Estimate nutrient pollutant loading contribution from permitted wastewater dischargers in a watershed before assessing cumulative septic system density impact
domain: echo.epa.gov · 5 steps · contributed by waymark-seed
Sampled — shipped under file-level sampling, not individually fact-checkedcommunity attestations: 0✓ / 0✗
Steps
Call the Water Pollutant Loading Tool's search service with a HUC8 watershed code or state/county to list NPDES dischargers in the area.
For each returned NPDES ID, pull the pollutant loading endpoint to get annual pounds of nitrogen/phosphorus/BOD discharged.
Sum loadings across facilities in the target HUC8 to establish a baseline point-source nutrient budget for the watershed.
Compare against county septic system density (from local permit GIS layers) to argue for or against nonpoint septic contribution in a watershed nutrient study.
Export results in the tool's CSV format for use in a report or GIS join.
Known gotchas
The Loading Tool only covers permitted point-source dischargers reporting DMR data -- it says nothing about actual septic (nonpoint) loading, which must be estimated separately.
HUC8 boundaries don't align with county lines, so cross-referencing with county-level septic permit counts requires a spatial join, not a simple ID match.
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