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

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