Nearly one-third of Seoul's sewer pipes over 50 years old, creating risk of sinkholes
Public concern is growing over sinkholes forming across South Korea, with aging underground infrastructure cited as a major cause in cities like Seoul and Busan.
According to data from the Seoul Metropolitan Government, 63 sinkholes were reported in the capital between March 2022 and March 2025.
District-level data shows some of the city’s most central and populous areas are home to the oldest sewer pipes, including those for rainwater. Jongno-gu has the highest proportion of 50-year-old sewer pipes with 53.5 percent, followed by Yongsan-gu at 48.5 percent, Seongbuk-gu at 47.7 percent and Mapo-gu at 45.4 percent.
When counting pipes older than 30 years, over 66 percent of the sewer systems in Jongno-gu and Dobong-gu fell into the "aging" category.
Sinkholes often form when cracks in deteriorated sewer pipes allow water to seep into the surrounding soil. The water erodes the ground and creates underground cavities that eventually collapse.
While such collapses are also associated with heavy rain in summer, several have occurred in spring, prompting experts to warn that "no place in Seoul can now guarantee safety beneath one’s feet."
On Sunday, a 40-centimeter-wide, 1.3-meter-deep sinkhole appeared in front of Aeogae Station on Subway Line No. 5 in Mapo District, forcing lane closures for nearly eight hours. Last month, a much larger sinkhole — 20 meters wide and 18 meters deep — opened up in Seoul’s Gangdong-gu, leading to the death of a motorcyclist. Busan also faced a scare on Sunday when a 5-meter-wide hole opened up under a pedestrian crossing in Sasang-gu.
While heavy rainfall and soil erosion have been typical culprits, officials say aging sewer lines are playing an increasingly central role. Data obtained by Rep. Jin Sun-mi of the main opposition Democratic Party of Korea revealed that 30 percent of Seoul’s sewer pipelines are over 50 years old — well beyond the 30-year benchmark used to classify old infrastructure.
Ministry of Land data shows that of the 867 subsidence incidents reported nationwide from 2020 to 2024, 45.4 percent — the largest single category — were linked to sewer pipe damage.
Seoul has introduced ground-penetrating radar systems to detect underground voids. However, with nearly 6,000 kilometers of sewer lines older than 30 years and only about 200 billion won ($140 million) allocated annually for maintenance, the pace of renewal is struggling to match the speed of deterioration.
City officials are now considering tapping into disaster relief funds to supplement the existing budget, acknowledging that regular maintenance alone will not be enough to stem the growing tide of sinkhole incidents.
jychoi@heraldcorp.com
