Employee Presentation 3-00 - p 1

Monitored Natural Attenuation in a Regulatory Context

Monitored Natural Attenuation in a Regulatory Context

Shane Moore

WasteMINZ Conference

Hamilton, November 2007

Employee Presentation 3-00 - p 3

OutlineOutline

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?

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Monitored Natural Attenuation - What is it?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 5

Monitored Natural Attenuation - What is it?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 6

Monitored Natural Attenuation - What is it?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 7

How Has it Been Applied in NZHow 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).

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MNA – Does It Actually Occur?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 9

How Do We Know It’s Occurring?How Do We Know It’s Occurring?

Typically recommended that three converging line of evidence are required:

1. Observed reduction in contaminant mass;

2. Geochemical and biochemical indicators; and

3. 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.

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Transformation and Reducing MassTransformation and Reducing Mass

(Source: Interstate Technology and Regulatory Cooperation - Natural Attenuation of Chlorinated Solvents in Groundwater: Principles and Practices presentation)

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Transformation and Reducing MassTransformation and Reducing Mass

MW

27

MW

24M

W2

6

MW

23

MW

17

MW

4

MW

3

MW

6

MW

14

0

5

10

15

20

25

30

35

40

45

50

0 20 40 60 80 100 120 140 160

Distance from Source (m)

Co

nce

ntr

atio

n (

gm

-3)

TCE

DCE

VC

Employee Presentation 3-00 - p 12

Transformation and Reducing MassTransformation and Reducing Mass

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Geochemical IndicatorsGeochemical Indicators

(modified from Bouwer and McCarty, 1984)

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Geochemical IndicatorsGeochemical IndicatorsM

W2

8

MW

6

MW

17

MW

26

MW

24

MW

4

0

100

200

300

400

-40 -20 0 20 40 60 80 100 120 140 160

Distance from Source (m)

CO

2 &

Cl (

gm

-3)

0.001

0.01

0.1

1

10

100

Co

nc

en

tra

tio

n (

gm

-3)

- N

ote

Lo

g S

ca

le

CO2

Cl

NO3

Fe2+

S

CH4

Alk

SOURCEBACKGROUND DOWN GRADIENT

Employee Presentation 3-00 - p 15

Geochemical IndicatorsGeochemical Indicators

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Screening Protocols - BiochlorScreening Protocols - BiochlorNatural Attenuation Interpretation Score

Screening Inadequate evidence for anaerobic biodegradation* of chlorinated organics 0 to 5

Protocol Limited evidence for anaerobic biodegradation* of chlorinated organics 6 to 14 Score: 31 Adequate evidence for anaerobic biodegradation* of chlorinated organics 15 to 20

Strong evidence for anaerobic biodegradation* of chlorinated organics >20 Scroll to End of Table

Concentration in PointsAnalysis Most Contam. Zone Interpretation Yes No Awarded

Oxygen* <0.5 mg/L Tolerated, suppresses the reductive pathway at higher 3concentrations

>5mg/L Not tolerated; however, VC may be oxidized aerobically 0

Nitrate* <1 mg/L At higher concentrations may compete with reductive 2pathway

Iron II* >1 mg/L Reductive pathway possible; VC may be oxidized under 3Fe(III)-reducing conditions

Sulfate* <20 mg/L At higher concentrations may compete with reductive 2pathway

Sulfide* >1 mg/L Reductive pathway possible 3

Methane* <0.5 mg/L VC oxidizes 0

>0.5 mg/L Ultimate reductive daughter product, VC Accumulates 3

Oxidation <50 millivolts (mV) Reductive pathway possible 1ReductionPotential* (ORP) <-100mV Reductive pathway likely 2

TO INPUT

* reductive dechlorination

The following is taken from the USEPA protocol (USEPA, 1998). The results of this scoring process have no regulatory significance.

(after USEPA, 1998)

Employee Presentation 3-00 - p 17

Screening Protocols – West. AustraliaScreening Protocols – West. Australia

Criteria High Feasibility Medium Feasibility Low Feasibility

Technical Screening Criteria:

Source of groundwater contamination Removed Being removed Continuing/ Unknown

Extent and severity of groundwater contamination

Well defined Poorly defined

Nature of contamination plume Shrinking Stable Growing

Persistence of contamination in groundwater

Readily attenuated (degraded) under site conditions

Not readily degraded under site conditions Attenuation processes poorly understood

Dominant attenuating processes Irreversible/ destructive Reversible/ non-destructive

Aquifer heterogeneity Homogenous and isotropic Heterogenous and anisotropic

Rate of groundwater flow Slow (less than 10 m/year) Medium (10-100 m/year) Rapid (more than 100 m/year)

Etc…

OVERALL ASSESSMENT OF FEASIBILITY

All Highs or Intermediates, no Lows No critically important criteria (i.e. those in bold type and underlined)

One or more critically important criteria, or no factors of High rating

(after Western Australia Department of Environment, 2004)

Employee Presentation 3-00 - p 18

Additional Lines of EvidenceAdditional 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.

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What Should be Considered?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

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What Should be Considered?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…

Criteria High Feasibility Medium Feasibility Low Feasibility

Practical Screening Criteria:

Objectives of land owner/consent holder

Long-term interest in the site (>10 years)

Medium-term interest in the site (3-10 years)

Short-term interest in the site (<3 years)

Financial provisions for monitoring and implementation of a contingency plan

Long-term, legally binding budget provisions secured

Long-term, non-legally binding provisions secured

No long-term budget provisions

Access to off-site monitoring locations Long-term access secured Long-term access possible Limited or no access possible

OVERALL ASSESSMENT OF FEASIBILITY

All Highs or Intermediates, no Lows No critically important criteria (i.e. those in bold type and underlined)

One or more critically important criteria, or no factors of High rating