Gas monitoring wells are essential for active demolition sites and sanitary landfills, ensuring ground monitoring for gas migration. Compliance with environmental regulations necessitates proper design and construction of these wells, as outlined in the Code of State Regulations 10 CSR 80-3.010(14) and 10 CSR 80-4.010(14). Just as understanding a gateway code 2054 in your VW’s OBD2 system is crucial for diagnosing car issues, comprehending the intricacies of gas monitoring wells is vital for environmental safety and regulatory adherence. This guide provides a detailed overview of gas monitoring well design, location considerations, and best practices, aiming to enhance your understanding and ensure effective monitoring.
Well Design: Ensuring Accurate Soil Gas Concentration Readings
The design and construction of gas monitoring wells are paramount to obtaining accurate soil gas concentration readings. Similar to how precise diagnostics are needed to interpret a “Gateway Code 2054 Vw Obd2 Code,” meticulous well design is necessary for reliable environmental data. A primary objective in well design is to minimize air intrusion, which can dilute samples and lead to unrepresentative results. For wells exceeding 10 feet in depth, it’s important to note that the Missouri Geological Survey regulates their installation, requiring certified well drillers. For further guidance, you can contact them at 573-368-2165.
The Waste Management Program recommends several well designs, each suited to different site conditions and monitoring objectives:
- Permanent Monitoring Well: These wells are designed for long-term monitoring and adhere to Missouri Well Construction Rules 10 CSR 23-4. Figure 1 illustrates the key components of a permanent monitoring well.
Figure 1: Diagram of a Permanent Monitoring Well, highlighting essential components for robust, long-term gas monitoring.
- Push Probe/Direct Push Well: While not fully compliant with current codes, a variance from MGS can be obtained for installing this type of well. Figure 2 details the components of a push probe/direct push well.
Figure 2: Illustration of a Push Probe/Direct Push Well, showcasing its structure and components suitable for specific soil conditions with proper variance.
- Spike Probe: Defined for use at depths less than 10 feet below ground surface, spike probes are not technically considered monitoring wells, and therefore do not require a variance from MGS. Figure 3 shows the components of a spike probe.
Figure 3: Spike Probe Diagram, depicting components of a shallow depth monitoring tool, ideal for specific near-surface gas monitoring needs.
Spike probes are particularly useful in scenarios where shallow groundwater (approximately 10 feet or less below the surface) prevents the construction of drilled wells. However, such instances should be infrequent. Bar punch testing for shallow soil migration is not considered an effective long-term monitoring method beyond instantaneous assessments of shallow lateral gas migration extent.
Effective monitoring well design should encompass all unsaturated soil and rock strata down to the landfill’s bottom elevation. Wells can be configured with a single riser, screened from just below the well seal to the landfill base. Alternatively, well clusters with multiple risers, each screened across different geologic units, can be employed. The critical aspect is ensuring monitoring coverage for every geologic unit between the surface and the landfill’s lowest waste elevation. Well clusters are especially beneficial for isolating distinct permeable zones, such as sand seams, fracture zones, karst features, or mine shafts, that are prone to gas transmission.
To consistently prevent atmospheric air intrusion, gas monitoring wells must feature a cap equipped with a valved or quick-connect sampling port. This design facilitates direct attachment of gas sampling instruments, enabling samples to be drawn directly from the well, maintaining sample integrity.
Well Locations: Strategic Placement for Effective Gas Migration Monitoring
The Waste Management Program must approve the locations of gas monitoring wells. Location decisions should be grounded in a thorough understanding of the landfill site’s geologic and hydrologic characteristics, as well as the nature of adjacent land uses.
Methane subsurface monitoring is mandatory around the perimeter of disposal areas. Regulations stipulate that the compliance point for methane migration regulatory limits is at the landfill property boundary. However, in situations where the fill area is significantly distant from the property boundary, operators often opt to position monitoring wells closer to the waste mass. This proactive approach allows for early detection and timely intervention to prevent gas migration beyond the landfill property. In these cases, these strategically placed wells become the points of compliance. Should methane levels exceed regulatory limits in these initial monitoring wells, landfill operators are obligated to implement actions as defined by the department’s Methane Gas Policy. Relocation of monitoring wells to the property boundary may be required as part of a gas migration investigation, contingent upon prior approval from the Waste Management Program. Achieving compliance with newly installed wells at the property boundary can negate the necessity for formal corrective actions. Landfill operators should consider these factors when determining gas monitoring well locations.
Prioritize locating monitoring wells in areas with a higher likelihood of gas migration or where gas migration poses a significant threat to public safety or the environment. Critical locations include areas between the landfill and nearby buildings, as well as sand or gravel bedded utility lines, which can act as preferential pathways for gas migration.
Monitoring locations should be spaced no more than 500 feet apart. Closer spacing may be necessary depending on ground permeability—higher permeability necessitates closer spacing—and the proximity of potentially vulnerable features. When positioning monitoring wells near the waste mass, avoid placing them directly opposite gas extraction wells within the fill area. Such placement can yield falsely low readings due to the extraction well’s zone of influence.
In areas where gas migration potential is demonstrably low, monitoring may be deemed unnecessary. For instance, a stream or valley can serve as a natural barrier (hydrologic or topographic) effectively preventing subsurface gas flow. However, in such cases, operators must provide a formal written demonstration of the natural cutoff’s existence, which must be approved by the Waste Management Program.
Conclusions: Optimizing Gas Monitoring Strategies
Minimizing air intrusion is a universal design principle for all gas monitoring wells. Air intrusion can dilute samples, rendering them unrepresentative and compromising data accuracy. The selection of well designs and locations must be driven by the specific zones targeted for monitoring and the site-specific hydrogeological context. A monitoring well certification record is mandatory for reporting new monitoring well construction. These forms and additional resources are accessible on the department’s Well and Pump Installation Contractor Permitting webpage, providing essential tools for compliant and effective gas monitoring practices.
References
- Farquhar, Grahame, Monitoring and Controlling Methane Gas Migration, course notes presented at April 1993 Sanitary Landfill Design and Management training, offered by the University of Wisconsin, Madison, College of Engineering.
- Missouri Department of Natural Resources, Flood Grant Team, An Analysis of Landfill Gas Monitoring Well Design and Construction.
