The ‘Magic Number’ Conundrum - Joint presentation
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The document discusses the evolution of soil assessment criteria for land contamination in the UK. It describes how criteria have progressed from early generic tables to the current system which includes Soil Guideline Values (SGVs), Generic Assessment Criteria (GACs), Category 4 Screening Levels (C4SLs), and Site-Specific Assessment Criteria (S4ULs). It examines differences between the various criteria and implications for land development costs. The talk concludes that knowledge of the conceptual models and exposure assumptions behind the criteria is important, that the industry has made progress but inconsistencies remain, and that future harmonization depends more on the industry than the government.
The ‘Magic Number’ Conundrum - Joint presentation
- 1. The ‘Magic Number’ Conundrum Land Condition Symposium 8th March 2018
- 2. In case you don’t know…. • Formed in 2008 • Now 30 people in 5 regional offices - Kent, Surrey, Sussex, Thames Valley & Midlands • We have provided Geotechnical & Geo-environmental advice for - Around 40,000 new homes - 50 new or extended schools - 50 Part 2A projects (2 Brownfield Briefing Awards) - Local and national government remediation projects - Commercial properties - Water Treatment Works - Landfills
- 3. The Magic Number Conundrum • Human Health Risk Assessment - Before CLEA - After CLEA - Generic Assessment Criteria • Comparisons of available assessment criteria - The assumptions behind the numbers - What is ‘right’? • Implications - Development costs
- 4. A long time ago…….. • We had tables of numbers for soil contamination - Kelly’s, ICRCL, Dutch • But unfortunately no-one could explain where they came from! • We dabbled with RBCA/BP Risc etc. for a while. • Then, in 2000, came Greenleaves II (DETR, EA, IEH) • Shortly followed by the CLR documents - CLR7 Assessment of risk - CLR8 Potential contaminants - CLR9 Tox data - CLR10 CLEA model
- 5. No more ‘magic numbers’ • We were given a model and a framework - To derive whatever assessment criteria we wanted - For whatever exposure scenario we faced • And we had a few Guideline Values to help us - As, Cd, Cr, Hg, Ni, Se, Pb • Different approach to other countries - UK-specific exposure assumptions
- 6. What happened next? • Not quite mayhem…. - But certainly an inconsistent response outside of SGVs • Two tier system - Standards stagnated/slipped largely at the smaller consultancy end of industry • DEFRA ‘Way Forward’ 2005 (CLAN 6/06) - Caused some Part 2A projects to stall or rethink • Environment Agency updates its approach - SR2 Tox - SR3 CLEA - SR4 Software Manual - SGVs
- 7. Life Rafts • Some practitioners sell GACs - Atkins (ATRISK) - LQM • The industry responds to the demand - EIC/AGS/CL:AIRE • Broad industry uptake for the ‘magic numbers’ - Standards improve (stop slipping) at ‘lower end’ of industry - But understanding of the exposure assumptions behind the numbers diminishes. • Consideration of ‘upper acceptable risk’ for Part 2A
- 8. The beginnings of the C4SLs • Part 2A Statutory Guidance 2012 • Provided clarity and additional assessment considerations - Reiterated the concept of SPOSH - Reminded us that the existing GACs were based on minimal risk - Introduced the ‘four category approach’
- 9. 1 Category 4 Screening Levels Categories for Determining SPOSH Current SGVs and GAC ContaminatedlandNotcontaminatedland Point above which land is ‘contaminated land’ under Part 2A Risk Amount of Land Category 4 Screening Levels 2 3 4
- 10. Current state of play • A small number of SGVs remain current. • The EIC/AGS/CL:AIRE GACs remain current. • A small number of C4SLs have been published. • A large number of S4ULs have been published by LQM and have replaced the LQM GACs.
