Groundwater sampling methods and best practices
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 that 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 two factors:
1) The length of the screened interval in the borehole.
2) 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...