Nassau County Department of Public Works Cedar Creek Water Pollution Control Plant Bay Park Sewage Treatment Plant Plant-wide Odor Control Improvements
Posted on August 3, 2015
Client: Nassau County Department of Public Works
Location: Nassau County, New York
Project Type: Cedar Creek Water Pollution Control Plant Bay Park Sewage Treatment Plant Plant-wide Odor Control Improvements
Dvirka and Bartilucci Consulting Engineers (D&B) was retained to develop air dispersion models for the Nassau County Department of Public Works (NCDPW) Cedar Creek Water Pollution Control Plant (WPCP) and Bay Park Sewage Treatment Plant (STP). The purpose of the air dispersion modeling was to support an overall Plant-wide Odor Control Improvement Project being undertaken by the County at its two major wastewater treatment plants on the south shore of Long Island.
The Cedar Creek WPCP is a 72 million gallon per day (MGD) sewage treatment plant which services portions of Nassau County, New York. The plant operates five 3,000 Kilowatt (KW) engine generators which can burn natural gas, digester gas, or fuel oil. The engines are used to provide power internally to the unit processes and equipment such as aeration tank blowers and main sewage pumps. The plant also operates four boilers rated at 29.95 million British Thermal Units per hour (MMbtu/hr) to produce hot water required for the central chillers and space heaters. Additionally, the plant employs eleven packed-bed wet scrubbers to control odors from the process operations. Sodium Hydroxide (NaOH) and Sodium Hypochlorite (NaOCl) are continuously added to neutralize sulfur compounds. The engines incorporate clean-burn modifications to reduce NOx emissions and catalytic oxidizers to reduce CO emissions. The boilers are designed with low NOx burners and flue recirculation to reduce NOx emissions.
The Bay Park STP is a 70 MGD sewage treatment plant which services portions of Nassau County, New York. The plant operates four 3,600 KW engine generators which can burn natural gas, digester gas, or fuel oil. The engines are used to provide the electric power for the processes and equipment such as aeration tank blowers and main sewage pumps. The plant also operates four 750 horsepower (HP) boilers to produce hot water required for the central chillers and space heating. The boilers can burn natural gas, digester gas, or fuel oil. Several other emission points associated with the treatment of sewage are located at the facility. The corresponding processes include primary screening, grit removal, primary settling tanks, aeration tanks, final settling tanks, sludge thickening, and sludge dewatering. Odors generated by most of the processes are controlled through the thirteen packed-bed wet scrubbers to control odors at the plant.
The objective of D&B’s assignment was to develop AERMOD dispersion models for Cedar Creek WPCP and Bay Park STP, including all sources of hydrogen sulfide (H2S), odor thresholds (D/T), and selected (process-related) speciated compound sources, terrain elevations, receptor grids, and five (5) years of representative, model-ready meteorological data. AERMOD is the United States Environmental Protection Agency’s (USEPA’s) steady-state plume model that incorporates air dispersion based on planetary boundary layer turbulence structure and scaling concepts, including treatment of both surface and elevated sources, and both simple and complex terrain.
Dispersion Model Development
Site plans and available aerial imagery for each Plant were imported into AERMOD and utilized as a base to input building information (i.e., size, location, height) and source information into the dispersion model. More than 40 site buildings and structures at Cedar Creek WPCP and more than 60 site buildings and structures at Bay Park STP were entered into the dispersion models. Potential odor sources entered into the model for each Plant included the following:
Cedar Creek WPCP
• 11 Pack-Bed Scrubbers
• 5 Combustion Engines
• 4 Hot Water Boilers
• 12 Final Sedimentation Tanks
Bay Park STP
• 13 Pack-Bed Scrubbers
• 4 Combustion Engines
• 4 Hot Water Boilers
• 10 Final Sedimentation Tanks
For point sources (e.g., exhaust stacks), the actual location, stack height, stack diameter, exit velocity and exhaust temperature was input. For area sources (e.g., open tanks), the actual location, size and release height were input. Unit emission rates were entered into the model so that NCDPW and its consultants could easily determine off-site impacts under varying emission scenarios. All buildings and sources were located in the dispersion models according to the WGS 1984, UTM Zone 18 coordinate system for modeling purposes.
Nassau County is a densely populated area, so urban boundary layer affects were incorporated into the dispersion models using United States Census Population data for the area surrounding each Plant. All sources were entered as “urban sources” for modeling purposes. To account for surface characteristics and terrain effects, an Auer land use analysis was performed for the area surrounding each site and National Elevation Dataset GeoTIFF Format terrain data from the United States Geological Survey was incorporated into each model for an approximate 10 kilometer by 10 kilometer area surrounding each Plant.
The project requirements specified the use of a 10 kilometer by 10 kilometer Cartesian receptor grid for an area surrounding each Plant, with a finely spaced grid from the center of the Plant sites out to 1 kilometer. As a result, a receptor grid at 20-meter spacing was utilized out to 1 kilometer and 100-meter spacing was utilized out to 10 kilometers. In addition, receptors were placed along the plant fence lines at 10-meter intervals. D&B also researched local sensitive receptors, such as schools and day care facilities, for incorporation into the dispersion models. Thirty seven sensitive receptors were incorporated into the dispersion model for Cedar Creek WPCP and 288 sensitive receptors were incorporated into the dispersion model for Bay Park STP.
Lastly, five years of model ready data from JFK International Airport was incorporated into the dispersion models per United States Environmental Protection Agency and New York State Department of Environmental Conservation modeling guidance.
D&B provided the dispersion models to NCDPW’s consultant responsible for implementing the Plant-wide Odor Control Improvements at Cedar Creek WPCP and Bay Park STP for use in evaluating off-site odor impacts from each Plant.
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