Colorado Biosolids Management Regulations: How CDPHE Land Application Rules Differ from Texas for Private Plant Operators

Who regulates biosolids in Colorado, and how is that different from Texas?

Colorado has two regulators for biosolids, and Texas has one. EPA's biosolids compliance page lists nine states authorized to run the federal program, and Texas is one of them. Colorado is not, so EPA implements the federal biosolids rules there.

On top of that, Colorado has its own rule, Regulation 64 (5 CCR 1002-64), administered by the Water Quality Control Division. In Texas, the state rules are 30 TAC Chapter 312, and TCEQ says you need a TCEQ permit before you land apply biosolids, with Class B beneficial use on its own application form.

EPA's annual biosolids report is required of larger publicly owned plants (1 million gallons per day design flow, or 10,000 people served), Class I sludge management facilities and others EPA names. A small private plant is usually outside that list, but Regulation 64 has its own reporting.

When does Regulation 64 apply to a private plant?

It applies when biosolids from your plant are withdrawn for beneficial use, whether or not the plant holds a discharge permit. Section 64.3 also covers anyone who treats, handles or applies biosolids to land. It does not cover grit and screenings, septage, drinking water plant sludge or industrial sludges.

Many small plants never land apply. They haul liquid sludge to a larger plant for treatment. In that case the land application rules fall mostly on whoever prepares and applies the final biosolids, but confirm the arrangement with the Division and put it in writing with the receiving plant.

What does land application need in Colorado?

A Notice of Authorization for each application site, issued after a Letter of Intent. Under §64.10(A)(3), a Letter of Intent goes to the Division and the local health authority for each site before the first application. Section 64.10(G) says no one may use biosolids for any beneficial use without that Notice of Authorization.

The site Letter of Intent includes:

• the site owner's signed agreement to follow the rules and allow monitoring access;
• metals, pathogen and vector attraction data for the biosolids;
• soil test results, NRCS maps for soil depth and a groundwater depth evaluation;
• a Biosolids Management Plan covering crops, access limits and any storage.

The Division tells you within 30 days if the letter is incomplete, then issues or denies the notice within 30 days after it is complete (§64.10(B)-(C)). The applier also notifies the Division and local health authority before applying, at least once a year (§64.15(B)(2)).

Which site rules decide where biosolids can go?

Groundwater, slope and distance to water rule out land before agronomics do. Section 64.15 sets these limits for agricultural use:

• no application where the annual high groundwater table is within five feet of the surface, unless §64.15(D)(2) conditions are met;
• no application on agricultural land steeper than 15 percent;
• no surface application within 200 feet of surface water, or 50 feet if injected or incorporated;
• no application within 100 feet of a private domestic well or 300 feet of a community supply well;
• no application within one mile upgradient of a public water system surface intake, unless runoff does not reach it or a site plan controls runoff.

Nitrogen sets the rate. Under §64.15(H), applied nitrogen cannot exceed the agronomic rate for the crop, counting other sources such as manure, fertilizer and irrigation water. Class B biosolids also bring access limits: no grazing for 30 days, and public access restricted for one year on high-exposure land or 30 days on low-exposure land (§64.15(J)).

How does winter change a Colorado biosolids plan?

Frozen, ice-covered or snow-covered ground closes many sites for months. Section 64.15(F) prohibits application to frozen, ice-covered or snow-covered sites steeper than six percent. Between three and six percent, you need 80 percent vegetative cover or an approved runoff containment plan.

Saturated land and land where water is ponding are off limits too (§64.15(C)(3)). For a mountain plant, that means storage or a hauling contract has to carry the winter. Plan the storage volume around your real wasting rate and the longest stretch your sites and roads can be closed.

How long can biosolids be stored in Colorado?

No more than two years, and storage outside the plant needs its own authorization. Under §64.13, long-term storage needs a Notice of Authorization, and stored biosolids must already meet Class B pathogen and vector attraction criteria when they go in. The two-year cap is in §64.13(C)(3).

