Environmental Sampling Techniques - Fundamentals of Environmental Sampling and Analysis - page 88

where V the volume (gallons) of well, r the radius of monitoring well in ft, and h the
difference between depth of well and depth to water, or the height of the water
column in ft; 7.48 is the conversion factor (the gallons of water per ft 3 of water).

Cross Contamination in Groundwater Sampling

In Section 4.1.4, we briefly discussed the potential contamination problem from the
sampling container in general. Groundwater sampling has many other potential
contamination sources, including contamination during well construction (well
casings), well purging (pump and tubing), and sampling-related equipments
(sampling tools, water level indicator, monitoring probes). Table 4.2 is a list of
potential contaminants contributed to water samples by materials used in sampling
devices or well casings (Cowgill, 1988). Cowgill (1988) recommended that all
sampling devices or well casings should be thoroughly cleaned using steam prior to
sampling.

Table 4.2 Contaminants contributed to water samples by materials used in sampling
devices, well casings, and other items

Material Contaminants contributed

PVC-threaded joints Chloroform
Stainless steel pump and casing Cr, Fe, Ni, and Mo
Polypropylene or polyethylene tubing Phthalates and other plasticizers
Polytetrafluoroethylene (Teflon) tubing None detected
Soldered pipes

Sn and Pb

PVC-cemented joints Methyl ethyl ketone, toluene, acetone, methylene

chloride, benzene, ethyl acetate, tetrahydrofuran,
cyclohexanone, three organic Sn compounds,
and vinyl chloride

Glass container B and Si

Marker used in labeling Volatile chemicals

Duct tape for all purposes Solvent

Adapted from Cowgill (1988).

Practical tips

Groundwater sampling requires more equipment and containers in numerous
wells. A good office preparation will help reduce field time by an increased
efficiency. Such preparations include containers, labels, coolers, freeze-
packs, preservatives, calibration of instruments used for well purging and
stabilization (pH, conductivity), sampling tools (pump, water level indica-
tor), calibration solution, spare batteries, ropes, baggies, borehole logs,
monitoring well development forms, sample collection forms, and many
others.