Colorado Wastewater Treatment Plants

Introduction

Colorado sits at a unique geographical and regulatory intersection within the United States water sector. As a headwaters state, the effluent quality from Colorado’s wastewater treatment plants (WWTPs) dictates the water health for millions of downstream users in the Colorado, Platte, Arkansas, and Rio Grande river basins. Consequently, the state maintains some of the most rigorous nutrient and temperature regulations in the country.

The state’s infrastructure is currently bifurcated. The rapidly urbanizing Front Range (Denver, Colorado Springs, Fort Collins) is seeing massive consolidation and capacity expansion to handle population growth. Conversely, mountain and rural communities are grappling with aging infrastructure and the technical challenges of treating water at high altitudes with extreme seasonal load variations due to tourism. Currently, the Colorado Department of Public Health and Environment (CDPHE) oversees over 250 permitted domestic wastewater treatment facilities, ranging from massive regional reclamation districts to small lagoon systems.

For consulting engineers and equipment vendors, Colorado represents a high-activity market driven primarily by Regulation 85 (Nutrient Management Control), water reuse initiatives (including recently approved Direct Potable Reuse regulations), and aging infrastructure replacement.

Among US wastewater treatment plants, Colorado’s occupy an unusual position: no significant river enters this state. Every drop originates here and leaves under one of nine interstate compacts, which means Colorado plants have downstream obligations and no upstream dilution to rely on. Two further conditions shape design in ways that do not apply elsewhere. Below Denver and Colorado Springs, the receiving streams run effluent-dominated for long stretches during low flow, so the plant is effectively setting the water quality of the river rather than contributing to it. And Colorado water law distinguishes native water, which must be returned to the stream for downstream appropriators, from transmountain water imported across the Continental Divide, which is fully consumable and can be reused to extinction. Whether a utility holds transmountain rights determines whether reuse is legally available to it at all. This page indexes every Colorado facility profiled on the site within that framework.

Recent Developments & Infrastructure Trends

In the last 36 months, Colorado’s wastewater sector has shifted focus from simple capacity expansion to advanced resource recovery and complex nutrient removal. The implementation of Regulation 85 has forced nearly every mechanical plant in the state to evaluate or upgrade their Biological Nutrient Removal (BNR) capabilities to meet strict Total Inorganic Nitrogen (TIN) and Total Phosphorus (TP) limits.

Key Market Drivers:

• Direct Potable Reuse (DPR): In late 2022/early 2023, Colorado became one of the first states to adopt formal regulations for Direct Potable Reuse. This is spurring new feasibility studies for “pipe-to-pipe” infrastructure projects in the drought-prone Front Range.
• Biogas and Energy Recovery: Facilities like Metro Water Recovery and South Platte Renew are heavily investing in co-generation and Renewable Natural Gas (RNG) pipeline injection, leveraging federal RIN credits.
• PFAS Mitigation: With the CDPHE intensifying testing requirements for Per- and Polyfluoroalkyl Substances, several municipalities are launching pilot studies for granular activated carbon (GAC) and ion exchange solutions.
• Funding Influx: The state has seen a significant injection of funds via the State Revolving Fund (SRF) and the Bipartisan Infrastructure Law (IIJA), specifically targeting disadvantaged communities and emerging contaminants.

Two structural pressures sit beneath these drivers. Colorado River shortage and the ongoing negotiation over post-2026 operating guidelines have raised the value of every consumable acre-foot on the Front Range, which strengthens the case for reuse infrastructure at utilities holding transmountain rights and weakens it at those without. Separately, Front Range growth has outpaced the collection systems serving it, so a substantial share of current capital is going into interceptors and regional conveyance rather than into treatment capacity itself.

Top 20 Largest Treatment Plants in Colorado

The following list ranks the largest wastewater treatment facilities in Colorado based on rated Design Capacity (MGD). Data is compiled from CDPHE discharge permits, utility master plans, and Metro Water Recovery annual reports.

