Colorado Package Wastewater Treatment Plant Permitting: CDPHE Approval, Operations, and Compliance

A Colorado package wastewater treatment plant designed for more than 2,000 gallons per day needs three things from CDPHE's Water Quality Control Division: site location approval, design approval and a discharge permit (or a reclaimed water authorization for reuse). It also needs a certified operator in responsible charge for as long as it runs. Order the equipment last, because Colorado counts equipment procurement as construction.

When does a package plant need CDPHE approval in Colorado?

Site location and design approval apply when its design capacity is more than 2,000 gallons per day (gpd). At that size it is a domestic wastewater treatment works, whatever the vendor calls it.

Regulation 22, Colorado's site location and design regulations (5 CCR 1002-22), covers treatment works above 2,000 gpd (section 22.1(2)). State law, C.R.S. 25-8-702, bars construction until the Division approves both the site location and the design. At or below 2,000 gpd, an onsite system follows the local board of health's rules under Regulation 43, Colorado's onsite wastewater rule (section 43.4(A)).

What goes into the site location application?

An engineering report that justifies the site, the treatment approach and the owner's ability to run the plant for its whole life.

For a package plant, these parts of section 22.6(1)(b) carry the most weight:

• Flow projections, phasing, alternative sites and treatment alternatives.
• Water quality planning targets from the Division, the limits your process must meet.
• Opportunities to consolidate with existing treatment works, which the Division encourages whenever feasible (section 22.3(1)(c)).
• Floodplain, natural hazard and geotechnical information.
• Staffing needs, a financial system for operation and replacement, and an emergency operations plan that covers backup power.

The county or nearby town, the local health authority and the 208 planning and management agencies each get 60 days to comment first (section 22.6(2)). You post a sign on the site for 15 days before submitting (section 22.6(3)). The approval expires if construction has not started by the date in the letter, 18 months by default (section 22.4(9)).

How does CDPHE design approval work?

It follows site location approval in two steps: a Process Design Report (PDR) for Division approval, then your engineer's self-certification of the final plans. A professional engineer registered in Colorado stamps both (section 22.13(1)).

The PDR is checked against CDPHE's Design Criteria for Domestic Wastewater Treatment Works (WPC-DR-1), effective June 7, 2022. If the plant will start well below design flow, as phased developments do, the PDR must show how it runs until loaded (section 1.3.3). A preliminary plan of operation covers staffing, operator certification, sludge quantities and disposal, and emergency backup power (section 1.3.6). After construction, a Colorado-registered engineer certifies the plant was built as approved (section 22.13(2)).

When can you order the package plant?

After site location approval, PDR approval and the Division's acceptance of the final design self-certification. Not before.

Section 22.13(1) allows preparation work such as clearing and access roads after site location approval, but not procurement or installation of equipment. The engineering reason: the planning targets set the process, and a unit bought before you know them may not meet them.

Which package plant technology fits a Colorado site?

The one that meets your limits in winter, at your altitude, at the flow you will see in year one. The criteria require design for the site's temperature ranges and altitude (section 2.2.3).

Sequencing batch reactors (SBRs), oxidation ditches and membrane bioreactors (MBRs) are reviewed as activated sludge processes, the same as a plant built in place (sections 7.4.0 to 7.6.0). Some rules hit package units directly:

• A single-train SBR under 40,000 gpd must hold peak hour influent through the settle and decant cycle.
• An oxidation ditch needs two mixers or aerators per ditch, and two trains or provisions for taking one train out of service.
• An MBR needs fully redundant fine screens, plus standby power to keep flow moving through the membranes in an outage or another way to handle that flow.

A new plant on a new site discharging to surface water also falls under Regulation 85, Colorado's nutrients management control regulation: 0.7 mg/L total phosphorus and 7 mg/L total inorganic nitrogen as rolling annual medians, unless an exception or variance applies. Matching the unit to those limits is most of the work in package wastewater treatment plant design in Colorado. If no standard unit fits, compare a custom-designed plant.

What redundancy and standby power does CDPHE expect?

Two units of each process at 40,000 gpd and above, firm capacity on pumps and blowers at any size, and a plan for power failures (sections 2.3.4 and 2.2.2).

