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Our Portfolio: Monitoring Projects
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Vadose Zone Monitoring System
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Information
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TTP#:
SR0-9-SS31; Tech ID: 647
Project
Overview
The Vadose Zone Monitoring System provides unattended, automated
monitoring of multiple vapor sampling locations for unsaturated zone
measurements. The vadose zone is the unsaturated area between the
ground surface and the water table. Deep vadose zone refers to sites
where the water table is generally deeper than 100 feet. Movement of
vapor or volatile contaminants in the vadose zone is by diffusion or
advection. Movement by diffusion is a result of a concentration gradient,
while advective movement forces vapor or volatile contaminants through
the vadose zone by some means, such as changes in barometric pressure
with time. By utilizing the Vadose Zone Monitoring System the predominant
mechanism of vapor or volatile contaminant movement can be made and,
hence, provide more accurate predictions of the rate of movement of the
contaminants to the water table.
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Technology Description
The Vadose Zone Monitoring System integrates pressure sensors and gas
sampling devices in a stand alone field system that performs real time
measurement at up to 45 sampling ports in single or multiple wells. The
wells can range from test holes of one to two inches in diameter to
boreholes eight inches in diameter. SEAMIST[TM] membranes are the
principal method of injection and sampling port emplacement. The
sampling system utilizes a Bruel and Kjaer gas analyzer, a barometric
pressure sensor, a differential pressure sensor, and a solenoid valve
system to sequentially connect each sampling port to a sensor. Also,
temperature sensors and thermocouple psychrometers which measure soil
water potential are located in selected wells. The system being tested at
Sandia's Mixed Waste Landfill (MWL) monitors trichloroethylene (TCE),
carbon dioxide (CO2 ), and sulfur hexafluoride
(SF6 ). To perform a gas
movement experiment, 250 parts per million sulfur hexafluoride (0.025%)
is injected into the ground through a sampling port and the monitoring
system is started. Pressure data from 45 ports are collected/stored once
every three hours and gas analysis data from 45 ports are collected/stored
every six hours. The system runs automatically without supervision. Data
are periodically downloaded using a standard portable personal computer
and analyzed using standard spreadsheet programs. The pressure data
are correlated to gas analysis data from each well to determine the effects
of changes in barometric pressure due to a change in weather on the
movement of the vapor through the soil. The movement of the vapor is
analogous to the movement of TCE, the contaminant of interest, in the soil.
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