During the last few sewer lateral installations in Miami Beach we encountered very high ground water levels. We have also seen the existing sanitary sewer lines backing up for extended periods of time making the installation very difficult.
The roadway elevations along the southern part of the beach near our project was at +4.0 NGVD. and we noticed the water level rising to about elevation +2.0 NGVD. During King Tide and high tide situations the water level was higher than that.
Dewatering was utilized but limited to the actual tie in connection. This is how we install in those conditions.
- Time the installation with the tide table. Excavate the tie in point and plate it.
- Project manager or other staff member measure’s water depth at the plate. We cross referance the sewer level on the downstream sewer manhole. Need to consider the time gap between low tide and actual water table elevation.
- Bring in two pump out trucks and dewatering pumps as needed.
- Pump out sewer mainline clean as needed, install sewage plug while keeping pump truck monitoring sewage levels
- Dewater to bring down water level with additional pump out truck monitoring the excavation in case we encounter any sewage. We had situations in high density areas that occasionally backed up from the down stream manhole. Most likely due to infiltration plus peak flow. That rarely happens but we prefer to mobilize two pump trucks during tie in work. The actual connection takes about 30 minutes.
The city of Miami Beach has very limited R/W. The installation of any utility within the R/W will be subject to significant permitting and restoration. In addition all stormwater or dewatering should be maintained within the property limits. No additional areas should be impacted during construction.