Formatted Title
The Use of Mathematical Models to Change the Remediation Approach for an Area Contaminated by TPH in São Paulo, Brazil
Background/Objectives
This work deals with an industrial unit located in São Paulo, SP, Brazil, whose production activities began in the 1950s, involving the production of various chemical products for the Brazilian construction industry. In 2012, environmental investigations began due to the detection of contamination in the local aquifer by hydrocarbons, mainly volatile aliphatic hydrocarbons, used in the manufacture of the products. Between June 2020 and June 2021, a LNAPL extraction system (DPE) was implemented, reducing the free phase plume by more than 97%, suggesting the need to explore other remediation technologies. To confirm this hypothesis, mathematical modeling was carried out using the American Petroleum Institute (API) tool, the results of which indicated the discontinuity of the DPE system and the application of a polishing technique. In this sense, in 2023, the process of "polishing" the mass of remaining contaminants began with the installation of the bioremediation system, with the aim of controlling the risks from the degradation of the products retained in the soil with a view to rehabilitation for the intended use.
Approach/Activities
Based on the operational history of the free phase extraction (FPE) system, modeling was carried out using the LNAPL Distribution and Recovery Model (LDRM2) tool - Version 2.0 developed by API (Charbeneau, 2007; 2014). This model estimates the total and recoverable volume of LNAPL in the porous medium based on the thickness of the free phase in the monitoring wells and the properties of the soil and the product. The capillary pressure properties of the soil are modeled according to the methods of van Genuchten (1980) and Brooks & Corey (1964). The calculations used data from monitoring the thickness of the free phase in monitoring wells adjacent to the extraction wells, as well as in the extraction wells themselves, during the period from June 2020 to June 2021, covering one hydrological year. This period takes into account variations in the availability of the free phase in the wells and the lowering of the aquifer water level due to the removal of the product by the DPE system. The models provided guidance for determining the remediation technique and projecting performance.
Results/Lessons Learned
The modeling results indicated that the remaining mass of petroleum hydrocarbons is retained in the soil (immobile), meaning that the multiphase extraction approach should be replaced by another, more effective approach. To support the decision on which technique should replace DPE, an investigation was carried out after the DPE system was demobilized at the site to identify possible LNAPL storage areas in the unsaturated and saturated zone, as well as updating the retained phase plumes and assessing the existence of active sources. Following this stage, the human health risk assessment study was updated, including vapor sampling, to identify risks in the current use scenarios for the area and with a view to updating the Area Intervention Plan. Thus, together with the complementary investigations, the API tool used was relevant in guiding the intervention in the area with a view to its rehabilitation.