From July through November 2018, 48 environmental samples and four quality-control samples were collected throughout the Lower Hudson, Chemung, and Eastern Lake Ontario River Basins. Samples were collected from seven production wells and eight domestic wells in the Eastern Lake Ontario Basin, 13 production wells and 12 domestic wells in the Lower Hudson River Basin, and four production wells and four domestic wells in the Chemung River Basin. Of the wells sampled, 27 were completed in bedrock and 21 were completed in sand and gravel. Approximately 20 percent of samples were collected from wells that were previously sampled in 2003, 2008, and 2013. Groundwater samples were collected prior to any treatment or filtration systems, from existing domestic and production wells equipped with permanently installed pumps.
Samples were collected and processed using standard USGS methods and were analyzed for 372 constituents including physicochemical properties, dissolved gases, major ions, nutrients, trace elements, pesticides, volatile organic compounds (VOCs), radiological activity, and indicator bacteria. All analytes are listed in the data release, along with the associated method detection and reporting limits, some of which changed over time. About 68 percent of constituents analyzed were not detected at concentrations greater than the method detection limit. Samples were analyzed at the USGS National Water Quality Laboratory (NWQL) in Denver, Colorado, and other certified laboratories following published methods. Quality assurance and quality control samples were collected and assessed in each of the sampled basins. In the Lower Hudson River Basin, one replicate was collected at well U4469 and analyzed for all constituents. A replicate analyzed for dissolved gases, radiological activity, and indicator bacteria was collected at well SV4356, as was a field blank analyzed for organics and inorganics. In the Chemung River Basin, one replicate was collected at well SB392 and analyzed for all constituents. In the Eastern Lake Ontario Basin, a replicate analyzed for dissolved gases, radiological activity, and indicator bacteria was collected at OW622, as was a field blank analyzed for organics and inorganics. The VOC 1,2,4-Trimethylbenzene was detected in blank samples and most of the groundwater samples, and contamination is suspected from the scintillation liquid in the radon sampling kits. Due to the potential for contamination bias, results for 1,2,4-Trimethylbenzene are not included.