Abstract The United States Environmental Protection Agency (USEPA) is responsible for overseeing the cleanup of sites that fall within the jurisdiction of the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA; also known as “Superfund”). This process almost always involves a remedial investigation/feasibility (RI/FS) study, including deriving upper confidence, prediction, and/or tolerance limits based on concentrations from a designated “background” area which are subsequently used to determine whether a remediated site has achieved compliance. Past USEPA guidance states outlying observations in the background data should not be removed based solely on statistical tests, but rather on some scientific or quality assurance basis. However, recent USEPA guidance states “extreme” outliers, based on tests that assume a normal (Gaussian) distribution, should always be removed from background data, and because “extreme” is not defined, USEPA has interpreted this to mean all outliers identified by a test should be removed. This article discusses problems with current USEPA guidance and how it contradicts past guidance, and illustrates USEPA’s current policy via a case study of the Portland, Oregon Harbor Superfund site. Additional materials, including R code, data, and documentation of correspondence are available in the online supplement.

中文翻译：

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EPA规定正态分布

摘要美国环境保护局（USEPA）负责监督《综合环境响应，赔偿和责任法》（CERCLA；也称为“超级基金”）管辖范围内的场地的清理工作。此过程几乎总是涉及补救调查/可行性（RI / FS）研究，包括根据来自指定“背景”区域的浓度得出较高的置信度，预测和/或公差极限，随后将其用于确定补救站点是否具有实现了合规性。过去的USEPA指南指出，不应仅基于统计测试，而应基于某些科学或质量保证来删除背景数据中的异常观察值。但是，最近的USEPA指南规定了“极端”异常值，基于假定正态分布（高斯分布）的测试，应始终将其从背景数据中删除，并且由于未定义“极端”，因此USEPA将其解释为意味着应删除由测试确定的所有异常值。本文讨论了现行USEPA指南存在的问题以及它与过去的指南相矛盾的地方，并通过对俄勒冈州波特兰市港口超级基金站点的案例研究来说明USEPA的当前政策。在线补充资料中提供了其他材料，包括R代码，数据和通信文档。并通过俄勒冈州波特兰市港口超级基金站点的案例研究说明了USEPA的现行政策。在线补充资料中提供了其他材料，包括R代码，数据和通信文档。并通过俄勒冈州波特兰市港口超级基金站点的案例研究说明了USEPA的现行政策。在线补充资料中提供了其他材料，包括R代码，数据和通信文档。