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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 topics explain the structure and content of a DEQ XPA sampling plan.


Discuss what site is being investigated, who will perform the sampling, and for what purpose the site is being investigated.


Describe the physical character and setting of the site. Include a brief discussion of site location, size, operational history, and apparent problems. Summarize all critical information presented in the PA or other documents that will provide background and justification for the proposed sampling and analytical regime, including explanation of pathways that will be addressed. Include a site location map in this section.

Sampling Objectives

Describe what data gaps and pathway factors you expect the sampling to address. For example:

One sampling objective at the XYZ site is to determine the identity and concentrations of hazardous compounds suspected to be present in stained surface soils in Area A. Sampling results will be used to determine the threat this source may pose to groundwater and surface water via migration, and to the nearby population by direct contact.

Sampling Rationale

Explain the reasoning behind proposed sample locations, number of samples, types of analyses, etc. For example:

The area of stained soil is small and homogeneous, so that two surface soil samples are expected to be sufficient to characterize this contamination. Because staining appears to be restricted to the top 2 inches of soil, no subsurface samples will be collected. The samples will be spaced to provide maximum coverage of the stained area. Soil contaminants are thought to be phenol-based (associated with past plywood gluing operations); therefore, samples will be analyzed only for base/neutral extractables (BNAs).

For QA/QC purposes, DEQ will collect a duplicate of whichever of the two samples appears to be most contaminated at the time of sampling. DEQ will collect one additional surface soil sample from an off-site location (within 1/8 mile of the site) to establish local background levels of BNAs.

Base sampling objectives and rationale on general factors such as operational history, hazardous substance usage, and waste handling practices at the site, as well as specific information such as visual identification of contamination, stressed vegetation, previous sampling results, and the characteristics of hazardous substances known or suspected to be present. The following is a listing of additional pathway-specific factors to consider in developing sampling objectives and rationale for each media:


  • Physical properties of soils: permeability and porosity, thickness;
  • chemical properties of soils: mineral/clay content, pH;
  • runoff and flood potential at and around site;
  • surface drainage patterns at site;
  • prevailing wind direction; and
  • amount and location of surface cover.


  • Physical and chemical properties of soils and underlying geologic materials;
  • local groundwater gradient and flow direction;
  • local hydrogeology: depth and horizontal extent of aquifers and aquitards;
  • presence of nearby groundwater wells: location, type, depth, pumping history, results of well sampling, potential hydraulic influence;
  • presence of other nearby potential hydraulic influences such as rivers or lakes;
  • known groundwater recharge or discharge areas; and
  • presence of nearby springs, seeps, or leachate.

Surface Water

  • Saturation rates for near-surface soils;
  • annual and 24-hour rainfall data;
  • runoff and flood potential at and around site;
  • past and present surface drainage patterns at the site;
  • location, size, use, etc. of nearby surface water bodies that could be affected by the release of contaminants from the site; and
  • amount and location of surface cover.


  • Prevailing wind patterns at the site;
  • particle size and organic content of surface soils;
  • moisture content of surface soils; and
  • amount and location of surface cover.

The Quality-Assurance Plan should discuss all of the following:

  1. data-quality objectives for precision, accuracy, and completeness, including description and frequency of QA/QC samples to be collected/analyzed, to assess data quality;
  2. data-quality assessment procedures; and
  3. data-quality reporting.

The following standards must be maintained during sampling and analysis to ensure that the data generated for the XPA meets DEQ data-quality objectives:


  • Collect background, duplicate, blank, etc. samples in percentages or numbers specified below in QA/QC SAMPLING GUIDELINES.
  • Use pre-cleaned equipment to perform all sampling , and follow sampling procedures specified in DEQ or EPA guidance.
  • Collect samples in pre-cleaned bottles; label, store, and transport the samples according to DEQ or EPA guidelines.
  • Maintain strict chain-of-custody from sample collection until the samples are received by the analytical laboratory.
  • Use field notes and photographs to document all sampling activities and any deviations from the original sampling plan.


