26 April 2017
I recently conducted a field training with the City of Daytona Beach. We were scheduled to stop active infiltration in a few storm boxes and a lift station. Early in the morning, we were near the lift station we were going to train at and I noticed a sanitary manhole in the middle of the street that had noticeable depressions in the asphalt on one side. I made the comment - only as an observation - that groundwater infiltration and loss of fines was likely the cause for the depression in the street. One of the City’s trucks was backed up to the hole so the the lid could be removed and the manhole could be inspected. With no warning, the road caved in approximately 3-5 feet and a massive sinkhole was exposed. Needless to say, we unexpectedly worked on the manhole as part of the day’s training. Surprisingly, the infiltration was not coming from a joint, crack, or faulty pipe penetration. The water and soil were entering the manhole through the bottom of the trench. Therefore, a quick inspection of the manhole may not have been effective in identifying the structure as needing rehabilitation.
Ultimately, if this had been someone’s small car, this situation could have been catastrophic. The crew had a hell of a time getting the truck out of this hole. For me, the real story is that I had never seen this happen in front of me so the incident was certainly a first. It reinforced to me that when manholes and storm boxes are sealed from infiltration, the value and benefit goes far beyond just saving money in the form of treatment costs for the municipality - it truly eliminates the root cause of sinkholes, and keeps the community and drivers safe.