The techniques we utilize have resulted in successfully interpreting subsurface conditions. Evidence of success is exemplified in finding a well site capable of yielding 300 to 800 gpm within the metamorphic rock
of North Georgia.
300- 800 gpm well
HYDROGEOLOGY OF FRACTURED BEDROCK AQUIFERS
Fractured bedrock aquifers are aquifers in which ground water exists within fractures or openings within the rock. Fractures exist within Igneous, Metamorphic and Sedimentary rock. Fractures typically develop along geologic contact zones and joint bedding planes. Ground water within Igneous and Metamorphic rock may exist within weathered / fractured quartz veins. Geophysical techniques are used to identify the fractures and quartz veins.
Ground Water In Fractured Bedrock Aquifers
The origin of ground water within fractured bedrock aquifers is local recharge. The recharge is from precipitation and may be from the saprolite (weathered rock zone) or local surface water. The degree of hydrologic connection between the saprolite and / or surface water and bedrock fractures determines the recharge to the aquifers. The recharge area may be tens to thousands of feet or even a mile from a pumping well drilled into the rock. The well production is dependent upon the extent of the fractures.
The term unconfined aquifer refers to the condition in which the aquifer is under atmospheric pressure. This water level is commonly referred to as the water table. The term confined aquifer refers to the condition in which the aquifer is under pressure greater than atmospheric pressure. The water level rises above the level at which the ground water was encountered in the well. In this case the well is termed an artesian well. If the water naturally flows out of the well, then the well is termed a flowing artesian well.
A majority of the wells drilled tap isolated bedrock fractures, which are under confined conditions and which are not hydrologically connected to surface water. Ground-water pumping from fractures hundreds of feet deep within the fractured bedrock aquifer generally does not impact the base flows of streams that are only a few inches to tens of feet deep.
EXPLORATION GEOPHYSICAL SURVEYS
Exploration geophysical surveys are measurements obtained from within the earth by instruments from the ground surface. The measurements obtained include electrical resistivity, gravity, magnetic or electromagnetic. The instrument is selected based on the site conditions, the geology and the depth of investigation. In small survey areas only one technique may be used, but in larger areas, two or more techniques may be used. The objective is to find where the fractures exist before drilling the well.
The use of these scientific techniques is based on the ability of the technique to distinguish the water-bearing units from solid rock. The water-bearing units, which are
fractures, weathered / fractured quartz veins and geologic contact zones in igneous and metamorphic rock and
fractures, joints and cavities in sedimentary rock,
are physically unique and / or naturally contain energy fields, which are detected by the techniques. The techniques measure naturally existing electrical, gravitational, magnetic and electromagnetic energy fields placed in the earth by God the Creator of Heaven and Earth. I distinguish these scientific techniques from so-called man-made abilities to detect the water-bearing units by dowsing or divining.
Topographic lineaments or the presence of low areas is used by some to find ground water. This technique, which is based on the lay of the land, is used to compare so-called successful wells in low areas versus so-called unsuccessful wells on uplands and hills. The premise is that fractures within the rock are more likely to develop beneath low areas than on hills. This technique has been used since the 1940s when it was introduced in print and has been used by well drillers and some geologists.
The technique is based on what is seen at the ground surface, however the real issue is the true presence of fractures beneath the ground surface, not what is interpreted to exist by just looking at the lay of the land. This technique is out dated and is not based on modern geophysical techniques, which “see” into the earth. Just as dentists do not guess where cavities are in teeth and surgeons do not guess where tumors are in the body, drillers and geologists should not guess where fractures exist. Dentists use x-rays and surgeons use x-rays, MRIs and other modern techniques to make wise decisions and improve the success of the dental and medical services. Likewise, the use of geophysical surveys helps the user and the customer to make wise decisions as to where and how deep to drill and improves the success of the well.
Ground-Water Services takes into account the presence of topographic lineaments on a case by case basis, but does not solely rely on their presence for well site selections. Geophysical techniques are applied to both low areas and hills. By so doing, the true picture of the subsurface can be understood better. There are many locations where geophysical techniques identified high-yielding wells on hills and identified low areas where no fractures were detected.
