EM conductivity surveys measure ground conductivity by the process of electromagnetic induction. Ground conductivity can be used to detect:
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Buried Foundations
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Buried metal objects
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Cavities, including Sinkholes
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Former landfill sites & associated Leachate plumes
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Geological features
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Land drainage systems
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Mine workings
The principal electromagnetic systems used for site investigation are the Geonics EM 31, EM 34-3 and EM 38 ground conductivity meters or the Geophex GEM-2 SKI system. The systems work on similar principles consisting of a transmitter and receiver coil spaced at a fixed configuration, but use different operating frequencies to provide a range of depth penetration and resolution for different applications. Low frequency EM 34-3 systems can be effective for finding large underground cavities such as caves and mine workings but are rarely applicable for smaller targets. The EM 31 operates at an intermediate frequency and is useful for locating discrete features such as sinkholes, abandoned mineshafts and underground storage tanks (UST's). The high frequency EM 38 system is best for detecting small targets buried at shallow depth, such as chemical waste drums and metal artefacts.
Above : Searching for buried metal artefacts with the EM 38.
The Method
EM survey is a rapid and cost effective technique in comparison to conventional resistivity surveys. A primary electromagnetic field output by the transmitting coil induces a secondary field in the ground. The receiving coil measures the magnitude of the secondary field (quadrature component) and the ratio between primary and secondary fields (in-phase component). Quadrature fields are proportional to ground conductivity, being responsive to bulk changes in lithology, groundwater and ground contamination. The presence of metal produces strong secondary fields, making the in-phase component a useful indicator of the presence of buried metal objects
EM data is typically collected as point readings of ground conductivity and in-phase taken at intervals along a survey grid that has been set out over the site area. The spacing of the grid-lines and reading stations is dependent upon the target size. Generally smaller targets require closer survey lines and denser spaced readings.
Processing and interpreting the collected data:
The site data is recorded on a digital data logger for later downloading to a PC for post-survey processing and interpretation. The most commonly used interpretation procedure is contouring, carried out with specialist interactive software to produce contour plans. The contoured data is analysed in detail by our experts to identify anomalous features relative to the general background. Once identified, the anomalies are correlated with local ground conditions. Survey results are presented as plans tied in to site co-ordinates, in a readily understandable engineering CAD format.
Above : Identifying a concealed landfill on a ground conductivity contour plan.
Example of ground conductivity used to investigate swallow holes:
The appearance of a hole in the middle of a school playing field understandably caused concern to the local education authority who commissioned a survey to investigate the area for further swallow holes in the chalk geology.
The survey was carried out using ground conductivity (EM31). The plot shows the vertical quadrature data collected with a notable high conductivity anomaly present to the right of centre. The results were interpreted as high conductivity occurring where saturated gravels are present over the chalk. It is likely that groundwater within the gravels has moved down to the chalk and is aiding the formation of solution features as this groundwater flow in the gravels.
Above : EM31 Ground Conductivity data showing the location of a buried mineshaft.
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How accurate is SUMO's underground utility survey and what types of utilities can it locate?Using cutting-edge technologies like electro-magnetics, signal induced threading, and Ground-Penetrating Radar (GPR), our underground utility surveys accurately detect a wide array of buried utilities including metal and plastic pipes, drainage systems, electricity cables, telecoms, and fiber optic cables. The methodology ensures high accuracy without the need for invasive trial holes.
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What is the turnaround time for obtaining results with SUMO's Underground Utility Detection service?SUMO’s service is built for rapid response. Contractors can receive immediate results onsite. Our equipment provides real-time information, and once we leave the site, the detected utilities are visibly marked on the ground surface for quick reference.
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Does SUMO provide detailed mapping of the detected utilities for permanent records or construction purposes?Absolutely, SUMO not only marks the detected utilities on-site but also offers high-quality, color-coded survey drawings. These drawings can include topographic features and a comprehensive record of the utility detection survey, ensuring it meets the client’s needs for future reference or pre-construction design works.
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Topographical and Geophysical surveyIn addition to mapping out utilities, our experience team can accurately survey the land, creating topographical drawings for use. With our state-of-the-art aerial technology, nothing is missed.
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What additional information can be included in the underground utility mapping service provided by SUMO?In addition to topographic features, SUMO’s mapping service can include fixed surface utility features such as inspection chambers, valve boxes, and telegraph poles. It can also incorporate key topographic details like building lines, fence lines, kerb lines, street furniture, street names, building names, and house numbers, facilitating easy site location.
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Does the utility mapping service by SUMO include standard referencing and compatibility with existing survey data?Yes, SUMO ensures the utility mapping references the ordnance survey grid and level datum as standard. Additionally, the drawings can be supplied to a specified grid and level datum and can overlay an existing topographical survey, making it a versatile and adaptable service for various project needs.
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What sets SUMO Services apart from other survey providers?SUMO stands out due to our impeccable level of service with nationwide coverage, state-of-the-art equipment, and our commitment to delivering top-quality, detailed colour-coded survey drawings in both hard and electronic formats.
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How do I request a survey quotation from SUMO Services?Requesting a quotation is easy. Just click on the "Request a Survey Quotation" button on this page, and our team will get in touch with you promptly.
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Can I book a SUMO Survey online?Yes, you can! Simply click on the "Book a SUMO Survey" button on this page, and you can schedule your survey with us at your convenience.
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What type of survey is suitable for my project or site?Our experienced team will work with you to determine the most appropriate survey for your specific needs. Contact us, and we'll assist you in making the right choice.
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Can I obtain both digital and hard copies of survey drawings?Absolutely. We offer the convenience of electronic copies for digital use and hard copies for your records. Just let us know your preference.
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Do you provide custom survey solutions for unique projects?Yes, we understand that every project is unique. Our team is highly adaptable and can tailor our surveying services to meet your specific requirements.
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How do I get in touch with SUMO Services for further questions?For any additional questions or inquiries, feel free to contact us through the contact form, and our dedicated team will assist you promptly.
Survey Methodologies
Detailed Magnetic Survey
Soil Self-Potential
Electrical Resistivity Tomography (ERT)
Soil Thermal-Resistivity Testing
Electromagnetic Ground Conductivity
Electromagnetic Location (EML)
Ground Penetrating Radar (GPR)
