Sources, transport, and fate of arsenic in ground water

这项研究的主要目的是描述新汉普郡地下水系统中砷的来源、迁移和去向，这些系统已知含有高水平的砷。我们将通过研究新汉普郡的四个地理区域来实现这一目标，在作为试点项目完成的区域调查中，我们发现这些区域的砷含量很高。这将包括砷可能来自地质来源或人类来源的地区。在我们最近的研究中(彼得斯等人，1999)，我们测量了从新罕布夏州随机选择的家庭中收集的992个饮用水样本中的砷浓度。在已钻探的基岩井中发现砷含量极高，其中约35%的井超过2g/L，这是美国环保局认为新的最高污染物水平标准的最低值。我们确定了四个砷含量较高的地理区域，所有这些区域都位于该州的南部。对最大的星系团(Bow，NH)进行了更详细的研究，发现基岩中砷含量极高，呈易浸出的形式。在这里提出的研究中，我们希望在地下水系统的水文和地球化学方面仔细研究这四个集群中的每一个。我们将使用1)基本的水文技术来绘制区域地下水流动模式，2)电子探针x射线地图来确定岩石和土壤中的砷载体相，3)柱实验来测量砷从基岩和土壤中溶解的化学条件，4)特定物种的水化学分析来详细地表征地下水系统的氧化还原条件和导致砷迁移的化学机制，以及5)柱实验来测量基岩和土壤的缓蚀特性。为了说明我们对这项研究的方法，我们在本提案中将重点放在我们已经做了一些初步工作的两个实地地点，这两个地点可能代表地质来源的砷来源与人类来源的砷来源的最终案例。这项工作的结果将进一步加深我们对含水层和矿山废弃区中砷的来源和化学的一般知识。我们的研究将集中在之前未被重视的结晶(即花岗岩)地质地体中的砷污染问题。我们的工作将提供信息，帮助就新英格兰和其他地方受砷污染的结晶基岩地区的管理和补救做出更明智的决定。

The main goal of this study is to characterize the sources, transport and fate of arsenic in groundwater systems in New Hampshire which are known to contain high levels of arsenic. We will accomplish this goal by studying each of the four geographic regions within New Hampshire where high arsenic levels were identified by us in a regional survey that was completed as a pilot project. This will include regions where arsenic may be derived from either geologic or human-derived sources. In our recent study (Peters et al., 1999) we measured arsenic concentrations in 992 drinking water samples collected from randomly selected households in New Hampshire. Arsenic was found to be highly elevated in drilled bedrock wells, with approximately 35% of these wells exceeding 2 g/L, which is the lowest value being considered by the USEPA for the new maximum contaminant level standard. We identified four geographic regions with high arsenic levels, all of which are in the southern half of the state. The largest cluster (Bow, NH) was studied in more detail and found to have highly elevated arsenic in bedrock, which was in an easily leachable form. In the study proposed here, we wish to closely investigate each of the four clusters with respect to the hydrology and geochemistry of the groundwater systems. We will use 1) basic hydrologic techniques to map the regional groundwater flow patterns, 2) electron microprobe x- ray mapping to determine arsenic carrier phases in rocks and soils, 3) column experiments to measure the chemical conditions under which arsenic is solubilized from the bedrock and soils, 4) species-specific chemical analyses of waters to characterize in detail the redox conditions of the groundwater system and the chemical mechanisms responsible for arsenic mobility, and 5) column experiments to measure the retardatioin properties of bedrock and soils. For the purposes of illustrating our approach to this study, we will focus in this proposal on two field sites where we have done some preliminary work and which may represent the end-member cases of geologically-derived versus human-derived arsenic sources. Results from this work will further our general knowledge of the sources and chemistry of arsenic in the aquifers and mine waste areas. Our study will concentrate on a previously under-emphasized arsenic contamination problem in crystalline (i.e., granitic) geological teranes. Our work will provide information that will aid in making more informed decisions with respect to the management and remediation of arsenic- contaminated crystalline bedrock regions in new England and elsewhere.