Quality of Groundwater Used for Public Supply in the Continental United States: A Comprehensive Assessment

The presence of contaminants in a source water can constrain
its
suitability for drinking. The quality of groundwater used for public
supply was assessed in 25 principal aquifers (PAs) that account for
84% of groundwater pumped for public supply in the U.S. (89.6 million
people on a proportional basis). Each PA was sampled across its lateral
extent using an equal-area grid, typically with 60 wells per PA. Samples
were analyzed for 502 constituents, of which 374 had either a regulatory
or nonregulatory human health benchmark (HHB). Nationally, elevated
concentrations (relative to HHBs) of geogenic constituents have a
larger effect than anthropogenic constituents, as indicated by three
metrics: detection frequency, 35% versus 8.1%; prevalence (based on
area), 41% versus 6.4%; and population potentially affected, 31.2
million versus 7.1 million. Prevalence of any constituent at elevated
concentrations was high40 to 75%in PAs comprising
unconsolidated sediment (eight PAs) and sandstone or interbedded sandstones
and carbonates (four PAs) in the West and Central Interior. Prevalence
was lower15 to 35%in PAs comprising sediment and sedimentary
rocks along the Gulf and Atlantic Coasts (four PAs), carbonates distributed
across the continental U.S. (seven PAs), and hard rock (two PAs).

源水中污染物的存在会限制其作为饮用水的适用性。针对美国公共供水系统使用的地下水水质，本研究对25个主要含水层（Principal Aquifers，PA）开展了评估，这些含水层的地下水抽取量占美国公共供水地下水总抽取量的84%，按人口比例折算的受益人口达8960万。每个主要含水层均采用等面积网格采样法，在其横向延展范围内布设采样点，每个含水层通常设置60口监测井。对采集的样本开展了502项组分分析，其中374项组分对应有监管类或非监管类人类健康基准值（Human Health Benchmark，HHB）。从全国范围来看，相较于人为源组分，天然成因组分浓度超标（相对于人类健康基准值）的影响更为显著，该结论可通过三项评价指标得以验证：检出频率分别为35%与8.1%、面积占比分别为41%与6.4%、潜在受影响人口数分别为3120万与710万。在西部与中部内陆地区，由未固结沉积物（8个主要含水层）、砂岩或互层砂岩与碳酸盐岩构成的主要含水层（4个）中，任意组分浓度超标的流行率较高，达40%至75%。而在墨西哥湾与大西洋沿岸的沉积物与沉积岩含水层（4个）、分布于美国本土的碳酸盐岩含水层（7个）以及硬岩含水层（2个）中，该流行率相对较低，为15%至35%。