GROUNDWATER IODINE ACROSS NEW YORK STATE: POTENTIAL LINKAGE TO METHANE?

Iodine is enriched in marine algae and ancient organic-rich source rocks of petroleum and natural gas. Iodine and halogen ratios were proposed as tracers to study the natural processes that control the migration of dissolved methane (CH₄) from the Marcellus and other black shales into shallow aquifers. We expand a previous data set in southern New York State (NYS) and present results from seven major basins: 1) Allegheny River Basin; 2) Niagara, Lake Erie, and Western Lake Ontario Basins; 3) Chemung River Basin; 4) Susquehanna River Basin; 5) Oswego, Seneca, Oneida, and Central Lake Ontario Basins; 6) Mohawk River Basin; and 7) Upper Hudson River Basin. In collaboration with the United States Geological Survey’s 305 (b) Ambient Groundwater Quality Monitoring Program, we sampled approximately 100 public and domestic water supply wells in NYS in 2016 and 2017. Samples were analyzed for over 200 constituents, including dissolved CH₄, and for total iodine and bromide (Br) on Inductively Coupled Plasma Mass Spectrometry (ICP-MS). Preliminary halogen concentrations show a possible West to East trend across central NYS. In southern NYS, both iodine and CH₄ are associated with sodium-rich water types. Wells completed in organic-rich geologic units typically have higher concentrations of iodine, and may have elevated CH₄ concentrations. Spatial relationships will be further examined for potential correlations between a range of solutes and gases. Local hydrogeology will also be taken into consideration. Concentrations of iodine in conjunction with Br may be a useful fingerprinting tool to differentiate the influence of deep formation waters from other sources of salinity found at depth.