Solutions for a complex world: Geophysics Mapping for Landfill Delineation
Article by: Hannah Peterson | hydroGEOPHYSICS
It is estimated that there are 4,000 active and over 10,000 closed municipal waste landfills in the United States, some with little to no information on the lateral extent and depth of waste material. Often closed landfills are unlined, which allows leachate and contaminants to migrate and possibly infiltrate into groundwater, posing a threat to the health of people and the environment. As a means to support monitoring landfill sites, geophysical methods are indispensable tools for delineating the lateral extent of the waste material as well as the depth and volume of waste. Additionally, geophysical methods can help predict the type of waste in the landfill based on measured responses.
Often closed landfills are unlined, which allows leachate and contaminants to migrate and possibly infiltrate into groundwater
At many landfill sites, the current extent and state of the waste materials are frequently unknown, with historical records sparse or geographically inaccurate. Therefore, it is critical to delineate the waste material boundaries, and thickness, to aid in cleanup efforts, assess potential impacts, and design and optimize remediation programs. Geophysical methods provide a rapid and cost-effective tool to survey large or small sites, providing accurate estimates of the waste extents and potential impacts resulting from leachate or contamination plumes, for example.
The EM-31 instrument was used to conduct the EM survey across the closed coastal landfill. It consists of a sensor housing, electronics console, and field computer. The depth of investigation is about 20 feet (6 meters).
Electromagnetic induction (EM) is a geophysical method used to image the subsurface using ground conductivity and in-phase measurements. This technology can be applied to landfill mapping to understand the extent of the waste materials, delineate any contamination plumes, and differentiate between waste types. The decomposition of municipal solid waste typically results in a conductive product, which can be contrasted from the generally more resistive background geologic material. The in-phase component of the measurement shows contrast between metal and non-metal materials, allowing the distribution of metallic debris to be map within the landfill boundary.
Electromagnetic induction (EM) can be applied to landfill mapping to understand the extent of the waste materials
EM technology detects variations in subsurface soil conductivity, which is a function of how well the material conducts electrical currents. In wet material, for example, electrical currents will flow with much less resistance than in dry areas, thus increasing the conductivity. Other subsurface properties, such as the porosity, grain size, soil moisture and saturation, and presence of bulk metals and infrastructure, will vary the conductivity over large or small spatial scales. The in-phase component of the measurement supplements the conductivity in that it is sensitive to the metallic content.
The Example
In 2020, HGI surveyed a 4-acre closed landfill that had been a solid waste disposal site until the late 1950s. After being graded and capped, the landfill has remained closed for over 20 years. The material had high exposure potential due to its proximity to the coastline, an environment prone to erosion, and the effects of sea-level rise. HGI was contacted to delineate the lateral extents of the landfill material. An electromagnetic induction (EM) survey was conducted across the area of interest. The results showed clear regions of waste material due to their high contrast in conductivity and in-phase properties from the natural background materials. When compared to the historical map of fill areas, the extent of the waste material was well aligned with these boundaries.
HGI performed an EM survey over a closed municipal waste landfill to delineate the lateral extent of waste material in comparison to the edge of the bluff and the historical fill areas. The results indicate there is potential for erosion and bluff failure to expose waste material based on the proximity of the mapped waste material boundary.
For more than 20 years, hydroGEOPHYSICS has been mapping landfills across the United States using non-invasive geophysical methods. In each case, the results have been remarkably successful in characterizing the waste materials using subsurface soil conductivity to understand each unique waste environment. Geophysical mapping of landfills has the following benefits:
Hannah Peterson carries the EM-31 instrument to map a landfill along coastal California.
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Can accurately measure the spatial extent of the material waste
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Detects and tracks leachate and contamination plumes
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Identifies metallic and non-metallic material
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Provides valuable information to mitigate and prevent harmful environmental effects
HGI will provide a unique solution for your landfill project, from survey design to acquisition, and reporting. We can also offer multi-method solutions to give better insight into the depth and volume of waste materials.
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About the Author: Hannah Peterson | hydroGEOPHYSICS
Hannah Peterson is a Staff Engineer and geophysicist for hydroGEOPHYSICS with a background in engineering, coding, and data analysis. She has broad field experience involving geophysical data processing, surveying, and geological interpretation in both land and marine settings. Her professional focus is on electromagnetics, electrical methods, data processing, and inversion.
Hannah holds a BS in Geophysical Engineering from the Colorado School of Mines and an MS in Earth Science from the University of California San Diego.
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