5.4 Field Handling of ISM Samples

5.4.1 ISM Samples for Non-VOCs

It is recommended that all ISM sample processing be performed in a controlled laboratory setting to minimize sampling errors.ISM sample processing techniques, such as milling and representative subsampling, are designed to ensure that the (typically small) mass of sample analyzed by the laboratory is representative of the DU or SU from which it was collected. These techniques reduce data variability as compared with conventional sample handling and processing approaches. However, these techniques introduce some amount of sampling error. It is recommended that all ISM sample processing be performed in a controlled laboratory setting to minimize these sampling errors. However, depending on site logistics, the type of soil, the total number and/or mass of ISM samples, etc., sample processing can be initiated in the field for some contaminants (e.g., SVOCs, pesticides, PCBs, and metals) with appropriate cautions as noted below.

Moist samples may need to be air-dried to facilitate sieving in an appropriate dust-free location where temperatures and ultraviolet (UV) light are not expected to cause degradation of COPCs. Samples with little vegetation and composed mostly of sands and silts that naturally have a very low moisture content and soils that have been air-dried can be sieved (typically using a #10 sieve, <2 mm particle size) in the field to remove pebbles and vegetative debris. Prior to air-drying or sieving or both, the field-moist sample weight should be recorded if specified in the SAP. The <2 mm soil particles are generally considered “soil,” while larger particles are considered gravel, rocks, or other materials (e.g., sticks and roots). Additionally, field sieving is an option that allows the user to calculate the mass of an bulk ISM sample needed to meet DQO requirements (including FE, see Hyperlink 14 and Hyperlink 18), based on the soil particle size. Although sieving to the <2 mm particle size is typical, there may be contaminant investigations or analyses where alternative particle sizes may be of interest. In these cases, the rationale for sieving to other specific particle sizes and associated changes to lab processing/analysis should be clearly discussed in the SAP. Unless field subsampling will be performed (see paragraphs below), the entire sieved ISM sample fraction should be submitted to the laboratory for appropriate processing and subsampling.

When dealing with contaminants that have been deposited as solid particulates (e.g., energetics, metals at firing ranges, etc.), field subsampling is not recommended. Studies on energetics have shown that representative subsampling prior to grinding is problematic and likely not possible (Hewitt et al. 2009). In cases where sieving is conducted in the field to obtain a targeted particle size (particle size selection), the entire sieved ISM sample should be ground prior to subsampling (if particle size reduction is part of the SAP). Similar studies evaluating field subsampling for contaminants deposited as liquids (e.g., fuels, solvents, etc.) are not available at this time.

The SAP may specify particle size selection (sieving) and subsampling in the field for the analysis of SVOCs and specific metals. This procedure constitutes, or is similar to, the normal laboratory subsampling step. It should be reiterated that it is recommended that all ISM sample processing be performed in a controlled laboratory setting.

If field subsampling is to be performed, the entire ISM sample should be air-dried (only if necessary) and sieved to the predetermined particle size (typically using a #10 sieve, <2 mm particle size). The sieved ISM sample should be spread out in a thin layer on a clean surface, e.g., a large, disposable, aluminum baking pan, allowing the entire sample to be accessed. A subsample is then obtained by removing 30 or more equal increments from systematic random locations (see Figure 5-5). The increments collected to form the subsample sample should equally represent the top and bottom of the processed material. This is achieved by using a rectangular, flat-bottom sampling tool with sides and a minimum 16 mm width (see Figure 5-9), as opposed to one that is curved or spoon-shaped (see Figure 5-10). Spoon-shaped sampling tools bias the mass of soil collected.

Examples of rectangular and flat-bottom sampling tools.

Figure 5-9. Examples of rectangular and flat-bottom sampling tools.

Example of subsample being collected in the field.

Figure 5-10. Example of subsample being collected in the field.

The mass of sample required for the analytical test or tests is used to determine the mass of each of the 30 or more increments. For example, if a mass of 30 g is required for the analytical extraction and analysis, 30 separate ~1 g increments are collected from systematic random locations. Depending on the project DQOs, replicates of the field processed soil should be collected and submitted for analysis to evaluate the precision of the ISM field processing procedure. The entire submitted subsample mass must be prepared for analysis due to possible particle size discrimination during sample transit (e.g., fines settling to the bottom of the sample container). If the entire contents of the submitted container are not to be analyzed, the laboratory must use proper techniques to ensure a representative particle size subsample is used for analysis. Laboratory replicates should be analyzed to evaluate the precision of the laboratory subsampling procedure. Refer to Section describing analytical subsampling techniques and specifically the description of 2-D Japanese slabcake sampling.

Simply dividing an ISM sample (sieved or not) into separate volumes and placing each volume into separate sample containers for analysis is not an acceptable method of mass reduction. Likewise, manually mixing samples (i.e., “homogenizing”) in the field or lab may just serve to further segregate different particle sizes, because particles may settle in layers by weight or size during mixing. The process of spreading the entire sample out to a thin layer and collecting many increments in a systematic random fashion with a tool that can scoop to the bottom of the sample is the best way to collect a representative subsample of all the different sizes and types of soil particles present in the ISM sample.

If ISM processing and/or subsampling is performed in the field, subsampling replicates are recommended to evaluate precision.

Finally, if ISM sample processing and subsampling is performed in the field, it is recommended that at a minimum of three replicate subsamples be collected and submitted to the laboratory for analysis. The subsampling (as described above) process is repeated on one ISM sample to form replicates. The replicate results are used to evaluate the precision of the field processing and subsampling. Note that the subsampling replicates should be collected in addition to the ISM field replicates described in Section 5.3.5.

Limitations to the field processing of ISM samples include the following:

  • not recommended for contaminants deposited as solid particulates (e.g., energetics, metals at firing ranges, etc.)
  • lack of commercially available, correct subsampling tools (e.g., 16 mm wide, flat-bottom scoop with sides)
  • requires a controlled environment to air-dry, sieve, and subsample, if necessary, to minimize the potential loss or introduction of COCs during processing
  • additional subsampling replicates need to be collected and analyzed to evaluate precision
  • more knowledgeable/trained field personnel required