Colloidal silica grout for the formation of hydraulic barriers : an investigation of the hydro-mechanical and gelling behaviour

Student thesis: Doctoral Thesis

Abstract

Hazardous waste sources such as heavy metals, chemical substances, gases, asbestos, and radioactive substances situated in the subsurface due to historical urban and industrial activities have contributed to a considerable legacy of contaminated sites both in the UK and worldwide. It is estimate that in England and Wales there is potentially 300,000 ha across 325,000 sites of contaminated land (Environment Agency, 2005). Furthermore, the numbers of potentially contaminated sites may increase from future closures and decommissioning of sites across various industries such as nuclear facilities (NDA, 2016). Contamination and its implications cannot be avoided; thus, remediation of contaminated waste sites and improvements to current technologies can provide global environmental benefits (Rivett et al., 2002). The Sellafield site located in northwest England is regarded to be one of “the most hazardous places in Europe” (McKie, 2009). With the most hazardous facilities including four legacy ponds, silos that hold large quantities of nuclear material, and stores housing the UK plutonium inventory. The Nuclear Decommissioning Authority (NDA) estimate costs of £121 billion for the completion of decommissioning work at the Sellafield site by 2120 (NAO, 2018). Statutory guidelines by DEFRA (2012) outline the legal obligations to minimise the risk posed to both humans and the environment from land contamination. In addition, specific industrial licence regulators state requirements of redundancy in the case of leakages (i.e. secondary containment systems) (ONR, 2016). Assessment of contaminated land and appropriate remediation method can be examined by considering three key factors: hazard, pathway, and receptor. The relationship between the three factors is known as pollutant linkage and can be used to determine risks (Angel et al., 2005, DEFRA, 2012). Remediation strategies adopted to minimise or control risks in contaminated land scenario typically comprise three main techniques: hazard reduction (e.g. removal or treatment of the contaminant), pathway modification (e.g containment barrier prevent contact between receptor and hazard), or receptor control (e.g modify the location or nature of the receptor). However, it is usually very difficult to modify receptor behaviour (i.e. humans/biological receptors). Therefore, remediation technologies generally fall into two categories: (i) hazard reduction and (ii) pathway modification. Hazard reduction methods include pump and treat, sparging, and venting. These methods can be implemented to remove and treat contaminated groundwater and volatile compounds. However, contaminants may still remain in situ sorbed onto soil particles. Permeable reactive barriers may also be used as an engineered treatment zone placed to remediate contaminated groundwater as it flows through utilising the mechanism of sorption, oxidation/reduction, precipitation, fixation, and biodegradation. Several other methods also exist including electro-remediation and phytoremediation treatment, these techniques can typically be applied both in-situ and ex-situ. (Nathanail et al., 2007, DEFRA, 2010, Angel et al., 2005). A common strategy for pathway modification is excavation and disposal, the main advantage is that it removes the contaminated soils and breaks the contaminant pathway. However, high costs with transporting and handling of waste, in addition to on site restrictions of operational structures or services are driving the development of alternative remediation strategies (SEPA, 2017). Hydraulic containment is another method of pathway modification utilising pumping to lower the water table to isolate contamination. However, the use of pumps to achieve hydraulic containment can be expensive due to the need for long-term intervention and monitoring. Physical containment barriers use low permeability barriers constructed in the subsurface to inhibit contaminant transport by controlling ground water flow (Persoff et al., 1998, Mulligan et al., 2001). For sites, with very large volumes of contamination or contamination beneath remaining buildings containment may be the only practical option. The advantage of physical containment systems is that they can be widely applied to sites with a range of different contaminants.
Date of Award27 Jan 2022
Original languageEnglish
Awarding Institution
  • University Of Strathclyde
SponsorsUniversity of Strathclyde
SupervisorGrainne El Mountassir (Supervisor) & Rebecca Lunn (Supervisor)

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