Performance of single skin masonry walls subjected to hydraulic loading.

Property owners are facing increasing threats from flooding and in response are likely to turn to products designed to waterproof or 'seal' the outside of the building in an effort to prevent the ingress of flood water. However, very limited research has been conducted on the effect of this sealing action and the consequent hydraulic load acting upon the structure of the building. The theoretical safe application of waterproofing products has been suggested to be between 0.6 and 1 m (published guidance suggests 0.9 m), although the experimental evidence supporting these suggestions is either absent or limited in nature. This paper presents the findings of an experimental programme that has examined the effect of out-of-plane hydrostatic loading on masonry walls typical of domestic or commercial buildings. The study, conducted at 1/6th scale using a geotechnical centrifuge considers wall panels constructed from a variety of masonry units (autoclaved aerated concrete block, brick and brick-block) bound together with two different types of mortar. The wall panels were subject to an axial load representative of 1 storey of loading and were simply supported on all 4 sides. The load-out-of-plane deflection response of the panels was captured by a 3D digital image correlation system, and the water level at failure was compared to that predicted from previous research and the established yield line analysis method with encouraging results. When partial material and load factors were taken into consideration the results illustrated that a safe sealing height of 0.9 m, as quoted in the literature, would generally be inappropriate, whilst the safe sealing height of 0.6 m was not suitable for every case investigated. This supports the need for a suitable approach for the calculation of water levels at failure rather than the use of fixed values given in published literature.

Altered chemical evolution in landfill leachate post implementation of biodegradable waste diversion.

Within the UK implementation of the European Union Landfill Directive (1999) has led to the diversion of biodegradable waste (BW) from municipal solid wastes away from landfills. It has been widely anticipated, but thus far not verified, that the diversion of BW and consequent reduction in BW reaching landfill would lead to a change in the degradation processes occurring within landfills and that this would be reflected in an altered evolution in leachate chemistry compared to pre-Directive landfills. This paper provides evidence based on leachate chemistry from two operational landfills together with calculations of the reduced BW content, that demonstrate the acetogenic phase that characterised pre-Directive landfill leachates is missing and is now more typical of methanogenic phase leachate. The paper demonstrates how data from national datasets and detailed landfill records can be used to constrain likely and upper estimates of the amount of BW going into post-Directive landfills, and the observed change in the evolution of leachate chemistry which has resulted from a decrease in BW content from typical values of BW (pre-Landfill Directive) of 22% to an inferred 12% in the case-study landfills. Data provided here add to the growing literature that estimates the amount of BW in recent post-Directive landfills which importantly allow the quantitative linkage between a decrease in landfilled BW and observed changes in leachate chemistry to be established such that future landfill operators can increase confidence in the effect of Directive implementation on landfill operational parameters.

Sustainability assessment of electrokinetic bioremediation compared with alternative remediation options for a petroleum release site.

Sustainable management practices can be applied to the remediation of contaminated land to maximise the economic, environmental and social benefits of the process. The Sustainable Remediation Forum UK (SuRF-UK) have developed a framework to support the implementation of sustainable practices within contaminated land management and decision making. This study applies the framework, including qualitative (Tier 1) and semi-quantitative (Tier 2) sustainability assessments, to a complex site where the principal contaminant source is unleaded gasoline, giving rise to a dissolved phase BTEX and MTBE plume. The pathway is groundwater migration through a chalk aquifer and the receptor is a water supply borehole. A hydraulic containment system (HCS) has been installed to manage the MTBE plume migration. The options considered to remediate the MTBE source include monitored natural attenuation (MNA), air sparging/soil vapour extraction (AS/SVE), pump and treat (PT) and electrokinetic-enhanced bioremediation (EK-BIO). A sustainability indictor set from the SuRF-UK framework, including priority indicator categories selected during a stakeholder engagement workshop, was used to frame the assessments. At Tier 1 the options are ranked based on qualitative supporting information, whereas in Tier 2 a multi-criteria analysis is applied. Furthermore, the multi-criteria analysis was refined for scenarios where photovoltaics (PVs) are included and amendments are excluded from the EK-BIO option. Overall, the analysis identified AS/SVE and EK-BIO as more sustainable remediation options at this site than either PT or MNA. The wider implications of this study include: (1) an appraisal of the management decision from each Tier of the assessment with the aim to highlight areas for time and cost savings for similar assessments in the future; (2) the observation that EK-BIO performed well against key indicator categories compared to the other intensive treatments; and (3) introducing methods to improve the sustainability of the EK-BIO treatment design (such as PVs) did not have a significant effect in this instance.

Impact of electrokinetic remediation on microbial communities within PCP contaminated soil.

