Civil-Environmental Engineering

California Uniform Plumbing Code

Summary of Requirements For Gravity Systems*


For general requirements and good practices see the FAQ page for Gravity System Requirements:

Specific Requirements:

  • Minimum disposal field: 150 sf
  • Maximum drain line length: 100'
  • Minimum depth of cover: 12"
  • Tench width: 18" min. to 36" max.
  • Trench depth, below leach line: 12" min. to 36" max.
  • Sidewall beyond minimum can be counted in absorption area.
  • Maximum drain line grade: 3" in 100'
  • Minimum gravel: 2" over drain line and 12" under
  • Minimum separation to ground water: 5'
  • Minimum center-to-center drain line spacing: 6'
  • Minimum spacing between trenches: 4' + (2' for each foot of depth beyond minimum)
  • Distribution boxes shall be set on a level concrete slab.
  • Leachfields greater than 500 lf require a pump (2 pumps at 1000 lf).
  • Bed style disposal field: areas must be increased by at least 50%; drain lines maximum 6' center-to-center.





UPC Setback Requirements

For a graphical representation of the UPC setback requirements:


*The information on this page is a summary for quick reference only and may not represent the latest standards.  For complete and up-to-date information, see the state's official website:

Link to State UPC Website

For a pdf of the UPC: