EFI USA

EFI field guide

Digester Cover Replacement

Start with the condition of the whole cover system. Damage location, access below the membrane and the work planned around it determine whether the scope is a repair, a rebuild or a replacement.

Historical sources reviewed September 23, 2026 · EFI USA

Build the inspection record before choosing the remedy

The questions below help an owner and engineer define an assessment. They apply to flexible membrane systems. A fixed steel or concrete tank roof needs a separate structural scope. Collect observations from authorized access points; the assessment team must define safe access and any sampling work.

Cover inspection records and the decisions they support
InspectRecordResolve with the assessment team
Membrane and seamsLocate holes, tears, open seams and previous patches on a plan. Record the installed material and available test records.Is damage confined to one area? What inspection or testing is needed to establish whether the adjacent material can accept a repair?
Edges and contact surfacesMark anchor details, penetrations and places where the cover contacts a slope, structure or pipe at different liquid levels.What caused the contact or movement, and what detail must change before a new patch or membrane goes in?
Components above and below the coverIdentify ballast, gas piping, rainwater equipment and any submerged material that must be removed or retained.Which components can remain, which need separate assessment, and how will the crew reach them?
Treatment and access constraintsProvide normal and allowable liquid levels, access restrictions, available work windows and other planned basin work.Can the work proceed at the required operating level? Who defines isolation, gas control and any specialist access plan?

Three project lessons for a replacement scope

These EFI case histories document different work sequences and cover details. The planning questions are drawn from that scope. The records describe historical installations and do not establish current condition or a standard service life.

Excel Corporation · Fort Morgan, Colorado · 1996

Define access below a damaged cover

At Excel, damaged cover material and weights had to be removed from an anaerobic treatment cell that needed to remain in operation. EFI provided divers for the removal, rebuilt one cover and modified the other. The original history identifies EFI's role as geomembrane repair work.

For a similar scope, identify submerged material and agree on its removal method before estimating the membrane work. Establish the liquid-level and treatment constraints with the operator. This project documents one operating-cell repair sequence; each site needs its own access and isolation plan.

Read the Excel Fort Morgan history

Brown Packing · Gaffney, South Carolina · 2006

Coordinate the work between old and new covers

Brown Packing's project combined replacement of a worn digester cover with a lagoon baffle. Sludge was removed after the old cover came off and before the new insulated cover went on. EFI fabricated and installed the replacement cover using Seaman 8130 XR-5.

Ask what other basin work needs that same access window. Put sludge removal, baffle changes and cover installation into an agreed sequence, with a responsible party for each. The source assigns cover fabrication and installation to EFI; it does not assign sludge removal to EFI.

Read the Brown Packing history
Light-colored lagoon cover with surface fittings and Brown Packing buildings behind it
The cover surface and plant buildings in EFI's original Brown Packing case-history photograph. The photograph does not show sludge removal or the baffle below the cover.

City of Staunton · Virginia · 2003 · Drinking-water application

Address the surface that contacts the cover

Staunton's reservoir inspection found holes, tears and seams beginning to debond in its existing floating cover. The replacement included a slope skirt down to low operating level to protect the cover from chafing against the gunite surface. EFI installed the cover, slope liner and floating baffles.

This was a drinking-water reservoir, so its material and process requirements differ from a digester's. The useful inspection question is about contact: where does the membrane touch a rough surface as levels change? Review those locations and the protection detail when defining the replacement.

Overview of Staunton's covered reservoir, perimeter fence and access walkway
The covered reservoir in the original Staunton case history. This overview shows the cover and access walkway; the slope-skirt purpose is documented in the project text.
Read the Staunton history

Close the scope before requesting a replacement price

  1. What is included in removal: membrane, ballast, submerged debris, existing piping and disposal? Name the owner of each task.
  2. Which existing liner, slope and anchor details need inspection before they are covered again? Allow a decision point for concealed conditions.
  3. Are sludge removal, liner repairs or baffle changes planned? Agree on their sequence and responsibility before the replacement panels are fabricated.
  4. Which gas connections, penetrations and rainwater components will be retained or replaced? Show the interfaces on the scope drawings.
  5. What inspection records, seam tests, repair records and acceptance checks must be delivered before handover? Assign who witnesses and accepts them.

For new-system requirements, see anaerobic digester covers. If the assessment includes the basin lining, use the lagoon liner scope guide alongside this checklist.

Cover repair and replacement questions

Document the location and extent of damage, the condition of the surrounding membrane and seams, and any contact or movement that could damage a repair. Ask the assessment team to define material testing and repair acceptance criteria for the installed system. Compare a localized repair scope with a replacement scope that also addresses anchorage, penetrations and operating constraints. Age alone does not establish the answer.

The work sequence depends on what must be reached below the cover. EFI's 1996 Excel Fort Morgan history documents a cover rebuild while the treatment cell remained in operation. At Brown Packing in 2006, the project included sludge removal between removal of the old cover and installation of the replacement. Define the liquid-level limits, submerged work and treatment requirements before agreeing on a sequence.

Send the site location, cover drawings and material records if available, an annotated plan locating damage, photos taken from authorized safe access points, previous repair records, normal and allowable liquid levels, and the required work window. Identify any planned liner, sludge, baffle or gas-system work so those interfaces can be included in the scope.

A photograph can locate visible features and support an inspection record. It cannot establish seam strength, submerged condition, gas tightness or remaining service life. Record what is visible and what still needs inspection or testing.

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Bring the cover condition and site constraints

Start with the location, observed damage, cover records and available work window. Include any planned sludge, liner or baffle work. EFI can review those details with you to define the repair or replacement scope.

Discuss Cover Repair or Replacement

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