An investigation into contaminant transport processes through single-phase cement–bentonite slurry walls

Cement–bentonite walls are commonly used for remediation by containment or pollution prevention, in addition to their use as a barrier to water flow in more conventional construction. The results from an investigation of an in situ single-phase cement–bentonite slurry wall are detailed, with particular attention paid to the role of advective and diffusive fluxes in contaminant transport.

The wall under investigation was installed, using standard methods and with a normal mix design, in August 1995 in order to contain leachates arising from ‘piggy-backing’ of an existing ‘dilute and disperse’ landfill site. In September 1998, the wall was investigated during which the top of the wall was exposed at adjacent locations allowing the drilling of three boreholes using rotary coring techniques. Core recovery and quality were high and samples obtained during coring were retained for testing in the laboratory.

The material recovered was quite strong and not treatable by conventional soil testing and preparation techniques. In addition, the material was susceptible to drying upon exposure to the atmosphere, with an accompanying loss of structure. In spite of this, meaningful laboratory tests were undertaken. Hydraulic conductivity of the samples was measured using constant flow-rate methods and the relative importance of the diffusive flux was investigated using a variety of simple techniques. The advective flux was found to be the dominant contaminant transport process. The results of the laboratory test programme are presented and placed in the context of the long-term performance of cement–bentonite slurry walls.     

塔里木沙漠石油公路半隐蔽式沙障区与流沙区沙物质粒度变化

运用沉积物的粒度分析方法，研究了塔里木沙漠石油公路半隐蔽式沙障区内外沙物质的粒度特征。指出了设置沙障后随时间的推移，障内沙物质平均粒径的Φ值将增大，分选程度变差，而偏度和峰态变化则不十分显著；累积概率曲线表现为四─六段式，含两组悬移组份；掩埋沙障的主要沙物质是跃移组份。此外，还分析了粒度分布与风沙运动的关系，为设置和维护机械沙障提供了粒度方面的依据。     

水成铀矿床含矿层中地浸成因的地球化学障

以层状淋滤成因铀矿床为例，研究主要成矿元素和伴生元素在地浸液向未变化的自然水过渡界限上的行为。这里确定了中和地球化学障以及与它有关的次级障──去气障、中和障等。在这些障上进行着铀、稀土元素和一系列其它元素的现代堆积。指出了这一过程中地下微生物的作用。测定了赋矿陆源岩石的中和容量。评估了所研究体系中物质的带出、迁移和再沉淀的规模。作出的主要结论是：所研究的地质介质具有足够的保护性质，以对抗地浸液的直接的、强烈的作用。     

Occurrence and consequences of acid sulphate soils and methods of site remediation

The oxidation of sulphides in acid sulphate soils (ASS) causes the acidification of many Australian coastal river systems. The acidity negatively impacts upon coastal ecosystems, aquaculture, agriculture and concrete and steel infrastructure. In the low-lying floodplains, relatively deep surface drains fitted with one-way floodgates lower the watertable, thereby exposing the sulphidic minerals to oxidation. On the Broughton Creek floodplain in SE Australia, four distinct remediation strategies have been developed to tackle the issue of acidification by ASS: (i) simple V-notch weirs that raise the level of the watertable surrounding the drains thereby submerging the pyrite and preventing the further formation of acidity; (ii) modified two-way floodgates that allow the inflow of tidal water into the drains, thereby buffering the acidity within the drain before it enters the river and raising the level of the watertable surrounding the drain; (iii) lateral impermeable lime barriers that both prevent oxidation of pyrite by stopping the downward movement of oxygen into the soil and neutralise the acidity in the groundwater; and (iv) permeable reactive barriers (PRB) that passively intercept the groundwater flow and neutralise the acidity. Each remediation strategy has a distinct role to suit the different terrain and groundwater conditions.     

Effect of Pumice and Sand on the Sustainability of Granular Iron Beds for the Aqueous Removal of CuII,NiII, and ZnII

Current knowledge of the basic principles underlying the design of Fe⁰ beds is weak. The volumetric expansive nature of iron corrosion was identified as the major factor determining the sustainability of Fe⁰ beds. This work attempts to systematically verify developed concepts. Pumice and sand were admixed to 200 g of Fe⁰ in column studies (50:50 volumetric proportion). Reference systems containing 100% of each material have been also investigated. The mean grain size of the used materials (in mm) were 0.28 (sand), 0.30 (pumice), and 0.50 (Fe⁰). The five studied systems were characterized (i) by the time dependent evolution of their hydraulic conductivity (permeability) and (ii) for their efficiency for aqueous removal of Cu^II, Ni^II, and Zn^II (about 0.3 mM of each). Results showed unequivocally that (i) quantitative contaminant removal was coupled to the presence of Fe⁰, (ii) additive admixture lengthened the service life of Fe⁰ beds, and (iii) pumice was the best admixing agent for sustaining permeability while the Fe⁰/sand column was the most efficient for contaminant removal. The evolution of the permeability was well‐fitted by the approach that the inflowing solution contained dissolved O₂. The achieved results are regarded as starting point for a systematic research to optimize/support Fe⁰ filter design.     

