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 (VR)

A single-family Dwelling Unit offering transient lodging accommodations to a single booking party at a time within that dwelling unit for a rental duration of fewer than 30 days where the entire dwelling unit is solely occupied by the rental party during the duration of the rental period.

Short-Term Rental (STR)

A Dwelling Unit offering transient lodging accommodations to a single booking party at a time within that dwelling unit for a rental duration of fewer than 30 days. A Short-Term Rental is the primary residence—the dwelling unit in which a person resides for more than six months out of the year—of an owner or tenant and generally rented while the owner or tenant is residing and present at the property.

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 12 of Boulder County OWTS Regulations 5 CCR 1002-43, Section 6.
  • 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.

Permitting Requirements

Property owners MUST get a permit before:

• Installing, changing, or repairing any septic system.
• Fixing a non‑compliant system. If BCPH sends a notice that the system is failing or unsafe, the owner must apply for a construction-related permit within two business days.
• Expanding or changing the use of a system – for example, adding bedrooms to a house – if the existing system is too small, or if the use of the OWTS will change the hydraulic or organic load to the system.
  • If an engineer says the current OWTS can handle the new use without changes, BCPH issues a Change in Use Permit instead of a construction-related permit.

OWTS Permits to Construct

A permit to construct, including alterations or repairs, documents when a septic system is built, changed, or repaired. As the name implies, construction is involved with these types of permits.

There are four (4) types of construction-related permits:

1. New Permit – Used for properties that have never been developed before.
2. Major Repair Permit (linked to a building permit) – Used when a septic system is replaced or expanded because of a development project beyond the OWTS construction.
3. Major Repair Permit (not linked to a building permit) – Used to replace, fix, or expand an existing septic system.
4. Minor Repair Permit – Used for small fixes, such as repairing a septic tank or replacing a part.

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.

OWTS Permits for Operation, Maintenance and Use

There are three (3) types of permits that aren’t associated with construction, although sometimes obtaining these permits may require additional permits.

OWTS Operating Permit (also referred to as Continued Use Permit)

The Operating Permit (OP permit) shows that an OWTS is functioning properly and is protecting public health. This permit functions as an operating permit and serves a similar function to a certificate of occupancy demonstrating that a house is safe to live in. The Continued Use Permit documents the allowed use based on approved permit and design.

This permit documents the maintenance requirements for the OWTS that the owner is required to perform. If a system is failing or does not meet requirements, BCPH can revoke the Continued Use Permit and require the owner to fix the problem. Under current regulations, BCPH issues the Operating Permit (which is referred to in records as USEP) when the OWTS construction permit is closed. The cost of an Operating Permit is included in the construction permit fee and there are no renewal requirements for the majority of OWTS.

• For OWTS installed between May 24, 2018 and Sept 24 2026, a BCPH-issued “use permit” shall be treated as an operating permit.
• For OWTS installed before May 24, 2018, documented BCPH approval of the OWTS shall be treated as an operating permit under these Regulations.
• As of May 24, 2018, OWTS that never completed the BCPH permitting or approval process will be deemed operating without a valid operating permit.

OWTS Change in Use Permit

There is a public health risk when hydraulically overloaded OWTS cannot properly treat wastewater, as the wastewater can contaminate ground water and surface water. Where it has been determined that activities on a property will increase hydraulic and/or organic load being received by the OWTS and the permitted and approved OWTS is determined to be able to adequately treat the additional load, a Change in Use Permit is required to be obtained by the property owner. The Change in Use Permit:

• Documents the expanded use of the OWTS.
• Ensures the OWTS is in good working order and continuing to operate as designed.

This policy complies with Colorado regulatory requirements in 5 CCR 1002-43 Section 4.B.8.

A Change in Use Permit requires an engineer evaluation of the current OWTS, documentation of treatment capacity for proposed increased flow, and an OWTS NAWT (National Association of Wastewater Technicians) inspection. In some cases, soil verification may be required.

BCPH issues a Change in Use Permit under the following conditions:

• Property development or renovation resulting in increased hydraulic and/or organic load received by the OWTS. For example, increasing bedrooms in a home, adding an accessory dwelling unit (ADU) or connecting another structure, including modular unit or mobile home, to the OWTS.
• New or change in activities or operations resulting in increased hydraulic and/or organic load. For example, changing tenants, adding new business processes, or increasing in production.
• When a septic system is failing and emergency use is requested.
• Note: If the OWTS cannot accommodate the additional hydraulic and/or organic load, the owner must apply for the appropriate construction-related permit to alter or replace the OWTS

OWTS Maintenance Permit

Boulder County sometimes encounters challenging site conditions when it comes to designing compliant OWTS. To protect public health, and in conformance with CO state regulations, BCPH allows the use of higher-level treatment (HLT) systems under a strict set of conditions. This allows for reduced setbacks and sizing of OWTS: it also requires BCPH to have an oversight and maintenance program for HLT systems. Oversight is important as the public health risk is higher if components are not operating properly due to the setback reductions granted to these systems.

Maintenance Permits are renewable permits and are required for the following:

• OWTS designed and permitted with a reduction in horizontal and vertical setback distances based on higher level treatment of effluent.
• NDDS (non-pressurized drip dispersal systems).
• Disinfection component.
• Compost and incinerating toilets.

Unrelated to HLT but also required:

• Owners documenting water usage to evaluate hydraulic load for new or expanded uses at the property.

BCPH staff reviews the inspection and maintenance reports at time of the renewal, ensures a new service contract is provided, and renews the Maintenance Permit for the length of the service contract.

When OWTS Construction is Not 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.