Formatted Title
Chlorinated Solvents and Hydrocarbon Remediation by Adsorptive and Oxidative Barriers
Background/Objectives
This project’s area of interest includes a 116.000 m2 industrial complex, where agricultural machinery and vehicles are produced. Site operations began around the late 1970s and decades of machining, tooling, painting and washing of vehicle parts, as well as other industrial processes resulted in the present-day environmental passive, which is defined by both LNAPL and dissolved plumes of a plethora of chlorinated solvents and hydrocarbon contaminants. These plumes not only affect the unconfined and shallower aquifer but also a deeper fractured aquifer, related to the regional bedrock, which is used for local water supply. This case has been studied since 2012 and Geoambiente™ is the latest environmental management consultant to tackle this problem, combining traditional expertise with 3D modeling.
Approach/Activities
The traditional approach of environmental management relies solely on groundwater and soil sampling to determine the extent and severity of contamination. After years of groundwater monitoring, the full scope of this site’s contamination has never been truly understood, especially when it comes to chlorinated solvents, which are the biggest threat to the fractured aquifer due to their higher density (DNAPL). While the more conventional investigation methods could never be discarded, new and more refined methods were required to advance our knowledge of the site’s subsurface. Therefore, new studies involving whole core soil sampling alongside 3D modeling enabled the creation of a hydrogeological conceptual model that allowed us to estimate with a high degree of certainty the contaminants’ sources and their total masses, as well as mapping entrapment and migration zones.
Results/Lessons Learned
In this case, the soil type and its specific characteristics, such as hydraulic conductivity, favor the remediation by injection of both an adsorptive and an oxidative barrier. The adsorptive barrier was created by injecting CarbonGEO™, an activated carbon dispersion developed by Geoambiente™. CarbonGEO™ is composed of activated carbon microparticles with a high specific surface area (of about 600 m²/g). These particles have a highly hydrophobic surface, which makes this material suitable for the adsorption of hydrophobic contaminants, such as BTEX and chlorinated ethenes. This type of barrier was placed downstream, in the northwest corner of the area, to interrupt the contaminant flow, preventing the plume from spreading even further. The oxidative barrier was created by injecting a combination of OxyGEO™ and SurfGEO™, two other remediation products developed by Geoambiente™. OxyGEO™ is an oxidizer composed of sodium persulfate activated with calcium peroxide, which is used to degrade organic contaminants. SurfGEO™, on the other hand, is a biodegradable surfactant, used to improve NAPL mobility and water miscibility, and consequently facilitate its oxidation. The oxidative barrier was placed in the upstream mass center, which shows the higher contaminant concentrations. The barriers were first applied in September 2022. By February 2023, the groundwater monitoring showed a great reduction in contaminant concentrations. The general concentration reductions observed (based on groundwater monitoring) were: 1,1-dichloroethylene (100%); benzene (99,08%); cis-1,2-dichloroethylene (87,72%); vinyl chloride (100%); tetrachloroethylene (42,43%); trichloroethylene (72,26%). The calculated cost savings ranged from R$5.0 million to R$1.5 million, considering mainly the material costs, which reduced from 106 ton to 31 ton based on comparison with previous projects. Previously, methods that are more conventional were not able to fully represent the stratigraphic complexity of the area’s subsurface and therefore did not provide enough information to solve the case. Using a 3D modeling software vastly improved our understanding of the hydrogeological data and correlated information. With these new tools and knowledge, we were able to reduce the amount of remediation products used, as well as operational cost and the necessary time to solve the case. By reducing contaminant mass in groundwater and soil, bringing these values closer to the acceptable values, we are improving the quality of life for those who use these aquifers as their water supply. In addition, we help the companies responsible for such environmental passives to act upon them, maintaining their operations active and providing jobs and opportunities to the local community.