The Cause Identified: Reaction Between Acidic Water from Acid Sulfate Soil and Domestic Wastewater in Heunghaeeup Area
Foam Removal Device Malfunction Confirmed, Repaired on July 24... Inspection System to Be Strengthened
Pohang City announced that the white foam observed along the coastal area of Jukcheon-ri, Heunghaeeup on July 23 was caused by strong acidic water originating from 'potentially unique acid sulfate soil' mixing with alkaline domestic wastewater and other sources.
This phenomenon often occurs after rainfall, and it is analyzed that the scale of foam generation increased due to the large influx of acidic water resulting from the heavy rain that persisted last week.
Previously, Pohang City conducted a study from 2022 to 2023 to investigate the causes of foam and sediment occurrence. The study confirmed that the main cause was the exposure of pyrite-rich mudstone layers distributed in the coastal and deltaic areas of Pohang, which have the characteristics of 'potentially unique acid sulfate soil (PASS)' and produce a strong acidic reaction with a pH below 3.5.
This soil is composed of 78% silt and 19% clay. When exposed to the atmosphere, acidic substances such as sulfuric acid are formed, which react with the alkaline water quality in the river, leading to the generation of white foam and sediment.
In fact, similar natural phenomena based on acid sulfate soil have been observed in various areas, including Iin-ri in Heunghaeeup, Gohyeon-ri in Cheonghamyeon, and Daejeon-ri in Songramyeon. The city explained that this naturally occurring foam, caused by these factors, appeared to be pollution, leading residents to express discomfort. To address this, a foam removal device was installed at the Jukcheon-ri discharge point in February last year and has been in operation. The recent large-scale foam occurrence was found to be due to a temporary mechanical failure.
The city completed repairs immediately on July 24, and the equipment is now operating normally. Moving forward, the city plans to regularly inspect the facility to prevent recurrence of similar incidents.
To prevent similar phenomena in the future, the city will actively implement measures such as strengthening the inspection cycle of foam removal devices, expanding patrols by private environmental monitors, installing buffer storage facilities, and providing technical support for zero-discharge treatment of secondary battery brine.
Park Sunyoung, Director of Environmental Policy, stated, "As this is a matter of great concern to citizens, we are focusing on transparent information disclosure and scientific responses. We will continue to inspect wastewater discharge businesses in the Yeongilman Industrial Complex and, in addition, strengthen patrols by private environmental monitors to do our utmost to create a pleasant living environment."
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