Before drilling a water well, call WaterSurveys (H2OSurveys)!
Serving all of California

Water Surveys (H2Osurveys.net) serves all Nevada and California Counties. We offer two survey methods to identify potential groundwater-bearing zones in which to construct a well: The Very Low Frequency (VLF) method, and the Seismoelectric Sounding method.

The VLF method is preferred when a property is large and the depth to water is thought to be less than 100 meters. With this method, several long traverses can be done in one day.

The Seismoelectric method is useful to determine, before drilling, which target sites revealed by a VLF survey will yield the most water. This method is also very useful when the property is not large and long VLF transects cannot be run. Several soundings can be done in one day.

Details —

THE VLF METHOD can detect conductive or resistive zones at depths up to 100 meters. There are military VLF transmitters around the world operated to communicate with submarines in 5 to30 kilohertz range. The VLF instrument measures the strength of a VLF signal, called the primary field, and compares it to the strength of a secondary field induced by the primary field in conductive bodies at depth. While holding the VLF instrument at a certain compass heading, the operator takes readings every 10 or 20 meters along a survey transect 100 to greater than 1000 meters long. With this method we are able to see the geological structures more than 100 meters beneath the surface by their differences in resistivity (ohm-meter), the opposite of conductivity. In areas of hard rock, only the fractures in the rock may yield enough water for a well. The contrast between the high resistivity of the hard rock and the low resistivity of the groundwater in a fracture allows the fracture to be detected. In sedimentary rock, the contrast will be between the high resistivity of dryclays and the low resistivity of saturated sand and gravels.

A typical resistivity profile with potential drill target 5A identified as shown below. Drilling targets are selected in low resistivity zones.

See our VLF Survey Report PDF

THE SEISMOELECTRIC METHOD

The Seimoelectric sounding method has the potential to determine the approximate depth of water-bearing geologic formations (aquifers) and the sustainable yield (gpm) of a well completed in them. The method is sometimes referred to as the electroseismic method. Seismoelectric effects are initiated by seismic waves compression/ rarification) which induce relative motion between the formation matrix and water in the pore space. Anions in the water move cyclically toward and away from cations attached to the formation. This cyclic motion creates changing electric dipoles (current) which generate electromagnetic signals that can be detected at the ground surface. At a vertical sounding location, a seismic wave is created using a hammer and plate or a blank shotgun cartridge that propagates into the ground at a speed depending on the density of geologic formations through which it passes. Generally this speed varies from about 1500 to 3000 meters/sec in sedimentary rocks, but can be greater in igneous or metamorphic rocks. The seismic wave spreads out to form a hemisphere. When the wave reaches a formation saturated with water, electrically charged ions move back and forth as described above, and the electromagnetic signal is transmitted back to the ground surface at approximately the speed of light. When the wave passes through a layer with little water, no electrical signal is generated. No electrical signal is generated if the water is saline, so the method can only detect abundant fresh water. The time between initiation of the seismic source and measurement of the voltage of the returning electromagnetic signal along with an assumed seismic velocity indicates the depth of the formation. The strength and time rate of increase of the measured voltage are measures of the yield of the formation. The electrical signal is measured at the surface using two sets of electrodes to get duplicate readings. The electrodes are one meter long, driven into the ground, and are spaced two meters apart. The electrical signals are processed using proprietary software embedded in the patented AquaLocate GF6 Seismoelectric Survey System.

A screen shot of a sounding taken at the potential drill target 5A is shown below. The electrode readings are shown in blue and red. The green line shows the estimated hydraulic conductivity with depth using the averages of the blue and red electrode signals.

See our Groundwater Soundings Report PDF

The seismoelectric method is useful to determine, before drilling, which drill targets revealed by a VLF survey will yield the most water.  This method is used alone when the property is not large and the potential well locations are limited.  Several soundings can be done in one day.

Contact us with all questions about locating water before drilling a well.

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Serving all of California

WaterSurveys
14054 Sugar Loaf Road
Grass Valley, CA  95949
Email:WaterSurveys@att.net

Donald McEdwards, PhD, CE, RG
Certified Hydrogeologist in CA
707-354-4618