Note: Colorado Springs Utilities operates a second major facility, the J.D. Phillips Water Resource Recovery Facility on Monument Creek, which does not appear in the ranking above. It is profiled in the regional directory below.

Profiles of the Top 5 Largest Facilities

Regional Plant Listings (Tiers 6-20)

Large Municipal Plants (Rank 6-10)

• Pueblo Water Reclamation Facility (19 MGD): Key discharger to the Arkansas River; utilizes activated sludge with significant nutrient removal upgrades planned.
• Drake WRF – Fort Collins (23 MGD): Known for environmental stewardship; heavily invested in biological phosphorus removal and energy optimization. Covered in detail in our profile of the City of Fort Collins Water Reclamation and Biosolids Facility.
• Greeley WPCF (14.7 MGD): Serving the agricultural hub of Weld County; recently underwent significant headworks and odor control improvements.
• Boulder WRF (25 MGD): Uses a modified Bardenpho process; famous for its Renewable Natural Gas (RNG) complex. See our article on the Boulder Wastewater Treatment Plant for the full treatment train and energy program.
• Longmont WWTP (17 MGD): Recently completed a Biogas Treatment Project to convert digester gas to Vehicle Fuel (RNG).

Significant Facilities (Rank 11-20)

• Big Dry Creek (Westminster): 12 MGD capacity, heavy focus on water reuse for irrigation (golf courses/parks).
• Boxelder Sanitation District: 10.6 MGD, serving rapid growth east of Fort Collins; recently expanded with new BNR basins.
• Plum Creek (Castle Rock): 10.6 MGD, a regional authority known for advanced oxidation processes to handle reuse water standards.
• Centennial (Marcy Gulch): 9.5 MGD, integral to the south metro water reuse strategy.

Colorado Treatment Plant Directory by Region and Basin

Colorado’s plants divide by basin, and the basin determines both the regulatory pressure and the reuse opportunity. The South Platte carries roughly three quarters of the state’s population and the bulk of its treated flow, running effluent-dominated below Denver during low-flow months. The Arkansas receives Colorado Springs and Pueblo, with Fountain Creek as the connecting reach and downstream agricultural users as the interested party. The Colorado River basin on the Western Slope handles the state’s mountain and resort communities plus Grand Junction. The Rio Grande in the San Luis Valley is the smallest of the four. The listings below index every Colorado facility profiled on this site, grouped accordingly.

Denver Metro and the South Platte

Metro Water Recovery treats the majority of Denver-area flow through two facilities, serving the city and more than sixty connector districts. This is a regional authority rather than a municipal utility, which changes how capital decisions get made: member districts contribute on a formula basis and capacity allocations are negotiated rather than assigned. The South Platte below the Robert W. Hite outfall is effluent-dominated for a substantial distance in late summer, meaning the plant’s effluent is not diluted into the river so much as it becomes the river. Ammonia, nitrogen, and temperature limits are set with that in mind, and the same condition makes downstream agricultural and municipal users in the lower South Platte direct stakeholders in plant performance.

Metro Water Recovery, district view. A second article on the Metro Wastewater Reclamation District Robert W. Hite Treatment Facility in Denver covers the plant from the district’s operating perspective: the interceptor network feeding it, the relationship with the Northern Treatment Plant that now absorbs growth in the northern service area, the METROGRO biosolids land application program, and the cogeneration and struvite recovery installations that have made the site a resource recovery reference in the interior West.

Aurora reuse and potable supply. Our article on the City of Aurora Prairie Waters Project covers the facility at the far end of the reuse chain rather than at the treatment end. Prairie Waters recovers water from the South Platte downstream of the metro area through riverbank filtration, then purifies it through ultraviolet advanced oxidation and carbon filtration for return to Aurora’s potable system. It works only because Aurora holds transmountain and other fully consumable water rights that entitle the city to recapture return flows it would otherwise have to leave in the river. The project is the clearest illustration in the state of why Colorado water law, not treatment technology, determines whether a reuse scheme is available to a given utility.

