Onsite Wastewater Treatment System (OWTS) Change in Use Policy

Onsite Wastewater Treatment System (OWTS) Change in Use Definitions

Accessory Dwelling Unit (ADU): a dwelling unit that is accessory to a permitted Principal Use (main dwelling). This building can have a shower, bathtub, and stove, if allowed by Community Planning. This includes a disaster recovery unit. These are managed under the Residential Change in Use policy.

Accessory Structure: a structure that is limited to a convenience bathroom, wet-bar sink, washer, and dryer, and is only to be used by the occupants of the main structure. This structure cannot have a shower, bathtub, or stove.

Convenience Bathroom: a half-bathroom (toilet and hand-sink only) that is only to be used by the occupants of the main structure.

Non-Residential Use: when wastewater is generated from activities not typical of a residential household. Examples include but are not limited to horse facilities, home offices with employees or regular clients, in-home daycares, restaurants, coffee shops, marijuana facilities, and other commercial establishments. Flows generated by rental, multi-family, or community systems also fall under non-residential use.

Multi-Family or Community Systems: duplex, triplex, community or cluster system, etc. These are managed under the Non-Residential Change in Use policy.

Vacation Rental: a dwelling unit that can be rented to a single booking party for a rental duration of fewer than 30 days where the entire unit is solely occupied by the rental party.

Short-Term Rental: a dwelling unit that can be rented to a single booking party for a rental duration of fewer than 30 days where the owner can reside on-site at the same time as the renters.

Adding Bedrooms or an Accessory Dwelling Unit

If residential use of the OWTS is changing based on what was previously permitted and approved, the following will be required:

• Submit an engineer report that includes:
  • Minimum of two test pits with soil analysis.
    • If soil analysis for the existing approved OWTS permit meets the current regulations, this requirement may be waived.
  • Evaluation of test pit soil analysis collected under current regulations.
  • Wastewater flow and strength calculations using Section 9 of Boulder County OWTS Regulations.
  • Verification of whether the current system is adequate to treat proposed wastewater and/or provide any required changes needed using current regulations.
  • Site plan that includes existing and proposed structures, setback features, current OWTS layout, and any proposed components.
  • Design of any new connections/sewer lines and components that may be required.
• Submit a certified NAWT inspection:
  • Required except in cases where the building(s) connected to the OWTS will be demolished.
  • Inspections completed within the past 12 months will be allowed.

Conditions that may apply:

• If seasonal groundwater is higher than when the soil treatment area (STA) was permitted and installed, STA replacement may be required.
• The septic tank must meet current requirements for retention time and size.
• Any existing single-compartment tanks will not be approved unless a second tank is added in series.
• Components that will not otherwise be altered won’t be required to meet the current code. (Example: risers above grade, effluent screens, pressure dosing, soil replacement with sand).

Adding an Accessory Structure

If the use of the OWTS is changing from what was previously permitted and approved by adding an Accessory Structure to the system, the following requirements will apply.

Submit an engineer report that includes:

• Site plan that includes existing and proposed structures, setback features, current OWTS layout, and any proposed components.
• Specifications for connecting the new sewer line to the existing OWTS.
• Verification that the wastewater generated in the accessory structure is only from the occupants of the main dwelling or structure; therefore, the system’s design flow is not changing.
  • If wastewater generated in the accessory structure will not come from the occupants of the main dwelling or structure and/or is not the typical composition of untreated domestic wastewater, see the requirements in the Non-Residential Change of Use.

Proposing Non-Residential Change in Use

If non-residential use of the OWTS is proposed or changing based on what was previously permitted and approved, the following will be required:

• Submit an engineer report that includes:
  • Minimum of two test pits with soil analysis
    • If soil analysis for the existing, approved OWTS permit meets the current regulations, this requirement may be waived.
  • Evaluation of test pit soil analysis collected under current regulations.
  • Wastewater flow and strength calculations using Section 9 of Boulder County OWTS Regulations.
  • Verification whether the current system is adequate to treat proposed wastewater and/or provide any required changes needed using current regulations.
    • This should include BOD and other pre-treatment requirements such as grease interceptors.
    • Class V well approval or other documentation from EPA, if required.
  • Site plan that includes existing and proposed structures, setback features, current OWTS layout, and any proposed components.
  • Design of any new connections/sewer lines and components that may be required.
• Submit a certified NAWT inspection:
  • Required except in cases where the building(s) connected to the OWTS will be demolished.
  • Inspections completed within the past 12 months will be allowed.
  • The pumping requirement may be waived if documentation demonstrates that pumping was completed within the past 3 years by the same NAWT inspector.

