Resource efficient remediation

Transcription

1 Case study Resource efficient remediation Achieving savings through remediation and onsite reuse of contaminated material Bellway, Taylor Wimpey and Hydrock Costs and savings achieved by housing developers on two remediation sites through adopting an efficient remediation strategy Site at Chinnor Site at Fenny Standard practice Material requiring remediation 9,720t 31,500t Vehicle movements 525 1,700 Cost of disposal 345,600 1,400,000 Best practice (actual) Material requiring remediation 11,000t 21,600t Cost of site remediation 206, ,000 Soils transported off 0t 100t Cost of additional 50,000 50,000 Avoided cost premium 89, ,000 for remediation Halving Waste to Landfill Overview The remediation of sites with contaminated soils can be a costly and complex exercise. Because of Escalating Landfill Tax and the pressure to demonstrate sustainability means clients and developers are now setting requirements for more efficient remediation solutions and asking their designers to develop strategies that avoid the traditional dig and dump solution. This can be the first step in cutting the costs of waste on a specific site. This case study looks at two projects that adopted a best practice approach to Materials Management Planning, in accordance with CL:AIRE s recently published Definition of Waste: Development Industry Code of Practice. In each case, the developer benefited from substantial reductions in cost, shortened programmes and reduced impact on the local environment. The case study looks at: Chinnor Cement Works 77ha, requiring a demolition, reclamation and remediation strategy; and the former BPC & Wheelspan site at Fenny a 2.5ha remediation scheme in a tight urban area. The work illustrates how CL:AIRE s Code of Practice can help to deliver practical savings. CL:AIRE (Contaminated Land: Applications in Real Environments) is an organisation established to stimulate the regeneration of contaminated land by raising awareness of, and confidence in, practical and sustainable remediation technologies. The Code of Practice provides a structured approach to the re use of soils on site, and provides a clear process for the project team in determining whether excavated materials are a waste. It is applicable in England and Wales.

2 Chinnor Cement Works The site at Chinnor is a 77ha former cement works, cement kiln dust landfill and series of chalk quarries, with a proportion of the site (7ha) identified as an area for residential development. The site is located above a major chalk aquifer and spring system, with previous s indicating that petroleum hydrocarbons (primarily from leaking fuel tanks) were present within both the soils and the groundwater. The challenge Chinnor is located on the edge of a village with poor access and resultant concerns from the public over the impact of demolition, remediation and development of the site. Because of the level of contaminants (which included petroleum hydrocarbon and polycyclic aromatic hydrocarbons) and the need to protect the local aquifer resource, the original remedial strategy suggested that 9,720t (~5,400m 3 ) 1 of soils would require disposal off-site rather than on site remediation. This solution was rejected as it would have required~525 vehicle movements, would be expensive, and impact heavily on the local community. The challenge was to find a solution that allowed materials to remain on site in a way that enabled subsequent re-development (residential and commercial) and at the same time mitigated the risk to the local chalk aquifer. The approach The client (Taylor Wimpey) instructed Hydrock to carry out an appraisal of the previous s/risk assessment, remedial strategy and costs. Early on, Hydrock identified gaps in the previous risk assessment and noted that the remedial strategy (dig and dump) was both unsustainable and costly. Taylor Wimpey was aware of the potential to save money through alternative solutions and instructed the design team to explore these. The works were carried out followed by a detailed hydrogeological assessment, groundwater risk assessment, human health risk assessment and remedial strategy in order to develop and refine the Conceptual Site Model. The Model is a simplified representation of the site conditions including geology, hydrogeology and any significant pollution linkages. Careful consideration was given to the final development plan and the cut & fill requirements, which helped the formulation of a viable remediation strategy and robust Material Management Plan. (This Plan is integral to the Code of Practice and can form part of the Site Waste Management Plan.) On site remediation techniques (using both bioremediation and soil stabilisation/solidification) were proposed for the impacted soils, as opposed to an excavation and disposal option. Upon further characterisation and testing, only 6,300t (~3,500m 3 ) of materials required treatment, with the remainder suitable for reuse without treatment. 1 Based on 1m 3 =1.8tonnes

3 Once the revised strategy was agreed with the regulators, Hydrock developed a Material Management Plan that took into account the volume of material produced by the following activities and identified areas within the site where these soil volumes could be suitably re used: demolition arisings; remediation volumes; cut & fill requirements; and soil use in the final development plan. In addition, all metal from the demolition of above-ground structures was recycled. A Material Management Plan provides a description of the materials in terms of potential use and relative quantities of each category, details of where and how these materials are to be stored, details of the final destination of the material, details of the material tracking system (i.e. from excavation to re-compaction) and any contingency arrangements (for example if more material is found). Base assessment Material requiring 9,720t remediation off site Vehicle movements 525 Cost of disposal 345,600 Final design Material requiring 11,000t remediation or reuse on site Cost of site remediation 206,000 Soils transported off 0t Cost of additional 50,000 Summary Cost premium (avoided) for 89,600 dig and dump solution Cost premium (avoided) 97,777 through import of new material Former BPC & Wheelspan Site (Fenny) This small site (2.5ha) is located in a sensitive residential area in Milton Keynes. The site was to be developed for residential use, with gardens and areas of public open space. It is bounded on one side by a canal and on the other side by a river (the main receptor), and in its history has had numerous former uses including: former town gasworks; paint pigment factory; and a transport yard. The client, Bellway NHC, was aware of the cost premium of a traditional (dig and dump) remedial strategy. Hydrock was instructed to carry out further and design a scheme that avoided a dig and dump solution and as such the associated cost premium. The challenge Previous s indicated sitewide gross contamination including: gasworks waste: - petroleum hydrocarbons; - running tars; - polycyclic aromatic hydrocarbons; - heavy metals; - cyanides; and cadmium impacted soils from paint pigment manufacturing. Due to the proximity of the river and the high level of contamination, the Environment Agency s original preferred strategy was to remove all grossly contaminated soils and install an impermeable barrier to prevent subsequent contamination of the river. The feasibility study identified that this solution would have required the excavation and disposal of between 27,000t 36,000t (15,000m 3 to 20,000m 3 ) of largely hazardous materials to a landfill miles away. This was considered neither economically viable nor sustainable. This Table shows the scale of the savings that were achieved, resulting both from the avoidance of landfill, and the avoidance of imported materials.

