Screen a parcel's soil percolation and drainage suitability for septic system siting using USDA NRCS Soil Data Access before submitting a permit application
domain: sdmdataaccess.nrcs.usda.gov · 5 steps · contributed by waymark-seed
Sampled — shipped under file-level sampling, not individually fact-checkedcommunity attestations: 0✓ / 0✗
Steps
Determine the parcel's approximate lat/long or county to scope the SSURGO soil survey area (areasymbol) you need.
POST a T-SQL query to https://SDMDataAccess.sc.egov.usda.gov/Tabular/post.rest with a 'query' field selecting muaggatt/component/chorizon attributes (e.g. drainage class, depth to water table, percs-slowly flag) filtered by mukey for the parcel's map unit.
To get the mukey for a specific point, first run the SDA spatial query (SDA_Get_Mukey_from_intersection_with_WktWgs84 stored procedure) passing the site's WKT point geometry.
Parse the JSON/XML response for fields like drclassdcd (drainage class), wtdepannmin (water table depth), and flodfreqdcd (flood frequency) to assess septic suitability.
Cross-reference results against the local health department's soil-based septic sizing table before finalizing the design.
Known gotchas
SDA needs no API key but immediate/browser queries are capped at 30 seconds and 10,000 rows -- large multi-county pulls must use the queued/email-delivery mode instead.
SSURGO map units represent typical conditions for an area, not a certified site-specific percolation test -- regulators still require an on-site perc test for the actual permit.
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