In this study, the concentration of polychlorinated biphenyls (PCBs) remaining in the sediment of Han River and its 4 tributaries was investigated in a cost-effective method using gas chromatography-electron capture detector (GC-ECD). The concentration of total PCBs was calculated by summing up the individual Aroclor concentration quantified using specific congeners of each Aroclor. By quantifying individual Aroclors, the concentration of dioxin-like PCBs (dl-PCBs) and toxicity equivalency quotient (TEQ) for sediment samples could be estimated using simple formulae derived from the information of dl-PCBs content in individual Aroclors. Although it was not possible to compare the estimated concentration of dl-PCBs with the concentration analyzed by high-resolution mass spectrometry (HRMS) for the same sample, acceptable results were obtained through comparison with the concentration of sediment samples at adjacent points in previous studies. As a result, PCB concentration remaining in the sediments in the urban stream was relatively high in the sediments near the industrial area. In the case of the two tributaries adjacent to the industrial area, the concentrations of PCBs in most sediment samples exceeded the effective range low (ERL) value and at certain points exceeded the effective range median (ERM) value. In addition, most high concentrations of PCBs were commonly detected at the junction of the river and its tributary where the flow rate slowed noticeably. Therefore, it is necessary to consider the junction of rivers as an important sampling point when investigating PCBs in sediments.

In this study, a survey of the number of excess water quality standards, an average concentration analysis, and a trend analysis to calculate the grade of groundwater contamination using data from the groundwater quality monitoring network (GQMN) in Gyeonggi-do were conducted. A water pollution map of underground water was provided, and the water quality characteristics between analysis items and influencing factors were identified by statistical analysis. The indication contamination rate-the ratio of three determined contamination indicators-from high to low was Cl- (31.2%) > NO3--N (27.9%) > pH (20.8%) > ‌Trichloroethylene (8.9%) > Arsenic (6.3%) > Tetrachloroethylene (1.5%). According to the contamination grade analysis, the 'clean grade (0)' was classified as less than 68.8% (Cl-), the 'possibly contaminated grade (1)' was less than 30.1% (Cl-), the 'contaminated grade (2)' was less than 7.1% (NO3--N), and the 'seriously contaminated grade (3)' was classified as less than 1.9% (NO3--N). A mean contamination index rank difference test was conducted for each influencing factor in highly contaminated areas, non-drinking facilities, unopened facilities, private facilities, industrial waters, and industrial areas that showed statistically significant differences.

While BOD5 has been improved in Korea's major rivers and reservoirs over the last 10 years, CODMn is still on the rise. The purpose of this study was to investigate the leakage characteristics of refractory organic oatter (ROM) in Juwon stream and Pumgok stream flowing into Daecheong Reservoir, the most important drinking water source of Geum River basin. ROM was extracted with hydrophilic (Hi) and hydrophobic (Ho) organics using the XAD resin method. XAD analysis showed that hydrophobic ratios were 52.1-77.1 % and 52.7-97.1 % of dissolved organic carbon (DOC), respectively, in the Juwon and Pumgok streams. Hydrophobic organic matters were classified as humic substances originating from forest areas upstream of the watershed. In addition, the Ho/Hi ratio increased during the rainfall period (seven-nine months) and decreased during the non-rain period, and the Ho component, including hydrophobic acid (HoA) during rainfall, was the main component flowing into Daecheong Reservoir through the runoff. Total organic carbon (TOC) and COD showed a strong positive correlation between organics to confirm the association between ROMs. The results of this study confirmed the characteristics and background concentrations of the ROMs of some tributaries into the Daecheong Reservoir. In the future, continuous investigation and research will be needed to manage the natural organic matter of the main stream of Geum-river, including Daecheong Reservoir.

The results of proficiency tests and on-site assessments regularly conducted by environmental testing and inspection organizations from 2011 to 2019 were analyzed. The non-conformity rate of the proficiency test decreased from 6.71% in 2011 to 1.17% in 2019, while the non-conformity rate of on-site assessments decreased from 17.9% in 2011 to 3.7% in 2019. By comparing the results of the two tests from 2011 to 2019, it was concluded that the quality control ability of environmental testing and inspection institutions has improved greatly. Moreover, it was established that the ability of the proficiency test to evaluate the physicochemical analysis capability and the ability of the on-site assessments to evaluate the operational capability of the laboratory were highly correlated.