Expanded Preliminary Assessment Sampling Plan Guidance

SAMPLING OBJECTIVES AND RATIONALE

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:

Soil

• 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.

Groundwater

• 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.

Air

• 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.

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