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20 June 2018

How to manage the unknowns of landfill gas well installation – plan for the worst, expect the best

Drilling landfill gas (LFG) collection wells keeps landfills in compliance, but it can potentially create other issues. Since LFG wells are installed into a waste mass that contains many unknowns, drilling wells can potentially result in accidental penetration into baseliners or puncture of existing piping. Damage like this may lead to environmental compliance issues and may also add operational requirements to the LFG collection and control operations. Not to mention that it can be expensive to repair! In this post, I am going to offer some tips on careful planning and data review that will reduce the likelihood of these dire events.

The techniques I offer for preventing punctures are simple, but tried and true. They have been collected (and used) by myself and many of my colleagues. We have been involved with more than 10,000 LFG well installations in our combined careers and we know that mishaps can be avoided if everyone involved takes a few precautions and practices diligent recordkeeping.

Well drilling is not quite as simple as it may first appear

Installing a new LFG well may seem like a simple task: Identify the top and bottom of the landfill, assume a safe distance above the baseliner, design the well, and drill. Well, it is not that simple! Landfills are complex systems with numerous components, including existing gas collection, leachate collection, active systems, passive systems, abandoned structures, and last but not least, special wastes.

LFG collection and control system designers must consider a three-dimensional maze of not only baseliners, but all potential infrastructure in the waste mass – LFG collection system laterals and headers, air lines, force mains, as well as leachate collection piping. They have to account for possible waste settlement and inadequate construction documentation of liner and piping systems. And need I remind you that all of this must be considered while trying to achieve the ultimate goals of getting the best LFG at the highest rate of flow and not damaging any existing infrastructure?

The potential for damaging laterals or other piping also has to be planned for. While it may not be as spectacular as a liner penetration, it is probably even more common – and could result in significant costs. Added to the cost is the time and effort of the multiple field investigations that may be needed to find and patch the damage. This is especially critical for air lines, which could flip an area back into an aerobic condition and create a subsurface oxidation (SSO) event. And let’s not forget that this may cause damage to downstream LFG control devices like combustion engines.

Prevent accidents with proper preparation and quality control

Once you design the LFG system, make sure everyone involved in installing it is on the same page. While it’s time consuming, be sure to locate, collect, and review all available historical site information. Remember, cutting corners may result in significant costs. The accompanying table quantifies just what these potential repair costs may amount to. The figures are based on estimates from construction bids for projects with related construction items. These estimated costs are based only on construction for immediate repairs, not any long-term monitoring or loss of airspace, LFGTE production revenue, or damage to ancillary systems.

Quality control processes

Use the following quality control processes from initial concept through design, proper contractor selection, implementation, and completion. Carrying out these actions while maintaining proper documentation sets the team up to make the next project a success.

  • Obtain the right information in the correct format (MS Word, PDF, AutoCAD, etc.)
  • Identify the obstacles early, revisiting them often to identify any gaps in information or contradictory information
  • Ask the right questions:
    • Are there items missing from the existing conditions plans?
    • Are there areas of concern?
    • Were piggy-back cells or overliners installed?
    • Has the system been expanded? If so, was anything abandoned?
    • How much differential settlement/lateral subsidence has occurred since previous components were installed?
  • 3D modelling of subsurface conditions can be key
  • Write a good contract to limit liability
  • In addition to staking well locations for drilling, be sure to verify the stakes
    • Follow through on stakes being labeled with coordinates and elevations
    • Verify that they are the same stakes used to prepare well schedules
    • If well locations or depths are modified, use a new, unique well ID to avoid location confusion
  • Hire an experienced LFG driller, installer, and CQA contractor
  • Make sure everyone (Owner, contractor, engineer, CQA, etc.) has reviewed the same final approved drawing set
  • Have meetings, calls, emails
    • Over communicate!
    • Kick-off meeting with representatives of the site, engineer, CQA, and driller present
    • Conduct weekly progress/review meetings and document meetings
  • Implement proper signoff on key project staff prior to commencing construction activities
    • Final sign-off only at the time of drilling
    • All involved parties must review and approve
  • Tailor the drilling activity to the level of accuracy and confidence engineers have in existing conditions documentation
  • Do not assume that just because the design of the system expansion was done with great confidence the installation will go smoothly
  • Identify lines of communications during drilling should issues occur

By implementing controls, sticking to the plan, and communicating often, LFG well installation can be conducted safely and you can significantly minimize the potential for damage to landfill systems.

Do you have any other tips for managing the unknowns of LFG well drilling?

Jessica Bernardini, PE, is a senior project manager with more than twelve years of experience in a range of solid waste related projects on a local, regional, and national level.

Categories: Biogas and Landfill Gas, Environmental Planning & Compliance, Landfill Engineering and Design, Solid Waste
Posted By Jessica Bernardini, PE at 11:30 AM  |  No Comments on How to manage the unknowns of landfill gas well installation – plan for the worst, expect the best

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