美国页岩气开发的水污染风险成因、争议及对中国的启示

国内一些文献在讨论美国页岩气开发环境影响问题时,选择了这样的预设立场,即认为页岩气开发的环境危害显著高于常规油气开发。事实上,无论在美国的研究领域还是在实践层面,对这个问题的认识都充满了争议,争议的源头和焦点是页岩气开发的潜在水污染风险。为了客观认识页岩气开发过程中的水污染风险问题,本文从污染成因入手,聚焦争议的关键点和产生来源,并在梳理各方观点和证据的基础上得出几点认识:①关于地表泄露,并没有证据表明与水力压裂相关的泄露对水环境的负面影响程度高于其他作业环节,也不能判定页岩气开发的水污染风险高于常规油气;②关于地下泄露,目前能够认定甲烷气是潜在的地下污染源,产生的原因是完井缺陷和特殊地质条件,而源自压裂液和深层含盐地层水的污染尚未得到证实;③尽管来自液体污染物的地下水污染尚未在页岩气采区得到证实,但当地下水层和压裂作业层距离过近时,存在水污染的可能。在中国页岩气开发环境影响防治过程中,除了要借鉴美国经验,还要注意到两国之间的差异,这些差异有可能让相似根源的问题产生相异的结果。建议考虑以下几方面差异:首先,要认识到规制强度的差异,上述认识是在美国各州普遍进行严格监管的条件下得到的,如果监管放松,页岩气开发对环境的不利影响确实高于常规(非水力压裂)油气开发;其次,要重视中国特殊地质条件可能引发的新问题,如天然裂缝滑动导致生产套管变形甚至破裂、地下溶洞发育等会增大地下水污染的风险;最后,与美国不同,中国页岩气井场多位于丘陵或山地,还有一些气田临近人口稠密的村镇,这些将增加地表泄露风险和泄露发生后的补救难度。

傍河水源地地下水污染风险评价

评价傍河水源地地下水污染风险。以傍河水源地地下水为研究对象,以河流为风险源、傍河区水源地地下水为风险受体,构建以河流风险性H、地下水脆弱性V、地下水水质容量指数C、水源地价值W为评价指标的傍河水源地地下水污染风险评价模型,并将该模型应用到榆次区西窑水源地地下水污染风险评价中。结果表明:西窑水源地地下水污染风险等级为"中",西窑水源地地下水越流补给和侧向补给强烈,评价结果符合实际。研究成果可为傍河水源地地下水污染风险评价提供依据。

长江上游宜宾至泸州江段突发水污染风险评估

为防控长江上游重大突发水污染事件的发生,收集整理长江宜宾至泸州江段沿江水环境污染源及受体基础资料,构建水环境潜在污染风险分级评价体系。采用地统计学理论和地理信息系统(Geographic Information System,GIS)相结合的方法开展突发水污染风险分区评价研究,以揭示研究区江段突发水污染风险空间分布差异性。结果表明,污染源或受体热点分布主要集中在城镇化、工业化较快的地区,如宜宾市叙州区污染源最多,泸州市龙马潭区高风险污染源最密集,宜宾县和南溪县高敏感受体数量最多;其他区域污染源或受体分布较为均衡,未形成明显的冷点区域。水环境潜在污染高风险区集中分布在龙马潭区江段和江阳区江段,须提高该区域对潜在污染的风险管理能力,以降低污染事故发生的可能性。

基于熵权模糊综合模型的水污染风险评价——以鄱阳湖流域为例

为科学评价流域水污染风险,结合压力-状态-响应模型(PSR模型)从社会经济、污染源危险性、水资源质量、生态环境脆弱性和水污染防控5个角度建立了包含21个指标的流域水污染风险评价指标体系,并将风险划分为4个等级,采用熵权法确定客观权重,最后利用模糊综合评价模型对2012~2018年鄱阳湖流域水污染风险开展综合评价。结果表明:2012~2016年鄱阳湖流域水污染风险表现为中度风险,2017~2018年转为轻度风险,风险等级整体呈现逐年降低的趋势,与实际情况相符。其中氨氮排放总量、水功能区水质达标率和湖泊Ⅲ类以上水质比例这几个指标对鄱阳湖流域水污染风险的影响较大,因此相关部门需要重点在这些方面做出积极响应。研究成果对于鄱阳湖流域水污染治理和水资源可持续利用有一定借鉴作用。

