I am working on a project involving the remediation of brownfields and vacant industrial parks. I was wondering about the details of capping contaminated soil mounds. Does there need to be a concrete or clay base layer under the mound of contaminated soil to prevent any seeping of the toxins? Or, can the soil mound just be capped? If the mound consists of only contaminated soils (relocated from other areas of the site), does the mound have to include a gas collection well?- Michael, Architecture student
It all depends. Capping of contaminated material is dealt with on a case-by-case basis. It is also determined by the type of contamination, type of use and potential receptors (i.e., people, groundwater, etc.). Ultimately, a regulatory agency would need to approve any capping system.
In this case, it sounds like you are digging up contaminated soil from around the site and forming a mound in one area (note: This in itself needs regulatory approval). There is usually some protective layer to separate the clean soil from the contaminated soil above it. Depending on the contamination, you may be required to use any combination of clay, concrete/asphalt, vapor or moisture barriers, drainage, geotextile, and vapor extraction, etc., along with some grading to draw water away from the mound. Generally, if the contaminants are metals, less protection is necessary. More protection is necessary for contaminants that volatilize. Before implementing any remediation plans or designing a capping system, you should contact your local regulatory agency for assistance.