South Platte Renew in Englewood, the Northern Treatment Plant in Brighton, and the Westminster, Broomfield, Centennial, Plum Creek, and Parker facilities are not yet covered by individual articles on this site.

Front Range North: Boulder, Fort Collins, and the Cache la Poudre

The northern Front Range combines fast municipal growth with intensive agriculture in Weld County, which puts nutrient management and biosolids land application in the same conversation. Both major facilities profiled here are known nationally for resource recovery rather than for scale. The receiving streams are smaller than the South Platte mainstem, so dilution is limited and Regulation 85 limits bind harder than they do at larger plants downstream.

The Fort Collins and Boulder facilities are linked in the rank 6-10 listings above. Fort Collins is notable for combining water reclamation and biosolids management in a single program with its Meadow Springs Ranch land application operation, and Boulder for pairing a modified Bardenpho train with one of the earlier municipal renewable natural gas installations in the state. Greeley, Longmont, Loveland, and the Boxelder Sanitation District plants are not yet covered individually.

Front Range South: Colorado Springs, Fountain Creek, and the Arkansas

Colorado Springs Utilities operates two major water resource recovery facilities on opposite ends of the city, and its situation differs from Denver’s in a way that has produced years of litigation and negotiation: Fountain Creek carries both treated effluent and stormwater from a rapidly developing, steeply sloped watershed down to Pueblo and the Arkansas River, where senior agricultural rights and a downstream municipality are directly affected. Sedimentation, flood flows, and effluent quality are managed together here in a way that is unusual for a municipal utility.

J.D. Phillips Water Resource Recovery Facility. The Colorado Springs Utilities J.D. Phillips Water Resource Recovery Facility serves the northern half of the city, discharging to Monument Creek above its confluence with Fountain Creek. It is the newer of the utility’s two plants and was designed with nutrient removal in mind rather than retrofitted for it, which makes it a useful reference for what a purpose-built Regulation 85 compliant facility looks like at this scale in Colorado conditions.

The utility’s Las Vegas Street facility, the largest plant in southern Colorado, appears in the top-20 table above. Pueblo, Fountain, and Security are not yet covered individually.

Western Slope and Mountain Communities

West of the Continental Divide the design problem changes character. Grand Junction’s Persigo plant discharges to the Colorado River shortly before it leaves the state, with selenium and salinity in the Grand Valley adding parameters that Front Range plants do not face. Higher up, resort communities in Summit, Eagle, Pitkin, and Routt counties operate small plants at elevations between 7,000 and 10,000 feet with seasonal load swings of several times between shoulder season and peak.

Altitude is a genuine engineering variable here rather than a footnote. Reduced atmospheric pressure lowers oxygen transfer efficiency, so blowers must be sized with a correction that grows with elevation, and a package plant specified against sea-level performance curves will not deliver its rated capacity at 9,000 feet. Cold influent temperatures slow nitrification kinetics at exactly the time of year when tourism load peaks, and receiving streams are cold-water fisheries with tight ammonia and temperature standards and very little dilution. None of the Western Slope or mountain facilities is yet covered by individual articles on this site.

Plants with Approved Budgets & Expansion Projects

Colorado’s wastewater sector is seeing high capital velocity. The following projects represent confirmed capital allocations derived from municipal CIPs, bond issuances, and SRF Intended Use Plans.

A. Major Projects Under Construction (2024-2026)

B. Projects in Design/Planning Phase (2025-2027)

• Aurora Water – Wild Horse Reservoir (Related Infrastructure): While primarily a water supply project ($600M+), this involves significant pumping and potential reuse integration that will impact wastewater strategy.
• Town of Erie – WRF Expansion: In planning to expand capacity from 3.5 MGD to 5+ MGD to accommodate one of the fastest-growing towns in the state. Budget est. $40M+.
• Pueblo West Metro District – Plant Expansion: Design phase for increasing hydraulic capacity to handle new housing developments.

