Storm pipes fail quietly for years before they fail catastrophically. By the time a sinkhole opens in a parking lot or a driveway drops six inches overnight, the pipe underneath has usually been deteriorating for a decade. The good news is that failing pipe almost always telegraphs its condition above ground if you know what to look for. After two decades of storm pipe repair across Metro Atlanta, we have learned to read those signs, and most of them are visible to a property manager on a routine walk.
Why Corrugated Metal Pipe Dominates the Failure List
Most of the storm drains we cut out and replace in Cobb, Fulton, and DeKalb counties are corrugated metal pipe, usually 24 to 60 inches in diameter, installed between 1975 and 2000. CMP has a service life of roughly 25 to 50 years depending on soil chemistry, water pH, and the gauge of the steel. Atlanta's mildly acidic red clay accelerates the lower end of that range, especially where stormwater carries road salt, fertilizer runoff, or pool chemicals. Corrugated metal pipe failure typically begins at the invert, the bottom of the pipe, where flow is constant and the protective galvanizing is consumed first.
Reinforced concrete pipe lasts longer, often 75 to 100 years, but it fails differently. Joints separate, gaskets deteriorate, and groundwater begins pulling soil into the pipe through the gaps. The surface symptoms are similar to CMP failure, which is why a proper diagnosis usually requires a camera inspection rather than guesswork from the surface.
Sign 1: Depressions or Soft Spots Above the Pipe Alignment
When stormwater leaks out of a failing pipe, it carries the surrounding soil with it. That soil has to go somewhere, and the void it leaves slowly migrates upward through the backfill. The first visible symptom is usually a gentle depression in the pavement or lawn that follows the pipe alignment. Walk the line of any storm drain on your property and watch for a saucer-shaped dip, a strip of grass that grows differently, or asphalt that cracks in a long oval pattern. These are pre-sinkhole conditions, and addressing them while the surface is still intact is dramatically cheaper than waiting for the collapse.
Sign 2: Sediment Discharging From an Outfall
Check the downstream outfall after a rain event. Clean stormwater should run clear within an hour or two of the rain ending. If the outfall is still discharging muddy water a day later, or if a fan of fresh sediment is building up below the pipe, something upstream is eroding internally. That sediment is your soil leaving through a hole in the pipe wall, and the volume tells you roughly how aggressive the failure has become.
Sign 3: Visible Rust-Through or Daylighting at the Inverts
If you can safely look into the pipe ends, shine a light along the invert. Healthy CMP has a continuous metal floor, often coated with a thin layer of sediment. Failing CMP shows rust-through perforations, exposed soil, or a clear gap where the bottom of the pipe used to be. Once the invert is gone, the pipe is functioning as an open trench, and structural collapse is a question of when, not if.
Sign 4: Cracks Radiating From a Catch Basin
Catch basins and pipe junctions are the highest-stress points in a storm drain system. When the connection between a pipe and a structure begins to fail, you often see a star-pattern of asphalt cracks radiating outward from the catch basin grate. This is the surface telling you that the soil supporting the basin is moving. Patching the asphalt without addressing the underlying connection is one of the most common and most expensive mistakes property owners make.
Sign 5: Standing Water Where Drainage Used to Work
If a parking lot drain that used to clear in 15 minutes now ponds for hours, the pipe downstream is likely partially collapsed or heavily blocked. A camera inspection will tell you which. We have pulled obstructions ranging from collapsed pipe walls to root masses to a single tennis ball, but the common factor is that the symptom appeared gradually over months, not overnight.
Sign 6: Pavement Heaving or Settling Seasonally
Pavement that rises in winter and settles in summer is responding to moisture in the subgrade. A leaking storm pipe creates exactly this kind of seasonal moisture cycle, and the surface above will telegraph it through ride quality changes that drivers notice before any visible damage appears. On commercial properties, complaints from tenants about a rough patch in the lot are often the earliest hint of a buried problem.
Sign 7: Audible Water Movement When It Has Not Rained
This one is rare but diagnostic. Stand near a catch basin during dry weather. If you hear running water, something is wrong, either groundwater is infiltrating the pipe through a failed joint or a nearby water line is leaking into the storm system. Both require investigation, and both are easier to fix before the surrounding soil is fully saturated.
What the Repair Actually Looks Like
When we confirm a failing pipe through CCTV inspection, the repair scope depends on the extent of the damage. For localized failures, a cured-in-place pipe liner can rehabilitate the existing pipe without excavation. For widespread loss of structure, particularly on older CMP, full replacement with HDPE or RCP is usually the right call. Sinkhole prevention is fundamentally about catching the failure before it migrates to the surface.
- CCTV inspection to map the location and severity of each defect
- Targeted spot repair for isolated joint failures or small perforations
- Cured-in-place pipe lining for long runs with intact host pipe geometry
- Open-cut replacement when the pipe has lost structural integrity
- Soil grouting to fill voids before resurfacing the pavement above
The cost difference between proactive repair and emergency response is rarely less than four to one. A planned liner installation on a 60-foot run of 36-inch pipe is a measurable line item. The same pipe collapsing under a fire lane during business hours is a six-figure event involving emergency excavation, traffic control, business interruption, and often legal exposure. If any of the seven signs above describes a pipe on your property, the right next step is a camera inspection, not a wait-and-see.