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The Preliminary Assessment/Site Inspection (PA/SI) phase evaluates site conditions to determine if further action is warranted under the CERCLA process. The PA/SI is typically initiated when the Department of the Navy (DON) discovers a potential waste disposal operation or a potential release at a site. 

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The PA identifies contaminated sites based primarily on the review of existing information about hazardous substance disposal practices at an installation. If the PA demonstrates evidence that a potential release or waste disposal has occurred at the site, an SI is conducted to gather field data to determine the nature of any releases and potential threat to any receptors. The majority of DON Environmental Restoration Program (ERP) sites have completed the PA/SI phase. However, new PA/SI evaluations can be initiated to address evolving issues (e.g., emerging contaminants). For these more recent PA/SIs, the United States Environmental Protection Agency (EPA) guidance encourages combined PA/SI activities (OSWER 9375.2-10FS) or conducting Integrated Assessments (IAs) to reduce repetitive efforts (OSWER 9360.0-39FS).

Preliminary Assessment

The PA compiles existing information to assess potential releases, contaminant migration pathways, and potential receptors. This information helps to formulate a preliminary conceptual site model (CSM). The PA establishes if further action is warranted or if the site should be designated as requiring no further action (NFA). The outcome of the PA may also result in a removal action to address imminent threats and/or the site may be recommended for further evaluation.

Site Inspection

The SI is needed if the PA demonstrates evidence of a potential release. The SI is an investigation intended to gather more information to characterize the nature of potential releases and associated risks to human health and the environment. The SI phase typically includes limited site sampling of various media to document the presence of contaminants, but does not fully delineate their extent. The SI must follow the Department of the Navy’s (DON’s) Systematic Planning requirements including the preparation of an approved Sampling and Analysis Plan (SAP) in accordance with the Uniform Federal Policy for Quality Assurance Project Plans (UFP-QAPP).

After the PA/SI is complete, the next step in the process depends on the outcome: 

  • For sites that do not pose an unacceptable risk or where a removal action fully addresses the issue, the DON designates these sites for NFA and Site Closeout (SC). The DON Remedial Project Managers (RPM) should obtain concurrence on the NFA designation from the appropriate regulatory authority in the form of a letter or signature on a technical report.
  • For sites requiring further evaluation, the site proceeds to the Remedial Investigation and Feasibility Study (RI/FS) phase. DON determines whether the site will be considered a new site or incorporated into an existing site.
  • In addition, the EPA uses the PA/SI information for input into the Hazard Ranking System (HRS) to determine eligibility for placement on the National Priorities List (NPL). 


For more information, Chapter 6 of the DON Environmental Restoration Program Manual details PA/SI considerations.



Title and Description

ERP Manual

DON Environmental Restoration Program Manual: Chapter 6 PA/SI (February 2018)

Describes the steps taken to advance an ERP site through the PA/SI phase.

Site Closeout

DON Guidance to Documenting Milestones Throughout the Site Closeout Process (March 2006)

Outlines a consistent approach for documenting specific milestones for achieving site closeout.


Title and Description



NAVFAC CSM Checklist - Terrestrial & Groundwater (January 2013)

Provides a checklist of key elements to consider for terrestrial and groundwater sites.



NAVFAC CSM Checklist - Munitions (January 2013)

Provides a checklist of key elements to consider for munitions response sites.



NAVFAC CSM Checklist - Sediment & Surface Water (January 2013)

Provides a checklist of key elements to consider for sediment and surface water sites.


Vapor Intrusion

NAVFAC CSM Checklist - Vapor Intrusion (VI) (October 2012)

Provides a checklist of key elements to consider for VI sites.


Title and Description

Hazard Ranking System 

EPA Hazard Ranking System (HRS)

A numerically-based screening system that uses information from the PA/SI to assess the relative potential of sites to pose a threat to human health or the environment.

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