Groundwater Sampling Methods
Determining the availability and quality of groundwater has become an issue for an increasing number of businesses and government agencies. Changes in legislation, pressure on aquifer supplies and a heightened awareness
of the impact of industrial activity have made groundwater sampling a hot topic. However, collecting a sample from a monitoring borehole which is truly "representative" of the quality of groundwater in the surrounding aquifer is not as easy
as it might seem.The water quality of a groundwater sample collected from a monitoring borehole or well is critically dependent on 2 factors.
The length of the screened interval in the borehole. The variability in permeability of the adjacent strata.Inflows from more permeable strata or fissures will dominate and bias the sample in the borehole and produce a flow-weighted average sample (FWA). This is not a "representative" sample. Mixing mechanisms within boreholes can be very complex and research demonstrates that boreholes with longer screened intervals lead to greater bias, and therefore uncertainty, in the sampling result.
There are essentially three methodologies that can be used to sample groundwater from a borehole.1. Fixed volume purging followed by sampling
2. Low flow purging followed by sampling
3. Zero Purge methods (passive sampling)
Fixed Volume Purge & Sample
Typically 3 or more times the volume of water in the well lining is pumped from the monitoring borehole or well prior to sampling using relatively high pumping rates.More detail on "Fixed Volume Purge and Sample"
Low Flow Purge & Sample
Low flow purging and sampling methods require pumping rates to be maintained at 0.5 litres per minute or less and provides optimal conditions for VOC (Volatile Organic Chemical) sampling.More detail on "Low Flow Purge and Sample"
Zero Purge Methods (Passive Sampling)
Zero purge methods use passive sampling devices to collect samples at discrete depths in the borehole column with minimal disturbance.More detail on "Zero Purge (Passive Sampling) Methods"
How can Waterra help?
Waterra has a full complement of equipment for pump/purge, low flow and passive sampling methodologies. Our groundwater sampling training courses (CPD accredited by the Geological Society) are designed to raise understanding and provide hands-on experience of the technologies and processes available for taking the most appropriate sample possible from a borehole or well.Click here for an up-to-date list of scientific papers and guidance documents related to groundwater monitoring
Currently Waterra are supporting a PhD studentship at the University of Birmingham on groundwater quality sampling from long-screened monitoring boreholes.
See Also:
Borehole Purge Volumes
Waterra Tubing Diameters and Volumes