Aelion C Marjorie, Conte Brian C
Department of Environmental Health Sciences and Marine Science Program, University of South Carolina, Columbia, South Carolina 29208, USA.
Environ Sci Technol. 2004 Mar 15;38(6):1648-53. doi: 10.1021/es030401p.
Water quality of residential wells is vital to public health and a complex issue for regulatory agencies. South Carolina, a typical southeastern rural state, has no required testing of residential well water quality after initial well construction. This study used site-selection criteria to identify susceptible residential wells based on a combination of geologic vulnerability and potential contaminant loading. Geologic vulnerability was defined as increased probability of contaminants being transported from the land surface into the groundwater based on geological properties. As a surrogate for potential general contaminant loading, wells were located within 800 m of an EPA Toxics Release Inventory facility reporting VOC emissions, thus sampling was nonrandom. Seventy private residential wells were sampled for volatile organic compounds (VOCs) and nitrate-nitrogen (NO3-N) and analyzed using gas chromatography/mass spectrometry and the cadmium reduction method, respectively. Geographic Information Systems (GIS) was used to quantify four explanatory variables that affect well susceptibility to nitrate: population density, land cover, local relief (percent slope), and soil texture. VOCs were detected in 11 wells, and two sites exceeded the MCL for 1,1-dichloroethylene (36.1 microg/L) and trichloroethylene (9.0 microg/L). Elevated NO3-N (defined as > or = 1.0 mg/L) was measured in 20 wells. Logistic regression identified grassland/cultivated land cover as a variable that significantly increased the probability of NO3-N contamination (p = 0.003). Using easily accessible databases to identify factors that increase the probability of groundwater pollution could lead to more effective programs for locating residential wells that are susceptible to contamination. Increased monitoring of well water quality, as is being considered in some states, is warranted to reduce potential human exposure to contaminated drinking water.
居民水井的水质对公众健康至关重要，也是监管机构面临的一个复杂问题。南卡罗来纳州是典型的东南部农村州，在水井初次建造后，并未要求对居民水井水质进行检测。本研究采用选址标准，基于地质脆弱性和潜在污染物负荷的综合因素来识别易受影响的居民水井。地质脆弱性被定义为基于地质特性，污染物从地表进入地下水的可能性增加。作为潜在一般污染物负荷的替代指标，水井位于美国环境保护局有毒物质排放清单设施800米范围内，该设施报告挥发性有机化合物排放情况，因此采样是非随机的。对70口水井进行了挥发性有机化合物（VOCs）和硝酸盐氮（NO3-N）采样，并分别采用气相色谱/质谱法和镉还原法进行分析。利用地理信息系统（GIS）对影响水井硝酸盐易感性的四个解释变量进行量化：人口密度、土地覆盖、局部地形（坡度百分比）和土壤质地。在11口水井中检测到挥发性有机化合物，有两个地点的1,1-二氯乙烯（36.1微克/升）和三氯乙烯（9.0微克/升）超过了最大污染物浓度标准。在20口水井中测得硝酸盐氮含量升高（定义为≥1.0毫克/升）。逻辑回归分析确定草地/耕地覆盖是显著增加硝酸盐氮污染可能性的变量（p = 0.003）。利用易于获取的数据库来识别增加地下水污染可能性的因素，可能会带来更有效的方案，以定位易受污染的居民水井。正如一些州正在考虑的那样，加强对水井水质的监测，对于减少人类接触受污染饮用水的潜在风险是必要的。
