WorldWide Drilling Resource

WTR Notes from the Groundwater Guy by Thomas E. Ballard, P.G., C.H.G. Southeast Hydrogeology, PLLC Well Design is More than just Drilling the Hole One of the things we find with our water well clients is they often do not understand everything that goes into the design and construction of a water supply well. So, many times a bit of education is in order. Important considerations in well design to produce the best well possible include: Filter pack sizing: If you are building a well using a filter pack, the gravel size should be selected which retains 40% of the formation. This generally means a sieve analysis must be done to evaluate the grain size profile of the surrounding for- mation prior to selecting a gravel size for the filter pack. Filter pack thickness: The ideal thickness of a filter pack should be about three inches. Any less can result in sanding in the well, and any thicker can make well development difficult. Screen type: Different screen types have different flow paths for the water to flow into the well. The more linear the path of water through the screen and to the pump, the more efficient the well. Screen opening size: The percentage of open space in the screen varies by screen type and opening size. Generally, the greater the open area in a screen section, the more efficient the well. Well diameter: The well casing diameter needs to be sufficient to install a pump capable of pumping at the rates supported by the well. For instance, you are not going to be able to get 1000 gallons per minute from a six-inch well, because you cannot install an adequate pump. Entrance velocity: For maximum efficiency, water should flow into wells at less than 0.1 foot per second during pumping conditions. Proper entrance velocity can be achieved by varying screen opening size, screen diameter, and screen length. Ability to develop the well: This may be one of the most important aspects of well design. If the well is not properly devel- oped, water cannot efficiently flow to the well. The screen type, screen opening size, filter pack size, and filter pack thick- ness can all directly affect the drilling professional’s ability to properly develop the well by determining how much energy can be transferred through the screen and filter pack to remove the residual drilling mud. All these factors, along with the actual drilling, can substantially affect the performance of the final well. Tom Tom Ballard may be contacted via e-mail to michele@worldwidedrillingresource.com --- *+ )#)('-()$* !(& )(%#'" +)""+ ,'.*,+ -'"/ 0 . 1 1 1 1 41 WorldWide Drilling Resource ® MAY 2018