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Notes from the Groundwater Guy by Thomas E. Ballard, P.G., C.H.G. Southeast Hydrogeology, PLLC What Makes an Efficient Well? Part 1 Technically, well efficiency is calculated as the actual drawdown in a well versus the theoretical drawdown. Therefore, if a well has an actual drawdown of 40 feet and theoretical drawdown of 30 feet, the well efficiency would be 75%. In actual practice, you will never get a 100% efficient well, but 70-85% is considered an efficient well. When all is said and done, well efficiency really boils down to how easily groundwater can flow into the well, to be extracted by the pump. Well efficiency can be determined by monitoring drawdown in the well with a comparison to nearby monitoring wells or by using step test data. It should be noted, excess drawdown can occur as a result of pumping an aquifer at a rate which exceeds the yield of the aquifer, and is unrelated to well efficiency. Pumping tests should be conducted in new wells and periodically in existing wells to determine the capacity of the well. The well should be operated accordingly, to not exceed the established capacity. So what factors determine how freely groundwater from an aquifer can flow to a well? There are certain friction losses that occur within the aquifer, which are generally unavoidable. For instance, a finer grained aquifer will result in a less efficient wel l than a coarser grained sand and gravel aquifer, due to the larg- er friction losses to the more numerous smal ler grains and the more twisted path the water flow to the wel l must take. Head losses in a well results from the flow of groundwater through the dis- turbed area around the well borehole; the gravel pack and the screen can be controlled to a great degree. These inef- ficiencies can result from drilling fluid being left in the hole, formation damage from drilling activities, a poorly designed gravel pack, or a screen with limited open area. A quality screen with a rela- tively high open area, surrounded by a properly designed gravel pack, sur- rounded by an aqui fer that has had dri l l ing mud and formation damage removed through a proper well develop- ment process will minimize head losses and maximize well efficiency. These are al l factors which can affect head losses in the well and, when taken together during the well design and construction process, can significantly enhance the efficiency of the well. Tom Tom Ballard may be contacted via e-mail to michele@ worldwidedrillingresource.com 25 WorldWide Drilling Resource ® JULY 2019 WTR September Issue Deadlines! Space Reservation: July 25 th Display & Classified Ad Copy: August 1 st