Gain a Basic Understanding of the Site

This section describes the types of information you will look at to get a basic understanding of the site.

In the initial phases of the PHA process, much of your information gathering will be directed toward understanding potential exposures and community concerns. As you collect each piece of information, consider how it will help you perform the scientific evaluations of the PHA process to determine whether site-specific conditions could be associated with exposures and if identified exposures might be associated with harmful health effects. There are four main scientific evaluation components in ATSDR’s PHA process.

Exposure pathway evaluations  are done first and inform the other scientific evaluations including (Screening Analysis, EPC and Exposure Calculations, and In-Depth Toxicological Effects Analysis). Not all sites will require all these evaluations; the results of each scientific evaluation component will inform whether the next evaluation is necessary.

At the end of the PHA process, you will develop a document that summarizes your findings about whether people could be harmed by coming into contact with site contaminants and provide recommendations to protect public health. ATSDR uses different types of products to communicate the PHA process findings, and it is important to consider the goal of your end product when collecting the site information discussed in this section.

Site-specific circumstances and professional judgment will influence the information to collect. At some sites, such as Superfund sites under remediation, much documentation will already exist. At other sites, background information and environmental data can be very limited or in forms that are difficult to use. Identify what information is most relevant for your evaluation and develop a conceptual site model—a diagram that helps you visualize how contaminants move in the environment at your site and how people may or may not be coming into contact with these contaminants.

Remember: The more specific your knowledge about the site and its potential hazards, the more representative your conclusions will be of actual exposures in the community.

You will not be collecting all this information at once. Information needs will evolve as you learn more about the site and identify issues requiring further examination. Each new source or piece of information will help you get a better understanding of the site.

Background Information

It is important to gain a basic understanding of your site by collecting background information, such as the site’s setting, regulatory history, and land use and natural resources. Background information about the site:

  • Provides the key to understanding the nature, magnitude, and extent of contamination.
  • Assists with identifying potentially exposed populations.
  • Lays the initial foundation for understanding potential associated exposures.
  • Supports detailed exposure evaluations to be conducted later in the PHA process.
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Learn what common types of site information you need to collect.

Use ATSDR’s Community Data Worksheet [PDF – 64 KB] to see various types of information to collect.

Site Operations and History

Information about a site’s past and current operations, such as hazardous substance and waste management practices, operating processes (changes to past, current, and planned changes to current processes), and historical development often indicates the:

  • Types of contaminants that may be present
  • Possible extent of contamination
  • Possible magnitude of human exposure
  • Possible changes to human exposure over time
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Learn about common types of operations and history information to collect.

Regulatory History and Activities

Certain information about a site’s regulatory history may assist you in evaluating its exposure pathways and public health implications. Activities associated with environmental releases, site investigations, and remedial actions will be most pertinent, such as:

  • CERCLA or RCRA status (e.g., Is the site on EPA’s NPL, and why?).
  • Results and types (e.g., scoping, investigation, characterization) of any site investigations.
  • Types of permits (air, water discharge, hazardous waste) held, compliance information, and monitoring data.
  • Air modeling to support air permits.
  • Actions taken by EPA, state agencies, or site operators to address contaminant releases and to eliminate or mitigate exposures.
  • Remedial activities and other risk management strategies implemented, planned, or proposed (including past, current, and future monitoring practices and/or institutional controls).

As you review regulatory information, consider the level of detail you need for understanding potential site exposures. For example, you might not need a detailed understanding of a site’s permitting history. However, you do want a general understanding of the site’s operational processes, regulated emissions, emission controls, and permitted effluents to help you relate specific environmental contaminants to particular site operations.

Land Use and Natural Resources

Reviewing information about land use and natural resources at and near a site can provide details about:

  • The types and frequency of the surrounding population’s activities.
  • The probability for human exposure (e.g., help to define exposure units).
  • Whether certain populations could experience increased exposure to contamination.
  • How different types of activities can affect whether people are exposed and the frequency and duration of exposure.
  • The degree of contact the population may have with contaminated media, such as soil, water, air, waste materials, plants, and animals.
  • How site conditions and exposure scenarios may have changed or may change over time including past and planned land use.
Aerial view of a power plant with multiple red and white smokestacks

Photographs (including aerial photographs) and maps indicating site conditions, proximity to populated areas, and land uses are often helpful.

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Learn about common types of land use and natural resources information to collect.

Environmental Contamination

Environmental contamination data can help you answer questions about:

  • What contaminants might people be/have been exposed to and at what concentrations?
  • Are there data for all identified exposure units in completed or potential pathways?
  • Are the sampling data (e.g., sampling methods, locations, analytes) representative of potential exposures?
  • When and for how long might people be/have been exposed to the contaminants of concern?
  • What is the likelihood of exposure to different levels of contaminants?
  • How reliable are the data on which you will base your conclusions?
  • What are the limitations of the data you will use to base your conclusions?
Related Resources

Refer to the detailed guidance on evaluating environmental contamination in these resources:

PHAT Module 5 Training Course (this link will take you to the module’s registration page in CDC TRAIN)

Selecting Sampling Data

You will use this information—along with the exposure and toxicologic data—to evaluate possible health implications of exposures. Efforts should focus on obtaining as extensive a data set as possible for those media for which past, current, or potential future exposures exist.

