Two Unrelated Incidents Last Week Put Biscayne Bay at Risk

Sediment in the bay can smother sponges, coral, and seagrass.
Sediment in the bay can smother sponges, coral, and seagrass. Photo by Ed Webster/Flickr
All eyes were on Biscayne Bay following an instance in which sediment appeared to spew into the water from a state-run construction site near the MacArthur Causeway on Friday, further jeopardizing the ever-vulnerable marine ecosystem that helps ensure a clean water supply for South Florida.

That came just two days after Miami Commissioner Ken Russell sounded the alarm on a breach of the Biscayne Aquifer at another nearby construction site where crews are working on a 236-car subterranean parking garage — reportedly Miami's deepest — that will sit beneath Una Residences, a waterfront luxury condominium complex on SE 25th Road in Brickell.

Rachel Silverstein, executive director of the local environmental advocacy group Miami Waterkeeper, describes the latest contamination to New Times as "death by a thousand cuts."

"Each incident might appear to just be a small amount of sediment or other debris washing off into the water," she says. "But over time, and when you consider how many construction sites are going on, it really starts to add up."

As the largest estuary in coastal southeast Florida, Biscayne Bay and its surrounding ecosystem comprises more than 400 square miles and is crucial for the region's economy and livelihood. The Biscayne Aquifer, spanning roughly 4,000 square miles under the surface, is an unconfined slab of porous limestone that holds groundwater that eventually flows into the bay and other bodies of water across South Florida and can be extracted for further treatment and use, including as drinking water.

Because the aquifer is unusually shallow, this complicates subterranean construction. (Notice how most homes in South Florida do not have basements.)

However, in order to build Una Residences' 50-foot deep parking garage, Construction Dive reports, project leads employed a tactic never before used in South Florida: drilling 800 50-foot-deep holes into the ground that would be filled with concrete and water to create the garage's pillars.

On October 20, crews were digging further into the crushed limestone and injecting "cement slurry" to create a waterproof, bathtub-like structure to protect the concrete slab that makes up the base of the garage. There was a breach, and groundwater suddenly pooled into the excavation site.

Observers were concerned that the contaminated water and silt that leaked into the garage would flow into the bay just a few feet away. But the breach was identified quickly and preventive measures were taken before that could happen.

"The flooding was quickly contained, and the remediation and de-watering process has already begun," a spokesperson for Civic Construction told Local10. "Construction of Una Residences will continue as planned over the coming weeks."

Just two days later, on October 22, Local10 anchor Louis Aguirre tweeted aerial video of grayish sediment that stood out in stark contrast against the bay's cool blue water as it pooled beneath the MacArthur Causeway. The Florida Department of Transportation (FDOT) has already been issued three citations by the Miami-Dade County Department of Environmental Resources Management for projects that contributed to the pollution of Biscayne Bay, including at the MacArthur Causeway construction site near where the aerial sediment video was most recently documented.

County officials are working to determine the cause of the most recent incident.

Meanwhile, says Silverstein, "That suspended sediment will eventually fall out of the water column and land on the seafloor or the bay bottom, where it can smother sponges, corals, and seagrass."

Russell, who is running as a Democrat to unseat Sen. Marco Rubio in 2022, expressed great concern about the latest incident and threatened to pursue legal action against FDOT for its role in contaminating the bay waters.

Residents are encouraged to report and photograph signs of contamination in Biscayne Bay to the city by emailing [email protected], or contacting Miami Waterkeeper.
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Michael Majchrowicz is a staff writer at Miami New Times. He studied journalism at Indiana University and has reported for PolitiFact, The New York Times, Washington Post, the Post and Courier, and Tampa Bay Times.