Citation:

Cormier, S., c. Wharton, AND Y. Wang. Arkansas Freshwater Explorer: Arkansas DEQ Briefing. Arkansas DEQ Briefing, Cincinnati, OH, October 20, 2022.

Impact/Purpose:

The Arkansas Freshwater Explorer is an interactive map of a network of stream in Arkansas.  The tool provides easy access to observed data for total ions [specific conductivity (SC)] and estimated background SC on a map of Arkansas. The EPA GeoPlatform tool also includes capabilities to extract, analyze, and overlay other data layers and precalculated SC levels estimated to result in the loss of 5% of native aquatic genera.  These data can be used to assess the protectiveness of site-specific water quality criteria proposed by third parties. The accompanying report describes the analyses and models used in a weight of evidence for characterizing background specific conductivity (SC) in Arkansas. It includes formulae for converting total dissolved solids to SC. It provides a deliberative process of characterizing background SC and a process for site specific background characterization. It describes the method for estimating the SC likely to lead to 5% extirpation of native aquatic life. These methods, data, and models may be used to assess the protectiveness of site-specific water quality criteria proposed by third parties. This information was developed for Region 6, Office of Water, and partners they work with such as the Arkansas Department of Environmental Quality.

Description:

The Arkansas Freshwater Explorer is an interactive map of streams, lakes and wells. The estimated background specific conductivity (SC) is shown as a color-coded stream network. Background SC was estimated with a national empirical model for most of the state at the stream reach scale. Minimally affected background is the recommended background for estimating 5% extirpation. Where such data or conditions are unavailable, the next most relevant estimated background is one from observed background at nearby minimally affected locations. The Arkansas Freshwater Explorer searches for the lowest observed SC within 10 Km to estimate least disturbed background from nearby stations. Where neither of these options are available in the Mississippi Alluvial Plain, Mississippi Valley Loess Plains, Ouachita Mountains, Ozark Highlands or South Central Plains, the recommended background is the stream segment empirically modeled background. In the unlikely case that minimally affected background cannot be estimated for the Boston Mountains and Arkansas Valley, the recommended background is the ecoregional 75th centile because the empirical model consistently over-predicts background. Arkansas Freshwater Explorer can be used to quickly access data and provide SC levels estimated to result in the loss of 5% of native aquatic genera.  These data can be used to assess the protectiveness of site-specific water quality criteria proposed by third parties. Arkansas Freshwater Explorer also includes capabilities to extract, analyze, and overlay other data such as waters designated as high quality streams, impaired streams, trout habitat, NPDES permit holders, among many others. Underlying analyses and models are described in metadata and in a technical report.  The ionic composition of waters in the state are described.  Formulae for converting total dissolved solids (TDS) to SC are provided for each ecoregion. Stream background was estimated using observed and empirically modeled data. Minimally affected background is the recommended background for estimating 5% extirpation. Where such data or conditions are unavailable, the next most relevant estimated background is one from observed background at nearby minimally affected locations. Where neither of these options are available in the Mississippi Alluvial Plain, Mississippi Valley Loess Plains, Ouachita Mountains, Ozark Highlands or South Central Plains, the recommended background is the stream segment empirically modeled background. In the unlikely case that minimally affected background cannot be estimated for the Boston Mountains and Arkansas Valley, the recommended background is the ecoregional 75th centile because the empirical model consistently over-predicts background. These methods, data, and models may be used to assess the protectiveness of site-specific water quality criteria proposed by third parties.  

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