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Geologic Controls on Contaminants in Crystalline Bedrock Aquifer Systems

The goal of this project is to develop methods to measure new contaminants and information on their environmental occurrence and potential environmental health effects in support of responses to emerging water quality issues, particularly in the New England Crystalline aquifer system.

Project objectives l Project's Relevance and Impact

The objectives of this project are twofold:
1. Develop a geohydrologic framework for contaminant evaluation in aquifer systems.
>Define a geohydrologic framework to evaluate water quality in aquifer systems in terms of intrinsic susceptibility and natural or anthropogenic vulnerability. Describe the factors affecting the framework components and determine if common themes exist among water-quality issues, such as: general reactivity of the aquifer; composition of aquifer materials; and susceptibility and vulnerability to contaminants.
>Document important controlling variables from previous studies: Summarize water-quality issues within the framework and highlight controlling variables that have been identified in previous reports. Variables that will be mentioned and highlighted, if previous studies identified correlations with water-quality issues, may include: regional bedrock geologic and associated features; physiographic subdivisions; secondary porosity and fracture patterns; gross hydraulic conductivity; well hydraulics; well depth and other well construction variables; proximity to hydraulic boundaries; overburden cover (type, character, and thickness); land use (current or historic); and topography.

2. Evaluate and model water-quality data for the New England Crystalline aquifer to define important geologic factors that influence contaminant occurrence and distribution.
>Describe and document geographic extent of geologic province and associated lithogeochemial features of the aquifer: Describe the major geologic and geochemical features related to the bedrock geologic setting of the aquifer and summarize the distribution of these geologic features. A stratification system designed for the New England Crystalline aquifer based on litho geochemical groupings also will be presented.
>Evaluate natural and anthropogenic drinking-water contaminants: Describe the major ions and redox conditions which control the fate and transport of common contaminants of concern for the New England Crystalline aquifer system relative to the lithogeochemical framework. Provide examples of how the conceptual model discussed in the framework can be used to: 1) study water-quality issues in the aquifer; and 2) explain water-quality conditions in major lithogeochemical groupings for constituent concentrations of interest. >Develop spatial models of contaminant occurrence and distribution.

Relevance and Impact of the project:
Relevance: The New England Crystalline aquifer system is the sole source aquifer for up to 50 per cent of the inhabitants in northern New England and is being increasingly tapped for new water supplies in areas where existing water-supply systems are fully utilized. Many natural and anthropogenic contaminants occur in the New England Crystalline aquifer system, but very few have been analyzed regionally. Nitrate, lead, manganese, fluoride, arsenic, uranium, and radon, among others, are associated with human health effects. Preliminary analysis of NAWQA data show that these contaminants occur more frequently and at higher concentrations in bedrock aquifers than in overlying glacial aquifers in New England.
Impact: There is ongoing research studying the relation between arsenic, radon, and uranium and health effects in New England. Also, some New England states are actively developing risk models for many ground water contaminants as an aid in interpreting health outcome data. Interpreted NAWQA data, especially combined with other data available from the states or health agencies, is of strong interest from both health and environmental agencies. Lastly, current work being conducted by NAWQA Trace Elements Synthesis on a national scale would provide additional context for this regional analysis.