Theme: 01. Remediation Technology Innovations

Topic Area: 01k. Innovations in ZVI Amendment Formulations and Applications

Formatted Title:

Bench Tests and Large-Scale Remediation via Reduction by ISCR-IR^® for a PCE Contaminated Site near São Paulo, Brazil

Background/Objectives:

The site is in a former industrial area located in the city of Jacareí/SP, State of São Paulo, Brazil,. Historically, the local aquifer presented concentrations up to 95,000 µg/L of perchloroethylene (PCE) associated with concentrations up to 5,400 µg/L of trichloroethylene (TCE) and 26,000 µg/L of cis-1,2-dichloroethylene (cis-1,2-DCE), in addition to other organochlorine compounds. The average water level is 2.4 mbgl for the shallow aquifer and the presence of clayey soil interspersed with sandy layers results in a low effective porosity (1.1 to 5.9%). Considering the abovementioned COCs and challenging lithological characteristics, a project considering detailed complementary site investigation and bench scale test were performed, making possible detailed planning of the products and dosages used and their horizontal and vertical distribution in the target area. A full-scale remediation was designed with the obtained data, with a focus on risk management due to the observed concentrations.

Approach/Activities:

Bench-scale tests were carried out to determine the effectiveness of organochlorines remediation by in situ chemical reduction, considering the natural conditions in the target area, and design the correct dosage of amendments. The reductive amendment used was a mixture of microscale ZVI with natural anti-methanogenic compounds, nutrient rich hydrophilic organic carbon source, chemical oxygen scavengers, vitamin and mineral sources. This mixture enhances the growth of existing microorganisms, stimulating biological oxygen consumption that subsequently create a favorable environment for anaerobic bacteria, thus promoting biotical reductive dichlorination of the COCs in a greater and longer lasting reductive environment. In addition to the biological process, the chemical reaction of oxidation of microscale ZVI also occurs through direct contact with the contaminant (e.g., beta-elimination). Individual reactors were set up to evaluate the physicochemical and analytical parameters over a period of 60 days. The reactors contained soil and groundwater in a ratio of 1:1 (m/v) in addition to 1% (m/m) of amendment. After 30 days, 99% of PCE concentrations decreased, with an increase in VC concentrations. With the success of the bench-scale tests, the large-scale step started. Considering the soil low effective porosity, the ZVI mixture was used in slurry form and injected by direct push. The composition used was 2.4 liters of water for each kilogram of amendment. First, nitrogen gas was injected at a pressure of 100 to 200 psi for 1 to 4 seconds. Based on the results of the complementary investigation step, the injection was distributed in 13 points over an area of 330 square meters and, vertically, the injection was distributed specifically at each point in an average of 4 meters in height, totaling 1,320 cubic meters. Each injection layer received 315 to 510 kilograms of amendment and 10 kilograms of sodium sulfite (buffer), totaling 6,000 kilograms of amendment. ORP and pH readings were performed before, during, and after injections. A baseline monitoring campaign was carried out and additional campaigns are planned throughout the second half of 2023.

Results/Lessons Learned:

Physicochemical in situ monitoring indicated ORP reductions, which is positive for the reductive dichlorination. However, a greater reduction in these parameters is expected in future monitoring so that the medium becomes effectively reductive. Analytical results from the first post-injection monitoring campaign are not yet available but, for the conference, it will be possible to evaluate the variations in COCs concentrations.

Renato Kumamoto

Affiliation

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(Group 1, Poster Board #221) Bench Tests and Large-Scale Remediation via Reduction by ISCR-IR® for a PCE Contaminated Site near São Paulo, Brazil