In-Situ Level TROLL 400/500/700/700H Operators Manual - Manual (Page 53)

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Logging Methods for Aquifer Testing
True Logarithmic
True Logarithmic log type captures early-time water-level data during aquifer testing.
Measurements are very closely spaced at the start of the test (4 measurements per
second) and move further apart on a logarithmically decaying schedule as the test
progresses. There are 40 measurements per log decade. This log type is commonly
used for rapid step-drawdown pump tests, constant-rate pump tests, and slug tests.
Fast Linear
Fast Linear log type measures and records at a user-defined fixed interval of one
minute or less. The interval is small (seconds, milliseconds), and the test is usually of
short duration due to the volume of data logged and the impact of very fast sampling on
battery life.
Step Linear
Step Linear log type measures and records data according to a number of user-defined
elapsed time intervals or "steps" within a schedule. Both the elapsed time and the
number of measurements within each step can vary. After completing the elapsed time
for each step, the schedule will automatically move to the next step. Up to 10 separate
steps can be defined.
About the Level Reference
A Level Reference, also called an offset, is a user-specified starting point for logged
Level readings. It is entered in the Logging Setup Wizard when a log is configured, or it
can be stored in the device without configuring a log using the Configure button in the
Sensors tab.
Depth mode does not require that you enter a Level Reference.
The Level Reference can be any value you choose. Here are some examples:
l
Elevation—If you calculate the water level above mean sea level (MSL) and enter
this as the Level Reference, then elevations above MSL will be logged.
l
Depth to Water—If you measure the depth to the water surface (DTW) from the
top of the well casing and enter this as the Level Reference, then DTW (also
called drawdown) values will be logged.
l
Gauge Height or Stage—Logged readings track water level as related to
markings on a nearby staff gauge.
l
Zero—A Level Reference of 0 effectively sets the probe to zero at the start of the
log. Changes, both positive and negative, from the starting water level, will be
logged.
Once you have determined the value of your Level Reference, the software gives you
three options for entering it. These control when the level reference is applied.