Ten “Simple” and Potentially Costly Groundwater Errors

Simple groundwater measurement errors can lead to very costly, and often times unnecessary, groundwater remediation.  That’s why our seminars on soil and groundwater remediation focus on the fundamentals of site characterization before we delve into the remediation options. 

One of the takeaways we provide at our seminars is this list of common groundwater errors.  While this really is a list of simple errors, the consequences are no laughing matter. 

  1. Some wells considered for groundwater flow direction determination are in a different aquifer from others. 
  2. Wells are placed in excavations where tanks had been removed, and the excavation backfilled with sand.  The water levels from these monitoring wells may not be representative of those in the surrounding native soil. 
  3. Wells are improperly screened.  A well screen may be too long (potential for vertical gradient effect);  too deep, if intended as a water table well; or too shallow, periodically resulting in its position above the water table. 
  4. Water levels in isolated and disconnected pockets of shallow groundwater are used to calculate directions of groundwater flow. 
  5. Top-of-casing elevation for a well is incorrect.  This may be the result of a surveying error on the well, the datum for the survey is incorrect, or the well elevation has changed (due to subsidence in landfills, frost heave, or slope movement). 
  6. The water level was not stable when measured.  This may occur because a well was not allowed to vent prior to measurement or for wells screened in a low permeability formation; the water level had not stabilized after construction or sampling. 
  7. There were errors in water level measurements.  This could occur because the depth to water was not measured from a specified mark on the well, someone read the measuring tape incorrectly, the measuring tape was faulty, or someone transcribed the observation incorrectly. 
  8. There are calculation errors.  Someone made an error in subtracting depth to water from top-of-casing elevation or failed to account for the effect of density of a free-phase chemical. 
  9. Wells are identified incorrectly or they are damaged (broken, bent, leaky). 
  10. Short-term changes in water levels are ignored.  These could be due to a recharge event, air entrapment, evapotranspiration, bank storage, tidal effects, atmospheric pressure, an external load, an earthquake, or groundwater pumping. 

Obtaining groundwater elevations and determining groundwater flow directions should be one of the easiest tasks your consultant or expert does.  Unfortunately, basic water level measurements are often done incorrectly.  When these basic steps generate bad data, then the conclusions are likely wrong as well.

If you have any questions about groundwater related issues, contact Michael Sklash, Ph.D., P.Eng (msklash@dragun.com).  For more information about The Dragun Corporation go to our website, www.dragun.com

 

 

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