Formaldehyde Emissions Impact Modeling and the Reality

The North River Wastewater Resource Recovery Facility ('WRRF') provides secondary treatment for 170 million gallons per day dry weather flow primarily residential wastewater for a population of approximately 500,000 residents in the New York City's Borough of Manhattan. The facility is unique in that a heavily used, 28 acre urban Riverbank State Park is located on top of the plant. New York City Department of Environmental Protection ('NYCDEP') conducted dispersion modeling analysis to evaluate the potential impact of the North River WRRF's emissions. Typical sources of airborne formaldehyde in an urban environment include direct formaldehyde emissions from incomplete combustion (oxidation) products, from motor vehicle exhaust byproducts, or indirectly from formation of formaldehyde in the ambient air from photo-oxidation of hydrocarbon precursors, also emitted from motor vehicle exhaust and other combustion sources. The NR WRRF has compression ignition reciprocating internal combustion engines for its raw sewage pumps and blowers and is thus a potential source of formaldehyde emissions. NYSDEC Air Guide 1 dispersion modeling analysis estimated the potential impact of formaldehyde emissions from the facility's compression ignition reciprocating internal combustion engines (RICE) may be >10 times of the NYSDEC Annual Guidance Concentration of 0.06 µg/M3 around the engines' exhaust stacks within the plant's rooftop Riverbank State Park. NYCDEP executed a stationary ambient air formaldehyde monitoring program at a location by the engines' exhaust stacks for a year started in September 2015 as follows: Stationary Formaldehyde Monitoring Using EPA TO-11A Method -- Two 12 hr samples at one location every 6 days -- Started 09/25/2015 and concluded 09/25/2016 The initial formaldehyde monitoring registered unexpected ambient air formaldehyde concentrations as high as 84 µg/m3, much higher than published results of a previous survey conducted in New York City. NYCDEP staff performed a top-down assessment of the sampling program and the elevated concentrations observed with the assistance of NYSDEC. NYSDEC installed a separate set of sampling equipment side by side with the NYCDEP sampling equipment to collect same samples on two days and sent the samples to a NYSDEC laboratory for analysis. The NYSDEC sampling and analysis results verified the NYCDEP monitoring data. The NYCDEP monitoring program was expanded to conduct portable sampling at up to 13 remote locations in and adjacent to the Riverbank State Park and the surrounding community: Additional Remote Locations Formaldehyde Sampling Using Modified NIOSH Method 2016 -- Two 1 hr samples per day and two days per week at initial 11 but expanded to 13 locations -- Started 12/15/2015 and concluded 09/22/2016 NYCDEP performed data analysis including spatial and temporal analysis and revealed the following: The stationary monitoring station data show an apparent correlation between measured formaldehyde concentrations, ambient temperatures and ozone concentrations The stationary monitoring station data show very limited difference between formaldehyde concentrations for day and night time sampling events The portable sampling data didn't show a correlation between measured formaldehyde concentrations, ambient temperatures and ozone concentrations, The portable sampling data show marginally higher concentrations at the east side of the park that is closer to the nearby NY 9A Henry Hudson Parkway The portable sampling data show no significant difference between average formaldehyde concentrations between locations The portable sampling data show that the highest formaldehyde concentrations at each locations were all registered when the wind was blowing from a southerly direction The portable sampling data and Pollution Rose analyses didn't show apparent impact contours of any point source NYCDEP has continued performing the stationary monitoring, and also performing the remote locations sampling at reduced effort. The data show a seasonable variation pattern of the ambient air formaldehyde concentrations, demonstrating that the elevated concentrations are likely due to formation of formaldehyde in the ambient air from photo-oxidation of hydrocarbon precursors, and emitted from motor vehicle exhaust and other combustion sources.