What Causes Compost Contamination in Denver and How Do You Stop It?
- Ethan Babil
- Aug 17
- 3 min read
The top contaminants in Denver organics are plastic bags used as liners, certified "compostable" serviceware, paper products, produce stickers, and glove fragments. Every one of them is preventable through signage placement, container placement, and training rather than capital spending.
Contamination is the single biggest threat to a composting program's economics, and it is almost entirely a behavior problem. This post covers what causes it, what it costs, and the fixes that actually move the number.
What counts as contamination?
Anything in the organics container that is not food scraps or yard and plant trimmings.
That definition is stricter than most people assume. It excludes paper. It excludes packaging. It excludes certified compostable serviceware. A1 Organics, which processes most Denver commercial organics, accepts food scraps and yard trimmings only, with 3-gallon CMA-certified compostable bags as the sole permitted liner.
What are the top five contaminants?
1. Plastic bags used as liners. The most common and most damaging. Plastic film shreds during processing and cannot be fully screened out.
2. "Compostable" serviceware. Cups, clamshells, cutlery, and lids, including certified ones. Not accepted in Denver.
3. Paper products. Napkins, paper towels, pizza boxes, coffee filters, paper plates.
4. Produce stickers. Small, plastic, and applied to exactly the items most likely to be composted.
5. Nitrile glove fragments. A back-of-house problem specifically, and easy to miss because gloves come off directly over the nearest bin.
Four of those five come from people trying to do the right thing. That is the key insight for fixing it.
Why does contamination cost you money?
Contaminated loads get rejected, downgraded, or landfilled, and the cost returns to the generator through contamination fees or service changes.
The second cost is quieter and larger. A program that keeps getting rejected loads stops being treated as real by the people running the property, and then it degrades into a second trash container that you are paying organics rates for.
What actually fixes it?
Four things, in order of impact per dollar.
1. Picture-based signage in English and Spanish. Photographs of accepted items, photographs of rejected items. Text-only signage in one language does not survive a busy shift or a diverse resident population.
2. Container placement. Put organics where the waste is generated. In a kitchen, that is the prep line and the dish pit. In an apartment, that is where residents already walk with their trash. Every extra step increases the chance material goes in the wrong container.
3. Consistency across stations. Same colors, same labels, same layout at every station. Inconsistency doubles error rates because people have to re-decide each time.
4. Correct liners. Provide 3-gallon CMA-certified compostable bags, or run loose. Do not leave a box of regular trash bags near the organics container and hope.
What does not fix it?
Signage in one language. A single training session at rollout. Assuming residents or staff will read a paragraph. Buying "compostable" serviceware and assuming that solves anything, since it is a contaminant in Denver regardless of certification.
How do you monitor contamination?
Visual checks at a set cadence, logged with dates.
Porters or kitchen leads should look in the container. Photograph problems. Record the corrective action taken. That log becomes part of your URCO records file and is genuinely useful evidence during a cure period.
Monitoring also tells you where the problem is. Contamination concentrated at one station is a signage or placement problem. Contamination everywhere is a training problem.
Frequently asked questions
Is a little contamination acceptable? Processors work to contamination limits and exceeding them causes rejection. Treat any plastic as a problem worth correcting.
Whose fault is a rejected load? Costs generally flow back to the generator. The responsible party for the premises carries the compliance exposure.
Do compostable bags reduce contamination? Only 3-gallon CMA-certified bags are permitted. Any other bag is itself a contaminant.
What if residents refuse to sort correctly? Focus on making the correct action easier than the incorrect one. Placement and picture signage outperform enforcement in residential settings.
Does contamination affect URCO compliance? Your obligation is to provide compliant service. A container so contaminated it functions as trash undercuts that, and creates overflow and pest issues that draw attention.
Signage built against the actual rules
Melly's Recycling is a Denver URCO compliance company, not a hauler. Our signage and education materials are built directly against current accepted-materials rules, in English and Spanish, with picture-based formats that hold up on a busy shift. We also handle Waste Diversion Plans, capacity in gallons, annual reporting, and documentation, and coordinate licensed Denver haulers through a sealed-bid process.
You finish what you started.
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