Site Assessment Program 

Expanded Preliminary Assessment Sampling Plan Guidance

The purpose of a Preliminary Assessment or PA Equivalent is to determine whether a site is releasing, has released, or could release hazardous substances to the environment, and whether a response action is required. Occasionally, however, following the completion of a PA or PAE there is insufficient information available to make such determinations about a site. In such cases, an Expanded Preliminary Assessment can be a useful means to gather the additional data needed to formulate the further-action conclusions that are expected from PA-level investigations. While XPAs typically involve the collection of samples to obtain information about the presence, type, or magnitude of contamination at a site, they are not remedial investigations, and are not designed to fully characterize site contamination.

There are two parts to an XPA investigation: preparing a sampling plan and producing the XPA report. DEQ has developed two guidance documents to explain these two parts of the XPA: this document, which covers XPA sampling plans, and the XPA Report Guidance.

The purpose of an XPA sample plan is to:

1. Document data gaps needed to complete a traditional PA-level evaluation at a site, based on review of the completed PA (or PA equivalent) and any new information about the site;
2. Formulate a sampling and analysis strategy to eliminate these data gaps, and;
3. Describe procedures to be used for sampling and analysis, ensuring that they meet DEQ quality assurance/quality control objectives.

As mentioned above, XPA sampling is typically performed to identify or further characterize sources of hazardous substances at a site, and determine if a release from these sources has contaminated soil, groundwater, surface water, or air.

At a minimum, the XPA sample plan should include the elements listed below, preferably using the format shown below. Note that site-specific considerations and information needs may require additional sample plan elements.

The following links explain the structure and content of a DEQ XPA sampling plan.

• Introduction and Site Background/Apparent Problem
• Sampling Objectives and Rationale
• Sampling and Analysis Plan
  • Summary of Sampling and Lab Analyses
• Quality Assurance Plan

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