Integration of Incremental and Discrete Sampling Methods to Optimize Site Investigation and Remediation

摘要

Background/Objectives. Recent advancements in methods, tools, and training in the application of incremental sampling methods (ISM) have prompted investigators to more closely examine tradeoffs between discrete and ISM sampling protocols for site investigation and remediation. ISM is a structured composite sampling approach that applies protocols that differ from discrete sampling both in the field and the laboratory. ISM yields estimates of the mean concentration of a chemical of concern (COC) through a physical process (compositing), whereas discrete sampling yields estimates of the mean by a mathematical process (calculation of the arithmetic mean of analytical results). In the field, ISM yields a tighter grid of samples and greater sample volume than conventional discrete protocols, thereby increasing the probability that areas of high and low concentrations within a defined decision unit (DU) are proportionately represented in the estimate of the mean. In the laboratory, ISM involves additional steps to process and subsample material to further reduce errors in the estimate of the mean. Because ISM does not provide the spatial resolution of concentrations within a DU that is afforded by discrete sampling, critical decision points become the sizing and placement of DUs and regulatory constraints on the definition of action levels as area-wide averages or “not-toexceed” concentrations. Based on nearly a decade of employing both ISM and discrete sampling at contaminated sites, we demonstrate a hybrid approach that utilizes both ISM and discrete sampling to address multiple study objectives in a cost-effective manner.