C.2.8 Discussion

Although the stockpile was shallow, it was compacted and difficult to excavate by hand. Field sampling was therefore labor-intensive, requiring approximately 15 person-hours to complete.

Data quality may have been affected by three factors:

  • Bulk samples were not cooled for shipping; hydrocarbon degradation due to an increase in microbial activity may have occurred.
  • The initial attempt at subsampling was challenging due to high soil moisture content, which caused clumping and clogged the #10 sieve. The next five subsamples were collected after first air-drying the remaining bulk samples; however, data comparability is assumed because of the requirement to report on a dry-weight basis.
  • The 14-day holding time and sample temperatures were exceeded. The increased microbial activity due to elevated temperatures may have biased sample results low.

FE is a result of not representing proportional concentrations of all particles in the population. Adequate mass (30 g) and a maximum particle size of 2 mm control FE. As expected, the FE for each of the samples was well below the required 15% since the particle size was ≤2 mm and the sample masses were >30 g.

RSD is a measure of data precision and is used as a QC measure to assess the MI sampling procedure and the mean concentration of the DU. The RSD calculations were 18.9% for Samples #1 and 23.7% for Samples #2. The RSD limit for a normal distribution is about 30%; therefore, one can be confident that the MI sampling results are representative.

The 95% UCL for Samples #1 was 176 and for Samples #2 was 157, indicating that the DRO cleanup level of 230 mg/kg has been met.