Quantitative Assessment of Monitoring Natural Attenuation on Carbon Tetrachloride Reduction at a Groundwater-Contaminated Site in Eastern China.

Monitored natural attenuation (MNA) technology is a groundwater remediation method that relies on risk management and long-term monitoring. However, there are currently few studies that have investigated the effectiveness of natural attenuation as a remediation method for carbon tetrachloride-contaminated sites. The objective of this study is to quantify the natural attenuation of tetrachloride contamination in a polluted site in eastern China through a 2-year MNA. Carbon tetrachloride was found to be the most severely pollutant in the saturated aquifers of the site, with a range of 76,696 m² (> 0.5 mg L⁻¹). Results show that the concentration in the deep quaternary first aquifer (QFA) was higher than that in the shallow aquifer. The maximum concentration at the center of the pollution plume in the bedrock aquifer (BA) was reduced from the initial 35.3 to 10.7 mg L⁻¹ after the implementation of MNA. The hypothesis that carbon tetrachloride was affected by the stratum fluctuation was verified through the field investigations. Specifically, the concentration of carbon tetrachloride decreased as the elevation of the monitoring point increased in the same aquifer generally. It was notable that the highly weathered bedrock fractured aquifer provided a large amount of relatively evenly fractured space for pollutant storage. Moreover, the heterogeneity of fracture network distribution also led to the appearance of the delamination characteristics of carbon tetrachloride. The diffusion of the carbon tetrachloride plume was mainly influenced with hydrodynamics and topographical fluctuations. The maximum concentration of carbon tetrachloride decreased with a rate of 48.84% in deep QFA, whereas it decreased with a rate of 69.69% in BA. The present study holds significant importance for the remediation of sites contaminated with DNAPL (dense non-aqueous phase liquid). Furthermore, the study can also help in identifying the key factors that influence the natural attenuation process and aid in developing effective remediation strategies for DNAPL-contaminated sites. [ABSTRACT FROM AUTHOR]