C.2.9 Conclusions and Recommendations

  • QC problems could cause ADEC to reject the data under some circumstances, such as closing the site to a human health–based threshold.

  • The random number generator worked well to establish 3-D, independent sampling coordinates. A simpler method, and equally effective, would be to generate a random location for the first cell and apply that coordinate to all other cells.

  • Even though the stockpile was shallow and had been periodically mixed, the MI sampling guidance was strictly followed to ensure that the top 6 inches was not sampled. This should be standard practice, even for shallow, well-tilled stockpiles.

  • While 20-penny galvanized nails worked to establish the field grid, they pulled out too easily; wooden stakes would have performed better. For large DUs, cell corner stakes would be sufficient rather than delineating the entire grid with twine.

  • To minimize field time, QC for properly designed MI sampling could possibly be reduced for low-risk petroleum sites where concentrations are expected to be well below levels that may be a human health concern. Examples are direct contact and inhalation where migration to groundwater is not a concern or where groundwater is already being monitored. The merits of this recommendation will be evaluated at the end of the 2007 field season.

  • Proper sampling oversight can best be achieved by the third-party contractor directly employed by the responsible party. For this reason, a contractor may wish to conduct subsampling in a controlled environment prior to shipment to the selected laboratory. The merits of this recommendation will be evaluated at the end of the 2007 field season.

  • Sieving wet soil is problematic. Although holding times and temperatures should be maintained to the extent practicable, contaminants such as weathered diesel are not expected to significantly degrade. Air-drying prior to sieving may therefore be justified for DRO and residual-range organics in some cases, particularly at lower-risk sites. If volatile contaminants are a concern, separate samples should be collected according to procedures in the guidance. The merits of air-drying prior to sieving will be evaluated at the end of the 2007 field season.

  • At sites where the action level is human health direct contact or inhalation, where migration to groundwater is a significant issue, or where another exposure pathway is a potentially significant concern, splitting each increment subsample as an additional laboratory QC measure may be prudent. FE, RSD, and 95% UCL calculations can be independently performed on the two data sets; archived lab samples could be evaluated if there are significant differences. The merits of this recommendation will be evaluated at the end of the 2007 field season.