What is a Cave-In?
A cave-in typically occurs when stormwater washes soil into a defective pipe or structure. Over time, the ground or pavement above the defective pipe or structure sinks. Cave-ins can be easily identified by depressions in the soil or pavement. Cave-ins can also happen around manholes or catch basins where pipes enter the structure.
Many cave-ins are not MSD problems. One of the most common causes of cave-ins is a defective private lateral line. Cave-ins caused by problems with the home or building’s private lateral line need to be repaired by a licensed plumber or drain layer. In the case of a cave-in, MSD personnel will investigate the cause. Please note, MSD is only responsible for the public stormwater system – MSD will not repair private stormwater systems and lateral lines, nor does MSD maintain or address naturally occurring sinkholes.
After a cave-in is reported, we send a crew to secure the cave-in area in order to protect the public’s safety. The crew will then conduct a dye test to determine if the cave-in is caused by a defect in the public sewer system. The hole is typically flooded with dye and the MSD-owned stormwater system is checked to see if the dye is entering through a defect in the system. If so, MSD will make necessary repairs.
Cave-ins are repaired by several methods, including:
- Grouting the joints from inside or outside the pipe
- Slip lining a section of pipe
- Repair or replace the pipe or structure
- Exposing and wrapping the failing joint with filter fabric
Prioritizing Cave-In Repairs
MSD’s goal is to secure a cave-in within 48 hours of receiving the report, unless it’s an emergency. We try to complete a field investigation to determine the necessary repair within one week. Depending on the type of repair, it can take between 30-60 days to repair a cave-in.
Cost of Repairing Cave-Ins
On April 5, 2016, 62% of voters in MSD’s service area approved Proposition S, putting all MSD customers under the same property tax rates to pay for stomwater service. The cost of repairing a cave-in depends on the depth of the cave-in, the size of the pipe or structure, and location of the cave-in.