In-Situ Virtual HERMIT Tutorial - Manual (Page 39)

Drawdown Calculations 39
Chapter 5 Drawdown Calculations
One of the key measurements in a pump test is the drawdown of the well for
each pumping rate. During the test, the aquifer level changes shape—from
having a flat water level to a cone-shaped level as the pump removes water
from the aquifer. The drawdown is the difference between the water depth
before pumping and the depth after pumping at a known pumping rate.
5.1 USING THE “STEP” FUNCTION
During the pump test, the pump will be run at a steady rate until the
drawdown stabilizes. After stabilization occurs, the hydrologist may need to
determine if the aquifer or well can sustain a higher rate of pumping, so the
pumping rate is increased, or “stepped”. Each period of data collection at
different pumping rates is called a “Step”.
By graphing the data collected from a Level TROLL during the first step, the
graph will typically show the falling water level, then a transition to a steady
state as shown in the example below.
Click the Step button
when you increase the
pumping rate to create
a second “step”. The
software will make
note of the time that
the new step began.
This option is most
useful for a
logarithmic data
collection schedule
where you wish to
begin collecting data
rapidly without
configuring and
starting a new log. If
you have a linear data
collection schedule set
up, the data will still
continue to be
collected in a linear
time frame, but you
will know the time at
which the pumping
rate changed.