This "Predicted Background Conductivity" view consists of a shapefile derived from National Hydrography Dataset Plus Version 2.0 which displays modeled natural background conductivity for the continental United States. The displayed information is based on specific conductivity predictions for stream segments in the contiguous United States from the Natural Background Specific Conductivity (NBSC) model. The NBSC model was developed using a random forest modeling approach and enables comparison with measured in-stream conductivity. Geology, soil, vegetation, climate and other empirically measured data were used as inputs. The NBSC model was designed for streams with natural background SC < 2000 µS/cm. Above this level (typical for freshwater), NBSC model estimates may be less reliable. Data for some parameters that affect background SC were not readily available and were therefore not included in the model. These include freshwater and marine interfaces, natural mineral springs, salt deposits which may affect groundwater and streams, and other natural sources of salts. In such areas, the model is likely to underestimate SC. Local knowledge is often necessary to assess differences between predicted and measured background SC. More information about the model and datasets can be found at Freshwater Explorer Story Metadata. The calculated predicted background conductivity for individual stream segments in the contiguous U.S.A. and metadata are accessible from the ArcGIS platform on Predicted Background Conductivity Data. Data is available as table (from Data) or in by pointing and clicking on a stream segment (from Visualization) (https://arcg.is/9vnrv). This data set is used in the Freshwater Explorer Beta 0.1 which on Jan. 2020 is password protected but can be obtained by requesting access from cormier.susan@epa.gov and then using the link: https://arcg.is/KHb9S.

This dataset is associated with the following publication: Olson, J., and S. Cormier. Modeling spatial and temporal variation in natural background specific conductivity. ENVIRONMENTAL SCIENCE & TECHNOLOGY. American Chemical Society, Washington, DC, USA, 53(8): 4316-4325, (2019).