Sludge tanks that are process units of a permitted or site-approved plant are exempt from those storage rules (§64.13(B)(1)). So is short-term staging of dewatered biosolids on a permitted application site for 14 days or less. A dewatered storage pad needs an impermeable base or underdrain with berms, or a cover with berms or runoff diversion (§64.13(E)).

Does Colorado test biosolids for PFAS?

Yes, under an interim strategy, not a rule. CDPHE's biosolids and PFAS page says the Division began its Biosolids-PFAS Interim Strategy on January 1, 2023, with monitoring for biosolids preparers. At 50 micrograms per kilogram (µg/kg) of PFOS or more, the preparer must look for industrial or commercial sources and act to reduce them.

CDPHE notes that the 50 µg/kg level is not risk based. In January 2026 the Division extended the strategy through 2026, added a Preliminary Source Investigation step and renamed the Source Control Program a Source Reduction Plan. Our post on PFAS monitoring in state discharge permits covers the effluent side.

How should a private plant plan biosolids before startup?

Decide the end use first, then size the plant and storage around it. Run this check during design. Any "no" is a gap to close before the plant starts making sludge.

1. Do you know whether the sludge will be hauled to another plant or land applied?
2. If land applied, do you have candidate sites that clear the groundwater, slope and setback rules?
3. Does the treatment process produce Class B pathogen and vector attraction results without extra steps?
4. Is storage sized for your wasting rate plus the longest winter closure?
5. Is a hauler under contract for your location and road conditions?
6. Do you know whether PFAS monitoring applies to your plant?
7. Have you allowed for odor and the distance from storage and application areas to homes?
8. Is someone assigned to the records, kept at least five years, and the annual report due February 19 (§64.17)?

Bring those answers to the package plant design discussion, along with expected flows and how often an operator will be on site.

This article is general education on Colorado and Texas rules as read in October 2026, including Regulation 64 as effective September 30, 2021. Requirements depend on your plant and sites, so confirm them with the Division and your engineer.

Frequently asked questions

Is biosolids land application covered by my Colorado discharge permit?

Not by itself. Regulation 64 requires a Notice of Authorization for each land application site, issued after a Letter of Intent to the Division and the local health authority (§64.10). Plan it as a separate approval.

What is the difference between Class A and Class B biosolids in Colorado?

The class is about pathogen reduction. Class A biosolids, with vector attraction reduction, may go to public contact sites. Class B biosolids may go to agricultural land or reclamation sites, with the harvest, grazing and public access waiting periods in §64.15(I) and (J).

We run package plants in Texas and are opening our first plant in Colorado. Can we reuse our Texas biosolids hauler and land application plan?

Not as written. Texas authorizes Class B land application through a TCEQ permit, while Colorado uses site-by-site Notices of Authorization under Regulation 64. Colorado's frozen ground, slope and groundwater rules will also change which sites work and when.

I'm the operator of a small mountain resort plant in Colorado. Can I store dewatered sludge on site all winter and spread it in spring?

Storage in the plant's own process units is exempt from the storage rules. A separate storage pad needs a Notice of Authorization, a protected base or cover with runoff control, and Class B treatment before storage, and nothing may sit more than two years (§64.13).

Related resources

• Sewage Sludge and Biosolids Land Application Permits in Texas: Rules, Fees, and Common Mistakes
• Colorado Package Wastewater Treatment Plant Permitting: CDPHE Approval, Operations, and Compliance
• CDPHE Site Application vs. Discharge Permit Application: The Two-Step Process Colorado Developers Often Confuse Into One
• Domestic Wastewater Treatment Works Design Criteria: The CDPHE Engineering Standards Package Plants Must Meet

Planning biosolids for a private plant in Colorado?

We build the sludge path into the plant design, from wasting and storage to hauling or land application sites, so the plant is ready before solids pile up.

We specialize in:

• Package wastewater treatment plant design
• Sludge handling and storage design
• CDPHE site location and design approvals
• Discharge permit applications
• Site civil engineering for land development
• Construction administration

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