基于熵权的TOPSIS模型在水污染风险评价中的应用

水污染风险评价是实现水资源可持续利用的重要依据,随着人们对水环境危险的认识,水污染问题逐渐引起了专家的重视。文章以大伙房浑河流域抚顺段为研究对象,根据已有文献提供的数据资料,选取6个指标,利用熵权法确定指标的权重,并应用TOPSIS模型对1996—2004年间的水质情况进行评价。结果表明:1997年的水质相对最好,2004年的水质情况相对最不好。

突发性跨界水污染事故环境风险源数据管理系统的建立

为了全面、准确、真实地展现跨界区域水污染事故环境风险源的分布和现状,并识别突发性跨界水污染事故风险源的风险等级,本文结合地理信息空间数据库技术,在数据管理系统功能框架与总体设计技术路线的指导下,建立了该风险源数据管理系统。结果显示,集合了Oracle属性数据库、ArcGIS空间数据库和识别指标模型的数据管理系统,实现了对跨界水污染事故风险源信息的可视化表征,并能对识别体系、对数据的需求进行及时响应,为风险源识别提供数据基础。

黄河呼和浩特段水体污染风险评估及其发生特性

通过建立风险评估模型、风险分级级别,对2011—2013年黄河呼和浩特段不同断面、时间和指标的水质数据进行时空分布上的水体污染风险分析。结果表明:水污染风险时空分布不具有相关性,但有较强的局地性、偶发性、变化性;常规指标、金属指标、有机化合物指标、阴离子及盐类指标在时间、空间上的水污染风险值分别为5.71~7.28、1.94~17.58,1.37~1.60、0.21~1.72,1.30~0.87、0.68~3.18,1.18~1.44、0.68~0.86;浑津桥、小入黄口断面处的污水排放致使常规指标在主干流、各支流均处于高风险状态,但其他3类指标均处低风险水平及以下,且整体上各支流风险程度高于主干流。如若无重大污染事件发生,则各项指标风险值较低且稳定,也无水污染风险事件引发的趋势。

渭河干流陕西段河流水质污染风险评价

依据模糊理论建立了河流水质风险评价模型,通过加权评价和熵值法确定了多个监测序列指标权重,给出了5级水质污染风险等级,评价了渭河干流陕西段污染物序列风险以及区间水质污染风险。结果表明:渭河主干河流中下游水质污染风险较大,上游风险相对较轻。这些研究为河流水质控制与恢复管理提供了依据。

山西省煤矿区域水源污染风险定性分析

从山西煤矿区域的基本状况、煤炭特点、采掘方式及功能区划和水源历史污染事故等方面,对全省煤矿区域的水污染风险进行了定性分析,提出了预防措施。

基于GMS的北京市朝阳区地下水环境数值模拟与预测分析

为研究北京市朝阳区地下水压采过程中硝酸盐污染发展趋势,基于近年来地下水观测资料及钻孔资料,利用地下水数值模拟软件GMS,建立地下水水流和溶质运移耦合模型,对研究区地下水硝酸盐的迁移扩散进行了数值模拟,并分别预测了5 a后在丰水年、平水年和枯水年三种情景下硝酸盐的分布状况和浓度变化趋势。研究表明:地下水压采过程中,研究区地下水位基本呈逐年上升的趋势,平水年地下水漏斗中心水位上升2.0~2.5 m,地下水呈西南向东北流向。硝酸盐污染羽的扩散方向与地下水流动方向较为一致,污染中心北侧污染羽向东北方向扩散,且丰水年扩散距离最远。整个区域内Ⅰ、Ⅱ类水质面积逐渐减小。污染较严重的西南地区硝酸盐浓度有所降低,且浓度梯度减小。研究区地下水流与溶质运移两者之间有着密切的联系,应加强对地下水资源的科学调度,防止地下水环境的进一步恶化。

Soil heavy metal(loid)s and risk assessment in vicinity of a coal mining area from southwest Guizhou, China

