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Environmental and Structural Geophysical Engineering and Surveying Services

Environmental and Structural Geophysical Engineering and Surveying Services

Acquire an accurate map of your company’s construction site with Nova Geophysical Services (NOVA). We offer cost-effective geophysical engineering solutions that help ensure the safety of the operations and everyone involved in the project.

Ensuring Efficiency With State-of-the-Art Innovations

Underground utilities can pose a variety of setbacks for construction and facilities management if their locations and depths are not accurately known. Drawings and maps of these are commonly inaccurate or, in many cases, not documented at all.

Geophysical surveys are a rapid and cost-effective means to map underground utilities in either a pre-construction or design phase. NOVA offers a variety of geophysical technologies for the location of underground utilities and various other applications. These include:

  • Borehole
  • Electrical Resistivity Imaging (ERI)
  • Ground Penetrating Radar (GPR)
  • Electromagnetic (EM) Survey
  • Comprehensive Subsurface Utility Location (CSUL)
  • Microgravity Surveying
  • Microseismic Monitoring
  • Seismic Refraction Surveying
  • Time Domain Electromagnetic Surveying (TDEM)
  • Concrete & Structural Imaging

BOREHOLE

Borehole Geophysical Logging

Borehole geophysical logging measures the physical and/or chemical properties of geologic strata and fluid penetrated by the borehole. These measurements are often a vital component of subsurface characterization, providing in-situ property measurements.

NOVA offers complete borehole logging services, including:

  • Caliper
  • Natural Gamma
  • Resistivity/Resistance
  • Inductive Conductivity
  • Temperature
  • Deviation
  • Flow (Impeller and Heat-Pulse)
  • Sonic Velocity
  • Video (Color and Monochrome)
  • Depth (m)

Applications

For each potential application, NOVA geophysicists will select the most appropriate instrumentation and recommend a program to suit the project’s requirements. Typical applications include:

  • Lithologic characterization and stratigraphic correlation
  • Fracture delineation for groundwater, resource monitoring, and remediation
  • Well assessments, including well completion, condition, and video inspection
  • Hydrophysical testing for aquifer properties such as hydraulic conductivity, porosity, and fracture permeability

Survey Requirements

Most geophysical logs can be acquired in both cased and uncased boreholes which are 50 mm in diameter or greater when using standard equipment. Specialized equipment for logging small diameter boreholes is also available.

Benefits

Borehole geophysical logging involves the recording of quantitative and real-time measurements. These provide a dependable means to correlate and compare borehole conditions. At the same time, it allows for the monitoring of changes within the borehole(s) over time.

Products

Geophysical log data can be presented in a variety of formats, including:

  • Borehole log sheets that integrate geologic, geochemical, and geophysical data, with cross sections showing geophysical logs correlated between boreholes
  • Plan maps showing elevation or depth of geologic contacts or isopachs showing geologic unit thickness
  • Cross-plots of geophysical responses for characterizing geologic units

Electrical Resistivity Imaging (ERI)

The electrical resistivity imaging (ERI) method maps subtle differences in the electrical properties of geologic materials that may be caused by variations in lithology, pore-water chemistry, water content, and the presence of buried debris. ERI involves transmitting an electric current into the ground between two electrodes and measuring the voltage between two other electrodes.

The direct measurement is an apparent resistivity of the area underneath the electrodes that includes deeper layers as the electrode spacing is increased. The spacing of electrodes can be increased about a central point, resulting in a vertical electric sounding (VES) that is modeled to create a 1-D geoelectric cross section.

Recent technological advances allow for rapid collection of adjacent multiple soundings along a transect that are modeled to create a 2-D geoelectric cross-section. The cross section is good for mapping both the vertical and horizontal fluctuations in the subsurface.

Applications

ERI can be used in mapping stratigraphy and aquifer boundary units, such as aquitards, bedrock, faults, and fractures. This is useful for:  

  • Delineation of voids in karstic regions
  • Mapping saltwater intrusion into coastal aquifers
  • Delineation of contaminated groundwater
  • Detecting leaks in dams
  • Mapping zones of mineralization as well as sand and gravel resources
  • Mapping subsurface conditions of pavements, retaining walls, or geologic foundations

Survey Requirements and Depth of Penetration

  • Electrode array lengths are tens to hundreds of meters.
  • Most are successful in long areas free of buried utilities and severe topography.
  • Depth of penetration is approximately one-fourth to one-eighth the array length.
  • Vertical and horizontal resolution decreases with depth and varies with array type.

Benefits

  • Fast, noninvasive, and inexpensive compared to drilling
  • Less susceptible to interference from overhead utility lines and other obstacles compared to electromagnetic methods such as TDEM and CSAMT
  • Easily referenced to existing boreholes and allows for interpreted cross-section between boreholes
  • Optimizes the location of water supply wells
  • Guides placement of geotechnical borings and monitoring wells

Ground Penetrating Radar (GPR)

When providing our services or collaborating with leading universities and national laboratories, we use state-of-the-art technologies. Our staff is knowledgeable in operating the finest Ground Penetrating Radar Systems in subsurface radar technology in the world.

In a ground penetrating radar (GPR) survey, radio-frequency electromagnetic pulses are transmitted into the subsurface and are reflected back to the surface at boundaries where there is a transformation in dielectric permittivity. These boundaries generally correlate well to subsurface material changes in a fresh water environment, as the dielectric permittivity of a material is predominately a function of its water content.

Where present, boundaries such as water bottom – soft sediment, soft sediment – hard sediment, and sediment – bedrock, are often good GPR targets, making GPR an efficient tool to rapidly determine bathymetry and characterize the sub-bottom in most fresh water bodies.

The penetration achieved with GPR depends primarily on the electrical conductivity of the subsurface materials such as the water, underlying sediments and rock, as well as the GPR antenna frequency used.

Lower frequencies penetrate deeper, but a lower resolution image is taken than would be with higher frequencies. Accordingly, a range of antenna frequencies, typically ranging from 25 to 500 MHz, are mobilized and field-tested to ensure that optimal results are obtained in a particular survey environment.

Requirements and Procedures

The GPR method provides a very quick means of nonintrusive data collection. The system is most commonly moved along the exterior at a consistent pace as data are collected continuously along profiles. The depth at which a feature can be imaged is largely dependent on subsurface material type, whether it’s resistive or conductive.

With prior knowledge of expected subsurface materials and clearly defined objectives, an experienced operator can optimize data collection parameters to compensate for less-than-ideal geologic environments.

Equipment

NOVA operates two GPR systems, a Sensors and Software Noggin and MALA RAMAC X3M. The MALA GPR system operates with a higher frequency range and is used when very near-surface high-resolution information is required. With shielded antenna to help remove aboveground reflections, this system is ideal for delineating features such as utilities and USTs in cluttered urban environments.

On the other hand, the Noggin system addresses the problem of ineffective penetration depth. This highly advanced digital recording system is capable of working at relatively low frequencies with very high pulsing power resulting in maximum depths of analysis.

Get In Touch With Us

If you are in need of professional surveying solutions, contact our team at NOVA. Our services are available throughout the northeastern US and the European Union.