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Horizontal Sub-Slab Depressurization Systems in California

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Fugitive emissions are a significant issue in many urban areas where industrial sites are being re-purposed for new uses. As industry recognizes horizontal wells can be installed with little disturbance to the site operations, more clients are requesting them as part of their sub-slab depressurization systems. We recently installed horizontal SVE wells at two sites in California. One, beneath a luxury car dealer in Los Angeles (see pic taken as we drill beneath some of the “merchandise”), and the other is detailed further below.

There are a number of Superfund sites in the San Francisco Bay Area related to Silicon Valley’s manufacturing history.  In the 60’s and 70’s silicon chip manufactures used a solvent containing trichloroethylene – TCE to make computer chips (detailed history here). This solvent was often stored in underground tanks and transported through pipelines to the point of use. Leaks in these tanks and pipelines are responsible for nearly half of the Superfund sites in Silicon Valley.

The particular horizontal depressurization system we installed in May was beneath the slab of building that is being renovated for a new use.  Although the site itself is not contaminated, the future tenants wanted to preemptively protect its workers in the event that contamination would migrate onto the property.  When TCE is present in groundwater, it can turn to vapor, seeping through cracks in building slabs, causing illnesses to the people breathing it.

A total of 4 horizontal soil vapor extraction wells were drilled and installed 5’ beneath the slab.  Each well was made from 3” diameter PVC material and the screen sections spanned the length of the 250′ long building.  The wells were spaced evenly across the footprint of the building, with about 40’ separation, to ensure adequate coverage.  The wells will later be connected to a riser pipe and fan that will divert soil vapors from underneath the building to the roof, where it’s released into the air.

The project was completed in 5 days, ahead of time and under budget.