National_Measured_Conductivity (FeatureServer)

View In: Map Viewer

Service Description: The "National Measured Conductivity Data - WQP" view consists of a shapefile derived from data stored in the U.S. EPA Water Quality Portal.

Service ItemId: ae5566099b0040b088347682784997f2

Has Versioned Data: false

Max Record Count: 2000

Supported query Formats: JSON

Supports applyEdits with GlobalIds: True

Supports Shared Templates: False

Source Schema Changes Allowed: true

Has Views: true

Has Sync Enabled Views: true

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Description:

The "National Measured Conductivity Data - WQP" view in the Freshwater Explorer is based on measured data obtained from the U.S. EPA Water Quality Portal (WQP) data inventory - the nation's largest source for water quality monitoring data. Data were downloaded from the WQP website using the following query criteria:

Country - United States.
Sample Media - Water.
Characteristics - Conductivity, Specific Conductivity, Specific Conductance, Calculated/Measured Ratio.
Date range - 1 January 2000 to 01 November 2019.

These water quality data records are provided by many federal, state and tribal organizations and other partners. As such, the U.S. EPA cannot ensure that the information is accurate, current or complete. Therefore, users should verify the data from the original sources before drawing site specific conclusions. Examples of errors found include negative specific conductivity (SC) values, units of measurements not consistent with SC measurements (e.g., NTU, volts, mg/l) and entries as mS/cm but reported as µS/cm. The U.S. EPA plans to update data and add new data; however, due to the large number of organizations involved, such an effort is beyond the scope of this story map. Users should verify the data from the original sources before drawing site specific conclusions.

An inventory of the SC data affected by such uncertainties has been compiled and a thorough data revision process has been planned to contact the individual organizations that provided the data and to regularly up-date data. However, due to the large number of organizations involved, it is necessary that users of the National Conductivity Data assume there will be some inherent measuring and reporting error.

The quality of the measured data was evaluated as follows. An automated Quality Assurance/Quality Control (QA/QC) protocol was developed using R-scripts to remove or identify potentially erroneous SC values (outliers) in WQP. The objective of the QA/QC protocol was to:

Remove SC values ≤ 0 (SC values cannot be negative).
Remove SC values reported with units of measurements different from Siemens or mho - these were considered ambiguous (e.g., SC reported as nephelometric turbidity units, degrees etc.).
Convert all relevant SC values to µS/cm (e.g., values expressed in mS/cm were multiplied by 1000). This allows direct comparison among samples.
Identify and flag (grey circles) SC values < 10 µS/cm - these SC values are uncertain and likely recorded incorrectly as µS/cm instead of mS/cm units.
Identify and flag (grey circles) SC values > 5000 µS/cm - these SC values likely represent marine waters or are errors in reported units of measurements (data reported as mS/cm but likely measured as µS/cm). It should be noted, however, that some SC values > 5000 µS/cm may have been correctly reported (e.g., brine waste outfalls, irrigation return water).

The data set is updated from time to time but is always very large. The initial dataset in 2020 contained almost 11 million records downloaded from WQP. About 50 thousand SC measurements were removed (incorrect units or erroneous values). More than 2 million values, representing about 25%, were flagged as uncertain (gray color). The subsequent QA/QC dataset contained about 9 million samples from more than 200,000 locations. The R code developed to perform the QA/QC steps are available from cormier.susan@epa.gov

Copyright Text: Cormier, S. M., Wharton, C., and Olson, J.R.

Spatial Reference: 102100 (3857)

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Units: esriMeters

Child Resources: Replicas Info

Supported Operations: Query ConvertFormat Get Estimates Create Replica Synchronize Replica Unregister Replica