Same Week, Same City—Two Underground Disturbances Unveiled

In Hiroshima City, in the Asaminami and Higashi districts, two underground anomalies surfaced in the same week, despite being about 10 kilometers apart.

In Asaminami, organic fluorine compounds (PFAS) were detected in a river near an industrial waste disposal site at a concentration approximately three times the national provisional guideline value of 50 ng/L. Residents’ groups have requested that Hiroshima City identify the source of the emissions and conduct ongoing water quality monitoring.

In Higashi, at Ushida Asahi, a stone retaining wall collapsed over a width of about 15 meters on the afternoon of the 23rd. Gas and water pipes buried beneath it were damaged, resulting in water outages for at least 35 households in the vicinity. Five residents living close to the collapse site were forced to evacuate.

There is no direct causal relationship between the two events. However, when viewed side by side, a common theme emerges: both incidents involved deterioration occurring in “invisible places” that suddenly broke through the surface of daily life.

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The Question PFAS Raises: “Who Will Continue to Measure?”

PFAS (Per- and Polyfluoroalkyl Substances) are a group of chemicals used in a wide range of applications, including foam fire extinguishers, non-stick coatings for frying pans, and semiconductor manufacturing, due to their water- and oil-repellent properties. Because the bond between carbon and fluorine is extremely strong, these substances do not break down in the environment, earning them the label “Forever Chemicals.”

Internationally, long-term exposure to PFAS has been linked to liver dysfunction, thyroid disease, immune system effects, and certain cancer risks. The U.S. Environmental Protection Agency (EPA) has tightened the standard for PFOS and PFOA in drinking water to 4 ng/L in 2024, which is more than ten times lower than Japan’s provisional guideline value of 50 ng/L.

The concentration detected in the river in Asaminami was approximately 150 ng/L, three times Japan’s guideline value and over 30 times the U.S. standard. It is only natural that residents’ groups feel anxious when they see these numbers.

However, it is important to clarify that the concentration of PFAS in river water is not the same as that in drinking water. Tap water undergoes purification processes before being supplied. Therefore, a high concentration of PFAS in the river does not immediately mean that “drinking water is dangerous.” This is why it is crucial to have a system in place for continuous monitoring from upstream to downstream, as well as at the inlet and outlet of the water purification facility, and to disclose this data to residents.

What residents’ groups are ultimately seeking boils down to two things: “identifying the source of emissions” and “establishing a system for continuous measurement.” Because substances like PFAS cannot be definitively classified as safe or dangerous based on a single measurement, a framework for ongoing monitoring is necessary. There are limits to individual efforts in continuously testing water quality. When asked who benefits from this, the answer is clear: the residents currently living there and the children who will be born in the future.

How Hiroshima City responds to this request will be a pivotal point, particularly whether it will provide a concrete investigation plan and a schedule for information disclosure.

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Slope Collapse—What the “Old Stone Wall” Tells Us

The slope collapse in Ushida Asahi represented a more immediate crisis.

The stone retaining wall is a construction method widely used during Japan’s economic growth period for land development. It is cost-effective and quick to construct compared to concrete retaining walls. However, over time, as drainage functions deteriorate, rainwater can increase soil pressure, leading to collapse. According to the Ministry of Land, Infrastructure, Transport and Tourism, there are approximately 50,000 “at-risk” retaining walls nationwide, but the understanding of their actual condition varies by municipality.

The damaged gas and water pipes were likely buried directly beneath or within the retaining wall. The integration of lifelines with the retaining wall reflects the design philosophy of the era when infrastructure was laid simultaneously during development. While this was efficient, it also carried the risk that if the retaining wall failed, the lifelines would be compromised as well.

With 35 water outages and five households evacuated, the numbers may appear to indicate a “localized accident.” However, for the evacuated residents, the sudden cessation of water and gas that had been taken for granted until the day before, and the inability to stay in their homes, is a significant experience. Restoring the area will likely require reconstructing the slope, relaying the gas and water pipes, and ensuring safety, which could take several weeks to months. The costs, just for reconstructing the retaining wall, can easily reach several tens of millions of yen. The question of who will bear this burden—whether it be the property owners, the municipality, or if it falls through the gaps of the system—remains quietly unresolved.

Hiroshima experienced a large-scale landslide disaster centered around the Asaminami and Asakita districts during the heavy rains in 2014. Since that disaster, the designation of landslide warning zones and the development of hazard maps have progressed. However, there are still areas where the aging of retaining walls and the lifelines buried within them in land development sites have not received adequate attention.

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The Shared Structure of Two Events—”Deterioration of the Invisible” and “Absence of Measurement Systems”

The river pollution by PFAS and the damage to lifelines from the slope collapse are fundamentally different in nature. However, when we extract the underlying structure, striking similarities emerge.

Both issues have been developing underground over a long period. Both have occurred in “invisible” places within daily life. And both could have potentially been addressed before surfacing if a system for regular measurement, inspection, and record-keeping had been functioning adequately.

For PFAS, this means identifying the source of emissions and establishing fixed-point monitoring. For retaining walls, it involves regular inspections of aging and maintaining a ledger. Neither is technically impossible. What is lacking is the personnel and budget to sustain these efforts continuously, as well as the decision-making to prioritize these issues.

Municipalities are chronically understaffed. Both the environmental and civil engineering departments are tasked with extensive duties with limited resources. This is why a system that functions as a framework, rather than relying on individual efforts, is necessary. A platform that automatically aggregates measurement data, detects anomalies, and makes this information available to residents. A digital ledger that overlays aging information of retaining walls with the locations of buried lifelines. The technical elements already exist. The question is whether the decision-making to implement them will be made.

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Three Points to Watch

Moving forward, here are the key points to follow regarding these two events.

First, the response schedule of Hiroshima City regarding the PFAS issue. Will the city specifically outline the timing and methods for source investigation, as well as the frequency and methods for monitoring and public disclosure in response to residents’ groups’ requests? Whether the response stops at “consideration” or delves into “what will be measured by when” will reveal the seriousness of the administration’s commitment.

Second, the recovery process in Ushida Asahi and the framework for cost-sharing. How will the ownership of the collapsed slope be determined, how will recovery costs be shared, and what support will be provided to evacuated residents? If there are gaps in the system here, it will not only be an issue for Ushida Asahi but a common challenge for residential areas across the country with similar land development.

Third, whether the visualization of aging infrastructure across Hiroshima City will progress. After the 2014 disaster, Hiroshima has accumulated many lessons in disaster prevention. Can this knowledge be connected to measures against the aging of underground infrastructure? The ability to transform individual responses into a systemic approach will determine safety in the next decade.

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The ground below is invisible. What is invisible may be broken without anyone noticing. If it goes unnoticed, there will be no budget allocated. If there is no budget, it will be left unattended until the next failure occurs—breaking this cycle requires continuous measurement, ongoing record-keeping, and someone to keep interpreting those numbers.

The two incidents that occurred beneath the ground in Hiroshima are not flashy disasters. However, they quietly ask: Who is watching your feet?