Total concentrations of arsenic, lead, cadmium, mercury, nickel, chromium, and copper in the soils from near a coal mine area in southwest Guizhou, China, were measured to evaluate the level of contamination, and the potential ecological risks posed by the heavy metals were quantitatively estimated. Results reveal that all heavy metals/metalloid exceeded the background values for soil environmental quality of heavy metals in Guizhou area. Geo-accumulation index(I_(geo)) showed that arsenic had the highest contamination level(I_(geo)=4) among the seven heavy metals/metalloid, and the contamination levels of mercury and lead were also relatively high(I_(geo)=3). Pearson correlation and cluster analysis identified that mercury, copper and arsenic had a relationship, and their presence might be mainly related to mining activity, coal and oil combustion, and vehicle emissions. Improved Nemerow index indicated that the overall level of heavy metal contamination in the studied area ranged from moderately–heavily contaminated to heavily contaminated level. Potential ecological risk index(R_I) analysis manifested that the whole ecological risk level ranged from high degree to very high degree(325.30≤R_I≤801.02) in the studied soil samples, and the potential ecological risk factors (E_r^i) of heavy metals/metalloid were as follows: Hg > As > Cd > Pb > Cu > Ni > Cr, and the E_r^i of Hg and As reached very high risk grade.

Risk-based water quality decision-making under small data using Bayesian network

A knowledge-based network for Section Yidong Bridge,Dongyang River,one tributary of Qiantang River,Zhejiang Province,China,is established in order to model water quality in areas under small data.Then,based on normal transformation of variables with routine monitoring data and normal assumption of variables without routine monitoring data,a conditional linear Gaussian Bayesian network is constructed.A "two-constraint selection" procedure is proposed to estimate potential parameter values under small data.Among all potential parameter values,the ones that are most probable are selected as the "representatives".Finally,the risks of pollutant concentration exceeding national water quality standards are calculated and pollution reduction decisions for decision-making reference are proposed.The final results show that conditional linear Gaussian Bayesian network and "two-constraint selection" procedure are very useful in evaluating risks when there is limited data and can help managers to make sound decisions under small data.

Distribution and pollution assessment of trace metals in seawater and sediment in Laizhou Bay

Selected trace metals （Pb, Cd, Cu, Hg） and arsenic in seawater and surface sediments of Laizhou Bay were determined, to evaluate their spatial distribution, pollution risk and potential ecological risk. Concentrations of the elements were 0.56-2.07, 0.14-0.38, 12.70-18.40, 0.014-0.094, and 1.13- 2.37 μg/L in the seawater and 8.94-32.2, 0.18-0.67, 4.51-30.5, 0.006-0.058, and 5.75-15.3 mg/kg in sediments for Pb, Cd, Cu, Hg and As, respectively. High concentrations of the trace metals and arsenic in seawater and surface sediments were generally observed near the fiver estuary. The pollution risk result of the elements showed that Cu was the prominent trace metal pollutant in seawater, followed by Hg, Pb, Cd and As. The metal complex pollution index in seawater was at a medium level. The most important trace metal pollutant in sediments was Cd, followed by As, Cu, Pb, and Hg. Our pollution assessment suggests that trace metal pollution in Laizhou Bay sediments was at a low level. The potential ecological risk was also low in surface sediment.

Chemical Contamination and Radiological Risk Assessment of Water Sources in Richards Bay

South Africa is pronounced a dry country. Though KwaZulu-Natal has a higher rain fall than most part of the country, it has recorded cases of austere droughts. The present study was aimed at examining the quality of water within Richards Bay precinct in relation to South African target water quality range （TWQR）. Fifty water samples were collected from five water sources （effluent, stream, Mzingazi River, Indian Ocean and Esikawini drinking tap water） and analyzed using ICP-MS technique to determine the concentrations of some traced metals i.e., Fe, Cu, T1, Zn, Pb, Cr, and Ni. The main impurities were found to be Cd, Mn and As with concentrations of 2.21 × 10^0mg. l-1, 7.19 × 10-1mg.l-1and 2.72 ×10-3mg. 1-1 respectively. The surface gross alpha contamination of mineral stores within the facilities ranges from 1.00 × 10-4 ± 1.5 × 10-2 Bq.cm-2 to 1.45× 10-2 ±4.20 ×10-3Bq.cm-2 with a mean concentration of 1.15 × 10-2 ±1.36 ×10-2Bq.cm-2while the gross beta contamination ranges from 1.00 ×10-3 ± 1.14 × 10-ZBq, cm-2 to 4.15 × 10-2 ± 2.17 × 10-2Bq. cm-2 with a mean concentration of 2.15 ×10-2 ±1.80×10-2Bq. cm-2. The result indicated that the water quality was acceptable.