Electrokinetic techniques have been used to stimulate the removal of organic pollutants within soil, by directing contaminant migration to where remediation may be more easily achieved. The effect of this and other physical remediation techniques on the health of soil microbial communities has been poorly studied and indeed, largely ignored. This study reports the impact on soil microbial communities during the application of an electric field within ex situ laboratory soil microcosms contaminated with pentachlorophenol (PCP; 100mg kg(-1) oven dry soil). Electrokinetics reduced counts of culturable bacteria and fungi, soil microbial respiration and carbon substrate utilisation, especially close to the acidic anode where PCP accumulated (36d), perhaps exacerbated by the greater toxicity of PCP at lower soil pH. There is little doubt that a better awareness of the interactions between soil electrokinetic processes and microbial communities is key to improving the efficacy and sustainability of this remediation strategy.

A comparison of the technical sustainability of in situ stabilisation/solidification with disposal to landfill.

Sustainability is becoming a very important issue in contaminated land remediation and should form one of the factors used in future selection of treatment technologies. In situ stabilisation/solidification (S/S) is a remediation technique that is increasingly being applied to the treatment of contaminated sites because of numerous advantages over other remediation techniques. This paper assesses and compares aspects of the technical sustainability of in situ S/S with landfilling. Criteria previously established for the assessment of the technical sustainability of the remediation of contaminated land are employed. The comparison is presented in the form of a case study based on a real remediation project in the UK. The analysis indicated that landfilling had a larger impact than S/S in the majority of areas investigated, such as waste production (1000 kg waste/t soil remediated for landfilling compared to none for S/S), transportation (12.9 km/t for landfilling, 0.4 km/t for S/S) and use of raw materials (1005.5 kg/t for landfilling, 88.9 kg/t for S/S), although S/S had high greenhouse gas emissions (12.6 kg/t for landfilling, 40.9 kg/t for S/S). In addition, a multi-criteria/cost-effectiveness analysis gave cost effectiveness scores of -34.2 to S/S and -138.1 to landfill (where more positive is better).

Heavy metal leaching and environmental risk from the use of compost-like output as an energy crop growth substrate.

Conversion of productive agricultural land towards growth of energy crops has become increasingly controversial. Closed landfill sites represent significant areas of brownfield land, which have potential for the establishment of energy crops. Increasingly composts are now being produced from the degradable fraction of mixed municipal solid waste (MSW) and are commonly referred to as Compost-Like-Output (CLO). However, leaching of heavy metal and other elements due to the use of CLO as soil amendment has the potential to pose a risk to the wider environment as a diffuse pollution source if not managed correctly. Salix viminalis and Eucalyptus nitens were grown at 5 different CLO application rates (equivalent to 250, 1000, 3000, 6000, 1,0000 kg N/Ha) with weekly leachate analysis to assess the solubility of heavy metals and the potential release into the environment. The change in plant total dry mass suggested 3,000 kgN/Ha as the optimum application rate for both species. Weekly leachate analysis identified excess soluble ions within the first 4 weeks, with heavy metals concentrations exceeding water quality limits at the higher application rates (>3,000 kg N/Ha). Heavy metal uptake and accumulation within each species was also investigated; S. viminalis accumulated greater levels of heavy metals than E. nitens with a general trend of metal accumulation in root>stem>leaf material. Heavy metal leaching from soils amended with CLO has the potential to occur at neutral and slightly alkaline pH levels as a result of the high buffering capacity of CLO. The use of CLO at application rates of greater than 250 kg N/Ha may be limited to sites with leachate collection and containment systems, not solely for the heavy metal leaching but also excess nitrogen leaching. Alternatively lower application rates are required but will also limit biomass production.

Electrokinetic-enhanced bioremediation of organic contaminants: a review of processes and environmental applications.

There is current interest in finding sustainable remediation technologies for the removal of contaminants from soil and groundwater. This review focuses on the combination of electrokinetics, the use of an electric potential to move organic and inorganic compounds, or charged particles/organisms in the subsurface independent of hydraulic conductivity; and bioremediation, the destruction of organic contaminants or attenuation of inorganic compounds by the activity of microorganisms in situ or ex situ. The objective of the review is to examine the state of knowledge on electrokinetic bioremediation and critically evaluate factors which affect the up-scaling of laboratory and bench-scale research to field-scale application. It discusses the mechanisms of electrokinetic bioremediation in the subsurface environment at different micro and macroscales, the influence of environmental processes on electrokinetic phenomena and the design options available for application to the field scale. The review also presents results from a modelling exercise to illustrate the effectiveness of electrokinetics on the supply electron acceptors to a plume scale scenario where these are limiting. Current research needs include analysis of electrokinetic bioremediation in more representative environmental settings, such as those in physically heterogeneous systems in order to gain a greater understanding of the controlling mechanisms on both electrokinetics and bioremediation in those scenarios.