Cumulative impact analysis

People’s health is affected by many outside factors including multiple sources of pollution and other social conditions and stressors. Some people and communities are burdened by higher levels of pollution and more social stressors than others. Minnesotans are increasingly interested in understanding the impact on their health from all of these multiple pollution sources and stressors combined together. This is referred to as a cumulative impact analysis.

The MPCA has many tools and methods that can begin to shed light on cumulative impacts. However, this is a developing field and there is not yet a method or tool or combination of methods and tools that can give a full picture of impacts. These tools vary in their ability to quantitatively estimate impacts, but can provide context around environmental decisions.

Types of analyses

When facilities and other emission-generating projects or rules are proposed that might affect pollution levels in an area, communities want to know what the cumulative impact might be on their health of the action along with the other stressors in their community. The MPCA has different methods for these analyses, and selecting the right method depends on the type of project and the conditions in the community involved.

A full cumulative impacts analysis would include all of the elements described below. The ideal cumulative impact analysis would include the integration of all these elements; however, such a model does not yet exist.

Elements of a cumulative impact analysis include:

Sensitivity: The magnitude of response to a stimuli. Everyone responds differently to stimuli. For example, a wasp sting: some people may need extensive medication, while others may simply need ice to relieve pain.

Additivity: The practice of summing impacts across many chemicals. The term refers to an analysis that integrates the impacts of multiple chemicals and is not a single-pollutant analysis.

Multiple pathways: People are exposed to environmental chemicals by breathing, eating, touching, etc. This element refers to the inclusion of more than one way people are exposed, whether it is eating plants and animals, swimming in a lake, or breathing outdoor or indoor air.

Multiple sources: The inclusion of more than one source of pollution. In some analyses only one source is assessed. In others only one emission unit or outflow is assessed. In others a whole facility, background sources, and nearby sources may all be assessed.

Non-chemical stressors: Physical or biological agents (i.e. non-chemical) that can cause an adverse impact. Examples might be radon (physical), noise (physical), or bacteria (biological). There are not currently methods to include both chemical and non-chemical stressors that have similar adverse impacts in a single analysis, but developments in these methods would be a tremendous improvement in current risk assessment practices.

Community vulnerability: A community’s ability to recover or repair. Health disparities are both an outcome of and a contributor to vulnerability in a community. Economic insecurity and fear of personal safety are also part of community vulnerability. Using the wasp sting example from above, a community’s vulnerability would be affected by their access to EpiPens, their ability to purchase protective clothing, the number and concentration of wasps in their community, etc.

Each of these elements may be more or less quantitative, may have more or less data available, and may be more or less within MPCA’s ability to regulate. The graphic below shows how each of these elements ranges along these three spectrums: quantitative/qualitative analysis, data availability, and level of MPCA influence.

Arrows show how each element of a cumulative impact analysis ranges along three spectrums: quantitative/qualitative analysis, data availability, and level of MPCA influence

Examples of cumulative impacts analyses in Minnesota include:

  • Cumulative levels and effects analysis — a unique requirement for evaluating air permit applications in parts of South Minneapolis.
  • Health impact assessment — uses public input and extensive information gathering to provide health context around a decision.
  • Environmental review — an information-gathering activity that helps determine a project’s potential environmental impacts.

How cumulative is an analysis?

Many analyses that the MPCA does are cumulative in some way, but they all include more or less elements described above.  For instance, environmental permitting processes assess one environmental medium (air, water, land) at a time. An analysis for an air permit, for example, would include assessment of all air pollutants from a facility and surrounding air quality, but there is no requirement to also include assessments of water quality, soil contamination, or community health unless a larger environmental review analysis (e.g. an environmental assessment worksheet) is triggered.

Under some circumstances, MPCA includes qualitative analysis of non-chemical stressors or community vulnerability when evaluating the potential cumulative impacts of a pollution source. Although there currently are no quantitative methods to incorporate these factors into typical regulatory evaluations, this field is growing and some non-regulatory evaluations are beginning to incorporate these concepts.

Cumulative impact analyses in regulatory evaluations

Regulatory agencies like the MPCA are working to expand existing assessments to include more elements of a cumulative impact analysis. In regulatory agencies, assessments are conducted according to the requirements of statutes, rules, laws, or advisory panel guidance. For that reason definitions have a large impact on the methods used for each analysis. The three definitions below describe different cumulative analysis types used in regulatory evaluations.

Cumulative risk assessment: The combination of risks posed by aggregate exposure to multiple agents or stressors (biological, chemical, physical, and psychosocial) in which aggregate exposure is exposure by all routes and pathways and from all sources of each given agent or stressor. The term “cumulative risk assessment” is defined as an analysis, characterization, and possible quantification of the combined risks to human health or the environment from multiple agents or stressors. (U.S. EPA 2003)

Cumulative effects: The impact on the environment which results from the incremental impact of the action when added to other past, present, and reasonably foreseeable future actions regardless of what agency (Federal or non-Federal) or person undertakes such other actions. (National Environmental Policy Act)

Cumulative impacts: Cumulative impacts means exposures, public health or environmental effects from the combined emissions and discharges in a geographic area, including environmental pollution from all sources, whether single or multi-media, routinely, accidentally, or otherwise released. Impacts will take into account sensitive populations and socio-economic factors, where applicable and to the extent data are available. (Cal EPA, 2012)