Decontaminating Groundwater Sampling Devices
LOUISE V. PARKER AND THOMAS A. RANNEY
With steam cleaning, pressure developed in
INTRODUCTION
the steam boiler imparts a high velocity to a
Decontamination methods are used primarily
mixture of water droplets and steam, which is
to reduce cross contamination, especially when
directed from a nozzle onto the target surface.
groundwater sampling devices are not dedicated
Detergent and heat from the steam weaken the
and are moved from well to well. In 1989, Mickam
bonds between the dirt and surface while the
et al. surveyed the various decontamination pro-
high velocity of the water droplets has sufficient
cedures required by state and other regulatory
power to remove debris from the surface (Sum-
agencies and in 1995 Parker conducted a litera-
mers 1982). Depending upon the contaminant,
ture review on decontamination methods. They
steam can also facilitate volatilization and hy-
found that 1) there are a number of published
drolysis, and may aid in the removal of subsur-
decontamination protocols, 2) there is a lot of
face contaminants. Problems associated with
disparity between these protocols, and 3) there
steam cleaning include workers being burned,
has been almost no systematic study on the effec-
corrosion of metal surfaces, warping of some poly-
tiveness of the various procedures.
mers, and liberation of toxic vapors. However,
Although decontamination procedures vary
from what we have been able to determine, most
considerably in their methodology, most utilize
"steam cleaners" used for decontaminating
some type of aqueous cleaning method, and often
groundwater sampling devices are actually high-
use solvent cleaning as a final or additional rinse.
temperature, high-pressure washing systems.
A typical protocol for decontaminating ground-
With pressurized water washing systems, high-
water sampling devices that have been used to
pressure pumps produce a stream of water rather
sample organic solutes is as follows: wash with
than the small droplets produced by steam clean-
detergent, rinse with tap water, rinse with (high
ing. The advantages of this type of cleaning over
quality) organic solvents, rinse with some type
steam cleaning are that there is increased force
of high-quality water (e.g., distilled, deionized,
available, the energy requirements are lower be-
organic-free reagent water), and air dry (Mickam
cause water does not have to be converted to
et al. 1989). In addition, steam cleaners or high-
steam, polymeric materials are less likely to be
pressure washing systems are sometimes recom-
degraded, and there is less likelihood of being
mended for decontaminating sampling devices,
burned.
especially to remove gross contamination such as
Organic solvent rinses are used to remove any
dirt and oils.
residual contaminants by dissolving them. Gen-
Aqueous cleaning is used to first remove gross
erally like dissolves like; i.e., polar solvents dis-
contamination and particles. Water acts as a sol-
solve polar contaminants and nonpolar solvents
vent medium for contaminants that are soluble in
dissolve nonpolar contaminants. Because water is
water, and as a dispersal medium for substances
a very polar solvent, nonpolar solvents are typi-
that do not dissolve in water but can be carried in
cally used to remove nonpolar organic contami-
suspension. A surface active agent (or surfactant),
nants (e.g., oils, tars) that have not been removed
such as detergent, is commonly added to improve
previously by aqueous cleaning.
the wetting ability of the cleaning solution and
Recommended organic solvents vary with the
aid cleaning by separating the contaminant from
particular protocol but typically include acetone,
the solid surface and then keeping the contami-
hexane, or methanol (Parker 1995). In most proto-
nants in suspension, thus preventing redeposition.
cols, these solvents are recommended without any
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