Overcoming barriers to knowledge exchange for adaptive resource management; the perspectives of Australian marine scientists

The sustainable science-based management of natural resources requires knowledge exchange between scientists and environmental decision-makers; however, evidence suggests that information flow is inhibited by a range of barriers. To date, our understanding of the range and importance of factors limiting knowledge exchange between scientists and decision-makers is based primarily on the perceptions of decision-makers, while the perceptions of scientists have been largely overlooked. This study addresses this knowledge gap by quantitatively assessing the perceptions of scientists, represented by a sample of 78 Australian marine scientists, regarding (i) the role and importance of engaging with environmental decision-makers on a personal level, (ii) the role and importance of engaging with environmental decision-makers at the institutional level, (iii) current barriers to engaging with environmental decision-makers and (iv) options for overcoming barriers to engaging with environmental decision-makers. Survey results suggest that Australian marine scientists feel that they have an obligation to engage decision-makers in their science, and that engaging with and communicating to environmental decision-makers is important on a personal level. This study also identifies a range of barriers that impede engagement activities, including inadequate measures of science impact that do not account for engagement activities, a lack of organisational support for engagement activities, insufficient time to conduct engagement activities in addition to other responsibilities and a lack of funding to support engagement activities. To overcome these barriers, participants identified the need for institutional innovation by research institutions, research funders and decision-making agencies alike to promote a culture whereby knowledge exchange activities are legitimised as core business for research scientists, and recognised and rewarded appropriately. Although difficulties exist in implementing such institutional innovations, doing so will improve two-way knowledge exchange among scientists and decision-makers and improve the likely success of environmental management.     

The right stuff? informing adaptation to climate change in British Local Government

Local government has a crucial role to play in climate change adaptation, both delivering adaptation strategies devised from above and coordinating bottom-up action. This paper draws on a unique longitudinal dataset to measure progress in adaptation by local authorities in Britain, comparing results from a national-scale survey and follow-up interviews conducted in 2003 with a second wave of research completed a decade later. Whereas a decade ago local authority staff were unable to find scientific information that they could understand and use, we find that these technical-cognitive barriers to adaptation are no longer a major problem for local authority respondents. Thanks to considerable Government investment in research and science brokerage to improve the quality and accessibility of climate information, local authorities have developed their adaptive capacity, and their staff are now engaging with the ‘right’ kind of information in assessing climate change risks and opportunities. However, better knowledge has not translated into tangible adaptation actions. Local authorities face substantial difficulties in implementing adaptation plans. Budget cuts and a lack of political support from central government have sapped institutional capacity and political appetite to address long-term climate vulnerabilities, as local authorities in Britain now struggle even to deliver their immediate statutory responsibilities. Local authority adaptation has progressed farthest where it has been rebranded as resiliency to extreme weather so as to fit with the focus on immediate risks to delivering statutory duties. In the current political environment, adaptation officers need information about the economic costs of weather impacts to local authority services if they are to build the business case for adaptation and gain the leverage to secure resources and institutional license to implement tangible action. Unless these institutional barriers are addressed, local government is likely to struggle to adapt to a changing climate.     

Theoretical investigation of the effects of consolidation on contaminant transport through clay barriers

Consolidation of clayey contaminant barriers such as landfill liners has been postulated as a cause of early breakthrough of contaminants. In this paper we theoretically investigate this proposition. For this purpose a sophisticated one‐dimensional, large‐deformation model of coupled mechanical consolidation and solute transport is employed. This new model is a generalization of existing coupled consolidation and solute transport models described in the literature. It takes into account both non‐linearities in geometry as well as constitutive relations. The latter relate the compressibility, hydraulic conductivity and coefficient of effective diffusivity to the deformation of the soil. The model is applied to a case study of a clay liner and geomembrane system. Results obtained from numerical solution of the model equations are compared with those from various simplified models, including a ‘diffusion only’ (i.e. a rigid soil) model traditionally used in contaminant barrier design. For barriers incorporating low compressibility soils (as for many well compacted clays), there is little difference between contaminant transit (i.e. breakthrough) times predicted by the two models. However, for contaminant barriers incorporating more compressible soils, consolidation is shown to significantly accelerate transport. These results indicate the potential importance of accounting for the effects of soil consolidation and highlight the limitations of existing models when modelling solute transport through composite barriers utilizing soft soils. Based on these limited results, we suggest a possible way of taking into account soil consolidation using simplified models. Copyright © 2008 John Wiley & Sons, Ltd.     

河北省电子政务的发展障碍及对策研究

电子政务是继电子商务之后的数字化管理的又一热点,当今社会各国都在积极进行电子政务的探索和实施。影响电子政务发展的因素有很多方面,本文在分析了中国和河北省电子政务发展概况的基础上,主要从地理方面论述河北省的电子政务发展过程中主要存在的空间障碍因素,并提出了相关的对策和建议。     

聚乳酸(PLA)网格沙障耐老化性能及防沙效果

通过甘南玛曲高海拔沙化草地实地铺设和实验室加速老化试验,探索在高原极端环境下透风率20％-49％聚乳酸(PLA)网格沙障的使用寿命和防沙效果.结果表明,PLA网格沙障不仅耐辐射、耐老化,且防沙效果好,可成为严酷气候环境下替代草方格的一种新型沙障.