DOI: 10.5066/p9m11aqx
title: Select elements of concern in surface water of three hydrologic basins (Delaware River, Illinois River and Upper Colorado River) — Data screening for the development of spatial and temporal models

description: This data release is focused on the analysis of surface water concentration data associated with 12 elements of concern from three hydrologic basins. Data is analyzed with respect to: a) reporting limits, b) the extent of censored data, c) co-location with USGS real-time sensor data, and d) median concentrations at the catchment spatial scale.

The Proxies Project (under the Water Quality Program of the USGS Water Mission Area) is a multi-year effort designed to develop rapid and cost-effective approaches for monitoring and risk assessment of a range of aquatic contaminants in riverine surface waters at multiple spatial scales. One component of this project is focused on 12 Elements of Concern (EoC; Al, As, Cd, Cr, Cu, Fe, Hg, Mn, Pb, Se, U and Zn) in three primary hydrologic basins: Delaware River Basin (DRB), the Illinois River Basin (ILRB) and the Upper Colorado (UCOL) River Basin (USGS, 2023).

Two modeling approaches being explored as part of the Proxies Project rely on the analysis of previously published EoC concentration data retrieved from the multi-agency supported Water Quality Portal (www.waterqualitydata.us/). This basin-specific retrieved data, covering the 1900-2022 timeframe, was subsequently screened, harmonized and published as part of an earlier USGS Data Release (Marvin-DiPasquale and others, 2022).

The two distinct modeling approaches that leverage this previously published data are: a) machine learning statistical analysis of EoC concentration distributions as a function of geospatial attributes; and b) time series analysis in support of estimating EoC concentrations in (near)real-time at a sub-set of USGS real-time stations using discharge in combination with a range of deployed in-situ sensors.

Prior to the final stages of model development, there were several data analysis steps required to further define which elements and aquatic fractions (i.e. filtered, unfiltered, and particulate) best lend themselves to further model exploration and development. These intermediate data analyses include: a) an analysis of the change in detection quantitation limits, by element and methods over time (DR_Table _1); b) an analysis of data censoring, by study basin, element, and fraction (DR_Table_2); c) a calculation of median EoC concentrations at the National Hydrography Dataset Plus (NHDPlus) catchment spatial scale (DR_Table_3); d) an analysis of the percentage of censored median EoC concentration values by study basin, element, and fraction (DR_Table_4); e) decision tree analysis associated with the geospatial machine learning modeling approach, by study basin, element and fraction (DR_Table_5); f) discrete EoC concentration data merged with continuous discharge and in-situ sensor data at USGS real-time stations, by station ID, element and fraction (DR_Table_6); and g) an analysis of the total number of observations and the percentage of censored EoC data associated with the merged discrete EoC and continuous discharge and sensor data retrieved from USGS real-time stations, by station ID, element, and fraction (DR_Table_7). The current data release documents the results of these data analyses. The associated seven data tables presented herein are provided in machine-readable comma separated value (*.csv) format and are more fully described in the associated meta-data.