Invisible 'Underground Defense Line': Investigation of Pollution Hazards at Municipal Solid Waste Landfills
A landfill is not simply a “big hole,” but a complex environmental engineering system. The most critical line of defense is the impermeable liner made of high-density polyethylene (HDPE), which acts like a “raincoat” for the earth, preventing harmful leachate from seeping into the soil and groundwater. However, this line of defense is not impregnable. Today, we’ll take an in-depth look at how to inspect and mitigate risks for this “underground defense line.”
A Shocking Reality: Damage to the Liners Is Widespread
According to a long-term study by the Institute of Solid Waste Pollution Control Technology at the Chinese Research Academy of Environmental Sciences, the situation is far from optimistic. Since 2008, they have conducted integrity tests on the liners of over 30 municipal solid waste and hazardous waste landfills across 10 provinces and cities nationwide. The results revealed that all surveyed landfills exhibited varying degrees of leakage.
The data provides a more vivid illustration of the severity of the problem: on average, approximately 34 leaks were found per landfill, which translates to 17 leaks per hectare (10,000 square meters) of the impermeable layer. These leaks allow large amounts of highly concentrated leachate to seep into the ground; in some areas, contamination has penetrated to depths of tens of meters, posing a long-term and severe threat to the surrounding groundwater and soil environment.
Why Is the Defense Line “Riddled with Holes”? An Analysis of the Causes of Damage
Damage to the geomembrane is not accidental; it occurs throughout the entire lifecycle of a landfill. As can be seen, damage is primarily concentrated in three stages:
Geomembrane installation stage (accounting for approximately 24%): This is a period with a high incidence of human error. Incomplete welds, missed welds, and burn-throughs are common issues. Additionally, unlicensed welders, a lack of technical oversight and inspection, and material quality issues (such as the use of substandard recycled materials) are also significant causes.
Drainage Layer Installation Phase (accounting for as much as 73%): This is the “hotspot” for damage. To protect the geomembrane, a layer of crushed stone or geosynthetic material is laid on top for drainage. However, the sharp edges of the crushed stone can easily puncture the membrane surface, and the compaction by heavy construction machinery is particularly devastating.
Operational Phase (accounting for approximately 3%): Even after the landfill begins operation, risks persist. Improper waste disposal (such as the mixing of sharp construction debris), mechanical damage, and uneven settlement of the foundation can all tear the geomembrane. For closure projects, cross-operations such as laying geomembranes and biogas collection pipes directly on the waste mass are also highly likely to cause new damage.
Performing a “CT Scan” on the Earth: Three Mainstream Leak Detection Technologies
The “Standard for Pollution Control of Municipal Solid Waste Landfills” (GB16889-2024) explicitly stipulates that after construction of the landfill area is completed, integrity testing of the high-density polyethylene (HDPE) liner must be conducted in accordance with the relevant technical provisions of CJJ/T214; During the landfill’s operational, closure, and post-closure maintenance and management periods, integrity testing of the impermeable liner must be conducted every three years. Based on the results of these tests and information on groundwater quality, the environmental risks of the landfill should be assessed periodically. Additionally, the integrity of the impermeable layer in the closure cover system must be tested upon completion of its construction.
Since damage is inevitable, how can these hidden leaks be detected promptly and accurately during the landfill’s long operational period and after closure? This relies on professional impermeable liner leak detection technology. According to the “Technical Specifications for Leak and Damage Detection of Impermeable Geomembranes in Municipal Solid Waste Landfills” (CJJ/T 214-2016), there are three primary methods:
Electrospark Method: A Health Check for the Exposed “Skin” Principle: Utilizes the insulating properties of HDPE geomembranes. During testing, a voltage is applied both on and beneath the membrane. When the probe passes over a perforated area, the current instantly breaks through the air to create a spark, triggering an alarm. Applicable Scenarios: Primarily used for exposed geomembranes during the construction phase that have not yet been covered, such as landfill liners, slopes, and rigid landfill cells. It can accurately detect holes no smaller than 1 millimeter.
Dual-Electrode Method: Penetrating the “Covering” to Find Leaks Principle: This method also utilizes the membrane’s insulating properties. An electric field is applied both above and below the membrane in the target area (even if covered by water or soil). When there are no leaks, the electric field is uniform; however, if a leak is present, a sudden change in electric potential occurs at the leak site, which can be precisely located using mobile measurement equipment. Applications: This is a powerful tool for inspecting impermeable layers covered by overburden. Whether the membrane is covered by standing water, soil, or gravel, it can penetrate and detect defects at depths of up to 1 meter, making it the primary method for monitoring landfills during operation and after closure.
