Multi-Element Analysis and Geochemical Spatial Trends of Groundwater in Rural Northern New York

Michael O’Connor,Matt Zabik,Brian Cousens,Carol Cady,Jeffrey Chiarenzelli

doi:10.3390/w2020217

Michael O’Connor, Matt Zabik + Show 3 more

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https://doi.org/10.3390/w2020217

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Abstract

Samples from private wells (n = 169) throughout St. Lawrence County, NY were analyzed by ICP-MS multi-element techniques. St. Lawrence County spans three diverse bedrock terranes including Precambrian crystalline rocks of the Adirondack Lowlands (mostly paragneisses) and Highlands (mostly orthogneisses), as well as Paleozoic sedimentary rocks of the St. Lawrence Valley. An ArcGIS database was constructed and used to generate contour plots for elements across the county. Strontium isotopes and unique geochemical signatures were used to distinguish water from various geologic units. The results were consistent with a large (7,309 km2), sparsely populated (~110,000), rural region with diverse bedrock and glacial cover.

Highlights

For purposes of our study we assumed that: (1) the vast majority of wells draw from bedrock; (2) bedrock maps of the area provide an excellent guide to the two-dimensional distribution of these units; (3) because of local relief, the complex structure of bedrock, and abundant discharge points most flow pathways in Precambrian basement rocks are relatively short; and (4) given the low water usage of individual private wells, the capture zones of most wells are limited
Even if these assumptions are largely valid, the possibility exists that the chemistry of many of the groundwater samples reflects a mixture of several sources and is influenced primarily by the most soluble unit in which it comes in contact with
The results suggest that it is less likely that water is transported long distance and/or mixed extensively with that derived from distant lithologies

Summary

Introduction

Purpose of the Study—St. Lawrence County is a large (7,306 km2) and sparsely populated, rural, heavily forested county in northern New York (Figure 1a). Due to its large area and rural nature, much of the region’s population utilizes private groundwater wells for potable water. While the Adirondack Highlands are underlain by large areas of metamorphosed, acidic, igneous crystalline bedrock (orthogneisses), in the Lowlands metasedimentary rocks (paragneisses), including a large proportion of marble and calc-silicate gneisses, predominate [2]. Interacting with these diverse bedrock units, groundwater geochemistry is variable and influenced by rock-water interactions and dissolution from these various lithologies, as well as widespread glacial deposits

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