Weld County, Colorado On-Site Wastewater Treatment System Regulations Study Guide.

I’m building out this message board thread to assist those attempting to pass the exam necessary to be an On-Site Wastewater Treatment System Contractor in Weld County, Colorado.


Absorption System: Leaching field and adjacent soils for the treatment of sewage in an On-Site Wastewater Treatment System by means of absorption into the ground.

Basal Area: Effective surface area available to transmit the treated effluent from the filter media in a mound system to the in-situ receiving soils. The perimeter is measured at the interface of the imported fill material and the in-situ soil.

In-situ soil means original soil.

Bed: Below-grade soil treatment area with a level sub-base at least 3’ wide, distribution media, and more than one lateral.

Note: It isn’t a bed unless it has two or more laterals.

Bedroom: A room with an egress window, a closet, and/or is intended for sleeping purposes.

Building Sewer: Piping that conveys wastewater to the first system component.

Cesspool: Underground pit into which household wastewater is discharged and from which the liquid seeps into surrounding soil.

Note: A cesspool doesn’t include a septic tank.

Chamber: An open, arch-shaped structure providing an open-bottom soil interface with permeable sidewalls.

Cistern: Underground tank for storing water.

Dosing: High rate, periodic discharge into a soil treatment area.

Drop Box: A device used to distribute effluent by gravity flow into a lateral of a soil treatment area.

Drywell: Underground pit into which drainage from roofs, basement floors, or other non-wastewater sources is discharged.

Effective Size: Size of granular media such that only 10% by weight of the media is finer.

Effluent Pipe: Non-perforated pipe that conveys effluent from one component to another.

Flow Daily: Measured volume of wastewater generated from a facility in gallons in a day.

Note: Expressed as Gallons/day.

Flow Equalizer: Adjustment device to evenly distribute flow between outlets in a distribution box, even when it is not level.

Infiltrative Surface: Interface where effluent moves from a distribution media into a treatment media or original soil.

Note: In a mound system there is an infiltrative surface between the distribution media and fill sand, and another between the fill sand and the in-situ soil.

Lateral: Pipe to carry and distribute effluent.

Limiting Layer: A condition in the soil profile that limits treatment or restricts movement of fluids. Examples include:

  • soils with low or high permeability.
  • impervious or fractured bedrock.
  • seasonal or current ground water surface.

Liner: Impermeable synthetic material used to prevent or restrict infiltration or exfiltration.

Note: The minimum thickness of a liner is 30 ml.