Conditions that may apply:

• If seasonal groundwater is higher than when the soil treatment area (STA)was permitted and installed, STA replacement may be required.
• The septic tank must meet current requirements for retention time and size.
• Any existing single-compartment tanks will not be approved unless a second tank is added in series.
• Components that will not otherwise be altered won’t be required to meet the current code. (Example: risers above grade, effluent screens, pressure dosing, soil replacement with sand).

Changing Non-Residential Tenant/Occupants or Property Ownership

If a non-residential property has a change of tenant (occupants operating in the facility) or a change in ownership, it is subject to the following:

Property ownership is changing, but the same tenant approved on the OWTS permit is continuing to operate in the facility:

• A property transfer inspection report is required.
• Boulder County may accept an affidavit certifying that use will not be changing. Contact our department to review your proposed plan.

Tenants/occupants operating in the facility AND property ownership are changing:

• A property transfer inspection report is required.
• If new or proposed changes to the property are known at the time of property transfer, the requirements in the Non-Residential Change of Use requirements above must be met.
• If changes to the property are unknown at the time of property transfer, or if the engineer chooses to collect new water usage (flow) data for calculations, a conditional property transfer certificate will be applied until the requirements above are met. Additional requirements include:
  • A Non-Residential Repair Agreement is required at the time of Conditional Property Transfer.
  • Submit the engineer’s report within 1 year of closing on the property.
    • If water usage data will be collected for calculations, a renewable Use Permit must be applied for within 1 year of closing on the property. The engineer’s report with new calculations must then be submitted within 1 year of applying for the renewable Use Permit.
• If the new business will be very similar (e.g., retail to retail), an affidavit in lieu of an engineer report may be allowed. Contact our department to review your proposed plan.

If only the tenants/occupants operating in the facility are changing:

• A certified NAWT inspection is required.
• If there is a new or proposed change(s) in use, the Non-Residential Change in Use requirements above must be met.
• If the new business will be very similar (e.g., retail to retail), an affidavit in lieu of an engineer report may be allowed. Contact our department to review your proposed plan.

Vacation Rentals

If the use of the OWTS is changing from what was previously permitted and approved by becoming a vacation rental, the following will be required:

• Submit a certified NAWT inspection.
  • Inspections completed within the past 12 months will be allowed.
  • The pumping requirement may be waived if documentation demonstrates that pumping was completed within the past 3 years by the same NAWT inspector.

Conditions that may apply:

• The OWTS is sized for a maximum allowable number of residents, and the rental must stay within this limit, including any permanent residents on-site.
• If the owner is requesting more occupancy than the OWTS can serve, the Non-Residential Change in Use requirements above must be met.
• For properties with vaults:
  • Vaults may be permitted on properties that cannot accommodate an OWTS with a soil treatment area or if the dwelling does not have running water. If documentation of this is not available and there is room to install a full system, a repair permit will be required.
  • The vault must utilize both audio and visual alarms. It is recommended to utilize a wireless notification alarm panel that directly alerts either the property owner or the service provider when the vault is full.
  • Owners must contact and submit documentation from a service provider stating that they will service the property when pumping is requested.
• For changes in vacation rental property ownership:
  • A property transfer certificate and Use Permit renewal are required.
• Properties will be issued a Renewable Use Permit that is valid for 2 years. At renewal, owners must submit all pumping receipts and any related service documentation. Renewal fees apply.

When OWTS Construction is Needed

*If a component has already been installed without an OWTS permit, it will still fall under one of the above scenarios and needs to be verified and approved by BCPH. BCPH does not verify any illegal installations or alterations of STAs.

When No OWTS Construction is Needed

*Renewal, revision, and additional inspection fees may apply.

Some situations will not meet these exact criteria. If you are unsure where you fit into these scenarios and definitions, please contact us at 303-441-1564 or HealthOWS@bouldercounty.gov.