Incremental sampling methodology for petroleum hydrocarbon contaminated soils: volume estimates and remediation strategies

Abstract

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.

Soil Buffering Capacity Can Be Used To Optimize Biostimulation of Psychrotrophic Hydrocarbon Remediation

“…To better replicate field conditions, intact soil columns can be used . Incremental sampling approaches can help obtain more representative samples for chemical and genomic analysis − though methods to link activity in soil volumes 10 billion times larger than a genomic sample are needed.…”

Assessing Space, Time, and Remediation Contribution to Soil Pollutant Variation near the Detection Limit Using Hurdle Models to Account for a Large Proportion of Nondetectable Results

“…During the three years, there were a total of 33 cores for Site 1, 37 cores for Site 2, 27 cores for Site 3, and 31 cores for Site 4 (SI Table S2 and Figure S1). For each core, soils were cut into different horizontal layers based on soil saturation, texture changes, and previously recorded contaminated layers to analyze the PHC concentration; soil samples were collected using an incremental sampling methodology . Benzene, toluene, ethylbenzene, and xylenes (BTEX) were analyzed according to Canadian Environmental Quality Guidelines protocols which briefly are (i) extract fresh soils with methanol; (ii) mix the methanol extractant with water; (iii) analyze the headspace for BTEX using gas chromatography equipped with a flame ionization detector (FID) (Bruker, SCION 436-GC).…”

“…Over a three year period, a biostimulatory solution (mainly nutrients and electron acceptors) was injected underground to increase microbial activity . Each year, approximately nine boreholes were drilled to assess the effect of biostimulation, and incremental sampling methodology was used to obtain a reliable estimate of soil pollutant concentrations . Laboratory analyses of soil benzene concentration showed a large proportion of soil concentrations that were below DL.…”

“…14 Each year, approximately nine boreholes were drilled to assess the effect of biostimulation, and incremental sampling methodology was used to obtain a reliable estimate of soil pollutant concentrations. 15 Laboratory analyses of soil benzene concentration showed a large proportion of soil concentrations that were below DL. We used this, fairly typical, industrial style data set to evaluate if gamma-based models are a practical and reasonable approach to estimate biostimulation success at concentrations near DL but still above environmental criteria.…”