Vadose Zone Monitoring System

Description

Vadose zone monitoring systems detect and or characterize changes in the zone between ground surface and the water table).

The first was developed to monitor contaminant changes after a site is remediated. The standard practice is to monitor groundwater wells for contaminants. This approach may be problematic at a site with a relatively deep groundwater table. By the time contaminants are detected in the groundwater, significant vadose zone contamination will have occurred. Therefore, monitoring the vadose zone instead of the groundwater permits earlier detection of a contaminant release. The Vadose Zone Monitoring System provides unattended, automated, real-time monitoring of soil vapor. An instrument, installed in single or multiple wells, provides gas sampling at up to 64 sampling ports. Measurements indicating changes in vapor movement suggest contaminant movement. This sampling system identifies, measures, and stores the concentration of up to five target gases. It shines an infrared light on the gas sample in a chamber, and sensors monitor the response of the gas to the light.

The second type of system was developed to detect contaminant migration from buried wastes.  In this system, several types of instruments were developed to obtain in situ hydrologic characterization data, to verify drainage potential, and to obtain estimates of current recharge fluxes under a range of surface conditions. One instrument, the Advanced Tensiometer (AT), measures soil water pressures in the vadose zone. Another new instrument, the water fluxmeter, measures drainage flux

Limitations and Concerns

In the first system, success depends upon gas vapor reaching the sampling locations. Barriers to vapor may give the false impression that a problem is not present. Also, the gas sampler can detect only five target gases. While vadose zone monitoring is important for soil contamination sites, risks associated with groundwater contamination may not be detected accurately.

With the second system, actual groundwater monitoring should be considered, even though hydrological monitoring of the vadose zone is important.

Applicability

These technologies are used for detection of soil contamination or changes in hydrology that may effect buried wastes. Contaminants detected are volatile organic compounds (VOCs) and semi volatile organic compounds (SVOCs). The first system could be used for soil gas detection if vapor intrusion is of concern.

Technology Development Status

This technology is field demonstrated.  Some of the hydrological instruments are deployed in the field.

Web Links

http://www.sandia.gov/Subsurface/factshts/ert/vzms.pdf

Other Resources and Demonstrations

See http://www.osti.gov/bridge/purl.cover.jsp?purl=/760291-fqpWiC/webviewable/.