The owner/operator should construct a minimum of two representative cross sections
for each hazardous waste management unit, one in the direction of ground water flow and one
orthogonal to ground water flow. Cross sections should be based on both the monitoring well
boring logs and on the boring logs from the subsurface boring program, and should depict
significant stratigraphic and structural trends and reflect stratigraphic and structural features in
relation to local and regional ground water flow. Site stratigraphy represented on the cross 
sections should be compared against known regional stratigraphy to verify the well/boring
logs and to prepare an analysis of site specific stratigraphy. In complex geologic settings, the
Agency recommends that borehole geophysical logging, surface geophysical surveys, and/or
cone penetrometer surveys be performed both to verify the logs of cuttings or samples and to
assist in establishing stratigraphic control. When planning such surveys it is important to
remember that drilling methods and well casings/screens will influence the selection of
geophysical methods (e.g., electrical resistivity logging cannot be performed in cased wells).
6.2
Well Casing and Screen Materials
Figure 13 is a drawing of a monitoring well. A casing and well screen are installed in
a ground water monitoring well for several reasons: to provide access from the surface of the
ground to some point in the subsurface, to prevent borehole collapse, to permit ground water
level measurements and ground water sampling, and (for casing) to prevent hydraulic
communication between zones within the subsurface. Access to the monitored zone is
through the casing and into either an open borehole or the screened intake.
Monitoring well casing and screen materials should meet the following performance
specifications:
Monitoring well casing and screen materials should maintain their structural
integrity and durability in the environment in which they are used over their
operating life;
Monitoring well casings and screens should be resistant to chemical and
microbiological corrosion and degradation in contaminated and uncontaminated
waters;
Monitoring well casings and screens should be able to withstand the physical
forces acting upon them during and following their installation, and during their
use    including forces due to suspension in the borehole, grouting,
development, purging, pumping, and sampling, and forces exerted on them by
the surrounding geologic materials; and
Monitoring well casing and screen materials should not chemically alter
ground water samples, especially with respect to the analytes of concern, as a
result of their sorbing, desorbing, or leaching analytes. For example, if a metal
November 1992
6 16






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