Groundwater%20Pollution

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Groundwater Pollution

• Monitored Natural Attenuation and Risk-Based
  Corrective Action

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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.

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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.

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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.

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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.

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

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

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• 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.

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

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• 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.

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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.

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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.

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Risk Assessment 4-Steps

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

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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?

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Risk assessment

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

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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?

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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)?

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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?

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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?

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Risk Characterization

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

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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?

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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.

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Ecological

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

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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.

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Improving Risk Assessment

• There are many uncertainties in risk assessments.
• There are limits in the available data.

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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.

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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.

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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.
  

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Integrated Risk Information System (IRIS)

• This can be found at
• http//www.epa.gov/iris/index.html