DOWNTOWN BROOKLYN — Con Edison officials said Thursday that they patched a four-inch hole they believe allowed an estimated 5,200 gallons of potentially toxic mineral oil spill into the East River after a May transformer failure on the DUMBO waterfront.
The utility still can't fully account for 37,000 of the dielectric oil that could still be trapped in the soil or lost in the river during the equipment failure.
The hole was discovered Thursday during a test in which Con Edison engineers squirted green dye into the soil around the facility and divers around the waterfront substation inspected the perimeter to see where the green water made its way into the East River, Con Edison officials said.
Several hours after the 6 a.m. test, divers had only found the one small hole, which they promptly plugged up, according to utility spokesman Michael Clendenin.
In the next month, Con Edison will build a new barrier around the substation to shore up the location against future spills, Clendenin said. This week they finished installing the new transformer, the utility said.
Officials now believe that most of the missing 37,000 gallons of mineral oil lost from the ruptured transformer ended up on land, and they've since excavated several hundred cubic yards of soil from the site, deeply saturated with mineral oil, though they don't yet have an estimate for how much it is, Clendenin said.
Five hundred and twenty gallons of synthetic mineral oil were skimmed from the water following the May 7 transformer failure, which the U.S. Coast Guard estimated was about a tenth of what actually made its way into the river, based on averages from oil spills they deal with.
The green dye which is non-toxic and won't harm fish or wildlife and is frequently used by agencies aiming to track leaks, may make its way into the East River Thursday, around their Farragut Substation.
If boaters, ferry riders and North Brooklyn residents spot green streaks or sheens in the river Thursday, they shouldn't be alarmed, officials said.
The substation had 179 prior leaks and more than 8,400 gallons of spillage of transformer oil, hydraulic oil and antifreeze into the soil and water according to records that date back to 1978, the worst record of spills of any Con Edison substation in the city.
The State's Department of Environmental Conservation didn't return a request for further comment immediately.