​​Ramboll were tasked to investigate the use of O.C.O.’s aggregate product in the UK construction industry as a recycled aggregate (for example 6F5 recycled aggregate, typically used for fill material, capping, and as a road sub-base) for bound and unbound applications, and for use in blocks, pre-formed cement or asphalt. Ramboll’s work provided an update to previous work carried out, to encompass new data and ensure compliance with current UK End of Waste and Land Contamination Risk Management regulatory guidance.

The End of Waste criteria established by the Waste Framework Directive (WFD) requires lines of evidence proving that:

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• The aggregate product is commonly used for the identified specific purpose (i.e., construction aggregates);

• There is an existing market or demand for the aggregate product;

• The use of the aggregate product is lawful and meets the existing legislation and standards applicable to products of its type; and

• Use of the aggregate product will not lead to adverse environmental or human health impacts.​

 

Ramboll’s assessment work addressed the final point of the above WFD requirements in the context of the current contaminated land regulatory framework. Concurrently, similar studies were being carried out in Spain and Australia by Ramboll.

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Approach / Activities

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Ramboll’s assessment comprised:

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• Understanding of the aggregate product manufacturing process in the UK;

• Defining the Conceptual Site Model detailing source-pathway-receptor pollutant linkages which may be present in the end use scenarios considered;

• Review of other studies from the UK, and Ramboll studies in Australia and Spain;

• Compilation of a dataset representative of the aggregate product sufficient to characterise the chemical composition for the human health and environmental risk assessments;

• Undertaking a generic quantitative risk assessment (based on UK guidance) to determine a shortlist of chemicals of potential concern (COPC) to consider further;

• Detailed quantitative risk assessment modelling for source-pathway-receptor linkages identified as of potential concern at generic risk assessment stage;

• Identification of any specific requirements for use of recycled aggregates e.g., from Highways Specification or End of Waste protocols, through literature research; and Discussion around the suitability of the aggregate product for the proposed construction end use.

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Results / Lessons Learnt

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The specific use scenarios for the manufactured aggregate considered in this study were;

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1. Aggregate product - uncompacted and uncovered e.g., a replacement for crushed rock or general fill for pipe bedding or in drainage lines, or embankments etc;

2. Aggregate product - compacted and uncovered e.g., use as a piling mat for construction, use in road base with a permeable cover (unsealed road) etc;

3. Aggregate product – compacted and sealed e.g., used in road base with a concrete or asphalt cover, or as fill underneath a building, open air car park etc; and

4. Bound in construction building blocks, pre-formed concrete or asphalt.

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A hypothetical source-pathway-receptor was developed for each of the above end use scenarios to determine potential exposure pathways and receptors.

 

Human Health Risk Assessment

The risk assessment was undertaken in accordance with the current UK framework and initially comprised a generic quantitative risk assessment as defined in the UK.GOV Land Contamination Risk Management guidance. Ramboll’s assessment methodology used the UK Contaminated Land Exposure Assessment (CLEA) approach. Analytical data (~100 samples) for the aggregate product were assessed in relation to Generic Assessment Criteria (GAC) for human health, derived using assumptions based on standard UK land quality management scenarios. Statistical analysis was used to present a comparison of average and 90th percentile from each data source.

Assessment for commercial, industrial and public open space scenarios identified no concentrations of contaminants or potential concern above the GAC. Minor exceedances of the GAC for a residential scenario were noted. However, the residential GAC are highly conservative, derived around assumptions of child exposure to garden soil in a residential setting. The aggregate is likely to be used at the surface for only minimal surface area in a residential setting. The exposure assumptions of times, duration and likely ingestion rates for a child using the likely surface area occupied by the aggregate product will be at least 10 times less than that assumed in the derivation assumptions used to generate the GAC.

The measured concentrations of metals and dioxins are all within an order of magnitude of the residential GAC. As such it was considered, given the inherent conservatism of at least an order of magnitude in the GAC model, risks to human health from placement of the aggregate product in the four end use scenarios (uncompacted and uncovered, compacted and uncovered, compacted and sealed, and bound) are low.

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Water Environment Assessment Risk

The Water Framework Directive (WFD) prevents the input of hazardous substances to the groundwater and limits the non-hazardous input to groundwater. The UK hazardous substances to groundwater are based on the UKTAG Technical Report on Groundwater. Analytical data for the aggregate product were assessed in relation to minimum reporting values (hazardous substances only) and GAC protective of groundwater resources and the surface water environment. Various metals, sulphate and chloride required further quantitative assessment.

Quantitative contaminant modelling was completed using ConSim to quantify likely contaminant movements based on the placement scenarios listed and in consideration of a reasonable worst case high sensitivity water environment (e.g. shallow aquifer potable water resource and nearby surface water environment). Typically, there are numerous uncertainties in the modelling process. Use of ConSim probabilistic modelling and additional sensitivity analysis for chloride (identified as the compound of most concern) was completed to address these uncertainties. The modelling concluded that there is a low risk to the water environment from all contaminant compounds given the placement scenarios considered and a wide variety of sensitive geological settings.

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Conclusions

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The aggregate product was demonstrated to be suitable for all the uses proposed, based on the data provided.

The standard precautionary approach to risk assessment has the potential to be overly restrictive on circular economy decision making when considering waste materials. Ramboll’s innovative approach in developing reuse specific CSMs coupled with challenging the inherent precautionary principles contained within the contaminated land risk assessment protocols has led to enhanced risk assessment procedures which demonstrated low risk and enabled and informed wider risk/cost/benefit decisions to be made on the benefit of different ‘waste’ uses versus landfilling or alternatives.

A key lesson learnt is that, gaining End of Waste accreditation is a long process but good sound science can be used to support the Regulator to think of waste products as a resource rather than a waste, allowing good sustainability practices and contributing to a circular economy. The project directly relates to UN SDGs Number 9 - Industry Innovation and Infrastructure; Number 11 Sustainable Cities and Communities and Number 12 - Responsible Consumption and Production.

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