EFI has more covered lagoon digester systems in the field than any other company in the United States -- over 500 installations spanning 32 years of operations. That installed base generates a continuous stream of maintenance, repair, and replacement work that provides unmatched data on how these systems age, what breaks first, and when replacement makes more economic sense than repair. In 2025 alone, EFI processed over 50 repair and replacement proposals, ranging from simple vent repairs to complete cover system replacements.
Common Failure Modes: What Breaks and When
After three decades of maintaining covered lagoon systems, the failure patterns are clear and predictable. Understanding these patterns allows operators to plan maintenance budgets, schedule interventions before failures become emergencies, and make informed decisions about repair vs. replacement.
- Vent system degradation (years 5-10): Gas vents, pressure relief valves, and vent piping are the first components to show wear. Exposure to biogas (particularly H2S), UV radiation, and thermal cycling degrades seals, corrodes metal components, and embrittles plastic fittings.
- Gas collection system (GCS) degradation (years 8-15): Gas collection piping, condensate drains, and manifold connections develop leaks as materials age. Condensate accumulation in low points of piping can accelerate corrosion.
- Anchor trench issues (years 10-15): Soil settlement, erosion, and thermal cycling can compromise anchor trench integrity, allowing the cover edge to shift and potentially creating leak pathways.
- Cover membrane degradation (years 15-25): The geosynthetic cover material itself degrades over time due to UV exposure (even with carbon black stabilization), chemical attack from H2S and other biogas components, and mechanical stress from wind loading and water ponding.
- Sump and pump degradation (years 5-12): Rainwater collection sumps, sump pumps, and associated piping require periodic replacement as they are continuously exposed to water, UV, and mechanical cycling.
Repair Projects: Targeted Interventions
EFI's 2025-2026 repair portfolio illustrates the range of targeted interventions that extend system life without full replacement. The DeBoer vent repair addressed a degraded gas vent assembly on an otherwise sound cover system -- a straightforward repair costing a fraction of a cover replacement. The Bar20 cover repairs targeted specific damage zones on a cover that was still structurally viable across most of its area. The Bladenboro liner repairs addressed localized damage to the lagoon liner beneath the cover.
The Gallo clamping ring repair is a representative example of component-level maintenance. Clamping rings secure piping penetrations through the cover membrane, and they experience thermal cycling stress that can loosen connections over time. Replacing a clamping ring assembly is a half-day job that prevents gas leaks and maintains cover integrity. The Maas vent repair, Blue Sky cover repairs, and DeBoer GCS repair follow similar patterns: targeted interventions on specific failing components.
Repair costs range from $5,000-$50,000 depending on scope, with most component-level repairs falling in the $10,000-$25,000 range. For systems with 5-10 years of remaining useful life in the cover membrane, these repairs are clearly the right economic choice.
When Repair Is the Right Call
Repair makes economic sense when the cover membrane retains adequate structural and chemical properties for continued service, the failure is localized to specific components rather than system-wide, the repair cost is less than 20-30% of full replacement cost, and the expected remaining useful life after repair is 5+ years.
EFI evaluates repair candidates through a combination of visual inspection, material testing (tensile strength, elongation, and thickness measurements on coupon samples), gas capture efficiency analysis (comparing current capture rates to historical performance), and component-by-component condition assessment. This systematic evaluation prevents the two most common mistakes: spending money on repairs that do not extend useful life, and replacing systems that could have been economically repaired.
Replacement Projects: Full System Renewal
When a cover system reaches the end of its useful life, replacement is the economically rational choice. EFI's 2025-2026 replacement portfolio includes several major projects. The Tyson Storm Lake cover replacement addressed a cover that had reached end-of-life after years of continuous service at the Iowa processing facility. The Manada cover replacement installed a new cover system on a lagoon where the original cover had degraded beyond economic repair.
The Pilgrims Sanford cover replacement is notable because it was combined with sludge line installation -- addressing both the aging cover and the sludge accumulation that had reduced lagoon volume over the cover's operating life. Combining replacement with sludge management makes the construction mobilization more efficient and returns the lagoon to full design capacity.
The Cargill Wahpeton liner replacement addressed the lagoon liner rather than the cover. Liner replacement is a more intensive operation because it requires draining or partially draining the lagoon, removing accumulated sludge, installing the new liner, and then reinstalling the cover system. Liner replacements are less common than cover replacements because HDPE liners in below-grade installations are protected from UV exposure and typically last 30-40 years.
Cover Removal: The Decommissioning Option
The Larson cover removal project represents the other end of the lifecycle decision: decommissioning a covered lagoon system entirely. This occurs when the operation has closed or changed, the carbon credit economics no longer justify continued operation, or the facility has transitioned to a different waste management approach. Cover removal requires careful sequencing -- gas collection systems must be safely purged, the cover material must be cut, folded, and disposed of, and the lagoon must be returned to an open condition that meets applicable environmental requirements.
EFI performs cover removal projects with the same engineering rigor as installations. The geosynthetic material is a industrial waste that requires proper disposal. Gas collection piping and flare equipment may have residual biogas or condensate that requires safe handling. The anchor trench must be restored to prevent erosion after the cover tensioning forces are removed.
The Decision Framework: Repair, Replace, or Remove
EFI applies a structured decision framework when evaluating aging covered lagoon systems. The framework considers four primary factors.
- Cover condition: Material testing results (tensile strength, elongation, oxidative induction time) compared to minimum acceptable values. If material properties have degraded below 50% of original specification, replacement is typically warranted.
- Gas capture efficiency: Current methane capture rate compared to system design capacity. A system capturing less than 70% of design capacity due to cover leaks, GCS degradation, or other system-level issues is a replacement candidate.
- Economic analysis: Present value of remaining credit revenue vs. cost of repair or replacement. If replacement generates a positive NPV over the expected new cover life, it is the right decision. If repair extends useful life at lower cost with adequate remaining revenue, repair wins.
- Regulatory status: Current and anticipated regulatory requirements. If regulations require methane capture that the current system cannot deliver without replacement, the decision is driven by compliance rather than economics.
Preventive Maintenance: Extending System Life
The most cost-effective lifecycle management strategy is preventive maintenance that extends system life and delays the replacement decision. EFI's maintenance programs include annual cover inspections with documented condition assessments, semi-annual GCS inspections including condensate drain maintenance and flow testing, quarterly vent and pressure relief system checks, continuous remote monitoring of gas flow and system pressures, and prompt repair of identified issues before they cascade into larger failures.
Operators who maintain consistent preventive maintenance programs typically achieve cover life of 20-25 years. Operators who defer maintenance may see cover failures as early as 12-15 years. The difference -- 5-10 years of additional useful life -- represents hundreds of thousands of dollars in deferred replacement costs and continued carbon credit revenue. Maintenance is not a cost center. It is the highest-return investment an operator can make in an existing covered lagoon system.
“We built these systems to last 20 years or more. But that requires maintenance. A cover that gets annual inspections and prompt repairs will outlast one that gets ignored until something breaks. We have the data from 500 systems to prove it.”
-- Marc Fetten, CEO, EFI USA