  • All sample analyses must be performed within the holding time specified for each individual analysis; note any exceptions in the final report.
  • Laboratories must follow the individual protocols specified by EPA or DEQ for the analytical methods used.
  • Internal laboratory procedures such as lab blank and surrogate analysis will be performed as follows, unless otherwise requested by DEQ:
  1. all VOC or BNA samples will receive surrogate spike analysis; and
  2. matrix spike analysis will be performed on at least every 20th sample; if less
  3. than 20 samples are collected, at least one matrix spike analysis will be performed.
  • Labs must report results of all internal laboratory QA/QC procedures such as lab blank, matrix spike, and surrogate analyses.
  • In addition to analytical results, analytical data sheets generated by the laboratory for the XPA will each contain the following information: sample number and laboratory identification number, analysis method type or number, detection limits, and date of analysis.
  • The lab must document any problems it encounters regarding chain-of-custody, sample holding times, sample analyses, lab contamination, etc., and these must be discussed in the XPA report.
QA/QC Sampling Guidelines

Background Samples
Sampling to determine the background levels of naturally occurring and man-made chemicals should be carried out as part of any routine sampling program. Background areas should be removed from facilities that may have contributed contamination to the environment, and should be upgradient, upwind, and upstream of such facilities. These areas should also be near enough to the site to have similar topographical features and the same or very similar soil types. The parent material for the soil should be the same, if at all possible. Collect at least one background sample, when appropriate, for each sample matrix and parameter selected. Background samples should be preserved, packaged, and sealed the same way as any other sample. Assign a separate sample number to each background sample, and submit it "blind" to the laboratory.

Duplicate Samples
Duplicates are two identical samples collected at the same time from the same source, but placed in separate sample containers. The purpose of collecting a duplicate is to assess laboratory performance by comparing what should be identical results. Duplicate samples should be collected from areas of known or suspected contamination, and should make up at least 10 percent of samples from each sample matrix and every analytical group to be tested.

Blank Samples
Blanks are used to determine whether sampling equipment, sampling technique, or sample transport has induced contamination that is not actually present in the environment. When required, one blank sample should be collected per day. There are several types of blanks, as explained below.

  1. Equipment Blanks
    An equipment blank should be collected when sampling equipment is decontaminated and reused in the field, or when a sample collection vessel (bailer, beaker) will be used. Equipment blanks are designed to evaluate field sampling and decontamination procedures. These blanks are prepared by passing organic-free (for organics) or deionized water (for inorganics) through decontaminated sampling equipment before filling the sample bottles. One equipment blank should be prepared per day when equipment blanks are needed. Note that the use of dedicated sampling equipment eliminates the need for blanks.
  2. Field Blanks
    Collect this type of blank when equipment decontamination is not necessary and when a sample collection vessel will not be used (bailer, pump, etc.). The purpose of field blanks is to evaluate the general sampling environment. The field bottle blank should be poured at a sampling point. Use the appropriate "blank" water: organic-free water for organic parameters, and deionized water for inorganic parameters.
  3. Trip/Travel Blanks
    Trip or travel blanks evaluate potential sample contamination from volatile organic compounds (VOCs) that may be present in the air on-site or in sample shipping containers. A trip blank consists of laboratory distilled, deionized water in a closed container. The blank accompanies the empty sample bottles to the field as well as the samples returning to the lab for analysis; it is not opened until the lab analyzes it with the actual site samples. When needed, one trip blank should be prepared by the sample laboratory and analyzed upon return for each sampling event.

Laboratory QC Samples
Laboratory quality control (QC) samples should be collected and analyzed as part of standard laboratory protocols. A laboratory QC sample is not an extra sample, but consists of additional sample volume from specific sample locations where there is known or suspected contamination. For a given sample, this extra volume provides the laboratory with sufficient material to duplicate its analyses or conduct matrix spike analyses. Bottle labels, traffic reports, and chain-of-custody records for these samples must identify them as laboratory QC samples. Designate one field sample per week or one per 20 samples (including blanks and duplicates), whichever is greater, as the QC sample. It is good practice to check with the analytical laboratory regarding the additional sample volume required for laboratory QC samples prior to sampling.

