Using Water Level Instruments in Soil Vapour Extraction Systems

Soil vapour extraction (SVE) is an easy, low-cost remediation method for removing volatile hydrocarbons, typically petroleum by-products, from contaminated soil and groundwater. SVE system designs vary, but the basic concept involves: 1) pumping air through the vadose zone to volatilise hydrocarbons to a gas and 2) pumping these vapours through an extraction well. As a result, these gases introduce new pressure fluctuations
into an aquifer that affect groundwater elevations (Wong, 1997). Pressure fluctuations caused by SVE systems, in conjunction with barometric pressure fluctuations, pose a challenge to accurately measuring groundwater
elevations in monitoring wells. By setting up the monitoring well using one of the methods described below, groundwater level fluctuations can be accurately measured in sealed well SVE systems.

Method 1: In this method, an absolute Level TROLL® instrument and a BaroTROLL® instrument are set up to log data (Figure 1). They are then sealed in the SVE well. The Level TROLL instrument records pressure changes due to water level elevation changes and borehole pressure changes. The BaroTROLL instrument collects borehole pressure changes. The two data sets are merged using Win-Situ® Baro Merge™ software in order to determine water level elevations in the well.

Method 2: In this setup, a gauged Level TROLL instrument, vented cable, and part of a TROLL® Com are sealed inside the SVE well using a well cap cable holder (Figure 2). Borehole pressure fluctuations are compensated for through the vent tube that runs from the TROLL Com, through the cable, and to the back of the pressure sensor. The vent tube allows the Level TROLL device to capture accurate water level elevations with varying pressure fluctuations within the borehole. Field engineers can communicate with the Level TROLL instrument to view data, download data, and set up additional logs without the need to post-correct data.
Please visit the Downloads section at www.in-situ.com for an SVE technical note.