9.2
Dry-Well Monitoring, Single-Wall Tank
Error! Reference source not found. represents a typical dry-well
monitoring layout for a single-wall tank. Monitoring wells are placed
around the perimeter of the tanks, and are dug as close as possible to
the tanks or product lines for optimal sensor response.
The manhole should be watertight and the monitoring well should be
at least 2 feet (61 cm) deeper than the bottom of the tanks to be
monitored. Either 2-inch (5.1 cm) or 4-inch (10.2 cm) well casing
should be used.
To obtain an adequate sample area, the perforated section should be
a large part of the well casing’s length. Place a cap on the bottom of
the well casing to prevent dirt entry. Backfill dirt around the casing.
The vapor sensor monitors hydrocarbon vapors. A liquid sensor
should also be installed and placed lower than the vapor sensor to
detect any liquid buildup.
Though vapor sensors are not damaged by submersion in liquid, they
will not function properly until removed from the liquid and given
sufficient time to dry. The sealed liquid sensor is protected from
particles such as dirt. It requires no particular placement. Any
combination of vapor and liquid sensors may be used.
Figure 9-2 Dry Well Monitoring, Single-Wall Tank
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