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Will Miami’s deepest underground garage cause problems for Biscayne Bay?

Inspectors hope to prevent groundwater from luxury condo site from flowing into bay

Concerns were raised when Commissioner Ken Russell posted a video on social media showing groundwater upwelling into where that garage is being constructed in Miami’s Brickell neighborhood.

MIAMI – City of Miami Commissioner Ken Russell and inspectors with Miami-Dade County Environmental Resources Management are working to ensure that sediment-rich water pooling at a luxury condo construction site in Miami’s Brickell neighborhood doesn’t end up in Biscayne Bay.

On its website, developer OKO Group said the waterfront site at 175 SE 25th Road will feature a 47-story luxury residential tower, Una Residences, with units starting at $2 million.

It will also include a three-level subterranean basement “which will become Miami’s deepest, most expensive underground garage.”

Wednesday night, Russell posted a video on Twitter showing groundwater upwelling into where that garage is being constructed.

On Thursday, Russell told Local 10 News his chief concern was that the sediment-rich water, which had pooled in the cavernous garage construction footprint, “stay contained on the job site and not be silting into the bay.”

The general contractor said by email Friday that “as of today the breach has been contained.”

According to ConstructionDive.com, project leads were using a “deep-soil-mixing construction process to create a waterproof bathtub-like structure that protects the building’s concrete mat above the tub from groundwater and forms the base of the garage.”

County officials said a contractor on site told a Miami-Dade County Department of Environmental Resources Management (DERM) water control inspector Thursday that there had been a breach in the soil mix causing the bubbling up of groundwater into the excavation site. Under investigation is whether the “issue was related to a void space that allowed the pressure to cause seepage or if there was a deficit amount of material in the soil mixture to address the pressure from the aquifer.”

“So when the tub fails it fills,” Russell said, “and so in order for them to plug it, there is so much pressure, they wait for it to equalize” and then send divers to plug the hole and drain the water.

The key, Russell said, is ensuring the contractors are following proper permitting procedure and removing all silt with dewatering containers so the water “is getting cleaned, going where it should” and that “none of this water is ending up in the bay.”

Rachel Silverstein of Miami Waterkeeper said that, generally speaking, developers and property owners of pricey waterfront condo units also have a vested interest in ensuring Biscayne Bay is healthy and clean. “Those developers and homeowners have a real interest in making sure their operations are not affecting water quality in the surrounding area because it is also affecting your investment,” she said.

She added that Miami’s natural resources are its economic engine supporting real estate, commerce, and tourism, “clean water is really what makes Miami.”

Challenges of building underground garages in South Florida

Silverstein notes that: “It is very difficult to do construction underground in South Florida because we have very porous limestone rock beneath us. We also happen to have a shallow water table, you only have dry rock for a short time before you hit water, so it can be very complicated to construct underground parking here in Miami.”

This is one of the reasons she said you don’t see basement construction in South Florida homes like in other parts of the country.

The Una Residences underground garage may consider itself the deepest, but building subterranean garages is not uncommon for Miami, said Russell, who pointed to the recently completed underground garage at Brickell City Center.

The groundwater breach Wednesday happened on an evening that Local 10 meteorologist Julie Durda said South Florida experienced “seawater coastal flooding,” and Local 10 meteorologist Jordan Patrick explained that the full moon helped to create the King Tides phase we expect through Thursday.

Local 10 News asked Russell about whether, at a time when the city is already grappling with the impacts of sea-level rise, it made sense to continue permitting development projects like this one.

“This is a standard [engineering] process,” he said. “It just has more challenges here in Miami with porous limestone and aquifers and bodies of water.” He said as long it has been deemed “safe” “the city will continue to permit these.”

That is because, Russell said “in the Florida building code this is acceptable,” adding, “my job here is making sure they are meeting requirements of permits from an environmental perspective.”

A Miami-Dade County Department of Environmental Resources Management (DERM) water control inspector visited the site on Thursday and noted that there did not appear to be any “turbidity plumes in Biscayne Bay.”

Private construction crews were at the site working to plug the hole with a concrete mixture to stop the seepage explained county officials. DERM will visit the property again tomorrow.

Local 10 reached out to the developers OKO Group and Cain International, general contractor Civic Construction, subcontractor Keller International, and architects Adrian Smith + Gordon Gill Architecture for comment.

In a statement to Local 10 News, Ant Yapi, of Civic Construction, said “On Wednesday October 20th, flooding took place on the UNA Residences construction site due to intrusion from the water table. The flooding was quickly contained, and the remediation and de-watering process has already begun. Construction of UNA Residences will continue as planned over the coming weeks.”

NOTE: You can submit water quality complaints to DERM by email at Environmentalcomplaints@miamidade.gov or via a 24-hour hotline at 305-372-6955.

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A spokesperson for the Department of Regulatory & Economic Resources sent the following summary of what the DERM inspector found:

“As explained by the contractor on site, there was an apparent breach in the soil mix and groundwater was upwelling into the excavation. The contractor is working to identify whether the issue was related to a void space that allowed the pressure to cause seepage or if there was a deficit amount of material in the soil mixture to address the pressure from the aquifer. Regardless of the reason, they are planning on plugging the hole with a concrete mixture to stop the seepage.

“The contractor had previously applied for a Class V dewatering permit from DERM. However, the permit was not issued yet because the discharge point for the effluent was to an onsite drainage well, which requires the approval from FDEP and that hasn’t been granted yet. While onsite, the DERM inspector did not observe any active dewatering, but it appeared dewatering activity had previously occurred as evidenced by turbid water in the settling tank that was connect to the drainage well. In addition, he noticed some housekeeping issues related to silt fence collapsing on one part of the construction site. Therefore, the inspector issued a Notice to Cease and Desist any dewatering activity until the permit has been obtained and a Pollution Prevention Field Notice identifying the need for additional silt fence around the perimeter of the construction area.

“It was noted that there did not appear to be any turbidity plumes in Biscayne Bay. An official report will be completed shortly. The inspector will be visiting the site tomorrow for follow-up.”

DERM inspection photos. (Photos courtesy of Department of Regulatory & Economic Resources)

About the Author:

Christina returned to Local 10 in 2019 as a reporter after covering Hurricane Dorian for the station. She is an Edward R. Murrow Award-winning journalist and previously earned an Emmy Award while at WPLG for her investigative consumer protection segment "Call Christina."