Guidelines for OWTS Installations

The following is a summary of frequently asked questions regarding construction requirements and code changes made during Larimer County’s adoption of Colorado’s Regulation 43 in June 2018.

Tank Lids and Access Risers
Access risers must be provided to grade on all tank lids, distribution boxes, and other components that require access for inspection or periodic maintenance. Lids must be watertight, and secured either with screws, bolts, chains or sufficient weight (>59 pounds). 

System Dimensions 

  • Standard, gravity style systems are limited to 12 feet wide and 100 feet long. If additional area is required, multiple beds may be installed with six feet of undisturbed soil between bed areas. 
  • Systems may be installed no more than 48” below grade (to bottom of gravel or chambers). Permit details will specify if a shallower depth is necessary to provide adequate separation to bedrock or groundwater. 

Distribution Boxes 
If a distribution box (d-box) is used, flow equalizers must be installed on the outlet lines to adjust flow, and the d-box must have a watertight riser to grade for access.

Piping type, Bedding, and Clean-outs

  • Piping must be a minimum of SDR 35, no less than 4”, buried 12” below grade, with no less than 1/8” per foot (1%) fall for the building sewer to and effluent line from the septic tank. 1/4” per foot (2%) fall is recommended, and SCH 40 pipe (pressure rated) is required in pressure distribution systems and under driveways. Bell ends of gasketed pipe must be installed on the uphill side of the pipe section. Connections to the interior building sewer at the foundation must be made with glued fittings or flexible couplers with shear rings or shear guards.
  • Bends in piping are limited to 45 degree or sweeping 90’s, two 45 degree fittings are preferred and should be used to turn 90 degrees in the building sewer (house to tank). A cleanout is required within 5 feet of the building, for every 100’ of building sewer (line from house to tank), and wherever a bend of greater than 45 degrees is made, unless a cleanout is already located within 40’ upstream.
  • Piping must be bedded in material free of rocks or large clods prior to backfilling, use of sand or squeegee is recommended. The tank inlet and outlet must be backfilled and compacted to support the pipe prior to installation.

Trench Style Systems

  • When chambers are installed in trenches they must be installed in a single row, not to exceed 100’ for gravity systems (150’ for pressure dosed systems), with a minimum of 48” of undisturbed soil between rows, and an observation port at the end of each row. A reduction in the total number of chambers is given for trench style systems vs bed systems.

Septic Systems

Questions? Contact OWTS

(970) 498-6775