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SWIM's meeting with DEP on City's Chlorination Plans

Updated: Sep 29, 2020

On February 14th, 2018, SWIM Coalition members had a long-awaited meeting with Commissioner Sapienza of the NYC Department of Environmental Protection (DEP) and some of his top-level staff to discuss the City's plans to chlorinate rather than capture Combined sewer overflows in several waterways. SWIM members at the meeting included representatives from Guardians of Flushing Bay, Riverkeeper, NRDC, Save the Sound, and Hutchinson River Restoration Project, as well as representatives from City Council.

Guardians of Flushing Bay and Riverkeeper had been anticipating a meeting with DEP since the fish kill in Flushing Creek last fall. SWIM and our members have raised many concerns, at public meetings and in public comment letters, regarding the City's plan to dump chlorine into several waterways since it was proposed in the Alley Creek CSO Long Term Control Plan in 2014.

SWIM and Guardians of Flushing Bay and Councilman Koo and others have been calling for the City to develop plans to capture, not chlorinate, combined sewer overflow. However, the plans to chlorinate Alley Creek, Flushing Creek and the Hutchinson River were approved by the State last spring, and DEP has already solicited and selected a firm for the design of the Alley Creek facility, and is currently reviewing bids for design of the Flushing Creek and Hutchinson River facilities. We are anxiously awaiting an environmental impact assessment, which DEP informed us at the Valentine’s Day meeting will be initiated when they are at the 30% design point on the facilities.

Water advocates’ major concern with chlorinating a CSO is total residual chlorine (TRC). While chlorine is effective in killing bacteria in the water, too much residual chlorine will also be detrimental to the waterbody ecology. Chlorine is toxic to aquatic life and reacts with organic material to create harmful byproducts like trihalomethane which are suspected as being carcinogenic.

To make sure there is no TRC, DEP has proposed dechlorination, which introduces another chemical to remove residual chlorine. While getting rid of one toxicant, we would simply be adding more chemicals, which could potentially create another compound whose toxicity we have yet to study. DEP must be careful when dosing chlorine in a CSO to make sure it has enough contact time to kill the desired amount of bacteria and use up all the chlorine, and leave no TRC.

Additionally, advocates are concerned about the effectiveness of chlorination if CSOs aren’t pre-treated, or screened of solids and particles. Solids can trap chlorine while acting as a shield for pathogens, ultimately transporting both chlorine and pathogens to the waterway.

While DEP acknowledges the challenges to adding chlorine to CSO flows that have high variability of rainfall intensity and duration, they assured us during the meeting that they will be looking into screening out floatables, solids and particles before dosing chlorine, will look into dechlorination at each facility, and will be erring on the conservative side when it comes to chlorine dosages. SWIM will be keeping close watch on all these factors as DEP proceeds through design and develops the environmental impact assessment.

Photo Courtesy of Summer Storm Sandoval, 2018 The team in front of DEP's headquarters!

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