Health and Safety Plan

Prepare a Health and Safety Plan with the XPA sample plan for all sites where DEQ personnel or persons performing contract work for DEQ will be involved in on-site activities. At a minimum, the Health and Safety Plan should:

  • Describe known site hazards and risks;
  • Identify appropriate levels of protective clothing and equipment for site work;
  • Describe decontamination procedures and means of handling, storing, and disposing of investigation-derived wastes;
  • Identify any special requirements or training needs, and verify that all staff participating in site work are adequately trained; and
  • Outline a contingency plan for emergencies.

The sampling and analysis plan (SAP) documents all sampling and analytical procedures to be performed. Describe all sampling activities by media. Include information on number of samples, type of samples (environmental, duplicate, etc.), sampling locations, methodologies, and equipment, and sample preservation techniques, if applicable. Describe what analyses are to be performed on each sample, including information such as EPA method number, detection limits, sample holding times, and any special analytical considerations.

The SAP should also include one or more maps of the facility that clearly indicate:

  • The location of all existing and proposed soil borings, surface samples, groundwater monitoring wells, surface drainage sampling points, and air sample points;
  • Important on-site structures, including tanks, sumps, catch basins, and pipelines;
  • The location of past spills, disposal areas, and other waste and product management areas; and
  • All pertinent structures adjacent to or near the site, such as drainage ditches, pipelines, roads, wells, and utility corridors.

The following information should be included in the SAP for all samples collected (by pathway):



  • number and locations of surface and subsurface samples
  • depth of any subsurface samples
  • type and category of samples (grab or composite; environmental, duplicate, or background)
  • sample collection methods and tools
  • equipment decontamination procedures
  • sample preservation techniques
  • types of sample containers to be used
  • collection/disposal of excavated soil, if necessary


  • analyses to be performed on each sample
  • EPA or other method reference number
  • detection limits
  • special analytical considerations

Sampling Existing Wells

  • number of samples
  • location of each sample, such as well number or location of well
  • type of samples (i.e., environmental, duplicate, trip blank)
  • screened interval of well being sampled
  • type of well being sampled (domestic, municipal, etc.)
  • well construction details, if known
  • purge methods and tools
  • sample collection methods and tools
  • sample filtration methods, if any
  • equipment decontamination procedures
  • sample preservation techniques
  • types of sample containers used
  • collection/disposal of purge water, if necessary

Installing and Sampling New Wells

In addition to the items listed above for sampling existing wells, include the following information in the SAP when the sampling plan calls for the installation of new wells:

  • proposed well locations
  • well construction details
  • well drilling and installation methods
  • well development and completion methods
  • decontamination of drilling equipment, casing, etc.
  • collection/disposal of drill cuttings and fluids, if necessary


  • analyses to be performed on each sample
  • EPA or other method reference number
  • detection limits
  • special analytical considerations
Surface Water


  • number and locations of samples
  • media sampled (water, sediment, or both)
  • depth of any sediment samples
  • type of samples (environmental, duplicate, etc.)
  • sample collection methods and tools
  • equipment decontamination procedures
  • sample preservation techniques
  • types of sample containers


  • analyses to be performed on each sample
  • EPA or other method reference number
  • detection limits
  • special analytical considerations


  • number and locations of samples
  • type of samples (i.e., environmental, collocated, filter blanks)
  • sample collection methods and tools
  • equipment decontamination procedures
  • special sampling handling procedures
  • predominant wind direction, diurnal wind shift
  • period of time to be sampled, volume of air to be sampled
  • filter type (PUF, cellulose fiber filter, etc.)
  • sample container
  • sample preservation techniques


  • analyses to be performed on each sample
  • EPA or other method reference number
  • detection limits
  • special analytical considerations

Prepare a table summarizing sampling and analysis information. Include sample ID, number of samples to be collected, sample type, analyses requested, method reference number, and detection limits.


For more information, contact 
the Environmental Cleanup Program 
or call 1-800-452-4011

To submit a report to DEQ, use Your DEQ Online.