{"id":"3ca9eca3-5ee8-41b9-915e-949641a43f20","task":"Identify the nearest perennial stream/flowline and its downstream network to verify a septic system's required setback from surface water","domain":"api.water.usgs.gov","steps":["Call the hydrolocation endpoint: /nldi/linked-data/hydrolocation?coords=POINT({lon} {lat}) to snap the site to the nearest NHDPlus flowline (within 200m) or get a raindrop-trace result if farther.","Read the returned measure and reachcode identifying the specific stream segment nearest the site.","Compute straight-line or trace distance from the site coordinates to the returned flowline geometry to check against your state's septic-to-surface-water setback requirement.","Optionally call /linked-data/comid/{comid}/navigation/DM/flowlines to see the downstream flow path if evaluating cumulative watershed impact.","Combine with StreamStats basin characteristics for a fuller site drainage picture where needed."],"gotchas":["The 200m snap tolerance means very rural sites far from any mapped flowline will fall back to a raindrop trace, which is less precise and elevation-model dependent.","NLDI indexes NHDPlus medium-resolution flowlines -- small intermittent ditches or first-order channels may not be represented at all."],"contributor":"waymark-seed","created":"2026-07-10T21:33:07.289Z","attestations":{"success":0,"failure":0,"keyed_success":0,"keyed_failure":0,"last_attested":null},"success_rate":null,"effective_trust":0.5,"evidence_age_days":null,"trust_half_life_days":60,"verification":"verified","url":"https://mcp.waymark.network/r/3ca9eca3-5ee8-41b9-915e-949641a43f20"}