Taxpayer Money Spent to Avoid 'Water Bombs,' But Shocking Reality Found Under Seoul's Streets

00:00 'Permeable Blocks': A Solution to Avoid Monsoon 'Water Bombs'?
02:49 Is Performance Being Maintained?
04:25 Two-Thirds Found 'Defective': What Is the Reason?
06:31 Why Inspections Have Not Been Conducted Properly
1. 'Permeable Blocks': A Solution to Avoid Monsoon 'Water Bombs'?
Hello, I am Jang Se-man, an SBS climate and environment correspondent. The monsoon season has arrived. In the past, this was a time of inconvenience due to frequent rain and high humidity. However, due to climate change, we now see extreme amounts of rainfall that were once unimaginable, causing massive damage. It has reached a point where the monsoon season is no longer just an inconvenience, but a time we must endure with anxiety. The danger is particularly high in urban areas because the ground around us is covered in asphalt or concrete. This structure prevents rainwater from seeping into the ground. In cities where many of us live, the soil has lost its role of absorbing rainwater, so when it rains, the water simply accumulates and flows. Conversely, because the surface cannot absorb or store water, we are left to suffer from water shortages during droughts. Permeable blocks were introduced to solve this problem of increasing impermeable surfaces. These are sidewalk blocks designed to allow rainwater to pass through and drain into the soil beneath. The principle is that the blocks are manufactured with countless microscopic pores that allow water to pass through.

[Jo Si-hyung / Seoul Metropolitan Government Official in Charge of Permeable Blocks: Permeable blocks play a role in preventing urban flood damage by absorbing some of the rainwater.]

When placed side-by-side with regular sidewalk blocks, the difference is clear. While existing blocks have a smooth appearance, permeable blocks are textured with many visible gaps. How do these blocks actually perform when it rains? In footage taken where permeable blocks are installed, you can see that while regular asphalt has puddles of water here and there, the areas with permeable blocks show significantly less water accumulation. Even in experiments where water is intentionally poured, it drains quickly. Because of these advantages, the Seoul Metropolitan Government established the Basic Ordinance on Water Cycle Restoration and Low Impact Development in 2015, making the use of permeable blocks mandatory. It has been over 10 years; how many have been installed? About 15% of the total sidewalk area in Seoul is covered with them. Permeable blocks are 10–20% more expensive than regular blocks, and since they are usually replaced when old blocks are removed for construction, only a portion has been replaced even after a decade.

2. Is Performance Being Maintained?
So, are the installed blocks actually maintaining their performance? The Seoul Institute conducted a field survey. They selected 30 locations in Seoul where permeable blocks had been installed for less than one year. The performance of permeable blocks is measured by how many millimeters of water they can absorb per second. There are currently Grade 1, 2, and 3 products. Until last year, it was required to install Grade 3 or higher, and starting this year, the standard was strengthened to Grade 2 or higher. Grade 1 means absorbing 1 millimeter or more per second, Grade 2 absorbs 0.5 millimeters per second, and Grade 3 absorbs 0.1 millimeters per second. All 30 locations were installed using Grade 3 products. However, the Seoul Institute's measurements showed that only 10 locations met the Grade 3 standard of 0.1 millimeters. Another 18 locations showed performance at only 40% of the Grade 3 standard, and the remaining 2 locations showed no permeability at all. In summary, two-thirds of the total were effectively judged to be defective.

[Park Dae-geun / Senior Research Fellow, The Seoul Institute: The results showed that about two-thirds were clogged or mostly clogged. This is to raise awareness of the severity (of the performance survey results).]

3. Two-Thirds Found 'Defective': What Is the Reason?
Why did this result occur? There are two possibilities. One is that the product was fine initially, but various foreign substances and pollutants clogged the pores after installation. The second is that defective products were used from the very beginning. The Seoul Institute maintains that it cannot conclude which is the case based on this survey alone. However, the block manufacturing industry is viewing this situation with suspicion. They question whether a product that was normal to begin with could have its pores clogged in less than a year. In fact, another study by the Seoul Institute supports this suspicion. They conducted a long-term tracking survey on how long the permeability of these blocks lasts. For the Grade 3 products mentioned earlier, it took approximately 3.2 years for the performance to drop to the management standard of 0.1 millimeters. This means that after installing a new product, it took 3.2 years for the performance to decline. For Grade 1 products, it took 5.1 years. There are also permeable blocks installed on roads, not just sidewalks. For Grade 1 blocks used on roads, the study found that it takes 17 years for the permeability to drop to 0.1 millimeters. Therefore, critics point out that it does not make sense for two-thirds of the blocks to lose their performance after only one year. Of course, one must consider that because the pores are artificially created, clogging due to dust and foreign substances over time is inevitable. That is why the current system requires performance checks every two years.

4. Why Inspections Have Not Been Conducted Properly
However, these performance maintenance checks have not been conducted properly. Why? Because there were no appropriate testing methods. International standards did not fit well in Korea, and testing in a laboratory was difficult because it required breaking the blocks. It was only last year that the Seoul Institute developed a testing method that could be used domestically, and through this, they released the measurement results for the 30 locations mentioned earlier. In addition, the Seoul Metropolitan Government is currently surveying the performance of permeable blocks at 1,000 locations across the city for a more precise assessment. The results are expected to be released around November of this year. It is essential to reveal the accurate status of the performance of the permeable blocks installed so far. Furthermore, this should serve as an opportunity to conduct a clear investigation into whether the cause of the defective products is natural clogging due to aging after installation or if defective products were installed from the start.

Reported by Jang Se-man | Produced by Shin Hee-sook | Video by Ahn Jun-hyeok | Graphics by Yook Do-hyun | Produced by SBS Digital News
※ Please note: This article was translated by AI and may contain errors.