An investment in the proper planning and evaluation of your condensate system design and operational practices is money very well spent.
By Ralph Hirshberg
The question most often directed to landfill gas collection system operators is: “Describe your most persistent, time-consuming, and costly operational issue?” The common answer? Condensate. Condensate from gas collection systems remains a problem for landfill operators despite decades of design, equipment, and engineering improvements in collection and management systems. Consider:
Accumulation of condensate within gas collection systems, both vertical and horizontal, impairs gas collection efficiency and remains an ongoing challenge for wellfield operators and compliance managers.
Significant percentages of operating vertical and horizontal gas collectors are rendered useless by accumulated condensate, diminishing the value of extensive capital investments.
Ongoing study of “heating-event” chemistry points to excessive condensate accumulation as a potential driver behind these costly and resource-consuming events.
Pneumatic pumping systems and other downhole extraction devices, while effective, remain expensive to install, monitor and maintain.
The combination of perched leachate and gas condensate can rapidly overwhelm collection and conveyance systems, and is often overlooked during condensate system design.
Current monitoring protocols, usually involving manual inspection on a monthly basis, are often inadequate to alert the landfill operator about condensate-related problems in real time … before they become an expensive and resource-consuming issue.
These points matter due to increased regulatory and public concern regarding landfill gas collection efficiency, odor control and health impacts related to landfill emissions. Gas collection systems are an established and well-developed way to capture those emissions. However, in many instances, excessive condensate accumulation and inadequately designed infrastructure can elevate these concerns to real-time problems for facility owners and operators that may range from public complaints to notices of violation or even litigation.
Yet condensate management is all too often assigned as a low priority in the design and operation of landfills. Landfill operations have made giant strides in the past few decades regarding the management of leachate and methane emissions. It is now time for the industry to take the next step and put its well-known problem-solving ability toward a new focus: condensate management.
Re-Thinking Condensate Management
While early design standards, developed by a variety of entities including the U.S. Army Corps of Engineers as well as many leading industry consultants, provided a baseline for condensate management, many have proven inadequate given the variables associated with both gas and associated condensate generation.
The evolution from passive “drip-leg” design to modern pneumatic extraction systems has greatly improved condensate management. However, even modern active extraction systems continue to be plagued by operating issues and higher-than-projected operation and maintenance costs.
While a conventional design approach has often centered on integration of condensate collection systems within the gas collection network, very few facilities fully integrate condensate collection within the framework of the leachate collection systems. Although some local regulations prohibit combined management of gas condensate and leachate, the integration of condensate collection and use of the leachate collection system for condensate removal can afford landfill owners significant benefits in terms of future reduced capital and operating costs.
Even fewer facilities consider condensate management during waste placement operations, especially where high-moisture or low-permeability waste, such as sludges, drilling wastes or similar materials, are being accepted for disposal. Proper waste placement planning in consideration of its impact on future gas and condensate collection can provide significant benefits.
Some ideas for better ways to manage condensate in landfills include:
Directly tie-in gas collection wells to gabions, rock mounds or similar drains placed at the base of cell leachate collection systems. Gas collection wells tied into these drains may significantly enhance condensate management within typical vertical installations.
Directly connect drip-legs, horizontal collector drains or similar condensate discharge points located in the horizontal components of the gas collection system to the leachate collection system.
Expanded use of drip-legs or condensate drains beyond system low points, particularly where horizontal collection components are used.
Use of appropriate gas collection piping slopes, including enhancement of slopes in portions of the landfill with potential for excessive settlement or higher-than-typical condensate yield.
Proper consideration of gas transmission temperatures and, in particular, zones of the gas collection system that may be exposed to cool ambient air temperatures. Such zones can significantly reduce the vapor-holding capacity of saturated landfill gas resulting in significant condensate dropout.
Proper consideration of condensate flow within gas collection piping, including enhancement of slopes where countercurrent flow may be occurring, and appropriate reduction in pipe effective diameter where significant condensate flow is anticipated.
Use of modular and adaptable designs. Traditional “rule-of-thumb” or industry-standard design factors are often required, as precise condensate yield rates from a particular collection well cannot be determined in advance. However, as condensate yield may vary considerably from well to well, the use of modular or adaptable well and wellhead designs will allow for cost-efficient adjustment to actual well operating conditions.
Anticipate collection of perched leachate within gas collection wells. Although traditional condensate yield estimates provided a reliable starting point for selection and design of condensate management components, many gas extraction wells will intercept perched leachate zones that may contribute significantly larger volumes of liquids than originally anticipated. Adaptable and modular designs will be able to accommodate these “unexpected” sources of liquids.
Operate the landfill with gas collection and condensate management in mind. Account for the future location of gas extraction wells during waste placement. Control the extent or areal coverage of high-moisture, low-permeability waste streams including sludges, drilling wastes, water treatment residue, etc., as they may contribute to increased condensate yield or perched leachate. Make sure operations personnel are knowledgeable regarding the type, location, and extent of planned gas and condensate management infrastructure.
Fully consider system redundancy and design it with potential failure in mind. During design, treat the condensate collection system and all its components as important systems that are relied upon to operate a large bioreactor plant (i.e. the landfill). The use of looped collection systems, accommodation of parallel piping and judicious use of design (safety) factors for all condensate management components can yield significant benefits during future operations.
Learning from Failures is Key to Success
Perhaps one of the most important aspects of gas and condensate management design is evaluation of failed systems. Proper evaluation of the initial installation should be considered as a design phase for future installations. Properly evaluate condensate management within initial installations and modify designs or operating practices accordingly. It is quite common to observe a failing gas collection system in one sector of a landfill while observing an identical system being installed in an expansion phase.
While routine data collection within gas collection systems is often driven and narrowly focused by regulatory criteria, consider expansion of data collection to include routine assessment of condensate yield, condensate levels within collection wells, changes in condensate quality, and expected versus actual gas yield. Are gas collection volumes being restricted by condensate accumulation? Is excessive condensate accumulation being observed?
Do waste placement operations play a significant role in condensate management? The simple answer is yes. In a typical vertical well system, at least a portion of the gas collection system will be impacted significantly by perched leachate and will have to accommodate leachate as well as gas condensate volumes. Plan for it.
In addition, perched leachate is often present for a reason, and that reason is often fine-grained, low-permeability waste that prohibits movement of perched liquids to the leachate collection system. These fine-grained materials easily migrate through well packing and screens and can rapidly diminish the effectiveness of a well or foul condensate pumps. The combination of increased liquid volume and reduced pump capacity can quickly overwhelm a collection system resulting in increased operational costs or the loss of a gas extraction well.
Can operations personnel eliminate perched leachate? The simple answer here is no. However, the disposal of significant quantities of waste that may enhance the potential perched leachate can be managed to minimize impacts to gas and condensate collection systems.
The cost to properly address these issues is but a small fraction of the cost of a response to a subsurface heating event, significant slope failure or reduced gas recovery. If your actions avoid litigation regarding odors, air toxics or nuisance complaints, multiply their value several fold.
Bottom line: an investment in the proper planning and evaluation of your condensate system design and operational practices is money very well spent.
Ralph Hirshberg, P.E., is a Principal in the Cincinnati, OH office of Civil & Environmental Consultants, Inc. He has nearly 30 years of consulting engineering experience working for the solid and hazardous waste industries with extensive expertise in the permitting and design of a wide range of waste disposal and environmental facilities. A specific area of focus is the beneficial use of landfill gas and consulting associated with renewable energy projects. He can be reached at (513) 985-0226 or via e-mail at [email protected].