• At 40,000 gpd or more, a two-unit design sizes each unit for at least half the flow, and the remaining units must pass peak flow with the largest out.
• A single train below that needs described bypass and backup, plus an emergency plan such as storage or hauling.
• Pumps, blowers and chemical feed pumps must deliver full design capacity with the largest unit out.
• Without power, the plant must still convey all flow without bypass and provide preliminary treatment, primary-equivalent treatment and disinfection. Standby power can be a self-starting generator or a second independent supply.
• Berms and basins for critical facilities, including generator and fuel storage, must be at least 12 inches above the 100-year flood level (section 2.2.4).

Who is allowed to operate the plant?

A certified operator in responsible charge, certified at or above the plant's class. No owner may run the plant without one (Regulation 100, the operator certification rules (5 CCR 1003-2), section 100.10.1).

The class comes from process and design flow, and the highest-rated process sets it (sections 100.5.2 and 100.5.4). Below 0.5 million gallons per day, an extended aeration SBR rates Class C, while activated sludge, oxidation ditches, MBRs and phosphorus removal rate Class B. So the technology choice sets who you can hire.

A limited-services contract, such as compliance sampling only, does not count (section 100.10.1(d)). A contract operator, a neighboring district or your own certified staff can fill it. The owner names the operator to the Division within 30 days of startup (section 100.10.4).

Which permit covers the treated effluent?

A Colorado Discharge Permit System (CDPS) permit for discharge to surface water or groundwater, a reclaimed water authorization for reuse, or both.

Regulation 61, the CDPS regulations, bars point source discharges to state waters without a permit (section 61.3(1)(a)). Apply for a new individual permit at least 180 days before discharge (section 61.4(1)(c)). The permit is a separate track from site and design review, so the two must agree; here is how the site application and the discharge permit application differ. For reuse, Regulation 84, the reclaimed water control regulation, requires a Treater Authorization, and each user files a User Application and Site Management Plan (sections 84.6 and 84.9).

Are you ready to order a package plant?

If any answer is no, you are not ready to buy.

1. Is the design capacity set from real flow projections, with phasing?
2. Do you have water quality planning targets from the Division?
3. Have you documented whether consolidation is feasible?
4. Are site location approval, PDR approval and self-certification acceptance in hand?
5. Do you know the operator class and who will be in responsible charge?
6. Is the discharge permit or reuse application filed on time?

Then ask your engineer how the plant runs at first-phase flow.

Scope: this is general education on the Colorado rules and CDPHE criteria in force in October 2026. Your limits, operator class and review outcome come from the Division and your engineer of record.

Frequently asked questions

Does a package plant under 2,000 gallons per day need CDPHE approval?

Not site location and design approval. An onsite system that size follows local board of health rules under Regulation 43. A discharge to surface water still needs a CDPS permit under Regulation 61 and a certified operator under Regulation 100.

What happens when the development outgrows the plant?

Added capacity is an expansion. It needs a site location application under section 22.7, design approval, and authorization in the discharge permit before use (section 22.2(14)). Reserve room for added units from day one.

I'm developing a 150-lot subdivision in a Colorado mountain county with no sewer nearby. Will CDPHE accept a package plant or push us to connect?

Your application must analyze consolidation. The Division weighs cost, the regional water quality management plan, and legal and physical limits, and relies substantially on a current, complete regional plan (sections 22.5(1)(c) and (k)). If connecting is not feasible, document why.

I manage a small water and sanitation district in Colorado replacing an old package plant with an MBR. Will our Class C operator still qualify?

Likely not. Below 0.5 million gallons per day an MBR rates Class B under Regulation 100, which needs a Class A or B operator in responsible charge. Confirm the class with the Division early.

Related resources

• Domestic Wastewater Treatment Works Design Criteria: The CDPHE Engineering Standards Package Plants Must Meet
• Colorado CDPHE Discharge Permit Process: Timeline, Requirements, and How It Differs from Texas
• Colorado Biosolids Management Regulations: How CDPHE Land Application Rules Differ from Texas for Private Plant Operators
• Antidegradation Policy in Colorado Water Permits: What It Means for New Discharge Permits

Planning a package wastewater plant in Colorado?

The permit path is easiest to settle during due diligence, before the site plan and the equipment are fixed. MES is licensed in Colorado, with an office in Golden, and handles the wastewater side from feasibility through construction.

We specialize in:

• Package treatment plant feasibility and design
• Site location applications and process design reports
• Discharge permit applications
• Lift stations and collection systems
• Construction administration

Modern Engineering Solutions, McKinney, Texas. Contact: (214) 833-6748 or mod-eng.com