Civil-Environmental Engineering

Lake County

Summary of Specific Requirements For Gravity Systems

for Single Family Dwellings*

The following is in addition to the items listed on the FAQ page for Gravity System Requirements.


  • Vertical Separation: 5' to Water Table, 18" to Rapid Soil
  • Trench Sidewall-to-Sidewall Separation: 8'
  • Trench Length:  10' to 125'
  • Bottom Width: 24" Min.
  • Trench Depth: 18" to 36"- Equal or Loop Distribution (<4% slope)                           24" to 36" - Serial Distribution Systems (>4% slope)
  • Minimum of 2" of gravel over drain lateral, and 6" under, with 6" backfill (12" backfill for serial distribution systems).
  • Maximum drop of 1" in 100' for drain lateral.
  • Field sizes should be based on 300 gpd for 2 bdrm and 75 gpd for each additional bdrm.  Minimum field total length based on soil depth and type. See Tables 4 & 5 in the Lake County Rules: 
  • Minimum septic tank capacity is 940 gal.; 1200 gal. for 3-4 bedrooms; 1500 gal. for 4 or more bedrooms.  An effluent filter is required.


Clearlake Oaks
Clearlake Riviera
Hidden Valley Lake
Loch Lomond

Lower Lake


North Lakeport
Parramore Springs
Soda Bay
Spring Valley
Upper Lake
Whispering Pines


Cities and towns (requirements may differ)​

Lake County Setback Requirements

For a graphical representation of Lake County 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 each counties official website.

Links to Lake County Website

For County home page:

For County's Rules for

On-Site Sewage Disposal: