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Monitored Natural Attenuation in a Regulatory Context

Monitored Natural Attenuation in a Regulatory Context. Shane Moore WasteMINZ Conference Hamilton, November 2007. Outline. Monitored natural attenuation – what is it? How has it been applied in NZ – the issues Does it actually occur? How do we know it’s occurring?

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Monitored Natural Attenuation in a Regulatory Context

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  1. Employee Presentation 3-00 - p 1

  2. Monitored Natural Attenuation in a Regulatory Context Shane Moore WasteMINZ Conference Hamilton, November 2007

  3. Outline • Monitored natural attenuation – what is it? • How has it been applied in NZ – the issues • Does it actually occur? • How do we know it’s occurring? • What should be considered? Employee Presentation 3-00 - p 3

  4. Monitored Natural Attenuation - What is it? • Term used to describe the naturally occurring physical, chemical and biological processes that act without human intervention to reduce the mass, toxicity, mobility or concentration of contaminants. • 2 main mechanisms: • Destructive mechanisms, such as biological and chemical degradation; • Non-destructive mechanisms such as sorption, dispersion and volatilisation - reduce concentration but not overall mass in the environment. Employee Presentation 3-00 - p 4

  5. Monitored Natural Attenuation - What is it? • “Monitored Natural Attenuation” or MNA refers to the reliance on NA processes to achieve remediation goals (after USEPA 1999) Employee Presentation 3-00 - p 5

  6. Monitored Natural Attenuation - What is it? • Biodegradation has been shown to be one of the principal mechanisms for the natural attenuation of organic compounds • Micro organisms obtain energy by transferring electrons from electon donors (e.g. fuel hydrocarbons and native carbon) to electron acceptors (e.g. O2, NO3, Fe, Mn, SO4 or in some cases chlorinated aliphatic hydrocarbons) Employee Presentation 3-00 - p 6

  7. How Has it Been Applied in NZ • In the past, often poorly: • Considered a presumptive or default option. • Limited characterisation (few wells and 1 or 2 rounds of data). • Inconsistent consenting requirements and conditions. • However, MNA is consistent with the risk based philosophy of our legislation. It can provide a more sustainable solution (e.g. lower energy and wastes). Employee Presentation 3-00 - p 7

  8. MNA – Does It Actually Occur? • Don’t see too many plumes of infinite length…. • A number of international jurisdictions have developed MNA policy and guidance documents including: • USEPA, 1997. Underground Storage Tank Sites. Directive 9200.4-17. • USEPA, 1998. Chlorinated Solvents. EPA/600/R-98/128. • ASTM, 1998. Petroleum Release Sites. ASTM 1943-98. • UK Environment Agency, 2000. R&D Publication 95. • Western Australia Department of Environment, 2004. Employee Presentation 3-00 - p 8

  9. How Do We Know It’s Occurring? • Typically recommended that three converging line of evidence are required: • Observed reduction in contaminant mass; • Geochemical and biochemical indicators; and • Microbiological laboratory data. • At a minimum the first two lines of evidence must be obtained. • However, as populations of native micro-organisms are generally considered to be ubiquitous the third line of evidence is generally only required where primary and secondary lines are inconclusive. Employee Presentation 3-00 - p 9

  10. Transformation and Reducing Mass (Source: Interstate Technology and Regulatory Cooperation - Natural Attenuation of Chlorinated Solvents in Groundwater: Principles and Practices presentation) Employee Presentation 3-00 - p 10

  11. Transformation and Reducing Mass Employee Presentation 3-00 - p 11

  12. Transformation and Reducing Mass Employee Presentation 3-00 - p 12

  13. Geochemical Indicators (modified from Bouwer and McCarty, 1984) Employee Presentation 3-00 - p 13

  14. Geochemical Indicators Employee Presentation 3-00 - p 14

  15. Geochemical Indicators Employee Presentation 3-00 - p 15

  16. Screening Protocols - Biochlor (after USEPA, 1998) Employee Presentation 3-00 - p 16

  17. Screening Protocols – West. Australia (after Western Australia Department of Environment, 2004) Employee Presentation 3-00 - p 17

  18. Additional Lines of Evidence • In addition to visual/graphical techniques, assessment may also include determination of: • Mass balance calculations. • Biodegradation kinetics such as half life or degradation constants. • Long term attenuation capacity of the aquifer (for example, supply and availability of electron donors/acceptors). • Rates of non-degradative attenuation mechanisms, such as sorption. • Fate and transport modelling. Employee Presentation 3-00 - p 18

  19. What Should be Considered? • Requires that the risks are either already acceptable or otherwise mitigated. • Selection of MNA requires appropriate site characterisation – potentially more detailed, e.g.: • Minimum of 4 rounds to assess stability • Geochemical indicators etc. • Need independent and converging lines of evidence. • Requires design and implementation of appropriate groundwater monitoring programmes, e.g.: • Frequency – don’t require ¼ in low K conditions Employee Presentation 3-00 - p 19

  20. What Should be Considered? • Can institutional controls be effectively implemented (refer presentation by Murray Wallis and Laurie Franks). • Appropriate contingency plan in the event that MNA proves to be ineffective or risk profile changes. • Education and national guidance… Employee Presentation 3-00 - p 20

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