Well venting and application of passive soil vapor extraction at Hanford and Savannah River

At the Hanford and Savannah River Sites, wells with open intervals in the unsaturated zone have been observed to open-quotes breatheclose quotes, i.e., to inhale ambient air from the surface and to exhale soil gas to the atmosphere. This breathing results primarily from the difference in pressure that develops between the soil pressure near the open interval of a well and the barometric pressure. Volatile organic compounds (VOC) have been identified at both Hanford (carbon tetrachloride) and Savannah River (trichloroethylene and tetrachloroethylene). Passive vapor extraction (PVE) refers to the enhancement and application of this natural breathing phenomenon as a remediation method for increased VOC removal rates from the unsaturated zone. Passive vapor extraction is proposed as a complementary technology to be used with active vapor extraction (AVE). The AVE system would be used to extract soil gas from the high VOC concentration, highly permeable zones. The enhanced PVE would be used to address those zones of lower VOC concentration and those zones where extraction is limited by mass transfer and diffusion. The primary advantages of PVE application are low capital costs and minimal operating costs. This combination allows for many small PVE systems to be placed on individual wells and for the systems to operate for the extended periods of time associated with remediation of sites in which soil-gas transport is diffusion limited