Risk of Getting Nosocomial Water-Borne Infections from the Main Water Systems in Hospitals

Drinking water may be a risk factor for human infections if the water supply is contaminated with biofilm producing bacteria such as Legionella pneumophilae or Pseudomonas aeruginosa. Several situations have to be considered when water supply to new buildings is planned. The aim of this paper is to review situations that have to be considered in new buildings and give an example on a new water supply contaminated with biofilm producing water bacteria and the precautions introduced to eliminate the contamination. When new buildings are planned it should be considered where to get the water and what is the microbiological quality of the water. If the water is contaminated there will be troubles from the beginning. The material for the pipes should be considered as biofilm which is produced in greater amounts and faster in PEG pipes than in stainless steel pipes. The choice of material depends on the expected lifetime of the building, the dimensions of the pipes, and the choice of forceps, how often the taps are used and thereby the flow in the system. The higher flow the less and slower biofilm formation. It is important to reduce the number of taps to a minimum to ovoid ＂dead ends＂ if they are not or only seldom used. Alternatively all taps could be opened automatically regularly. It is important to establish precautions to ovoid contamination of the water system in the period from when it is established until the building is taken in use. The period can be several months during which the system can act as a ＂dead end＂ if no precautions, such as regularly opening of all taps, are taken. The microbiological quality of the water in the system should be controlled before the building is taken in use. In a new building, where the water supply and the water in the building was not controlled before the building was taken in use, extremely high total and Legionella germ counts were found. The water was disinfected with low concentrations of chloride with very little effect. After disinfection with high concentrations of chloride for few hours and placing a sterile filter at the water entrance both the total and Legionella germ count decreased to an acceptable level.

Health Risks Assessment Due to Exposure to Vinyl Chloride in Groundwater from a Closed Landfill： A Case Study as a Contaminant of Concern and Effect of Subsurface Characteristics

The purpose of this study was to analyze the migration pathways of contaminants from closed landfills and to estimate health risks based on soil characteristics. The health risks were estimated using Framework for Risk Analysis Multimedia Environmental Systems （FRAMES） software. The sensitivity of human health risks and hazard indices due to vinyl chloride contamination in groundwater were performed in relation to soil characteristics such as Darcy velocity, thickness of soil layer, mass of contaminant present in the aquifer. Based on the analysis, Darcy velocity showed no effect on estimated risks. Since soil layer thickness had a significant effect on the estimated health risks, effects of different soil types on estimated risks were analyzed. The results showed that soils from the least appropriate to the most appropriate for risk management due to groundwater contamination were sand, sandy clay, sandy loam, loam and clay loam. FRAMES model was suitable for assessing the health risks due to vinyl chloride contamination in groundwater originating from a municipal solid waste landfill. The model showed the changes in both carcinogenic and non carcinogenic risks over time. The estimated health risks were directly correlated with the levels of vinyl chloride detected in groundwater.

Evaluation and Hotspots Identification of Shallow Groundwater Contamination Risk in the Lower Reaches of the Liaohe River Plain

As a prerequisite for groundwater protection and contamination control, evaluation of groundwater con- tamination risk was the extension of groundwater vulnerability assessment. Based on disaster theory and using shallow groundwater of the lower reaches of Liaohe River Plain as the study area, we built an evaluation index system and a contamination index model for groundwater contamination risks from the perspectives of intrinsic vulnerability, external stresses, and functional value. We used data acquisition technology （remote sensing） and spatial analysis technology （GIS） to calculate the value of groundwater contamination risks. The spatial distribution of hotspots was obtained by calculating G index. Results show that groundwater contamination is above a mid-level risk in most of the study area. Areas with extreme high risk account for 37.86%, areas with high risk 32.47%, areas with moderate risk 12.07%, areas with light risk 3.17%, and areas with slight risk 14.43%. Hotspots areas are mainly located in central Shenyang City, northwest of Xinmin City, Beizhen City and Liaozhong County. Coldspots are mainly in Panjin City, Yingkou City, Dashiqiao City, Dawa County and Panshan County. The results reflect the spatial distribution and mechanism of groundwater contamination risk in the study area and provide relative references for land use planning and groundwater resource protection in the lower reaches of the Liaohe River Plain.