C. Summary Statistics: Colorado Market

• Total Active Capital Investment: ~$650 Million (Active & Planned Major Projects)
• Primary Project Drivers:
  1. Nutrient Removal Compliance (Reg 85) – 40%
  2. Capacity Expansion (Front Range Growth) – 35%
  3. Aging Infrastructure/Solids Handling – 25%
• Key Funding Sources: Colorado Water Resources & Power Development Authority (CWRPDA) SRF Loans, Municipal Revenue Bonds, WIFIA.

Regulatory & Compliance Landscape

Colorado’s regulatory environment is among the strictest in the interior United States, driven by the need to protect headwaters.

• Regulation 85 (Nutrients): The defining regulation for the decade. It sets effluent limits for Total Inorganic Nitrogen (TIN) and Total Phosphorus (TP). It applies to all domestic wastewater treatment works discharging to surface waters. Phase 2 implementation is tightening limits further, driving BNR retrofits.
• Regulation 31 (Temperature): Strict temperature standards to protect aquatic life (trout/fisheries) are forcing plants to investigate thermal reduction strategies, including effluent cooling or riparian shading.
• Regulation 84 & DPR: Colorado governs reclaimed water use under Reg 84. The recent adoption of Direct Potable Reuse (DPR) rules creates a new compliance pathway for utilities to treat wastewater to drinking water standards, opening a new market for advanced oxidation and membrane technologies.
• PFAS/PFOA: The CDPHE is currently in a rigorous data-collection phase, requiring sampling from facilities. Future discharge limits are anticipated, which will require capital investment in GAC or Ion Exchange systems.
• Ammonia standards: Colorado applies aquatic-life-based ammonia criteria that vary with pH and temperature, and cold-water fishery designations across much of the state produce limits that bind hardest in winter, when nitrification kinetics are slowest. This combination is the reason so many Colorado plants carry excess aeration basin volume relative to their rated flow.
• Biosolids: Land application is regulated by CDPHE with site authorizations, agronomic loading limits, and setback requirements. Large Front Range utilities have secured dedicated application acreage on the eastern plains, which is why biosolids strategy here is a land holding question as much as a treatment one.

Water rights determine whether reuse is even available

Colorado’s prior appropriation system creates a distinction with no equivalent in most states. Native water diverted from a stream must have its return flows delivered back for downstream appropriators, so a utility using native water generally cannot reuse its effluent. Water imported across the Continental Divide through a transmountain diversion, along with certain non-tributary groundwater and some changed agricultural rights, is fully consumable and may be used, reused, and successively used to extinction.

The practical consequence is that two Front Range utilities of identical size can face completely different reuse economics based on the composition of their water portfolios rather than on anything at the plant. Aurora, Denver, Colorado Springs, and several south metro districts hold consumable supplies and have built or planned reuse infrastructure around them. Utilities without such rights cannot capture the same value no matter how well they treat. Any reuse feasibility work in this state should begin with a water rights review, not a treatment train evaluation, and any vendor proposing reuse technology should establish that the customer has the legal right to the water before discussing how to purify it.

Altitude changes the design basis

Atmospheric pressure at Denver is roughly 83 percent of sea level, and at a 9,000-foot mountain district closer to 72 percent. Oxygen transfer efficiency falls accordingly, so blower and diffuser systems must be sized with an elevation correction, and equipment rated on sea-level curves will underperform. Cold influent temperatures compound the problem by slowing nitrification, and solids settling behavior differs enough that clarifier loading rates carried over from lower-elevation practice can produce disappointing results. These are not marginal corrections at Colorado’s elevations, and they are a common source of underperformance in package plants specified from out-of-state catalogs.

