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Early slug testing was conducted by quickly adding water to a well or quickly removing a bailer full of water from the well. When environmental monitoring wells are being tested, you don’t want to add (or remove) water from the well. This either alters the ambient water quality or generates potentially hazardous waste. Thus a “mechanical slug” is used to run a slug test. This is simply a 3 to 5-foot long section of PVC pipe filled with sand and capped on each end. A cord is attached to one end of the mechanical slug so it can be quickly lowered below the water level (slug-in test/falling head test) and then later quickly raised above the water level (slug-out test/rising head test). Again the change in water level and time are recorded. Quickly lowering or raising the mechanical slug in or out of the water may cause splashing in the well. For slug tests lasting several minutes or longer this is not a significant problem. However, for wells that recover from a slug test in less than a minute, the splashing will interfere with a lot of the early time data so that a good determination of the changes in the water level can not be made. Because of these problems the pneumatic slug testing method was developed. In this method, the wellhead is sealed and air pressure is used to displace the water level.


Enviroprobe owns a Pneumatic Slug Test System of Geoprobe Systems for determining hydraulic conductivity (K) at multiple depths.

  • Installation of permanent monitoring wells is not required

  • Tests can be conducted at multiple depths and at several locations across the site in a timely manner to determine vertical and horizontal variations in K

  • High-quality depth discrete data on K can be obtained in many unconsolidated formations

  • U.S. EPA recommends the use of direct push methods for determining vertical and lateral variations in K so that contaminant migration pathways can be located and assessed

  • Real-time observation of field tests and data storage capacity

  • Allow for slug tests in probe rods and PVC casing as small as 0.5" in diameter

  • Allow for pneumatic slug tests in PVC casing from nominal 0.5" to 2.0" in diameter

  • A sampling rate of 1, 2, 10 and 38 Hertz to meet requirements for low-K formations and high-K formations producing oscillatory responses

  • Allow for performing rising or falling head tests

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