Levelogger Series User Guide
Page 73
10.1.3 Barologger Installation
The Solinst Barologger is a Levelogger with a small range adequate to monitor the
fluctuations that occur in barometric pressure. The Barologger’s readings are used
to barometrically compensate Levelogger readings. As a rule of thumb, a Barologger
can be used to compensate all the Leveloggers in a 30 km (20 mile) radius and/or
with every 300 m (1000 ft) change in elevation.
Note:
The Barologger should not be used to monitor water, as the internal mathematics
for temperature compensation are based on air rather than water.
To monitor barometric pressure correctly, the Barologger should never be submerged.
In well installations, it is recommended that the Barologger be suspended in one of
the monitored wells above the high water point (the well must be vented). For best
reading accuracy, the Barologger should be installed in a similar thermal environment
to that of the Levelogger. In groundwater wells, the Barologger should be suspended
beyond the frost line and deep enough to avoid large temperature fluctuations. In
surface water applications, the Barologger is best deployed in a dry well—a well
embedded in the bottom of the water body, but sealed at the base from water entry
and vented to the atmosphere. If a dry well cannot be installed, the Barologger can
be installed on a float in the stilling well. Further information on the Barologger and
barometric pressure can be found in Section 8.2.
10.1.3.1 Barometric Efficiency
The influence of barometric pressure on a groundwater surface can follow three
scenarios. In confined aquifers with capillary or vadose head space, increased
atmospheric pressure can tighten the pore spaces in the overlying soil and produce
a capillary effect as the water level rises in response to having nowhere else to go
but up. Second, some deeper aquifer systems can be quite barometrically isolated
from the relatively small change in level that barometric influences can produce.
The third scenario occurs in an unconfined aquifer, with high barometric efficiency,
in which a barometric pressure change results in an equivalent or highly proportional
drop or rise in groundwater pressure. In essence, depending on the aquifer type
and depth, increased barometric pressure can result in either increased, static or
decreased water levels. Barometric efficiency, the relationship of a barometric
change on groundwater pressure, in confined aquifers generally ranges from
20 to 75%, whereas in unconfined aquifers the efficiency can range from 80 - 100%.
Figure 10-18 Levelogger
and Barologger in Well
A second important element of Barometric efficiency is time lag—the time differential between a unit change
in barometric at the surface to the time of transmission of that change to the aquifer. Calculating general
barometric efficiency should not be done on a single barometric event, but rather on a statistically significant
number of events. As a result, it may take a month or more of submerged Levelogger and Barologger data to
determine barometric efficiency and time lag. As Barometric pressure fluctuates over time in excess of 60 cm
water column equivalent pressure and as barometric efficiency can be such an important factor in accurately
monitoring groundwater levels, it is vital that barometric compensation of the Levelogger data be performed.
The absolute pressure method used in the Levelogger and Barologger provide the user with the data necessary
to determine barometric efficiency and time lag. If a barometric efficiency value has been determined from the
Levelogger and Barologger data, that value can be applied to Barologger data in the Data Wizard.
Wells puncturing an aquifer have a negligible to non-existent effect on directly transmitting barometric
changes to the larger aquifer. Barometric pressure is transmitted through overlying layers. To obtain the best
and most accurate long term water level readings from Leveloggers, the user must first understand how the
Levelogger calculates a depth of water above the transducer and second whether barometric efficiency should
be considered in barometric compensation.
