2001年1月，《联邦公报》公布了砷规则。这一规则后来被美国环境保护局（EPA）撤销，以供进一步审查。该规则规定，社区和非瞬态非社区（NTNC）水系统的饮用水中砷的最大污染物水平（MCL）为10 ug/L。受这一规则影响的水系统中，99%以上依赖地下水。尽管颁布推迟，但据报道，砷规则仍将于2006年生效。在接下来的几年里，将有大量研究开发简单且成本效益高的饮用水中砷去除处理技术。尽管技术有所改进，但从地下水中去除砷的成本仍然很高。 本文的目的是概述砷的地质和地球化学，以便公用事业可以考虑非治疗方案时遵守砷规则。在美国各地的地下水中发现砷的浓度高于最近提出的MCL。这些超过10微克/升的系统中有很大一部分位于美国西部，该地区被定义为最西部的11个州。尽管本文主要关注这些州的地质情况，但从工业中西部到新英格兰部分地区，美国许多其他地区的地下水砷浓度超过10 ug/L。包括24篇参考文献、表格和图表。

In January 2001, the Arsenic Rule was published in the Federal Register. This rule, which has since been rescinded for further review by the United States Environmental Protection Agency (EPA), established a maximum contaminant level (MCL) of 10 ug/L for arsenic in drinking water for both community and non-transient non-community (NTNC) water systems. More than 99 percent of the water systems affected by this rule depend upon groundwater. Despite the delay in promulgation, the Arsenic Rule will reportedly still come into effect in 2006. In the intervening years, there will be a great deal of research into developing simple and cost effective treatment technologies for arsenic removal from drinking water. Despite the technological improvements, it will still be costly to remove arsenic from groundwater. The purpose of this paper is to outline the geology and geochemistry of arsenic, so that utilities may consider non-treatment alternatives when complying with the Arsenic Rule.Arsenic has been found in groundwaters throughout the United States in concentrations higher than the most recently proposed MCL. A large percentage of these systems that exceed 10 ug/L are in the Western United States, which is defined as the eleven most western states. Although this paper focuses on the geology of these states, many other regions of the United States,from the industrial Midwest to parts of New England, have groundwaters with arsenic concentrations greater than 10 ug/L. Includes 24 references, table, figures.