High-Density Resistivity Method (ERT) and 3DX Technology: Performing a “CT Scan” of the Earth Principle: This is a geophysical exploration method. It involves supplying an electrical current into the ground to measure the resistivity of media at different depths. Since clean soil, contaminated leachate, waste bodies, and HDPE membranes have distinct electrical conductivities, analyzing the resistivity distribution map allows for a “clear view” of the distribution of underground contamination plumes, leachate water levels, and even potential areas of geomembrane damage. Advanced Technology—3DX Multifunctional High-Density Electrical Survey: As described in the document, traditional methods are akin to two-dimensional cross-sections. In contrast, the upgraded 3DX technology uses multi-angle scanning, intelligent data modeling, and three-dimensional visualization to generate a three-dimensional underground “CT image.” This truly achieves a comprehensive view of the landfill’s internal environment, making hidden pollution “visible and tangible.”
National Action: A Policy Roadmap from Inspection to Remediation
In response to environmental risks posed by landfills, the national government is advancing remediation efforts with unprecedented intensity. From 2025 through the 15th Five-Year Plan period, a series of major policies and standards have been introduced in rapid succession, forming a rigorous regulatory network. The core action plans are the “Action Plan for Comprehensive Management of Solid Waste” (State Council Document [2025] No. 14) and the “Work Plan for the Identification and Remediation of Environmental Pollution Hazards at Municipal Solid Waste Landfills” (Ministry of Ecology and Environment Document [2025] No. 44). These documents outline a clear “timeline” and “task list”:
• By the end of 2025: Compile a comprehensive inventory of landfills nationwide, complete the investigation of environmental pollution risks, and establish a registry of issues.
• By the end of June 2026: For landfills with identified risks, develop comprehensive remediation plans based on the “one landfill, one strategy” principle.
• By the end of 2027: Complete the closure and remediation of landfills that were decommissioned by the end of 2024, ensuring that environmental risks at operational landfills are generally under control.
Furthermore, the new “Standard for Pollution Control of Municipal Solid Waste Landfills” (GB16889-2024) is a mandatory standard that explicitly stipulates: During the operational, closure, and post-closure maintenance periods of a landfill, integrity testing of the impermeable liner must be conducted every three years. This marks a shift from impermeable liner testing being a “recommended item” to a “mandatory requirement.”
Inspection Process: How Is the “One Landfill, One Strategy” Approach Developed?
The risk assessment and remediation of a landfill follow a rigorous set of procedures:
Hazard Identification and Information Collection: Compile the landfill‘s “dossier,” including design drawings, operational records, geological conditions, and the design of the impermeable system. Simultaneously, conduct a comprehensive investigation of safety and environmental risks—such as embankment stability, landfill gas explosions, and groundwater contamination—and establish a database of foundational information.
Preliminary Risk Classification Assessment: Based on the inspection results, standardized assessment forms are used to score the landfill’s risks, preliminarily classifying them into high, medium, and low risk levels. For issues that are obvious and easily rectified, “immediate action” is required.
Selection of Remediation Technologies by Risk Level: Based on the final confirmed risk level and in conjunction with future land use plans (whether to create green space or build a park), the most suitable remediation path is selected.
Two Remediation Pathways: In-Situ Closure vs. Off-Site Screening
Currently, there are two main mainstream remediation approaches:
1. In-Situ Closure: This can be understood as “on-site containment and ecological restoration.” By reshaping the landfill body, applying a sealing cover, and improving stormwater and wastewater separation systems along with gas drainage systems, the landfill is physically isolated from the external environment to prevent the spread of pollutants, ultimately transforming it into an ecological park or green space.
Advantages: Relatively low investment, short construction period, and minimal impact on the surrounding area.
Disadvantages: Limited land use value; long-term monitoring and maintenance are still required after closure.
2. Off-site screening and disposal: This is equivalent to “excavation surgery and resource regeneration.” All aged waste is excavated and separated using screening equipment into lightweight combustible materials, humus, inorganic aggregates, and other components. Light materials can be incinerated for power generation; humus, after treatment, can be used as soil for landscaping; and inorganic aggregates can serve as construction materials, achieving waste reduction and resource recovery.
Advantages: It can completely eliminate pollution sources and release valuable land resources.
Disadvantages: Requires massive investment, has a long construction cycle, and poses significant challenges in controlling odors and dust during excavation.
Conclusion
The identification and remediation of pollution risks in municipal solid waste landfills is an “underground battle” critical to ecological safety and public health. It requires advanced detection technology as the “eyes,” strict regulatory standards as the “guidelines,” and, most importantly, scientific remediation plans as the “scalpel.” As national requirements for ecological civilization continue to rise, the operation and management of landfills will move beyond a crude approach toward a new era of precision and transparency. For each of us, understanding these “invisible” challenges, practicing waste sorting, and reducing waste generation at the source is the best way to support this “battle.”
Resource:https://mp.weixin.qq.com/s/OBA2b3FR2aXwTIiCK3IWGw