Remediation of polycyclic aromatic hydrocarbons (PAHs) contaminated soil has drawn increased interest in the last few years due to health concerns and the efforts of companies to comply with environmental regulatory agencies. PAHs, also known as polynuclear aromatic hydrocarbons (PNAs), are a group of compounds produced through the incomplete combustion of fossil fuels, wood, tobacco and refuse. Soils can become contaminated with PAHs through a number of pathways, such as spillage of byproducts utility gas manufacturing (combustion of oil and coal to manufacture gas), disposal of wastes in landfills, spills during plant operation, transportation of petroleum products such as coal tar and creosote, and leakage from underground storage facilities. This research is primarily concerned with PAHs associated with "lampblack", a by-product of the utility gas manufacturing process that is commonly found at former manufactured gas plant (MGP) sites. PAHs are adsorbed onto the surface and in the interstitial cavities of the soot-like particles comprising lampblack. Several of these PAHs are known to cause cancer in animals and humans by dermal contact and oral administration (both inhalation and ingestion).

This research is conducted to test the feasibility of in situ soil venting thermal desorption (SVTD) process for the remediation of soils containing PAHs associated with lampblack residuals. The heat source evaluated for this technology as applied here is natural gas combustion. It is demonstrated that SVTD thermally desorbs persistent non- or semi-volatile hydrocarbons by forcing heat into an impacted soil zone generating hot vapors (known as combustion products). Traditional Soil Vapor Extraction (SVE) techniques (i.e. air flow and a vacuum) can then be employed to collect the hot vapors generated during the process. Thus, the proposed technique extends SVE to compounds with much lower volatilities. The proposed SVTD process combines the salient features of ex situ thermal desorption with in situ SVE to enhance the contaminant recovery. The mild thermal desorption conditions used for this process are intended to volatilize---and not combust---the PAHs.

Bench scale experimentation as wells as field pilot studies are conducted to obtain the necessary parameters to assess the feasibility of the proposed in situ thermal desorption technology. Bench scale results indicated that given a sufficiently long heating period, the vapor pressure enhancement effect, caused by exposure to mild temperatures, is sufficient to mobilize all the PAHs in the soil and reduce their concentration considerably [2]. Extension of the laboratory-based process to a field pilot-scale setting is discussed considering the additional complications posed by soil moisture and heterogeneity. The working hypothesis during this research is that SVTD can be proven to be a technically and economically attractive technology. History of the study area; geology; chemical and physical description of soil/lampblack; description and layout of the Phase I SVTD pilot setup including construction, data collection and evaluation will be discussed. Description of Phase I and II pilot studies including setup, data collection and evaluation, heat transfer modeling; and results will also be presented. Value engineering analysis and cost evaluations indicate that this technology is both economically and technically feasible for certain projects.

The findings of this research were used to develop a value engineering analysis for the application of in-situ thermal treatment in commercial scales. The value engineering analysis for this technology was compared to all other commercially available technologies being utilized for cleanup of similar sites. This research shows that the proposed in-situ technology can be unique in its application specifically for sites that conventional excavation and backfill (dig and haul) will not be feasible from technical and economical stand points. The proposed technology is therefore considered to be viable due to its very unique application in areas of no or limited access (such as buildings) with considerable cost savings and less interruptions as well as being less expensive at certain open sites such as contamination in deep subsurface.