目前，美国20%的用水量来自地下水，地下水的污染正在引起相当大的警惕。在人口稠密的皮尔斯县中部（华盛顿州），发现地下水污染源于化粪池排水场。地下水中最高的硝酸盐和大肠菌群浓度出现在渗透性降雨溶解并向下淋滤这些污染物时。包括7个参考图表。

Currently 20 percent of US water consumption is supplied by groundwater, and its contamination is causing considerable alarm. In densely populated Central Pierce County (Wash.), groundwater contamination was found to originate from septic tank drainfields. The highest nitrate and coliform concentrations in groundwater occur when infiltrating rainfall dissolves and leaches these contaminants downward. Includes 7 references charts graphs tables.