2
ERDC/CRREL TR-02-12
volume exceeds the rate of recharge by the aquifer, water can be pulled into the
well from the most permeable zone, thereby giving misleading information on
plume location and concentrations. In addition, studies of mobile colloidal
particles revealed that high rates of pumping (for purging or sampling) or using
devices such as bailers disturbed the aquifer and sand pack (Kearl et al. 1992;
Puls and Powell 1992, 1997; Puls et al. 1992; Backhus et al. 1993). This disrup-
tion was caused by the stress of high water velocities or from surging due to
sampling from bailers or high-speed pumps (Powell and Puls 1997). These
stresses can cause grain flow within the sand pack and exceed the cohesive forces
of aquifer mineral cementation resulting in artificially high turbidity (Powell and
Puls 1997), which can increase the concentrations of metals and highly hydro-
phobic organic contaminants such as PCBs and pesticides (Puls and Powell 1992,
Powell and Puls 1997, Backhus et al. 1993). Also, insertion of sampling devices
can cause mixing between the screened and cased interval and adequate time is
needed for equilibrium to be reestablished. To reduce these effects, dedicated
pumps and low-flow (minimal drawdown) sampling is commonly used (Puls and
Barcelona 1995, USEPA 1996), and more emphasis is being placed upon discrete
interval sampling and shorter screened intervals within the well.
We recently surveyed the market to see what new products were available
that allow discrete interval sampling and are less expensive to use than conven-
tional slow-flow sampling protocols (using dedicated pumps) but which yield
comparable results. We found several types of samplers that were designed for
sampling discrete intervals within wells. Most were grab, or thief, samplers,
including several pressurized systems that sample only when activated. The
remainder were diffusion-based samplers that rely upon diffusion of analytes
through a polymer membrane. All these samplers were designed to be used
without purging or could be used without purging and thus assume that the flow
in the well is horizontal and laminar. We selected five of these devices to study
in more depth to determine whether they were able to recover representative
samples as designed. It was not within the scope of this project to examine no-
purge sampling per se. The five devices we selected were the Kabis Sampler
(SIBAK Industries Limited, Inc.), HydraSleeve (GeoInsight), Solinst's Discrete
Interval Sampler (Solinst Canada Ltd.), the PneumoBailer (Best Environmental
Subsurface Sampling Technologies, Inc. or BESST Inc.), and the USGS Passive
Diffusion Bag (PDB) sampler (available through Columbia Analytical Services,
Inc. or Eon Products).
Kabis Sampler
The Kabis Sampler is a bullet-shaped device made of type-321 stainless steel,
and has a small collection tube and a longer, larger discharge tube at the top (Fig.
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