A COMPARISON OF GROUNDWATER AND ROCK GEOCHEMISTRY IN CENTRAL UPSTATE NEW YORK

Many factors play a role in groundwater chemistry, such as rainfall chemistry, flow path length and duration of contact with rocks, and rock chemistry. We compile detailed geochemical data of Devonian sedimentary rocks and drinking water wells located around Otsego County, NY and begin the process of understanding of how water and rock geochemistry are related. The data will be made public via an online interface.

Several water sampling campaigns at SUNY Oneonta have collected water samples from wells throughout Otsego County and surrounding areas. The samples were analyzed at a commercial geochemical laboratory (ActLabs) for detailed chemical analysis using ICP-MS/ICP-OES, which tested for 30 to 60 elements. The current campaign sampled exposed bedrock located close (< 1 km) to previously sampled water wells, and within the same mapped geologic formation. Screen depth of the water wells was used to target the elevation at which exposed bedrock would correlate with the screened interval. It was inferred that bedrock collected was representative of the rock through which the well water flowed. Once collected the rock samples were crushed and mixed (several layers were sampled) and sent to a commercial geochemical laboratory (ActLabs) for detailed chemical analysis, and thin sections were created from hand specimens. Some rock specimens were analyzed by XRD.

We construct similarity plots of elemental concentration in water and adjacent rocks, in which the concentration of an element in the water is plotted against the concentration in the rock, and perform this for all elements measured in both water and rock. To first order, the water looks somewhat like the rock, only dilute by a factor of 200,000. However, there is a far greater scatter in water chemistry than rock chemistry. We investigate an equilibrium model of water-mineral reactions as a more rigorous check on controls of water chemistry. We present these tests, and provide access to the datasets online.