Site-Identification System

A local number based on the cadastral-survey system of the U.S. Government (well) identifies each
network site. The number consists of an abbreviation of the county name, township, range, and section,
and a unique four-digit number assigned to the well. For example, the well with the local number BN-
24/20E/1 8-0013 is in Brown County (BN), township 24 north, range 20 east, section 18, and has
sequence number 0013. The location of the 16 wells that are a part of this study are identified on Figure
1 using an abbreviated local well number, which includes only the county abbreviation and the well
sequence number.


Geophysical logs - caliper, natural gamma, spontaneous potential, and single-point resistivity - were run
in the wells, where it was possible, which could help interpret geologic units in a wellbore. A Mount
Sopris MGX Digital Logger was used for geophysical logging. Methods of logging and interpretation
are described in Keyes and MacCary (1971).

The hydraulic conductivity of geologic units tapped by the wells were estimated by
displacement/recovery tests (slug tests). A slug test is conducted by displacing the static water level in a
wellbore by quickly adding to, or removing from, the water a solid volume (the slug). The rate at which
the water level returns to static is controlled by formation characteristics. Hydraulic conductivity was
estimated from slug tests using the Hvorslev method (Hvorslev, 1951).

                                     Results and Discussion

The data that have been collected or compiled during the course of this study are listed in Table 1.
Geophysical logs were obtained from 9 of the 16 selected network wells, and are presented on single-
page well reports in the appendix. Displacement/recovery tests were conducted in all 16 of the wells.
Well construction information and the results of tests are listed in Table 1 and presented on the single-
page well reports in the appendix. Displacement/recovery tests provided reliable data for estimation of
hydraulic conductivity for 9 wells, 7 wells exhibited very slow recovery during the test. Slow recovery
in well SK-3 is believed to be due to low formation conductivity, the other 6 are interpreted to have a
poor hydraulic connection with the aquifer.

The 6 wells that exhibited very slow recovery due to poor hydraulic connection (indicated by an asterisk
in Table l and included in Table 2) are open to sand and gravel units. Wells open to sand and gravel units
would be expected to exhibit quick recovery during the tests, so these 6 are probably restricted due to
encrustation of the well screen, plugging of the well screen by fines, or collapse of the well casing.
These problems frequently occur with older wells. These 6 wells include some of the oldest wells in the
network, 5 were constructed between 1937 and 1956. However, there are 6 other similarly aged wells
for which reliable estimates of hydraulic conductivity was made, so well age is not necessarily the
primary factor. Regardless, the usefulness of the 6 slow recovering wells for showing short-term changes
in water level are doubtful, and their usefulness for reflecting long-term trends may be questionable.