Electrical Resistivity & VES Surveys in Billings, MT

Q: How much does an electrical resistivity survey cost for a typical Billings lot?

For a standard commercial lot with three 2D resistivity lines covering 400 linear feet each, the survey typically falls between US$610 and US$950 per line, depending on electrode spacing, terrain, and the number of array types run. A full report with depth sections and interpreted lithology is included in that range.

Q: How deep can resistivity see in the Billings area?

With a 20-foot electrode spacing and a full 84-electrode spread, we routinely image to 140 to 150 feet depth. The limiting factor in Billings is usually the low-resistivity Pierre Shale, which shunts current near the surface, but we compensate by increasing transmitter power and using dipole-dipole arrays that improve resolution at depth.

Q: Does frozen ground affect the VES readings?

Yes, significantly. Frozen soil has resistivity values three to ten times higher than the same material at 50 degrees Fahrenheit. We either schedule surveys between April and October for shallow targets, or we install thermistor strings at reference boreholes and apply a temperature correction algorithm during inversion processing to remove the ice effect from the final section.

Q: Can resistivity distinguish between sandstone and shale in the Rimrock area?

Generally yes. The Eagle Sandstone typically reads above 150 ohm-m when dry, while the Pierre Shale sits below 30 ohm-m due to its high clay and pyrite content. The transition zone is sharp enough that we can map the dipping contact to within five vertical feet, which is critical for estimating excavation volumes and rock socket lengths for piles.

We ran a resistivity line last fall near the Rimrock Mall for a proposed stormwater detention basin, and the data revealed a buried paleochannel at 22 feet that the borings had missed. That’s exactly why VES belongs in the site investigation program. Billings sits on a complex interface of Cretaceous sandstone, alluvial terrace deposits, and shale interbeds—formations that change electrical response sharply over short distances. A calibrated electrical resistivity survey sorts out where the competent rock begins, where lenses of saturated silt hide, and where differential settlement could become a problem. We deploy Wenner and Schlumberger arrays with 84-electrode cables and automatic switching to build 2D sections that the structural engineer can work with directly. For deep utility corridors along the Yellowstone River floodplain, we complement the resistivity lines with a CPT investigation to tie the geoelectric boundaries to cone tip resistance and pore pressure, giving you a continuous profile from grade to refusal.

A 2D resistivity line costs less than two additional borings and gives you a continuous picture of the subsurface that point data alone cannot provide.

Our service areas

Our approach and scope

Billings grew in bursts—the railroad yards, the refinery corridor, the westward expansion onto the Rimrocks—and each phase left behind fill, slag, or disturbed ground that behaves unpredictably under load. Electrical resistivity cuts through that history because it reacts to porosity, salinity, and clay content rather than just grain size. Our field setup uses a 250-watt transmitter with automatic stacking, which pushes current deep enough to resolve the contact between the Quaternary gravels and the underlying Eagle Sandstone, typically between 40 and 120 feet in the Heights. The same survey picks up perched water tables on the slopes below the airport, a detail that changes excavation support design. We process the raw apparent resistivity through RES2DINV and deliver a color-coded cross-section with RMS error below 5 percent, annotated with interpreted lithology and moisture zones.
When the site straddles the boundary between terrace deposits and Pierre Shale—common on jobs east of Shiloh Road—we run parallel lines at two spacings to separate lateral variation from vertical layering, then tie the geophysics back to lab data from grain-size analysis to confirm the resistivity-to-soil-type correlation.

Electrical Resistivity & VES Surveys in Billings, MT — Technical reference — Billings

Local geotechnical context

The contrast between the Heights and the South Side illustrates why resistivity matters. Up on the sandstone benches, bedrock is shallow but fractured, and a VES survey quickly maps the transition from dry, high-resistivity caprock to water-filled joints that can collapse during auger drilling. Down along the river, the alluvium is thick and conductive, but clay lenses and hydrocarbon-impacted zones from historical refinery operations create false lows that look like groundwater—until you cross-check with induced polarization. Without that cross-check, you risk designing a dewatering system for water that is not there, or worse, missing a contaminated plume. We have seen resistivity contrasts of 10 ohm-m to 400 ohm-m across a single Billings site, and the difference between those two numbers is the difference between rippable overburden and blasting rock.
Temperature swings complicate the picture: a survey run in February on frozen ground at 20 degrees Fahrenheit will read higher resistivity than the same line in August, so we apply temperature corrections tied to soil thermistor readings at depth.

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Relevant standards

ASTM D6431-18: Standard Guide for Using the Direct Current Resistivity Method for Subsurface Site Characterization, IBC 2024 Chapter 18 (Soils and Foundations) with Montana-specific amendments, ASCE 7-22 Section 20.4 for site classification using shear wave velocity correlated with resistivity

Technical data

Parameter	Typical value
Array configurations	Wenner, Schlumberger, dipole-dipole
Electrode count per line	84 (expandable to 168)
Maximum investigation depth	150 ft (45 m) with 20-ft electrode spacing
Transmitter power	250 W, automatic stacking
Inversion software	RES2DINV, EarthImager 2D
Typical RMS error	< 5% after 5 iterations
Output deliverables	2D resistivity sections, fence diagrams, depth-to-bedrock maps

Q&A

How much does an electrical resistivity survey cost for a typical Billings lot?

For a standard commercial lot with three 2D resistivity lines covering 400 linear feet each, the survey typically falls between US$610 and US$950 per line, depending on electrode spacing, terrain, and the number of array types run. A full report with depth sections and interpreted lithology is included in that range.

How deep can resistivity see in the Billings area?

With a 20-foot electrode spacing and a full 84-electrode spread, we routinely image to 140 to 150 feet depth. The limiting factor in Billings is usually the low-resistivity Pierre Shale, which shunts current near the surface, but we compensate by increasing transmitter power and using dipole-dipole arrays that improve resolution at depth.

Does frozen ground affect the VES readings?

Yes, significantly. Frozen soil has resistivity values three to ten times higher than the same material at 50 degrees Fahrenheit. We either schedule surveys between April and October for shallow targets, or we install thermistor strings at reference boreholes and apply a temperature correction algorithm during inversion processing to remove the ice effect from the final section.

Can resistivity distinguish between sandstone and shale in the Rimrock area?

Generally yes. The Eagle Sandstone typically reads above 150 ohm-m when dry, while the Pierre Shale sits below 30 ohm-m due to its high clay and pyrite content. The transition zone is sharp enough that we can map the dipping contact to within five vertical feet, which is critical for estimating excavation volumes and rock socket lengths for piles.

Location and service area

We serve projects in Billings and surrounding areas.

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