Groundwater%20Pollution - PowerPoint PPT Presentation

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Groundwater%20Pollution

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Groundwater Pollution Monitored Natural Attenuation and Risk-Based Corrective Action – PowerPoint PPT presentation

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Title: Groundwater%20Pollution


1
Groundwater Pollution
  • Monitored Natural Attenuation and Risk-Based
    Corrective Action

2
Monitored natural attenuation
  • A strategy for in situ remediation.
  • MNA relies on the naturally occurring physical,
    chemical, and biological processes.
  • MNA can lessen concentrations of certain
    contaminants in groundwater, enough to protect
    human health and the environment.

3
Monitored natural attenuation
  • The changes in contaminant concentrations are
    monitored through wells that are placed
    throughout the contaminated groundwater zone.
  • These show the level of contamination over time
    and its movement in the subsurface.

4
Monitored natural attenuation
  • Some chlorinated solvents and explosives may be
    resistant to natural attenuation.
  • MNA can still be used in cases of non-halogenated
    chlorinated solvents and some inorganic compounds.

5
Monitored natural attenuation
  • If it works for a site, natural attenuation can
    often be less costly because it requires less
    construction, and maintenance.
  • Less surface structures are necessary and it may
    be used in all or selected parts of a
    contaminated site, alone or with other types of
    remediation.

6
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9
  • Organic versus inorganic contaminant plume.
    Natural processes are active within the
    ground-water aquifer.

10
  • Natural attenuation of inorganic contaminants is
    good only if the immobilized contaminant remains
    stable and resistant to remobilization during
    changes in ground-water chemistry.

11
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12
  • This and the previous slide show an example of a
    network design for performance monitoring,
    including target zones for monitoring
    effectiveness with respect to specific remedial
    objectives.

13
  • An EPA site for Monitored Natural Attenuation is
    at http//www.epa.gov/ada/gw/mna.html

14
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15
  • The site must be monitored enough.
  • If something changes at the site then it must be
    checked to see if there has been a change in
    risk.
  • This is risk assessment.

16
Risk
  • Risk assessments look at human health problems
    that are caused by pollutants in the environment.
  • Risk assessments look at exposure and the bad
    outcomes with exposure.

17
Risk
  • Health risks look at cancer, birth defects,
    developmental disorders, and other serious health
    problems that can be caused by pollutant.
  • Ecological risk look at effects of pollution on
    organisms and ecosystems.

18
Risk Assessment 4-Steps
  • There are four steps in the process of risk
    assessment
  • hazard identification,
  • dose-response assessment,
  • exposure assessment, and
  • risk characterization.

19
Risk assessment
  • Does exposure to a pollutant cause injury or
    disease in humans or to the environment?
  • Are certain groups more at risk than others?

20
Risk assessment
  • When are these bad effects are caused?
  • Are the effects in experiments the same as in the
    real-world?

21
Dose-Response Assessment
  • What is the relationship between the amount of
    pollution (or dose) and the health effects?
  • How is this relationship influenced by factors
    such the pattern of exposure or age and
    lifestyle?

22
Dose-Response Assessment
  • Can we compare animal responses (observed through
    experiments) and human responses (resulting from
    real-life exposures).
  • Can we compare high-dose responses (observed in
    the laboratory) and low-dose responses (resulting
    from environmental exposures)?

23
Exposure Assessment
  • What is the intensity, frequency, and duration of
    a persons exposure to a pollutant?
  • What part of the ecosystem are at risk? Is the
    risk mainly to aquatic organisms, to insects and
    insect-eating birds, to sediment-dwelling
    organisms, or to mammals and game such as deer?

24
Risk Characterization
  • How much of a pollutant can people be exposed to
    before their health is affected?
  • How likely is it that people or other living
    things in the environment will suffer bad
    effects?

25
Risk Characterization
  • How certain is this information? What questions
    and uncertainties remain?
  • What is the risk to people who are exposed the
    most?

26
Human Health
  • What types of health problems are caused by
    substances in the environment?
  • How likely is it that people will experience
    problems when exposed at different levels?
  • How severe is this harm likely to be?

27
Human Health
  • Assessments have been produced for hundreds of
    compounds.
  • These are available on-line through a searchable
    database called the Integrated Risk Information
    System or IRIS.

28
Ecological
  • Ecological risk assessments evaluate the bad
    effects that human activities and pollutants have
    on the plants and animals that make up
    ecosystems.

29
Ecological
  • When conducted for a particular place such as a
    watershed, the ecological risk assessment can
    identify vulnerable and valued resources,
    prioritize data collection activity, and link
    human activities with their possible effects.

30
Improving Risk Assessment
  • There are many uncertainties in risk assessments.
  • There are limits in the available data.

31
Improving Risk Assessment
  • There are complex interactions between the
    sources and environmental concentrations of
    contaminants, the amount a person gets, and
    differences in people's responses.

32
Assumptions
  • Assumptions and uncertainty may show the risk as
    bigger than it really is.
  • This may result in standards which are too strong
    and costs which are too high.

33
Assumptions
  • Oversimplifying the risk assessment may
    underestimate risks, particularly for some groups
    such as children or the elderly.
  • Errors of this type present an unacceptable cost.

34
Integrated Risk Information System (IRIS)
  • This can be found at
  • http//www.epa.gov/iris/index.html
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