Floodplain, FEMA flood zone, and wetland limitations.

The 100-year floodplain for every tract must be determined from FEMA maps — or from a professional engineer's flood study when FEMA maps are unavailable — and the boundaries (or a note that none exists on the tract) must be shown on the site drawing (30 TAC §285.30(b), TCEQ RG-472); FEMA's own flood hazard products define the Special Flood Hazard Area, base flood elevations, zone designations, and regulatory floodways used for that determination (FEMA, map change status). Floodplain siting is not an absolute bar but triggers special planning: the system must be located so a flood will not damage it, planning materials must show how tank flotation is prevented, and inside a regulated floodway a P.E. must show the system will not raise flood height, that components (other than risers, chlorinators, cleanouts, sprinklers, inspection ports) are fully buried without added fill, and that alarms, junction boxes, and compressors sit above the 100-year flood elevation (30 TAC §285.31(c)(2)); Table V rates floodplain/floodway areas and undrained depressional areas as unsuitable for standard subsurface absorption systems unless designed under §285.31(c)(2) (30 TAC §285.91(5)). Chapter 285 contains no wetlands-specific setback, but separately, Clean Water Act §404 requires Corps of Engineers authorization for any discharge of dredged or fill material into waters of the U.S. including wetlands — expressly including site-development fills for residential uses and road fills — so filling or grading a wet area for a drainfield or access road can require a federal permit (U.S. Army Corps of Engineers, Section 404).

Reviewed August 2026. Links go to the sources this answer was checked against.