WorldWide Drilling Resource

Environmental Monitoring by Thomas Kwader, Ph.D., P.G. How Deep Should a Pump be Set? My wife and I are currently on our annual fall trip to the Smoky Mountains. I can’t help but notice a lot of pump trucks on the highway, and often after dark. It is an unusually dry fall and I suspect the groundwater levels are dropping and many wells are going dry. The first sign of a well starting to go dry is when the pump is running for ex- tended periods of time and air bubbles are appearing in the water. During droughts (extended periods of low rainfalls or lack of snow melt), groundwater levels may also drop due to low recharge from a lack of saturated ground and/or an increase in groundwater usage in the area. Also, new larger capacity wells or a new neighbor’s well could affect an existing well’s ability to supply water. Each well develops a cone of depression which can extend for hundreds of feet or yards, depending upon: the amount of water pumped per day; gallons per minute pumped; and the transmissivity of the aquifer (ability of the aquifer to transmit water both laterally and vertically). Also, if a well loses its ability to produce water (a plugged screen) or encrustation of the wellbore, the well will drawdown to lower depths when the pump is running. If a well starts to pump air, one solution would be to lower the pump intake to a lower depth in the well. This can usually be performed with a pump truck fitted with a mast and spool of cable. In our area (North Florida), most wells are four inches in diameter and have nominal four-inch submersible pumps. The drop pipes are 21 feet in length. Usually, lowering the pump one joint (21 feet) is sufficient to take care of the problem. If the pump is already near the bottom, it may be necessary to deepen the well or redevelop the well to improve the efficiency of the well. Another solution would be to reduce or lower the flow rate with a valve at the top of the well. Reducing the flow could help the pump keep up with the demand. However, the pump will need to run longer to supply the water needed. Tom Tom Kwader may be contacted via e-mail to michele@worldwidedrillingresource.com --- *+ )#)('-()$* !(& )(%#'" +)""+ ,'.*,+ -'"/ 0 . 1 1 1 1 & $ & & !' & "$!(! & ! % "$ & $ ( & % & #' % % ) & +!' ) $ ( ! !$,% ( %& *" $ % & !& ( & ! % % & $% " %" $ !( $ "$ % & & ! % !' &$ % " '% ) " +!'$ ' " !+ % &!& + 42 JANUARY 2017 WorldWide Drilling Resource ®