Perfluoroalkyl substances (PFASs) in shallow groundwater are increasingly being studied due to the global occurrence, environment persistence, bioaccumulation, and potential human health risk. In this research, 16 PFAS (11 perfluorinated carboxylic acids and 5 perfluorinated sulfonic acids) concentrations in groundwater were quantified to obtain information on geographical distribution and PFAS detection pattern for 4 years in South Korea. In the results, groundwater PFAS concentration ranged from non-detectable to average 45.2 ng/L (sum of PFASs). The major PFAS compounds were perfluorooctanoic acid (PFOA), perfluoropentanoic acid (PFPeA), perfluorohexanoic acid (PFHxA), perfluorohexane sulfonate (PFHxS), and perfluorooctane sulfonate (PFOS). The short chain (C < 8) PFASs were more prevalent than long chain (C > 8) PFASs in shallow groundwater. However, the detection patterns of 15 PFASs were different for each aquifer. Subsequently, through a health risk assessment, a non-carcinogenic risk level through ingestion, inhalation, and dermal contact for PFOA and PFOS was determined at 10⁻¹, and it presents the need for PFAS management of groundwater.

In the result of monitoring nitrate in about 6,000 groundwater wells around agricultural area, an average detection is about 9.0 mg/L and the excess rate of quality standard for drinking water was serious level as 45%. A shallow aquifer in some agricultural sites was highly contaminated showing 105–311 NO₃-mg/L. In this work, we evaluated monitored-natural attenuation (MNA) of nitrate by biological denitrification in highly nitrate-contaminated aquifer, known as effective technology to clean-up high concentration of nitrate, for confirming whether the groundwater is naturally remediated. We monitored nitrate degradation rate, microbial reaction (sulfate reduction, etc.) for 16 months according to oxidant and reduction rate. We also monitored microbial community change and amount of functional genes (noeZ and nirK) that encode for enzyme involved in denitrification pathway. In the result, since the groundwater was quiet oxidant condition, nitrate reduction was not monitored. However, there are functional genes and various microbial families related to denitrification process were detected such as methylomonas and methylomirabilis. These results indicate that there are possibilities of natural denitrification if the redox condition and other factors (carbon source, etc.) are supported. We also calculated the Hazard Index using RBCA Tool Kits to obtain remediation need of nitrate-contaminated groundwater.

In this work, a method of simultaneously analyzing pesticide concentration and assessing its risks was developed. Assessments were conducted to evaluate the distribution characteristics and risks to human health of pesticides in shallow groundwater in agricultural areas. We developed multi-residue analytical methods using liquid chromatography (LC-MS/MS) and gas chromatography–tandem mass spectrometry (GC-MS/MS) to analyze 57 pesticides in groundwater. In addition, risk assessments were performed by setting scenarios considering the routes of pesticide infiltration into groundwater. For the simultaneous analysis of 57 pesticides, the liquid–liquid extraction method was applied twice using dichloromethane under acidic and alkaline conditions. The extract was concentrated and analyzed using LC-MS/MS (41 pesticides) and GC-MS/MS (16 pesticides). The precision and accuracy ranges of the analytical methods were 0.1~12.9% (within ±15%) and 80.3~113.6% (within ±20%), respectively. The limit of quantification was found to range from 0.0004 to 0.0677 μg/L. In total, 57 pesticides were monitored in 200 groundwater wells from 2019 to 2020. Twenty-six pesticides, including metolachlor and imidacloprid, were detected, with an average concentration of 0.0008 μg/L in groundwater. The pesticide types and detection levels differed depending on the survey period and surrounding land. When the risks associated with alachlor, metolachlor, and carbofuran were assessed, their health risks when found in groundwater were evaluated to be negligible (non-carcinogenic risk: less than 10⁻³, carcinogenic risk: less than 10⁻⁶).

Few studies have evaluated how rainfall recharges affect biological dechlorination of trichloroethene (TCE). In this study, a sequence of three well-to-well tests (Phases I, II, and III) were performed for 100 d to investigate the variation of biological dechlorination of TCE at a highly recharged and TCE-contaminated aquifer. Test solutions containing different nutrients were delivered into the aquifer through a nitrogen gas spray. In Phase I, where only formate was supplied, the degradation of TCE to cis-dichloroethene (cis-DCE) was negligible. However, when sulfate as well as formate was introduced during Phase II, the reductive dechlorination of TCE occurred. During Phase III, fumarate was also provided as an alternative electron donor. High cis-DCE production rates were observed with complete degradation of formate and sulfate at 65th day monitoring, the end of dry period in Phase III. Since then, there were heavy rainfalls that accounted for approximately 36% of total annual precipitation in this area. Although oxygenated rain was rapidly infiltrated into the bioactive zone, the consumption of formate and sulfate were not significantly affected, with the DO as low as <0.2 mg/L. Nonetheless, the dechlorination activity of TCE was decreased as evidenced by 70% reduction in the cis-DCE production rate compared to that before the heavy rainfall. In 10 d after heavy rainfall ceased, the dechlorination activity was partially recovered (approximately 60%), while sulfate and formate consumptions were fully recovered. These results suggest that the dechlorination activity of TCE at the tested aquifer was sustained even in the presence of heavy rainfall recharges. This was probably due to the growth of the dechlorinating microbes on solid surfaces by forming biofilms.

Slow-releasing tablets combined with persulfate acting as an oxidant and ferrous iron acting as an activator were manufactured for in situ chemical oxidation. The trichloroethylene (TCE) removal efficiency according to the molar ratio of the oxidizer and activator in the 0, 0.5, 1, 1.5, 2, and 2.5 molar ratio (persulfate: ferrous iron) reactors were 15%, 89%, 90%, 82%, 71%, and 55%, respectively. In a batch reactor injected with an oxidation-activation combined tablet (OACT) and a liquid oxidizing/activator, the TCE removal efficiencies were 100% and 70%, respectively, showing that the tablet form had a high efficiency in contaminant removal. The evaluation of the dissolution characteristics and TCE removal efficiency of OACT 0.5 (tablet with a 1:0.5 molar ratio of persulfate to activator) and OACT 1.0 (tablet with a 1:1 molar ratio of persulfate to activator) under continuous flow conditions showed that the TCE removal efficiency of the OACT 1.0 column was approximately 1.4 times higher than that of OACT 0.5. The longevities of persulfate and ferrous iron of the OACT 1.0 tablet were 43.2 days and 41.7 days, respectively. Thus, OACT 1.0, which was manufactured effectively, was suitable for in situ slow-release chemical oxidation systems.

This study aimed to establish an economical and rapid response system for carcass leachate leakage using a real-time groundwater monitoring system with sensors. In this work, four parameters, namely electrical conductivity (EC), chloride (Cl), nitrate nitrogen (NO₃-N), and ammonia nitrogen (NH₄-N), were monitored. Three actual livestock burial sites were selected as pilot areas and monitored for three years, from 2019 to 2021, using these four parameters. As a result of sensor quality control, the accuracy and precision range of the four parameters were found to be acceptable, within 75~125% and ±25%, respectively. When compared to the laboratory measurement value, the field measurement value recorded by the sensors was 1.1 times higher for EC, 1.6 times higher for Cl, and 2.5 times higher for NO₃-N. The correlation analysis between the lab measurement and sensor measurement results showed that the EC had the highest correlation coefficient of 0.3837. Additionally, the factor extraction results showed that the EC showed a relatively significant correlation compared to the other parameters. In summary, based on the results of this study, EC may be considered a key sensor parameter for evaluating leachate leakage from groundwater near disposal sites.