A Critical Review of Discrete Soil Sample Data Reliability: Part 1 – Field Study Results

Part 1 of this study summarizes data for a field investigation of contaminant concentration variability within individual, discrete soil samples (<i>intra-sample</i> variability) and between closely spaced, “co-located” samples (<i>inter-sample</i> variability). Hundreds of discrete samples were collected from three sites known respectively to be contaminated with arsenic, lead, and polychlorinated biphenyls. <i>Intra-sample</i> variability was assessed by testing soil from ten points within a minimally disturbed sample collected at each of 24 grid points. <i>Inter-sample</i> variability was assessed by testing five co-located samples collected within a 0.5 m diameter of each grid point. <i>Multi Increment</i> soil samples (triplicates) were collected at each study site for comparison. The study data demonstrate that the concentration of a contaminant reported for a given discrete soil sample is largely random within a relatively narrow (max:min &lt;2X) to a very wide (max:min &gt;100X) range of possibilities at any given sample collection point. The magnitude of variability depends in part on the contaminant type and the nature of the release. The study highlights the unavoidable randomness of contaminant concentrations reported discrete soil samples and the unavoidable error and inefficiency associated with the use of discrete soil sample data for decision making in environmental investigations.

本研究第一部分总结了针对单个离散土壤样品内（intra-sample）污染物浓度变异性，以及间距极近的“同位（co-located）”样品间（inter-sample）污染物浓度变异性的野外调查数据集。研究人员分别从已知受砷、铅与多氯联苯污染的三个场地采集了数百份离散土壤样品。样本内变异性通过对24个采样点各采集的一份轻度扰动土壤样品内的10个点位开展检测进行评估；样本间变异性则通过对每个采样点直径0.5米范围内采集的5份同位样品开展检测进行评估。各研究场地均采集了多增量（Multi Increment）土壤样品（三份平行样）用于对照分析。本研究数据表明，针对任意给定采样点的单份离散土壤样品所报告的污染物浓度，在较窄（最大值:最小值<2倍）至极宽（最大值:最小值>100倍）的区间内均呈现显著随机性。变异性的大小一定程度上取决于污染物类型与污染物释放的性质。本研究凸显了单份离散土壤样品所报告的污染物浓度不可避免的随机性，以及利用此类离散土壤样品数据开展环境调查决策时必然存在的误差与低效性。