Other important considerations with environmental data include:

  • Environmental measurements (sampling data) provide direct measurements of contamination levels in the environment. Sampling data are standard inputs to the PHA process. Another important input to the PHA process is modeled data, which provide estimated contamination levels. Modeled data can be used in addition to sampling data and where sampling data are unavailable or limited.
  • Environmental data may be available in many different forms, including laboratory reports, summary tables, and databases. Be sure to request environmental sampling data in the preferred electronic format (though other formats are acceptable) from data owners, such as EPA and other government agencies, site owners, and contractors.
  • When using sampling and/or modeled data, be sure to ask for quality assurance/quality control (QA/QC) information associated with the data. Seek information about the objectives, limitations, and uncertainties of the data.
  • Be aware that environmental data are collected for many different reasons and some data may not be useful for determining human exposure. Health assessors must understand why data were collected and what they represent before using them to evaluate environmental exposures, as outlined in the Selecting Sampling Data section.

You should obtain the following types of information for each contaminated medium:

  • Specific contaminants identified at and near the site from on-site and off-site sampling data.
  • Contaminant concentrations found, including naturally occurring background levels (e.g., metals in soil).
  • Location and sample depth where contaminants were found (using maps when possible).
  • Dates when samples were collected.
  • Time of day for shallow groundwater and indication if there are any known tidal influences.
  • Indication if any samples were taken concurrently.
  • Sampling collection and analysis methods used, including detection limits.
  • Field measurements, such as conductivity and field pH of monitoring and water supply wells.
  • Quality assurance/quality control (QA/QC) data to support the information obtained is adequate for assessing possible human exposures.
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Learn about key environmental contamination information to collect.

Exposure Pathways

Because harmful health impacts can only occur if people are exposed to contaminantsyou will use much of the information you seek to address aspects of the exposure pathway evaluationincluding determining the presence or absence of each of the five components of a potential or completed exposure pathway shown in the diagram below and discussed in the Exposure Pathways Evaluation section.

Exposure Pathway Elements diagram

For a detailed description of the image click here.

You can gather much of the information about the contaminant source, the fate and transport in affected media, exposure point, exposure route, and potentially exposed populations through your review of site background information. The fate and transport of contaminants in the environment (how contaminants get from a source to a potentially exposed population) influence, if not dictate, exposure routes. Fate- and transport-related information varies somewhat from one medium to another and may include the following: 

  • Topography: The relative steepness of slopes and elevation of the site may affect the direction and rate of water runoff, rate of soil erosion, and potential for flooding.  
  • Soil types and locations: Can influence percolation, groundwater recharge, contaminant release, and transport rates. 
  • Ground cover/vegetation: Greatly influences the rates of rainwater infiltration and evaporation and soil erosion, as well as the accessibility of contaminants to people. 
  • Local climate conditions: Affect the amount of moisture contained in the soil and the amount of percolation, as well as the water runoff and groundwater recharge rates. Temperature conditions affect contaminant volatilization rates and the frequency of outdoor human activity.  
  • Meteorological factors: Can influence dispersion and volatilization of airborne contaminants and soil erosion rates. 
  • Groundwater hydrology and geologic composition: Affect the direction and extent of contaminant transport in groundwater. 
  • Locations of surface-water bodies and their current/future use: Can significantly affect the migration of contaminants off the site and into other media. 
  • Frequency of flooding events: Can significantly affect the contaminant migration off the site and into other media. 
  • Building factors: Building foundation, construction, air exchange rates, drains, sump pumps, and plumbing can affect vapor intrusion. 
  • Land use: Past, current, and future land use can affect how or if people are or could be exposed in the area under investigation. 
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Learn about common types of contaminant fate and transport information to collect.

Contaminant-Specific Information

After you review the site-specific information and gain an understanding of what hazardous contaminants are present, you may seek information on contaminant-specific properties to support your scientific evaluations (Exposure Pathways Evaluation, Screening Analysis, EPC and Exposure Calculations, and In-Depth Toxicological Effects Analysis).

Specifically, you may need the following: 

  • General information on the chemical and physical properties of environmental contaminants within the media of concern. 
  • Contaminant-specific toxicologic and epidemiologic data. 
  • General information on biologic and physiologic effects of different contaminants.  

Work with toxicologists, epidemiologists, hydrologists, and other specialists to use this information as you evaluate the nature and extent of contamination and the likelihood of harmful health effects.  

ATSDR's PHAT Module 7

ATSDR’s PHAT Module 7 provides criteria to help you decide whether and what health outcome data you should obtain. The link below will take you to the module’s registration page in CDC TRAIN.


ATSDR's Toxicological Profiles

ATSDR’s Toxicological Profiles provide comprehensive evaluations and interpretations of available toxicological and epidemiological information on hundreds of hazardous substances.