Incremental sampling methodology for petroleum hydrocarbon contaminated soils: volume estimates and remediation strategies
Current environmental assessments for petroleum hydrocarbon (PHC) contaminated sites are dependent on discrete soil sampling to estimate the degree and extent of contamination, leading to unreliable and non-reproducible results. Incremental sampling methodology (ISM) involves collecting and combining samples within a targeted area and holds promise for being a cost-effective, representative, and reproducible sampling strategy for contaminated site characterization. We hypothesized that traditional Phase II Environmental Site Assessments (ESA) discrete and ISM sampling protocols were not mutually exclusive, and the two approaches can be used to formulate a responsible land management strategy. Results gathered through ISM were compared to those from Phase II ESA for two PHC contaminated sites in Canada. Both methods indicated the sites were impacted with PHC beyond Saskatchewan Tier I guidance, however, the delineation of the PHC plume differed by as much as 75% for the heavier hydrocarbons. The Phase II ESA methods had higher incidences of false positive results and an overestimation of contamination at depth. A laboratory experiment confirmed that ISM does not “dilute” the samples as to cause underestimation, whereby the hydrocarbon concentrations for a single combined sample was equivalent to the mean of 30 discrete samples. Based on our results, sites should undergo risk assessment based on the estimates of the Phase II ESA results using vapor phase logs to estimate contaminant extent. If exposure pathways cannot be eliminated through the risk assessment process, remediation planning based on the ISM results is justified given the demonstrated cost-effectiveness, representativeness, and reproducibility.