Electrical Resistivity Testing in Lexington: VES Surveys for Karst Terrain

With a Schlumberger array and AB/2 spacing pushed to 150 meters, we typically reach investigation depths of 80 to 120 meters in Inner Bluegrass geology. Practical depth depends on site access — we need clear space to lay out the full spread — and on background electrical noise from nearby power lines or buried utilities. In urban Lexington neighborhoods with tight lots, we sometimes cap at 40–50 meters and supplement with shallower 2D lines.

For a standard package of four to six VES soundings on a single residential or small commercial parcel in the Lexington area, costs generally range from US$660 to US$1,090 depending on site size, surface conditions, and whether we're also running 2D tomography lines. We provide a fixed-price proposal after a brief site visit — no surprises after mobilization.

Yes, and that distinction matters enormously for foundation design. A water-filled cavity in limestone typically reads between 30 and 80 ohm-m, while a clay-plugged sinkhole drops below 25 ohm-m — sometimes as low as 5 ohm-m in saturated montmorillonitic clay. The resistivity contrast is strong enough that our inversion models clearly separate the two, which tells you whether you're dealing with a drainage pathway or a compressible soil pocket.

A single VES sounding takes about 45 minutes to an hour once electrodes are placed. For a full site with four to six soundings, expect us on the ground for one day. We need walking access to lay out four cables in a straight line — up to 300 meters total for deep soundings — and permission to drive small stainless steel stakes at each electrode position. Tall grass and pavement slow us down but don't stop the work; we adjust contact resistance with salt water or bentonite mud at each pin.

We reference the KGS sinkhole inventory and karst potential maps on every Lexington project. The database gives us a regional context — known sinkhole density, nearest mapped features, underlying formation contacts — that informs where we place our resistivity lines and how we interpret anomalies. It doesn't replace field geophysics, but it makes our survey design smarter from the start.