Surface geophysical exploration

DGI performs and interprets 2DR surveys for:  identifying water-bearing fractures for bedrock well supplies; delineating recharge pathways for aquifer replenishment; mapping top of rock and identifying geologic hazards for site development; and finding leakage zones in water impoundment structures.

For large sites, DGI sometimes performs an initial reconaissance using VLF to identify potential water-bearing fractures zones.  This survey can be performed with much less time and cost compared to 2DR. The most promising areas can then be investigated in more detail using 2DR.

In this example, VLF was performed first with multiple traverses across a large site underlain by a siltstone/mudstone/sandstone sequence.  The VLF survey suggested a large fracture zone crossing the site.  2DR traverses were then performed in select areas that would allow access for air-rotary drilling.  A capacity of 300 GPM was obtained in a steeply-dipping fracture zone identified at approximately 650 feet on this traverse.

In this example, 2DR was used to evaluate the presence of karst hazards in carbonate rock terrain underlying a large warehouse site.  The features indentified in this example were caves up to 30 feet in height relative to vertical boreholes.

Finding areas that can accept large volumes of recharge to ground-water can be challenging.  In this example, multiple resistivity traverses were performed and the results were combined into a three-dimensional map showing thickness of sand and gravel deposits overlying bedrock.  Subsequent test wells and hydraulic testing confirmed capacity for a large-scale ground-water recharge project.

Working with Engineers Without Borders, our team mobilized 2DR equipment to Kenya for the Kolunje Water Supply Project.  On our last day in country, we performed this kilometer-long survey, revealing a potential water-bearing zone.  Subsequent drilling and testing confirmed a viable water supply with a capacity in excess of 60 GPM.