Dowsing or Divining
This technique, which is not used by Ground-Water Services, is based on so-called man-made abilities to detect water veins. The energy fields exist naturally and were placed there by God the Creator of Heaven and Earth. I understand that the energy fields are present, but I do not recognize a “gifted” person’s ability to locate the water-bearing units, and an “ungifted” person’s lack of ability to find them. The presence of ground water is for God’s glory, not man’s glory. The Bible states in Deuteronomy 18: 10-12, “There shall not be found among you any one that … useth divination, or an observer of times, or an enchanter, or a witch, Or a charmer, or a consulter with familiar spirits, or a wizard, or a necromancer. For all that do these things are an abomination unto the Lord: …”.
A study conducted by GWS shows the difference between the scientific techniques and divining and shows the truth behind an ancient myth. Contact GWS for a copy of the study article.
WATER WELL DESIGN AND INSTALLATION SUPERVISION
Water Well Design
After the exploration phase of the well project, Ground-Water Services recommends a water well design that will meet the intended use of the ground water. The design parameters are obtained by an analysis of the geophysical data, which help to determine the
(1) expected depth to the top of rock for the well casing,
(2) expected depth of the well based on the fractures present, and
(3) expected yield of the well based on the significance and number of the fractures.
The well design may be simple for a home or lawn irrigation well or complex for a high-yielding public drinking water, large scale irrigation or farm well. These wells may require larger diameter casings with different depth settings.
Home or lawn irrigation wells usually require 6-inch diameter casing. PVC casing is used most often if the depth setting is 60 feet or less and if no drilling problems are encountered. A 5-foot section of steel casing is recommended for the casing bottom to prevent breakage of the PVC casing at the bottom. Breakage at the bottom may allow sand, sediment or mud to enter the well. The casing bottom should be set at least 5 feet below the top of solid rock to ensure a proper seal at the bottom. Cement grout is also recommended to seal the casing bottom and all the way up the outside of the casing to completely seal the surface water and shallow ground water from entering the well.
Public drinking water wells require steel casing. Also, where drilling problems are encountered, steel casing is recommended. Drilling problems may include caving sand and loose weathered rock, which may be encountered just above the solid rock. In these cases, the mud rotary drilling method must be employed to properly set the casing. Air rotary drilling is then resumed inside the rock itself. Some inexperienced drillers will want to move to a new location, but another favorable location may not exist. Usually, but not always, where caving sand and loose weathered rock are encountered, adequate to abundant ground water is usually encountered within the shallow bedrock fractures at the original location.
Ground-Water Services offers water well installation supervision to ensure the proper construction of the well. Having worked for a driller in the past, GWS has first-hand experience installing wells. Installation supervision is part of our ground-water development services.
AQUIFER PUMPING TESTS AND WATER QUALITY SAMPLING
Aquifer Pumping Tests
Aquifer pumping tests are conducted after the well is drilled to determine the safe yield of the well. The safe yield is the flow rate that the well will yield without over pumping or dewatering the well. The safe yield may vary depending upon the time that the well will be pumped. For example, if the well will be pumped continuously for an extended period of time, the safe yield will probably be less than if the well will be pumped periodically at a higher flow rate. Pumping tests are recommended to ensure the well will yield a dependable flow rate for the intended purpose of the well. Tests may range in time from a short period of 4-6 hours for a lawn irrigation system to 24-36 hours or longer for a public drinking water well or pond or lake replenishment well. Knowing the safe yield prevents over pumping, pump burn out and premature dewatering, which may result in well failure.
The pumping test is conducted by installing a test pump and pumping the well at various flow rates while measuring the water level drawdown in the well. The time, water levels and flow rates are plotted on computer graphs to obtain a picture of how the well responds to various flow rates. From the plots and other calculations the aquifer hydrologic properties can be determined as well as the expected drawdown over an extended period of time. These data help to determine the depth setting and size of the permanent pump to be installed in the well.
Water Quality Sampling
Water quality sampling is conducted to ensure safe drinking water and / or to ensure unwanted parameters are in the water. For example, it is desirable not to have excessive iron or silica in ground water that is used in cooling towers. The pH (acidic or basic) of the water is also important. Water quality analyses are selected based on the intended use of the water.
Water quality analyses for human consumption include testing for coliform bacteria. Analyses for public drinking water include radiological, organic, inorganic, bacteria and microscopic particulate testing. Age dating of ground water is also applicable to determine the travel time within the earth and the location of recharge areas.
300 gpm well
Search Techniques and Facts
In order to find fractures containing ground water beneath the ground surface, surface geophysical techniques are employed which allow us to "see" into the earth at depths down to 1000 feet.