Manhole Inspection Program

Manhole inspections are being done as a routine part of our system cleaning and inspection program. Any manholes found to be needing repairs are noted and repairs are made as soon as possible. We have found that an effective method of finding leaking manholes is to do inspections during a period of heavy rainfall or high water table conditions. Leaks are noted and usually sealed right away by DLSD staff. More serious leaks or deterioration are repaired by a contractor.

Routine manhole inspections also help us pinpoint areas of the system where we have pumped or excess inflow. Clear water coming into the manhole is obvious and when pumping occurs, the flows into the manhole reflect the sump pump cutting on and off.

Manhole Rehab and Repair

One of the more critical projects that we have been working on this year involves the repair of some badly corroded manholes.  When sewage resides in the system long enough to become anaerobic (without air) either due to flat lines, or low flows in the vicinity of force mains, hydrogen sulfide gas is formed.  This gas is then oxidized by specialized bacteria to form Sulfuric acid, which eats into the concrete of the sewers and manholes.  The following photos show some of the damage in a few manholes upstream of our Lift Station 9.  We also have similar problems in other areas of the system, however, the repair of the Area 9 manholes are the highest priority.

The generally accepted repair system involves the high pressure cleaning of the manhole interior followed by a coating of lean concrete.  After the concrete is cured, it is finally coated with an epoxy, which is resistant to this acid corrosion.

Before
 

                                             After
                                    

  Concrete Spray Nozzle                                              Final Prep 
      

Typical Operations Set Up for Grout Spraying - Note work involved in moving fiberglass mats