- 11. Which approach is ‘correct’? C4SL SGVs & EIC/AGS/CL:AIRE GACs S4UL Residential soil to skin and dermal exposure reduced. Inhalation rates updated for residential and commercial. Homegrown produce consumption rates updated for residential and allotments. ‘Top two’ approach to homegrown produce consumption rates for residential and allotments. Public Open Space scenarios. SOM 6% 6 substances/congeners/fractions SGVs & EIC/AGS/CL:AIRE GACs S4UL No change needed (represents minimal risk). Change adopted. Not minimal risk? SGVs & EIC/AGS/CL:AIRE GACs S4UL No change needed (represents minimal risk). Change adopted. Not minimal risk? Not changed. But should be? Change adopted. SGVs & EIC/AGS/CL:AIRE GACs S4UL No change needed (represents minimal risk). Change adopted. Not minimal risk? Not changed. But should be? Change adopted. Not changed. But should be? Document does not state that these changes have been adopted. SGVs & EIC/AGS/CL:AIRE GACs S4UL No change needed (represents minimal risk). Change adopted. Not minimal risk? Not changed. But should be? Change adopted. Not changed. But should be? Document does not state that these changes have been adopted. No change needed (represents minimal risk). Change not adopted (represents minimal risk). SGVs & EIC/AGS/CL:AIRE GACs S4UL No change needed (represents minimal risk). Change adopted. Not minimal risk? Not changed. But should be? Change adopted. Not changed. But should be? Document does not state that these changes have been adopted. No change needed (represents minimal risk). Change not adopted (represents minimal risk). Not included, but should be. Included. SGVs & EIC/AGS/CL:AIRE GACs S4UL No change needed (represents minimal risk). Change adopted. Not minimal risk? Not changed. But should be? Change adopted. Not changed. But should be? Document does not state that these changes have been adopted. No change needed (represents minimal risk). Change not adopted (represents minimal risk). Not included, but should be. Included. SOM 6% SOM 6%. Also 1 and 2.5% which is more representative of many brownfield sites. SGVs & EIC/AGS/CL:AIRE GACs S4UL No change needed (represents minimal risk). Change adopted. Not minimal risk? Not changed. But should be? Change adopted. Not changed. But should be? Document does not state that these changes have been adopted. No change needed (represents minimal risk). Change not adopted (represents minimal risk). Not included, but should be. Included. SOM 6% SOM 6%. Also 1 and 2.5% which is more representative of many brownfield sites. SGVs – 10 EIC/AGS/CL:AIRE GACs - 35 82
- 12. The Postcode Lottery • What is accepted depends on the CLO. - Some will only accept minimal risk GACs. - Some will only accept S4ULs. - Some prefer GACs for imported material but will accept C4SLs for material re-use. - Some will not accept anything else even when newly published toxicity studies have reduced a published screening value. • Scotland has not adopted C4SLs - But some CLOs will accept them and/or the S4ULs. - Others will not.
- 13. How Far Have We Come? Contaminant Kelly’s ‘B’ Limit (Slight Contamination) ICRCL (threshold) SGV S4UL C4SL Arsenic 30-50 10 32 37 37 Cadmium 1-3 3 10 11 26 Lead 500-1,000 500 (450 withdrawn) N/A 200 Nickel 20-50 70 130 (withdrawn) 180 N/A Phenol(s) 2-5 5 420 280-1,100 N/A Free cyanide 1-5 25 N/A N/A N/A PAHs 500-1,000 (as coal tar) 50 (as surrogate for coal tar) N/A 0.79-1.1 (BaP as surrogate marker for coal tar) 5.0 (BaP as surrogate marker for genotoxic PAHs) Domestic gardens - soil assessment criteria (mgkg-1):
- 14. What difference does it make? • Simple site • Heavy metal & PAHs • Notably As, Pb, BaP • Remediation (cut / cover)
- 15. What difference does it make? • Approximate Remediation Costs • ICRCL - £300k • S4UL - £250k • C4SL - £175k
- 16. In Conclusion • Knowledge! • The positive of striving for industry consistency can have the negative consequence of complacency • Know the assumptions behind the numbers. • Understand the conceptual model (and follow it through the process) • Progress! • We have moved on from the early days of DQRA • Other countries are looking to UK experience • The future will depend on industry more than government
- 17. Thank You for Listening Midlands Andy Norman– 01684 214155 Surrey & London Tim Thorpe – 01306 646522 Kent & Essex Darren Beesley – 01580 211605 Sussex & Hampshire Sarah Cook – 01444 230385 Thames Valley Barry Gore – 01189 880155