Formatted Title
High-Resolution Site Characterization Workflow for Hydrocarbon Remediation
Background/Objectives
The following case study begins with a fuel theft at a gas pipeline, leading to a hydrocarbon spill in the middle of a highly populated neighborhood of São Paulo. The spillage impacted soil and groundwater in a 100-meter radius. The dissolved plume reached a nearby river and the LNAPL led to both explosive and vapor inhalation risks. After the emergency measures were taken and the surrounding population evacuated, a series of studies were conducted to better understand the contamination extension and severity. The main focus of these studies was to provide orientation and subsidize actions to mitigate the risks and promote site remediation.
Approach/Activities
A 3D hydrogeological model was elaborated based on historical whole core soil samples (WCSS) and high-resolution data (Geoprobe™ MIP-HPT) to estimate the contaminant's total mass, as well as mapping entrapment and migration zones. The original WCSS database included the description of 196 boreholes used for various purposes, such as monitoring well installation and soil sampling. These soil descriptions were then compiled into 10 soil units, considering their grain size and composition, ranging from clayey, loamy and sandy soils. The 3D model was then compared and validated by the high-resolution data. The MIP-HPT analysis started by setting up an electronic data deliverable (EDD) database in which the electric conductivity (EC), HPT pressure and estimated hydraulic conductivity (Est. K) values were assigned to soil classes in order to draft geological profiles. This method, implemented by Geoambiente™, uses an indirect way to generate geological data and make the most out of HRSC. The soil class ranges were obtained in established literature as well as Geoprobe’s operations manual. In addition to the geological profiles, the EDD also provides valuable information in mapping the contaminant mass center regarding its location in unsaturated or saturated zones and entrapment or migration layers.
Results/Lessons Learned
The LNAPL mass was estimated at about 21 ton, by 3D modeling the results of analytical monitoring and generating plumes volumes. The geological data obtained by HRSC analysis allowed us to refine the model and target the mass center with a high degree of certainty which greatly reduced the amount of oxidizer necessary to reach the main goals from 50 to 20 ton approximately, thus promoting an overall operational cost reduction. The oxidizer injection is composed by a combination of OxyGEO™ and SurfGEO™, with the first being an oxidizer composed of sodium persulfate activated with calcium peroxide, which is used to degrade organic contaminants, and the latter being a biodegradable surfactant, used to improve NAPL mobility and water miscibility, and consequently facilitate its oxidation. The field operation is scheduled for October 2023 and new data concerning the remediation efficiency will be provided as soon as possible.