Incremental Sampling

I attended the 1st of the four part Clu-In training titled: "Incremental-Composite Sampling Designs for Surface Soil Analyses”

The main purpose of Incremental-Composite Sampling is to provide a method that will:

· Statistically reduce the variability of results because of the heterogeneous nature of soils

· Provide a more accurate mean of an area known as the “Decision Unit”

· Address grain size / contamination relationship.

How is it done?

First, one must develop a sampling plan that will address the goals of the study and the needs for risk assessment. Items that must be addressed in the sampling plan are:

· Sample areas – Sites are divided into smaller units known as “Decision Units”. The Decision Unit can be subdivided into “Sample Units”. See slide 67 of the 2/16/12 webinar – link provided below.

· Sample locations are calculated utilizing statistical software such as Visual Sample Plan (Free DOE & EPA funded software package)

· Target grain size. Studies have shown that there is an inverse relationship between grain size and concentrations of contamination. The smaller the grain size of the sample, the higher the contamination. See slides 32-29 of the 2/16/12 webinar – link provided below.

· Depth of sample, cross section of sample, and volume of each sample.

· How samples will be prepared and composited.

Second is the fieldwork. This will vary from project to project but here is a quick summary:

· Lay out sample points as described in the sampling plan

· Collect each sample

· Dry each sample, break it up, sieve to the correct grain size, homogenize, and collect the part of the sample to be composited. (Note: this may be done in the field or lab)

Advantages:

· Better data.

· Less chance of results at the extremes of the data population.

· Less cost because there are fewer samples run.

· If you use sample units within the decision unit and the decision unit fails, you can then run the samples for the sample units to determine the area that need to be addressed. See slide 67.

Disadvantages:

· More cost per sample submitted to laboratory because of the prep.

· Limited use for VOCs, although Alaska and Hawaii include volatile organics in state specific ISM guidance documents.

· Currently used for surface soils. Although it could be used for various soil depths / horizons.

Resources:

Archives of the 4 Incremental-Composite Sampling Designs for Surface Soil Analyses webinar

Other Resources