Technology Trends in Colorado

Due to the specific constraints of altitude, temperature, and nutrients, Colorado plants are adopting specific technologies:

• MagPrex / Struvite Recovery: To prevent phosphorus feedback loops in BNR plants, facilities like Metro Water Recovery are recovering struvite as a fertilizer product.
• Intensified Resource Recovery: Moving beyond simple digestion, plants are adopting Thermal Hydrolysis Processes (THP) and advanced gas scrubbing for RNG pipeline injection.
• Membrane Bioreactors (MBR): Increasing adoption in smaller, high-altitude ski town districts where footprint is constrained and effluent quality must be pristine.
• Granular Sludge: Pilot programs are investigating aerobic granular sludge to increase capacity within existing tank footprints.
• Sidestream deammonification: Applied to digester centrate to remove a nitrogen load that would otherwise recycle to the head of the plant and consume aeration capacity that altitude has already made expensive.
• Advanced oxidation for potable reuse: Ultraviolet advanced oxidation paired with carbon filtration or membranes, now with a defined regulatory pathway under the state’s direct potable reuse rules.
• Fine-bubble aeration with dissolved oxygen control: The single highest-value energy retrofit at most Colorado plants, because the elevation penalty makes every point of transfer efficiency worth more here than at sea level.

Comparing Colorado Facility Classes

Colorado facilities sort by basin, by whether the receiving stream is effluent-dominated, and by whether the utility holds consumable water rights. The table below summarizes how those classes differ.

Benchmarking and Site Selection

A state directory gets used to size a market, to find a comparable facility for a design or bid basis, and to anticipate permit requirements. In Colorado all three start with the basin and the water portfolio.

Selecting a comparable facility

Match on receiving stream character before matching on capacity. A plant discharging to an effluent-dominated reach faces limits calculated with essentially no dilution credit, while a plant of the same size on a larger flowing reach may carry limits an order of magnitude looser for the same parameter. Then check elevation, because aeration equipment and energy cost per unit of oxygen delivered are not transferable between a 5,000-foot Front Range plant and a 9,000-foot mountain district. Only after those two filters does process configuration become a useful comparison.

Worked example: sizing a comparison set

Suppose a northern Front Range district needs a benchmark for a 15 MGD Regulation 85 nutrient upgrade with an ammonia limit driven by a cold-water fishery designation. Filtering by basin and dilution eliminates the Denver and Colorado Springs plants, whose scale and effluent-dominated conditions produce different limit calculations. What remains is the Fort Collins, Boulder, Greeley, and Longmont group. Two adjustments are needed before normalizing to a per-MGD figure. Separate the biosolids and energy recovery scope, since both Fort Collins and Boulder bundled resource recovery work into projects that also delivered nutrient compliance, and the combined figure overstates the cost of nutrient removal alone. And confirm whether the comparable plant had spare aeration basin volume, because a nutrient retrofit into existing tankage costs a fraction of one that requires new basins, and Colorado’s winter ammonia limits mean older plants here often have more usable volume than their rated flow would suggest.

Comparing Colorado to other state markets

Colorado’s constraints are a mix of arid-West water accounting and cold-water stream protection, and neighboring directories help separate the two. The Nevada wastewater treatment plants directory covers the closest analog for effluent-as-supply accounting, where return flow credits against the Colorado River apportionment perform a function similar to Colorado’s consumable-rights reuse but through a federal allocation rather than through state water law. The Arizona wastewater treatment plants directory covers the downstream Colorado River partner, where aquifer storage credits create a third variation on the same theme and where recharge rather than direct reuse is the dominant pathway. The California wastewater treatment plants directory covers the national reuse benchmark, useful for advanced purification cost data as Colorado utilities build the first generation of direct potable reuse facilities under the state’s new rules.

Field Notes

Check the water rights before the treatment train

A reuse project in Colorado is a water rights transaction that happens to involve treatment equipment. If the utility’s supply is native tributary water, the return flows belong to downstream appropriators and no amount of advanced purification changes that. Feasibility work that starts with technology selection and discovers the rights problem later has wasted the study. The first question on any Colorado reuse inquiry is what fraction of the utility’s supply is legally consumable.

