fracture of bone plate caused by stress concentration is the common fracture pattern. In addition, the article summarized the performance optimizations according to the cause of failure, then discussed its future development trends.

Most of the shale gas production in northwest China is from continental shale. Identifying hydrogeochemical and isotopic indicators of toxic hydraulic fracturing flowback fluids (HFFF) has great significance in assessing the safety of drinking water from shallow groundwater and streamwater. Hydrogeochemical and isotopic data for HFFF from the Dameigou shale formations (Cl/Br ratio (1.81 × 10–4–6.52 × 10–4), Ba/Sr (>0.2), δ11B (−10–1‰), and eSWSr (56–65, where eSWSr is the deviation of the 87Sr/86Sr ratio from that of seawater in parts per 104)) were distinct from data for the background saline shallow groundwater and streamwater before fracturing. Mixing models indicated that inorganic elemental signatures (Br/Cl, Ba/Sr) and isotopic fingerprints (δ11B, eSWSr) can be used to distinguish between HFFF and conventional oil-field brine in shallow groundwater and streamwater. These diagnostic indicators were applied to identify potential releases of HFFF into shallow groundwater and streamwater during fracturi...

Responses of hydrochemical parameters, bacterial community structures, and microbial activities during the natural biodegradation of hydrocarbons leaking from a crude oil pipeline at a site in northeastern China were studied using the hydrochemical method, the polymerase chain reaction amplification of 16S rDNA genes, and denaturing gradient gel electrophoresis (DGGE).The concentrations of PHs and the main physicochemical characteristics (Eh and pH) were increased gradually at longitudinal ZK1–ZK3–ZK6 section in June 2010, suggesting that the degree of biodegradation decreased gradually from the pollutant source to downstream. The electron acceptor (SO42−) participated in biodegradation process responds identical trend to the degree of biodegradation at the same section while the biodegradation reduction products (Fe2+, Mn2+, and HCO3 −) respond to it in opposite trend. The concentrations of Fe2+, Mn2+, and SO4 2− at wells ZK1 and ZK3 indicate that sulfate-reducing biodegradation was the dominant process experienced at contaminated sites rather than iron–manganese reduction processes. The dynamic changes of hydrochemical parameters suggest that the degree of biodegradation would be intensified at the center of pollutant plume and iron–manganese reduction processes experienced earlier than sulfate-reducing biodegradation. The community diversities and microbial activities in different soil depths were responded to PHs, but the relationship is not simply linear. The community diversities and microbial activities increased significantly with rise in PH concentration of soil until about 20 mg/kg and then peaked off sharply, suggesting that community succession would be occurred in microhabitat when the PH concentration in soil exceeds 20 mg/kg. The major DGGE bands found in the soil samples were sequenced. One sequence affiliated with γ-Proteobacteria showed high similarities to uncultured bacteria which had been found in offshore oil pollution environment. These bacterial species were found to have similar petroleum degradation functions to the bacteria at the sites studied here.

Traditional groundwater quality evaluation methods often need to set the weight of evaluation factors, and the evaluation results were to a large extent influenced by the subjective factors and there would be a poor grade of evaluation result because of one factor that had a larger content. To solve above problems, the artificial neural network theory and ideology was introduced, and use the RBF neural network to construct the multi-layer feed-forward groundwater quality evaluation model. This model was used to evaluate the 25 deep confined groundwater samples' water quality in Changchun region. According to the water quality characteristic of Changchun region and the demand of drinking water supply, choose 10 evaluation factors. The evaluation results showed that groundwater quality in Changchun region were more than Grade III, With GIS data fusion to analyze and express the spatial distribution information on water quality, from the distribution information, we can get that the ratio of the distribution area of Grade I, Grade II, Grade III water quality in Changchun City to the whole area are 6%, 72%, 22% respectively.