4 The approach Additional s were undertaken to ascertain the full extent of impacted soils (including treatment trials). This also allowed revised human health and groundwater risk assessments to be carried out, resulting in a robust Conceptual Site Model which was presented to the Regulators. This included a revised hydrogeological assessment and potential migration pathways, in addition to the further delineation of gross contamination locations. This allowed Hydrock to review the original remedial proposal and construct a more sustainable and economically viable strategy. A robust remedial strategy and Material Management Plan was then formulated that included the treatment (soil stabilisation/solidification) and re use of impacted soils on site. Lab-scale treatment trials were presented to the Environment Agency who agreed the new approach. Hydrock also re-evaluated site levels and agreed a revised strategy with Bellway, allowing more soils to be retained on site. The works involved the selective excavation of grossly impacted soils for ex-situ treatment using soil stabilisation/ solidification technology. Impacted groundwater was used in the soil stabilisation process or treated separately for regulated discharge to the foul sewer. Upon validation of the soil stabilisation process, treated soils were replaced and compacted in suitable fill areas. Works were phased to allow Bellway to begin construction works on a proportion of the site, whilst still undertaking remedial works in other areas. Prior to remediation, all hardstanding, foundations and in-ground obstructions were removed and crushed for re use on the site. With the benefit of the site trials, soil stabilisation/solidification was carried out on both the cadmium impacted soils and the gasworks impacted soils (both of which were UK firsts for the material type), enabling a 100% retention rate on site for these soils of a formerly hazardous nature. The adoption of the Material Management Plan and remedial strategy, which focused on mitigating the risks posed to the nearby river, allowed the re use of the materials on site below hardstanding (e.g. car parks, footpaths) and in road construction. The site re use of materials as non-waste was in accordance with the procedures set out in the newly published Code of Practice i.e. they were suitable for use without any further treatment; they had certainty of use; and there was space available for the material on site. Base assessment Material requiring 31,500t remediation Vehicle movements 1,700 Cost of disposal 1,400,000 Final design Material requiring 21,600t remediation Cost of site remediation 500,000 Soils transported off 0t Cost of additional 50,000 Summary Cost premium (avoided) for 850,000 dig and dump solution Cost premium (avoided) 192,000 through import of new material

5 CL:AIRE Definition of Waste: Development Industry Code of Practice The challenge facing the industry Retaining excavated soils on site is often the most sustainable and economic solution due to landfill costs, reduced transport impacts and reduced aggregate import costs. This is not a technical or regulatory problem for uncontaminated sites; but where there are contaminants then barriers to site re use exist. The Code of Practice (CoP) The CoP provides a structured approach to the re use of soils on site. It serves two purposes: It sets out good practice for the development industry to use: - when assessing whether materials are classified as a waste or not; and - when determining when treated waste can cease to be waste for a particular use. It describes an auditable system to demonstrate that this CoP has been adhered to on a site by site basis. The CoP is applicable in England and Wales and provides a clear process for decision makers (designers/developers/house builders) in determining whether excavated materials are a waste. The benefits Adoption of the CoP will benefit the construction industry by: providing a clear method by which soils generated during construction activity can be designated a non-waste; diverting materials away from landfill for use as a resource on the site of origin or potentially on other sites; saving developers substantial costs in waste disposal and in the need to import clean soils/aggregates; unlocking land for redevelopment that may otherwise be commercially unviable; and substantially reducing vehicle movements. Further information on the Code of Practice is available from: Definitions Bioremediation process operated above ground (ex-situ) is a process in which excavated soil is placed in an appropriate treatment area and stimulated to enhance the biodegradation of contaminants present. Aeration of the soil and the addition of microbes and nutrients are effective measures to enhance this process. The net result is that levels of hydrocarbons will reduce at an accelerated rate. Solidification and stabilisation are processes that are used together as part of a remedial approach in order to reduce the mobility of contaminants in soils. In turn, this prevents contaminants reaching sensitive receptors (the aquifer system in the case of Chinnor, and the adjacent river in the case of Fenny). While steps have been taken to ensure its accuracy, WRAP cannot accept responsibility or be held liable to any person for any loss or damage arising out of or in connection with this information being inaccurate, incomplete or misleading. This material is copyrighted. It may be reproduced free of charge subject to the material being accurate and not used in a misleading context. The source of the material must be identified and the copyright status acknowledged. This material must not be used to endorse or used to suggest WRAP s endorsement of a commercial product or service. For more details, please refer to our Terms & Conditions on our website Waste & Resources Action Programme The Old Academy 21 Horse Fair Banbury, Oxon OX16 0AH Tel: Fax: info@wrap.org.uk Helpline freephone