Elevation corrections are not optional

Oxygen transfer efficiency drops with atmospheric pressure, and Colorado’s population lives between 4,500 and 10,000 feet. Blowers, diffusers, and any oxygen-transfer-dependent process must be sized with an elevation correction, and vendor performance data developed at sea level should be treated as a starting point rather than a specification. This is the most common source of underperformance in equipment brought into the state from elsewhere, and it compounds with cold winter influent temperatures that slow nitrification precisely when ammonia limits bind hardest.

Permitting & Design Standards Reference

CDPHE administers discharge permitting, while water rights sit entirely outside the environmental regulatory system, in the state’s water courts.

Discharge permitting in Colorado is administered by the Colorado Department of Public Health and Environment, Water Quality Control Division, under the Colorado Discharge Permit System. The governing regulations include Regulation 31 for basic standards and methodologies, Regulation 85 for nutrient management control, Regulation 84 for reclaimed water use, and the drinking water regulations that establish the direct potable reuse pathway. Water rights, including the consumable status that determines whether effluent may be reused, are adjudicated separately through the state’s water courts and administered by the Division of Water Resources.

Specification checklist for a Colorado project

1. Identify the basin, the receiving stream, and whether the reach is effluent-dominated at design low flow.
2. Obtain the Regulation 85 nutrient values applicable to the facility and the schedule for any tightening phase.
3. Confirm the aquatic life designation and the resulting ammonia and temperature limits, noting that winter conditions often govern.
4. Establish the site elevation and apply oxygen transfer corrections to all aeration equipment sizing.
5. Determine the consumable fraction of the utility’s water supply before evaluating any reuse or potable reuse component.
6. If reuse is pursued, establish the Regulation 84 category or the direct potable reuse pathway that applies.
7. Assess existing aeration basin volume against nutrient removal requirements before assuming new tankage is needed.
8. Characterize influent temperature range, since cold winter influent governs nitrification design.
9. For resort and seasonal communities, establish the peak-to-shoulder load ratio and the strength of the peak-season waste stream.
10. Determine biosolids end use and whether dedicated land application acreage is secured, including haul distance.
11. Confirm sidestream nitrogen loading from digestion and whether sidestream treatment is warranted.
12. Check for interstate compact or downstream water quality obligations affecting the discharge.
13. Verify operator certification class requirements under CDPHE rules for the facility class.
14. Confirm CWRPDA State Revolving Fund or WIFIA participation and the conditions attached.

Resources for Engineers & Operators

Professionals working in the Colorado water sector should engage with the following organizations:

• Rocky Mountain Water Environment Association (RMWEA): The primary member association for wastewater professionals in CO, NM, and WY. Hosts the annual Joint Conference.
• CDPHE Water Quality Control Division: The regulatory body issuing discharge permits and operator certifications.
• Colorado Certification Office (CCWP): Manages testing and licensure for Class D through Class A wastewater operators.
• Colorado Water Resources & Power Development Authority: The financial vehicle for SRF loans.
• Colorado Division of Water Resources: Administers water rights, including the consumable status that governs reuse eligibility.
• Colorado Water Conservation Board: Manages the state water plan and grant programs supporting reuse and efficiency projects.
• Water Quality Control Commission: The rulemaking body that adopts and revises Regulations 31, 84, and 85.
• Colorado WaterWise and WateReuse Colorado: Industry groups focused on efficiency and reclaimed water policy.

Frequently Asked Questions

Conclusion

Colorado’s wastewater sector is shaped by two things that sit outside the plant fence: prior appropriation water law, which determines whether a utility may reuse what it treats, and headwaters geography, which gives every discharge a downstream obligation and no upstream dilution. Regulation 85 supplies the immediate capital driver, and direct potable reuse rules have opened a pathway that a handful of Front Range utilities are now positioned to use. But which utilities those are was settled decades ago in water court, not in an engineering study.

Use this directory as an index organized around that reality. Start from the basin and the receiving stream’s dilution condition, establish the consumable fraction of the utility’s supply, apply the elevation correction, and only then compare capacity and cost. The regional listings above link to detailed profiles of every Colorado facility covered on this site, and the cross-state comparisons help separate an interior-West water accounting problem from a Colorado-specific one.