Concentration Data for 12 Elements of Concern Used in the Development of Surrogate Models for Estimating Elemental Concentrations in Surface Water of Three Hydrologic Basins (Delaware River, Illinois River and Upper Colorado River)

The release of metals (or metalloids) to surface water can involve both natural and anthropogenic sources. Elevated metals concentrations can pose a risk to human health, wildlife, and ecosystem health, with the modes of toxicity and extent of risk varying as a function of the specific metal, its chemical form and the matrix with which it is associated (for example, dissolved versus particulate). As part of the U.S. Geological Survey (USGS) Water Mission Area (WMA) Water Quality Processes Program, the Proxies (Surrogate) Project was created, in part, to develop models that can be used to estimate the concentration of metals in riverine surface water at spatial scales ranging from (sub)basin to multi-basin. Three hydrologic basins were selected for metals proxy model development; the Delaware River Basin (DRB), the Illinois River Basin (ILRB) and the Upper Colorado (UCOL) River Basin. These basins are part of the USGS network of integrated water science basins identified by the USGS WMA Integrated Water Availability Assessments (IWAAs) program (LINK) and the Next Generation Water Observing System (NGWOS) program (LINK). Based on a survey of NGWOS basin coordinators and others familiar with these three hydrologic units, 12 metals (or metalloids) were identified as contaminants of concern and targeted for potential detailed modeling by the Proxies project. These 12 metals include: aluminum (Al), arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), iron (Fe), mercury (Hg), manganese (Mn), lead (Pb), selenium (Se), uranium (U), and zinc (Zn). This data release contains surface water concentration data for the above 12 elements and co-collected water quality parameter data (pH, temperature, specific conductance, turbidity, total suspended solids, and dissolved oxygen) from the DRB, ILRB and UCOL, as obtained from the Water Quality Portal (WQP, www.waterqualitydata.us/). With over 1,500,000 observations, the primary metals database includes both historic and contemporary measurements (collected between 1900 and 2022) and among the three NGWOS basins. The initial data retrieval results were screened to exclude any aqueous data that was not true surface water (groundwater, well water, sewer, and atmospheric measurements were excluded). A separate WQP data retrieval associated with additional sample location information was also conducted and merged with the initial metals data retrieval results. The metals data was further harmonized (coded) for three water matrix fractions (filtered, particulate, and unfiltered), data source (USGS, EPA, and other), monitoring location type, analytical method, and the type of data censoring (if any). Metal concentrations were also harmonized to common units, such that those associated with both the dissolved and whole water fractions are reported in micrograms per liter (µg/L) and those associated with the particulate fraction are reported on either a volumetric basis as µg/L or on a gravimetric basis as milligrams per kilogram (mg/kg), depending on the information retrieved. The various WQP data retrieval steps were automated using ‘R’ scripts (‘R’ version 4.1.0), as were all the subsequent data conversion, data merging, data harmonization, and file clean-up steps. This ‘R’ script is publicly available as a provisional software release (https://zenodo.org/record/6986087#.Y02Dh3bMJPb). This product comprises six data files in machine readable (comma separated value, *.csv) format. The primary metals data results, along with the additional sampling site information, are provided as three individual files organized by NGWOS basin, which include: metals_DRB.csv, metals_ILRB.csv, and metals_UCOL.csv. Similarly, the co-collected discrete ancillary water quality data are provided as three individual files organized by NGWOS basin, and include: ancillary_DRB.csv, ancillary_ILRB.csv, and ancillary_UCOL.csv.