Formatted Title

Remediation of Heavy Petroleum Hydrocarbons by Thermal Conductive Heating

Background/Objectives

The treatment area of about 10,000m2, was used as a garage for a public transport company between 1950 and 1995 and has been the target of environmental investigations since 2012. At that time, the city of São Paulo began site assessment to assess what would be required for the implementation of a real estate project. Due to low permeability of the organic clay in the treatment volume, a free phase pumping process was not effective at removing the LNAPL. After further investigation and assessment, thermal conductive heating was chosen to achieve the remediation goals for petroleum hydrocarbons

Approach/Activities

In this area, two distinct geological units have been identified: "Technogenic Deposits" (referring to landfill) and "Alluvial Deposits" (referring to alluvium). Additionally, there is a local aquifer present. 

Concentrations of Lead, Vinyl Chloride, Polycyclic Aromatic Hydrocarbons (PAHs), and Total Petroleum Hydrocarbons (TPHs) were detected in both the soil and groundwater. Moreover, we've found the presence of a dark oil. The risk assessment was carried out for direct contact with groundwater and for potential inhalation exposure in both closed and open environments due to the substances volatilizing.

To eliminate the secondary source of contamination and reduce TPH concentrations in both dissolved groundwater and soil to levels within the Maximum Acceptable Concentrations (MAC) limits, the chosen method was Thermal Desorption. This approach has a short duration of implementation, spanning a maximum of 12 months, covering the stages of initiation, execution, and conclusion.

The thickness of the free phase LNAPL at each location was measured, as well as the soil horizons where TPH concentrations were detected, in order to define the volume requiring remediation.

Results/Lessons Learned

The remediation efforts were simultaneously taking place in three sub-areas, with the aim of achieving the set goals at the conclusion of the operation. In one of the sub-areas, contaminated soil was excavated and layered over the other two sub-areas. This was done to facilitate thermal desorption. The thermal system's efficiency was monitored by tracking the mass of contaminants being removed, observing the stabilization of vapor concentrations, and regularly checking the water-oil separator.

In March 2022, during operation of the thermal system, there was a notable shift in the characteristics of the LNAPL, indicating the desorption of a product previously adsorbed in the soil. This accumulation facilitated pumping and removal, resulting in a significant reduction by April and complete removal in May 2022.

As of May 2022, a total of 1,758.91 kilograms of contaminants were extracted from the vapor phase, along with an additional 256 liters of fuel oil, resulting in a cumulative mass removal of approximately 1.98 tons.