Grand Canal muck dredging gets underway

A dredge began vacuuming up a black mayonnaise-like muck from Grand Canal and other nearby canals this month, removing decades of built-up rot.

While barely anything but bacteria can survive in the low-oxygen gunk, recent tests showed the muck safe enough to spread on pastures on the south side of U.S. 192, west of Interstate 95, where the muck will be tilled into the ground as fertilizer. Those pastures lie along the floodplains of the St. Johns River, a main source of drinking water for Melbourne, Cocoa and other city utilities along its northerly flow. 

The $26.4 million project is expected to dredge deeper, cleaner canals by November 2022. Gator Dredging of Clearwater will remove 479,000 cubic yards of muck from Grand Canal, three entrance canals and 16 residential finger canals south of Pineda Causeway.

Muck is formed from rotted algae, grass clippings and silt from stormwater runoff. Because of low oxygen levels, nothing other than mostly bacteria lives in the organic muck along canal bottoms. 

Algae blooms and the resulting fish kills create a vicious cycle. Rotted fish are fermenting fodder for new algae blooms, and ultimately add to the pasty black muck that also helps fuel blooms. Bacteria decomposing dead fish and algae consume oxygen in the water, further increasing risk of more dead fish.

The Grand Canal dredging project removes a huge source of nitrogen and phosphorus that fuel toxic algae blooms in the lagoon.

It is the most complicated local dredging project to date in the county's $486 million Indian River Lagoon cleanup plan, Brevard County officials say. The dredge must work among densely populated residential canals, frequented by government-protected manatees, and haulers must carefully load muck and exit along a heavily trafficked causeway.

The plan is to spread the dried muck on pasture land. After most of the water flows out of the muck in a containment area on site, trucks will haul the remaining solid material to Platt Ranch, at the south side of U.S. 192, west of Interstate 95. 

Some local environmentalists have raised concerns that the muck could contain excess arsenic, propellants, explosives of other contaminants from past military activities. So, in response to those concerns, the county conducted further muck sampling last month.

Muck sampling results recently showed that none of the 45 volatile organic compounds, dozens of pesticides, metals or the seven PCBs tested exceeded state cleanup target levels for soils. Arsenic, however, exceeded state target levels in three of four samples. The muck can be brought within target levels by mixing it with other soils when spread on land, county officials assured.

The muck is first pumped to a Dredge Material Management Area, or DMMA, along the south side of Pineda Causeway, where it's dried out before being hauled to Platt Ranch.

"Only 1 of 21 samples collected in October would require blending with cleaner material at the DMMA before relocation to Platt Ranch," Virginia Barker, director of Brevard's Natural Resources Management Department, said via email. "The mixing that happens throughout the dewatering process, may be sufficient to meet compliance targets for agricultural use." 

Early results of the muck sampling had shown Total Recoverable Petroleum Hydrocarbons, or TRPH — which can include marine engine oils from a nearby marina, asphalt from roads and roof shingles and other sources —  exceeded state target levels for soils. TRPHs include hydrocarbons in crude oil used to make petroleum products, encompassing hundreds of compounds, including those in grease and mineral oil.

More detailed follow-up testing to distinguish between the different types of hydrocarbons "demonstrated no concerns," Barker said.

Jim Waymer is environment reporter at FLORIDA TODAY.

Contact Waymer at 321-261-5903

or jwaymer@floridatoday.com.

Twitter: @JWayEnviro

Facebook: www.facebook.com/jim.waymer

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