A tenant reported poor drainage and standing water near a drainage catch basin on the building premises. This prompted the building owner to request an inspection of the drainage system to identify the cause and assess the current condition.

The purpose of our visit was to accurately determine where the problem was occurring, why it was happening, and how serious it was. We inspected the following items in sequence.

• Visual inspection of the drainage catch basin and surrounding ground surface for subsidence, cracks, and abnormalities in the surrounding pavement

• Visual inspection inside the catch basin after opening the manhole, including checks for sediment buildup, structural damage, and the condition of the drainage channel

• Flow testing of the upstream and downstream drainage routes
• Operational check of the underground sewage pump, including operating noise, drainage performance, and any alarms

The inspection identified the following conditions.

• The structure of the drainage catch basin had collapsed, blocking the flow path inside the basin
• As a result, drainage from upstream was backing up, creating a risk of wastewater overflowing beyond the property
• The underground sewage pump was unable to discharge wastewater properly, resulting in a serious situation in which the tenant’s restrooms could no longer be used

The extent of the collapse and flow blockage could not be determined from an external visual inspection alone. By inspecting the inside of the catch basin, we were able to identify structural failure of the basin itself as the root cause.

We determined that the problem was caused by structural deterioration of the drainage catch basin itself and that cleaning or partial repairs would not prevent the problem from recurring. Based on the inspection results, we proposed renovation work to fundamentally resolve the issue with the collapsed drainage catch basin.

At the site, we removed the existing drainage components and carried out renovation work to establish a new drainage route. The main work processes were as follows.

• Removal of the existing paving stones using a crane truck
• Removal of the existing concrete frame and drainage pipes
• Installation of new drainage pipes
• Backfilling and soil compaction
• Installation of weed-control sheeting
• Gravel surfacing
• Drainage testing

After the work was completed, we conducted a drainage test and confirmed that wastewater was flowing smoothly. As a result, the following functions were restored.

• Drainage function of the underground sewage pump was restored
• The tenant’s restrooms were once again fully operational

The drainage system was restored to normal operating condition, allowing the tenant to use the facilities with confidence.

• By carrying out an inspection at the stage when the only visible symptom was “poor drainage,” we were able to prevent secondary damage, including wastewater overflowing beyond the property
• By combining visual inspection, internal inspection, flow testing, and pump operation checks, we identified the cause during a single site investigation
• Based on the inspection findings, the customer was able to make an informed decision after fully understanding the required scope and urgency of the renovation work
• By providing a complete service from inspection through renovation work and drainage testing, we restored the drainage system to normal and enabled the tenant’s facilities to resume operation quickly

Problems with drainage systems often begin progressing underground before visible signs appear at the surface. If you notice anything unusual, we recommend arranging an inspection as soon as possible. Identifying the cause early and proceeding promptly with the necessary renovation work can ultimately minimize both costs and inconvenience.

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