An ADU project may involve foundation work, grading, a service trench, or other excavation. A pipeline map can help identify whether to ask another question about the site, but a public map is not a line locator or permission to dig.
Use the federal viewer as a broad screen
The U.S. Department of Transportation’s Pipeline and Hazardous Materials Safety Administration (PHMSA) publishes a National Pipeline Mapping System (NPMS) Public Map Viewer. It shows selected gas transmission and hazardous-liquid pipelines, LNG plants, breakout tanks, and incident information under PHMSA jurisdiction. The viewer does not include gas distribution or gas-gathering pipelines, and its map scale is restricted.
PHMSA states that NPMS geospatial data have a minimum accuracy of plus or minus 500 feet. That is too coarse to determine a line’s exact position on a parcel, its depth, an easement boundary, or a safe building setback. A visible line is a reason to investigate; it is not a survey or a final property record.
Confirm the operator and the proposed work
If a viewer result is near the property, use NPMS’s “Find Who’s Operating in Your Area” tool to identify pipeline-operator contacts by state, county, or ZIP code. Ask the operator what current location information, right-of-way records, access limits, or project review apply to the proposed ADU and its service connections. If a line or corridor may cross the parcel, compare the operator’s information with the parcel and title records; a map viewer does not establish the exact route or legal rights.
Before any excavation, contact the applicable One Call system and pipeline operator as PHMSA directs. Follow the required local locate and clearance process for the actual work area. Do not use a line shown in NPMS to mark the ground or to decide that digging outside the displayed corridor is clear.
Treat an empty result carefully
No result in the public viewer does not prove that no pipeline or other buried service is present. The viewer excludes some pipeline types, and its scale and accuracy are not designed for parcel-level clearance. Check other utility records and the appropriate local locate service for the work being planned.
Keep the lookup date, map result, parcel identifier, operator response, and locate instructions together. The map can direct the next inquiry, but the operator and One Call process must establish the current information needed before excavation. This guide does not determine whether a pipeline crosses a particular property or whether a proposed ADU can be built there.