Rochester sits on a complex stack of glacial till, outwash sands, and weathered shale, with the Irondequoit Creek valley cutting through the eastern suburbs. Water table depth varies wildly, from 4 feet in the lowlands near the Genesee River to over 30 feet in the drumlin uplands of Pittsford. That mix of conductive clays and resistive dry sands makes vertical electrical sounding ideal for mapping the subsurface without drilling every 50 feet. The VES method drives direct current into the ground and reads apparent resistivity at increasing electrode spacings, building a layered model of the soil and rock beneath the site. We run surveys across active construction zones in downtown Rochester and the suburban developments pushing into former farmland in Henrietta, where knowing exactly where the competent bedrock lies saves foundation overruns. Combined with a CPT test program, resistivity data helps engineers correlate mechanical behavior with geophysical signatures, reducing the number of boreholes needed for large commercial pads.
A VES sounding can distinguish a 3-foot clay lens inside a sand deposit at 25-foot depth—information a standard boring log might miss between split-spoon intervals.
Questions and answers
How much does a VES electrical resistivity survey cost in Rochester?
Most single-sounding surveys run between US$610 and US$1,070, depending on the line length and depth of investigation. A full 2D resistivity profile across a typical half-acre commercial lot with multiple soundings generally falls in the upper end of that range per line. Sites with heavy brush, steep slopes along the Genesee gorge, or limited access between buildings add mobilization time. We provide a fixed-price quote after reviewing the site plan and target depths—no hidden line-item charges for data processing or reporting.
What depth can electrical resistivity surveys reach in Rochester's glacial soils?
With a 200-foot electrode spread in Schlumberger configuration, we typically investigate down to 100 or 150 feet. The actual depth of signal penetration depends on the subsurface resistivity contrast. Rochester's dry drumlin tills are more resistive and let current go deeper; saturated clays along the Irondequoit basin attenuate the signal faster, so effective depth might be 60 to 80 feet. We adjust the maximum electrode spacing on-site based on the real-time apparent resistivity curve to ensure we're reading well into the bedrock layer.
Can you do resistivity surveys in winter when the ground is frozen?
Yes, but with modifications. Frozen topsoil has high contact resistance, so we use bentonite slurry around each electrode stake to improve coupling. The frost layer itself shows up as a thin high-resistivity cap in the inversion model—we account for it during processing. Survey speed drops a bit because electrode installation takes longer, but the data quality underneath the freeze zone is unaffected. We run winter surveys for clients needing results before spring construction starts.
How does VES compare to MASW or seismic refraction for bedrock mapping?
They measure different physical properties. VES maps electrical resistivity, which responds to moisture, clay content, and pore fluid chemistry. MASW and seismic refraction measure stiffness—shear wave velocity or P-wave velocity. We often run both methods on the same line because a resistive sand layer could be loose (low Vs) or dense (high Vs), and only the combination tells you which. In Rochester's glacial stratigraphy, seismic methods struggle with velocity inversions where soft clay sits under stiff till; resistivity doesn't have that problem, so VES complements seismic data well.
How long does it take to get results from a VES survey?
Field work for a single VES sounding takes about an hour once the electrode line is laid out. A full day of surveying might cover four to six soundings across a site. We process the raw data the same evening and run the inversion models overnight. Clients receive a preliminary interpreted cross-section within two business days, with the final stamped report following within five working days. We can expedite to next-day delivery for time-sensitive foundation redesigns.
