Cost comparison of soil vapor extraction and subslab depressurization for vapor intrusion mitigation

Abstract

Soil vapor extraction (SVE) can be applied for remediation, and also as an alternative to sub-slab depressurization (SSD) for vapor intrusion (VI) mitigation. This study compares capital, operation, and treatment costs of SVE and SSD systems using data collected during a multi-year demonstration project conducted at eight buildings in an urban setting. The capital cost of the SVE system is substantially less than the estimated total capital cost of individual SSD systems. The SVE operating costs are higher, especially in the early operating years when it is being operated for mass removal and treatment. As a result, the cumulative SVE system cost rises above that of the SSD systems in the sixth year of operation. A significant portion of the operations and maintenance cost advantage of the SSD systems comes from the assumption that off-gas treatment is not required. Alternative cases show SVE costs are likely to be lower in scenarios where numerous small buildings requiring independent SSD systems overlie the SVE zone of influence. Conversely, SSD systems are less costly for cases with few small buildings overlying the SVE zone of influence. An additional benefit of SVE is continued mass removal. In a situation where an existing SVE can be repurposed for VI protection from residual volatile organic carbon (VOC) mass, the SVE cumulative costs over 30 years can remain lower than the cost of installing and operating SSD systems in multiple buildings.